Exposure method

Abstract

The present invention provides an exposure method, comprising: forming a first photoresist layer on a substrate, the first photoresist layer comprising a photoacid generator in a first ratio; forming a second photoresist layer on the first photoresist layer, the second photoresist layer comprising a photoacid generator in a second ratio; forming a third photoresist layer on the second photoresist layer, the third photoresist layer comprising a photoacid generator in a third ratio, the values ​​of the first ratio and the third ratio being both greater than the value of the second ratio; using a mask plate as a mask, using light generated by a light source to expose the third photoresist layer, the second photoresist layer and the first photoresist layer at one time, forming a groove located in the third photoresist layer, the second photoresist layer and the first photoresist layer, and the depth-to-width ratio of the groove is greater than 10. The reaction of the second photoresist layer to light can be reduced, and the reaction of the first photoresist layer and the third photoresist layer to light can be accelerated, thereby averaging the reaction of the three photoresist layers to light, so that the sidewall of the finally formed groove is straight.

Description

Technical Field

[0001] The present invention relates to the field of semiconductor technology, and in particular to an exposure method. Background Art

[0002] When photoresist is exposed to light sources such as ultraviolet light, laser, electron beam, ion beam and X-ray, its solubility will change. Since photoresist has photochemical sensitivity, it can be used for photochemical reaction. After exposure and development, the soluble part is removed, and the desired pattern will be formed in the photoresist layer. The remaining part protects the bottom layer, and its thickness must be thick enough to achieve the function of blocking etching. For example, some grooves are formed, and the structure and method of forming the grooves are as follows: Figure 1 A substrate 110 is provided, a photoresist layer 120 of a desired thickness is formed on the substrate 110, a mask plate 130 is arranged at a certain height on the photoresist layer 120, a desired pattern is provided on the mask plate 130, and a light source 140 is arranged above the mask plate 130 at a certain distance. A light beam 141 emitted by the light source 140 is incident on the photoresist layer 120 through the holes of the mask plate 130, and the photoresist layer 120 is dissolved during the exposure process to form a desired pattern. The holes on the mask plate 130 can be arranged according to the desired pattern. For example, if there are holes on the mask plate 130, the light beam 141 can be emitted to the photoresist layer 120 through the holes, and the photoresist layer 120 irradiated by the light beam is dissolved to form a groove.

[0003] However, in forming a groove with an aspect ratio (ratio of depth to width) greater than 10, if only one exposure is used, the exposure focus plane 142 is often set in the middle of the thickness of the photoresist layer 120. The energy begins to diffuse at the focus plane 142 (the middle of the photoresist thickness), but because the thickness of the photoresist layer 120 is too thick, insufficient energy will appear in the upper and lower halves of the photoresist layer 120. In order to achieve the corresponding critical dimensions, the exposure energy has to be increased to ensure that there is enough energy in the upper and lower halves of the photoresist layer 120, which results in excessive energy in the middle of the photoresist layer 120 at the focus plane 142. After development, the photoresist layer 120 will be bent in the middle, for example Figure 2 It can be clearly seen that the sidewall of the trench 150 is curved and is bent toward the remaining photoresist layer 120 , causing the trench 150 to be deformed, affecting subsequent processes.

[0004] Please refer to Figure 3 and Figure 4 The existing practice is to use two exposures. In the first exposure, the light source 140 is set far away from the surface of the photoresist layer 120, so that the focal plane 142 incident on the photoresist layer 120 is in the upper half of the photoresist layer 120, for example. Figure 3At this time, the focal plane 142 of the light beam incident on the photoresist layer 120 through the hole of the mask 130 is not in the middle of the photoresist layer 120, but in the upper half of the photoresist layer 120. At this time, the energy of the upper half of the photoresist layer 120 can be made to meet the standard. During the second exposure, the light source 140 is set closer to the surface of the photoresist layer 120, so that the focal plane 142 incident on the photoresist layer 120 is set in the lower half of the photoresist layer 120, so that the energy of the lower half can meet the standard, for example Figure 4 After two adjustments, the exposure energy can be evenly distributed at different depths of the photoresist layer 120, and a relatively straight sidewall of the groove can be obtained after development, that is, a relatively straight photoresist morphology on both sides of the groove can be obtained. However, a photolithography process uses two exposures, which greatly increases production costs and production time. Summary of the invention

[0005] The object of the present invention is to provide an exposure method, which can form a groove with relatively straight side walls by only one exposure, that is, can form photoresist morphologies on both sides of the relatively straight groove.

