TEM detection method for damaged layer of silicon wafer

Abstract

The invention relates to a TEM (Transmission Electron Microscope) detection method for a damaged layer of a silicon wafer, which belongs to the technical field of surface defect analysis of semiconductor silicon wafers and comprises the following steps of: depositing a protective layer on the surface of a wafer, and protecting the surface structure of the wafer during ion beam cutting by using a focused ion beam machine; therefore, the influence of the deformation of the surface structure of the TEM sample on the detection result of the TEM sample is avoided. A relatively flat area is selected in a deposition protection layer, a Pt layer protection layer is uniformly deposited on the surface of the area, and a focused ion beam is used for etching and marking in a target area. A thinning technology is utilized, so that the thickness meets the requirement of TEM observation; the copper net is used as the metal conductive net, so that the basic conductive performance can be met, the stable physical property is achieved, and the effect of supporting and fixing the sample is achieved. And the morphology of the damaged layer is clearly observed by utilizing the high-resolution characteristic of the TEM, so that the quality and success rate of surface damaged layer analysis are improved.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor silicon wafer surface defect analysis, and in particular to a TEM detection method for a silicon wafer damaged layer. Background Art

[0002] Silicon is the most widely used material in the semiconductor industry. Today, more than 95% of semiconductor devices are made of silicon, and more than 99% of integrated circuits are silicon integrated circuits. Processing a high-quality silicon single crystal rod into a polished wafer is an extremely complex process involving nearly 20 complex process steps. These processing steps must ensure that no additional processing defects or contamination will be introduced.

[0003] However, the processing process of silicon wafers is very long. In particular, mechanical damage to the surface is inevitable during many mechanical processing processes, such as slicing and grinding. The residual damage layer on the surface will seriously affect the application of integrated circuits and devices. The ground silicon wafer can be roughly divided into polycrystalline layer, mosaic layer, high defect layer and complete crystal layer from the surface downward. Among them, the polycrystalline layer and mosaic layer are usually collectively referred to as the processing damage layer. It can be generally considered that the depth of the processing damage layer is approximately equivalent to the average particle size of the abrasive particles.

[0004] Therefore, it is very important to repair the surface damage of silicon wafers through the corrosion process and polishing process. In order to better remove and repair the surface damage of silicon wafers, it is necessary to test and understand the thickness of the surface damage layer of the grinding sheet to obtain a clean, non-processing-damaged, flat (mirror-smooth) silicon wafer surface and perfect surface quality. Therefore, testing and understanding the thickness of the damage layer generated at different process stages has important guiding significance for how to repair the damage layer in the corrosion and polishing processes.

[0005] Testing the thickness of the damaged layer on the surface of the polishing wafer is an important step to ensure the stability of the process. On the silicon wafer production line, the surface damage of the silicon wafer is usually determined by visual inspection, so the degree of surface damage often depends on the observer's eyes, experience and detection method. Summary of the invention

[0006] The present invention mainly solves the deficiencies in the prior art and provides a TEM detection method for a silicon wafer damaged layer. By depositing a protective layer on the surface of the wafer, the surface structure of the wafer is protected during ion beam cutting using a focused ion beam machine, thereby avoiding the deformation of the surface structure of the TEM sample and affecting the detection results of the TEM sample. The thinning technology is used to make the thickness meet the requirements of TEM observation; the copper mesh is used as the metal conductive mesh, which not only meets the basic conductive properties, but also has stable physical properties, and plays a role in supporting and fixing the sample.

[0007] The above technical problems of the present invention are mainly solved by the following technical solutions: A TEM detection method for a silicon wafer damaged layer comprises the following steps: Step 1: Use a focused ion beam to perform rough cutting on the upper, lower and one side of the periphery of the target area protected by Pt, respectively, to obtain a rough cutting sample.

[0008] Step 2: Use a focused ion beam to cut off the bottom side of the rough-cut sample and one side of the connection with the bulk sample.

[0009] Step 3: When welding to the manipulator, an electron beam is used to spray metal organic gas between the nanomanipulator and the target sample to weld the nanomanipulator and the target sample together.

[0010] Step 4: Use a focused ion beam to cut the connection between the target sample and the bulk sample.

[0011] Step 5: A sample table for placing samples and holes for perspective observation have been cut out on the metal conductive mesh. Metal organic gas Pt is sprayed on the contact surface between the sample and the metal conductive mesh to achieve welding between the sample and the metal conductive mesh, thereby completing the fixation of the target sample and the metal conductive mesh.

