Semiconductor silicon-germanium thin film preparation method

Abstract

A semiconductor silicon-germanium thin film preparation method, comprising the following steps: cleaning a mono-crystalline silicon substrate and then disposing the same on a substrate table; respectively sputtering a silicon single thin film and a germanium single thin film; depositing a silicon-germanium alloy thin film having different components on another single crystal silicon substrate using a co-sputtering method, measuring the thickness of the deposited thin film, and obtaining a silicon-germanium alloy thin film having different component ratios.

Claims

1. A method for preparing a semiconductor silicon-germanium thin film, comprising the following steps: (1) cleaning a mono-crystalline silicon substrate by ultrasound in acetone for 5 min to 10 min; cleaning the substrate by ultrasound in methanol for 5 min to 10 min; cleaning the substrate by ultrasound in isopropanol for 5 min to 10 min; washing the mono-crystalline silicon substrate repeatedly with deionized water; drying and placing the mono-crystalline silicon substrate on a platform; (2) vacuumizing a vacuum chamber of a deposition system to between 810.sup.8 Torr and 910.sup.8 Torr; maintaining the chamber temperature between 20 C. and 30 C.; maintaining the pressure of the vacuum chamber between 810.sup.8 Torr and 910.sup.8 Torr; and (3) performing co-sputtering to deposit a silicon-germanium alloy thin film on a mono-crystalline silicon substrate under conditions: sputtering pressure from 410.sup.4 Torr to 510.sup.4 Torr, bias voltage on a target from 600V to 700V, argon as the sputtering gas, gas flow rate from 30 sccm to 50 sccm, sputtering duration from 30 min to 50 min; and obtaining silicon-germanium alloy thin film.

2. The method for preparing the semiconductor silicon-germanium thin film according to claim 1, wherein the mass rate of silicon and germanium in the silicon-germanium alloy thin film is from 3:4 to 2:5.

3. The method for preparing the semiconductor silicon-germanium thin film according to claim 1, wherein the thickness of the silicon-germanium alloy thin film is from 64 nm to 280 nm.

Description

BRIEF DESCRIPTION OF DRAWINGS

(1) FIG. 1 is the 2D micrograph of the surface of the silicon-germanium alloy thin film obtained in Example 1 under atomic force microscope.

(2) FIG. 2 is the 3D morphology image of the surface of the silicon-germanium alloy thin film obtained in Example 1 under atomic force microscope.

DETAILED DESCRIPTION

(3) The present disclosure will be further described in conjunction with the figures.

Example 1

(4) (1) A mono-crystalline silicon substrate is cleaned by ultrasound in acetone for 10 min; the substrate is cleaned by ultrasound in methanol for 10 min; the substrate is cleaned by ultrasound in isopropanol for 10 min; the substrate is washed repeatedly with deionized water; and the mono-crystalline silicon substrate is dried and placed on a platform.

(5) (2) The vacuum chamber of deposition system is vacuumizied to 910.sup.8 Torr; the chamber temperature is maintained at 25 C.; and the pressure of vacuum chamber is maintained at 910.sup.8 Torr.

(6) (3) A single thin film of silicon is sputtered on the mono-crystalline silicon substrate under conditions: 510.sup.4 Torr of sputtering pressure, 600V of bias voltage of the cathode, argon as the sputtering gas, 40 sccm of gas flow rate, 30 min of sputtering duration. The thickness of the deposited film is measured, which is 24 nm; and the deposition rate of the silicon thin film is calculated under the current parameters, which is 0.8 nm/min.

(7) (4) A single thin film of germanium is sputtered on another mono-crystalline silicon substrate under conditions: 510.sup.4 Torr of sputtering pressure, 600V of bias voltage of the cathode, argon as the sputtering gas, 40 sccm of gas flow rate, 30 min of sputtering duration. The thickness of the deposited film is measured, which is 60 nm; and the deposition rate of the silicon thin film is calculated under the current parameters, which is 2 nm/min.

(8) (5) Co-sputtering is performed to deposit a silicon-germanium alloy thin film with different compositions on another mono-crystalline silicon substrate under conditions: 510.sup.4 Torr of sputtering pressure, 600V of bias voltage of the cathode, argon as the sputtering gas, 40 sccm of gas flow rate, 30 min of sputtering duration. The thickness of the deposited film is measured, which is 84 nm; and the mass rate of silicon and germanium in the final alloy thin film is 2:5.

(9) As shown in FIG. 1 and FIG. 2, the silicon-germanium alloy thin film prepared in Example 1 is measured by atomic force microscope and the root mean square roughness is 0.46 nm.

Example 2

(10) (1) A mono-crystalline silicon substrate is cleaned by ultrasound in acetone for 8 min; the substrate is cleaned by ultrasound in methanol for 8 min; the substrate is cleaned by ultrasound in isopropanol for 8 min; the substrate is washed repeatedly with deionized water; and the mono-crystalline silicon substrate is dried and placed on a platform.

(11) (2) The vacuum chamber of deposition system is vacuumizied to 810.sup.8 Torr; the chamber temperature is maintained at 25 C.; and the pressure of vacuum chamber is maintained at 810.sup.8 Torr.

(12) (3) A single thin film of silicon is sputtered on the mono-crystalline silicon substrate under conditions: 410.sup.4 Torr of sputtering pressure, 700 V of bias voltage of the cathode, argon as the sputtering gas, 40 sccm of gas flow rate, 40 min of sputtering duration. The thickness of the deposited film is measured, which is 64 nm; and the deposition rate of the silicon thin film is calculated under the current parameters, which is 1.6 nm/min.

