Double-layer photoresist photoetching process method for stripping

Abstract

The invention relates to a double-layer photoresist photoetching process method for stripping, which comprises the following steps of: firstly, sequentially spin-coating positive photoresist and reverse photoresist on a substrate, then performing exposure for the first time and reverse drying to enable the reverse photoresist to form protruding eaves on two sides of a T-shaped photoresist structure insoluble in a developing solution, and then performing exposure for the second time to form a T-shaped photoresist structure. And dissolving the photoresist outside the T-type photoresist structure in a developing solution, and finally developing to obtain the T-type photoresist structure. According to the invention, an obvious undercut T-type photoresist structure can be formed, the subsequent stripping of a film is facilitated, the precision of a photoetching pattern is high, the size of the undercut structure is controllable, and the problem of floating glue caused by long-time development can be avoided.

Description

Technical Field

[0001] The invention belongs to the field of semiconductor technology, and in particular relates to a double-layer photolithography process method for stripping. Background Art

[0002] The stripping process is a common method for patterned coating in semiconductor processes. The steps include photolithography to produce a patterned photoresist on a substrate, then coating the film, dissolving the photoresist with a solvent and stripping off the film on the photoresist to obtain a patterned film on the substrate. The photolithography step is particularly critical. After photolithography, a positive trapezoidal photoresist structure is formed, which is not conducive to the subsequent stripping of the film. After photolithography, a negative photoresist forms an inverted trapezoidal photoresist structure with an undercut, which is conducive to the subsequent stripping of the film. However, the negative photoresist process has the problem of low graphic accuracy and unclear undercut. In order to solve these problems, a double-layer photoresist photolithography process based on non-photosensitive photoresist has been developed, which effectively improves the quality of the stripping process.

[0003] The double-layer photolithography process is to spin-coat non-photosensitive photoresist and positive photoresist on the substrate in sequence, and then expose and develop with a slightly excessive time. Since only the exposed area of ​​the positive photoresist is soluble in the developer, and the non-photosensitive photoresist is soluble in the developer regardless of whether it is exposed or not, a slight excessive development will make the dissolution range of the bottom non-photosensitive photoresist slightly larger than the top positive photoresist, thereby forming an undercut T-shaped photoresist structure. The width of the protruding eaves of the T-shaped photoresist structure is determined by the excessive development time. The longer the overdevelopment time, the more the bottom photoresist dissolves, and the wider the protruding eaves of the T-shaped structure. Therefore, the size of the T-shaped protruding eaves in the double-layer photolithography process is difficult to control and has poor repeatability. The overdevelopment time is set entirely by personal experience, and the bottom photoresist becomes very narrow or even completely dissolved after long-term development, and there is a risk of floating glue. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an improved double-layer photoresist lithography process method based on positive photoresist and reverse photoresist to form a T-shaped photoresist structure with obvious undercut, thereby facilitating the subsequent stripping of a thin film.

[0005] Based on the positive and reverse photoresist characteristics, the present invention provides a double-layer photoresist lithography process method for stripping, comprising the following steps:

[0006] (1) Applying a double layer of photoresist: spin-coating a first photoresist on a substrate, fully drying it on a hot plate, and then spin-coating a second photoresist, and drying it on a hot plate; the first photoresist is a positive photoresist, and the second photoresist is a reverse photoresist;

[0007] (2) First exposure, reverse baking: The substrate is exposed to the first light with a first mask and a first exposure UV light, and after exposure, it is placed on a hot plate for reverse baking to form a first exposure area and an unexposed area; the unexposed area is insoluble in a developer, the first exposure area of ​​the first photoresist is soluble in a developer, and the first exposure area of ​​the second photoresist is cross-linked and insoluble in a developer after reverse baking. Based on this step, the reverse photoresist forms protruding ridges on both sides of a T-shaped photoresist structure that is insoluble in a developer;

[0008] (3) Second exposure: The substrate is exposed for a second time using a second mask and a second exposure ultraviolet light, and no heating is performed after exposure to form an overlapping exposure area of ​​the two exposures, a second exposure area, and an unexposed area; the unexposed area is insoluble in the developer, the overlapping exposure area and the second exposure area of ​​the first photoresist are soluble in the developer, the overlapping exposure area of ​​the second photoresist is insoluble in the developer, and the second exposure area of ​​the second photoresist is soluble in the developer. Based on this step, the photoresist other than the T-shaped photoresist structure is soluble in the developer;

[0009] (4) Development: The twice exposed substrate is developed with a developer to form a T-shaped photoresist structure with a protruding eaves.

