A method for controlling the sidewall morphology of photoresist

Abstract

The invention provides a method for controlling the side wall morphology of photoresist, which comprises: positioning the center of a pre-treated wafer and coating it with photoresist; sequentially pre-baking, exposing and developing the wafer to obtain a photoresist pattern; pre-defining the size of the photoresist pattern; removing residual photoresist and hard film. The technical solution provided by the invention greatly improves the quality of pattern conversion caused by different substrate materials and pattern sizes, improves the process and reduces the cost.

Description

Technical Field

[0001] The invention relates to a semiconductor device preparation process, in particular to a photoresist side wall morphology control method. Background Art

[0002] With the advancement of integrated circuit manufacturing technology and the reduction of feature size, the integration of integrated circuit chips is getting higher and higher. The use of photoresist to achieve accurate transfer of mask patterns has become a key factor that directly affects chip integration and yield. According to process requirements, severe deformation of the photoresist sidewall morphology will directly affect the quality of patterning in subsequent processes. Therefore, the quality of the photoresist sidewall morphology is an important parameter to distinguish the process capabilities of various photoresists. The subsequent processes of different photolithography, such as etching, wet etching, and metal lift-off, have different requirements for the sidewall morphology of photoresists. In the photolithography process, due to the different properties of different photoresists, different feature sizes of photolithography patterns, and different related process requirements, the selected glue type is also different.

[0003] For the same photoresist of fixed thickness on different substrate materials, due to the different reflectivities of the substrates, the optical path difference between the photoresist sidewall exposure and the incident light is exactly an integer multiple of the wavelength of the light source, which leads to differences in the photoresist sidewall morphology; different graphic sizes and the resulting sidewall morphology are also difficult to be consistent, which in turn affects the graphic quality in subsequent processes. Summary of the invention

[0004] In view of the shortcomings of the prior art, the present invention provides a method for controlling the sidewall morphology of a photoresist of the same type with a fixed thickness. The technical solution provided by the present invention is as follows:

[0005] A method for controlling the sidewall morphology of a photoresist comprises the following steps:

[0006] (1) Centering the pre-treated wafer and applying photoresist;

[0007] (2) pre-baking, exposing, and developing the wafer obtained in step (1) in sequence to obtain a photoresist pattern, wherein the size of the photoresist pattern is predefined by the exposure, and residual photoresist exists in the developed area;

[0008] (3) removing the residual photoresist in the developed area, and reducing the size of the photoresist pattern by removing the photoresist. The final size of the photoresist pattern is obtained by subtracting the reduced size of the photoresist pattern from the size of the photoresist pattern predefined in step (2) and making the final size of the photoresist pattern reach the target size, and finally hardening the film.

[0009] Further, the preprocessing includes:

[0010] a) dehydrating and baking the wafer;

[0011] b) treating the wafer obtained in step a) with hexamethyldisilazane or trimethylsilyldiethylamine to increase adhesion in a coating developer.

[0012] Furthermore, the wafer is a wafer formed by a semiconductor substrate.

[0013] Furthermore, the glue coating has a thickness of 1.8 μm.

[0014] Furthermore, the pre-baking includes: baking at 120° C. for 90 seconds and then cooling for 30 seconds.

[0015] Furthermore, the exposure dose is 315-345ms, and the focus is -1.5-0.

[0016] Furthermore, the developing includes: developing for 60 seconds after center positioning to obtain a pattern.

[0017] Furthermore, the film hardening temperature is 120° C. and the time is 120 s.

[0018] The substrate material of the photoresist described in any of the above items includes silicon or silicon carbide wafers; the sidewall morphologies of the photoresist of the same fixed thickness include: inverted trapezoid, right angle and regular trapezoid, the exposure dose of the photoresist is 315-345ms, and the focus is -1.5-0.

[0019] Compared with the closest prior art, the technical solution provided by the present invention has the following beneficial effects:

[0020] 1) The technical solution provided by the present invention includes pretreatment, coating, pre-baking, exposure, development, pre-defining size, and removing residual photoresist and hard film. By fine-tuning the exposure dose and exposure focal length of the same type of photoresist, the morphology of the photoresist sidewall at different positions is stable and controllable, and high-quality pattern transfer is obtained. The sidewall morphology has good matching with the subsequent process, and the disadvantage of inconsistent sidewall morphology caused by substrate material and pattern size is effectively solved, overcoming the problem of poor quality of pattern conversion in the prior art;

[0021] 2) The technical solution of selectively changing the exposure dose and focus with less correlation provided by the present invention overcomes the drawbacks of the photoresist sidewall morphology caused by different substrate materials and pattern sizes, obtains a pattern with high conversion quality, and simplifies the process;

[0022] 3) The technical solution provided by the present invention greatly promotes the volatilization of the solvent in the film and the drying of the film by controlling the time and temperature of the pre-baking, so that the adhesion and wear resistance of the film to the wafer surface are improved.

