A method for improving total thickness deviation of gallium arsenide single crystal wafer

Abstract

The present application relates to the technical field of semiconductor material preparation, and particularly relates to a method for improving total thickness deviation of a gallium arsenide wafer, which comprises the following steps: cutting a fixed-size circular notch from the center of a PE film, and sticking the remaining circular ring-shaped film layer on a polishing machine plate; placing the wafer on an adsorption pad sprinkled with a reducing agent, and sticking the adsorption pad on a ceramic disc; arranging the wafer on the ceramic disc along a circumference at equal intervals, and pointing the main positioning edge of the wafer to the center of the ceramic disc; placing the ceramic disc on the polishing machine plate, and starting the polishing machine to process; placing the wafer on the adsorption pad again, pointing the main positioning edge of the wafer to the edge of the ceramic disc, and starting the polishing machine to process again. The present application ensures that the total thickness deviation of the gallium arsenide wafer is within 5 um after processing, and the obtained wafer has good thickness consistency and high flatness, and the present application solves the problem of epitaxial defects caused by excessive thickness deviation, and meets the surface requirement of wafer epitaxy.

Description

Technical Field

[0001] This invention relates to semiconductor material preparation technology, and more particularly to a method for improving the total thickness deviation of gallium arsenide single wafers. Background Technology

[0002] Gallium arsenide (GaAs) wafers are manufactured from single-crystal GaAs material synthesized and grown from pure arsenic and gallium, through processes such as cutting, grinding, polishing, and cleaning. Among these processes, polishing is crucial for achieving the ultra-high precision surface finish required for GaAs wafers. The most commonly used polishing process for GaAs wafers both domestically and internationally is chemical mechanical polishing (CMP). CMP combines the synergistic effects of chemical etching and mechanical grinding, utilizing the chemical etching and mechanical grinding actions of the polishing slurry to create a smooth and flat surface on the polished medium.

[0003] Currently, the total thickness deviation of gallium arsenide single wafers under processing conditions is maintained between 10-15 μm. This is because existing technologies generally use single-sided polishing machines and adsorption pads to adsorb the wafers for processing. Due to the differences in thickness and hole depth at the bottom of the adsorption pad, the force and contact thickness between the wafer and the polishing cloth during the polishing process are inconsistent, which leads to excessive deviation in the overall thickness of the processed wafer. In addition, because the wafer travels through the outer part of the polishing cloth during processing is different, the linear velocity of the outer ring is greater than that of the inner ring, resulting in a greater amount of material removed from the outer ring than from the inner ring, thus causing excessive deviation in the overall thickness.

[0004] Smaller wafer thickness deviation offers several advantages: First, it allows for effective integration with chemicals and polishing cloths during mechanical and chemical polishing, resulting in superior surface roughness. Second, it enables close contact with the epitaxial furnace during epitaxy, ensuring uniform temperature control and reducing temperature variations. Third, it ensures consistent and uniform epitaxial layer thickness throughout the growth process. As market and customer demands increase, current standards are insufficient and require further improvement. Wafers with smaller overall thickness deviations are better positioned for market control, enhancing overall competitiveness while maintaining processing and epitaxial quality. Currently, gallium arsenide wafers are required to have an overall thickness deviation of less than 10µm, and even less than 5µm.

[0005] Patent document CN209207245U discloses a device for improving the overall thickness variation of germanium single-crystal wafers. The device includes a fixed disk with an adsorption hole at its top. One end of the adsorption hole, away from the surface of the fixed disk, is connected to a pressure groove located inside the fixed disk. A retaining ring is fixedly connected to the top edge of the fixed disk. A piston groove is formed on one side of the inner wall of the pressure groove. A threaded hole is formed at the end of the inner wall of the piston groove, penetrating the fixed disk. A piston is slidably connected to the inner wall of the piston groove. A piston rod is rotatably connected to the side of the piston near the threaded hole. The piston rod passes through the threaded hole, penetrates the fixed disk, and extends to the outside of the fixed disk. Due to the complex structure and cumbersome operation of this device, it is difficult to promote its application in industrial settings.

