JP2002151381A - Pattern formation method - Google Patents

Abstract

(57) Abstract: Two patterns can be simultaneously formed by one photolithography using exposure with a gray tone mask, and after removing a thin photoresist pattern by ashing or the like, a thick photoresist is removed. The second patterning is performed while leaving the resist pattern. However, the shape of the thick photoresist pattern varies depending on post-baking conditions after development, and the variation increases the variation of the thick photoresist pattern remaining after ashing. Occurs. The post-baking after development is performed at 110 to 115 ° C.
By performing under the temperature range of 130 to 150 seconds,
The thickness of the edge portion of the thick resist pattern 72 is made nearly vertical, the thickness of the photoresist in the lateral direction is reduced by ashing, and the variation of the opening width d0 of the remaining resist pattern 73 is 0.4 to ₀ . Can be as small as 6 μm,
The opening width can be formed with good uniformity.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a method for forming a pattern for a semiconductor device, and more particularly to a method for forming a plurality of patterns with one photoresist pattern.

[0002]

2. Description of the Related Art When manufacturing a thin film transistor or the like, there is a photolithography technique as a technique for forming a pattern. Photolithography is a series of three steps consisting of applying a photoresist having photosensitivity, irradiating a predetermined pattern of ultraviolet rays to expose the photoresist, and dissolving the photoresist in the exposed or unexposed portions. It is.

Usually, one pattern can be formed by one photolithography, and a thin film transistor or the like is completed by passing the photolithography 5 to 8 times.

[0004] In recent years, as the price of liquid crystal panels has been reduced, it has become necessary to reduce the manufacturing cost of thin film transistors. In the case of thin film transistors, the manufacturing cost can be greatly reduced by reducing the number of photolithography operations. Had limitations.

In recent years, however, two techniques such as exposure using a gray-tone mask (disclosed in Japanese Patent Application Laid-Open No. 2000-066240) or a half-tone mask, or double exposure, use two techniques. A pattern can be formed simultaneously.

[0006]

However, when this technique is used, the photoresist pattern is divided into two regions having different thicknesses, that is, a thick photoresist pattern and a thin photoresist pattern (of course, three types of photoresist patterns). A photoresist pattern having the above film thickness is also conceivable.) After forming this photoresist pattern, the thin photoresist pattern is removed by ashing or the like.
Leave a thick photoresist pattern. However, at this time, the shape of the photoresist pattern, particularly the shape of the thick photoresist pattern, varies depending on the post-baking conditions after development, and the variation increases the variation of the thick photoresist pattern remaining after ashing. Occurs.

An object of the present invention is to form a photoresist pattern having a different film thickness by one photolithography, and to form two patterns using the same, a photoresist pattern used for the second pattern formation. It is an object of the present invention to provide a pattern forming method capable of accurately forming a pattern.

[0008]

According to the present invention, there is provided a pattern forming method comprising the steps of forming a resist pattern comprising a thick resist pattern and a thin resist pattern having different film thicknesses on a film to be etched, and using the resist pattern as a mask. Removing the film to be etched from its surface over its entire thickness, and etching the resist pattern uniformly from its surface to stop etching when the thin resist pattern is removed, Leaving a part of the thick resist pattern of the resist pattern on the film to be etched and leaving the thick resist pattern as a residual resist pattern, wherein the step of forming the resist pattern comprises: A positive resist film is applied on the film to be etched, and a second resist is applied to the resist film. After performing the heat treatment, the resist film in the region of the resist film where the resist pattern is not formed has a first exposure dose, and the region of the resist film where a thin resist pattern is to be formed is less than the first exposure dose. Each of which is selectively exposed with a smaller second exposure amount, and subsequently, the resist film is developed.
Basically, the second heat treatment is performed at a temperature in the range of ° C. The pattern forming method of the present invention has various application modes as described below.

First, the heat treatment time of the second heat treatment is as follows:
When performed at a temperature in the range of 110-115 ° C, 1
30 to 150 seconds, when performed at a temperature in the range of 20 to 110 ° C, 30 to 130 seconds, and when performed at a temperature in the range of 115 to 145 ° C, 10 to The range is 30 seconds.

