CN106567130A - Method for improving roughness of wafers - Google Patents

Abstract

The invention discloses a method for improving roughness of wafers. The method comprises the following steps: pre-wetting; electrochemical polishing; electroplating; and drying. During the electroplating step, thickness of a metal layer to be electroplated on the surface of a wafer will not exceed 15 nm. By the method, the metal layer on the surface of the wafer can be removed and the wafer will not be damaged. Meanwhile, roughness of wafer surface can be improved and the wafer can be brighter and cleaner.

Description

A method of improving wafer roughness

technical field

The invention relates to the field of semiconductor production and processing, more specifically, to a method for improving the roughness of a wafer.

Background technique

The stress-free electrochemical polishing process can remove the metal layer on the surface of the wafer. Compared with the chemical mechanical polishing process, it has many advantages and is not easy to damage the wafer.

Figure 1 reveals the devices and principles involved in the existing stress-free electrochemical polishing process. The devices therein include a wafer holder 101 , a shower head 103 and a power source 104 . The wafer holder 101 is used to hold the wafer 102 and drive the wafer 102 to rotate. The nozzle 103 sprays the polishing liquid 105 on the surface of the wafer 102 , and the nozzle 103 can translate relative to the center of the wafer 102 . During the polishing process, the nozzle 103 is connected to the negative pole of the power supply 104, and the wafer 102 is connected to the positive pole of the power supply. The power supply 104, the nozzle 103, the polishing solution 105 and the wafer 102 form a closed loop to generate current. According to the principle of electrochemical reaction, the metal layer (usually Cu) on the surface of the wafer 102 will lose electrons and enter the solution, so as to achieve the purpose of removing the metal layer.

The existing stress-free electrochemical polishing process mainly includes a polishing step and a drying step, but does not contain an electroplating step. That is, after the polishing is completed, since the metal layer is removed, no electrochemical reaction occurs, so the wafer 102 is directly dried to end the entire process. Although the metal layer can be removed by using the existing stress-free electrochemical polishing process, the surface of the wafer 102 is not smooth enough and has high roughness after the process is completed.

Contents of the invention

The present invention discloses a method capable of improving wafer roughness in a stress-free electrochemical polishing process.

To achieve the above object, the present invention provides the following technical solutions:

A method for improving wafer roughness, comprising: a pre-wetting step; an electrochemical polishing step; an electroplating step; and a drying step.

Further, the thickness of the metal layer electroplated on the surface of the wafer in the electroplating step does not exceed 15 nm.

Further, in the electrochemical polishing step, the nozzle sprays the polishing liquid onto the wafer, the nozzle is connected to the negative electrode, and the wafer is connected to the positive electrode.

Further, in the electroplating step, the nozzle sprays the polishing solution to the wafer, the nozzle is connected to the positive electrode, and the wafer is connected to the negative electrode.

Further, the wafer rotates, and the shower head translates relative to the wafer along the radial direction of the wafer.

Further, in the electroplating step, the thickness of the electroplated metal layer is controlled by adjusting the rotation speed of the wafer and the moving speed of the shower head.

Further, in the pre-wetting step, the showerhead sprays the polishing liquid onto the wafer, and the showerhead or the wafer is not connected to electrodes.

Further, in the drying step, the spray head stops spraying the polishing fluid to the wafer, and the wafer rotates at a high speed to shake off the residual polishing fluid on the wafer surface.

The invention discloses a method for improving the roughness of the wafer, which not only retains the advantages of the stress-free electrochemical polishing process that is not easy to damage the wafer, but also can improve the roughness of the wafer surface, so that the polished wafer is more bright and clean.

Description of drawings

Fig. 1 discloses the structural representation of the device in the stress-free electrochemical polishing process in the prior art;

Figure 2 discloses a flow chart of a specific embodiment of the invention;

Figure 3 discloses a schematic diagram of the pre-wetting step in a specific embodiment of the invention;

Fig. 4 reveals the schematic diagram of the electrochemical polishing step in the embodiment of the present invention;

Fig. 5 reveals the schematic diagram of electroplating step in the specific embodiment of the present invention;

Fig. 6 discloses a schematic diagram of the drying step in an embodiment of the present invention.

detailed description

In conjunction with the accompanying drawings and the following detailed description, the present invention will be easier to understand:

2-6 disclose specific embodiments of the present invention. Among them, FIG. 2 discloses a flowchart of a specific embodiment of the present invention, that is, a method for improving wafer roughness, including: a pre-wetting step 201 ; an electrochemical polishing step 202 ; an electroplating step 203 ; and a drying step 204 . Wherein, the thickness of the metal layer electroplated on the surface of the wafer 302 in the electroplating step 203 is not more than 15 nm. After the wafer 302 has been subjected to electrochemical polishing, the obtained wafer surface has a relatively high roughness and is not very smooth. In order to overcome this defect, the present invention adds an electroplating process at the end of polishing, and re-plates a small amount of metal on the surface of the wafer 302, thereby improving the roughness of the surface of the wafer 302 and making the wafer 302 smooth and bright. At the same time, since the thickness of the electroplated metal layer is very thin, no more than 15 nm, such a thin metal layer will not have adverse effects on the performance of the wafer 302 and subsequent processes, and thus can be allowed. The metal to be plated is usually copper.

