JPH0831726A - Method for forming photoresist pattern - Google Patents

Abstract

(57) [Abstract] [Purpose] To provide a method for forming a photoresist pattern, which can suppress the influence of the standing wave effect and can form a photoresist pattern having a stable dimension even if the photoresist film thickness varies. To do. In the method of forming a photoresist pattern, a step of forming a first photoresist on an underlayer, a step of exposing a mask pattern on the first photoresist, and a step of forming a sidewall of the first photoresist by exposure. By including the step of developing with the formed uneven portion remaining and the step of filling the concave portion of the uneven portion, it is possible to suppress the influence of the standing wave effect and form a photoresist pattern of stable dimensions.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for forming a photoresist pattern, and more particularly to a method for forming a photoresist pattern capable of suppressing dimensional fluctuations of a circuit pattern, a wiring pattern, etc. due to a standing wave effect which occurs during exposure. It relates to a forming method.

[0002]

2. Description of the Related Art In recent years, miniaturization of circuit patterns and wiring patterns has been required with the progress of miniaturization and high integration of semiconductor integrated circuits. In forming these patterns, after applying a photoresist on a substrate or an insulating film which is a base layer, the mask pattern is exposed and developed to pattern the photoresist, and the patterned photoresist is used to form a substrate or the like. This is done by selectively removing a desired region of the underlayer.

However, in the above-mentioned conventional photoresist pattern forming method, a standing wave is generated in the photoresist due to the reflection of the light emitted during exposure from the underlayer, and as a result, the photoresist pattern becomes unstable. Therefore, there is a problem that the line width of a circuit pattern or the like finally formed is not stable.

The above-mentioned problems of the conventional technique will be described in more detail. In the exposure process of the photoresist pattern, for example, a reduction projection exposure device using a mercury lamp g-line or i-line as an exposure light source is used. Since the wavelengths of these exposure light sources are constant, the irradiated light generates a standing wave in the photoresist formed on the underlayer due to reflection from the underlayer, and the light from the light source in each part of the photoresist is emitted. The light intensity will change. This is largely due to the difference in the photoresist film thickness, and the slight difference in the photoresist film thickness causes a great difference in the light intensity of the portions in the photoresist having different film thicknesses. Therefore, even if the photoresist pattern is formed by exposing with the same exposure amount, the dimension thereof may largely change due to a slight change in the photoresist film thickness, and the shape may change due to the dimension change. Further, when such a photoresist pattern is used to form a circuit pattern or the like by etching, the line width becomes unstable. The fluctuation of the light intensity caused by such a standing wave is called the standing wave effect, and is the largest cause of the dimensional fluctuation and the shape instability of the photoresist pattern.

On a silicon substrate which actually forms a semiconductor device, a step of several hundred nm to several μm occurs due to repetition of formation of various thin films and etching. The film thickness of the resist spin-coated on the stepped substrate varies depending on the unevenness of the step. Therefore, due to the difference in the effect of the standing wave effect on the film thickness variation, even if the patterns on the photomask are designed to have the same dimensions, the finished dimensions of the resist pattern may differ greatly. Suppressing such a standing wave effect that has an adverse effect is one of the major problems for accurately forming a fine circuit pattern.

In order to suppress the standing wave effect, an antireflection film is formed in the lower layer or the upper layer of the photoresist to prevent the light from the exposure light source from being reflected by the underlying layer, which is generated in the photoresist. A method of suppressing the standing wave itself has been proposed.

The photoresist patterning method described in Japanese Unexamined Patent Publication No. 4-290218 is an example in which an antireflection film is formed under the photoresist. In this photoresist patterning method, a semi-transparent thin film having a refractive index different from that of the photoresist is provided under the photoresist applied on the substrate to be patterned, so that the standing wave effect under the photoresist is reduced. It is something to reduce.

In addition, "SPIE vol. 1674 O
optical / Laser Microlithogr
pp. 157 to 164 of "Aphy V (1992)" shows an example in which an antireflection film is formed on the upper layer of photoresist. This is an ARCOR (Anti-Reflective Coat) layer on the photoresist.
By forming an antireflection film called an ing on resist film, the exposure light is reflected at both the interface between the atmosphere and the ARCOR film and the interface between the ARCOR film and the resist film, and when the exposure light does not have the ARCOR film. As described above, it is prevented that the light is uniformly reflected at the air / resist film interface to cause unnecessary interference. This method can also reduce the standing wave effect.

