A method for realizing low-temperature Si-Ge and Si-InP bonding using microcrystalline germanium film

Abstract

The present invention provides a method for realizing low-temperature Si-Ge and Si-InP bonding using a microcrystalline germanium film, and a method for realizing high-quality low-temperature Si-Ge and Si-InP bonding using a microcrystalline germanium film intermediate layer, which can not only avoid the stress problem caused by high-temperature bonding, but also avoid the formation of an oxide layer at the interface, reduce interface bubbles and improve bonding strength. The present invention uses a magnetron sputtering method to prepare a microcrystalline Ge film to realize Si-Ge or Si-InP bonding, and this method is a simple and low-cost material preparation method.

Description

Technical Field

[0001] The invention relates to a method for bonding Si-Ge and Si-InP, and in particular to a method for bonding Si-Ge and Si-InP at low temperature by using a microcrystalline germanium film as an intermediate layer. Background Art

[0002] The integration of Si and III-V materials is a key issue in the design and manufacture of future optoelectronic and electronic devices. Monolithic integration of materials with different properties, such as silicon, germanium, indium gallium arsenide, and lithium niobate, can improve device performance ([1]Pasquariello,Donato, et al. "Crystalline defects in InP-to-silicon direct wafer bonding." Japanese Journal of Applied Physics 40.8R (2001): 4837.). Using a metal film as an intermediate layer to bond two wafers is a very promising method to achieve room temperature wafer bonding and surface activated bonding ([2]Shimatsu, Takehito, and M. Uomoto. "Atomic diffusion bonding of wafers withthin nanocrystalline metal films." Journal of Vacuum Science & Technology B,Nanotechnology and Microelectronics: Materials, Processing, Measurement, andPhenomena 28.4 (2010): 706-714;[3] Shimatsu, Takehito, and Miyuki Uomoto. "Room temperature bonding of wafers with thin nanocrystalline metal films."ECS Transactions 33.4 (2010): 61.). This technology is very attractive for high-speed semiconductor devices made of hybrid material systems such as IV / III-V semiconductors ([4] Uomoto, Miyuki, et al. "Interface structure of InGaAs wafers bonded using thin amorphous Ge films in vacuum." Japanese Journal of Applied Physics 57.2S1 (2017): 02BA03.).

[0003] Although direct hydrophilic bonding of Si-Ge or Si-InP can be achieved through van der Waals forces at room temperature, annealing at 500-650 °C is required to achieve high bonding strength ([5] Huang, Hui, et al. "Lowtemperature In P∕ Si wafer bonding using boride treated surface." Applied physics letters 90.16 (2007): 161102.), and the thermal expansion coefficients of Si, Ge and InP are quite different, which will bring great thermal stress during high temperature annealing ([5]Liu, Jifeng, et al. "Ge-on-Si optoelectronics." Thin Solid Films 520.8 (2012): 3354-3360;[6]Sanjoh, Takaaki, et al. "Thermal properties of III–V on a SiC platform for photonic integrated circuits."Japanese Journal of Applied Physics 58.SB (2019): SBBE06.). Some researchers have used plasma surface treatment technology to achieve low-temperature Si-Ge or Si-InP heterojunction bonding at 300 °C ([7] Gity, Farzan, et al. "Characterization of germanium / silicon p–n junction fabricated by lowtemperature direct wafer bonding and layer exfoliation." Applied Physics Letters 100.9 (2012): 092102;[8]Pasquariello, Donato, and Klas Hjort. "Plasma-assisted InP-to-Si low temperature wafer bonding." IEEE Journal of Selected Topics in Quantum Electronics8.1 (2002): 118-131.), the bonding strength reaches the bulk fracture strength of Ge or InP, however, this method will result in the generation of an oxide layer at the interface and it is difficult to exhaust the bonding interface. Therefore, to achieve high-quality Si-Ge and Si-InP bonding, a method is required that can both reduce the annealing temperature and reduce the density of bubbles and the oxide layer at the bonding interface. In the method used in the present invention, the crystal structure of the microcrystalline intermediate layer is loose, and the interface gas and oxide can diffuse out along the intermediate layer during the experiment, thereby reducing the density of interface bubbles and the oxide layer. Summary of the invention

[0004] The purpose of the present invention is to provide a method for achieving high-quality low-temperature Si-Ge and Si-InP bonding using a microcrystalline germanium film intermediate layer, in order to address the problems of large thermal stress in high-temperature Si-Ge and Si-InP direct bonding and the appearance of an oxide layer and difficulty in exhausting at the bonding interface using surface treatment methods.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for realizing low-temperature Si-Ge and Si-InP bonding using a microcrystalline germanium film comprises the following steps:

[0007] 1) Preparation of microcrystalline Ge thin film, the specific method is as follows:

[0008] (1) The Si wafer was first ultrasonically cleaned with acetone and anhydrous ethanol for 10 min to remove organic matter on the surface.

