US 4,618,938 AGranted

Method and apparatus for automatic wafer inspection

AssigneeKLA Instruments Corporation

InventorsPaul Sandland, Curt H. Chadwick, Russell M. Singleton, Howard Dwyer

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Abstract

An automatic semiconductor wafer inspection system including a wafer inspector, a system computer that performs movement and function control and data storage functions and a high speed image computer. Patterned wafers selected for inspection are automatically transported from cassette storage to a vacuum chuck located on the X-Y stage and positioned in a macro inspection station. The wafer is aligned and the surface illumination is changed to test for macro defects under different lighting conditions and levels of magnification. The reflected light is applied to a camera where the optical image is converted to an electrical representation thereof, stored, and then processed by the high speed image computer. After a wafer has been positioned and inspected in the macro inspection station at low magnification, it is moved by a macro-micro transport arm to the micro inspection station and a unique image previously found in the low power image is found again and used for initial alignment. An autofocus arrangment automatically focusses the objective lens to accomplish the micro inspection tests. Tests are typically carried out at a number of sites, each of which is positioned automatically by the machine.

Claims25

Dependent claims

Apparatus for automatically inspecting a patterned wafer, comprising:

a high-speed image computer for developing image data from input image signals;
a system control computer;
data storage means for storing image data corresponding to either pre-established image patterns or previously stored image patterns from an inspected wafer under control of said system computer, the stored image data being selectively used in accordance with a test program for test comparison with image data obtained from the wafer under inspection and processed by said high-speed image computer;
a wafer inspection subsystem including:
camera means for developing said input image signals corresponding to a wafer under inspection;
a macro inspection station for casting an image within a first range of magnification of the wafer under inspection onto said camera means;
a micro inspection station for casting an image of the wafer within a second range of magnification of the wafer onto said camera means;
a base for supporting both macro and micro inspection stations above a floor surface;
means for vibrationally isolating said wafer inspection subsystem from said base portion to minimize the effect of outside disturbances;
means for holding a plurality of cassettes, each said cassette being capable of storing a plurality of wafers;
an X-Y inspection stage for carrying a wafer under inspection from a position within said macro inspection station to a position within said micro inspection station;
a vacuum chuck on said X-Y stage for holding said wafer under inspection;
means for loading a wafer from one said cassette onto said vacuum chuck when it is in said macro inspection station;
means for automatically macro inspecting a wafer under different illumination conditions and powers of magnification to find if there are any serious macro defects;
means for automatically shifting the position of the vacuum chuck on the stage so as to align it and the carried wafer with the micro inspection station;
means for automatically performing micro inspection of the wafer to determine if it meets pre-established criteria for a good wafer;
and
means for unloading the wafer from said chuck;
and control means associated with said system computer and operative to control operation of said subsystem.

16 more elements

In a system for automatic inspection of patterned wafers, an improved wafer inspection subsystem comprising:

a macro inspection station for inspecting a wafer at magnifications within a first range of magnification;
a micro inspection station for inspecting a wafer at magnifications within a second range of magnification;
a base for supporting both macro and micro inspection stations from a floor surface;
means for vibration isolating said macro and micro inspection stations from said base to minimize the effects of outside disturbances;
means for holding a plurality of cassettes, each said cassette being capable of storing a plurality of wafers;
an X-Y inspection stage for carrying a wafer from a position associated with said macro inspection station to a position associated with said micro inspection station;
a vacuum chuck on said X-Y stage for holding said wafer;
means for loading a wafer from said cassette onto said vacuum chuck when said chuck is in said macro inspection station;
means for automatically macro testing a wafer under different illumination conditions and powers of magnification to find if there are any serious macro defects;
means for automatically shifting the position of the vacuum chuck on the stage so as to align it and the wafer with the micro inspection station;
means associated with said micro inspection station for automatically performing micro inspection tests to determine if the wafer meets preestablished criteria for a good wafer;
and
means for unloading the wafer from said chuck.

10 more elements

Dependencies are inferred from the claim text.