[0010] Preferably, in the step (1), after spin coating the first photoresist, the drying temperature is 80-150° C., and the drying time is 1-30 min; after spin coating the second photoresist, the drying temperature is 80-150° C., and the drying time is 1-10 min.

[0011] Preferably, in step (2), the light-transmitting area of ​​the first mask plate corresponds to the protruding eaves of the T-shaped photoresist structure, and the width of the protruding eaves is the same as the width of the light-transmitting area of ​​the first mask plate and is greater than the photolithography alignment accuracy.

[0012] Preferably, the protruding eaves width of the T-shaped photoresist structure is 2-10 μm.

[0013] Preferably, the temperature of the reverse baking in step (2) is 80 to 150° C. and the time is 1 to 10 minutes.

[0014] Preferably, in the step (3), the width of the light-transmitting area of ​​the second mask is greater than the width of the gap between the T-type photoresist structure and less than the sum of the width of the gap between the T-type photoresist structure and the width of two adjacent protruding eaves, and during photolithography alignment, the light-transmitting area of ​​the second mask spans the gap between the T-type photoresist structure and does not exceed the positions of two adjacent protruding eaves.

[0015] More preferably, in step (3), the width of the light-transmitting area of ​​the second mask is equal to the sum of the width of the gap between the T-shaped photoresist structure and the average width of two adjacent protruding eaves.

[0016] Preferably, the gap width and position of the T-shaped photoresist structure in step (4) correspond to the width and position of the patterned film to be subsequently peeled off.

[0017] For positive photoresist, it is insoluble in developer before exposure to ultraviolet light, but soluble in developer after exposure to ultraviolet light. For reverse photoresist, it is insoluble in developer before exposure to ultraviolet light, but soluble in developer after exposure to ultraviolet light, and insoluble in developer again after exposure to ultraviolet light and reverse baking.

[0018] Beneficial Effects

[0019] The width of the protruding eaves on both sides of the T-shaped photoresist structure manufactured by the process method of the present invention is only determined by the width of the light-transmitting area of ​​the first mask, and has little to do with the development time. As long as the development time is appropriate, the photolithography pattern is basically revealed, and if the development time is continued to increase, the bottom and top photoresists will not continue to dissolve significantly. Therefore, the parameters of the undercut T-shaped structure are easy to control and have good repeatability. It avoids the problems of poor repeatability of the size of the T-shaped protruding eaves in the conventional double-layer glue process and the risk of floating glue after long-term development. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a schematic diagram of the overall process of the double-layer photolithography process method for stripping of the present invention.

[0021] Figure 2 It is a schematic diagram of the overall process of performing a stripping process using a double-layer photolithography process in an embodiment of the present invention.

[0022] Figure numerals: 1-substrate, 2-first photoresist, 3-second photoresist, 4-first mask, 5-first exposure to ultraviolet light, 6-first exposure area, 7-second mask, 8-second exposure to ultraviolet light, 9-overlapping exposure area, 10-second exposure area, 11-T-type photoresist structure, 12-thin film on photoresist, 13-thin film on substrate. DETAILED DESCRIPTION

[0023] The present invention will be further described below in conjunction with specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and are not intended to limit the scope of the present invention. In addition, it should be understood that after reading the content taught by the present invention, those skilled in the art can make various changes or modifications to the present invention, and these equivalent forms fall within the scope limited by the appended claims of the application equally.

[0024] The double-layer photolithography process for stripping of the present invention has the following overall process: Figure 1 As shown, the steps are as follows:

[0025] (1) Applying a double layer of photoresist: first, spin-coat a first photoresist 2 on a substrate 1, and fully dry it on a hot plate to prevent the two photoresists from dissolving each other when spin-coating a second photoresist 3; then, spin-coat the second photoresist 3, and dry it on a hot plate; wherein the first photoresist 2 is a positive photoresist, and the second photoresist 3 is a reverse photoresist;

