JP2845014B2 - Minority carrier recombination lifetime measurement device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an apparatus for measuring the minority carrier recombination lifetime of a semiconductor crystal substrate, and more particularly to an apparatus for measuring the minority carrier recombination lifetime of a silicon crystal substrate.

[0002]

2. Description of the Related Art When a metal atom diffuses into a silicon substrate, the metal atom forms a deep level in the forbidden band of silicon and becomes a trapping center of carriers, so that the minority carrier recombination life is significantly deteriorated. Therefore, the minority carrier recombination lifetime is correlated with the density of deep levels, that is, the concentration of metal atoms diffused in the silicon substrate, and by utilizing this relationship, undesired metal atoms can be introduced into the silicon substrate. It is possible to monitor the degree of diffusion (metal contamination). A minority carrier recombination lifetime measuring device (hereinafter, referred to as a measuring device) is often used for the purpose of monitoring metal contamination in a silicon substrate by using such a principle.

FIG. 6 shows a configuration of a conventional measuring apparatus. FIG.
Referring to FIG. 1, the measuring apparatus basically includes a microwave generating unit 1 for generating microwaves, a circulator 2 for controlling the flow of microwaves, and a reflected microwave detection for detecting microwaves reflected from the silicon substrate 3. Unit 4, an amplifying unit for amplifying the detected reflected microwave 5, a laser diode for generating a laser beam 6, a pulse generating unit 7 for generating a laser pulse from the laser beam, a signal of the amplified reflected microwave and a laser pulse. The oscilloscope 8 comprises an oscilloscope 8 for outputting an attenuation waveform of the reflected microwave intensity from the base, a vacuum suction table 9 for fixing the silicon substrate 3, and a suction rotary pump 10.

The minority carriers generated in the silicon substrate 3 by the laser pulse from the pulse generator 7 diffuse in the silicon substrate 3 and recombine inside the silicon substrate and inside and outside of the silicon substrate. On the other hand, since the reflection intensity of the reflected microwave is proportional to the concentration of the minority carrier, from the attenuation curve of the reflected microwave displayed on the oscilloscope 8, the reflected microwave intensity is 1 / e of the maximum value (e is the natural logarithm). The minority carrier recombination lifetime can be determined by determining the time of decay to the bottom. An example of the attenuation waveform is shown by a curve B in FIG. Referring to FIG. 3, two slopes are observed in the attenuation curve.
The initial steep slope indicates the effect of surface recombination, and the gentle slope in the latter half indicates the effect of recombination in the silicon substrate and front and back surface recombination.

[0005]

Factors affecting the minority carrier recombination lifetime described above include not only metal contamination but also surface recombination due to surface levels. However, since it is difficult to separate the two using the conventional measuring device shown in FIG. 6, the level of metal contamination cannot be accurately evaluated from the change in the minority carrier recombination lifetime due to surface recombination.

Also, since the minority carriers diffuse widely from the inside of the silicon substrate to the front and back surfaces and recombine, it is impossible to obtain a relationship between the diffusion depth of the contaminant and the minority carrier recombination lifetime. That is, the conventional measuring device has a problem that the level of metal contamination in the depth direction cannot be monitored.

[0007]

A minority carrier recombination lifetime measuring apparatus according to the present invention irradiates a laser pulse from one surface of a silicon crystal substrate to generate minority carriers, and enters the laser beam from one surface of the silicon crystal substrate. A minority carrier recombination lifetime measuring device of the type that determines the recombination lifetime of minority carriers from the temporal change in the intensity of reflected microwaves, wherein at least the silicon crystal substrate is supported on the other surface, the insulation An electrode coated with a material, a transparent electrode coated with a transparent insulator, which is in contact with the laser pulse and microwave incident surface of the silicon crystal substrate, and a depletion layer formed inside from both surfaces of the silicon crystal substrate. Power supply to cause
The voltage of the power supply is variable .

