Wafer spin coating method

Abstract

This invention provides a wafer spin coating method. When the wafer's rotation speed reaches a first speed, the rotation speed is increased from the first speed to a second speed within a first preset time, while liquid is dripped onto the center of the wafer to allow the liquid to diffuse from the center to the edge. The dripping stops after the first preset time. Within a second preset time, the wafer's rotation speed is reduced from the second speed back to the first speed, allowing the liquid to move from the edge to the center. This wafer spin coating method, by increasing the rotation speed from the first speed to the second speed within the first preset time, generates centrifugal force in the liquid, making it more spreadable and easier to coat the wafer surface, thus saving the amount of liquid required for film formation. Within the second preset time, the rotation speed is reduced to the first speed, decelerating the liquid and generating centrifugal force to move it towards the center of the wafer, preventing liquid accumulation at the wafer edge.

Description

Technical Field

[0001] This invention relates to the field of semiconductor technology, and in particular to a wafer spin coating method. Background Technology

[0002] PSS (Patterned Sapphire Substrate) technology is commonly used in semiconductor fabrication processes. PSS can significantly reduce epitaxial growth defects and improve the quality of epitaxial wafer growth.

[0003] The PSS process technology includes four steps: mask layer fabrication, mask layer patterning, mask layer pattern transfer to sapphire substrate, and mask layer removal. Mask layer fabrication primarily involves forming a layer of photoresist or SiO2 on the sapphire substrate as the mask layer material.

[0004] In existing technologies, a spin coater is typically used to form a mask layer on a sapphire wafer. The spin coater vacuum-holds the back of the sapphire wafer, and after reaching a stable rotation speed, photoresist is dropped onto the wafer to ensure uniform distribution. The spin coater then accelerates and rotates to form the mask, with the required rotation speed selected based on the desired film thickness. However, using a spin coater to form the mask requires a large amount of photoresist, and during the rotational film formation process, photoresist tends to accumulate at the wafer edges, affecting subsequent PSS (Photoresist Separation and Partitioning) processes. Summary of the Invention

[0005] Based on this, the purpose of the present invention is to provide a solution to the problems of using a large amount of photoresist and the tendency for photoresist to accumulate at the wafer edge in the rotary dispensing process in the prior art.

[0006] This invention provides a wafer spin coating method, applied to a wafer spin coating equipment. The equipment includes a drive mechanism and a rotating shaft connected to the drive mechanism. The method includes:

[0007] A wafer is obtained and fixed at the center of the rotating shaft so that the wafer rotates synchronously with the rotating shaft. The drive mechanism is controlled to rotate the rotating shaft so that the rotating shaft drives the wafer to rotate.

[0008] When the wafer rotation speed reaches the first speed, the wafer rotation speed is increased from the first speed to the second speed within a first preset time, and liquid is dripped onto the center of the wafer so that the liquid spreads from the center of the wafer to the edge of the wafer. The dripping stops after the first preset time ends.

[0009] During the second preset time period, the wafer rotation speed is reduced from the second speed to the first speed to allow the liquid to move from the edge of the wafer towards the center.

[0010] The wafer spin coating method of this invention controls the wafer rotation speed to a first speed, drips liquid onto the wafer center, and increases the wafer rotation speed from the first speed to a second speed within a first preset time, dripping liquid onto the wafer center again. The acceleration generated by the speed increase causes the liquid to generate centripetal force, which in turn makes the liquid extensible, allowing it to spread outwards and more easily cover the wafer surface, thus saving the amount of liquid required for film formation. Then, within a second preset time, the second speed is reduced to the first speed, and the deceleration causes the liquid to generate centrifugal force and move towards the wafer center, avoiding liquid accumulation at the wafer edge. This solves the problems of using a large amount of photoresist and the tendency for photoresist to accumulate at the wafer edge in the spin coating process of the prior art.

[0011] Furthermore, after the step of increasing the rotational speed of the spindle from the first rotational speed to the second rotational speed within a first preset time period and before the step of decreasing the rotational speed of the wafer back to the first rotational speed for rotation, the method further includes:

[0012] Keep the wafer rotating at the second rotation speed for 5-8 seconds.

[0013] Furthermore, after the step of reducing the wafer's rotational speed from the second speed back to the first speed to move the liquid from the wafer edge towards the center, the process further includes:

[0014] The wafer rotation speed is increased from the first speed to the third speed, which is greater than the first and second speeds, and the wafer is kept rotating at the third speed for a third preset time so that the liquid forms a film on the wafer surface.

[0015] Furthermore, after the step of maintaining the wafer at a third rotation speed for a third preset time to allow the liquid to form a film on the wafer surface, the following steps are included:

[0016] Reduce the wafer rotation speed from the third speed to the fourth speed, keep the wafer rotating at the fourth speed, and continuously spray solvent onto the back of the wafer for 5-8 seconds.