[0009]

However, when an antireflection film is formed in the lower layer of the photoresist, it is difficult to obtain a high resolution with a type that is removed at the same time as the photoresist during development. FIG. 7 is a diagram for explaining this, and shows a pattern in which the antireflection film 13 and the photoresist 14 are formed on the underlayer 12, and the photoresist is patterned by exposure and development. As shown in FIG. 7A, during development, the antireflection film on the portion other than the portion covered with the resist is removed, but as the pattern becomes finer, the same size as the resist is formed under the patterned resist. It becomes difficult to leave the antireflection film accurately, and the resist pattern collapses as shown in FIG. 7B, or the dimension of the portion where the antireflection film is left over and the underlying layer is actually masked is It may change from the dimensions. For this reason, high resolution is difficult to obtain, which is inappropriate. For the type that remains after development, the antireflection film under the resist is removed by etching, but the dimensional variation of the photoresist pattern depends on the etching selectivity between the resist and the antireflection film under the resist. Therefore, it becomes difficult to control etching. That is, for example, when the selection ratio is low, the resist is also largely etched during the etching of the antireflection film, which makes it difficult to obtain the required resist pattern size. Furthermore, when the antireflection film formed on the upper layer of the photoresist is used, the thickness of the antireflection film varies depending on the unevenness of the photoresist surface, and the dimensional variation of the photoresist pattern due to the standing wave effect is caused. There is a problem that the effect of suppressing the influence is not sufficient.

The present invention has been made in order to solve the above-mentioned problems of the prior art, suppresses the influence of the standing wave effect, and has a stable size even if the photoresist film thickness varies. It is an object of the present invention to provide a method for forming a photoresist pattern that can form a pattern.

[0011]

In order to achieve the above-mentioned object, a method of forming a photoresist pattern according to the present invention comprises a step of forming a first photoresist on an underlayer and a step of forming a first photoresist on the underlayer. The method is characterized by including a step of exposing the mask pattern, a step of developing while leaving an uneven portion formed on the side wall of the first photoresist by the exposure, and a step of filling the concave portion of the uneven portion.

Further, in the method of forming a photoresist pattern of the present invention, in the step of filling the concave portion, the first photoresist is filled with a second photoresist which is exposed to light of a wavelength which is not exposed, and only the second photoresist is provided. Is exposed to light, and the second photoresist is exposed and developed.

Further, the method of forming a photoresist pattern of the present invention is characterized in that the step of filling the recess is filled with a by-product generated by introducing an etching gas.

[0014]

By using the method for forming a photoresist pattern of the present invention, it is possible to suppress the influence of the standing wave effect and form a photoresist pattern having a stable dimension even if the photoresist film thickness varies. Therefore, if the underlying layer is etched, ions are implanted, and a film is formed using such a photoresist pattern, the expected result can be obtained.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The principle of the present invention will be described with reference to FIG. Note that, in FIG. 1, the relative thicknesses of the underlayer and the photoresist are shown differently from the actual ones so as to clarify the characteristic part of the present invention. The same is true for. FIG. 1 shows the variation of the photoresist pattern size due to the influence of the standing wave of the exposure light generated in the photoresist, and the standing wave effect strongly occurs during the process of exposing and developing the photoresist formed on the underlayer. The parts where the standing wave effect is weakly generated are shown in contrast with each other. 1A to 1C relate to a portion where the standing wave effect is strongly generated, and FIG.
The symbols (e) to (e) relate to portions where the standing wave effect is weakly generated. The magnitude of this standing wave effect is largely due to the photoresist film thickness. FIG. 1A and FIG.
(D) shows up to the step of forming the positive photoresist 2 on the underlayer 1 such as a semiconductor substrate and exposing the positive photoresist 2 through a mask pattern (not shown), and 3 indicates An unexposed portion of the positive photoresist 2 is an exposed portion of the positive photoresist 2, and a reference numeral 5 is a boundary portion (uneven portion) between the unexposed portion 3 of the photoresist 2 and the exposed portion 4. As can be seen from the comparison between FIG. 1A and FIG. 1D, the influence of the standing wave effect is represented by the size of the uneven portion 5 formed on the side wall of the photoresist pattern, where the standing wave is strongly generated. The uneven portion 5 is large, and the uneven portion 5 is small where it is weak. This uneven portion 5
About the bake after exposure (PEB: PO)
By performing ST EXPOSURE BAKE), the uneven portion 5 is relaxed before the development. FIG.
(B) and FIG. 1 (e) show a baking process which is usually performed after exposure and before development. Uneven portion 5 on the side wall of the photoresist pattern when PEB is performed
Are alleviated, and the unexposed portion 3 and the exposed portion 4 of the photoresist 2 are
Has a substantially planar shape, and the boundary is located approximately in the middle between the concave portion and the convex portion. Therefore, the size of the photoresist pattern after development is as shown in FIG.
The size is defined at a position approximately midway between the concave portion and the convex portion as indicated by symbols A and A ′ in (f). 1C and 1F show the steps of developing the baked photoresist. The exposed portion 4 of the photoresist 2 is removed by the development, and a photoresist pattern that can be used for etching or ion implantation is completed.

