Method for reducing the edge film thickness of high viscosity photoresist

Abstract

The application discloses a method for reducing the edge film thickness of high-viscosity photoresist, and belongs to the photoetching process technical field in the integrated circuit manufacturing industry. After photoresist spraying is performed on a wafer to be coated, the photoresist is spread to the whole wafer surface by glue throwing to form a stable film with a certain thickness; then the EBR nozzle is moved for two or more times with different distances to perform edge thinning, the flow of edge dissolving solvent is 10-20 ml / min, and the wafer rotating speed is 300-800 rpm; after coating and thinning are completed in the glue coating unit, the wafer is taken out by a robot, is baked, is sent into exposure, then is developed, and finally is transmitted back to a wafer box. The method optimizes the film uniformity, reduces wafer and equipment pollution, improves the process quality, and reduces the number of "invalid bands" in the subsequent photoetching process under the premise of guaranteeing the original standard requirements.

Description

Technical Field

[0001] This invention relates to the field of photolithography technology in the integrated circuit manufacturing industry, and specifically to a method for thinning the edge film thickness of high viscosity (CP value) photoresist. Background Technology

[0002] Microelectronics technology is a high-tech electronic technology built upon various semiconductor devices centered on integrated circuits. Semiconductor products and devices developed using this technology are characterized by small size, light weight, high reliability, and high operating speed. During spin-coating of high-viscosity (viscosity greater than 100 cP) photoresist, excess adhesive is pushed to the wafer edge by centrifugal force. Most of it is ejected from the wafer, but some remains. Due to the high viscosity of the photoresist, under the combined effects of surface tension and wafer rotation, the photoresist remaining at the wafer edge will form a wave-like or hill-like undulating accumulation and edge protrusion after spin-coating. Figure 1 This results in uneven thickness at the edges of the photoresist film. Therefore, reducing the edge thickness of high-viscosity photoresist is imperative.

[0003] Currently, high-viscosity photoresist coating processes rarely involve moving the EBR nozzle two or more times at different distances. The disadvantages are: 1. Photoresist deposited at the wafer edge can flow along the edge to the back of the wafer, causing contamination; 2. Photoresist deposited at the wafer edge can detach during baking, contaminating the hot plate, robotic arm, and other equipment used in subsequent processes; 3. Poor uniformity of the photoresist film after spin coating, especially at the edges, leads to poor results in subsequent processes and reduces the number of "effective bands" on the chip; 4. Poor uniformity of the photoresist film after spin coating results in more defects in subsequent processes such as development and etching, leading to lower process yields and failing to meet the requirements of high-performance integrated circuit devices; 5. The high relative velocity of the airflow at the wafer edge causes the photoresist to solidify quickly. The solidified adhesive deposited on the back of the wafer can prevent the wafer from being placed horizontally on subsequent photolithography equipment, interfering with wafer surface testing. Summary of the Invention

[0004] To address the issue of uneven photoresist film thickness at the wafer edges during spin coating of high-viscosity photoresist, which results in wavy or hilly accumulation and edge protrusions after coating, contaminating the wafer backside and equipment, this invention provides a method for thinning the edge film thickness of high-viscosity photoresist. By employing specific techniques and selecting appropriate process parameters, after the photoresist spin coating has formed a film of a certain thickness, the EBR nozzle is moved two or more times at different distances to thin the edges. This method optimizes film uniformity, reduces wafer and equipment contamination, improves process quality, and reduces the number of "invalid bands" in subsequent photolithography processes, while maintaining the original standard requirements.

[0005] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0006] A method for thinning the edge film thickness of high-viscosity photoresist, the method comprising the following steps:

[0007] (1) Clean and dry the surface of the wafer to be coated, then apply the tackifier as a base coat, and then send the wafer to be coated into the spin coating unit to prepare for photoresist coating.

