METHOD OF IN-SITU TEM NANOINDENTATION FOR DAMAGED LAYER OF SILICON

Abstract

A method of in-situ TEM nanoindentation for a damaged layer of silicon is disclosed. Wet etching and ion beam lithography are used for preparing a silicon wedge sample. An etched silicon wedge is thinned and trimmed by a focused ion beam; thinning uses ion beam of 30 kV: 50-80 nA, and trimming uses ion beam of 5 kV: 1-6 pA; and the top width of the silicon wedge is 80-100 nm. The sample is fixed on a sample holder of an in-situ TEM nanomechanical system by using a conductive silver adhesive. The sample is indented with a tip in the TEM, so that the thickness of the damaged layer of the sample is 2-200 nm; and an in-situ nanoindentation experiment is conducted on the damaged layer of the sample in the TEM.

Claims

1. A method of in-situ TEM nanoindentation for a damaged layer of silicon, using wet etching and ion beam lithography for preparing a silicon wedge sample, pressing a damaged layer of silicon by using a diamond tip in the TEM, and conducting an in-situ nanoindentation experiment on the damaged layer of silicon, wherein (1) the sample is a monocrystalline silicon wafer; the diamond tip is a cube-corner tip; and the curvature radius of the tip is 50-70 nm; (2) the silicon wafer is cut by a diamond pen into bulks with a length of 3-5 mm and a width of 2-3 mm; (3) a layer of electron beam photoresist with a thickness of 100-300 nm is shaken on the surface of the monocrystalline silicon wafer, and a rectangular pattern with a width of 400-800 nm and a length of 10-60 m is made by electron beam lithography; (4) a protective layer of SiO.sub.2 with a thickness of 1-3 m is plated on the surface of the sample; (5) the whole sample is immersed in acetone to conduct ultrasonic cleaning for 10-30 minutes; (6) the sample is cleaned with deionized water, and blow-dried with compressed gas; the whole sample is immersed in NaOH solution for etching, and the etching time is 15-30 minutes, to form a silicon wedge; (7) the silicon wedge is cleaned with deionized water, and blow-dried with compressed gas; the whole sample is immersed in HF solution for etching, and the etching time is 5-10 minutes; (8) the sample is cleaned with deionized water, and blow-dried with compressed gas; the etched silicon wedge is thinned and trimmed by a focused ion beam; thinning uses ion beam of 30 kV: 50-80 nA, and trimming uses ion beam of 5 kV: 1-6 pA; and the top width of the silicon wedge is 80-100 nm; (9) the sample is fixed on a sample holder of an in-situ TEM nanomechanical system by using a conductive silver adhesive; (10) the sample holder is fixed on a sample rod by screws; the sample is indented by using the diamond tip in the TEM; and the thickness of the damaged layer of the sample is 2-200 nm; (11) the damaged layer of the sample is subjected to the in-situ nanoindentation experiment in the TEM, thereby realizing real-time observation for the origin and evolution of stress-induced damage of the damaged layer.

Description

DESCRIPTION OF DRAWINGS

[0019] FIG. 1 shows views of a TEM image, a is a low magnification TEM morphology image of a silicon wedge sample without damaged layer, and b is a high resolution TEM image of a block part of a.

[0020] FIG. 2 shows views of a TEM image, a is a low magnification TEM morphology image of a silicon wedge sample with damaged layer of thickness of 67 nm, and b is a high resolution TEM image of a block part of a.

[0021] FIG. 3 shows views of a TEM image, a is a low magnification TEM morphology image after a damaged layer of a silicon wedge sample is subjected to in-situ TEM nanoindentation, and b is a high resolution TEM image of a block part of a.

DETAILED DESCRIPTION

[0022] Specific embodiments of the present invention are further described below in combination with accompanying drawings and the technical solution.

Embodiments

[0023] The silicon wafer is cut by the diamond pen into bulks with a length of 4 mm and a width of 3 mm. A layer of electron beam photoresist with a thickness of 200 nm is shaken on the surface of the silicon wafer, and a rectangular pattern with a width of 600 nm and a length of 30 m is made by electron beam lithography. A protective layer of SiO.sub.2 with a thickness of 1.5 m is plated on the surface of the sample. The whole sample is immersed in the acetone for conducting ultrasonic cleaning for 20 minutes to remove the electron beam photoresist and the protective layer of SiO.sub.2 on the photoresist, thereby leaving only the protective layer of SiO.sub.2 with the rectangular pattern. The sample is cleaned with deionized water, and blow-dried with compressed gas. The whole sample is immersed in NaOH solution for etching, and the etching time is 25 minutes. The sample is cleaned with deionized water, and blow-dried with compressed gas. The whole sample is immersed in HF solution for etching, and the etching time is 8 minutes, to remove the protective layer of SiO.sub.2. The sample is cleaned with deionized water, and blow-dried with compressed gas. The etched silicon wedge is thinned and trimmed by a focused ion beam; thinning uses ion beam of 30 kV: 50 pA, and trimming uses ion beam of 5 kV: 20 pA; and the top width of the silicon wedge is 80 nm. The sample is fixed on a sample holder of an in-situ TEM nanomechanical system by using a conductive silver adhesive. The sample holder is fixed on the sample rod by screws. The TEM image of the prepared silicon wedge sample is shown in FIG. 1a. FIG. 1b is a high resolution TEM image of a block part of FIG. 1a. It can be seen that the sample is crystalline silicon without lattice defect. The sample is indented by using a cube-corner diamond tip with a curvature radius of 66 nm in the TEM; and the thickness of the damaged layer of the sample is 67 nm, as shown in FIG. 2a. FIG. 2b is a high resolution TEM image of a block part of FIG. 2a. The damaged layers of the sample are subjected to the in-situ indentation experiment in the TEM. FIG. 3a is a low magnification TEM morphology image after a damaged layer of a silicon wedge sample is subjected to in-situ TEM nanoindentation, and FIG. 3b is a high resolution TEM image of a block part of FIG. 3a.