CN105118804B - The method that ultra-thin silicon thin film passivation prepares germanium on insulator - Google Patents

Abstract

The invention discloses a method for preparing germanium on insulator by passivation of ultra-thin silicon film, and relates to a preparation method of GeOI. 1) Clean the Ge wafer and grow an ultra-thin silicon passivation layer on the Ge wafer to obtain a Si/Ge wafer; 2) Clean the Si wafer and oxidize it with dry oxygen to grow a SiO ₂ layer on the Si wafer to obtain a SiO ₂ /Ge wafer Si wafer; 3) After cleaning the Si/Ge wafer obtained in step 1) and the SiO ₂ /Si wafer obtained in step 2), oxygen plasma treatment is performed to oxidize and activate the ultra-thin silicon passivation layer to obtain SiO ₂ /Si wafer Ge, and simultaneously obtain activated SiO ₂ /Si wafers; 4) Soak the SiO ₂ /Ge and SiO ₂ /Si wafers treated in step 3) with ammonia water, dry them, bond them, and then heat and pressurize them to obtain bonding 5) wet-etching the bonded sheet obtained in step 4), thinning the Ge layer and then polishing it to obtain germanium-on-insulator with a smooth surface.

Description

Method for preparing germanium-on-insulator by passivation of ultra-thin silicon film

technical field

The invention relates to a method for preparing GeOI, in particular to a method for preparing germanium on insulator by passivating an ultra-thin silicon film.

Background technique

Due to the high mobility of electrons and holes in germanium materials, MOSFETs based on germanium materials have received extensive attention in recent years ([1] Zhan Da, Ma Xiaobo, Liu Weili, etc. Preparation of GOI materials by smart-cut method and research[ J].Journal of Functional Materials and Devices,2007,13(3):207-212;[2]Tracy C J,Fejes P,Theodore N D,etal.Germanium-on-insulator substrates by wafer bonding[J].Journal ofelectronic materials , 2004, 33(8):886-892). However, because the forbidden band width of germanium is very small, germanium devices also suffer from the fatal shortcoming of large leakage current, which seriously hinders the wider application of germanium devices. Just as SOI solves the shortage of bulk silicon materials in semiconductor devices, germanium-on-insulator (GeOI) combines the advantages of high carrier mobility of Ge and SOI structure, and is also a good solution for bulk Ge materials. Candidate materials for shortcomings.

At present, there are many methods for preparing GeOI, but the ideal GeOI manufacturing technology needs to ensure that a good single-crystal Ge thin film is produced on the Si wafer, including a low-defect GeOI structure. A variety of technologies for preparing GeOI cannot be achieved ([3]Taraschi G, Pitera AJ, Fitzgerald EA. Strained Si, SiGe, and Ge on-insulator: review of wafer bonding fabrication techniques[J]. Solid-State Electronics, 2004 ,48(8):1297-1305; [4]Tezuka T, Sugiyama N, Takagi S, et al.Dislocation-free formation of relaxed SiGe-on-insulator layers[J].Applied physics letters,2002,80(19 ):3560-3562; [5] AkatsuT, Deguet C, Sanchez L, et al.Germanium-on-insulator (GeOI) substrates—A novelengineered substrate for future high performance devices[J].Materials science in semiconductor processing, 2006,9 (4):444-448). Although the smart lift-off method is currently the most effective method to prepare GeOI structures with low defect density and better single-crystal performance, the direct bonding of Ge and SiO ₂ is easy to generate GeO _x at the interface between Ge and SiO ₂ . During the process of annealing at a temperature (≥400°C) to strengthen the bonding strength, GeO is easily generated in the interface, and GeO is unstable and will form volatile gases, which seriously affects the bonding quality ([6] Clavelier L, LeRoyer C, Morand Y, et al.Review of some critical aspects of Ge and GeOIsubstrates[J].ECS Transactions,2006,3(7):789-805;[7]Seo JW,Dieker C,Tapponnier A,et al.Epitaxial germanium -on-insulator grown on (001) Si [J]. Microelectronic engineering, 2007, 84 (9): 2328-2331.). Moreover, Ge is hydrophobic and needs to be hydrophilically treated by plasma to bond with SiO ₂ , and the plasma treatment will also generate GeO _x on the surface. Compared with the method of intelligent stripping, wafer bonding and back etching technology is another method with great potential for preparing GeOI. Wafer bonding and back etching technology can obtain GeOI materials with high interface flatness and steep interface, and can reduce the steps of ion implantation in smart stripping, but there is also the problem of GeO _x generated at the interface between Ge and SiO ₂ .