[0009] (2) After the Si wafer is treated in step (1), it is first boiled and soaked in a mixed solution of H2SO4:H2O2=4:1 by volume for 10 minutes, rinsed with deionized water 15 times, and then soaked in a mixed solution of HF:H2O=1:20 by volume for 3 minutes, and rinsed with deionized water 15 times.

[0010] (3) After the treatment in step (2), the Si wafer was immersed in a mixture of NH4OH:H2O2:H2O in a volume ratio of 1:1:4 and boiled for 10 min, rinsed with deionized water 15 times, and then immersed in a mixture of HF:H2O in a volume ratio of 1:20 for 3 min, and rinsed with deionized water 15 times.

[0011] (4) After the treatment in step (3), the Si wafer was immersed in a mixture of HCl:H2O2:H2O in a volume ratio of 1:1:4 and boiled for 10 min, rinsed with deionized water 15 times, and then immersed in a mixture of HF:H2O in a volume ratio of 1:20 for 3 min, and rinsed with deionized water 15 times.

[0012] (5) The Ge and InP wafers were ultrasonically treated with acetone, anhydrous ethanol, and deionized water for 10 min respectively to remove surface adsorbed particles and organic pollutants. Then, they were immersed in a mixed solution with a volume ratio of HCl:H2O = 1:4 for 30 s, rinsed with deionized water 15 times, and repeated 3 times; finally, they were immersed in a mixed solution with a volume ratio of HF:H2O = 1:20 for 4 min and rinsed with deionized water 15 times.

[0013] (6) After the Si wafer has been processed in step (4), it is dried and placed in a high vacuum thin film deposition system. The vacuum is evacuated so that the vacuum degree of the sputtering chamber reaches 1×10 -4 Pa.

[0014] (7) After step (6), the temperature control system is adjusted to increase the temperature of the sample tray.

[0015] (8) After step (7), wait for the temperature to stabilize and the vacuum degree to be less than 1×10 -4 Pa, introduce 5 N pure Ar gas into the sputtering chamber, maintain it for 10-15 min, then adjust the vacuum pumping rate to make the chamber pressure 0.5-0.8 Pa, maintain it for 5-10 min.

[0016] (9) After processing in step (8), the rate of sputtering the a-Ge film is adjusted by setting the DC sputtering power supply power and the rotation speed of the sample tray to sputter a layer of a-Ge film with a thickness of 5 nm-10 nm on the Si wafer.

[0017] (10) By controlling the holding time, the a-Ge film is partially crystallized to obtain a microcrystalline Ge film.

[0018] In step 1) (7), the sample tray is subjected to a heating treatment, and the temperature is controlled between 300°C and 400°C.

[0019] In step 1) part (9), the DC sputtering power and rotation speed are set to 20-100 W and 5-10 rpm / min, respectively.

[0020] In step 1) (10), the holding time is controlled by a temperature control system. Enter a holding time of 10-30 minutes, and the temperature will automatically drop after the time is reached.

[0021] 2) Use microcrystalline Ge layer to achieve high-strength Si-Ge and Si-InP bonding. The specific method is as follows:

[0022] (1) Dry the Ge and InP wafers cleaned in step 1) (5).

[0023] (2) The Ge or InP wafer obtained in step (1) is directly bonded to the Si wafer on which the microcrystalline Ge has been grown.

[0024] (3) Hot pressing the laminated sheet obtained in step (2).

[0025] (4) Annealing the hot-pressed bonded sheet obtained in step (3) to achieve low-temperature Si-Ge and Si-InP bonding.

[0026] In step 2) (1), the drying can be carried out by spinning at high speed using a glue spreader.

[0027] In step 2) (3), the hot pressing is performed using a normal pressure bonding machine, and the hot pressing conditions are heating at 5 °C / min to 100-150 °C at room temperature for 1-2 h, and then naturally cooling to room temperature before sampling.

[0028] In step 2) (4), the annealing is low-temperature annealing performed in an annealing furnace. The annealing conditions are: starting temperature 30°C, heating to 300°C at a rate of 0.5°C / min, and keeping at 300°C for 20 h.

