Preparation method of photoresist structure for lift-off

Abstract

The present invention relates to the field of photolithography technology, and discloses a method for preparing a photoresist structure for lift-off. After the photoresist structure is developed, a maskless exposure is performed, and the maskless exposure is performed using light of a photoresist-sensitive wavelength, and the exposure dose is 800-1000 mj / cm 2 After development, a maskless exposure is performed to allow the photochemical reaction to proceed more fully, effectively improving the stability of the photoresist structure. Combined with the three-stage baking, the baking temperature range of the Lift-off vapor-deposited film layer is broadened, the density and environmental tolerance of the deposited film layer are improved, and the anti-deformation ability is significantly enhanced, and the product quality and yield are steadily improved.

Description

Technical Field

[0001] The invention relates to the technical field of photolithography, and in particular to a method for preparing a photoresist structure for lift-off. Background Art

[0002] The lift-off process is a process for patterning some materials that are difficult to etch (such as precious metals, materials that are difficult to corrode, and materials that are not selective enough for other exposed materials). Metal patterning is performed in multi-layer dielectric films (such as IR films) and semiconductor processes, especially back-end processes. Metal patterning requires the use of a lift-off structure.

[0003] At present, the stripping structure used for metal patterning has a single-layer eaves or a two-layer eaves structure. There are two ways to obtain a single-layer eaves. One is to use LOR (Lift-off resist) photoresist as a substrate, coat a layer of photoresist on the substrate and pattern it to obtain a patterned stripping structure; the other way is to first coat a layer of photoresist on the substrate, then expose the photoresist layer as a whole, and then coat another layer of photoresist and perform photolithography development to obtain a patterned stripping structure. The two-layer eaves structure has a film structure layer located on the upper surface of the substrate, and the film structure layer has a first step upward; the first photoresist layer is located on the surface of the film structure layer away from the substrate, and the first photoresist layer and the film structure layer form a second step upward.

[0004] Usually, after obtaining the metal patterned stripping structure, the required film layer is deposited, and then the photoresist is stripped to obtain the patterned film layer. However, the stripping structure obtained by the first method in the previous paragraph has a patterned film layer thickness limited by the height of the LOR photoresist, and the patterned edge has burrs and unevenness, which is not beautiful enough and even affects the device performance. The stripping structure obtained by the second method is affected by the photoresist development, so that the suspended structure of the overall exposed photoresist is hollowed out and eaten by the development is too large, which easily causes the upper photoresist to collapse, and it is impossible to make a good patterned film layer. The stripping structure obtained by the third method requires spin coating twice, the steps are cumbersome, and the coated film layer is limited by the thickness of the film structure layer located on the upper surface of the substrate.

[0005] At present, multi-layer dielectric films or thick film layers usually have a baking temperature during the evaporation process, and the coating time is usually relatively long. As the film material particles bombard and deposit onto the substrate for a long time, the temperature of the coating chamber will continue to rise, posing new challenges to the lift-off peeling structure. Summary of the invention

[0006] The technical problem solved by the present invention is to overcome the defects of the prior art and provide a method for preparing a photoresist structure for lift-off. The photoresist structure obtained by the method has good tolerance to complex coating environments, and the edge of the film layer obtained after coating stripping is smooth.

[0007] The purpose of the present invention is achieved through the following technical solutions:

[0008] A method for preparing a photoresist structure for lift-off includes performing a maskless exposure after developing the photoresist structure.

[0009] Furthermore, the maskless exposure uses light of a photoresist-sensitive wavelength for exposure.

[0010] Furthermore, the exposure dose of the maskless exposure is 800 to 1000 mj / cm 2 .

[0011] Furthermore, after the maskless exposure, the photoresist structure is baked three times, and the temperatures of the three bakings are increased in a gradient manner.

[0012] Furthermore, the three baking steps are:

[0013] First time: baking at 80-90℃ for 60-90s; second time: baking at 100-110℃ for 120-150s; third time: baking at 120-125℃ for 90-150s.

