Radiant energy – Means to align or position an object relative to a source or...
Reexamination Certificate
1999-01-08
2002-06-04
Anderson, Bruce (Department: 2878)
Radiant energy
Means to align or position an object relative to a source or...
C250S310000, C250S492200
Reexamination Certificate
active
06399953
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a scanning electronic microscope (SEM) for a step of controlling the yield of wafers.
An important step for controlling the yield of wafers has been to detect abnormal regions on the surface of wafers and to identify regions having process-related defects from information based on the observation of the features thereof and the analysis of elements.
Such detection of abnormal regions and observation of features have conventionally been carried out with optical wafer surface inspectors utilizing scattered laser beams, inspectors of foreign substances on wafer surface such as optical wafer surface inspectors which perform die-to-die comparison, review stations and the like. A review station is an optical observation apparatus of foreign substances which is linked with a defect and foreign substance detector when used.
However, as wiring patterns on wafers become finer, it has become impossible to observe closely features of abnormal regions to be observed with a laser system when they are in sizes of 0.3 &mgr;m or less.
Conventional scanning electronic microscopes for observing the features on wafers have been scanning electronic microscopes having a stage for the observation of wafers added with automatic wafer loader, and abnormal regions have been observed with the following steps. (A3) among the following steps has been automatically carried out by a CPU. A1 through All below are steps for inspecting a single wafer as a unit.
(A1) A wafer is loaded into a scanning electronic microscope.
(A2) An inspector of foreign substances on wafer surface acquires information on features on the wafer and information on abnormal regions.
(A3) A coordinate transformation coefficient between the coordinate systems of a wafer surface inspector based on the recognition of wafer outline and the scanning electronic microscope is automatically obtained according to Japanese Patent Publication Tokkaihei-06-174644 “Method for Automatically Setting Coordinate Transformation Coefficient”.
(A4) The coordinate positions of alignment marks on the wafer are observed to obtain a coordinate transformation coefficient between the coordinate systems of the wafer surface inspector and the scanning electronic microscope according to Japanese Patent Publication Tokkaihei-06-258240 “Method for Coordinate Transformation”.
(A5) The stage is moved to the positions of abnormal regions identified by the inspector of foreign substances on wafer surface.
(A6) Adjustment of the lens system including focusing is carried out to acquire electron beam images or optical images.
The present invention relates to a scanning electronic microscope (SEM) and to techniques for automatically observing features on a semiconductor wafer to control the yield of the semiconductor wafers.
(A7) The abnormal regions are recognized.
(A8) The stage is moved to the positions thereof.
(A9) Magnifications in accordance with the size of the abnormal regions are set to acquire electron beam images or optical images.
(A10)) The process proceeds to the next step if the acquisition of images of all abnormal regions to be observed is completed and, if not, the process continues from step (A5) on the next abnormal region.
(A11) The wafer is unloaded from the scanning electronic microscope to terminate the process.
A problem arises here in that a scanning electronic microscope for observing features on a wafer has throughput which is slower than a laser system by a factor of several dozens and is backward in automation.
As a solution to this, there has been a need for full automation of conventional scanning electronic microscopes for observing features on wafers and improving operator throughout.
SUMMARY OF THE INVENTION
In order to solve the above-described problems, information on wafers to be observed is acquired from an operator, and steps for observing features on the wafers are sequentially and automatically carried out by a CPU.
The observation of repetitive patterns such as those of a memory cell region of a DRAM (hereinafter referred to as “repetitive pattern observation method”) is carried out with the following steps. The steps other than (B1) are all automatically performed by a CPU.
(B1) Information on the type of wafers to be observed and information on queries from an inspector of foreign substances on wafer surface regarding the wafers is acquired from an operator. The information on the type of wafers to be observed is the size of the wafers (e.g., 6 inches and 8 inches), origin marks on the wafers (e.g., an orientation flat and a notch) and the like. The information on queries from the inspector of foreign substances on wafer surface is device IDs, process IDs, lot IDs, slot IDs and the like.
C1 through C8 described below are steps preceding alignment which are a pre-process.
(C1) Wafers are loaded into a scanning electronic microscope in accordance with the information on the type of wafers to be observed.
(C2) Information on the positions and sizes of abnormal regions is acquired from the inspector of foreign substances on wafer surface in accordance with the information on queries from the inspector of foreign substances on wafer surface.
(C3) A coordinate transformation between the coordinate systems of a wafer surface inspector based on the recognition of wafer outline and the scanning electronic microscope is automatically obtained according to Japanese Patent Publication Tokkaihei-06-174644 “Method for Automatically Setting Coordinate Transformation Coefficient”.
(C4) Movement is made to the positions of alignment marks or defects at a predetermined distance from the alignment marks. Specifically, the stage is moved such that the positions of the alignment marks or the features at a predetermined distance from the alignment marks are centered in the field of view. Corners of the die or cross marks are frequently used as the alignment marks.
(C5) Automatic adjustment of the lens system including automatic focusing is carried out to acquire electron beam images or optical images.
(C6) The stage positions of the features are recognized from the images.
(C7) The process proceeds to the next step if the observation of all of the alignment marks or the features at a predetermined distance from the alignment marks is completed and, if not, continues from (C4) for the next alignment mark. The alignment marks or the features a predetermined distance from the alignment marks are normally measured at three points or more.
(C8) A coordinate transformation coefficient between the coordinate systems of the wafer surface inspector and the scanning electronic microscope is obtained by observing the coordinate positions of the alignment marks on the wafer using the above-described stage position according to the Japanese Patent Publication Tokkaihei-06-258240 “coordinate transformation method”. D1 through D7 below are steps for acquiring images of abnormal regions using the repetitive pattern observing method.
(D1) The stage is moved such that the abnormal regions whose positions and sizes have been acquired from the inspector of foreign substances on wafer surface are centered in the field of view.
(D2) Automatic adjustment of the lens system including automatic focusing is carried out to acquire electron beam images or optical images as images of the abnormal regions (image acquisition at a low magnification).
(D3) Partial images of the abnormal regions are recognized from the images of the abnormal regions.
(D4) Visual inspection is carried out to classify the abnormal regions. That is, shorts (shortcircuits), breaks (breakage), scratches and the like are identified.
(D5) The stage is moved to positions where they are detected.
(D6) Magnifications in accordance with the sizes of the detected abnormal regions are set to acquire electron beam images or optical images (image acquisition at high magnifications).
(D7) The process proceeds to the next step if the acquisition of all of the images of the abnormal regions to be observed is completed and, if not, continues from (D1) for t
Adams & Wilke
Anderson Bruce
Seiko Instruments Inc.
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