Cleaning method of gallium arsenide wafer

Abstract

The invention belongs to the field of semiconductors, and particularly discloses a method for cleaning a gallium arsenide wafer. According to the cleaning method, the processes of cleaning with the cleaning solution containing the alkaline reagent and the complexing agent, water washing, drying in the inert gas atmosphere, static electricity removal and plasma cleaning are sequentially carried out, the atomization or white spot surface defect existing on the surface of the gallium arsenide wafer can be completely avoided, the thickness of an oxide layer on the surface of the gallium arsenide wafer is reduced, and the yield of the gallium arsenide wafer is improved. The content of pollutants and particles on the surface of the gallium arsenide wafer is reduced, and the yield of the gallium arsenide wafer is improved.

Description

Technical Field

[0001] The invention belongs to the field of semiconductors, and in particular relates to a method for cleaning a gallium arsenide wafer. Background Art

[0002] At present, GaAs products, as the second generation of semiconductors, are gradually becoming more high-end in terminal applications, and low-end GaAs substrate products are gradually being eliminated. For GaAs wafer manufacturers, improving the surface quality of GaAs wafer products is an important task. In order to improve the surface quality of wafers, polishing and cleaning processes are generally required. The cleaning process is the last process in the production of GaAs substrates and directly affects the quality of downstream products. Improving the cleaning quality of wafer products is an important link in improving the surface quality of wafers.

[0003] At present, various chip manufacturers use traditional alkaline solutions or acidic solutions as liquid medicines to clean gallium arsenide chip products. After alkaline or acid washing, the chip is washed with deionized water, dried and packaged. Because the liquid medicine is highly corrosive, the cleaning method of liquid spraying is generally adopted. In this cleaning process, the chip will be exposed to the air for a long time, and the chip surface is easily oxidized and contaminated. In addition, this cleaning process may cause excessive corrosion, atomization, oxidation, etc. on the chip surface due to the reaction of various components in the liquid medicine with the chip surface or elements in the air. It often causes surface defects such as Cl residue, atomization, white spots, oxidation, and particles on the surface of some chips, resulting in abnormal chip quality. For chips with the above-mentioned surface defects, they cannot be used in high-end products and cannot be used any more, resulting in direct scrapping of the chip, reducing the product qualification rate and increasing production costs. Summary of the invention

[0004] In view of the gallium arsenide wafer cleaning process involved in the above-mentioned prior art, which often leads to surface defects such as atomization, white spots, oxidation, particles, and Cl residue on the wafer surface, the present invention will provide a gallium arsenide wafer cleaning method.

[0005] To achieve the above purpose, the following technical solutions are specifically included:

[0006] A gallium arsenide wafer cleaning method comprises the following steps:

[0007] (1) using a cleaning solution and water to clean a gallium arsenide wafer in sequence to obtain a cleaned gallium arsenide wafer; the cleaning solution comprises an alkaline reagent, a complexing agent and water; the alkaline reagent comprises at least one of ethanolamine, ammonia water and hydrogen peroxide, and the complexing agent comprises at least one of polyethyleneimine, polyethyleneamine and ethylenediamine;

[0008] (2) drying the cleaned gallium arsenide wafer under an inert gas;

[0009] (3) The dried gallium arsenide wafer is sequentially subjected to a destaticizing treatment and a plasma cleaning treatment.

[0010] In the cleaning method of the present invention, a cleaning solution containing an alkaline agent and a complexing agent is first used to clean the gallium arsenide wafer, wherein the alkaline agent can remove organic matter in the polishing solution remaining on the wafer surface in the previous polishing process; the complexing agent can remove or adsorb pollutants on the surface of the gallium arsenide wafer through ion exchange; and then the cleaned wafer is dried in an inert gas atmosphere without using a conventional drying process exposed to the air, thereby reducing the risks of oxide layer thickness, microparticle pollution, etc. on the surface of the gallium arsenide wafer; static electricity will remain in the cleaning or drying process, and the static electricity will adsorb impurity elements such as dust in the air, causing pollution on the wafer surface. The present invention performs static electricity removal treatment on the dried wafer to eliminate static electricity on the surface of the gallium arsenide wafer, thereby avoiding surface pollution caused by surface static electricity; finally, the gallium arsenide wafer is placed in a plasma in a vacuum environment for cleaning, and plasma such as inert ions, electrons, and active groups reacts with the wafer surface to further remove pollutants on the surface of the gallium arsenide wafer. The cleaning method of the present invention can completely avoid the surface defects of atomization or white spots on the surface of the gallium arsenide wafer, reduce the thickness of the oxide layer on the surface of the gallium arsenide wafer, reduce the content of pollutants and particulate matter on the surface of the gallium arsenide wafer, and improve the yield of the gallium arsenide wafer.

