KR20030074237A - Polishing apparatus - Google Patents

Abstract

A polishing apparatus according to the present invention comprises: a polishing table; A polishing pad mounted on the polishing table, the polishing pad having a polishing surface thereon for polishing a workpiece to be polished; A top ring to hold the workpiece and press the workpiece against the polishing pad; And an optical sensor provided in the polishing table for measuring the thickness of the film formed on the workpiece. The polishing pad includes: a pad having a hole formed therein; A translucent window disposed in said hole for passing light; And a supporting member which prevents the light transmitting window from protruding from the polishing surface of the polishing pad.

Description

Polishing Device {POLISHING APPARATUS}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polishing apparatus having a polishing pad, and more particularly, to a polishing apparatus having a polishing pad for polishing a workpiece such as a semiconductor substrate to finish flat mirror finish.

In recent years, highly integrated semiconductor devices require narrow wiring and multiple wiring, and therefore, it is necessary to make the surface of the semiconductor substrate highly flat. In particular, finer wiring in highly integrated semiconductor devices has led to the use of light with shorter wavelengths in photolithography so that the height difference at an acceptable focal point on the substrate is smaller by using light with shorter wavelengths. . Therefore, the height difference at the focus should be as small as possible. In other words, the surface of the semiconductor substrate needs to be highly flat. One conventional method of planarizing the surface of a semiconductor substrate is to remove the unevenness on the surface of the semiconductor substrate by a chemical mechanical polishing (CMP) process.

In the chemical mechanical polishing (CMP) process, after the surface of the semiconductor substrate is polished for a predetermined time, the polishing process must be completed at a predetermined position or timing. For example, some integrated circuit designs need to leave an insulating film (layer) such as SiO ₂ on metal wiring such as copper, aluminum, or the like. Since the metal layer or other layers are further deposited on the insulating layer in a subsequent process, this insulating layer is called an interlayer. In this case, if the semiconductor substrate is excessively polished, the underlying metal layer is exposed on the polishing surface. Therefore, the polishing process needs to be finished in a state in which an intervening layer having a predetermined thickness remains unpolished.

According to another polishing process, a wiring groove having a predetermined pattern is formed on the surface of the semiconductor substrate, and after the Cu layer is deposited on the semiconductor substrate, the wiring groove is filled with copper or a copper alloy, and then the unnecessary Cu layer is formed. It is removed by a chemical mechanical polishing (CMP) process. In particular, the Cu layer on the semiconductor substrate is selectively removed by a chemical mechanical polishing process, leaving only the Cu layer in the wiring groove. More specifically, the insulating film of SiO _{2 or the} like needs to be removed until it is exposed to a surface other than the wiring groove.

Further, in some cases, wiring grooves for a predetermined wiring pattern are formed in the semiconductor substrate, and a conductive material such as copper (Cu) or copper alloy is filled in the grooves of the semiconductor substrate and then unnecessary of the conductive material on the surface of the semiconductor substrate. The part is removed by a chemical mechanical polishing (CMP) process. When the copper layer is polished by the CMP process, the copper layer needs to be selectively removed while remaining in the wiring circuit groove, that is, the wiring groove. More particularly, the copper layer on the surface of the semiconductor substrate other than the wiring groove needs to be removed until the insulating layer of SiO _{2 or the} like is exposed on the polishing surface.

In this case, if the semiconductor substrate is excessively polished until the Cu layer in the wiring groove is removed together with the insulating layer, the resistance of the circuit on the semiconductor substrate increases, which may cause the semiconductor substrate to be discarded, causing a large resource loss. . On the contrary, if the semiconductor substrate is insufficiently polished to leave a copper layer on the insulating layer, the wirings on the semiconductor substrates will not be separated from each other as desired and cause a short circuit between them. As a result, the manufacturing cost is increased because the semiconductor substrate has to be polished again. In addition, the above-described problems may also occur when other metal films such as aluminum are formed on the semiconductor substrate and polished by the CMP process.

Therefore, a method of detecting the end point of the CMP process using an optical sensor has been proposed. In particular, an optical sensor comprising a light-emitting and photodetecting element is provided in a polishing apparatus. The light emitting device of the optical sensor applies light to the polished surface of the semiconductor substrate, and the light detecting device detects a change in reflectance of light reflected from the polished surface and measures the thickness of the insulating layer or the metal layer on the polished surface. Thus, the end point of the CMP process is detected from the measured film thickness.

In the polishing apparatus for performing the CMP process, the polishing pad mounted on the upper surface of the polishing table generally has low light transmittance. Thus, when light from the optical sensor is applied to the polished surface of the semiconductor substrate located on the polishing table from the bottom of the polishing pad, a high translucent window through which the light can pass is provided to the polishing pad, and The emitted light is applied to the polished surface of the semiconductor substrate through the transparent window.

1 is an enlarged partial cross-sectional view showing a conventional double layer polishing pad including a light transmitting window. As shown in FIG. 1, the polishing pad 310 includes an upper pad 311 and a lower pad 312. The upper pad 311 has a hole 311a formed therein, and a transparent window 341 is disposed in the hole 311a of the upper pad 311. The lower pad 312 has light passing holes 312a therein. The light passing hole 312a has a smaller diameter than the hole 311a. A step 313 is provided between the holes 311a and 312a having different diameters.