As shown by the symbols A and A'in FIGS. 1 (c) and 1 (f), respectively, when a hole pattern is formed in the positive photoresist 2, a photoresist film thickness where a standing wave is strongly generated. The size of the photoresist pattern (in this case, the size of the hole bottom) formed is larger than where the photoresist film thickness is such that the standing wave is weakly generated (A> A ′). That is, the variation width of the photoresist pattern dimension due to the standing wave effect is such that the pattern size A of the portion where the standing wave is strong and the pattern size A ′ of the portion where the standing wave is weak are generated.
Will be determined by the difference A-A '. Therefore, if a method of correcting so that the size of the hole is reduced in a portion where the standing wave effect is strongly generated, the width of the size variation due to the standing wave effect can be suppressed. In this case, of course, it should be taken into consideration that the corrected size becomes the hole size to be finally obtained.

However, in each pattern of the portion where the standing wave is strongly generated and the portion where the standing wave is weakly generated, the difference in the width of the portion where the width of the hole is the smallest (the interval between the opposing convex portions) is different. , The width is smaller than the difference in width at the intermediate position of the unevenness. The variation amount of the photoresist pattern will be described with reference to FIG. Figure 2 (a)
(Halls where strong standing waves are generated) and Fig. 2
As shown in (b) (Hole in the portion where the standing wave is weakly generated), B is the hole width of the portion where the width of the strongest standing wave is smallest and B is the standing B'is the hole width at the portion where the hole width is smallest in the portion where the wave is weak, and C is the hole width at the intermediate position of the unevenness in the portion where the standing wave is strongly generated.
If the hole width at the middle position of the unevenness in the portion where the standing wave is weakly generated is C ', the difference between B and B'BB'
Is smaller than the difference C-C 'between C and C'. Therefore, by making it possible to etch, for example, the substrate or the insulating film that will be the underlying layer at the positions B and B ′, it is possible to minimize the influence of the dimensional variation of the photoresist pattern due to the standing wave effect. .

However, as shown in FIG. 3, the unevenness on the sidewall of the photoresist pattern adversely affects subsequent processes. That is, when an attempt is made, for example, to perform etching using such a photoresist pattern, the concavo-convex portion formed on the sidewall of the photoresist pattern is
As shown in FIG. 3A, the inflow direction of the etching gas 6 at the time of etching the underlayer 1 is changed, or as shown in FIG. 3B, the photoresist itself is etched (see FIG.
(In the direction of the arrow in (b)) to cause a change in the size and shape of the underlayer 1 to be etched, the uneven portion 5 is formed.
It is difficult to use the photoresist pattern in which the photoresist remains as a mask for etching. Therefore, in the present invention, this problem is solved by using another photoresist or the like and embedding the uneven portion 5 on the side wall of the photoresist pattern as shown in FIG.

The present invention based on the above technical idea will be described in more detail with reference to embodiments. (Embodiment 1) In this embodiment, a process is used in which a resist pattern is formed by an i-line positive photoresist, and the concave portion on the side wall of the resist pattern is filled with a positive photoresist for KrF excimer laser. i-
A general naphthoquinonediazido novolac resin is used as a line positive photoresist, but this material system has a transmittance of almost 0 for light having a wavelength of 300 nm or less.
%, Light of KrF excimer laser (248 nm)
Is known not to penetrate.

