Surface inspection apparatus and surface inspection method for strained silicon wafer
View Patent ↗An image pickup device disposed in a predetermined position relative to a surface of a strained silicon wafer photographs the surface of the strained silicon wafer in a plurality of rotation angle positions on photographing conditions under which bright lines appearing on the surface of the strained silicon wafer can be photographed, in an environment where a light source device illuminates the surface of the strained silicon wafer which is rotating. A composite image in a predetermined angle position is generated from surface images of the strained silicon wafer in a plurality of rotation angle positions obtained by the image pickup device.
1. A surface inspection method for inspecting strain that occurs in a surface layer of a strained silicon wafer, the method comprising:
illuminating a surface of the strained silicon wafer;
photographing, in a plurality of rotation angle positions, bright lines that appear on the surface of the strained silicon wafer, which is rotated in an environment where the surface of the strained silicon wafer is illuminated;
generating a composite image from surface images of the strained silicon wafer photographed in the plurality of rotation angle positions; and
determining the strain in the surface layer of the strained silicon wafer based on information obtained from the bright lines in the composite image.
2. The surface inspection method according to claim 1 , wherein the generating a composite image includes: generating a differential image representing a difference in brightness between a surface image obtained by photographing in each of the rotation angle positions and a predetermined reference image; and generating a composite image by composing differential images in the respective rotation angle positions.
3. The surface inspection method according to claim 1 , wherein the photographing is carried out under photographing conditions including at least brightness of the surface of the strained silicon wafer and an exposure time in the photographing.
4. The surface inspection method according to claim 1 , further comprising extracting brightness information indicative of brightness of bright lines that appear in the composite image from the composite image.
5. A surface inspection apparatus for inspecting strain that occurs on a surface of a strained silicon wafer, the apparatus comprising:
illuminating means for illuminating the surface of the strained silicon wafer;
drive control means for rotating the strained silicon wafer in a circumferential direction;
photographing means for photographing, in a plurality of rotation angle positions, bright lines that appear on the surface of the strained silicon wafer in an environment where the surface of the strained silicon wafer is illuminated;
image processing means for generating a composite image from surface images of the strained silicon wafer photographed in the plurality of rotation angle positions;
output means for outputting information on the bright lines to inspect the strain in a silicon layer of the composite image generated by the image processing means; and
determining the strain in the surface layer of the strained silicon wafer based on information obtained from the bright lines in the composite image.
6. The surface inspection apparatus according to claim 5 , wherein the illuminating means illuminate the surface of the strained silicon wafer, while keeping a dark-field environment for the photographing means.
7. The surface inspection apparatus according to claim 5 , wherein the illuminating means include a plurality of light sources, optical axes of which are not parallel to each other and cross at a center of rotation of the strained silicon wafer.
8. The surface inspection apparatus according to claim 5 , wherein the drive control means comprise a turntable on which the strained silicon wafer is held, and a stepping motor which drives and rotates the turntable by a predetermined angle.