[0017] Furthermore, after maintaining the wafer at a fourth rotation speed and continuously spraying solvent onto the back of the wafer for 5-8 seconds, the process also includes:

[0018] Reduce the wafer rotation speed from the fourth speed to the fifth speed, keep the wafer rotating at the fifth speed, and continuously spray solvent onto the back of the wafer for 10-13 seconds to allow the solvent to spread to the edge of the front of the wafer.

[0019] Furthermore, the first rotational speed is 100 rpm.

[0020] Furthermore, the second speed is 1000-1200 rpm.

[0021] Furthermore, the third speed is 3000-4000 rpm.

[0022] Furthermore, both the first and second preset times are 1-2 seconds.

[0023] Furthermore, the third preset time is 20-30 seconds. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the wafer spin coating method in an embodiment of the present invention;

[0025] Figure 2 This is a schematic diagram of the spin coater structure in an embodiment of the present invention;

[0026] Figure 3 This is a schematic diagram of the rotating mechanism structure in an embodiment of the present invention;

[0027] The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation

[0028] To facilitate understanding of the present invention, a more complete description will be given below with reference to the accompanying drawings. Several embodiments of the invention are illustrated in the drawings. However, the invention can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete.

[0029] It should be noted that when a component is said to be "fixed to" another component, it can be directly on the other component or there may be an intervening component. When a component is said to be "connected to" another component, it can be directly connected to the other component or there may be an intervening component. The terms "vertical," "horizontal," "left," "right," and similar expressions used in this document are for illustrative purposes only.

[0030] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the invention. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0031] In this embodiment, the wafer spin coating method is implemented using a uniform coating machine, such as... Figure 2The diagram shows the basic architecture of the equalization machine, including a rotating mechanism and a robotic arm. The rotating mechanism comprises a platform, a rotating shaft located in the center of the platform, and a drive mechanism connected below the rotating shaft. A vacuum suction cup is mounted on the platform, and a vacuum pump is connected below the suction cup. The vacuum suction cup and vacuum pump are used to adhere and fix the wafers to the platform. The drive mechanism includes a drive motor for driving the rotating shaft to rotate. First, the robotic arm picks up and places the wafers from the feed bin, lays the wafers flat on the rotating mechanism, and aligns the center of the wafers with the center of the rotating shaft, allowing the wafers to rotate synchronously with the shaft. The rotating mechanism can be set with parameters such as the shaft rotation speed and time.

[0032] like Figure 3 As shown, after the wafer is placed on the rotating shaft, vacuum adsorption is activated, and the wafer is adsorbed onto the rotating mechanism. A swing arm is located above the rotating shaft and the wafer, and a guide tube is provided on the swing arm. Liquids such as photoresist can be dripped onto the center of the wafer through the guide tube. Backwash nozzles are located on both sides of the rotating shaft on the rotating mechanism, which can spray cleaning agent onto the back of the wafer. The timing and flow rate of the liquid dripping from the swing arm onto the wafer can be controlled by the settings.

[0033] Example

[0034] like Figure 1 As shown, this embodiment provides a wafer spin coating method, including the following steps S11-S16.

[0035] S11. Obtain a wafer and fix it at the center of the rotating shaft so that the wafer rotates synchronously with the rotating shaft. Control the drive mechanism to rotate the rotating shaft so that the rotating shaft drives the wafer to rotate.

[0036] The wafer is fixed at the center of the rotating shaft so that the wafer and the rotating shaft can rotate synchronously and reach the same speed. Then, the drive mechanism is controlled to rotate the rotating shaft, so that the speed of the rotating shaft and the wafer is increased. First, the speed of the wafer is controlled to the first speed, which is 100 rpm.

[0037] S12. When the wafer rotation speed reaches the first rotation speed, the wafer rotation speed is increased from the first rotation speed to the second rotation speed within a first preset time, and liquid is dripped onto the center of the wafer so that the liquid spreads from the center of the wafer to the edge of the wafer, and the dripping stops after the first preset time ends.

[0038] After the spindle rotates, it drives the wafer to rotate synchronously at the same speed. When the spindle reaches the first speed, within a first preset time, the wafer speed is increased from the first speed to the second speed, and simultaneously the swing arm is moved to directly above the center of the wafer. During the first preset time, the guide tube of the swing arm drips liquid towards the center of the wafer. The first preset time is 1-2 seconds, and the dripping time is also 1-2 seconds. After the first preset time, the dripping stops. The dripping time can be further adjusted according to the size of the wafer to ensure that the liquid required for film formation is dripped into the center of the wafer within the first preset time. The second speed is approximately 1000 rpm, which can be set according to the size of the wafer.