FIG. 4 shows a method of forming a photoresist pattern according to the first embodiment. First, as shown in FIG.
An i-line positive photoresist is applied to the underlayer 1 and exposed by a reduction projection exposure device using a monochromatic light source (in this case, the i-line of a mercury lamp). This can be formed in the same manner as a normal photoresist pattern forming process. Then, baking is performed to such an extent that the irregularities 5 on the side wall of the photoresist generated during development are not lost. By baking, the resist in the exposed and non-exposed areas can be mutually diffused, and the irregularities on the side wall of the resist pattern due to the standing wave effect can be mitigated. It is possible to adjust the dimensional difference in the weakly generated portion. That is, since the interval between B and B ′ in FIG. 2 increases depending on the baking time when baking is performed, the dimensional difference between the two can be made smaller by appropriately adjusting the baking time. At this time, for example, when B and B ′ are almost equal to each other, it is not necessary to perform the baking if it is convenient to carry out the development without baking to suppress the pattern size difference. After that, development is performed and the photoresist surface is further dried. At this time, if necessary, baking is performed to cure the photoresist.
Next, as shown in FIG. 4B, a positive photoresist 7 for KrF excimer laser is applied on the underlayer 1 and the photoresist 2. Next, as shown in FIG. 4C, the entire surface is irradiated with light 8 of a KrF excimer laser. At this time, the positive photoresist 7 for KrF excimer laser is exposed to light to form the exposed portion 9, but the i-line photoresist 2 does not pass the light 8 of the excimer laser, so that the uneven portion 5 on the side wall of the photoresist 2 is exposed. The excimer laser photoresist 7 portion that has entered the recess is not exposed. Therefore, if development is performed thereafter, the excimer laser photoresist other than the concave portions on the side wall of the i-line photoresist 2 is removed as shown in FIG. It can be embedded with a laser photoresist 7. That is, the irregularities due to standing waves appearing on the sidewalls of the photoresist are embedded with a photoresist that is sensitive to light of a wavelength that does not pass through (is not exposed to) the patterned photoresist, and only the latter photoresist is exposed over the entire surface. It is possible to embed only the concavo-convex portion due to the standing wave by exposing and developing with light.

By forming a photoresist pattern by such a method, as shown in FIG. 5A, when etching is performed, for example, the etching gas 6 is directed in a desired direction without causing unnecessary scattering. And can be etched as expected as shown in FIG. 5 (b). Furthermore, the photoresist pattern formed as in this embodiment can be applied to fine processing even when ion implantation or film formation is performed after the photoresist pattern is formed.

(Embodiment 2) In Embodiment 2, the deposits formed on the photoresist during dry etching are used to fill the irregularities on the sidewall of the photoresist. FIG. 6 shows a method of forming a photoresist pattern according to the second embodiment. First, as shown in FIG. 6A, a positive photoresist 2 is formed on the underlayer 1, and a photoresist pattern is formed on the side wall of the photoresist 2 which is caused by the standing wave effect, and which has an uneven portion 5. Up to this point, it can be formed in the same manner as in the first embodiment described with reference to FIG. After that, as shown in FIG. 6B, the underlayer 1 is etched using a gas-based etching gas 10 having a strong deposition property. For example, when the underlayer 1 is a silicon substrate or a silicon oxide film, if etching is performed with a gas containing CHnFm (n and m are integers), a fluorocarbon-based deposit is generated as a by-product of the etching, and as a result, the uneven portion 5 is formed. The recessed portions are filled with the deposit 11. Further, if etching with strong anisotropy is performed, the inside of the concave portion of the concave-convex portion 5 on the side wall of the photoresist 2 is less likely to be etched, so that the deposit 11 is likely to collect and it is more effective. Since the ratio between the amount of the deposit 11 generated by etching and the etching amount of the underlayer 1 can be adjusted by controlling the gas-based flow rate ratio, etc., the etching of the underlayer and the filling of the photoresist sidewall can be performed simultaneously. Alternatively, by changing the conditions such as the flow rate ratio during etching, it is possible to efficiently fill the unevenness of the photoresist sidewall at the initial stage of etching to weaken the depositability and then perform the etching of the underlayer. By etching the underlayer while embedding the irregularities in a deposit generated during etching, as shown in FIG. 6C, the etching gas does not cause unnecessary scattering as in the case of the first embodiment. It can be introduced in the direction of the underlayer and etching can be performed as expected.

