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Optical Determination of Semiconductor Device Edge Profiles

IP.com Disclosure Number: IPCOM000086031D
Original Publication Date: 1976-Jul-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 4 page(s) / 78K

Publishing Venue

IBM

Related People

Habegger, MA: AUTHOR

Abstract

The shape and height of edges, such as the edge of a developed resist pattern or a line etched in silicon oxide, are determined by a nondestructive optical technique.

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Optical Determination of Semiconductor Device Edge Profiles

The shape and height of edges, such as the edge of a developed resist pattern or a line etched in silicon oxide, are determined by a nondestructive optical technique.

The amount of light scattered by an edge is measured for different angles of illumination and observation. Typical edges with heights from 0.2 to 2 mu m's are comparable to the wavelength of visible light; and therefore the scattered light intensity spectrum is a diffraction pattern produced by the edge. The edge slope angle and edge height are then determined from the measured diffraction pattern.

The optical equipment is shown in Fig. 1. Source arm 1 consists of a light source 2 and optics 3 to project a collimated, narrow bandwidth, light beam 4 on the edge to be examined in the wafer surface 5. This edge should be coincident with the axis of rotation of the wafer 6, source arm 1 and observation arm 10. Observation arm 10 consists of optics 11 to focus a magnified image of the edge on a precision slit 12. Microscope 13 at the end of arm 10 is used to view the edge in the plane of slit 12.

The light through slit 12 can either be directed through microscope 13 or onto the face of photomultiplier 14. Oscillating glass plate 15 in the optical path is used to alternatively place the edge of slit 12 and the background adjacent to the edge. The output of photomultiplier 14 is fed to a lock-in amplifier whose reference is derived from the drive voltage for oscillating glass plate 15.

The lock-in amplifier output is proportional to the difference in light intensity of the edge and the background adjacent to the edge. The resolution of the observation arm optics is only approximately 7 mu m; and therefore, the edge to be examined must not have any other edges closer than approximately 15 mu m.

Mounted on source arm 1 is a second chopper 7 which chops the light at a higher frequency than oscillating glass plate 15. Chopper 7 is used as a reference for a second lock-in amplifier whose input is also the output of photomultiplier 14. The output of this second lock-in amplifier is proportional to the sum of the edge intensity and the background. The visibility of the edge is the ratio of the first and second lock-in outputs.

The most useful setup for gathering information about the edge is with the angle between the observation and source arms as small as possible. The wafer 6 is rotated and the outputs of the lock-in amplifiers as well as the wafer angle recorded. A wafer angle range up to 180 degrees can be utilized. For interpreting the edge shape, a plot of the difference lock-in output against the wafer angle is used. Such a plot for a silicon edge is shown in Fig. 2.

Another method of collecting information about the edge is to hold wafer 6 and source...