[0006] In order to achieve the above object, the present invention provides an exposure method, comprising:

[0007] providing a substrate;

[0008] forming a first photoresist layer on the substrate, wherein the first photoresist layer comprises a photoacid generator in a first ratio;

[0009] forming a second photoresist layer on the first photoresist layer, the second photoresist layer comprising a second ratio of a photoacid generator;

[0010] forming a third photoresist layer on the second photoresist layer, wherein the third photoresist layer comprises a photoacid generator in a third ratio, wherein the first ratio and the third ratio are both greater than the second ratio;

[0011] A mask plate and a light source are provided, and the mask plate is used as a mask. The light generated by the light source is used to sequentially expose the third photoresist layer, the second photoresist layer and the first photoresist layer at one time to form a groove, and the aspect ratio of the groove is greater than 10.

[0012] Optionally, in the exposure method, the mask is located above the third photoresist layer, and the light source is located above the mask.

[0013] Optionally, in the exposure method, the light source is located directly above the mask.

[0014] Optionally, in the exposure method, the groove exposes the substrate.

[0015] Optionally, in the exposure method, the sidewalls of the groove are straight and perpendicular to the substrate.

[0016] Optionally, in the exposure method, the thicknesses of the first photoresist layer, the second photoresist layer and the third photoresist layer are the same or different.

[0017] Optionally, in the exposure method, the photoacid generator is uniformly distributed in the first photoresist layer, the photoacid generator is uniformly distributed in the second photoresist layer, and the photoacid generator is uniformly distributed in the third photoresist layer.

[0018] Optionally, in the exposure method, photoresist is spin-coated to form the first photoresist layer, the second photoresist layer and the third photoresist layer.

[0019] Optionally, in the exposure method, a plurality of grooves are formed.

[0020] Optionally, in the exposure method, the light generated by the light source is laser.

[0021] In the exposure method provided by the present invention, a photoresist layer of a required thickness is divided into three layers, namely, a first photoresist layer, a second photoresist layer and a third photoresist layer which are sequentially located on a substrate, the first photoresist layer contains a first proportion of a photoacid generator, the second photoresist layer contains a second proportion of a photoacid generator, and the third photoresist layer contains a third proportion of a photoacid generator, and the first proportion and the third proportion are both greater than the second proportion. During exposure and development, since the photoacid generator reacts with light, the reaction of the first photoresist layer and the third photoresist layer with light can be accelerated, thereby averaging the reaction of the three photoresist layers with light, so that the sidewalls of the groove finally formed are straight, that is, the morphology of the photoresist on both sides of the groove is straight. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 is a schematic diagram of an exposure device of the prior art;

[0023] Figure 2 is a schematic diagram of a groove formed using an exposure device of the prior art;

[0024] Figure 3 is a schematic diagram of the first exposure in forming a groove using two exposures in the prior art;

[0025] Figure 4 is a schematic diagram of the second exposure in forming a groove using two exposures in the prior art;

[0026] Figure 5 is a flow chart of an exposure method according to an embodiment of the present invention;

[0027] Figure 6 is a schematic structural diagram of an exposure method according to an embodiment of the present invention;

[0028] Figure 7 is a schematic diagram of a structure for forming a groove according to an embodiment of the present invention;

[0029] In the figure: 110-substrate, 120-photoresist layer, 130-mask, 140-light source, 141-light beam, 142-focusing plane, 210-substrate, 220-first photoresist layer, 230-second photoresist layer, 240-third photoresist layer, 250-mask, 260-light source, 261-light beam, 270-groove. DETAILED DESCRIPTION

[0030] The specific implementation of the present invention will be described in more detail below in conjunction with the schematic diagram. The advantages and features of the present invention will become clearer based on the following description. It should be noted that the drawings are all in a very simplified form and are not in exact proportions, and are only used to facilitate and clearly assist in explaining the purpose of the embodiments of the present invention.