The conventional polishing pad 310 is manufactured as follows. Adhesive is applied to the lower surface of the upper pad 311 and the upper surface of the lower pad 312, and the upper pad 311 and the lower pad 312 are pressed in a vertical direction with respect to each other. Thus, the upper pad 311 and the lower pad 312 are bonded to each other. Then, the transparent window 341 is fitted into the hole 311a. The transparent window 341 is bonded to the lower pad 312 by an adhesive applied to the upper surface of the step 313.

However, the transparent window 341 is bonded to the lower layer pad 312 only on the upper surface of the step 313, so the bonding area and the bonding strength thereof are small. Therefore, there is a possibility that the transparent window 341 is separated from the bonding pad 310. Depending on the force applied to the polishing pad 310, the transparent window 341 may not partially fall but partially fall off, and a gap may occur between the transparent window 341 and the lower layer pad 312 or the step 313. . Thus, the formed gap causes the polishing liquid used on the upper surface of the transparent window polishing pad 310 to leak onto the lower surface of the transparent window 341. When the polishing liquid is buried on the lower surface of the transparent window 341, the reflectance of the transparent window 341 is greatly reduced, making it difficult to detect the reflectance change of the polished surface of the semiconductor substrate using an optical sensor. In this case, the film thickness of the semiconductor substrate cannot be measured with high accuracy.

When the polishing liquid is introduced into the gap between the transparent window 341 and the step 313, an area in which the elasticity is not uniform in the polishing pad 310 is created due to expansion. Such regions may adversely affect the polishing process of the semiconductor substrate. In addition, when the polishing liquid having low light transmittance is unevenly introduced between the light transmissive window 341 and the optical sensor, the signal detected by the optical sensor becomes unstable and the reliability of the detection result is inferior.

As described above, the transparent window 341 is fitted into the hole 311a formed in the upper pad 311. Since the hole 311a has a slightly larger dimension than the transparent window 341, the transparent window 341 is easily fitted into the hole 311a. Therefore, after the light transmitting window 341 is located in the hole 311a, there is a small gap 314 between the light transmitting window 341 and the hole 311a. Thus, a polishing liquid tends to be introduced into the small gap 314 and solidify in the small gap 314. The solidified polishing liquid may cause scratches on the semiconductor substrate polished on the upper surface of the polishing pad 310.

Accordingly, it is an object of the present invention to provide a polishing apparatus having a polishing pad in which an optical sensor has a high accuracy and stably measures the film thickness of the polishing surface and prevents scratches on the polished pad.

1 is a partially enlarged cross-sectional view showing a conventional polishing pad;

2 is a schematic view showing an overall arrangement of a polishing apparatus according to the first embodiment of the present invention;

3 is a partially enlarged cross-sectional view showing a polishing pad according to the first embodiment of the present invention;

4 is a plan view of a polishing table of the polishing apparatus shown in FIG. 2;

5 to 8 are vertical cross-sectional views showing the continuous steps of the process of manufacturing the polishing pad shown in FIG. 3;

9 is a perspective view showing a polishing apparatus according to another embodiment of the present invention;

10 is a partially enlarged cross-sectional view showing a polishing pad according to a second embodiment of the present invention;

FIG. 11 is a bottom view of the polishing pad shown in FIG. 10; FIG.

12 is a partially enlarged cross-sectional view showing a polishing pad according to a third embodiment of the present invention;

FIG. 13 is a partially enlarged cross-sectional view showing a modification of the polishing pad shown in FIG. 12; FIG.

FIG. 14 is a partially enlarged cross-sectional view illustrating another modified example of the polishing pad illustrated in FIG. 12.

According to a first aspect of the present invention, there is provided a polishing table comprising: a polishing table; A polishing pad mounted on a polishing table and having a polishing surface thereon to polish the workpiece to be polished; A top ring that holds the workpiece and presses the workpiece against the polishing pad; And an optical sensor provided on the polishing table for measuring the thickness of the film formed on the workpiece, the polishing pad comprising: a pad having a hole formed therein; A translucent window disposed in a hole through which light passes; And a support member for preventing the light transmissive window from protruding above the polishing surface of the polishing pad.

According to a preferred aspect of the present invention, the support member is disposed on the lower surface of the translucent window.

According to a preferred embodiment of the present invention, the pad and the transparent window are bonded to each other by an adhesive.

According to a preferred aspect of the present invention, the support member includes an elastic support seal which prevents the polishing liquid supplied onto the polishing surface of the polishing pad from being introduced between the translucent window and the optical sensor.

According to a preferred aspect of the present invention, the pad includes an upper pad and a lower pad disposed below the upper pad.

According to a preferred aspect of the present invention, the support member comprises a light transmissive support.

According to a preferred aspect of the present invention, the polishing pad further includes a reinforcing member interposed between the transparent support and the transparent window for preventing the transparent window from bending under the pressure applied while the workpiece is polished.

According to a preferred aspect of the present invention, the reinforcing member has a shape memory capability.

According to a preferred aspect of the present invention, the pad includes an upper pad and a lower pad disposed below the upper layer.

