Gallium arsenide wafer thinning method

Abstract

The invention provides a gallium arsenide wafer thinning method, which is characterized by comprising the following steps of: 10, providing a gallium arsenide wafer, and coating hydrolysis UV (ultraviolet) glue on the surface of the gallium arsenide wafer; step 20, providing a sapphire substrate, and bonding the sapphire substrate to the surface of the gallium arsenide wafer to form a bonding wafer; 30, the bonding sheet is placed in a UV exposure machine to be cured; 40, the bonding sheet is placed on a grinding disc to be thinned; 50, the bonding wafer is placed on a polishing disc to be polished; step 60, plating gold on the back surface of the bonding sheet; and step 70, the bonding sheet is hydrolyzed, and the gallium arsenide wafer is separated out. According to the method, the gallium arsenide wafer and the sapphire substrate are bonded through the hydrolyzed UV glue, the whole technological process is simple and easy to implement, pungent smell is not released, meanwhile, the requirement for equipment is low, thinning of the wafer can be achieved without high-end equipment, and the fragment rate in the technological process is greatly reduced.

Description

Technical Field

[0001] The invention relates to the field of semiconductor process methods, and in particular to a method for thinning a gallium arsenide wafer. Background Art

[0002] Gallium arsenide is an important semiconductor material, belonging to the III-V group compound semiconductor. Gallium arsenide can be made into semi-insulating high-resistance materials with resistivity more than 3 orders of magnitude higher than silicon and germanium, and is used to make integrated circuit substrates, infrared detectors, gamma photon detectors, etc. Because its electron mobility is 5-6 times greater than that of silicon, it is widely used in the production of microwave devices and high-speed digital circuits. Semiconductor devices made of gallium arsenide have the advantages of high frequency, high temperature, low temperature performance, low noise, and strong radiation resistance.

[0003] In the processing technology of gallium arsenide, thinning and polishing are the most critical semiconductor processes. The wafer thinning process in the prior art is to bond the wafer to a carrier through rosin or wax, and then place the carrier together with the wafer in a machine for thinning and polishing. However, the rosin and wax in the prior art take a long time to solidify and have a strong irritating odor, which makes the entire thinning process take a long time and causes great harm to the human body.

[0004] Therefore, there is an urgent need for a high-efficiency, low-hazard GaAs wafer thinning process. Summary of the invention

[0005] In view of the above defects and improvement needs of the above-mentioned prior art, the present invention provides a method for thinning a gallium arsenide wafer, the purpose of which is to select a non-volatile and non-hazardous gallium arsenide wafer bonding material. Without affecting the safety of personnel, the curing rate of the gallium arsenide wafer bonding material is improved, thereby further improving the process rate of wafer thinning.

[0006] To achieve the above object, according to one aspect of the present invention, a method for thinning a gallium arsenide wafer is provided, characterized in that it comprises:

[0007] Step 10: providing a gallium arsenide wafer, wherein a hydrolyzed UV adhesive is coated on a surface of the gallium arsenide wafer;

[0008] Step 20: providing a sapphire substrate, wherein the sapphire substrate is bonded to the surface of the gallium arsenide wafer to form a bonding sheet;

[0009] Step 30: The bonding sheet is placed in a UV exposure machine for curing;

[0010] Step 40: placing the bonding sheet on a grinding disc for thinning;

[0011] Step 50: placing the bonding sheet on a polishing plate for polishing;

[0012] Step 60: Gold-plating the back of the bonding sheet;

[0013] Step 70: The bonding wafer is hydrolyzed to separate the GaAs wafer.

[0014] In one embodiment, the sapphire substrate and the gallium arsenide wafer are bonded in a vacuum bonding machine, and the vacuum degree in the vacuum bonding machine is 50 mtorr-500 mtorr.

[0015] In one embodiment, the curing wavelength of the UV exposure machine is 365-395nm, and the curing condition is greater than 1000mj / cm 2 , curing time 30-300s.

[0016] In one embodiment, a grinding and polishing fixture is provided, and the solidified bonding sheet is attached to the grinding and polishing fixture with wax, and the temperature during the attachment is 70-100°C.

[0017] In one embodiment, a grinding liquid is provided, and the gallium arsenide wafer surface contained in the bonding sheet is placed on the grinding disk for grinding. The rotation speed of the grinding disk is 30-60 revolutions per minute. The grinding liquid is an aluminum oxide water-based component, wherein the weight percentage of the aluminum oxide is 5%-20%, and the particle size of the aluminum oxide is 3-10 microns.