[0012] Step 6: After completing the welding between the sample and the metal conductive mesh, use a focused ion beam to clean the Pt contamination and damage on the sample surface.

[0013] Step 7: Use a focused ion beam to cut the weld between the nanomanipulator and the target sample.

[0014] Step 8: Use a focused ion beam to finely cut and thin the upper and lower surfaces of the roughly cut sample to obtain a target sample.

[0015] Step 9: After the sample is made, use TEM to observe and analyze the surface damage layer of the sample. The high-resolution characteristics of TEM can be used to clearly observe the morphology of the damage layer, thereby improving the quality and success rate of surface damage layer analysis.

[0016] Preferably, a relatively flat area is selected for depositing the protective layer, a Pt protective layer is uniformly deposited on the surface of the area, and a focused ion beam is used to perform etching marking on the target area.

[0017] As a preferred choice, TEM is an important instrument for the research and development of semiconductor industrial processes or academic research, and is often used to study semiconductor crystals and defects. The working principle of TEM is that the high-energy electrons generated by the tungsten filament lamp or hexaboride blue in the electron gun are directly impacted on the surface of the test piece after being focused by the electromagnetic lens and the objective lens. However, since the test piece is quite thin, the electron beam directly penetrates the test piece.

[0018] Preferably, the penetrating or scattered electrons produce a special magnified diffraction image on the fluorescent film below the specimen; since the contrast effect of the TEM image is caused by the movement of atoms relative to their perfect positions, the form of the lattice defect is obtained by observing the images under different diffraction conditions.

[0019] Preferably, the illumination source of TEM is an electron beam with a wavelength much shorter than that of visible light, so its resolution is much higher than that of an optical microscope, and can achieve a high resolution of 1.8 to 2 angstroms, directly displaying point defects in silicon crystals in the form of images.

[0020] Preferably, the transmission electron microscope commonly uses two working modes: selected area electron diffraction and imaging. When a beam of high-energy monochromatic electrons is projected onto a silicon crystal sample, if the sample is thin enough, part of the electron beam can pass through the sample, and the other part is diffracted by the crystal planes in the crystal to form diffraction spots.

[0021] Preferably, the diffraction spots are used to determine the type, structure and lattice constant of the sample, and the contrast between the transmitted electron and diffracted electron images can be used to understand the integrity of the crystal, the type and nature of the crystal defects; the production of TEM test pieces must be combined with mechanical polishing, chemical etching and ion beam milling to make the thickness of the test piece very thin, about 100nm, to facilitate the penetration of the electron beam.

[0022] Preferably, a focused ion beam machine is used to prepare samples for TEM inspection. A high-energy GA+ ion beam is emitted and accelerated by an ion gun. After being focused by an electrostatic lens, the ion beam size is adjusted using different apertures. Finally, the beam is focused by an objective lens and directly hits the test piece.

[0023] Preferably, when the ion beam moves back and forth along the specimen in a straight line, the specimen is cut to prepare a TEM sample with a high aspect ratio structure; however, if the area to be analyzed is close to the surface of the TEM sample, during the sample cutting process, the strong irradiation of the high-energy ion beam output by the focused ion beam machine may cause changes in the sample surface, thereby affecting the detection results of the TEM sample.

[0024] The present invention can achieve the following effects: The present invention provides a TEM detection method for a silicon wafer damaged layer. Compared with the prior art, a protective layer is deposited on the surface of the wafer, and the surface structure of the wafer is protected during ion beam cutting using a focused ion beam machine, thereby avoiding the deformation of the surface structure of the TEM sample and affecting the detection result of the TEM sample. The thinning technology is used to make the thickness meet the requirements of TEM observation; the copper mesh is used as the metal conductive mesh, which not only meets the basic conductive performance, but also has stable physical properties, and plays the role of supporting and fixing the sample. DETAILED DESCRIPTION

[0025] The technical solution of the invention is further specifically described below through embodiments.

[0026] Embodiment: A TEM detection method for a damaged layer of a silicon wafer comprises the following steps: Step 1: Use a focused ion beam to perform rough cutting on the upper, lower and one side of the periphery of the target area protected by Pt, respectively, to obtain a rough cutting sample.