According to a second aspect of the present invention, there is provided a polishing table comprising: a polishing table; A polishing pad mounted on a polishing table, the polishing pad having a polishing surface thereon to polish the workpiece; A top ring that holds the workpiece and presses the workpiece against the polishing pad; And an optical sensor provided in a polishing table for detecting a polishing end point of the workpiece, the polishing pad comprising: a pad having a hole formed therein; A transparent window disposed in a hole through which light passes (the pad and the transparent window are bonded to each other by an adhesive); And a support member disposed on the lower surface of the transparent window to prevent the transparent window from protruding above the polishing surface of the polishing pad after the dressing process of the polishing surface.

According to a preferred aspect of the present invention, the support member includes an elastic support seal which prevents the polishing liquid supplied onto the polishing surface of the polishing pad from being introduced between the translucent window and the optical sensor.

According to a preferred aspect of the present invention, the support member comprises a light transmissive support.

According to a preferred aspect of the present invention, the apparatus further includes a reinforcing member interposed between the transparent support and the transparent window which prevents the transparent window from bending under the pressure applied while the workpiece is polished.

According to a preferred aspect of the present invention, the reinforcing member has a shape memory capability.

According to the present invention, since the transparent window is firmly supported by the support member, the transparent window is not easily pushed downward when the polishing pad is dressed. This, together with the advantages provided by the light-transmissive window being made of soft materials, can more effectively prevent scratches on the workpiece.

Since the transparent window is supported by a supporting seal having excellent sealing ability, it is possible to minimize the leakage of the polishing liquid onto the lower surface of the transparent window. Thus, the polishing pad polishes the workpiece to a high quality finish and the optical sensor can stably measure the film thickness of the workpiece surface with high accuracy. In addition, since the support seal is effective in preventing the polishing liquid having low light transmittance from being introduced between the light transmissive window and the optical sensor, the optical sensor can stably measure the film thickness with high accuracy.

According to a third aspect of the present invention, there is provided a polishing table comprising: a polishing table; A polishing pad mounted on a polishing table, the polishing pad having a polishing surface thereon to polish the workpiece; A top ring that holds the workpiece and presses the workpiece against the polishing pad; And an optical sensor provided on the polishing table for measuring the thickness of the film formed on the workpiece, the polishing pad comprising: a pad having a hole formed therein; A transparent window disposed in a hole through which light passes (the pad and the transparent window are bonded to each other by an adhesive); And a translucent support disposed on the lower surface of the translucent window to prevent the translucent window from protruding above the polishing surface of the polishing pad. And a reinforcing member interposed between the translucent support and the translucent window which prevents the transparent window from bending under the pressure applied while the workpiece is polished, wherein the reinforcing member is provided with a polishing apparatus having a shape memory capability.

According to a preferred aspect of the present invention, the pad includes an upper pad having a hole formed therein and a lower pad having a light passing hole disposed below the upper pad and having a diameter substantially the same as that of the upper pad.

Under the pressure applied while the workpiece is polished, if the transparent window is bent, sufficient light cannot be transmitted through the transparent window or dissipated in the transparent window, so that the film thickness cannot be measured accurately and stably. According to the present invention, since a reinforcing member having a high flexibility is interposed between the transparent window and the transparent support, a support for supporting the transparent window to prevent the transparent window from bending under the pressure applied while the workpiece is polished is provided. Is reinforced. Also, because the reinforcing member has excellent adhesion, that is, the reinforcing member can be in close contact with other objects, the optical system can be maintained to stably measure the film thickness with high accuracy.

According to a preferred aspect of the present invention, there is provided an upper pad having a hole therein; A translucent window disposed in the hole of the upper pad to allow light to pass therethrough; A lower layer pad disposed under the upper pad and having light passing holes having a diameter substantially the same as that of the upper pad; And a film interposed between the upper pad and the lower pad. The adhesive is preferably applied to the surface of the film in contact with the upper pad and the lower pad.

The entire bottom surface of the light transmissive window is kept in contact with the transparent film so that the entire bottom surface of the translucent window is bonded to the transparent film. Since the bonding area of the transparent window is larger than that of the conventional transparent window, the bonding strength of the transparent window is increased. Thus, the transparent window can prevent the polishing pad from peeling off. As a result, the polishing liquid can be prevented from leaking onto the lower surface of the transparent window, so that the polishing pad can polish the workpiece to a high quality finish. At the same time, the optical sensor can stably measure the film thickness of the surface of the workpiece with high accuracy.

Since the transparent window and the lower layer pad can be completely separated from each other by the transparent film, the polishing liquid with low transparency can be prevented from being introduced between the transparent window and the optical sensor. Therefore, the optical sensor can stably measure the film thickness of the surface of the workpiece with high accuracy.

According to a preferred aspect of the present invention, there is provided an upper pad having a hole therein; A transmissive window disposed in a hole to allow light to pass therethrough, the polishing pad comprising the translucent window made of a softer material than the surface of the pad is provided.

Since the light transmissive window is softer than the surface of the pad, less scratches may occur when the polishing pad is dressing, thereby preventing scratches on the workpiece being polished by the light transmissive window. Since the transparent window is soft, even after the polishing pad is dressed, even if the transparent window protrudes above the surface of the polishing pad, the workpiece may be less damaged if the workpiece is polished.