[0029] The beneficial effects of the present invention are as follows: the present invention creatively proposes a method for realizing high-quality Si-Ge or Si-InP bonding by using a microcrystalline Ge intermediate layer, which can not only avoid the stress problem caused by high-temperature bonding, but also avoid the formation of an oxide layer at the interface, reduce interface bubbles and improve bonding strength. The present invention uses a magnetron sputtering method to prepare a microcrystalline Ge film to realize Si-Ge or Si-InP bonding, and this method is a simple and low-cost material preparation method. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] Figure 1 This is an AFM test result diagram of a grown microcrystalline Ge thin film sample obtained in an embodiment of the present invention;

[0031] Figure 2 The tensile test results of the samples obtained in the embodiments of the present invention are shown in Figure 1; (a) is a Si-Ge bonding sample; (b) is a Si-InP bonding sample;

[0032] Figure 3 TEM test results of samples obtained in the embodiments of the present invention; (a) is a Si-Ge bonding sample; (b) is a Si-InP bonding sample. DETAILED DESCRIPTION

[0033] The following embodiments will further illustrate the present invention in conjunction with the accompanying drawings.

[0034] Example 1

[0035] The equipment used is a CK-450 high vacuum magnetron sputtering thin film deposition system, with two DC targets and one RF target in the vacuum chamber. The target material used is a 5N (99.999%) Ge circular target, the Si wafer used is an N-type single crystal wafer with a crystal orientation of (100), the InP wafer is a P-type single crystal wafer with a crystal orientation of (100), and the Ge wafer is an undoped single crystal wafer with a crystal orientation of (100).

[0036] 1. The specific method for processing Si wafer substrate materials is as follows:

[0037] 1) Select a Si substrate material with a crystal orientation of (100) and clean it with acetone and anhydrous ethanol to remove organic matter on the surface of the Si substrate;

[0038] 2) Soak the cleaned Si wafer in a mixed solution of H2SO4:H2O2=4:1 by volume for 10 min, rinse with deionized water 15 times, then soak in a mixed solution of HF:H2O=1:20 by volume for 3 min, and rinse with deionized water 15 times;

[0039] 3) The Si wafer treated in 2) was immersed in a mixture of NH4OH:H2O2:H2O=1:1:4 by volume and boiled for 10 min, rinsed with deionized water 15 times, and then immersed in a mixture of HF:H2O=1:20 by volume for 3 min, and rinsed with deionized water 15 times;

[0040] 4) The Si wafer treated in 3) above was immersed in a mixture of HCl:H2O2:H2O=1:1:4 by volume and boiled for 10 min, rinsed with deionized water 15 times, and then immersed in a mixture of HF:H2O=1:20 by volume for 3 min, and rinsed with deionized water 15 times;

[0041] 2. Surface treatment of Ge and InP wafers. The specific methods are as follows:

[0042] 1) Select Ge and InP wafers with a crystal orientation of (100), and use acetone, anhydrous ethanol, and deionized water to ultrasonicate for 10 minutes in sequence;

[0043] 2) Soak in a mixture of HCl:H2O = 1:4 by volume for 30 s, rinse with deionized water 15 times, repeat 3 times; finally soak in a mixture of HF:H2O = 1:20 by volume for 4 min, rinse with deionized water 15 times;

[0044] 3. Use microcrystalline Ge thin film to achieve high-quality Si-Ge or Si-InP bonding. The specific method is as follows:

[0045] 1) After cleaning, the Si wafer is dried by a glue spreader and placed in a high vacuum thin film deposition system. The vacuum is pumped until the vacuum degree in the chamber reaches 1×10 -4Pa, adjust the temperature control system to heat the sample tray, and the temperature is controlled at 315°C;

[0046] 2) After the temperature stabilizes at the set value, high-purity Ar gas is introduced into the chamber for 10 minutes, the vacuum pumping rate is adjusted so that the pressure is stabilized at 0.6 Pa for 5 minutes, and the sputtering power is turned on;

[0047] 3) Set the DC sputtering power to 20 W, the sample tray rotation speed to 10 rpm / min, and sputter for 60 s to leave a 5 nm thick a-Ge film on the Si wafer substrate;

[0048] 4) The vacuum rate was turned up to the maximum, and the sample tray was kept at 315°C for 20 min. The a-Ge part was crystallized to obtain a microcrystalline Ge layer;

[0049] 5) Use a glue spreader to spin dry the cleaned Ge and InP wafers;

[0050] 6) Take out the Si wafer with the microcrystalline Ge layer grown and quickly (within 1 minute) bond it to the Ge or InP wafer, and use your fingers to apply a certain amount of pressure to the bonded sample to increase the sample bonding strength;

[0051] 7) Place the bonded sheet into a normal pressure bonding machine for hot pressing at 150 °C for 1 h, with a heating rate of 5 °C / min;

[0052] 8) Place the bonded sheet in an annealing furnace and anneal at 300 °C for 20 h with a heating rate of 0.5 °C / min to obtain Si-Ge bonded samples and Si-InP bonded samples;