Contents of the invention

The purpose of the present invention is to prepare GeOI by bonding and back etching method and have problems such as GeO _x interface, provide and grow a layer of Si passivation layer after Ge wafer is cleaned, avoid the contact of Ge and air and plasma, avoid unstable GeO _x A method for the generation of germanium-on-insulator by the passivation of ultra-thin silicon films.

The present invention comprises the following steps:

1) Cleaning the Ge wafer and growing an ultra-thin silicon passivation layer on the Ge wafer to obtain a Si/Ge wafer;

2) Cleaning the Si sheet, oxidizing it with dry oxygen, and growing an SiO ₂ layer on the Si sheet to obtain a SiO ₂ /Si wafer;

3) After cleaning the Si/Ge wafer obtained in step 1) and the SiO ₂ /Si wafer obtained in step 2), oxygen plasma treatment is performed to oxidize and activate the ultra-thin silicon passivation layer to obtain SiO ₂ /Ge, and at the same time An activated SiO ₂ /Si wafer is obtained;

4) Soak the SiO ₂ /Ge and SiO ₂ /Si wafers treated in step 3) with ammonia water, dry them and bond them together, then heat up and pressurize them to obtain a bonded sheet;

5) performing wet etching on the bonding sheet obtained in step 4), thinning the Ge layer and then polishing it to obtain germanium-on-insulator with a flat surface.

In step 1), the ultra-thin silicon passivation layer can be grown by UHV/CVD system; the thickness of the ultra-thin silicon passivation layer can be 1-2nm.

In step 2), the dry oxygen oxidation is used to grow the _SiO2 layer on the Si wafer by controlling the oxidation time under high temperature conditions to obtain the required _SiO2 layer, the temperature of the high temperature>1000 °C; the _SiO2 layer The thickness can be 40-300nm.

In step 3), the oxygen plasma treatment can be carried out in an inductively coupled plasma etching machine with an oxygen flow rate of 40 sccm, a power of 100 W, and a treatment time of 15 s.

In step 4), the volumetric composition of the ammonia water may be: NH ₄ OH:H ₂ O=1:10, and the ammonia water soaking time may be 30s, so as to further improve the hydrophilicity and bonding strength of the wafer surface.

In step 5), the specific method for wet etching the bonded sheet can be: prepare 10mL of 50wt% sodium hydroxide solution, and after the initial temperature of the solution reaches 40°C, add 20mL of H ₂ O ₂ After the wafer, continue to add hydrogen peroxide solution in the solution at a speed of 7.5mL/min; the polishing can adopt the method of mechanical polishing in combination with chemical mechanical polishing; the composition of the polishing liquid of the mechanical polishing can be Nalco2398:H by volume ₂ O=1:20; the composition of the chemical mechanical polishing polishing solution by volume is Nalco2398: _{H 2} O:H ₂ O ₂ =1:20:0.2.

The present _invention first grows a layer of ultra-thin Si passivation layer on the Ge substrate, and then utilizes oxygen plasma treatment to oxidize & activate the Si passivation layer; The support wafer is bonded to finally obtain a GeOI structure; the present invention can prevent Ge from being directly in contact with air and plasma to generate GeO _x . In addition, the use of plasma oxidation of the Si passivation layer can avoid heat treatment and has the effect of activating the surface. The invention utilizes the hydrophilicity of _SiO2 and bonding back etching technology, and is a simple and low-cost new method for preparing GeOI.

Description of drawings

FIG. 1 is a tensile test curve of bonding strength between SiO ₂ /Ge and SiO ₂ /Si wafer according to an embodiment of the present invention.