Further, the first exposure amount and the second exposure amount are obtained by irradiating light to a mask pattern on which three patterns having different light transmission amounts are formed. The second exposure amount is obtained through a pattern having the largest light transmission amount among the three different patterns, and the second exposure amount is obtained through a pattern having the second largest light transmission amount among the three different patterns.

Further, the step of uniformly etching the resist pattern from its surface is performed by ashing the resist pattern, and the ashing is performed by reactive ion etching in an oxygen gas atmosphere or oxygen etching. This is plasma etching in a gas atmosphere, and the oxygen gas atmosphere is a mixed gas of an oxygen gas and a gas containing F (fluorine).

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS When a different pattern is formed by one photolithography, a positive photoresist is applied on a film to be etched, and then exposure using a gray tone mask or a half tone mask, or Simultaneously forming a thick resist pattern (unexposed part) and a thin resist pattern (half exposed part) with different film thicknesses by a double exposure method or the like, and using the thick resist pattern and the thin resist pattern as masks for the film to be etched. Forming a first etching, followed by removing the thin resist pattern by etching to leave a thick resist pattern, and performing a second etching on the film to be etched using the remaining thick resist pattern as a mask; Is adopted. The present invention is characterized by a method of forming a thick resist pattern and a thin resist pattern simultaneously.

That is, the positive photoresist applied on the film to be etched is exposed using a gray-tone mask or a half-tone mask, or is exposed by a double exposure method or the like, and is subsequently developed. Bake (below,
(Referred to as post-baking) in a predetermined temperature range and a heat treatment time so that the shape of the edge portion of the thick resist pattern remaining after the thin resist pattern is removed by etching is nearly vertical, and the line of the remaining thick resist pattern is formed. The feature is that the width variation is reduced.

Next, an embodiment of the present invention will be described by taking a method of forming a thin film transistor used in a liquid crystal display device as an example.
This will be described with reference to FIGS. 1 to 3 are sectional views showing a method of forming a pattern of an amorphous silicon island and a source / drain electrode forming an active layer of a thin film transistor by one photolithography in the order of manufacturing steps.

First, a base insulating film 2 for forming islands and source / drain electrodes of a thin film transistor is deposited on a transparent substrate 1. Next, an amorphous silicon (hereinafter abbreviated as a-Si) film 3 is formed.
A metal film (chromium, aluminum, molybdenum, etc.) 4 is deposited. Transparent substrate 1 on which a-Si film 3 and metal film 4 are deposited
Then, a positive type photoresist film 5 is applied using an application device. Here, the positive photoresist film 5 is a metal film 4
A positive photoresist is applied to a thickness of about 2.0 μm by a method such as a spin coater, and prebaked.

Next, a predetermined photoresist pattern is formed by photolithography. Exposure is performed using a half-tone mask 6 (or a gray-tone mask) by an exposure apparatus such as an aligner or a stepper. The gray-tone mask 6 is divided into a complete light-transmitting portion 61 that transmits light, a semi-light-shielding (half-tone) portion 62 corresponding to a channel region between the source and drain electrodes, and a complete light-shielding portion 63 corresponding to other regions. (In the case of a gray-tone mask, the semi-light-shielding portion corresponding to the channel region between the source and drain electrodes is formed in a lattice pattern). The positive photoresist film 5 is exposed using a halftone mask 6 (FIG. 1A). Here, when a halftone mask or a graytone mask is not used, the mask for the island and the source / drain electrodes may be exposed separately and continuously by a double exposure method.

Next, using a developing device, the positive type photoresist film 5 is dissolved with an alkaline developing solution, and rinsed with pure water, dried, post-baked and cooled. As a result, the resist pattern 7 is formed in the region corresponding to the island and the source / drain electrodes, but the resist pattern in the region corresponding to the channel region of the island is formed thin to form the thin resist pattern 71, and is not included. The resist pattern is formed thick to form a thick resist pattern 72 (FIG. 1B).

At this time, the post-baking is performed at 110 to 11
It is applied at a temperature of 5 ° C. for 130 to 150 seconds.

Next, the metal film 4 is etched by a method such as wet etching or dry etching using the resist pattern 7 as a mask, and the a-Si film 3 is further etched by dry etching. A laminated film pattern 8 composed of the film 4 is formed (FIG. 2).
(A)).

