JPS6144437A - Semiconductor characteristics measurement equipment - Google Patents

Abstract

PURPOSE:To enable the non-contact and non-breakdown measurement of the lifetime of minority carriers by a method wherein the difference in phase between the modulation frequency of light is detected by leading out a photo voltage generated in a semiconductor sample by irradiating this sample with a modulated light beam. CONSTITUTION:A clear electrode 3 is arranged in opposition to an Si wafer 1, and a photoelectromotive voltage generated in the wafer 1 is picked up by capacitance coupling. A beam emitted from a light source 8 is modulated in intensity by a modulator 7, partly split by a beam splitter 6, and converted into electric signals by a photoelectric converter 9. The other part of light transmitting through the splitter 6 is reflected on a reflection mirror and made to irradiate the sample of Si wafer 1 through a lens 4. The phase of the photo voltage generated between electrodes 2 and 3 is detected by a phase meter 10 as the relative ratio to the output signal of the converter 9, and then displayed by a signal processing circuit 11 in output as the lifetime of minority carriers.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an apparatus for non-contact and non-destructive measurement of the lifetime of minority carriers in a semiconductor sample such as a Si wafer.

[Background of the invention]

Conventionally, the lifetime of minority carriers in a semiconductor has been determined by attaching an electrode with ohmic contact to a semiconductor sample, irradiating it with impulse light from a xenon lamp, and measuring the attenuation of the output signal. This measurement is a contact measurement;
Moreover, since it is a type of destructive measurement, it is only suitable for sampling inspections. Therefore, measurements cannot be performed online.

On the other hand, as a non-contact measurement method, there is a method in which the minority carriers are injected by irradiating light, and then the lifetime of the minority carriers is determined from the time response of the absorption by applying microwaves. , Journal of Applied Physics, Vol. 30, No. 7, July 1959, pp. 1054-1060.
Applied Physics VoL, 30. No.7
; uLy 1959 pp. 1054-1060) However, this method has the disadvantage that it requires an expensive and complex microwave transmitter, receiver, etc., making the entire device complex and expensive. Furthermore, this method has the disadvantage that when the signal is small, reading errors from the attenuation characteristics tend to increase.

[Purpose of the invention]

An object of the present invention is to provide a simple and inexpensive semiconductor characteristic measuring device for online non-contact and non-destructive measurement of the lifetime of minority carriers in a semiconductor wafer, typically silicon.

[Summary of the invention]

In order to achieve the above object, the present invention irradiates a sample with a modulated light beam that passes through a transparent electrode provided to capacitively couple a sample (silicon wafer) placed on a sample stage. The method is characterized in that the photovoltage generated in the sample is extracted, the phase difference with the modulation frequency of the light is detected, and the lifetime of minority carriers is determined from the phase difference.

In other words, the present invention has been made based on the following operating principle. Now, when measuring with a phase meter with a large input impedance close to infinity, the optical voltage Vo is such that the optical absorption coefficient α in silicon is equal to the minority carrier diffusion ratio 1
When it is sufficiently smaller than the reciprocal of 1ffiL, that is, when the wavelength of the light is relatively long, for example, 900 nm, it is approximately expressed by the following equation.

VO=KZ, αL ・・・・・・・・・(1
) It is known that the photovoltage vo is generated in the case of p-type St due to the presence of an oxide film, and in the case of n-type Si due to alkaline cleaning with hydrogen peroxide, ammonia, or the like. Now, in equation (1), K is a constant and impedance Zd
using the junction resistance R, and junction capacitance Cj between silicon and oxide film.

It is expressed by the following equation for an AC signal of frequency f.

Here, i=r. Furthermore, it is well known that the diffusion distance is related to the minority carrier lifetime τ as follows, where D is the diffusion coefficient of minority carriers.

From equations (1), (2), and (3), the phase of the photovoltage is TJ=
It can be seen that C,3 changes depending on two time constants, RJ and τ.1 Normally, the minority carrier lifetime τ is on the order of μsec below 1 m5 ec, and the time constant TJ is 10 m5 ec.
It is an order of magnitude larger than that.

Therefore, when the frequency f is changed, the phase change due to the minority carrier life τ and the phase change due to the time constant TJ can be sufficiently separated. From equation (3), minority carrier lifetime τ
The maximum phase change is 45 degrees, and an example of the phase characteristics of the photovoltage ■o is shown in Figure 1.The frequency at which the phase changes by 45 degrees due to the 0 time constant TJ is fJ, and the phase is 22.5 degrees due to the minority carrier life τ. If the changing frequency is fτ, then usually fJ<<fτ. In other words, f7 is found.

Since the photovoltage VO is extracted through capacitive coupling, the measurement is non-contact and non-destructive, and can be measured without contaminating or destroying the surface of the silicon wafer.

As described above, according to the present invention, it is possible to measure the lifetime of minority carriers in a silicon wafer in a non-contact and non-destructive manner, and since the phase of the signal is measured, it is relatively easy to read even if the signal strength is small, and Since no waves are used, the device is simple and can be manufactured at low cost.

[Embodiments of the invention]

This will be explained below using examples. The second @ shows the basic structure of the semiconductor characteristic measuring device according to the present invention. In FIG. 2, 1 is a silicon wafer, 2 is an electrode/sample stage (metal), and 3 is a transparent electrode (indium oxide is deposited on a glass plate). Transparent electrode 3 is silicon wafer 1
The photoelectromotive voltage generated in the silicon wafer 1 can be picked up by capacitive coupling. The light emitted by the light source 8 is intensity-modulated by the modulator 7, partially split by the beam splitter 6, and converted into an electrical signal by the photoelectric converter 9.

The other light transmitted through the beam splitter 6 is sent to the reflecting mirror 5.
The light is reflected by the lens 4 and irradiated onto the silicon wafer 1 sample. The phase of the photovoltage generated between the electrodes 2 and 3 is detected by a phase meter 10 as a relative change with respect to the output signal of the photoelectric converter 9, and is output and displayed by a signal processing circuit 11 as a minority carrier lifetime.

〔Effect of the invention〕

As described above, according to the present invention, non-contact, non-destructive measurement of the minority carrier lifetime of a semiconductor wafer can be realized at low cost with a simple device.

[Brief explanation of drawings]

FIG. 1 is a principle explanatory diagram showing the relationship between the phase change of a photovoltage and frequency, and FIG. 2 is a basic configuration of a semiconductor characteristic measuring device for measuring the lifetime of minority carriers from the phase of a photovoltage according to the present invention. It is a diagram. 1... Silicon wafer, 2... Electrode (
Sample stage) 3...Transparent electrode, 4...Lens, 5...Reflector, 6...Beam splitter, 7...Modulation vessel, 8... light source,
9...Photoelectric converter, 10...Phase meter,
11...Signal processing circuit. Figure 1↑

Claims (1)

[Claims] 1. A means for generating a light beam modulated by a modulation signal, a semiconductor sample placed on a sample stage, a transparent electrode disposed facing the semiconductor sample so as to be capacitively coupled, and the transparent electrode means for transmitting the modulated light beam onto the semiconductor sample; means for extracting the photovoltage generated in the semiconductor sample as an electrical signal and detecting a phase difference with the modulation signal; A semiconductor characteristic measuring device comprising: a signal processing circuit that calculates the minority carrier lifetime of the semiconductor sample based on the relational expression.