Fig. 2 is a topography diagram of the GOI surface of the embodiment of the present invention.

Fig. 3 is a scanning electron micrograph of a cross section of a GOI structure according to an embodiment of the present invention.

Detailed ways

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

1. The Ge wafer 3 is cleaned. A certain amount of Ge oxides still exist on the surface of the cleaned Ge wafer. After being put into the UHV/CVD chamber, a high-temperature deoxidation treatment is first performed to remove the oxides on the surface of the sample. Since the growth rate of the Si passivation layer is too fast at high temperature, it is difficult to effectively control its thickness, and the diffusion of Ge at high temperature also has adverse effects, so a low temperature (390° C.) is used to grow the Si passivation layer 4 of 1-2 nm. The surface part of the Si passivation layer was naturally oxidized when exposed to air, but the Si in contact with Ge was not oxidized. Therefore, the Ge below the Si passivation layer is also protected from being oxidized, and the purpose of reducing the formation of the GeO _x intermediate layer is achieved.

2. Put the Si wafer 1 into an oxidation furnace after cleaning, and obtain the required SiO ₂ layer thickness by controlling the oxidation time under high temperature (>1000° C.), which can be 40-300 nm. In this example, dry oxygen oxidation was carried out at 1100° C. for 2 hours to obtain a SiO ₂ buried oxide layer 2 with a thickness of about 200 nm, and SiO ₂ /Si was used as a supporting sheet.

3. Clean the Si/Ge and SiO ₂ /Si wafers obtained in steps 1 and 2, put them into an inductively coupled plasma etching machine, and use oxygen plasma for oxidation and activation treatment. Set the oxygen flow rate to 40sccm, the power to 100W, and the time to 15s. The Si passivation layer is oxidized to a _SiO2 thin layer 2, resulting in an activated _SiO2 /Ge wafer, and an activated _SiO2 /Si wafer.

4. Soak the activated SiO ₂ /Ge and SiO ₂ /Si wafers in ammonia water (NH ₄ OH:H ₂ O = 1:10) solution for 30 seconds to further improve the hydrophilicity of the two wafers. The two wafers were blown dry with nitrogen at room temperature and bonded together. The bonded wafers were transferred to the bonding machine, and after the vacuum degree reached 10 ^-4 mbar, the temperature began to rise slowly. The heating rate of the whole process was 5°C/s, and the temperature was kept at 100°C for 2 hours, and at 150°C for 1 hour. , and apply 2MPa pressure to achieve pre-bonding. Continue to raise the temperature, keep the temperature at 250°C for 1h and apply a pressure of 0.5MPa. Raise the temperature to 350°C and 400°C, and keep the temperature constant for 1 hour to strengthen the bond strength. Finally, slowly cool down and cool down.

5. Thinning the back side of the bonded GeOI wafer 3/2/1 by wet etching. Prepare 10mL of 50wt% sodium hydroxide solution. After the initial temperature of the solution reaches 40°C, add 20mL of H ₂ O ₂ , and add hydrogen peroxide solution to the solution at a rate of 7.5mL/min after placing the bonded chip. Take out until the Ge layer is thinned to about 10 μm.

6. The thinned GeOI is further polished, and finally a GeOI structure with a uniform surface thickness and a flat surface is obtained. The surface of GeOI after etching is rough, and the method of mechanical polishing combined with chemical mechanical polishing is used to control the polishing thickness more accurately.

a. Mechanical polishing is adopted, the polishing liquid is Nalco2398:H ₂ O=1:20, and the thickness of the Ge layer is reduced to 2 μm.

b. Using chemical mechanical polishing, the polishing liquid is Nalco2398: _{H 2} O: _{H 2} O ₂ =1:20:0.2, and the Ge layer is further polished to the required thickness of the Ge layer.