[0011] Preferably, in step (1), the cleaning method is spray cleaning, and the time of the spray cleaning is 10-20s.

[0012] The cleaning solution of the present invention still contains a certain amount of alkaline reagent and has a certain degree of corrosiveness. It is more suitable to adopt rapid spray cleaning, and has a better cleaning effect on gallium arsenide wafers.

[0013] Preferably, in step (1), the temperature of the cleaning solution is 15-20°C.

[0014] The cleaning liquid is kept at 15-20℃ during the cleaning process, which can speed up the cleaning efficiency while ensuring a good cleaning effect.

[0015] Preferably, in step (1), the aqueous ammonia is concentrated aqueous ammonia, wherein the mass percentage of ammonia gas is 25-28%.

[0016] Preferably, in step (1), the hydrogen peroxide is a hydrogen peroxide solution, and the mass percentage of hydrogen peroxide in the hydrogen peroxide solution is 30-35%.

[0017] Preferably, in step (1), the water is deionized water.

[0018] The water used for cleaning is deionized water with a resistivity of more than 18MΩ, which is more conducive to cleaning and removing pollutants and residues on the surface of the gallium arsenide wafer, and has a better cleaning effect.

[0019] Preferably, in step (1), the mass ratio of the alkaline agent, the complexing agent and water is alkaline agent: complexing agent: water = (1-3): (0.5-1.5): (8-10).

[0020] By preparing the cleaning solution with the mass ratio of the alkaline agent, the complexing agent and water, the use of the alkaline agent and the complexing agent can be reduced while ensuring the gallium arsenide cleaning effect. The cleaning solution in the present invention only needs to use a weakly alkaline alkaline agent, which can reduce the burden on the environment after the cleaning solution is scrapped and reduce costs.

[0021] Preferably, in step (2), the drying temperature is 15-20° C., and the drying time is 50-150 s.

[0022] The present invention places the cleaned gallium arsenide wafer in an inert gas atmosphere for relatively gentle drying, which not only avoids surface contamination caused by drying in the air in the traditional process, reduces the thickness of the oxide layer on the surface of the wafer and the content of pollutants, but also shortens the drying time, which can meet the actual production pursuit of efficiency.

[0023] Preferably, in step (3), the time for the anti-static treatment is 1-10 s.

[0024] The traditional wafer cleaning process does not have a static electricity elimination step. There may be residual static electricity during the cleaning and drying process. The generation of static electricity will absorb dust and other impurities in the air, causing contamination of the wafer surface. In the method of the present invention, a rapid static electricity elimination process is added, which can not only avoid pollution caused by static electricity, but also meet the actual production pursuit of efficiency.

[0025] Preferably, in step (3), the vacuum degree of the plasma cleaning process is 10 -3 -10 -5 Torr, and the plasma cleaning treatment time is 8-10 min.

[0026] When the GaAs wafer is placed in the plasma cleaning equipment, the equipment is evacuated to a vacuum of 10 -3 -10 -5Torr, and then industrial gases such as argon, hydrogen, and nitrogen are injected through the inert gas inlet. After the plasma equipment is started, an alternating electric field will be generated in the equipment, and the industrial gas will be converted into plasma such as inert ions, electrons, and active groups. These plasmas have high reactivity or high energy, and they collide with pollutants on the surface of the wafer to produce volatile substances. These volatile substances are pumped out of the chamber through the vacuum pump to achieve the cleaning of the gallium arsenide wafer.

[0027] Compared with the prior art, the present invention has the following beneficial effects: in the cleaning method of the present invention, by sequentially cleaning with a cleaning solution containing an alkaline reagent and a complexing agent, washing with water, drying under an inert gas atmosphere, removing static electricity, and a plasma cleaning process, the atomization or white spot surface defects on the surface of the gallium arsenide wafer can be completely avoided, the thickness of the oxide layer on the surface of the gallium arsenide wafer can be reduced, the content of pollutants and particulate matter on the surface of the gallium arsenide wafer can be reduced, and the yield of the gallium arsenide wafer can be improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 Flow chart of the cleaning method of the present invention. DETAILED DESCRIPTION

[0029] In order to better illustrate the purpose, technical scheme and advantages of the present invention, the present invention will be further described below through specific examples. The test methods used in the examples and / or comparative examples are conventional methods unless otherwise specified; the materials, reagents, etc. used can be obtained from commercial channels unless otherwise specified.