[0023] 4) The technical solution provided by the present invention effectively compensates for the effect of the photoresist processing technology on the reduction of the photoresist pattern size by pre-defining the photoresist pattern, so that the photoresist pattern reaches the target size. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 Exposure schematic diagram of stepper lithography machine;

[0025] Figure 2 Schematic diagram of positive focal exposure;

[0026] Figure 3 Positive focus exposure exposes the side wall topography;

[0027] Figure 4 Schematic diagram of adhesive plane exposure;

[0028] Figure 5 Glue plane exposure exposure side wall topography;

[0029] Figure 6 Negative focal length exposure principle diagram;

[0030] Figure 7 Negative focal length exposure exposure side wall morphology,

[0031] Among them, 1 exposure source; 2 upper lens; 3 mask; 4 lower lens; 5 wafer; 6 stage; 7 ultraviolet light; 8 focal plane; 9 photoresist. DETAILED DESCRIPTION

[0032] The technical solution provided by the present invention is described clearly and completely below. Obviously, the described embodiments are only a part of the present invention, but not all.

[0033] The purpose of the present invention is to provide a method for controlling the sidewall morphology of a photoresist of the same type with a fixed thickness. The method can effectively improve the sidewall morphology problem caused by the difference in exposure dose received by photoresists of different thicknesses due to different reflectivities of substrate materials, as well as the inconsistency of the sidewall morphology caused by the size of the pattern, thereby obtaining a photoresist sidewall morphology that matches the requirements of subsequent processes and improving the quality of pattern transfer brought about by the photolithography process.

[0034] The technical solution provided by the present invention includes photoresist, a coating developer, and a stepper photolithography machine. The photoresist lines and through holes used therein can be applied. The coating developer is used for coating of photoresist, pretreatment of wafer surface cleaning and adhesion enhancement before coating, pre-baking of photoresist after coating, slow and sufficient volatilization of solvent in photoresist, and drying of film; the properties of photoresist change after exposure, and it is easier to dissolve in developer to form a pattern. The stepper photolithography machine used is a projection exposure, which adopts a stepper scanning method, realizes changing the exposure dose and focus by changing the exposure time and focus offset, and controls the photoresist sidewall morphology by fine-tuning the exposure dose and focus.

[0035] The exposure principle of the stepper lithography machine in the technical solution of the present invention is as follows Figure 1 As shown, the exposure source 1 is focused by the upper lens 2 and passes through the mask 3 to form an image of the mask 3. The image is focused and reduced by the lower lens 4 and then projected onto the surface of a photosensitive material wafer 5 coated with photoresist. The wafer 5 is placed on a stage 6. After exposure, the wafer 5 is developed, and the photoresist dissolves the area that receives light during exposure, thereby replicating the area with and without photoresist on the mask. Figure 2 As shown, the focal plane 8 of the ultraviolet light 7 is located a distance above the photoresist 9. At this time, since the light irradiated onto the wafer 5 is not parallel light, the light diffuses in the photoresist so that the photoresist 9 on the lower plane absorbs more light, thus forming the following Figure 3 The inverted trapezoidal or photoresist 9 has a photoresist sidewall morphology with an obtuse angle to the wafer; Figure 4 As shown, the focal plane 8 of the ultraviolet light 7 is located on the upper surface of the photoresist 9. At this time, the photoresist 9 is prone to form a sidewall morphology close to 90°, such as Figure 5 as shown; Figure 6 As shown, the focal plane 8 of the ultraviolet light 7 is located on the lower surface of the photoresist 9. Since the light processed by the lower lens is non-parallel and converges inward, the exposure area on the upper surface of the photoresist 9 is slightly larger than the lower surface, forming a positive trapezoid, that is, the side wall morphology of the photoresist and the wafer at an acute angle is shown in FIG. Figure 7 shown.

[0036] The technical solution provided by the present invention includes pretreatment, glue coating, pre-baking, exposure, development, pre-definition of size, removal of residual photoresist and hard film, and by fine-tuning the exposure dose and changing the exposure focal length at a fixed thickness of the same type of photoresist, a stable and controllable sidewall morphology is formed at different positions of the photoresist sidewall, thereby obtaining high-quality graphic transfer and a sidewall morphology matching the subsequent processability, effectively solving the problem of inconsistent sidewall morphology caused by substrate material and graphic size, which leads to poor quality of graphic conversion. By pre-defining the photoresist pattern, the effect of the photoresist processing process on the reduction of the photoresist pattern size is effectively compensated, so that the photoresist pattern reaches the target size.