[0027] The focused ion beam machine is used to prepare samples for TEM inspection. The high-energy GA+ ion beam is emitted and accelerated by the ion gun. After being focused by the electrostatic lens, the ion beam size is adjusted with different apertures. Finally, it is focused by the objective lens and directly hits the test piece.

[0028] When the ion beam moves back and forth along the specimen in a straight line, the specimen is cut to prepare a TEM sample with a high aspect ratio structure; however, if the area to be analyzed is close to the surface of the TEM sample, during the sample cutting process, the strong irradiation of the high-energy ion beam output by the focused ion beam machine may cause changes in the sample surface, thereby affecting the detection results of the TEM sample.

[0029] The common working modes of transmission electron microscope are selected area electron diffraction and imaging. When a beam of high-energy monochromatic electrons is projected onto a silicon crystal sample, if the sample is thin enough, part of the electron beam can pass through the sample, and the other part is diffracted by the crystal plane in the crystal to form diffraction spots. The diffraction spots are used to determine the type, structure and lattice constant of the sample, and the contrast of the transmitted electron and diffracted electron images can be used to understand the integrity of the crystal, the type and nature of the crystal defects. The production of TEM test pieces must be combined with mechanical polishing, chemical etching and ion beam grinding to make the thickness of the test piece very thin, about 100nm, to facilitate the penetration of the electron beam.

[0030] Step 2: Use a focused ion beam to cut off the bottom side of the rough-cut sample and one side of the connection with the bulk sample.

[0031] Step 3: When welding to the manipulator, an electron beam is used to spray metal organic gas between the nanomanipulator and the target sample to weld the nanomanipulator and the target sample together.

[0032] Step 4: Use a focused ion beam to cut the connection between the target sample and the bulk sample.

[0033] Step 5: A sample table for placing samples and holes for perspective observation have been cut out on the metal conductive mesh. Metal organic gas Pt is sprayed on the contact surface between the sample and the metal conductive mesh to achieve welding between the sample and the metal conductive mesh, thereby completing the fixation of the target sample and the metal conductive mesh.

[0034] Step 6: After completing the welding between the sample and the metal conductive mesh, use a focused ion beam to clean the Pt contamination and damage on the sample surface.

[0035] Step 7: Use a focused ion beam to cut the weld between the nanomanipulator and the target sample.

[0036] Step 8: Use a focused ion beam to finely cut and thin the upper and lower surfaces of the roughly cut sample to obtain a target sample.

[0037] Step 9: After the sample is prepared, use TEM to observe and analyze the surface damage layer of the sample.

[0038] A relatively flat area is selected during the deposition of the protective layer, a Pt protective layer is uniformly deposited on the surface of the area, and a focused ion beam is used to perform etching marks on the target area.

[0039] TEM is an important instrument in the research and development or academic research of semiconductor industrial processes. It is often used to study semiconductor crystals and defects. The working principle of TEM: high-energy electrons generated by the tungsten filament lamp or hexaboride blue in the electron gun are directly hit on the surface of the test piece after being focused by the electromagnetic lens and the objective lens. However, since the test piece is quite thin, the electron beam directly penetrates the test piece. The penetrating electrons or scattered electrons will produce a special magnified diffraction image on the fluorescent film under the test piece. Since the contrast effect of TEM images is caused by the movement of atoms relative to their perfect position, the form of lattice defects is obtained by observing images under different diffraction conditions. The illumination source of TEM is an electron beam with a wavelength much shorter than that of visible light, so its resolution is much higher than that of an optical microscope, and can reach a high resolution of 1.8 to 2 angstroms, directly showing the point defects in the silicon crystal in the form of images.

[0040] In summary, the TEM detection method of the silicon wafer damaged layer deposits a protective layer on the surface of the wafer and protects the surface structure of the wafer during ion beam cutting using a focused ion beam machine, thereby avoiding the deformation of the surface structure of the TEM sample and affecting the detection results of the TEM sample. The thinning technology is used to make the thickness meet the requirements of TEM observation; the copper mesh is used as the metal conductive mesh, which not only meets the basic conductive properties, but also has stable physical properties, and plays the role of supporting and fixing the sample.

[0041] The above description is only a specific embodiment of the present invention, but the structural features of the present invention are not limited thereto. Any changes or modifications made by any technician in the field of the present invention are included in the patent scope of the present invention.