[0018] In one embodiment, a polishing slurry is provided, wherein the proportions of the components of the polishing slurry by weight percentage are 15% silica gel, 10% hydrogen peroxide, 0.002% silicate, 0.15% pH regulator, and the remainder is deionized water, wherein the silica gel is 40-150um granular silica gel.

[0019] In one embodiment, the bonding wafer is first cleaned after polishing, and the first cleaning uses a solution prepared by a neutral detergent and deionized water in a ratio of 1:10.

[0020] In one embodiment, the bonding sheet is removed from the polishing fixture, and the polishing fixture together with the bonding sheet is placed on a 100° C. hot plate, and after the wax melts, the bonding sheet is separated from the polishing fixture and the bonding sheet is taken out.

[0021] In one embodiment, the bonding sheet is cleaned for a second time using an isopropyl alcohol organic solvent. The bonding sheet is placed in a quick-drain rinse tank and rinsed repeatedly for 10 times. After the rinsing is completed, the bonding sheet is taken out and placed in a spin dryer for spin drying.

[0022] In one embodiment, the gold-plated bonding sheet is taken out from the equipment, and then immersed in a pure water container at 95° C. for 30-120 minutes. The gallium arsenide wafer is taken out after the sapphire substrate and the gallium arsenide wafer contained in the bonding sheet are completely separated.

[0023] Compared with the prior art, the present invention has the following beneficial effects:

[0024] The present application adopts hydrolyzed UV glue to replace the rosin and wax of the prior art to achieve the bonding of the gallium arsenide wafer and the sapphire substrate, which not only solves the problem of the irritating odor of the prior art rosin and wax that is harmful to the human body, but also the whole process is simple and easy. The hydrolyzed UV glue and consumables used are inexpensive and easy to obtain. At the same time, the requirements for equipment are low, and high-end equipment is not required to achieve wafer thinning, which greatly reduces the fragmentation rate in the process. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the gallium arsenide wafer thinning method of the present application;

[0026] Figure 2 This is a schematic diagram of the structure of the gallium arsenide wafer coating of the present application;

[0027] Figure 3 This is a schematic diagram of the structure of the bonding between the gallium arsenide wafer and the sapphire substrate of the present application;

[0028] Figure 4 A schematic diagram of bonding and photocuring of a gallium arsenide wafer and a sapphire substrate according to the present application;

[0029] Figure 5 A schematic diagram of the bonding sheet of the present application during the thinning process;

[0030] Figure 6 A schematic diagram of the bonding wafer of the present application during the polishing process;

[0031] Figure 7 This is a schematic diagram of the structure of the gold-plated back side of the bonding sheet of the present application;

[0032] Figure 8 This is a schematic diagram of the separation of the bonded sheet of the present application in pure water. DETAILED DESCRIPTION

[0033] In order to enable those skilled in the art to better understand the scheme of the present invention, the technical scheme in the embodiment of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiment of the present invention. Obviously, the described embodiment is only a part of the embodiment of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without making creative work are within the scope of protection of the present invention.

[0034] It should be noted that if the embodiments of the present application involve directional indications (such as up, down, left, right, front, back...), the directional indications are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0035] In addition, if there are descriptions involving "first", "second", etc. in the embodiments of the present application, the descriptions of "first", "second", etc. are only used for descriptive purposes and cannot be understood as indicating or suggesting their relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such combination of technical solutions does not exist and is not within the scope of protection required by this application.

[0036] The present application provides a method for thinning a gallium arsenide wafer, which is characterized by comprising:

[0037] Step 10: providing a gallium arsenide wafer, wherein a hydrolyzed UV adhesive is coated on a surface of the gallium arsenide wafer;

[0038] Step 20: providing a sapphire substrate, wherein the sapphire substrate is bonded to the surface of the gallium arsenide wafer to form a bonding sheet;

[0039] Step 30: The bonding sheet is placed in a UV exposure machine for curing;

[0040] Step 40: placing the bonding sheet on a grinding disc for thinning;

[0041] Step 50: placing the bonding sheet on a polishing plate for polishing;

[0042] Step 60: Gold-plating the back of the bonding sheet;

[0043] Step 70: The bonding wafer is hydrolyzed to separate the GaAs wafer.

[0044] The following describes the invention in conjunction with specific embodiments.

[0045] like Figure 1 As shown, Figure 1 The present invention provides a method for thinning a gallium arsenide wafer, which comprises the following steps:

[0046] Step 10: providing a gallium arsenide wafer, and coating the surface of the gallium arsenide wafer with hydrolyzed UV glue;

[0047] Specifically, the hydrolyzed UV glue is spin-coated on the GaAs wafer, and the spin-coating process can improve the thickness uniformity of the hydrolyzed UV glue on the surface of the GaAs wafer.