(13) (4) A single thin film of germanium is sputtered on another mono-crystalline silicon substrate under conditions: 410.sup.4 Torr of sputtering pressure, 700V of bias voltage of the cathode, argon as the sputtering gas, 40 sccm of gas flow rate, 40 min of sputtering duration. The thickness of the deposited film is measured, which is 128 nm; and the deposition rate of the silicon thin film is calculated under the current parameters, which is 3.2 nm/min.

(14) (5) Co-sputtering is performed to deposit a silicon-germanium alloy thin film with different compositions on another mono-crystalline silicon substrate under conditions: 410.sup.4 Torr of sputtering pressure, 700V of bias voltage of the cathode, argon as the sputtering gas, 40 sccm of gas flow rate, 40 min of sputtering duration. The thickness of the deposited film is measured, which is 192 nm; and the mass rate of silicon and germanium in the final alloy thin film is 2:3.

Example 3

(15) (1) A mono-crystalline silicon substrate is cleaned by ultrasound in acetone for 5 min; the substrate is cleaned by ultrasound in methanol for 5 min; the substrate is cleaned by ultrasound in isopropanol for 5 min; the substrate is washed repeatedly with deionized water; and the mono-crystalline silicon substrate is dried and placed on a platform.

(16) (2) The vacuum chamber of deposition system is vacuumizied to 810.sup.8 Torr; the chamber temperature is maintained at 25 C.; and the pressure of vacuum chamber is maintained at 810.sup.8 Torr.

(17) (3) A single thin film of silicon is sputtered on the mono-crystalline silicon substrate under conditions: 410.sup.4 Torr of sputtering pressure, 700V of bias voltage of the cathode, argon as the sputtering gas, 40 sccm of gas flow rate, 50 min of sputtering duration. The thickness of the deposited film is measured, which is 120 nm; and the deposition rate of the silicon thin film is calculated under the current parameters, which is 2.4 nm/min.

(18) (4) A single thin film of germanium is sputtered on another mono-crystalline silicon substrate under conditions: 410.sup.4 Torr of sputtering pressure, 700V of bias voltage of the cathode, argon as the sputtering gas, 40 sccm of gas flow rate, 50 min of sputtering duration. The thickness of the deposited film is measured, which is 160 nm; and the deposition rate of the silicon thin film is calculated under the current parameters, which is 3.2 nm/min.

(19) (5) Co-sputtering is performed to deposit a silicon-germanium alloy thin film with different compositions on another mono-crystalline silicon substrate under conditions: 410.sup.4 Torr of sputtering pressure, 700V of bias voltage of the cathode, argon as the sputtering gas, 40 sccm of gas flow rate, 50 min of sputtering duration. The thickness of the deposited film is measured, which is 280 nm; and the mass rate of silicon and germanium in the final alloy thin film is 3:4.

(20) It can be concluded from the above examples:

(21) (1) In magnetron sputtering deposition, circular magnetic field is used to control the plasma, which causes erosion track, leading to low utilization of the target. In ion beam deposition, the ion beam is sent obliquely, which gives uneven etches on the targets, also leading to low utilization of the target. Therefore, both magnetron sputtering deposition and ion beam deposition shorten the service life of the target. In comparison, in biased target ion beam deposition, negative bias voltage is applied to the target to control the plasma, which does not form erosion track and uneven etches, prolonging the service life of the target efficiently.

(22) (2) In magnetron sputtering deposition, due to the instability of the plasma, uneven etchings are formed on the surface of target, causing target poisoning, which inevitably leads to the doping of films in the target poisoning area, decreasing the purity of the thin film. While in biased target ion beam deposition, plasma source with low energy is used, which has stable properties, avoiding the uneven etches on the surface of the target and target poisoning, effectively increasing the purity of the thin film.

(23) (3) In ion beam deposition, some ion beams can escape and sputter on the vacuum chamber materials, leading to the generation of impurity ions which can contaminate the silicon-germanium thin film. While the energy of plasma emitted in biased target ion beam deposition is pretty low, the escaped ion beam will not sputter on the vacuum chamber, improving the purity of the thin film.

(24) (4) As the target area of the ion beams is too small, resulting in low deposition rate, which makes it difficult to perform deposition on thick silicon-germanium thin film. While in biased target ion beam deposition, plasma sheath is installed near the target, which increases the speed of the positive ions when entering the sheath, therefore ensuring that the bombarding area of the ion beam is larger than the area of the target. In addition, by regulating the voltage, the deposition rate can be regulated to reach a relative high deposition rate, which makes the deposition on relative thick thin film materials possible.

(25) (5) In biased target ion beam deposition, by choosing suitable voltage and with the help of the effect of the voltage on the sputtering energy, the atoms mixing on the thin film interface and the entire roughness of the thin film are regulated efficiently.

(26) In view of the above, biased target ion beam deposition can effectively overcome the disadvantages of magnetron sputtering deposition and ion beam deposition during preparing semiconductor thin films such as silicon-germanium alloy thin film and so on. By regulating the bias voltage and deposition duration, silicon-germanium alloy thin films with different compositions are prepared on the silicon substrate. Compared with the thin film in conventional art, the roughness of the silicon-germanium alloy thin film prepared in the present disclosure decreases form 1.08 nm to 0.46 nm, which is very important to the development of photoelectric MEMS.