[0014] Furthermore, the photolithography steps before the photoresist structure is developed are as follows:

[0015] S1. Clean the substrate and apply glue;

[0016] S2. The substrate obtained by coating in S1 is baked at a temperature of 115 to 120°C for 120 to 180 seconds;

[0017] S3. Exposing the substrate obtained in S2;

[0018] S4. The exposed substrate in S3 is baked at a temperature of 105 to 110° C. for 110 to 120 seconds;

[0019] S5. Develop the chip obtained in S4.

[0020] Furthermore, the substrate in S1 needs to be baked at a temperature of 65-75°C for 30 minutes before coating.

[0021] Furthermore, in S1, the glue coating speed is controlled at 1000-1250 rpm, and the glue coating thickness is greater than or equal to 10 um.

[0022] Furthermore, the exposure time in S3 is 16 to 21 seconds.

[0023] Furthermore, the development time in S4 is 90 to 105 seconds.

[0024] Compared with the prior art, the present invention has the following beneficial effects:

[0025] 1) After development, a maskless exposure is performed to allow the photochemical reaction to proceed more fully, effectively improving the stability of the photoresist structure. Combined with the three-stage baking, the baking temperature range of the lift-off evaporation film layer is broadened, the density and environmental tolerance of the deposited film layer are improved, and the anti-deformation ability is significantly enhanced, so that the product quality and yield are steadily improved;

[0026] 2) The photolithography step of the present application can realize that the angle of the inverted trapezoid can be controlled within a certain range. Generally speaking, the present application can control the angle of the inverted trapezoid within 55-75°, which is more conducive to the subsequent stripping;

[0027] 3) The photoresist structure obtained by this preparation method has good tolerance to complex coating environments. The edge of the film layer obtained after coating stripping is smooth and the line width is controllable. DETAILED DESCRIPTION

[0028] The present invention will be further described below in conjunction with specific implementation modes.

[0029] Example 1

[0030] A method for preparing a photoresist structure for lift-off, taking thick negative resist (AZ2070 photoresist) as an example, the morphology made after photolithography is an inverted trapezoidal morphology, and the steps are as follows:

[0031] S1. Clean the substrate and bake it at 65-75°C for 30 min, then apply glue. The coating speed is controlled at 1000-1250rpm, and the coating thickness is greater than or equal to 10um.

[0032] S2. The substrate obtained by coating in S1 is baked at a temperature of 115 to 120°C for 120 to 180 seconds;

[0033] S3. Expose the substrate obtained in S2 using a mask with a photolithography hole of 23-25 ​​μm, with an exposure time of 16 to 21 seconds;

[0034] S4. The exposed substrate in S3 is baked at a temperature of 105 to 110° C. for 110 to 120 seconds;

[0035] S5. Place the chip obtained in S4 into AZ MIF 300 for development, with the development time being 90 to 105 seconds.

[0036] S6. The photoresist structure obtained after development in S5 is subjected to a maskless exposure. The maskless exposure is performed using light of a photoresist-sensitive wavelength, and the exposure dose is 800 to 1000 mj / cm2.

[0037] S7. After the maskless exposure, the photoresist structure is baked three times, and the three baking temperatures are gradually increased. Specifically, the three bakings are:

[0038] The first time: baking at 80-90°C for 60-90s; the second time: baking at 100-110°C for 120-150s; the third time: baking at 120-125°C for 90-150s; the above temperatures do not exceed the transition temperature of the photoresist.

[0039] Compared with the traditional photolithography steps, the present application can achieve controllable angle of the inverted trapezoid within the range of 55 to 75° by adjusting parameters such as exposure and baking in steps S1 to S5.