[0039] Within the first preset time, the rotation speed of the wafer is controlled to increase. As the rotation speed increases, the liquid on the wafer will accelerate simultaneously. The accelerated liquid will generate centripetal force. Due to the centripetal force, the liquid can increase the extensibility between liquids, thereby pulling the liquid apart and making it easier to cover the entire wafer surface. The liquid in the center of the wafer will diffuse towards the edge of the wafer, achieving a more uniform distribution effect and reducing the amount of liquid used to cover the entire wafer surface.

[0040] After the liquid covers the wafer surface, the wafer rotation speed is controlled to be kept at the second rotation speed for buffering. The buffering time is about 5 seconds. During the buffering time, the wafer is rotated at high speed at the second rotation speed, which can make the liquid flow distribution more uniform.

[0041] S13. Within a second preset time period, the rotation speed of the wafer is reduced from the second rotation speed to the first rotation speed to allow the liquid to move from the edge of the wafer towards the center.

[0042] After the buffer time, the rotation speed is controlled to decrease from the second rotation speed to the first rotation speed within a second preset time, which is 1-2 seconds. During this time, due to the deceleration, the liquid on the wafer surface will generate centrifugal force. Therefore, the liquid will move from the edge of the wafer to the center due to centrifugal force, thus avoiding excessive liquid accumulation at the edge, making the liquid distribution more uniform, and improving the quality of the wafer.

[0043] S14. Increase the wafer rotation speed from the first rotation speed to the third rotation speed, the third rotation speed being greater than the first and second rotation speeds, and maintain the wafer at the third rotation speed for a third preset time, so that the liquid forms a film on the wafer surface.

[0044] The first rotational speed is increased to the third rotational speed required for the film deposition process. At this third rotational speed, the liquid can form a film on the wafer. Different film deposition rotational speeds can be selected according to the viscosity coefficient of the liquid, with the film deposition rotational speed for photoresist viscosity coefficients being 3000–4000 rpm. After the speed increase, the third rotational speed is maintained for a third preset time, which is 20–30 seconds, until the film is formed on the wafer surface, achieving the required film thickness of approximately 1–3 μm. In this embodiment, the third rotational speed is 3000 rpm, and the third preset time is 20 seconds.

[0045] Through the steps S11-S14 described above, a film layer of uniform thickness can be formed on the wafer surface. The greater the liquid mass, the greater the centripetal and centrifugal forces generated. Furthermore, the higher the liquid viscosity, the greater the improvement in ductility and the more obvious the effect. This allows for more detailed liquid saving and avoidance of edge accumulation.

[0046] S15. Reduce the wafer rotation speed from the third speed to the fourth speed, keep the wafer rotating at the fourth speed, and continuously spray solvent onto the back of the wafer for 5-8 seconds.

[0047] After the wafer surface is coated, the wafer rotation speed is reduced from the third speed to the fourth speed. The back-wash nozzle on the rotating mechanism is controlled to spray liquid solvent onto the back of the wafer. The liquid solvent cleans and dissolves excess liquid on the back of the wafer, preventing it from affecting subsequent processes and quality. The fourth speed is 200 rpm, and the cleaning time is 5-8 seconds, which can be adjusted according to the wafer size and the degree of back-side contamination.

[0048] S16. Reduce the wafer rotation speed from the fourth speed to the fifth speed, keep the wafer rotating at the fifth speed, and continuously spray solvent onto the back of the wafer for 10-13 seconds so that the solvent spreads to the edge of the front of the wafer.

[0049] Continue reducing the wafer rotation speed from the fourth speed to the fifth speed, and continue spraying solvent for 10-13 seconds. The fifth speed is 50 rpm. Due to the low speed, the solvent will diffuse to the edge of the wafer, and due to the surface tension of the solvent, the solvent will spread slightly upwards along the side of the wafer to about 0.2 mm from the outermost edge of the wafer, achieving the purpose of back-side cleaning and deburring. Control the wafer to maintain a low rotation speed and a stable solvent flow rate to avoid contaminating the front side of the wafer.

[0050] The slight unevenness of the wafer edge during edge cleaning can cause the cleaning solution to splash onto the wafer front, resulting in wafer scrapping. Backside cleaning utilizes rotation speed to allow the solvent to avoid splashing onto the wafer front during edge cleaning, thus maintaining film quality.

[0051] Tables 1 and 2 below show the fabrication of photoresist on the wafer surface according to the technical solution of this embodiment.

[0052] First rotational speed (RPM) Second rotational speed (RPM) Time taken (s) Light obstruction reduction 100 300 1 10％ 100 500 1 25％ 100 700 1 35％ 100 1000 1 40％ 100 1200 1 40％

[0053] Table 1

[0054] As shown in Table 1, within the preset time (1s), when the initial speed is low, the higher the second rotation speed, the less photoresist is used. When it reaches 1000-1200RPM, the photoresist usage is reduced from 1cc / piece to 0.6cc / piece under CP7 photoresist, which can save 40% of the photoresist usage.