[0030] The ethanolamine used in the following examples and comparative examples is all diethanolamine.

[0031] Example 1

[0032] A gallium arsenide wafer cleaning method, the flow chart is as follows Figure 1 As shown, the specific steps include:

[0033] (1) using ethanolamine, polyethyleneimine and deionized water, a cleaning solution is prepared in a mass ratio of 2:1:8, and the temperature of the cleaning solution is maintained at 15° C.;

[0034] (2) Place the polished GaAs wafers in the designated card box, with two card slots between each wafer, for a total of 5 wafers. Place the cleaning liquid on the card slots in the spray chamber, turn on the spray switch, and the nozzle will continuously spray the cleaning liquid onto the GaAs wafers. Stop cleaning after spraying for 10 seconds.

[0035] (3) Turn on the deionized water cleaning switch, and the nozzle starts to spray deionized water to rinse the gallium arsenide wafer for 15 seconds;

[0036] (4) The cleaned GaAs wafer is transferred to a drying box, and the drying box switch is turned on. Inert gas (nitrogen) is flushed into the drying box and the GaAs wafer is dried at the same time. The drying temperature is 15° C. and the drying time is 80 seconds.

[0037] (5) Move the dried GaAs wafer to a static elimination chamber, turn on the corresponding switch, and remove static electricity for 3 seconds to eliminate the static charge on the surface of the GaAs wafer;

[0038] (6) Then transfer the GaAs wafer to the plasma cleaning chamber, turn on the chamber switch, and use the vacuum pump to evacuate the air in the chamber and reduce the pressure to a vacuum degree of 10 -3 Torr, industrial gases such as argon, hydrogen, and nitrogen are injected through the inert gas inlet. After the ion cleaning machine switch is turned on, an alternating electric field is generated, generating highly reactive or high-energy plasma. The plasma cleaning gun scans the surface of the wafer, and the plasma collides with the pollutants on the wafer surface to produce volatile substances, thereby cleaning the surface of the gallium arsenide wafer. When it is detected that the wafer surface has been completely cleaned, it automatically resets to complete the cleaning. The whole process takes 9 minutes. During the cleaning process, the volatile substances are pumped out of the chamber in real time through the vacuum pump to complete the cleaning of the gallium arsenide wafer.

[0039] Example 2

[0040] The only difference between this embodiment and embodiment 1 is that in step (1), the mass ratio of ethanolamine, polyethyleneimine and deionized water in the cleaning solution is 2:1:10.

[0041] Example 3

[0042] Compared with Example 2, the time for cleaning with cleaning solution, cleaning with deionized water, drying and removing static electricity is prolonged, the drying temperature is increased, and the vacuum degree in plasma cleaning is 10 -5 Torr, the specific steps are as follows:

[0043] (1) preparing a cleaning solution using ethanolamine, polyethyleneimine and deionized water in a mass ratio of 2:1:10, and maintaining the temperature of the cleaning solution at 15° C.;

[0044] (2) Place the polished GaAs wafers in the designated card box, with two card slots between each wafer, for a total of 5 wafers. Place the cleaning liquid on the card slots in the spray chamber, turn on the spray switch, and the nozzle will continuously spray the cleaning liquid onto the GaAs wafers. Stop cleaning after spraying for 15 seconds.

[0045] (3) Turn on the deionized water cleaning switch, and the nozzle starts to spray deionized water to rinse the gallium arsenide wafer for 20 seconds;

[0046] (4) The cleaned GaAs wafer is transferred to a drying box, and the drying box switch is turned on. Inert gas (nitrogen) is flushed into the drying box and the GaAs wafer is dried at the same time. The drying temperature is 18° C. and the drying time is 100 s.

[0047] (5) Move the dried GaAs wafer to a static elimination chamber, turn on the corresponding switch, and remove static electricity for 5 seconds to eliminate the static charge on the surface of the GaAs wafer;

[0048] (6) Then transfer the GaAs wafer to the plasma cleaning chamber, turn on the chamber switch, and use the vacuum pump to evacuate the air in the chamber and reduce the pressure to a vacuum degree of 10 -5 Torr, industrial gases such as argon, hydrogen, and nitrogen are injected through the inert gas inlet. After the ion cleaning machine switch is turned on, an alternating electric field is generated, generating highly reactive or high-energy plasma. The plasma cleaning gun scans the surface of the wafer, and the plasma collides with the pollutants on the wafer surface to produce volatile substances, thereby cleaning the surface of the gallium arsenide wafer. When it is detected that the wafer surface has been completely cleaned, it automatically resets to complete the cleaning. The whole process takes 10 minutes. During the cleaning process, the volatile substances are pumped out of the chamber in real time through the vacuum pump to complete the cleaning of the gallium arsenide wafer.