According to a preferred aspect of the present invention, the method includes: preparing an upper pad having a hole formed therein; Forming a light transmitting window in a hole formed in the upper pad to allow light to pass therethrough; Preparing a lower pad having a light passing hole having a diameter substantially the same as that of the upper pad; Interposing a film having an adhesive applied to the upper and lower surfaces between the upper and lower pads, with the lower and upper pads positioned so that the light passing holes in the lower pad are aligned with the holes in the upper pad; And pressing the upper pad and the lower pad toward each other to bond the upper pad and the lower pad to each other with a film interposed therebetween. The forming step preferably includes injecting material into the hole formed in the upper pad.

According to the method described above, the polishing pad does not have a gap created between the transparent window and the upper pad. Therefore, since the polishing liquid is not solidified between the transparent window and the upper pad, it is possible to prevent the scratches from being formed on the workpiece by the solidified polishing liquid.

The above and other objects, features and advantages of the present invention will become apparent from the following description with reference to the accompanying drawings which illustrate preferred embodiments of the present invention by way of example.

A polishing apparatus having a polishing pad according to the first embodiment of the present invention is described below with reference to Figs.

Fig. 2 is a side elevation view showing a partial cross section of a polishing apparatus according to the first embodiment of the present invention. As shown in Fig. 2, the polishing apparatus grasps the workpiece W to be polished, such as the polishing table 20 and the semiconductor substrate, on which the polishing pad 10 is mounted, and on the upper surface of the polishing pad 10. It includes a top ring 30 for pressing the workpiece (W) against. The polishing pad 10 has an upper surface that serves as a polishing surface in sliding contact with the semiconductor substrate W to be polished. The polishing surface may alternatively be formed by an upper surface of a fixed grinding plate comprising fine grinding particles made of CeO _{2 or the} like which is fixed by a binder of synthetic resin.

The polishing table 20 is coupled to a motor 21 disposed below it. When the motor 21 is activated, the polishing table 20 is rotated about its own axis indicated by the arrow in FIG. The polishing liquid supply nozzle 22 is disposed above the polishing table 20 to supply the polishing liquid Q onto the polishing pad 10.

The top ring 30 is coupled to the top ring shaft 31 and coupled to the motor and the up / down cylinder (not shown). Thus, the top ring 30 may move vertically by the up / down cylinder, as indicated by the arrow in FIG. 2, and may rotate about the top ring shaft 31 by the motor. The top ring 30 has an elastic pad 32 mounted on its lower surface, which is made of polyurethane or the like. The semiconductor substrate W to be polished is attracted and held on the lower surface of the elastic pad 32, for example, under vacuum. While the top ring 30 is rotated, the semiconductor substrate W held on the lower surface of the elastic pad 32 is pressed against the polishing pad 10 under a predetermined pressure. The top ring 30 has a guide ring 33 disposed around its lower outer edge in order to keep the semiconductor substrate W from being separated from the top ring 30.

As shown in FIG. 2, an optical sensor 40 is provided in the polishing table 20 to measure the film thickness of the insulating film (layer) or metal film (layer) formed on the surface of the semiconductor substrate W. As shown in FIG. The optical sensor 40 includes a light emitting element and a light detecting element. The light emitting element of the photosensor 40 applies light to the surface to be polished of the semiconductor substrate (W). Since the photodetecting element of the optical sensor 40 receives the light reflected from the surface of the semiconductor substrate W, the thickness of the insulating layer or the metal layer on the surface of the semiconductor substrate W can be measured. The light emitting device can, for example, apply light emitted from a laser beam or an LED to a surface of a semiconductor substrate. In some cases, the light emitting element may use white light.

The polishing pad 10 has a cylindrical transmissive window 41 mounted therein to allow light from the light sensor 40 to pass therethrough. The transparent window 41 has an outer diameter of 18 mm, for example. 3 is a partially enlarged cross-sectional view illustrating the polishing pad 10 including the transparent window 41. As shown in FIG. 3, the polishing pad 10 includes a double layer polishing pad having an upper pad 11 and a lower pad 12. Upper pad 11 is Rodel Inc. It can be made of foamed polyurethane, such as IC-1000 manufactured by, and the lower pad 12 is, for example, Rodel Inc. It can be made of a nonwoven fabric such as SUBA400 manufactured by. The transparent window 41 is preferably made of a transparent material. In particular, the translucent window 41 is made of a material with high transparency, such as, for example, unfoamed polyurethane. In general, the upper pad 11 is made of a hard material, and the lower pad 12 is made of a softer material than the upper pad 11.

As shown in FIG. 3, the upper pad 11 has a hole 11a formed therein, and the transparent window 41 is disposed in the hole 11a of the upper pad 11. The lower layer pad 12 has a light passing hole 12a having a diameter substantially the same as the diameter of the hole 11a. The transparent adhesive film 13 coated with the adhesive on the upper and lower surfaces is interposed between the upper pad 11 and the lower pad 12. The upper pad 11 and the lower pad 12 are bonded to each other by the transparent adhesive film 13. The transparent adhesive film 13 may include a core sheet of polyethylene terephthalate (PET) having a thickness of 50 μm, and a pressure-sensitive adhesive of acrylic rubber applied to upper and lower surfaces of the core sheet.