[0055] First rotational speed (RPM) Second rotational speed (RPM) Time taken (s) Adhesive thickness 1000 1000 0 2um 100 300 1 1.8um 100 500 1 1.5um 100 700 1 1.3um 100 1000 1 1.1um 100 1200 1 1.1um

[0056] Table 2

[0057] As shown in Table 2 above, when the wafer rotation speed is reduced from the second speed to the first speed within a preset time, the greater the speed reduction between the second and first speeds, the less adhesive buildup occurs at the 0.2mm edge. When the second speed reaches over 1000, and then the speed is reduced back to the first speed, the adhesive buildup thickness decreases from 2µm to 1.1µm as the speed reduction difference increases, improving the edge adhesive buildup problem compared to the 1µm thickness at the wafer center.

[0058] At the wafer edge of 0.2mm, the adhesive buildup thickness is reduced from 2µm to 1.1µm-1µm, which improves the edge adhesive buildup problem compared to existing technologies;

[0059] In summary, the wafer spin coating method in the above embodiments of the present invention controls the wafer rotation speed to a first rotation speed, drips liquid onto the center of the wafer, and increases the wafer rotation speed from the first rotation speed to a second rotation speed within a first preset time and drips liquid onto the center of the wafer. By increasing the speed, acceleration is generated, causing the liquid to generate centripetal force. This centripetal force gives the liquid extensibility, enabling it to spread outwards and making it easier to cover the wafer surface, thereby saving the amount of liquid required for film formation. Then, within a second preset time, the second rotation speed is reduced to the first rotation speed. At this time, the deceleration causes the liquid to generate centrifugal force and move towards the center of the wafer, avoiding liquid accumulation at the wafer edge. This solves the problems of using a large amount of photoresist and easy accumulation of photoresist at the wafer edge in the spin coating process of the prior art.

[0060] In the description of this specification, references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples.

[0061] The embodiments described above are merely illustrative of several implementations of the present invention, and while the descriptions are specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the scope of protection of the present invention. Therefore, the scope of protection of this patent should be determined by the appended claims.

Claims

1. A wafer spin coating method, characterized in that, A method applicable to a wafer spin coating apparatus, the apparatus comprising a drive mechanism and a rotating shaft connected to the drive mechanism, the method comprising: A wafer is obtained and fixed at the center of the rotating shaft so that the wafer rotates synchronously with the rotating shaft. The driving mechanism is controlled to rotate the rotating shaft so that the rotating shaft drives the wafer to rotate. When the wafer reaches the first rotational speed, the wafer rotational speed is increased from the first rotational speed to the second rotational speed within a first preset time, and liquid is dripped onto the center of the wafer so that the liquid spreads from the center of the wafer to the edge of the wafer, and the dripping stops after the first preset time ends. During a second preset time period, the rotational speed of the wafer is reduced from the second rotational speed to the first rotational speed again, so that the liquid moves from the edge of the wafer to the center; The step of reducing the rotational speed of the wafer back from the second rotational speed to the first rotational speed to move the liquid from the edge of the wafer towards the center includes: The rotational speed of the wafer is increased from the first rotational speed to a third rotational speed, the third rotational speed being greater than the first rotational speed and the second rotational speed, and the wafer is kept rotating at the third rotational speed for a third preset time, so that the liquid forms a film on the wafer surface; The step of maintaining the wafer at the third rotation speed for a third preset time to allow the liquid to form a film on the wafer surface includes: The rotational speed of the wafer is reduced from the third rotational speed to the fourth rotational speed, the wafer is kept rotating at the fourth rotational speed, and solvent is continuously sprayed onto the back of the wafer for 5-8 seconds; The step of maintaining the wafer at the fourth rotation speed and continuously spraying solvent onto the back of the wafer for 5-8 seconds further includes: The rotational speed of the wafer is reduced from the fourth rotational speed to the fifth rotational speed, the wafer is kept rotating at the fifth rotational speed, and solvent is continuously sprayed onto the back side of the wafer for 10-13 seconds so that the solvent spreads to the edge of the front side of the wafer; Wherein, the first rotational speed is 100 rpm, the second rotational speed is 1000-1200 rpm, the third rotational speed is 3000-4000 rpm, and the third preset time is 20-30 seconds.

2. The wafer spin coating method according to claim 1, characterized in that, The step of increasing the rotational speed of the spindle from the first rotational speed to the second rotational speed within a first preset time period and the step of decreasing the rotational speed of the wafer back to the first rotational speed for rotation also includes: The wafer is kept rotating at the second rotation speed for 5-8 seconds.

3. The wafer spin coating method according to claim 1, characterized in that, Both the first preset time and the second preset time are 1-2 seconds.

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