Claims

1. A TEM detection method for a silicon wafer damaged layer, characterized in that The steps are as follows: Step 1: Use a focused ion beam to perform rough cutting on the upper, lower and one side of the periphery of the target area protected by Pt, respectively, to obtain a rough cutting sample; Step 2: Use a focused ion beam to cut off the bottom side of the rough-cut sample and the connection between one side and the bulk sample; Step 3: When welding to the manipulator, the metal organic gas is sprayed between the nanomanipulator and the target sample by using an electron beam to weld the nanomanipulator and the target sample together; Step 4: Use a focused ion beam to cut off the connection between the target sample and the bulk sample; Step 5: A sample table for placing the sample and holes for perspective observation have been cut out on the metal conductive mesh. Metal organic gas Pt is sprayed on the contact surface between the sample and the metal conductive mesh to achieve welding between the sample and the metal conductive mesh, thus completing the fixation of the target sample and the metal conductive mesh; Step 6: After the welding between the sample and the metal conductive mesh is completed, the Pt contamination and damage on the surface of the sample are cleaned by using a focused ion beam; Step 7: Use a focused ion beam to cut the weld between the nanomanipulator and the target sample; Step 8: Using a focused ion beam to thin the upper and lower surfaces of the rough-cut sample to obtain a target sample; Step 9: After the sample is prepared, use TEM to observe and analyze the surface damage layer of the sample.

2. The TEM detection method for a damaged silicon wafer layer according to claim 1, characterized in that: A relatively flat area is selected during the deposition of the protective layer, a Pt protective layer is uniformly deposited on the surface of the area, and a focused ion beam is used to perform etching marks on the target area.

3. The TEM detection method for a damaged silicon wafer layer according to claim 1, characterized in that: TEM is an important instrument in the research and development of semiconductor industrial processes or academic research. It is often used to study semiconductor crystals and defects. The working principle of TEM is that the high-energy electrons generated by the tungsten filament lamp or blue hexaboride in the electron gun are directly impacted on the surface of the test piece after being focused by the electromagnetic lens and objective lens. However, since the test piece is quite thin, the electron beam directly penetrates the test piece.

4. The TEM detection method for a damaged silicon wafer layer according to claim 3, characterized in that: Penetrating or scattered electrons produce special magnified diffraction images on the fluorescent film below the specimen; since the contrast effect of TEM images is caused by the movement of atoms relative to their perfect positions, the form of lattice defects is obtained by observing images under different diffraction conditions.

5. The TEM detection method for a damaged silicon wafer layer according to claim 3, characterized in that: The illumination source of TEM is an electron beam with a wavelength much shorter than that of visible light, so its resolution is much higher than that of an optical microscope, and can achieve a high resolution of 1.8 to 2 angstroms, directly displaying point defects in silicon crystals in the form of images.

6. The TEM detection method for a damaged silicon wafer layer according to claim 1, characterized in that: The commonly used working modes of transmission electron microscope are selected area electron diffraction and imaging. When a beam of high-energy monochromatic electrons is projected onto a silicon crystal sample, if the sample is thin enough, part of the electron beam can pass through the sample, and the other part is diffracted by the crystal planes in the crystal to form diffraction spots.

7. The TEM detection method for a damaged silicon wafer layer according to claim 6, characterized in that: Diffraction spots are used to determine the type, structure and lattice constant of the sample, and the contrast of transmitted electron and diffracted electron images can be used to understand the integrity of the crystal and the type and nature of crystal defects. The production of TEM test pieces must combine mechanical polishing, chemical etching and ion beam milling to make the thickness of the test piece very thin, about 100nm, to facilitate the penetration of the electron beam.

8. The TEM detection method for a damaged silicon wafer layer according to claim 1, characterized in that: The focused ion beam machine is used to prepare samples for TEM inspection. The high-energy GA+ ion beam is emitted and accelerated by the ion gun. After being focused by the electrostatic lens, the ion beam size is adjusted with different apertures. Finally, it is focused by the objective lens and directly hits the test piece.

9. The TEM detection method for a damaged silicon wafer layer according to claim 8, characterized in that: When the ion beam moves back and forth along the specimen in a straight line, the specimen is cut to prepare a TEM sample with a high aspect ratio structure; however, if the area to be analyzed is close to the surface of the TEM sample, during the sample cutting process, the strong irradiation of the high-energy ion beam output by the focused ion beam machine may cause changes in the sample surface, thereby affecting the detection results of the TEM sample.