[0048] It should be noted that the hydrolyzed UV glue of the present application can be cured by UV irradiation and can be decomposed by boiling or soaking in warm water.

[0049] like Figure 2 As shown, a gallium arsenide wafer 1 is spin-coated with a hydrolyzed UV glue 2 on one side of the gallium arsenide wafer 1 , and the hydrolyzed UV glue 2 should be evenly spread over the surface of the gallium arsenide wafer 1 .

[0050] Step 20: providing a sapphire substrate, and bonding the sapphire substrate to the surface of the gallium arsenide wafer to form a bonding wafer;

[0051] Specifically, the sapphire substrate 3 and the gallium arsenide wafer 1 coated with the hydrolyzed UV glue 2 are bonded in a vacuum bonding machine to form a bonding sheet 100. The vacuum degree of the bonding is selected to be 50mtorr-500mtorr (micrometers of mercury). Bonding in a vacuum can prevent the glue from bubbling and affecting the bonding yield.

[0052] like Figure 3 As shown, a sapphire substrate 3 is bonded to one side of a gallium arsenide wafer 1 by hydrolyzed UV glue 2 to form a bonding sheet 100. Since the gallium arsenide wafer 1 has a relatively low hardness, a sapphire substrate with relatively high bonding hardness is used to facilitate the subsequent process of the gallium arsenide wafer.

[0053] Step 30: The bonded sheet is placed in a UV exposure machine for curing;

[0054] Specifically, the bonded wafers that have been initially bonded are placed in a UV exposure machine for UV light irradiation, and the hydrolyzed UV glue is cured under UV light to cure the sapphire substrate and the gallium arsenide wafer. It should be noted that the UV exposure machine has a curing wavelength of 365-395nm and a curing condition of more than 1000mj / cm 2 (millijoules per square centimeter), curing time 30-300s (seconds).

[0055] like Figure 4 As shown, the bonding sheet 100 is UV-cured in a UV exposure machine. Since the sapphire substrate is a light-transmitting material, the UV light is irradiated on the hydrolyzed UV glue through the sapphire substrate to achieve the curing of the hydrolyzed UV glue, and the solidified bonding sheet 100 including the sapphire substrate and the gallium arsenide wafer is formed.

[0056] It should be noted that since the present application uses hydrolyzed UV glue, compared with the rosin and wax bonding in the prior art, the process of the present application will not produce irritating and harmful odors and will not cause harm to the human body. In addition, the hydrolyzed UV glue has a short fixing time, and the bonding of the sapphire substrate and the gallium arsenide wafer can be achieved within a few minutes. Compared with the rosin and wax in the prior art, the process time is greatly shortened and the process efficiency is greatly improved.

[0057] Step 40: The bonded sheet is placed on a grinding disc for thinning;

[0058] Specifically, if Figure 5 As shown, the solidified bonding sheet 100 is placed as a whole on the grinding disc 6 for thinning. Before the formal thinning, the solidified bonding sheet 100 needs to be glued to the grinding and polishing fixture 4 with wax. The grinding and polishing fixture 4 provides a force for the gallium arsenide wafer 1 during subsequent thinning and polishing. In this embodiment, by controlling the temperature at 70-100°C, the sapphire substrate 3 surface of the bonding sheet 100 is bonded to the grinding and polishing fixture 4 through wax.

[0059] like Figure 5 As shown, further, the gallium arsenide wafer 1 of the bonding sheet 100 is placed on the grinding disc 6 for grinding, the rotation speed of the grinding disc 6 is 30-60 revolutions per minute, and the grinding progress of the gallium arsenide wafer 1 is monitored in real time. When the thickness of the gallium arsenide wafer 1 is thinned to 80-120 microns required by the back process of the wafer substrate, the thinning can be stopped. It should be noted that the thinning process requires the addition of grinding fluid, which is an aluminum oxide water-based component, wherein the weight percentage of aluminum oxide is 5%-20%, and the particle size of aluminum oxide is 3-10 microns. Further, the grinding disc 6 of the present application adopts a glass grinding disc. In order to increase the grinding rate, in one embodiment, a counterweight 5 can be added to the grinding and polishing fixture 4, and the counterweight 5 can increase the force between the gallium arsenide wafer 1 and the grinding disc 6, and increase the friction between the grinding disc 6 and the gallium arsenide wafer 1 during the rotation process, thereby improving the grinding efficiency.