[0008] (2) Photoresist spraying is performed, with a photoresist viscosity greater than 100 cP; after spraying, the photoresist is spun out to spread evenly across the entire wafer surface, forming a stable film with a certain thickness.

[0009] (3) Use PGMEA or EGMEA edge removal solvent and spray it through the EBR nozzle at the edge of the wafer to thin the photoresist at the edge of the wafer. During the thinning process, move the EBR nozzle two or more times at different distances to thin the edge. The edge removal solvent flow rate is 10-20 ml / min and the wafer rotation speed is 300-800 rpm.

[0010] (4) After the wafer is coated and thinned in the coating unit, it is taken out by the robot, baked, exposed, developed, and finally transferred back to the wafer cassette.

[0011] In step (3) above, the EBR nozzle is moved N times, where N = 2-5 and N is an integer; during thinning, the distance the EBR nozzle moves in the next movement is less than the distance it moves in the previous movement.

[0012] Preferably, when the EBR nozzle is moved twice, the first movement distance is A mm and the time is 5-15s, and the second movement distance is B mm and the time is 10-30s; A>B.

[0013] In step (3) above, the process of moving the EBR nozzle to perform edge thinning is specifically as follows:

[0014] First movement: Move the EBR nozzle from the outermost edge of the wafer radially inwards by a distance of A mm, then keep it stationary and start spraying the edge removal solvent. Stop spraying after the spraying time is reached. Second movement: Move the nozzle by a distance of B mm, that is, the distance from the position where the EBR nozzle stops after moving radially along the wafer to the outermost edge of the wafer is B mm. After moving to the desired position, keep it stationary and start spraying the edge removal solvent. Stop spraying after the spraying time is reached.

[0015] In step (3) above, the spraying distance, number of times, duration and edge removal solvent consumption of the EBR nozzle are determined based on the thickness and characteristics of the photoresist spin-coated on the wafer.

[0016] In step (3) above, the distance the EBR nozzle moves each time is determined based on the edge thickness of the thin film formed by the photoresist spin-coated on the wafer.

[0017] Before step (1) above, check the environmental conditions of the equipment homogenizing chamber, such as ventilation, temperature and humidity, and the movement of mechanical parts. Only proceed with step (1) after confirming that everything is normal.

[0018] The advantages and beneficial effects of this invention are as follows:

[0019] 1. This invention provides a method for reducing the edge film thickness of high CP value photoresist. This method utilizes the following steps: after the photoresist coating process is completed and a film of a certain thickness is formed, the EBR nozzle is moved two or more times at different distances to perform edge cleaning and thinning. This prevents the formation of wavy or hilly undulations of photoresist at the wafer edge and edge bulges, which could contaminate the back of the wafer and subsequent equipment.

[0020] 2. Improved process quality: By moving the EBR nozzle two or more times at different distances to thin the edges, photoresist buildup at the wafer edges is prevented. While ensuring the original standard requirements are met, the uniformity of the photoresist film is optimized, wafer and subsequent equipment contamination is reduced, process quality is improved, defects in subsequent development and etching processes are reduced, the number of "invalid bands" in subsequent photolithography processes is reduced, the process yield is improved, and the needs of high-performance integrated circuit devices are further met.

[0021] 3. For photoresists with different compositions and thicknesses, the parameters such as the distance, number of sprays, duration and flow rate of EBR spraying can be adjusted by increasing or decreasing them to find the conditions for achieving the best photoresist edge thinning effect (observed by the photoresist film thickness change curve obtained by subsequent optical film thickness gauge measurement). Attached Figure Description

[0022] Figure 1 The diagram shows the accumulation of photoresist and the raised edges; where: (a) hill-like undulations; (b) wave-like undulations.

[0023] Figure 2 This is a schematic diagram of the movement of the edge-removing solvent nozzle during the edge thinning process. Detailed Implementation

[0024] To further understand the present invention, the following description is based on examples, but the examples are only for further illustrating the features and advantages of the present invention, and are not intended to limit the scope of the claims of the present invention.