Since the entire lower surface of the transparent window 41 is kept in contact with the transparent adhesive film 13, the entire lower surface of the transparent window 41 is bonded to the transparent adhesive film 13. Since the bonding area of the transparent window 41 is larger than that of the conventional transparent window, the bonding strength of the transparent window 41 is increased. Therefore, the transparent window 41 can prevent the polishing pad 10 from peeling off. As a result, since the polishing liquid Q can be prevented from leaking onto the lower surface of the transparent window 41, the polishing pad 10 can polish the semiconductor substrate W to a high quality finish. At the same time, the optical sensor 40 can stably measure the film thickness of the surface of the semiconductor substrate W with high accuracy.

Since the transparent window 41 and the lower layer pad 12 can be completely separated from each other by the transparent adhesive film 13, a polishing liquid Q having low transparency is introduced between the transparent window 41 and the optical sensor 40. Can be prevented. Therefore, the optical sensor 40 can stably measure the film thickness of the surface of the semiconductor substrate W with high accuracy.

The optical sensor 40 is controlled by a cable 42 extending through a polishing table 20, a table support shaft 20a and a rotary connector 43 mounted on the lower end of the table support shaft 20a. Is electrically connected). The controller 44 is connected to the display unit 45. Alternatively, a signal for measuring the film thickness may be transmitted from the light sensor 40 to the controller 44 via a wireless signal transmitter (not shown).

4 is a plan view showing a polishing table 20 of the polishing apparatus shown in FIG. As shown in FIG. 4, the polishing table 20 has a center point C _{T that} rotates about it, and the semiconductor substrate W held by the top ring 30 has a geometric center point C _W. The optical sensor 40 has a polishing table 20 to pass through the center point C _W of the semiconductor substrate W held by the top ring 30 while the top ring 30 is rotated to polish the semiconductor substrate W. Is located within. While the optical sensor 40 moves under the semiconductor substrate W, the optical sensor 40 is polished surface of the semiconductor substrate W along an arc-shaped path including the center point C _W of the semiconductor substrate W. The film thickness of can be detected continuously. In order to shorten the time interval for detecting the film thickness, other optical sensors 40 can be added as indicated by the imaginary line in Fig. 4, so that at least two optical sensors can be used to detect the film thickness.

While the polishing table 20 is rotated once, the light emitted from the light emitting element of the optical sensor 40 passes through the transparent window 41 and is applied to the polished surface of the semiconductor substrate W. As shown in FIG. The applied light is reflected by the polishing surface of the semiconductor substrate W and then detected by the photodetecting element of the optical sensor 40. Light detected by the photodetector element of the optical sensor 40 is converted into an electrical signal, which is processed by the controller 44 to measure the film thickness of the polishing surface of the semiconductor substrate W. As shown in FIG.

The principle of detecting the film thickness of an insulating layer such as SiO ₂ or a metal layer such as Cu, Al or the like using an optical sensor is briefly described below. The measurement of the film thickness using an optical sensor utilizes the optical interference generated by the uppermost layer and the media adjacent to the uppermost layer. In particular, when light is applied to a thin film on a substrate, a portion of the light is reflected from the surface of the thin film while the remaining light passes through the thin film. Some of the light passing through the thin film is then reflected from the surface of the substrate or substrate, while the remaining light passes through the substrate or substrate. In this case, if the base layer is made of metal, the remaining light is absorbed by the base layer. The phase difference between the light reflected from the surface of the thin film and the light reflected from the surface of the base layer or the substrate causes interference. When the light reflected from the surface of the thin film and the light reflected from the surface of the base layer or the substrate are in phase with each other, the light intensity is increased. When the light reflected from the surface of the thin film and the light reflected from the surface of the base layer or the substrate have a phase difference with each other, the light intensity is reduced. Therefore, the reflection intensity is changed depending on the wavelength of the incident light, the film thickness and the refractive index of the film. The light reflected from the substrate is separated by a diffraction grating or the like, and the profile shown is analyzed by indicating the intensity of the reflected light with respect to each wavelength in order to measure the thickness of the film on the substrate.

When other available optical sensors are used, monochromatic light of white light (light having a single wavelength) is applied to the thin film on the substrate, and the reflectance including a combination of the reflectance on the surface of the thin film and the surface on the substrate or the substrate It is measured based on the reflected light. Since the reflectance varies with the thickness and type of the film to be polished, the change in reflectance can be monitored to detect the end point of the polishing process.

The manufacturing process of the polishing pad 10 is described below with reference to FIGS. 5 to 8.

(1) As shown in Fig. 5, an upper pad 11 made of foamed polyurethane is prepared to form a hole 11a in the upper pad 11 at a given position.

(2) As shown in Fig. 6, the unfoamed polyurethane 14 is injected into the holes 11a in the upper pad 11, and melted (bonded) with the upper pad 11. Thus, the transparent window 41 is formed of unfoamed polyurethane in the hole 11a. Alternatively, the translucent window 41 having a shape coinciding with the hole 11a may be manufactured separately from the upper pad 11 and then fitted into the hole 11a in the upper pad 11.

(3) As shown in Fig. 7, the upper pad 11 and the transparent window 41 thus produced are sliced to a given thickness of 1.9 mm, for example.