[0060] Step 50: placing the bonded wafer on a polishing plate for polishing;

[0061] like Figure 6As shown, specifically, the gallium arsenide wafer 1 in the thinned bonding sheet 100 is subjected to CMP (chemical mechanical polishing) treatment, and the gallium arsenide wafer 1 contained in the bonding sheet 100 is placed on the polishing disk 7 for polishing, wherein a polishing cloth is provided on the polishing disk 7, and the polishing cloth is made of polyamino resin and polyamide resin. It should be noted that the polishing process requires the addition of polishing slurry, and the polishing slurry includes silica gel, hydrogen peroxide, silicate, PH regulator and deionized water, wherein the proportion of each component of the polishing slurry by weight percentage is 15% of silica gel, 10% of hydrogen peroxide, 0.002% of silicate, 0.15% of PH regulator, and the rest is deionized water, wherein the silica gel adopts 40-150um granular silica gel.

[0062] Step 60: Gold plating on the back side of the bonding sheet 100;

[0063] Specifically, the bonding sheet 100 is placed in an evaporator for backside gold plating to facilitate external leads to provide electrical drive for the wafer. It should be noted that the back side of the bonding sheet is the other side opposite to the side where the GaAs wafer is bonded to the sapphire substrate, and can also be considered as the exposed side of the GaAs wafer contained in the bonding sheet.

[0064] Furthermore, before gold plating, the bonding wafer 100 needs to be cleaned twice. The first cleaning uses a solution prepared by a neutral detergent and deionized water in a ratio of 1:10 to clean the oxide colloidal body remaining in the polishing section of the bonding wafer 100 to prevent the oxide colloidal body from affecting the evaporation yield of the gallium arsenide wafer; the second cleaning uses an organic solvent such as isopropyl alcohol to clean the wax on the sapphire substrate in the bonding wafer 100. Specifically, the bonding wafer 100 with the sapphire substrate 3 is placed in a QDR (QuickDump Rinser) and rinsed repeatedly for 10 times. After rinsing, the bonding wafer 100 with the sapphire substrate is taken out and placed in a spin dryer for spin drying. After spin drying, the back side gold plating operation can be performed.

[0065] It should be noted that after the first cleaning is completed, the bonding sheet 100 needs to be removed from the polishing fixture 4. Since the sapphire substrate 3 contained in the bonding sheet 100 is bonded to the polishing fixture 4 by wax, the removal method is to place the polishing fixture 4 together with the bonding sheet 100 on a 100°C hot plate to melt the wax. After melting, the sapphire substrate 3 contained in the bonding sheet 100 is separated from the polishing fixture 4, and the bonding sheet is taken out from the polishing fixture 4.

[0066] Furthermore, the back-side gold plating scheme of the present application adopts the method of evaporation. First, the gallium arsenide wafer is placed in a vacuum chamber, and the film material is heated by resistance, electron beam, laser and other methods. The film material of the present application is gold, so that the gold evaporates or sublimates and gasifies into particles with a certain energy. The gaseous particles are rapidly transmitted to the substrate in a linear motion without collision. Part of the particles reaching the surface of the substrate are reflected, and the other part is adsorbed on the substrate and diffused on the surface. Collisions occur between the deposited atoms to form clusters. The particle clusters continuously collide with the diffused particles. This process is repeated. After a period of reaction, when the number of aggregated particles exceeds a certain critical value, they become stable nuclei, and then continue to adsorb diffused particles and gradually grow. Finally, through the contact and merging of adjacent stable nuclei, a continuous film is formed.

[0067] like Figure 7 As shown, a gold-plated layer 8 is formed on the exposed side of the gallium arsenide wafer included in the bonding wafer 100 through evaporation.

[0068] It should be noted that the gold-plated layer 8 of the present application can also be electroplated by placing the gallium arsenide wafer contained in the bonding sheet to be gold-plated into an electroplating tank for electroplating. The electroplating process controls parameters such as current density, electrolyte concentration, and electrolyte temperature to ensure the quality of the electroplated layer.

[0069] Step 70: The bonded wafer is hydrolyzed to separate the gallium arsenide wafer.

[0070] Specifically, the bonding wafer 100 after gold plating is taken out from the equipment, and then immersed in a pure water container at 95°C for 30-120 minutes. During the immersion period, the separation of the sapphire substrate 3 and the gallium arsenide wafer 1 contained in the bonding wafer 100 is observed. After the sapphire substrate 3 and the gallium arsenide wafer 1 are completely separated, the gallium arsenide wafer is taken out to complete the thinning, polishing and gold plating process of the entire gallium arsenide wafer.