[0026] (2) First exposure, reverse baking: The substrate 1 is exposed for the first time using the first mask plate 4 and the first exposure ultraviolet light 5, and after exposure, it is placed on a hot plate for reverse baking. The unexposed area is insoluble in the developer, the first exposure area 6 of the first photoresist 2 is soluble in the developer, the unexposed area of ​​the second photoresist 3 is insoluble in the developer, and the molecules of the first exposure area 6 of the second photoresist 3 are cross-linked after reverse baking and are also insoluble in the developer. This step allows the reverse photoresist to form protruding eaves on both sides of the T-shaped photoresist structure 11 that are insoluble in the developer, and the width of the protruding eaves is the width of the light-transmitting area of ​​the first mask plate 4, which is greater than the photolithography alignment accuracy;

[0027] (3) Second exposure: The substrate 1 is exposed for the second time using the second mask plate 7 and the second exposure ultraviolet light 8, and no heating or baking is performed after the exposure. This step can make the photoresist outside the T-type photoresist structure 11 soluble in the developer. The width of the light-transmitting area of ​​the second mask plate 7 is greater than the gap width of the T-type photoresist structure 11, and less than the sum of the gap width of the T-type photoresist structure 11 and the width of the two adjacent protruding eaves. During the photolithography alignment, the light-transmitting area of ​​the second mask plate 7 spans the gap of the T-type photoresist structure 11 and does not exceed the position of the two adjacent protruding eaves. Therefore, there is an overlapping area between the two exposures. The overlapping exposure area 9 and the second exposure area 10 of the first photoresist 2 are soluble in the developer; the overlapping exposure area 9 of the second photoresist 3 is insoluble in the developer. Since there is no reverse baking after the second exposure, the second exposure area 10 of the second photoresist 3 is soluble in the developer, and the unexposed area is insoluble in the developer.

[0028] (4) Development: The twice-exposed substrate 1 is developed with a developer to form a T-shaped photoresist structure with a T-shaped cross section, a narrow bottom and a wide top. The gap width and position of the T-shaped photoresist structure correspond to the width and position of the patterned film to be subsequently peeled off.

[0029] Example

[0030] In this embodiment, a periodic arrangement of metal stripes with a width of 16 μm and a spacing of 14 μm is fabricated on a substrate by a lift-off process. The overall process is as follows: Figure 2 As shown. First, a double-layer photoresist process is used for photolithography to form a T-shaped photoresist structure with a width of 14μm and a spacing of 16μm. The photolithography steps are as follows:

[0031] (1) Double-layer photoresist coating: First, spin-coat AZ1500 positive photoresist (first photoresist 2) on substrate 1 at a speed of 3000 rpm for 30 seconds. Dry on a hot plate at 90°C for 10 minutes. Then spin-coat AZ5214 reverse photoresist (second photoresist 3) at a speed of 3000 rpm for 30 seconds. Dry on a hot plate at 100°C for 3 minutes.

[0032] (2) First exposure, reverse baking: The substrate 1 is exposed for the first time using the first mask plate 4 and the first exposure ultraviolet light 5. The first mask plate 4 is a stripe plate, and the light-transmitting stripes are 4 μm wide and arranged at intervals of 6 μm and 16 μm. A SUSS MA8 photolithography machine is used, and the exposure time is 20 s, followed by reverse baking at a temperature of 100°C for 3 min. After exposure and reverse baking, the molecules of AZ5214 reverse photoresist are cross-linked and insoluble in the developer. AZ1500 positive photoresist is decomposed after exposure and is soluble in the developer.

[0033] (3) Second exposure: The substrate 1 is exposed for the second time using the second mask plate 7 and the second exposure ultraviolet light 8. The second mask plate 7 is a stripe plate, and the light-transmitting stripes are 20 μm wide and arranged at intervals of 10 μm. A SUSS MA8 photolithography machine is used, and the exposure time is 30 s. The second exposure decomposes the photoresist in the gap of the T-type photoresist structure 11. During the photolithography, the 16 μm wide stripes that are not exposed in step (2) are located in the 20 μm wide light-transmitting stripes of the second mask plate 7 and are aligned in the center. The overlapping exposure area 9 and the second exposure area 10 of the AZ1500 positive photoresist are soluble in the developer; the overlapping exposure area 9 of the AZ5214 reverse photoresist is insoluble in the developer. Since there is no reverse baking after the second exposure, the second exposure area 10 of the AZ5214 reverse photoresist is soluble in the developer, and the unexposed area is insoluble in the developer.