[0053] 9) Perform atomic force microscopy test on the microcrystalline Ge thin film sample grown in step 4), such as Figure 1 As shown in the figure, it can be seen that the surface of the sputtered microcrystalline Ge is flat. The RMS roughness is only 0.185 nm, which meets the subsequent bonding requirements (RMS < 0.5 nm). The sample annealed in step 8) was subjected to a tensile test. Figure 2 As shown in (a), it is the tensile test curve of the Si-Ge bonding sample. The bonding strength of the Si-Ge bonding sheet reaches 3.23 MPa. From the inset, it can be seen that the bonding sample has reached body fracture. Figure 2 (b) shows the tensile test curve of the Si-InP bonded sample. The bonding strength of the Si-InP bond sheet reaches 1.59 MPa. From the illustration, it can be seen that the bonded sample has reached body fracture. The bonded sample in step 8) is tested by TEM. Figure 3 As shown in (a), it is a TEM image of the Si-Ge bonding sample. It can be clearly seen that the bonding interface presents a microcrystalline morphology, realizing a microcrystalline bonding interface. Figure 3As shown in (b), it is a TEM image of the Si-InP bonding sample. It can be clearly seen that the interface presents polycrystalline and single crystal forms with the white interface as the boundary, and the microcrystalline bonding interface is successfully realized.

[0054] Matters not covered by the present invention are known technologies.

[0055] The above embodiments are only for illustrating the technical concept and features of the present invention, and their purpose is to enable people familiar with the technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for realizing low-temperature Si-Ge and Si-InP bonding using microcrystalline germanium film, characterized in that: The following steps are involved: (1) Preparation of microcrystalline Ge thin film. The specific method is as follows: (1-1) After surface treatment, the Si wafer was dried and then placed in a high vacuum thin film deposition system. The vacuum was evacuated to a vacuum degree of 1×10 -4 Pa; (1-2) After the treatment in step (1-1), adjusting the temperature control system to heat the sample tray; (1-3) After step (1-2), wait for the temperature to stabilize at the set value and the vacuum degree to be less than 1×10 -4 Pa, introduce 5N pure Ar gas into the sputtering chamber, and then adjust the vacuum pumping rate to stabilize the chamber pressure at 0.5-0.8 Pa; (1-4) sputtering a-Ge thin film by setting the DC sputtering power and the rotation speed of the sample tray; (1-5) The a-Ge film is partially crystallized by the heat preservation time to obtain a microcrystalline Ge film; (2) Use microcrystalline Ge layer to achieve high-quality Si-Ge and Si-InP bonding. The specific method is as follows: (2-1) After surface treatment, the Ge or InP wafer is dried and then directly bonded to the Si wafer on which microcrystalline Ge has been grown; (2-2) hot pressing the laminated sheet obtained in step (2-1); (2-3) annealing the bonded sheet obtained in step (2-2), i.e., achieving low-temperature Si-Ge and Si-InP bonding; In step (1-2), the sample tray is heated to a temperature between 300°C and 400°C; In step (1-3), first introduce Ar gas for 10-15 min, then control the pressure to 0.5-0.8 Pa and maintain for 5-10 min; The holding time in steps (1-5) is controlled by a temperature control system. A holding time of 10-30 min is input, and the temperature is automatically lowered after the time is reached.

2. A method for realizing low-temperature Si-Ge and Si-InP bonding using a microcrystalline Ge film according to claim 1, characterized in that: In steps (1-4), the DC sputtering power and rotation speed are set to 20-100 W and 5-10 rpm / min, respectively.

3. A method for realizing low-temperature Si-Ge and Si-InP bonding using a microcrystalline Ge film according to claim 1, characterized in that: The microcrystalline Ge film in step (1-5) is a film in which a-Ge and crystallized Ge coexist.

4. The method for realizing low-temperature Si-Ge and Si-InP bonding using microcrystalline Ge thin film according to claim 1, characterized in that: In step (2-1), direct bonding is to bond the wafers using a bonding mold in an atmospheric environment within 1-3 minutes after sampling.

5. The method for realizing low-temperature Si-Ge and Si-InP bonding using microcrystalline Ge thin film according to claim 1, characterized in that: In step (2-2), the hot pressing is performed by using a normal pressure bonding machine to hot press the bonding sheet, and the hot pressing conditions are heating at 5 °C / min to 100-150 °C for 1-2 h.

6. The method of realizing low-temperature Si-Ge and Si-InP bonding using microcrystalline Ge thin film according to claim 1, characterized in that: In step (2-3), annealing is performed in an annealing furnace at a low temperature, and the annealing condition is to increase the temperature to 300°C at 0.5°C / min and anneal for 20 hours.

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