[0071] It should be noted that due to the hydrolyzed UV glue used in this application, there is no need to add chemical reagents in the subsequent separation process. Instead, ordinary heated pure water can separate the sapphire substrate and the gallium arsenide wafer. Compared with the use of chemical reagents for separation in the prior art, the loss of chemical reagents to the gold-plated layer and the gallium arsenide wafer is further reduced, thereby improving the yield level of the entire process.

[0072] Compared with the prior art, the present application adopts hydrolyzed UV glue instead of the rosin and wax in the prior art to realize the bonding between the gallium arsenide wafer and the sapphire substrate, which not only solves the problem of the irritating odor of the rosin and wax in the prior art that is harmful to the human body, but also the whole process is simple and easy. The hydrolyzed UV glue and consumables used are inexpensive and easy to obtain. At the same time, the equipment requirements are low, and high-end equipment is not required to achieve wafer thinning, which greatly reduces the fragmentation rate in the process.

[0073] The various embodiments in this specification are described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the various embodiments can be referenced to each other.

[0074] The above description is only an implementation mode of the present invention, and does not limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made by using the contents of the present invention specification and drawings, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A method for thinning a gallium arsenide wafer, It is characterized in that include Step 10: providing a gallium arsenide wafer, wherein a hydrolyzed UV adhesive is coated on a surface of the gallium arsenide wafer; Step 20: providing a sapphire substrate, wherein the sapphire substrate is bonded to the surface of the gallium arsenide wafer to form a bonding sheet; Step 30: The bonding sheet is placed in a UV exposure machine for curing; Step 40: placing the bonding sheet on a grinding disc for thinning; Step 50: placing the bonding sheet on a polishing plate for polishing; Step 60: Gold-plating the back of the bonding sheet; Step 70: The bonding wafer is hydrolyzed to separate the GaAs wafer.

2. The method for thinning a gallium arsenide wafer according to claim 1, It is characterized in that The sapphire substrate and the gallium arsenide wafer are bonded in a vacuum bonding machine, and the vacuum degree in the vacuum bonding machine is 50mtorr-500mtorr.

3. The method for thinning a gallium arsenide wafer according to claim 1, It is characterized in that The curing wavelength of the UV exposure machine is 365-395nm, and the curing condition is greater than 1000mj / cm 2 , curing time 30-300s.

4. The method for thinning a gallium arsenide wafer according to claim 1, It is characterized in that A grinding and polishing fixture is provided, and the solidified bonding sheet is pasted on the grinding and polishing fixture with wax, and the temperature during pasting is 70-100°C.

5. The method for thinning a gallium arsenide wafer according to claim 4, It is characterized in that A grinding liquid is provided, and the gallium arsenide wafer surface contained in the bonding sheet is placed on the grinding disk for grinding. The rotation speed of the grinding disk is 30-60 revolutions per minute. The grinding liquid is an aluminum oxide water-based component, wherein the weight percentage of the aluminum oxide is 5%-20%, and the particle size of the aluminum oxide is 3-10 microns.

6. The method for thinning a gallium arsenide wafer according to claim 5, It is characterized in that A polishing slurry is provided, wherein the proportions of the components of the polishing slurry by weight percentage are 15% silica gel, 10% hydrogen peroxide, 0.002% silicate, 0.15% pH regulator, and the remainder is deionized water, wherein the silica gel is a 40-150um granular silica gel.

7. The method for thinning a gallium arsenide wafer according to claim 6, It is characterized in that The polished bonding wafer is cleaned for the first time, and the first cleaning adopts a solution prepared by a neutral cleaning agent and deionized water in a ratio of 1:

10.

8. The method for thinning a gallium arsenide wafer according to claim 7, It is characterized in that The bonding sheet is removed from the grinding and polishing fixture, and the grinding and polishing fixture together with the bonding sheet is placed on a 100° C. hot plate. After the wax melts, the bonding sheet is separated from the grinding and polishing fixture, and the bonding sheet is taken out.

9. The method for thinning a gallium arsenide wafer according to claim 8, It is characterized in that The bonding sheet is cleaned for the second time using an isopropyl alcohol organic solvent. The bonding sheet is placed in a quick-drain rinse tank and rinsed repeatedly for 10 times. After the rinsing is completed, the bonding sheet is taken out and placed in a spin dryer for spin drying.

10. The method for thinning a gallium arsenide wafer according to claim 1, It is characterized in that The gold-plated bonding sheet is taken out from the equipment, and then immersed in a 95° C. pure water container for 30-120 minutes. The gallium arsenide wafer is taken out after the sapphire substrate and the gallium arsenide wafer contained in the bonding sheet are completely separated.

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