Next, with respect to the resist pattern 7,
O ₂ or a mixed gas containing O ₂ (SF ₆ + O ₂ , CF ₄ +
If dry etching is performed by reactive ion etching in O ₂ or the like and only the thin resist pattern 71 corresponding to the channel region is removed by ashing, the thick resist pattern 72 is also etched at the same time, but a part remains. It becomes the resist pattern 73 (FIG. 2)
(B)).

Next, using the remaining resist pattern 73 as a mask, only the region of the metal film 4 corresponding to the channel region is etched by a method such as wet etching or dry etching (FIG. 3A).

Finally, if the remaining resist pattern 73 is peeled off, the pattern of the island 9 and the source / drain electrodes 10 can be obtained simultaneously by one photolithography (FIG. 3B).

As described above, the island 9 and the source / drain electrodes 10 are formed by one photolithography. Here, the effect of the post-bake which is a feature of the present invention will be described.

The post-bake after development volatilizes and removes impurities (such as a developing solution and a rinsing solution) in or on the photoresist to give the photoresist a plasma resistance.
Further, it is performed to improve the adhesion between the photoresist and the underlayer. Further, the photoresist undergoes a shape change due to a thermal softening phenomenon due to the heat of the post-baking. As the post-baking temperature increases, the shape of the edge portion of the photoresist pattern (the inclination angle θ, which is the inclination from the surface of the transparent substrate 1, increases). Point) becomes gentler (the inclination angle θ becomes smaller).

However, if the post-baking is performed under optimal conditions (temperature and time at which the photoresist on the entire substrate does not undergo thermal softening), the photoresist does not undergo thermal softening, so the inclination angle of the edge portion, as shown in FIG. 2 (a), showing the inclination angle theta ₀ nearly perpendicular.

That is, 110 to 11 employed in this embodiment
By performing the baking time in the temperature range of 5 ° C. for 130 to 150 seconds, the inclination angle of the edge portion of the photoresist pattern can be made almost vertical.

As described above, by making the shape of the edge portion of the photoresist pattern nearly vertical, when the remaining resist pattern 73 is formed by ashing or the like, the film thickness of the photoresist in the horizontal direction due to ashing is reduced. In order to reduce the variation, the variation of the opening width d ₀ (= 10 μm) of the remaining resist pattern 73 after ashing can be reduced to 0.4 to 0.6 μm, and the opening width can be formed with high uniformity (FIG. b)).

If the shape of the edge portion of the resist pattern 107 corresponding to FIG.
As shown in (a), when the 'tail' portion of the thick resist pattern 172 is gentle and exhibits an inclination angle θ (θ <θ ₀ ), the thin resist pattern 171 is removed by etching by ashing or the like, and the remaining resist pattern 173 is removed. When forming the resist pattern, the thickness of the resist pattern 172 in the lateral direction due to ashing is greatly reduced, so that the variation in the opening width d (= 10 μm) of the remaining resist pattern 173 after ashing is as large as 0.8 μm or more. It will vary (FIG. 4B).

Further, depending on the difference in the post-baking conditions,
The inclination angle θ of the edge portion of the thick resist pattern 172 varies within the substrate. This thick resist pattern 17
The variation in the inclination angle θ of the edge portion 2 causes one variation in the opening width d of the remaining resist pattern 173 after ashing.

As shown in FIG. 5, when the correlation between the opening width d of the remaining resist pattern and the post-bake temperature is plotted, when the baking time is fixed at 140 seconds, the opening width d is increased from 115 ° C. or higher. Shows a tendency to worsen rapidly. At this time, the shape of the edge portion of the remaining resist pattern changes to a rounded shape from about 120 ° C. after the post-bake temperature because a shape change due to the thermal softening phenomenon starts to occur.