Figure 3 discloses a pre-wet step 201 of an embodiment of the present invention. Pre-wetting the wafer 302 before electrochemical polishing can obtain better polishing results. During the pre-wetting process, the spray head 303 sprays the polishing liquid 305 on the surface of the wafer 302, and the wafer 302 rotates under the drive of the wafer holder 301, and at the same time, the spray head 303 translates relative to the wafer 302 along the radial direction of the wafer 302, so that the entire The surface of wafer 302 is pre-wetted. The shower head 303 can move from the center of the wafer 302 to the edge of the wafer 302 , or vice versa, from the edge of the wafer 302 to the center of the wafer 302 . In the pre-wetting step 201 , no electrochemical reaction is required, so the circuit formed by the shower head 303 , the polishing liquid 305 , the wafer 302 , and the positive and negative converter 306 is disconnected. The way of disconnection may be that the shower head 303 is not connected to the electrode, or the wafer 302 is not connected to the electrode. Wherein the positive and negative pole converter 306 is connected with the power supply 304 for changing the polarity of the electrodes in the circuit.

FIG. 4 illustrates an electrochemical polishing step 202 of an embodiment of the present invention. During the polishing process, the nozzle 303 is connected to the negative electrode and the wafer 302 is connected to the positive electrode through the adjustment of the positive and negative pole converter 306. At the same time, the nozzle 303 sprays the polishing liquid 305 on the wafer 302, so that the circuit maintains a path. According to the principle of electrochemical reaction, the metal layer on the surface of the wafer 302 will lose electrons and become metal ions into the solution, thereby achieving the purpose of removing the metal layer on the surface of the wafer 302 . The rotational movement of the wafer 302 and the relative translational movement of the shower head 303 ensure that the entire surface of the wafer 302 is polished without missing areas.

FIG. 5 discloses an electroplating step 203 of an embodiment of the present invention. During the electroplating process, the polarity of the electrode is changed by the positive and negative converter 306, so that the shower head 303 is connected to the positive electrode, and the wafer 302 is connected to the negative electrode. The shower head 303 continues to spray the polishing liquid 305 to the wafer 302, and the circuit remains open. At this time, according to the principle of electroplating, the metal ions in the polishing solution are reduced to metal, and electroplated on the surface of the wafer 302 , thereby improving the roughness of the wafer 302 . Since the amount of electroplated metal is extremely small, the electroplating process needs to be precisely controlled to ensure that the thickness of the metal layer electroplated on the surface of the wafer 302 does not exceed 15 nm. Therefore, precise control can be achieved by adjusting the rotation speed of the wafer 302 and the moving speed of the shower head 303 . That is, during the electroplating process, the wafer 302 rotates at high speed, and the nozzle 303 quickly translates along the radial direction of the wafer 302. The nozzle 303 moves from the center of the wafer 302 to the edge, or from the edge of the wafer 302 to the center of the circle. Quickly disconnect the circuit and end the electroplating process, so as to ensure that the thickness of the electroplated metal layer does not exceed 15nm.

Figure 6 illustrates the drying step 204 of an embodiment of the invention. Combined with the device of the electrochemical polishing process, the present invention adopts a drying method to dry the wafer 302 . During the drying process, the spray head 303 no longer sprays the polishing liquid 305, so the circuit is disconnected. The wafer 302 rotates at a high speed to shake off the residual polishing fluid attached to the surface to achieve the purpose of drying. The wafer 302 is taken off after drying, and the whole process is completed.

The above embodiments are intended to illustrate the principles and effects of the present invention, and are not intended to limit the technical solutions of the present invention. Practitioners skilled in the art and related fields can implement the above-mentioned implementation without departing from the spirit and scope of the present invention. Examples are modified or changed, but still belong to the inventive concept of the present invention.

Claims (8)

1. A method for improving wafer roughness, comprising: pre-wetting step; an electrochemical polishing step; an electroplating step; and Drying step. 2. The method for improving wafer roughness according to claim 1, characterized in that, the thickness of the metal layer electroplated to the wafer surface in the electroplating step is no more than 15nm. 3. The method for improving wafer roughness according to claim 1, characterized in that, in the electrochemical polishing step, the nozzle sprays polishing fluid to the wafer, the nozzle is connected to the negative electrode, and the wafer is connected to the positive electrode. 4. The method for improving wafer roughness according to claim 3, characterized in that, in the electroplating step, the nozzle sprays the polishing solution to the wafer, the nozzle is connected to the positive electrode, and the wafer is connected to the negative electrode. 5. The method for improving the roughness of a wafer according to claim 3 or 4, wherein the wafer is rotated, and the shower head is translated relative to the wafer along the radial direction of the wafer. 6. The method for improving wafer roughness according to claim 5, characterized in that, in the electroplating step, the thickness of the electroplated metal layer is controlled by adjusting the rotational speed of the wafer and the moving speed of the shower head. 7. The method for improving wafer roughness according to claim 3, characterized in that, in the pre-wetting step, the shower head sprays polishing fluid to the wafer, and the shower head or the wafer is not connected to electrodes. 8. The method for improving wafer roughness according to claim 3, characterized in that, in the drying step, the shower head stops spraying the polishing fluid to the wafer, and the wafer rotates at a high speed to get rid of the remaining residue on the wafer surface. Polishing fluid.