JPS59181549A - Life time measurement of semiconductor wafer - Google Patents

Abstract

PURPOSE:To reduce the surface recombination speed S without providing a charged film or an electrode to the surface of a wafer and facilitate noncontact measurement of the effective life time taueff by applying a light which produces pairs of electrons and positive holes in the neighborhood of the surface of the semiconductor. CONSTITUTION:While a bias light 4, which has energy higher than forbidden band width, is applied to one surface of a semiconductor wafer 1 by a light source B, a pulse light (measuring light) 5, which has energy higher than forbidden band width, is applied by a light source A. A microwave 3a is applied to another surface of the wafer 1 through a waveguide 2 and the effective life time taueff is measured from a recombination attenuation curve, obtained by a reflected signal 3b, of minority carriers excited in the semiconductor wafer 1. If the wavelength of the bias light is selected properly, the condition suitable for reducing the surface recombination speed S can be maintained.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for measuring the lifetime of semiconductor wafers.

It is a well-known fact that when external energy is injected into a semiconductor by irradiating it with light, etc. or a particle stream such as magnetic waves or alpha rays, pairs of electrons and holes are generated.2For example, if the semiconductor is N-type, The holes become excess minority carriers, and these excess minority carriers recombine with electrons and disappear one after another, and the concentration of excess minority carriers decreases exponentially. The time it takes for the concentration of excess minority carriers to decrease to 1/e is called the lifetime of a semiconductor. Since this lifetime is significantly affected by impurity atoms, dislocations, lattice defects, etc. in the semiconductor crystal, measuring the lifetime value is considered important as one of the methods for evaluating the quality of semiconductor crystals.

Generally, when measuring the lifetime of semiconductor wafers,
The actually measured effective line time τeff is determined not only by the lifetime τb of the bulk (crystal matrix) determined by the purity of the semiconductor crystal and crystal defects, but also by the lifetime value component τ5 determined by the contamination of the semiconductor device, the surface processed layer, etc. In what is involved.

τ5 is related to the speed S of surface recombination occurring near the surface of the semiconductor wafer. When measuring τeff of a wave-shaped semiconductor crystal, the light guide decay curve, which shows the situation in which the concentration of excess minority carriers excited by injecting external rays and energy decreases over time due to recombination, is τb. appears as a function of S, and if the value of S is large, the ratio of excited excess minority carriers diffusing and recombining on the surface increases, and the value of τeff becomes small, making measurement impossible in extreme cases. Ru.

Therefore, when measuring τeff of a semiconductor wafer, it is necessary to reduce the speed S of nine surface ρ+ bonds. For this reason, conventionally 2 occurrences occur near the surface of the semiconductor wafer. ′
As a means of slowing down the recombination of electrons and holes, for example,
N-type semiconductor wafers are treated with a positively charged film on their surfaces, and P-type semiconductor wafers are treated with a negatively charged film on their surfaces near the surface of the semiconductor wafer. A method has been used to reduce the surface recombination rate of semiconductor wafers by forming a potential barrier (Usami, Kandatsu, Kudo, Applied Chemistry 49 (1980) 1192-1197). Another method is to attach an electric bolt to a semiconductor wafer and immerse it in an electrolytic solution.
A method has been proposed in which a potential barrier is formed near the surface of a semiconductor wafer by applying pressure. However, with the method of attaching a charge film, the surface of the semiconductor wafer becomes contaminated and must be cleaned after lifetime measurement, and with the method of attaching an electrode, the measurement sample wafer cannot be reused. .

Therefore, the present invention has been made in view of the drawbacks of the above-mentioned conventional methods.

When measuring τeff of semiconductor wafers such as silicon, a charge film is applied to the wafer surface.

S is reduced without any direct processing such as attaching electrodes. Non-contact semiconductor wafer lifetime 1l
ii] The purpose is to provide a fixed method.

+: Invention (/c) The semiconductor wafer line time measuring method provided by /c irradiates the semiconductor wafer with light having an energy higher than that of the semiconductor wafer, detects the recombination decay curve of the excited minority carriers, and measures the semiconductor wafer. In the method of measuring the effective time τeff of a wafer, the same surface of the semiconductor wafer is irradiated with light from two lights #, A and B, respectively, and the semiconductor wafer is This method consists of measuring τeff by detecting the recombination decay curve of minority carriers excited by pulsed light irradiated from light source A while generating pairs of electrons and holes near the surface.