(4) A light passing hole 12a having a diameter substantially the same as that of the hole 11a is formed in the lower pad 12. Then, as shown in FIG. 8, a transparent adhesive film 13 having an adhesive applied to its upper and lower surfaces is interposed between the upper pad 11 and the lower pad 12. In this case, the lower pad 12 and the upper pad 11 are positioned so that the light passing holes 12a in the lower pad 12 are aligned with the holes 11a in the upper pad 11. Conventional polishing pads are provided with notches in an upper pad and a lower pad, and the notches are aligned with each other, thereby allowing the upper pad and the lower pad to be positioned at appropriate positions. However, according to the present invention, since the light passing holes 12a in the lower pad 12 have substantially the same diameter as the holes 11a in the upper pad 11, these holes are the upper pad 11 and the lower pad. Can be used to position 12 in a suitable position. Therefore, it is not necessary to provide notches in the upper pad and the lower pad.

(5) Next, since the upper pad 11 and the lower pad 12 are pressed in the vertical direction toward each other, the pads are adhered to each other by the transparent adhesive film 13. Thus, the polishing pad 10 shown in FIG. 3 is completed.

When the unfoamed polyurethane 14 is injected into the hole 11a of the upper layer pad 11 to form the light transmissive window 41 in the hole 11a, the polishing pad 10 is formed of the light transmissive window 41 and the upper layer. There is no gap between the pads 11. Therefore, the polishing liquid will not be solidified between the transparent window 41 and the upper pad 11, so that the semiconductor substrate W can be prevented from scratches which may otherwise be caused by the solidified polishing liquid.

The operation of the polishing apparatus for polishing the semiconductor substrate W will be described below.

The semiconductor substrate W held on the lower surface of the top ring 30 is pressed against the polishing pad 10 on the upper surface of the polishing table 20 which is being rotated. At this time, the polishing liquid Q is supplied onto the polishing pad 10 from the polishing liquid supply nozzle 22. Thus, the semiconductor substrate W is polished with the polishing liquid Q between the lower surface to be polished of the semiconductor substrate W and the polishing pad 10.

While the substrate W is being polished, the optical sensor 40 passes just below the polished surface of the substrate W each time the polishing table 10 is rotated once. The optical sensor 40 is positioned on an arc path passing through the center Cw of the semiconductor substrate W, and the optical sensor 40 is along the arc path on the semiconductor substrate W. The film thickness of the polished surface of can be detected continuously. Specifically, the light emitted from the light emitting element of the optical sensor 40 passes through the light passing hole 12a and the transparent window 41 of the lower pad 12 to reach the polished surface of the semiconductor substrate W. do. Then, the polished surface of the semiconductor substrate W reflects the applied light, and the reflected light is received by the photodetector element of the optical sensor 40. The signal output from the optical sensor 40 is sent to the controller 44 which measures the film thickness of the polished surface of the semiconductor substrate W. When the film on the polished surface of the semiconductor substrate W is polished to the desired thickness, the controller 44 processes and monitors the signal from the optical sensor 40 for detection. Thus, the end point of the CMP process can be determined. The optical sensor 40 may be positioned in a curved path that does not pass through the center Cw of the semiconductor substrate W.

In this embodiment, the polishing pad 10 is composed of a double layer pad. However, the polishing pad 10 may be made of a multilayer pad having three or more layers. When the polishing pad 10 is made of such a multilayer pad, the transparent adhesive film may be placed at the position where it can be held in contact with the lower surface of the transparent window. In this case, the layers located above the transparent adhesive film serve as upper layer pads, and the layers located below the transparent adhesive film serve as lower layer pads. Therefore, the present invention can be applied to such multilayer pads.

In this embodiment, a polishing pad mounted on a polishing table is used to polish the workpiece. However, the present invention can be applied to other kinds of polishing apparatuses. For example, the present invention can be applied to a polishing apparatus having a belt-type polishing pad 51 that provides a polishing surface as shown in FIG. In the polishing apparatus shown in Fig. 9, a belt-type polishing pad, ie a belt 51 having grinding particles on its surface, is wound on two spaced rotary drums 52, 53. The rotary drums 52 and 53 are rotated to move the belt 51 by the circular rotational motion or the reciprocal linear motion in the direction indicated by the arrow 54. The support 55 is located between the upper and lower bands of the belt 51. Since the semiconductor substrate W held by the top ring 56 is pressed against the region of the belt 51 supported by the support 55, the surface of the semiconductor substrate W is polished by the belt 51. The support 55 has an optical sensor (not shown) embedded therein. The optical sensor applies light to the semiconductor substrate W held by the top ring 56 and detects light reflected from the semiconductor substrate W. Based on the reflected light detected by the optical sensor, the film thickness of the insulating layer or the metal layer on the polished surface of the semiconductor substrate W can be measured. The belt 51 has a transmissive window 41 integrated therein at a position corresponding to the light sensor.

10 to 11, a polishing pad according to a second embodiment of the present invention will be described. 10 is a partially enlarged cross-sectional view illustrating a polishing pad according to a second embodiment of the present invention, and FIG. 11 is a bottom view of the polishing pad shown in FIG. 10. 10 and 11, the same parts and components have the same reference numerals and characteristics as those of the first embodiment, and are not described below repeatedly.

In the first embodiment, the transparent window 41 is made of the same hard polyurethane (IC-1000) as the upper pad 11. Therefore, when the surface of the polishing pad 10 is dressed (regenerated) by the dresser, the surface of the transparent window 41 can be scratched. The scratches generated on the surface of the translucent window 41 can advance the scratches of the semiconductor substrate while the semiconductor substrate is polished.