[0031] Hereinafter, the terms "first", "second", etc. are used to distinguish between similar elements and are not necessarily used to describe a particular order or chronological sequence. It is to be understood that these terms used in this manner are interchangeable where appropriate. Similarly, if the method described herein includes a series of steps, the order of these steps presented herein is not necessarily the only order in which these steps can be performed, and some of the steps described may be omitted and / or some other steps not described herein may be added to the method.

[0032] Positive photoresist is a type of photoresist, the part that is exposed to light will dissolve in the photoresist developer, while the part that is not exposed to light will not dissolve in the photoresist developer. Negative photoresist is a type of photoresist, the part that is exposed to light will not dissolve in the photoresist developer, while the part that is not exposed to light will dissolve in the photoresist developer. Therefore, the dissolution of photoresist is affected by the energy of light irradiation.

[0033] Please refer to Figure 5 The present invention provides an exposure method, comprising:

[0034] S11: providing a substrate;

[0035] S12: forming a first photoresist layer on the substrate, wherein the first photoresist layer comprises a photoresist containing a photoacid generator in a first ratio;

[0036] S13: forming a second photoresist layer on the first photoresist layer, wherein the second photoresist layer comprises a photoresist containing a photoacid generator in a second proportion;

[0037] S14: forming a third photoresist layer on the second photoresist layer, wherein the third photoresist layer comprises a photoacid generator in a third ratio, and the values ​​of the first ratio and the third ratio are both greater than the value of the second ratio;

[0038] S15: setting a mask plate and a light source, using the mask plate as a mask, and using the light generated by the light source to sequentially expose the third photoresist layer, the second photoresist layer and the first photoresist layer at one time to form a groove, wherein the aspect ratio of the groove is greater than 10.

[0039] For details, please refer to Figure 6 and Figure 7 First, a substrate 210 is provided, which may be a wafer, and a first photoresist layer 220, a second photoresist layer 230, and a third photoresist layer 240 are sequentially formed on the substrate 210. Next, a mask plate 250 is placed above the third photoresist layer 240 and at a certain distance from the third photoresist layer 240, and a light source 260 is placed above the mask plate 250 and at a certain distance from the mask plate 250.

[0040] Preferably, the thickness of the first photoresist layer 220, the second photoresist layer 230 and the third photoresist layer 240 is the same. In other embodiments of the present invention, the thickness of the first photoresist layer 220, the second photoresist layer 230 and the third photoresist layer 240 may also be different. But the thickness of the sum of the first photoresist layer 220, the second photoresist layer 230 and the third photoresist layer 240 is the required thickness, that is, if the groove with a depth-to-width ratio greater than 10 is to be formed, the depth of the groove needs to be determined according to the width of the groove, and the total thickness of the first photoresist layer 220, the second photoresist layer 230 and the third photoresist layer 240 needs to be determined. Therefore, the thickness of the first photoresist layer 220, the second photoresist layer 230 and the third photoresist layer 240 or the relationship between them can be unlimited. And the specific straightness of the first ratio, the second ratio and the third ratio can be determined according to the actual production situation, and the scope can be unlimited. However, the photoacid generator is evenly distributed in the first photoresist layer 220 , the photoacid generator is evenly distributed in the second photoresist layer 230 , and the photoacid generator is evenly distributed in the third photoresist layer 240 .

[0041] Preferably, the mask plate 250 is located above the third photoresist layer 240, and the light source 260 is located above the third mask plate 250, and the best embodiment of the light source 260 is located directly above the mask plate 250. This makes the light beam 261 emitted by the light source 260 uniform and able to fully cover the mask plate 250, and finally makes the light beam 261 incident on the third photoresist layer 240 uniform.