The present invention focuses on the fact that S can be reduced by irradiating L(C) light that generates pairs of electrons and holes near the surface of a semiconductor. That is,
The surface recombination rate of a semiconductor is expressed by the following formula (A, S
, by Grove 2-chohn Wiley andS6
．． Published by n's, Inc., rPhysics a
nd Technology of Sem1condu
ctor Devices J, p. 139)
.

S=S □ On5 +p5 + 2nl S: Surface recombination rate So2 Table 1 without surface space charge region *1 Recombination rate ND: Donor concentration n 5 s Surface electron concentration p5: Surface hole concentration nia intrinsic Carrier concentration Therefore, if the electron concentration n and hole concentration p5 at the semiconductor surface can be increased, the value of S will be reduced. The uninvented method is
By continuing to irradiate the semiconductor wafer surface with bias light having an energy larger than the forbidden band width and a skin length of f corresponding to iM from light source B, n and p in the vicinity of the surface are
, increases.

Next, the present invention will be explained in more detail with reference to Examples, but the scope of the present invention is not limited thereto.

FIG. 1 is a schematic diagram showing an example of a lifetime measuring device suitable for applying the method of the present invention.

While bias light 4 with energy greater than the forbidden band width is applied to one surface of the semiconductor wafer 1 shown in the figure from light source B, pulsed light (measuring light) 5 with energy greater than the forbidden band width is emitted from light 1117. irradiate waveguide 2 onto the other surface of wafer 1 by irradiating :j! i, the microwave 6a is sent, and the semiconductor wafer is exposed by the reflected signal 3b.
From the write coupling decay curve of minority carriers excited to 1, τef
Measure f.

The maximum position of the distribution in the wafer depth direction of the single electron and hole concentration generated in the seed semiconductor wafer 1 with a short bias source 40 wavelength approaches the light-receiving surface of the wafer.

Therefore, if the wavelength of the bias light is selected as n
5 and p5 can be kept appropriate to reduce S.

A specific resistance of 10 Ω/min was obtained using the apparatus shown in 1.

Using a 5001 tON type silicon wafer as a sample, τeff was calculated under each of the following conditions (a) and (b).
was measured.

(a) Bias light wavelength 660 nm (continuous irradiation on the entire surface of one side of the wafer) 3, measurement light wavelength 940 nm, pulse 11 m 100 μse
c (spot irradiation on the same side of the wafer).

(b) Don't let the bias light shine between the +! :' Irradiate the measuring light of the four eels in J.

In the case of result (a), τeff-20μsec,
(ml), a value of τeH=10 μSeC was obtained. The same silicon wafer as above was subjected to a process of attaching a positive film to the surface and the value of τeff was measured by the conventional method, and the result was a value of τeff - 22 μsec. This value agreed well with the measurement results in case (a), and the reliability of the present invention was confirmed. Result of bias light irradiation τeff
An increase in the value of S means that S is reduced.

A method for calculating S based on the deviation from the exponential change in the photoconductivity decay curve for the same silicon wafer as above (Usami, Kandatsu, Kudo, Applied Physics 49 (1980)
As a result of calculating the value of S using
c, i), S = 22 D 7Cm
Obtained 15ec. Bias light irradiation reduces the value of S by about 1/
It has been reduced to 2.

Since the present invention uses the method described above, it is possible to reduce the value of 8 in a non-contact manner without applying direct force to the surface of the semiconductor wafer. It is convenient because it can be used not only in semiconductor wafer manufacturing processes, but also in semiconductor device manufacturing processes such as integrated circuits. This is a method for measuring the lifetime of semiconductor wafers that is effective as a non-contact, in-line evaluation method.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing an example of lifetime measurement and fixed RF suitable for implementing the method of the present invention.

Claims (1)

[Claims] In the method of measuring the effective lifetime τeff of a semiconductor wafer by irradiating the semiconductor wafer with light having energy exceeding the forbidden band width and detecting the recombination decay curve of the excited minority carriers, Then, two light sources A and B each emit light, and the 9Vζ emitted from light source B causes - to near the surface of the semiconductor wafer.
A method for measuring the lifetime of a semiconductor wafer, which comprises measuring τeff by detecting a recombination decay curve of minority carriers excited by pulsed light irradiated from a light source A while generating pairs of m-sons and holes.