Further, in the first embodiment, the lower end portion of the transparent window 41 is supported only by the thin transparent adhesive film 13 (see Fig. 3). As a result, once the polishing pad 10 is dressed by the dresser, the surface of the polishing pad 10 is scraped by the dresser while the transparent window 41 moves downward due to the elasticity of the transparent adhesive film 13. After the polishing pad 10 is dressed by the dresser, the transparent window 41 is pushed upward again due to the restoring force of the transparent adhesive film 13, so that the surface of the transparent window 41 is removed from the polishing pad 10. It protrudes above the surface of the polishing pad 10 by a distance equal to the thickness thereof. In the first embodiment, since the transparent window 41 is made of a hard material, the semiconductor substrate is polished with the polishing pad 10 in a state where the transparent window 41 protrudes above the surface of the polishing pad 10. The semiconductor substrate is very likely to be damaged by the protruding transparent window 41.

According to the second embodiment, the polishing pad 110 is made of a material that is softer than the upper pad 11 (IC-1000), preferably a material that is softer than the upper pad 11 and harder than the lower pad 12. It has a light transmitting window 141. The light transmitting window 141 is placed in the hole 11a in the upper pad 11. The transparent window 141 is preferably made of a transparent material. Since the transparent window 141 is softer than the upper pad 11, less scratches will occur when the polishing pad 110 is dressed, so that the semiconductor substrate being polished is prevented from being scratched by the transparent window 141. Since the transparent window 141 is soft, even if the polishing pad 110 protrudes on the surface of the polishing pad 11 after dressing, it is less likely to damage the semiconductor substrate when the semiconductor substrate is polished.

In the second embodiment, as shown in FIG. 10, a high elastic support seal 120 having excellent sealing ability is placed under the transparent window 141 to support the transparent window 141. As shown in FIG. 11, the support seal 120 is annular and is mounted on the inner peripheral surface of the optical path hole 12a in the lower pad 12. The support seal 120 is made of an adhesive having excellent sealing ability and elasticity.

Since the transparent window 141 is supported by the support seal 120 having excellent sealing ability, it is possible to minimize the polishing liquid leaking on the lower surface of the transparent window 141. Therefore, the polishing pad 110 can polish the semiconductor substrate with a high quality finish, and the optical sensor can stably measure the film thickness of the surface of the semiconductor substrate with high accuracy. Furthermore, since the support seal 120 is effective to prevent the polishing liquid having low transparency from being introduced between the transparent window 141 and the optical sensor, the optical sensor can stably measure the film thickness with high accuracy. In addition, as long as the transparent window 141 is firmly supported by the high elastic support seal 120, the transparent window 141 is less likely to be pressed downward when the polishing pad 10 is dressing, so that after completion of the dressing process It is prevented from protruding above the surface of the polishing pad 110. This fact, together with the advantages of the transparent window 141 made of a soft material, can more effectively prevent the semiconductor substrate from being scratched.

In the second embodiment, the transparent window 141, the upper pad 11 and the lower pad 12 are bonded to each other by an adhesive 130 having excellent sealing ability, so that the transparent window 141, the upper pad 11 And no gap is created between the lower pad 12. Therefore, since the polishing liquid will not solidify between the transparent window 141, the upper pad 11 and the lower pad 12, otherwise the semiconductor substrate is prevented from scratches that may occur due to the solidified polishing liquid.

A polishing pad according to a third embodiment of the present invention will be described with reference to FIG. 12. In Fig. 12, the same parts and components have the same reference numerals and characteristics as those of the first embodiment, and are not described below repeatedly.

As shown in FIG. 12, the polishing pad according to the third embodiment has a light transmitting window 241 supported by a light transmitting support 220 made of acrylic resin, polyethylene gel, polyethylene resin, or the like. The transparent window 241 and / or the transparent support 230 is preferably made of a transparent material. A reinforcing member 230 having high flexibility and excellent adhesiveness is interposed between the transparent window 241 and the transparent support 22. For example, the reinforcing member 230 has a refractive index of about 1 to about 2. The reinforcing member 230 may be made of a jelly type elastomer having a thickness of 1.27 mm (50 mil). The transmissive window 241, the reinforcing member 230, and the translucent support 220 collectively produce an optical system having a refractive index of 1.4, as shown in FIG. 12. A laser beam from a laser beam source having a wavelength of 800 nm is applied to a semiconductor substrate on a polishing pad in an angular range of 6 ° to 48 ° with respect to the vertical direction through an optical system to measure the film thickness of the semiconductor substrate.

When the transparent window is bent under the applied pressure while the semiconductor substrate is polished, the film thickness cannot be measured accurately and stably because sufficient light cannot travel through the transparent window or dissipate in the transparent window. For example, when cerium slurry (CeO ₂ ) having an average diameter of approximately 0.2 μm is used as the grinding particles, the above problem becomes more important because light does not easily reach the semiconductor substrate. In this embodiment, since the reinforcing member 230 having high flexibility is interposed between the transparent window 241 and the transparent support 220, the support for supporting the transparent window 241 is reinforced to transmit the transparent window 241. ) Prevents the semiconductor substrate from bending under the pressure applied while it is being polished. The reinforcing member 230 preferably has substantially the same flexibility as the lower pad 12 (SUBA400).