7. Perform a tensile test on the bonded sheet obtained in step 4, and obtain a bonded sheet with a bonding strength greater than 2.5 MPa. The tensile strength curve is shown in Figure 1, which meets the manufacturing requirements of subsequent devices. The surface roughness of the GeOI obtained in step 6 was characterized, and an atomic force microscope was used to measure, and a Ge surface with a roughness of 0.543 nm was obtained, as shown in FIG. 2 . A cross-sectional scanning electron microscope test was performed on GeOI, and the bonding interface between Ge and SiO ₂ was clear and flat, as shown in Figure 3 .

After the above steps, the GeOI structure is finally obtained. The above descriptions are only preferred examples of the present invention.

Claims (10)

1. The method for preparing germanium on an insulator by ultra-thin silicon film passivation, is characterized in that comprising the following steps: 1) Cleaning the Ge wafer and growing an ultra-thin silicon passivation layer on the Ge wafer to obtain a Si/Ge wafer; 2) Cleaning the Si sheet, oxidizing it with dry oxygen, and growing an SiO ₂ layer on the Si sheet to obtain a SiO ₂ /Si wafer; 3) After cleaning the Si/Ge wafer obtained in step 1) and the SiO ₂ /Si wafer obtained in step 2), oxygen plasma treatment is performed to oxidize and activate the ultra-thin silicon passivation layer to obtain SiO ₂ /Ge, and at the same time An activated SiO ₂ /Si wafer is obtained; 4) Soak the SiO ₂ /Ge and SiO ₂ /Si wafers treated in step 3) with ammonia water, dry them and bond them together, then heat up and pressurize them to obtain a bonded sheet; 5) performing wet etching on the bonding sheet obtained in step 4), thinning the Ge layer and then polishing it to obtain germanium-on-insulator with a flat surface. 2. the method for preparing germanium-on-insulator by ultrathin silicon film passivation as claimed in claim 1, is characterized in that in step 1), described growing ultrathin silicon passivation layer adopts UHV/CVD system to grow ultrathin silicon passivation Floor. 3. The method for preparing germanium-on-insulator by ultra-thin silicon film passivation as claimed in claim 1, characterized in that in step 1), the thickness of the ultra-thin silicon passivation layer is 1-2 nm. 4. as claimed in claim 1, ultra-thin silicon film passivation prepares the method for germanium on an insulator, it is characterized in that in step 2) in, described adopting dry oxygen oxidation, growing SiO ₂ layers on Si sheet is by under high temperature condition Control the oxidation time to get the desired _SiO2 layer, the high temperature is >1000°C. 5. The method for preparing germanium-on-insulator by ultra-thin silicon film passivation as claimed in claim 1, characterized in that in step 2), the thickness of the _SiO2 layer is 40-300nm. 6. as claimed in claim 1, ultra-thin silicon film passivation prepares the method for germanium on insulator, it is characterized in that in step 3) in, described carrying out oxygen plasma treatment is to put into inductively coupled plasma etching machine, oxygen The flow rate is 40sccm, the power is 100W, and the processing time is 15s. 7. The method for preparing germanium-on-insulator by ultra-thin silicon film passivation as claimed in claim 1, characterized in that in step 4), the composition of the ammonia water by volume ratio is: NH ₄ OH: H ₂ O=1: 10. The soaking time in ammonia water is 30s. 8. the method for preparing germanium-on-insulator by passivation of ultra-thin silicon film as claimed in claim 1, is characterized in that in step 5), the concrete method that described bonding sheet carries out wet etching is: prepare 50wt% sodium hydroxide 10mL solution, after the initial temperature of the solution reaches 40°C, add 20mL H ₂ O ₂ , put the bonded chip into the solution and continuously add hydrogen peroxide solution at a rate of 7.5mL/min. 9. The method for preparing germanium-on-insulator by ultra-thin silicon film passivation as claimed in claim 1, characterized in that in step 5), the polishing adopts the method of mechanical polishing combined with chemical mechanical polishing. 10. as claimed in claim 9, ultra-thin silicon film passivation prepares the method for germanium on insulator, it is characterized in that the polishing liquid of described mechanical polishing is composed of Nalco2398: H ₂ O=1: 20 by volume ratio; The volumetric composition of the polishing liquid for mechanical polishing is Nalco2398: _{H 2} O: _{H 2} O ₂ =1:20:0.2.