[0049] Example 4

[0050] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, an equal amount of ammonia water (with a mass percentage of 25-28%) is used to replace ethanolamine as the alkaline reagent in the cleaning solution, and the rest is the same.

[0051] Example 5

[0052] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, an equal amount of polyvinylamine is used to replace polyethyleneimine as the complexing agent in the cleaning solution, and the rest is the same.

[0053] Example 6

[0054] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, an equal amount of hydrogen peroxide solution (35% by mass) is used to replace ethanolamine as the alkaline reagent in the cleaning solution, and an equal amount of ethylenediamine is used to replace polyethyleneimine as the complexing agent in the cleaning solution, and the rest is the same.

[0055] Example 7

[0056] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, an equal amount of hydrogen peroxide solution (35% by mass) is used to replace ethanolamine as the alkaline reagent of the cleaning solution, and the rest is the same.

[0057] Example 8

[0058] The difference between this embodiment and embodiment 1 is that in step (1) of this embodiment, an equal amount of hydrogen peroxide solution (35% by mass) is used to replace ethanolamine as the alkaline reagent in the cleaning solution, and an equal amount of polyethyleneamine is used to replace polyethyleneimine as the complexing agent in the cleaning solution, and the rest is the same.

[0059] Comparative Example 1

[0060] This comparative example adopts the gallium arsenide wafer cleaning process in the prior art, and the specific steps are as follows:

[0061] (1) Use ammonia water (mass percentage of 25-28%) as the cleaning solution and maintain the temperature at 15°C;

[0062] (2) Place the polished GaAs wafers in the designated card box, with two card slots between each wafer, for a total of 5 wafers. Place the chemical solution on the card slot of the spray chamber, turn on the spray switch, and the nozzle will continuously spray the chemical solution on the GaAs wafers. Stop cleaning after spraying for 10 seconds.

[0063] (3) Turn on the deionized water cleaning switch, and the nozzle starts to spray deionized water to rinse the gallium arsenide wafer for 30 seconds;

[0064] (4) Turn on the ethanol cleaning switch again, and the nozzle starts to spray ethanol to rinse the gallium arsenide wafer. The rinsing time is 10 seconds and the temperature is 15°C.

[0065] (5) Turn on the deionized water cleaning switch, and the nozzle starts to spray deionized water to rinse the gallium arsenide wafer for 30 seconds;

[0066] (6) preparing a solution of ammonia water (25-28% by mass), hydrogen peroxide solution (35% by mass), and deionized water in a mass ratio of 1:1:8 as a cleaning solution, opening the nozzle to start spraying the solution to clean the wafer for 20 seconds at a temperature of 18° C.;

[0067] (7) Turn on the deionized water cleaning switch, and the nozzle starts to spray deionized water to rinse the gallium arsenide wafer for 30 seconds;

[0068] (8) The gallium arsenide wafer is dried for 60 seconds, and the cleaning is completed.

[0069] Comparative Example 2

[0070] The difference between this comparative example and Example 1 is that step (4) of this comparative example adopts a spin-drying method for drying, and the spin-drying time is 60 seconds.

[0071] Comparative Example 3

[0072] The difference between this comparative example and Example 1 is that this comparative example does not perform the static electricity elimination process in step (5).

[0073] Comparative Example 4

[0074] The difference between this comparative example and Example 1 is that this comparative example does not perform the plasma cleaning process in step (6).

[0075] Comparative Example 5

[0076] The difference between this comparative example and Example 1 is that in step (1) of this comparative example, an equal amount of isopropanolamine is used to replace ethanolamine as the alkaline reagent of the cleaning solution, and the rest is the same.

[0077] Comparative Example 6

[0078] The difference between this comparative example and Example 1 is that in step (1) of this comparative example, an equal amount of sodium nitrilotriacetate is used to replace polyethyleneimine as the complexing agent of the cleaning solution, and the rest is the same.

[0079] The gallium arsenide wafers cleaned in the above embodiment and comparative example were subjected to surface inspection, and the specific method is as follows:

[0080] (1) White spots or fog spots: Observe the surface of each wafer under a strong light and count the number of white spots or fog spots. If there are no white spots or fog spots, it is considered qualified.

[0081] (2) Oxide layer: The oxide layer thickness of each wafer surface was tested using an ellipsometer. Each wafer with an oxide layer thickness of ≤0.90 nm was considered qualified. The average oxide layer thickness of five wafers was calculated.