In the embodiment of the present invention, the post-baking after the development is performed at a temperature of 130 to 15 ° C. under a temperature range of 110 to 115 ° C.
Although it is performed for 0 second, it is sufficient that the photoresist does not undergo a shape change due to the thermal softening phenomenon by the post-baking. Therefore, as another embodiment of the post-baking, the following method is also possible. (1) Post bake temperature: 20 to 110 ° C, bake time: 30 to 130 seconds (2) Post bake temperature: 115 to 145 ° C, bake time: 10 to 30 seconds (3) No post bake treatment is performed

[0032]

As described above, in the pattern forming method of the present invention, when forming a thick resist pattern and a thin resist pattern by one photolithography, the post-baking conditions are optimized and the thick resist pattern is formed. By preventing the 'hem' shape from flowing,
After removing the thin resist pattern by etching, the 'hem' of the thick resist pattern can be made more vertical so that the line width variation of the pattern can be kept small, so that pattern formation by subsequent etching can be performed with high precision It can be.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view showing a manufacturing method according to an embodiment of the present invention in the order of manufacturing steps.

FIG. 2 is a schematic cross-sectional view showing a manufacturing step following FIG. 1;

FIG. 3 is a schematic cross-sectional view showing a manufacturing step following FIG. 2;

FIG. 4 is a schematic cross-sectional view showing a photoresist pattern shape when a softening phenomenon occurs in a photoresist pattern due to a difference in post-bake conditions.

FIG. 5 is a graph showing the post-bake temperature dependence of the variation in the opening width of the photoresist pattern.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Transparent substrate 2 Base insulating film 3 a-Si film 4 Metal film 5 Positive photoresist film 6 Gray tone mask 7, 107 Resist pattern 8, 108 Stacked film pattern 9 Island 10 Source / drain electrode 61 Fully transparent part 62 Semi-light-shielding Part 63 Complete light shielding part 71, 171 Thin resist pattern 72, 172 Thick resist pattern 73, 173 Residual resist pattern

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H01L 21/3065 H01L 21/30 502P 514C 21/302 H

Claims (8)

[Claims] 1. A step of forming a resist pattern comprising a thick resist pattern and a thin resist pattern having different film thicknesses on a film to be etched, and using the resist pattern as a mask to move the film to be etched from its surface to the entire film thickness. And removing the resist pattern, the etching is stopped when the thin resist pattern is removed by uniformly etching the resist pattern from the surface thereof, and a part of the thick resist pattern in the resist pattern is removed. Leaving the thick resist pattern on the film to be etched to form a remaining resist pattern, wherein the step of forming the resist pattern comprises forming a positive resist film on the film to be etched. After applying and subjecting the resist film to a first heat treatment, The resist film in the region where the resist pattern is not formed is selectively exposed at the first exposure amount, and the region of the resist film where the thin resist pattern is to be formed is selectively exposed at the second exposure amount smaller than the first exposure amount. Exposed, followed by developing the resist film,
A pattern formation method, wherein the second heat treatment is performed at a temperature in a range of from about 145 ° C. to about 145 ° C. 2. The heat treatment time of the second heat treatment is 11
When performed at a temperature in the range of 0 to 115 ° C, 130
2. The pattern forming method according to claim 1, wherein the time is in the range of from 150 to 150 seconds. 3. The heat treatment time of the second heat treatment is 20 times.
When carried out at a temperature in the range of ~ 110 ° C, 30 ~ 1
2. The pattern forming method according to claim 1, wherein the period is 30 seconds. 4. The heat treatment time of the second heat treatment is 11
When performed at a temperature in the range of 5 to 145 ° C, 10 to
2. The pattern forming method according to claim 1, wherein the period is 30 seconds. 5. The method according to claim 1, wherein the first exposure amount and the second exposure amount are obtained by irradiating light on a mask pattern on which three patterns having different light transmission amounts are formed. 5. The method according to claim 1, wherein the second exposure amount is obtained through a pattern having the highest light transmission amount among the three different patterns, and the second exposure amount is obtained through a pattern having the second highest light transmission amount among the three different patterns. The pattern forming method according to any one of the above. 6. The pattern forming method according to claim 1, wherein the step of uniformly etching the resist pattern from its surface is performed by ashing the resist pattern. 7. The pattern forming method according to claim 6, wherein the ashing is reactive ion etching in an oxygen gas atmosphere or plasma etching in an oxygen gas atmosphere. 8. An oxygen gas atmosphere comprising oxygen gas and F gas.
The pattern forming method according to claim 7, wherein the pattern forming method is a mixed gas with a gas containing (fluorine).