[0040] After photolithography, the entire surface of the photoresist is exposed again. The exposure dose is controlled to allow the developed photoresist to fully undergo photocrosslinking reaction. Combined with the S7 three-step film hardening baking procedure, the resulting photoresist structure will not deform even when baked at 160°C. This shows that the above process steps effectively improve the temperature resistance and deformation resistance of the glue.

[0041] The processed photoresist was verified by a high-temperature 180°C multi-layer dielectric film. After the photolithography and evaporation of the multi-layer dielectric film, the SEM slice showed no obvious deformation of the cross-sectional morphology of the photoresist edge, the morphology of the evaporated film layer was better, the size of the transition zone after evaporation was effectively controlled, and the difficulty of stripping after evaporation was basically the same as before. As the coating baking temperature increases, the density and firmness of the coated film layer are higher, and the film layer has stronger environmental tolerance. The lift-off structure can effectively widen the baking temperature during evaporation, effectively improve product quality, and increase yield.

[0042] The preparation method of the present application can also be applied in other fields such as detector or LED industry, and is suitable for lift-off of thicker film layers.

[0043] Example 2

[0044] The difference between this embodiment and the first embodiment is that after the photoresist structure is developed, the hardening baking is directly performed, and the maskless exposure operation is omitted.

[0045] When the photoresist hardening baking temperature is higher than 100°C, the sidewall morphology of the photoresist edge will be deformed, and the effect of improving the stability of the photoresist structure is limited.

[0046] Example 3

[0047] The photoresist structure of this embodiment is formed by conventional technology. When the photoresist structure obtained in this embodiment is evaporated at a temperature of 180° C., the cross-sectional morphology of the edge of the film layer photoresist is severely deformed, affecting the product quality.

[0048] Example 4

[0049] Referring to Example 1, the exposure dose is increased during the first exposure in S3 to improve the degree of photoresist cross-linking, and the obtained photoresist has a small adjustable angle range of the inverted trapezoid, which cannot achieve the effect of the controllable angle adjustment range described in Example 1.

[0050] Obviously, the above embodiments are merely examples for clearly illustrating the technical solutions of the present invention, and are not intended to limit the implementation methods of the present invention. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all implementation methods here. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the claims of the present invention.

Claims

1. A method for preparing a photoresist structure for lift-off, characterized in that: After the photoresist structure is developed, a maskless exposure is performed; after the maskless exposure, the photoresist structure is baked three times, and the three baking temperatures are gradually increased; First time: bake at 80-90℃ for 60-90s; second time: bake at 100-110℃ for 120-150s; The third time: bake at 120-125℃ for 90-150s.

2. The method for preparing a lift-off photoresist structure according to claim 1, characterized in that: Maskless exposure uses light of the photoresist-sensitive wavelength.

3. The method for preparing a lift-off photoresist structure according to claim 2, characterized in that: The exposure dose of maskless exposure is 800~1000mj / cm 2 .

4. The method for preparing a lift-off photoresist structure according to claim 1, characterized in that: The photolithography steps before developing the photoresist structure are as follows: S1. Clean the substrate and apply glue; S2. The substrate obtained by coating in S1 is baked at a temperature of 115 to 120°C for 120 to 180 seconds; S3. Exposing the substrate obtained in S2; S4. The exposed substrate in S3 is baked at a temperature of 105 to 110° C. for 110 to 120 seconds; S5. Develop the substrate obtained in S4.

5. The method for preparing a lift-off photoresist structure according to claim 4, characterized in that: The substrate in S1 needs to be baked at 65-75°C for 30 minutes before coating.

6. The method for preparing a lift-off photoresist structure according to claim 4, characterized in that: In S1, the glue coating speed is controlled at 1000-1250 rpm, and the glue coating thickness is greater than or equal to 10 μm.

7. The method for preparing a lift-off photoresist structure according to claim 4, characterized in that: The exposure time in S3 is 16 to 21 seconds.

8. The method for preparing a lift-off photoresist structure according to claim 4, characterized in that: The development time in S4 is 90 to 105 seconds.