[0006] Patent document CN205765548U1 discloses a device for improving the overall thickness variation of germanium single-crystal wafers. This device consists of a ceramic disk, wax-free pads, circular pads, a circular iron disk, and a cylindrical iron block. Several wax-free pads are adhered to the surface of the ceramic disk, and circular grooves are formed within the wax-free pads. The circular pads are placed within the circular grooves of the wax-free pads, and the circular iron disk presses down on the circular pads, ensuring that the surfaces of all the circular pads are on the same plane. A cylindrical iron block is positioned at the center of the circular iron disk. This device is cumbersome, requires excessively long pressing times, and is prone to damaging the adsorption pads. Summary of the Invention

[0007] To address the problem of excessive total thickness deviation in existing gallium arsenide (GaAs) single-wafer processing technologies, this invention proposes a method to improve the total thickness deviation of GaAs single-wafers.

[0008] A method for improving the total thickness deviation of gallium arsenide single wafers, utilizing existing PE films, adsorption pads, ceramic disks, and polishing machines, is characterized by the following steps: 1) The PE film is a circular film layer with adhesive backing. Cut a circular notch of a fixed size from the center of the PE film, and then flatly paste the remaining circular film layer onto the polishing machine plate. Continue to paste polishing cloth onto the polishing machine plate for later use. 2) Place the wafer on an adsorption pad sprinkled with reducing agent. The adsorption pad is attached to the ceramic disk. The wafers are arranged equidistantly along the circumference of the ceramic disk. The main positioning edge of the wafer points to the center of the ceramic disk along the radius of the ceramic disk. Then place the ceramic disk on the polishing machine plate and start the polishing machine for processing. 3) Reposition the wafer and place it back on the adsorption pad, with the main positioning edge of the wafer pointing towards the edge of the ceramic disk. Then restart the polishing machine for processing. Specifically, the overall thickness of the PE film is 100-400 μm. The thickness of the PE film is determined by the thickness of the wafer obtained, corresponding to a wafer thickness of 350-550 μm.

[0009] Specifically, the PE film has a diameter of 1265mm, with a circular notch of 370-390mm in diameter cut from its center. The outer diameter of the PE film is determined by the diameter of the polishing machine plate, which is 1300mm in diameter.

[0010] Specifically, the reducing agent is a mixture of sodium thiosulfate pentahydrate and deionized water, with a weight ratio of 1:15~25. Sodium thiosulfate pentahydrate is chosen primarily because it is readily soluble in water, and its aqueous solution is weakly alkaline, allowing it to react with the Cl component in the processing solution, ensuring the cleanliness of the wafer's back side and preventing corrosion by the solution. Furthermore, its water solubility allows for reduced dosage; using a higher proportion would waste the solution, while using a lower proportion would compromise the corrosion prevention of the back side.

[0011] The present invention has the following beneficial effects: 1) By improving the PE film structure, the problem of less material removal due to the thinner polishing cloth and lower friction when in contact with the wafer at high online speeds and the thicker polishing cloth and higher friction when in contact with the wafer at low online speeds can be improved. 2) By spraying a reducing agent into the adsorption pad, the wafer is ensured to rotate within the adsorption pad during processing, thereby ensuring full contact between the entire wafer and the polishing cloth, resulting in consistent wafer polishing. 3) By adopting a two-stage processing method with rotating wafers, the problem of some wafers being removed more than others due to their limited rotation within the adsorption pad is solved, further improving the overall thickness deviation.

[0012] This invention achieves the technical effect of ensuring that the total thickness deviation of gallium arsenide single wafers is within 5µm after processing by improving the PE film structure, spraying reducing agent inside the adsorption pad, and the process of secondary reversal of single wafers. The obtained single wafers have good thickness consistency and high flatness, solving the epitaxial defects caused by excessive thickness deviation and meeting the surface requirements of wafer epitaxy. Attached Figure Description

[0013] Figure 1 To obtain thickness deviation test data using conventional methods.

[0014] Figure 2 To process thickness deviation test data using the method of the present invention.

