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Semi-Quantitative Measurement of Wafer Surface via Infrared Spectroscopy

IP.com Disclosure Number: IPCOM000049343D
Original Publication Date: 1982-Apr-01
Included in the Prior Art Database: 2005-Feb-09
Document File: 4 page(s) / 44K

Publishing Venue

IBM

Related People

Engelbrecht, JAA: AUTHOR [+2]

Abstract

Determination of interstitial atomic oxygen and substitutional atomic carbon impurities in silicon is based on the absorption of the energy associated with infrared radiation. The process is best described in simplest terms by regarding the infrared radiation as a beam of light being shown through a window pane. Upon encountering the window pane, the following can happen to the beam: Some of it can be transmitted through the pane. Some of it can be absorbed by the window pane material. Some can be scattered from the pane surface.

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Semi-Quantitative Measurement of Wafer Surface via Infrared Spectroscopy

Determination of interstitial atomic oxygen and substitutional atomic carbon impurities in silicon is based on the absorption of the energy associated with infrared radiation. The process is best described in simplest terms by regarding the infrared radiation as a beam of light being shown through a window pane. Upon encountering the window pane, the following can happen to the beam: Some of it can be transmitted through the pane.

Some of it can be absorbed by the window pane material.

Some can be scattered from the pane surface.

The above is depicted in Fig. 1, and can be written in equation form as:

E(in) = E(t) + E(a) + E(s) where E(in) is the incident energy
E(t) is the transmitted energy
E(a) is the absorbed energy
E(s) is the scattered energy
The amount of absorbed energy relates to the amount of material in the window pane causing the absorption, which is the point of interest. Since the intensity of the light is a measure of the energy thereof, the absorbed energy is obtained as the difference between the incident and transmitted plus scattered intensities. In terms of equation 1 E(a) = E(in) - (E(t) + E(s)).

For a clear glass window pane, the scattering will be minimal and can hence be ignored in equation 2, leaving E(a) = E(in) - E(t).

If the surface of the window pane is now made uneven, scattering of the incident light will occur (Fig. 2). Since the material that the window consists of is unaltered, E(a) will remain the same. As E(in) is constant, it is clear from equation 1 that, as scattering increases, the amount of transmitted light decreases. (In terms of equation 3, this implies that one will measure a smaller amount of absorbed energy E , resulting in a false impression as to the amount of absorbing material in the window pane.)

Consider now a slice of silicon material in place of the window, meter. The spectrometer can determine only E(in) and E(t), thus one is stuck with equation 3 to obtain E. (In the approach here, E(t) is related to the height of the wavepeak of silicon in the spectrum of the transmitted radiation (see Fig. 3).) Analogous to the window pane, if the silicon sample is highly polished and flat on both sides, little or no scattering will occur and equation 3 will be valid to use. However, if the surface is uneven or rough, scattering will occur, causing less radiation to be transmitted and hence a decrease in the height of the silicon wavepeak. The more rough the surface, the more scattering will occur and the greater the decrease in the height of the peak.

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By measuring the decrease in the silicon peak, it is possible to get some idea of how rough or uneven a particular specimen surface is, as compared to the ideal case of double-side polished, flat samples. Note that this is a contact-less method of evaluating silicon substrate surfaces. One possible application may be as a quick check to evaluate the quality of...