[0034] (4) Development: The twice exposed substrate 1 is developed with AZ300 MIF developer for 90 seconds, leaving a periodically arranged T-shaped photoresist structure 11. The T-shaped photoresist structure 11 has a width of 14 μm and a spacing of 16 μm. The cross section is T-shaped, the bottom glue width is 6 μm, and the protruding eaves on both sides of the top are 4 μm wide.

[0035] The substrate 1 is coated and then stripped: the substrate 1 after photolithography is placed in an electron beam evaporation device for TiAu (10 / 300nm) metal film deposition. Electron beam evaporation has good directionality, and the film is deposited almost vertically on the substrate. The T-shaped photoresist structure 11 completely separates the film 12 on the photoresist and the film 13 on the substrate, which is very beneficial for the subsequent stripping of the film on the photoresist. After the metal film is deposited, the substrate 1 is placed in an 80°C water bath to heat the stripping solution to remove the photoresist, and the metal film on the photoresist is subsequently stripped off. Finally, periodically arranged metal stripes with a width of 16μm and an interval of 14μm are obtained on the substrate 1.

Claims

1. A double-layer photolithography process for stripping, comprising the following steps: (1) coating a double layer of photoresist: spin coating a first photoresist (2) on a substrate (1), fully drying it on a hot plate, and then spin coating a second photoresist (3), and drying it on a hot plate; the first photoresist (2) is a positive photoresist, and the second photoresist (3) is a reverse photoresist; (2) first exposure, reverse baking: the substrate (1) is exposed for the first time using a first mask plate (4) and a first exposure ultraviolet light (5), and after exposure, it is placed on a hot plate for reverse baking to form a first exposure area (6) and an unexposed area; the unexposed area is insoluble in a developer, the first exposure area (6) of the first photoresist (2) is soluble in a developer, and the first exposure area (6) of the second photoresist (3) is insoluble in a developer due to cross-linking of molecules after reverse baking, and based on this step, the reverse photoresist (3) forms protruding ridges on both sides of a T-shaped photoresist structure (11) that is insoluble in a developer; (3) second exposure: the substrate (1) is exposed for the second time using a second mask (7) and a second exposure ultraviolet light (8), and no heating is performed after the exposure to form an overlapping exposure area (9), a second exposure area (10) and an unexposed area of ​​the double exposures; the unexposed area is insoluble in a developer, the overlapping exposure area (9) and the second exposure area (10) of the first photoresist (2) are soluble in a developer, the overlapping exposure area (9) of the second photoresist (3) is insoluble in a developer, and the second exposure area (10) of the second photoresist (3) is soluble in a developer. Based on this step, the photoresist other than the T-shaped photoresist structure (11) is soluble in a developer; (4) Development: The twice-exposed substrate (1) is developed with a developer to form a T-shaped photoresist structure (11) with a protruding eave.

2. The double-layer photolithography process for stripping according to claim 1, characterized in that: In the step (1), after spin coating the first photoresist (2), the drying temperature is 80-150° C. and the drying time is 1-30 min; after spin coating the second photoresist (3), the drying temperature is 80-150° C. and the drying time is 1-10 min.

3. The double-layer photolithography process for stripping according to claim 1, characterized in that: In the step (2), the light-transmitting area of ​​the first mask plate (4) corresponds to the protruding eaves of the T-shaped photoresist structure (11), and the width of the protruding eaves is the same as the width of the light-transmitting area of ​​the first mask plate (4) and is greater than the photolithography alignment accuracy.

4. The double-layer photolithography process for stripping according to claim 3, characterized in that: The protruding eaves width of the T-shaped photoresist structure (11) is 2-10 μm.

5. The double-layer photolithography process for stripping according to claim 1, characterized in that: The temperature of the reverse baking in step (2) is 80 to 150° C. and the time is 1 to 10 minutes.

6. The double-layer photolithography process for stripping according to claim 1, characterized in that: In the step (3), the width of the light-transmitting area of ​​the second mask (7) is greater than the gap width of the T-shaped photoresist structure (11) and less than the sum of the gap width of the T-shaped photoresist structure (11) and the width of two adjacent protruding eaves; and during photolithography alignment, the light-transmitting area of ​​the second mask (7) spans the gap of the T-shaped photoresist structure (11) and does not exceed the positions of the two adjacent protruding eaves.

7. The double-layer photolithography process for stripping according to claim 1, characterized in that: The gap width and position of the T-shaped photoresist structure (11) in the step (4) correspond to the width and position of the patterned film to be subsequently peeled off.

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