[0015] Figure 3 Two-dimensional and three-dimensional test data on thickness deviation were processed using conventional methods.

[0016] Figure 4 The method of this invention is used to process two-dimensional and three-dimensional test data of thickness deviation. Detailed Implementation

[0017] Example 1: A method for improving the total thickness deviation of gallium arsenide single wafers, using a Chuangji 50B single-sided polishing machine, a Model X single-sided polishing cloth, and a 4-inch 300mm deep suction pad. The specific implementation method is as follows: The selected PE film structure is an annular film layer with an inner diameter of 895mm and an outer diameter of 1265mm, and an overall thickness of 208um with adhesive backing. The PE film is pasted onto a 50B single-sided polishing machine, and an X-type single-sided polishing cloth is attached for later use.

[0018] Nine 4-inch monocrystalline wafers with a thickness difference within 10µm were selected. The wafers were placed on a ceramic disk with the larger edge of the wafer aligned with the center of the disk. An absorbent pad containing a reducing agent (sodium thiosulfate pentahydrate and deionized water) was placed on top. The ceramic disk was then placed on a polishing plate. The polishing machine was started for processing. After 15 minutes, the ceramic disk was removed, and the thickness of the wafers was measured and recorded. The wafer was rotated and placed on a ceramic disk, aligning its larger edge with the disk's edge. An absorbent pad sprinkled with reducing agent was placed on top. The ceramic disk was then placed on a polishing machine plate, and the machine was restarted for processing. After 15 minutes, the ceramic disk was removed, and the wafer thickness was measured again. After being spun dry, the wafer was sent to a dedicated testing device for total thickness deviation measurement. The test results are as follows: Figure 2 and Figure 4 As shown, where: TTV represents total thickness deviation, TIR represents total indication reading, BOW represents curvature, and WARP represents warping.

[0019] Comparative Example 1: The current conventional processing method is as follows: A polishing cloth is directly adhered to the polishing plate, with direct contact and adhesion between the two; then, an adsorption pad is adhered to the ceramic disk, with the adsorption pads evenly spaced along the circumference of the ceramic disk; a gallium arsenide single crystal wafer is placed on the adsorption pad, without spraying a reducing agent onto the adsorption pad; the main positioning edge of the wafer points towards the center of the ceramic disk along its radius; finally, the ceramic disk is placed on the polishing plate with the polishing cloth attached, and the polishing machine is started for processing, which is performed only once, without changing the orientation of the large edge of the wafer during the process. Test results are as follows... Figure 1 and Figure 3 As shown.

Claims

1. A method for improving the total thickness deviation of gallium arsenide single wafers, utilizing existing PE films, adsorption pads, ceramic disks, and polishing machines, characterized in that... This will be implemented through the following steps: 1) The PE film is a circular film layer with adhesive backing. Cut a circular notch of a fixed size from the center of the PE film, and then flatly paste the remaining circular film layer onto the polishing machine plate. Continue to paste polishing cloth onto the polishing machine plate for later use. 2) Place the wafers on an adsorption pad sprinkled with reducing agent. The adsorption pad is attached to a ceramic disk. The wafers are arranged equidistantly along the circumference of the ceramic disk, with the main positioning edge of the wafer pointing towards the center of the ceramic disk along its radius. Then, place the ceramic disk on a polishing plate and start the polishing machine for processing. 3) Reposition the wafer back onto the adsorption pad, with the main positioning edge of the wafer pointing towards the edge of the ceramic disk, and start the polishing machine again for processing.

2. The method for improving the total thickness deviation of a gallium arsenide single wafer as described in claim 1, characterized in that... The overall thickness of the PE film is 100-400um.

3. The method for improving the total thickness deviation of a gallium arsenide single wafer as described in claim 1, characterized in that... The PE film has a diameter of 1265mm, and a circular notch with a diameter of 370-390mm is cut from the center.

4. The method for improving the total thickness deviation of a gallium arsenide single wafer as described in claim 1, characterized in that... The reducing agent is a mixture of sodium thiosulfate pentahydrate and deionized water, with a weight ratio of 1:15~25.

Images