[0082] (3) Surface particle content: The particle content on the wafer surface is tested using a Tencor surface particle analyzer. Each wafer is considered qualified if the particle content is ≤ 25 particles @ 0.3 μm (where @ 0.3 μm indicates a specification for the number of particles tested). The average particle content of the five wafers is calculated.

[0083] (4) Surface roughness: The roughness of the wafer surface was observed using an AFM instrument. Each wafer with a roughness of ≤0.25 nm was considered qualified, and the average roughness of the five wafers was calculated;

[0084] (5) Cl content: The Cl content on the wafer surface was measured using a TXRF surface element analyzer. A Cl content of ≤35 ppb on each wafer was considered acceptable, and the average Cl content of 5 wafers was calculated.

[0085] (6) Finished product qualification rate: Products that simultaneously meet the above five items (1)-(5) are considered qualified finished products, and the finished product qualification rate (%) = n / N*100, where n is the number of qualified chips, N = 5; otherwise, they are unqualified. The above test results are shown in Table 1.

[0086] Table 1

[0087]

[0088] It can be seen from Examples 1-8 and Comparative Example 1 that the cleaning method of the present invention can overcome the defects of white fog or white spots on the surface of the gallium arsenide wafer when using alkaline or acidic cleaning solutions in the prior art, reduce the oxide layer thickness, particle content, surface roughness, and Cl content on the surface of the gallium arsenide wafer, and improve the finished product qualification rate of the gallium arsenide wafer.

[0089] It can be seen from Example 1 and Comparative Examples 2-4 that the present invention adopts inert gas drying to significantly reduce the thickness of the wafer oxide layer and the Cl content; the present invention adds static electricity removal and plasma cleaning processes to significantly reduce the particle content and Cl content on the wafer surface.

[0090] It can be seen from Example 1 and Comparative Examples 5-6 that in the system of the present invention, using isopropanolamine as an alkaline reagent or using sodium nitrilotriacetate as a complexing agent will increase the particle content and Cl content on the chip surface. Therefore, only by using at least one of ethanolamine, ammonia water, and hydrogen peroxide as an alkaline reagent and at least one of polyethyleneimine, polyethyleneamine, and ethylenediamine as a complexing agent can the qualified rate of finished gallium arsenide chips be comprehensively improved.

[0091] In Examples 1 and 2, there is no significant difference in the effects of cleaning solutions of different concentrations in removing residual polishing solution (chlorine content); in Examples 1-8, the surface oxide layer thickness in Example 3 is lower, the number of surface particles is less, and the surface roughness is lower, resulting in a better cleaning effect.

[0092] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that the technical solution of the present invention can be modified or replaced by equivalents without departing from the essence and scope of the technical solution of the present invention.

Claims

1. A gallium arsenide wafer cleaning method, characterized in that: The steps include: (1) using a cleaning solution and water to clean a gallium arsenide wafer in sequence to obtain a cleaned gallium arsenide wafer; the cleaning solution comprises an alkaline reagent, a complexing agent and water; the alkaline reagent comprises at least one of ethanolamine, ammonia water and hydrogen peroxide, and the complexing agent comprises at least one of polyethyleneimine, polyethyleneamine and ethylenediamine; (2) drying the cleaned gallium arsenide wafer under an inert gas; (3) The dried gallium arsenide wafer is sequentially subjected to a destaticizing treatment and a plasma cleaning treatment.

2. The gallium arsenide wafer cleaning method according to claim 1, characterized in that: In step (1), the cleaning method is spray cleaning, and the time of the spray cleaning is 10-20s.

3. The gallium arsenide wafer cleaning method according to claim 1, characterized in that: In step (1), the temperature of the cleaning solution is 15-20° C., and the water is deionized water.

4. The gallium arsenide wafer cleaning method according to claim 1, characterized in that: In step (1), the mass ratio of the alkaline agent, the complexing agent and water is alkaline agent: complexing agent: water = (1-3): (0.5-1.5): (8-10).

5. The gallium arsenide wafer cleaning method according to claim 1, characterized in that: In step (2), the drying temperature is 15-20° C., and the drying time is 50-150 seconds.

6. The gallium arsenide wafer cleaning method according to claim 1, characterized in that: In step (3), the time for the static electricity removal treatment is 1-10s.

7. The gallium arsenide wafer cleaning method according to claim 1, characterized in that: In step (3), the vacuum degree of the plasma cleaning process is 10 -3 -10 -5 Torr.

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