[0025] The present invention provides a method for reducing the edge thickness of high CP value photoresist, the specific process of which is as follows:

[0026] The first step involves removing the 12-inch wafer to be coated from the wafer cassette, transferring it to a cold plate at 23°C for cooling, and then sending it to the coating unit for the coating process. A coating formula is selected to prepare for photoresist coating. After coating, the wafer is removed by a robot, baked, and then returned to the wafer cassette. Measurements taken with an optical film thickness gauge show that before multiple EBR steps at different distances, the photoresist film thickness at the wafer edge is T1 μm, and the photoresist film thickness in the central region of the wafer is T2 μm.

[0027] The second step involves modifying the coating formula, adding two or more EBR movement steps at different distances, and setting the EBR flow rate to 10-20 ml / min and the wafer rotation speed to 300-800 rpm; taking two steps as an example ( Figure 2 The first movement distance is A mm, and the time is 5-15 s. The second movement distance is B mm, and the time is 10-30 s (the EBR spraying distance, number of times, and duration are determined according to the thickness and characteristics of the photoresist spin-coated on the wafer).

[0028] The third step involves repeating the above steps. The optical film thickness gauge measures the thickness of the photoresist film at the wafer edge (T3μm) and the thickness of the photoresist film in the central region of the wafer (T4μm) after two or more EBR movement steps at different distances.

[0029] Example 1:

[0030] Thin-film processing was performed on a 12-inch wafer using photoresist with a viscosity of 500 CP and a coating thickness of 15 μm. First, the wafer to be coated was removed from the wafer cassette and placed in a cold plate unit for cooling at 23°C for 60 seconds to stabilize the wafer temperature. Then, the stabilized wafer was placed in the coating unit to prepare for the coating process. The coating process formula was selected, and after coating, the wafer was removed by a robot, baked, and then returned to the wafer cassette. Optical film thickness gauge measurements showed that, before multiple EBR steps with varying distances, the photoresist film thickness at the wafer edge was 16.5 μm, the thickness in the central region was 14.9 μm, the film thickness uniformity was 5.11%, and the wafer edge protrusion distance was approximately 2-6 mm.

[0031] Repeat the above steps, modify the coating formulation, and add two steps of moving the EBR nozzle at different distances. Set the edge removal solvent flow rate to 15 ml / min, the wafer rotation speed to 350 rpm, the first EBR nozzle movement distance to 5 mm, and the spraying time to 8 s; the second EBR nozzle movement distance to 2 mm, and the spraying time to 20 s. Optical film thickness gauge measurements showed that, with the addition of the two EBR nozzle movement steps, the photoresist film thickness at the wafer edge was 15.68 μm, the photoresist film thickness in the central region of the wafer was 14.8 μm, and the film thickness uniformity was 2.91%.

[0032] Data comparison reveals that adding two steps to move the EBREBR nozzle by different distances resulted in a 0.82 μm decrease in the thickness of the photoresist film at the wafer edge and a 43.1% improvement in film thickness uniformity.

[0033] Example 2:

[0034] Thin-film processing was performed on a 12-inch wafer using photoresist with a viscosity of 12800 CP and a coating thickness of 35 μm. First, the wafer to be coated was removed from the wafer cassette and placed in a cold plate unit for 23°C cooling for 60 seconds to stabilize the wafer temperature. Then, the stabilized wafer was placed in the coating unit for the coating process. The coating process formula was selected, and after coating, the wafer was removed by a robot, baked, and then returned to the wafer cassette. Optical film thickness gauge measurements showed that, without multiple steps of moving the EBR nozzle at different distances, the photoresist film thickness at the wafer edge was 40 μm, the thickness in the central region was 34.3 μm, the film thickness uniformity was 7.67%, and the wavy photoresist stacking distance at the wafer edge was approximately 3-15 mm.