In the above-mentioned two embodiments, the positive type photoresist was taken as an example of the photoresist for forming the resist pattern, but the photoresist in the present invention is not limited to the positive type photoresist and may be a negative type photoresist. It goes without saying that it can also be applied to photoresist. Similarly, in Example 1, a positive photoresist is used also as a resist for filling the concave portions of the concave and convex portions on the side wall of the photoresist forming the resist pattern. This is the treatment of the underlying layer after the formation of the photoresist pattern. Anything that does not adversely affect

Further, the present invention can be applied to a substrate such as a semiconductor substrate, a conductor substrate or an insulating substrate as the underlayer, as well as various films such as a silicon oxide film used in a semiconductor device. Further, the method of forming the photoresist pattern of Example 1 can be used as the method of forming the photoresist pattern for performing the etching as described above, and also the method of forming the photoresist pattern for performing the ion implantation and the film formation. The forming method can be applied without departing from the spirit thereof.

[0025]

As described above, in the method for forming a photoresist pattern of the present invention, development is performed while leaving a wavy step (uneven portion) generated on the photoresist sidewall during exposure,
Then, by filling the recesses to form flat photoresist sidewalls, it is possible to suppress dimensional fluctuations caused by standing waves generated when the mask pattern is exposed on the photoresist formed on the stepped underlying layer. it can. Therefore, by forming a circuit pattern or the like using such a photoresist pattern, a fine circuit pattern or the like can be accurately formed. Further, by burying the concave portion of the uneven portion formed on the photoresist side wall with a by-product generated when dry etching is performed, the side wall can be embedded and etched simultaneously or successively. Further, the photoresist pattern formed according to the present invention enables the processing of the underlayer such as etching without variation in dimension above and below the step even on the underlayer having the step. Further, by using the photoresist pattern formed according to the present invention, it is possible to manufacture a semiconductor device in which the characteristic fluctuations above and below the step are small even on the underlying layer having the step.

[Brief description of drawings]

FIG. 1 is a diagram showing a variation of a photoresist pattern dimension due to an influence of a standing wave of exposure light generated in a photoresist.

FIG. 2 is a diagram for explaining a variation amount of a photoresist pattern.

FIG. 3 is a diagram for explaining the influence of unevenness on the sidewall of the photoresist pattern on subsequent steps.

FIG. 4 is a diagram showing a method for forming a photoresist pattern according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a process of etching an underlayer using a photoresist pattern according to the present invention.

FIG. 6 is a diagram showing a method for forming a photoresist pattern according to a second embodiment of the present invention.

FIG. 7 is a diagram for explaining a problem when an antireflection film is used as a lower layer of a resist which is a conventional technique.

[Explanation of symbols]

1 Underlayer 2 Positive type photoresist 3 Unexposed part of positive type photoresist 4 Exposed part of positive type photoresist 5 Uneven part 6 Etching gas 7 KrF excimer laser positive type photoresist 8 KrF excimer laser light 9 KrF excimer laser type Exposed part of positive photoresist 10 Gas-based etching gas with strong depositability 11 Deposit

Claims (3)

[Claims] 1. A step of forming a first photoresist on an underlayer, a step of exposing a mask pattern on the first photoresist, and an uneven portion formed on the sidewall of the first photoresist by the exposure. A method of forming a photoresist pattern, which comprises: a step of developing the photoresist pattern while leaving the above; and a step of filling the concave portion of the uneven portion. 2. In the step of filling the recess, the first photoresist is filled with a second photoresist that is exposed to light of a wavelength that is not exposed, and the second photoresist is exposed to light that is exposed only to the second photoresist. 2. The method for forming a photoresist pattern according to claim 1, further comprising the step of exposing and developing the photoresist. 3. The method for forming a photoresist pattern according to claim 1, wherein the step of filling the recess is performed by filling with a by-product generated by introducing an etching gas.