Apparatus and method for photoluminescent analysis

• US 4,572,668 A
• Filed: 08/26/1982
• Issued: 02/25/1986
• Est. Priority Date: 08/26/1982
• Status: Expired due to Fees

• Current Assignee: MIDAC Corporation
• Original Assignee: MIDAC Corporation
• Inventors: Auth, Gerry L.
• Primary Examiner(s): Evans, F. L.
• Application Number:
  US06/411,603
• Time in Patent Office: 1,279 Days
• Field of Search: 356/301, 356/317, 356/318
• US Class Current: 356/318
• CPC Class Codes: G01J 3/02 Details
• CPC Class Codes: G01J 3/0208 using focussing or collimating elements, e.g. lenses or mirrors; performing aberration correction
• CPC Class Codes: G01J 3/021 using plane or convex mirrors, parallel phase plates, or particular reflectors
• CPC Class Codes: G01N 21/6489 Photoluminescence of semiconductors

Abstract

An optical system is disclosed which significantly enhances the throughput of a grating spectrometer intended to determine impurity concentrations on the surface of semiconductor materials (usually single crystal silicon) used for integrated circuits. The system, which uses a laser beam as the photo-excitation means impinging on a Dewar-contained sample, includes a pre-sample series of lenses which so shapes the laser beam that its shape at the point of impingement on the sample is proportionally similar to the shape of the monochromator slit in the spectrometer. The same lens which provides final focusing of the laser beam on the sample also collects the sample-emitted radiation, which is thereafter focused by suitable optics on the monochromator slit, where it preferably substantially matches the shape of the slit, but slightly overfills the slit.

Claims

1. In a system for determining the intensity of photoluminescence emitted at the surface of a sample, such system having in its input portion a laser radiation source which provides a highly concentrated, essentially circular beam of radiation for sample-excitation purposes, and having in its output portion a photodetector and a grating spectrometer which receives sample-emitted radiation at its entrance slit and sends radiation through its exit aperture to the photodetector;

an optical apparatus, operative between the source of excitation radiation and the grating spectrometer, comprising;

pre-sample optical means for reshaping the laser beam radiation in such a way that it has cross-sectional dimensions proportionally similar to those of the grating spectrometer slit at the location of excitation contact of the laser beam with the sample, the pre-sample optical means including (a) a first optical element which widens the laser beam in one dimension, and (b) a second optical element which receives the laser beam from the first optical element and narrows the beam in the other dimension; and

post-sample means for collecting the radiation emitted by the sample as a result of such excitation and focusing such collected radiation in such a way that its cross-sectional dimensions at the grating spectrometer entrance slit are similar to those of the slit, the post-sample optical means including (a) a first optical element which collects the relatively dispersed radiation emitted by the sample, and (b) a second optical element which focuses the radiation collected by the first optical element on the grating spectrometer entrance slit;

a single dual-purpose lens constituting both the second optical element of the pre-sample optical means and the first optical element of the post-sample optical means.

2. The optical apparatus of claim 1 wherein the dual-purpose lens acts as a shaping and collimating lens in the pre-sample optical means, and as a collecting and collimating lens in the post-sample optical means.

3. The optical apparatus of claim 1 or claim 2 wherein the dual-purpose lens is the optical element closest to the sample, and has a flat surface facing toward the sample and a spherically-shaped surface facing away from the sample.

4. In a system for determining the intensity of photoluminescence emitted at the surface of a sample, such system having in its input portion a laser radiation source which provides a highly concentrated, essentially circular beam of radiation for sample-excitation purposes, and having in its output portion a photodetector and a grating spectrometer which receives sample-emitted radiation at its entrance slit and sends radiation through its exit aperture to the photodetector;

a method of enhancing radiation throughput to the photodetector comprising the steps of;

reshaping the laser beam in such a way that it has cross-sectional dimensions proportionally similar to those of the grating spectrometer slit, by first widening the laser beam in its one cross-sectional dimension and thereafter narrowing the laser beam in its other cross-sectional dimension;

causing the reshaped laser excitation beam to impinge on the surface of the sample;

collecting the radiation emitted by the sample as a result of the excitation effect of such refocused laser beam; and

focusing such collected radiation in such a way that its cross-sectional dimensions at the grating spectrometer entrance slit are similar to those of the slit;

a single dual-purpose lens being used to accomplish both the final shaping of the pre-sample laser radiation beam which impinges on the sample, and the collecting of the sample-emitted radiation.