Further, since the reinforcing member 230 has excellent adhesion, that is, since the reinforcing member 230 can be in close contact with another object, the optical system can be maintained to stably measure the film thickness with high accuracy. Can be. It is preferable that the reinforcing member 230 is less likely to generate bubbles therein, because the bubbles foamed therein can dissipate light passing therethrough. The reinforcing member 230 is preferably capable of restoring its original shape after being deformed. For example, the reinforcing member 230 is preferably made of an elastomer having a shape memory capability, such as polyester elastomer.

In FIG. 12, the reinforcing member 230 is supported on the protrusion 220a provided on the upper surface of the translucent support 220. However, as shown in FIG. 13, the light transmitting support 220 has no protrusion, but the reinforcing member 230 may be directly supported on the upper surface of the light transmitting support 220. The outer diameter of the reinforcing member 230 is not limited to that shown in FIGS. 12 and 13, but may be the same as the diameters of the transparent window 241 and the transparent support 220 as shown in FIG. 14. For more accurate film thickness measurement, light emitted from Xe (xenon) or a halogen beam source is applied almost perpendicularly to the semiconductor substrate, so that the film thickness thereon can be measured as shown in FIGS. 13 and 14. The Xe or halogen beam source emits light having a plurality of frequencies.

In the second and third embodiments, the polishing pad is composed of a double layer pad. However, the polishing pad may be made of a multilayer pad or a single layer pad having three or more layers.

While certain preferred embodiments of the present invention have been shown and described in detail, it is to be understood that various changes and modifications can be made therein without departing from the scope of the appended claims.

Industrial use possibility

The present invention is preferably applied to a polishing apparatus having a polishing pad for polishing a workpiece such as a semiconductor substrate with a flat mirror finish.

According to the present invention, it is possible to provide a polishing apparatus having a polishing pad in which the optical sensor stably measures the film thickness of the polishing surface with high accuracy and prevents scratches on the polished pad.

Claims (16)

A polishing table; A polishing pad mounted on the polishing table, the polishing pad having a polishing surface thereon for polishing a workpiece to be polished; A top ring to hold the workpiece and press the workpiece against the polishing pad; And A polishing apparatus comprising an optical sensor provided on the polishing table for measuring a thickness of a film formed on the workpiece, The polishing pad, A pad formed with a hole therein; A translucent window disposed in said hole for passing light; And And a support member for preventing the light transmitting window from protruding above the polishing surface of the polishing pad. The method of claim 1, And the support member is disposed on a lower surface of the translucent window. The method of claim 2, And the pad and the transparent window are bonded to each other by an adhesive. The method of claim 3, And the support member includes an elastic support seal which prevents the polishing liquid supplied onto the polishing surface of the polishing pad from being introduced between the light transmitting window and the optical sensor. The method of claim 4, wherein And the pad includes an upper pad and a lower pad disposed under the upper pad. The method of claim 3, And the support member comprises a light-transmissive support. The method of claim 6, And the polishing pad further comprises a reinforcing member interposed between the transparent window and the transparent support to prevent the transparent window from bending under pressure exerted while the workpiece is polished. The method of claim 7, wherein And the reinforcing member has a shape memory capability. The method of claim 8, And the pad includes an upper pad and a lower pad disposed under the upper pad. A polishing table; A polishing pad mounted on the polishing table, the polishing pad having a polishing surface thereon for polishing a workpiece to be polished; A top ring to hold the workpiece and press the workpiece against the polishing pad; And A polishing apparatus comprising an optical sensor provided in the polishing table for detecting an end point for polishing the workpiece. The polishing pad, A pad formed with a hole therein; A translucent window disposed in the hole for passing light, the pad and the translucent window being bonded to each other by an adhesive; And And a support member disposed on the lower surface of the transparent window to prevent the transparent window from protruding above the polishing surface of the polishing pad after the dressing process of the polishing surface. The method of claim 10, And the support member includes an elastic support seal which prevents the polishing liquid supplied onto the polishing surface of the polishing pad from being introduced between the light transmitting window and the optical sensor. The method of claim 10, And the support member comprises a light-transmissive support. The method of claim 12, And the polishing pad further comprises a reinforcing member interposed between the transparent window and the transparent support to prevent the transparent window from bending under pressure exerted while the workpiece is polished. The method of claim 13, And the reinforcing member has a shape memory capability. A polishing table; A polishing pad mounted on the polishing table, the polishing pad having a polishing surface thereon for polishing a workpiece to be polished; A top ring to hold the workpiece and press the workpiece against the polishing pad; And A polishing apparatus comprising an optical sensor provided on the polishing table for measuring a thickness of a film formed on the workpiece, The polishing pad, A pad formed with a hole therein; A translucent window disposed in the hole for passing light, the pad and the translucent window being bonded to each other by an adhesive; A translucent support disposed on a lower surface of the translucent window to prevent the translucent window from protruding above the polishing surface of the polishing pad; And A reinforcing member interposed between the light transmissive window and the light transmissive support to prevent the light transmissive window from bending under pressure applied while the workpiece is polished, the reinforcing member having a shape memory capability; Polishing device. The method of claim 15, And the pad includes an upper pad having a hole formed therein, and a lower pad having a light passing hole disposed below the upper pad, the light passing hole having a diameter substantially the same as that of the upper pad. .