[0037] Factors affecting the sidewall morphology of photoresist include: photoresist type, adhesion to wafer, spin coating method, thickness, pre-baking time and temperature, exposure time and focal length, and development time and temperature, etc. These factors are complex and changeable and affect each other. The present invention is to fix some interrelated factors affecting the photoresist morphology, select to change the exposure dose and focus with less correlation, thereby simplifying the change of the sidewall morphology of photoresist caused by different substrate materials and pattern sizes and other factors, improving the sidewall morphology matching the subsequent process requirements, thereby enabling the pattern to be converted with high quality, and simplifying the process complexity.

[0038] The development speed of photoresist is affected by the solvent content in the photoresist. If the solvent content is too high, the dissolution speed of the photoresist during development is relatively fast, which is easy to cause floating glue and the pattern is also easy to deform; however, a certain amount of solvent needs to remain in the photoresist to facilitate the conversion of the photosensitive agent diazoquinone into carboxylic acid. Therefore, the present invention strictly controls the time and temperature of pre-baking, greatly promotes the volatilization of the solvent in the film, the drying of the film, and improves the adhesion and wear resistance of the film to the surface of the wafer.

[0039] Example 1

[0040] The photoresist sidewall morphology control method provided in this embodiment includes the following steps:

[0041] (1) Glue coating: HMDS (hexamethyldisilazane) is applied to the surface of the wafer using a glue developer to enhance its adhesion, and then the center is positioned and 1.8um thick photoresist AZ 703 is spin-coated;

[0042] (2) Pre-baking: Bake at 120°C for 90 seconds and then cool for 30 seconds to remove excess solvent in the photoresist to prevent dust from sticking to the silicon wafer;

[0043] (3) Exposure: Expose the silicon wafer with the photoresist cured on the pre-baked surface, with an exposure dose of 345 ms and a focus of 0;

[0044] (4) Development: The exposed Si wafer with a 1.8 μm thick photoresist is positioned in the center of a coating and developing machine, and automatically developed for 60 seconds to dissolve the photoresist in the exposed area to obtain a pattern;

[0045] (5) predefining the size of the photoresist pattern by the exposure, and residual photoresist exists in the developed area;

[0046] (6) Removing residual photoresist in the developed area, and reducing the size of the photoresist pattern by removing the photoresist. The final size of the photoresist pattern is obtained by subtracting the reduced size of the photoresist pattern from the predefined size of the photoresist pattern, and the final size of the photoresist pattern reaches the target size.

[0047] (7) Hardening: Hardening includes treatment at 120°C for 120 seconds;

[0048] (8) Observation: The Si wafer after photolithography was sliced ​​and the cross section was observed by SEM. Figure 5 .

[0049] Example 2

[0050] This embodiment is the same as the steps of Embodiment 1 except that the substrate material is silicon carbide, the exposure dose is 315ms and the focus is -1.5.

[0051] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, a person skilled in the art can still modify or make equivalent substitutions to the specific implementations of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention are within the scope of protection of the claims of the present invention to be approved.

Claims

1. A method for controlling the sidewall morphology of a photoresist, characterized in that: The method comprises the following steps: (1) Position the center of the pre-treated wafer and apply photoresist; (2) pre-baking, exposing, and developing the wafer obtained in step (1) in sequence to obtain a photoresist pattern, wherein the size of the photoresist pattern is predefined by the exposure, and residual photoresist exists in the developed area; (3) removing the residual photoresist in the developed area, and reducing the size of the photoresist pattern by removing the photoresist, and obtaining the final size of the photoresist pattern by subtracting the reduced size of the photoresist pattern from the size of the photoresist pattern predefined in step (2) and making the final size of the photoresist pattern reach the target size, and finally hardening the film; The photoresist coating in step (1) has a thickness of 1.8 μm; The pre-baking comprises: baking at 120° C. for 90 seconds and then cooling for 30 seconds; The development comprises: developing for 60 seconds after center positioning to obtain a pattern; The film hardening temperature is 120°C and the time is 120s; The substrate material of the photoresist includes silicon or silicon carbide wafer; the sidewall morphology of the photoresist with the same fixed thickness includes: inverted trapezoid, right angle and regular trapezoid; the exposure dose of the photoresist is 315-345ms, focusing -1.5-0.

2. The method for controlling the sidewall morphology of photoresist according to claim 1, characterized in that: The pre-processing comprises: a) dehydration baking the wafer; b) treating the wafer obtained in step a) with hexamethyldisilazane or trimethylsilyldiethylamine to increase adhesion in a coating developer.

3. The method for controlling the sidewall morphology of photoresist according to claim 1, wherein: The wafer is a wafer formed of a semiconductor substrate.

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