[0042] Preferably, the trench 270 exposes the substrate 210 . The sidewalls of the trench 270 are straight and perpendicular to the substrate. After the photoresist is dissolved by exposure, the bottom of the formed trench 270 directly exposes the surface of the substrate 210 .

[0043] Preferably, the light generated by the light source 260 is laser. In other embodiments of the present invention, the light may be ultraviolet light, laser, electron beam, ion beam and X-ray.

[0044] Further, the number of the grooves 270 formed is multiple. For example, there may be four grooves 270, which are respectively located at different places on the substrate, and there is a certain distance between the four grooves, and the four grooves 270 are all obtained by exposing and dissolving the first photoresist layer 220, the second photoresist layer 230 and the third photoresist layer 240. The depth and width of the four grooves 270 may be different, but the ratio of the depth to the width is greater than 10. In other embodiments of the present invention, there may be other numbers of grooves 270.

[0045] Furthermore, photoresist is spin-coated to form the first photoresist layer 220, the second photoresist layer 230 and the third photoresist layer 240. In other embodiments of the present invention, the first photoresist layer 220, the second photoresist layer 230 and the third photoresist layer 240 may also be formed by other methods.

[0046] In summary, in the exposure method provided in the embodiment of the present invention, the photoresist layer of the required thickness is divided into three layers, which are the first photoresist layer, the second photoresist layer and the third photoresist layer sequentially located on the substrate, the first photoresist layer contains a first proportion of a photoacid generator, the second photoresist layer contains a second proportion of a photoacid generator, and the third photoresist layer contains a third proportion of a photoacid generator, and the first proportion and the third proportion are both greater than the second proportion. During exposure and development, since the photoacid generator reacts with light, the reaction of the first photoresist layer and the third photoresist layer with light can be accelerated, thereby averaging the reaction of the three photoresist layers with light, so that the side walls of the finally formed groove are straight, that is, the morphology of the photoresist on both sides of the groove is straight.

[0047] The above is only a preferred embodiment of the present invention and does not limit the present invention in any way. Any technician in the relevant technical field, without departing from the scope of the technical solution of the present invention, makes any form of equivalent replacement or modification to the technical solution and technical content disclosed in the present invention, which does not depart from the content of the technical solution of the present invention and still falls within the protection scope of the present invention.

Claims

1. An exposure method, characterized in that: include: providing a substrate; forming a first photoresist layer on the substrate, wherein the first photoresist layer comprises a photoacid generator in a first ratio; forming a second photoresist layer on the first photoresist layer, the second photoresist layer comprising a second ratio of a photoacid generator; forming a third photoresist layer on the second photoresist layer, wherein the third photoresist layer comprises a photoacid generator in a third ratio, wherein the first ratio and the third ratio are both greater than the second ratio; A mask plate and a light source are provided, and the mask plate is used as a mask. The light generated by the light source is used to sequentially expose the third photoresist layer, the second photoresist layer and the first photoresist layer at one time to form a groove, and the aspect ratio of the groove is greater than 10.

2. The exposure method according to claim 1, wherein: The mask is located above the third photoresist layer, and the light source is located above the mask.

3. The exposure method according to claim 2, wherein: The light source is located directly above the mask.

4. The exposure method according to claim 1, wherein: The trench exposes the substrate.

5. The exposure method according to claim 1, wherein: The sidewalls of the trench are straight and perpendicular to the substrate.

6. The exposure method according to claim 1, wherein: The thicknesses of the first photoresist layer, the second photoresist layer and the third photoresist layer are the same or different.

7. The exposure method according to claim 1, wherein: The photoacid generator is evenly distributed in the first photoresist layer, the photoacid generator is evenly distributed in the second photoresist layer, and the photoacid generator is evenly distributed in the third photoresist layer.

8. The exposure method according to claim 1, wherein: Photoresist is spin-coated to form the first photoresist layer, the second photoresist layer and the third photoresist layer.

9. The exposure method according to claim 1, wherein: The number of grooves formed is plural.

10. The exposure method according to claim 1, wherein: The light generated by the light source is laser.

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