[0035] Repeat the above steps, modify the coating formulation, and add three steps with different distances for moving the EBR nozzle. Set the edge removal solvent flow rate to 20 ml / min. The first step involves a 10 mm nozzle movement distance, a 10 s spray time, and a wafer rotation speed of 300 rpm. The second step involves a 6 mm nozzle movement distance, a 30 s spray time, and a wafer rotation speed of 500 rpm. The third step involves a 3 mm nozzle movement distance, a 60 s spray time, and a wafer rotation speed of 800 rpm. Optical film thickness gauge measurements show that with these three steps, the photoresist film thickness at the wafer edge is 36.71 μm, the photoresist film thickness in the central region is 34.5 μm, and the film thickness uniformity is 3.1%.

[0036] Data comparison reveals that, before and after adding multiple steps to move the EBR nozzle at different distances, the thickness of the photoresist film at the wafer edge decreased by 3.29 μm, while the film thickness uniformity improved by 59.58%.

Claims

1. A method for reducing the thickness of a high-viscosity photoresist edge film, characterized in that: The method includes the following steps: (1) Clean and dry the surface of the wafer to be coated, then apply the tackifier as a base coat, and then send the wafer to be coated into the spin coating unit to prepare for photoresist coating. (2) Photoresist spraying is performed. After the spraying is completed, the photoresist is spun out to spread evenly over the entire wafer surface, forming a stable film with a certain thickness. (3) Use PGMEA or EGMEA edge removal solvent and spray it through the EBR nozzle at the edge of the wafer to thin the photoresist at the edge of the wafer. During the thinning process, move the EBR nozzle at different distances several times to thin the edge. The first movement is to move the EBR nozzle from the outermost edge of the wafer along the inner radial side of the wafer. The second movement is to move the EBR nozzle from the position where it stopped after moving along the radial side of the wafer to the outermost edge of the wafer. The edge removal solvent flow rate is 10-20 ml / min and the wafer rotation speed is 300-800 rpm. (4) After the wafer is coated and thinned in the coating unit, it is taken out by the robot, baked, exposed, developed, and finally transferred back to the wafer cassette.

2. The method for reducing the edge thickness of high-viscosity photoresist according to claim 1, characterized in that: In step (3), the EBR nozzle is moved N times, where N = 2-5 and N is an integer; during thinning, the distance the EBR nozzle moves in the next movement is less than the distance it moves in the previous movement.

3. The method for reducing the edge thickness of high-viscosity photoresist according to claim 2, characterized in that: When the EBR nozzle is moved twice, the first movement distance is A mm and the time is 5-15 s, and the second movement distance is B mm and the time is 10-30 s; A>B.

4. The method for reducing the edge thickness of high-viscosity photoresist according to claim 2 or 3, characterized in that: In step (3), the process of moving the EBR nozzle to perform edge thinning is specifically as follows: First movement: Move a distance of A mm, then remain stationary and begin spraying the edge-removing solvent. Stop spraying after the spraying time is reached. Second movement: Move a distance of B mm, move to the desired position, remain stationary, and begin spraying the edge-removing solvent. Stop spraying after the spraying time is reached.

5. The method for reducing the edge thickness of high-viscosity photoresist according to claim 2, characterized in that: In step (3), the spraying distance, number of times, duration and edge removal solvent consumption of the EBR nozzle are determined based on the thickness and characteristics of the photoresist spin-coated on the wafer.

6. The method for reducing the edge thickness of high-viscosity photoresist according to claim 2, characterized in that: In step (3), the distance the EBR nozzle moves each time is determined based on the edge thickness of the thin film formed by the photoresist spin-coated on the wafer.

7. The method for reducing the edge thickness of high-viscosity photoresist according to claim 1, characterized in that: Before step (1), check the exhaust, temperature and humidity of the equipment's uniform coating chamber and the movement of mechanical parts. Only proceed with step (1) after confirming that everything is normal.

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