[0008]

Next, a preferred embodiment of the present invention will be described with reference to the drawings. First, to facilitate understanding of the invention
Therefore, a reference example will be described. FIG. 1 is a reference of the present invention.
It is a figure showing composition of an example . FIG. 2 schematically shows, in an enlarged manner, the silicon substrate and the electrode portion in FIG. 1, and also shows a depletion layer formed in the silicon substrate, an arrangement of electric charges, and the like.
FIG. 9 is a diagram showing a state of reconnection of the minority carriers (these are shown only on the back surface side of the silicon substrate for simplicity). In the present invention, as shown in FIG.
By applying a voltage to the front and back surfaces using the electrodes 12A and 12B coated with the insulators 11A and 11B, a depletion layer 13 is formed on the front and back surfaces of the silicon substrate 3. Thereby, the minority carrier (indicated by an electron in FIG. 2) 1
4 is prevented from diffusing to the front and back surfaces of the silicon substrate 3, and the minority carrier recombination lifetime due to surface recombination is not changed. And later
As described in the embodiment described above, the thickness of the depletion layer 13 is changed by changing the voltage applied to the silicon substrate 3 by using a variable power supply as the power supply 15, thereby enabling monitoring of the metal contamination level in the depth direction. And The insulator 11A and the electrode 12A on the front side of the silicon substrate 3 are:
Since the laser pulse 16 is incident from this surface, it is made transparent.

Referring to FIG. 1 and FIG. 2, in this embodiment , a transparent electrode 12A covered with a transparent insulator 11A and an electrode 1 covered with an insulator 11B are used by using a power source 15.
A voltage that causes the depletion layer 13 to be generated in the silicon substrate 3 is applied between 2B and the silicon substrate 3. When the silicon substrate 3 is irradiated with the laser pulse 16 generated by the pulse generator 7 and the laser diode 6, a minority carrier 14 is generated in the silicon substrate 3. The minority carriers 14 recombine after diffusion, but do not diffuse to the front and back surfaces of the silicon substrate where the depletion layer 13 is formed, and do not recombine on the front and back surfaces. Since the intensity of the microwave generated by the microwave generation unit 1 and reflected by the silicon substrate 3 through the circulator 2 is proportional to the concentration of the minority carrier, the state of attenuation of the minority carrier 14 is determined by the reflected microwave detection unit 4 and the amplification unit 5. And is output to the oscilloscope 8 as a function of time. The minority carrier recombination lifetime obtained from the attenuation waveform output in this manner is not an apparent minority carrier recombination lifetime but a minority carrier recombination in a true silicon substrate because minority carriers do not recombine on the front and back surfaces of the silicon substrate. Life is long. An example of the output waveform of the oscilloscope 8 is shown by a curve A in FIG. In FIG. 3, the silicon substrate used in this reference example is the same as the silicon substrate used in the observation example according to the conventional technique,
Originally, the minority carrier recombination lifetimes shown by the two should match. However, in the observation example according to the prior art, the influence of surface recombination is the initial steep slope of the waveform, and the gentle slope in the second half of observed effect of front and back surfaces recombination, the ginseng
Compared to the minority carrier recombination lifetime of 160 microseconds in the example , it is observed to be 70 microseconds, which is apparently significantly degraded.

Next, an embodiment of the present invention will be described. FIG. 4 is a diagram showing the configuration of one embodiment of the present invention .
Referring to FIG. 4, in this embodiment, the minority carrier recombination lifetime is measured by changing the voltage applied to the silicon substrate 3 and changing the thickness of the depletion layer by changing the power supply to the variable power supply 17. ing. As a result, the acceptor concentration or the donor concentration in the silicon substrate becomes 1 × 10 ¹⁵ cm.
^In the case of about ^-3 , analysis in the depth direction is possible up to about 1 micrometer. If the acceptor concentration or the donor concentration in the silicon substrate is further reduced, the analysis can be performed in a deeper part. FIG. 5 shows an example of the observation result according to the present embodiment. The concentration of the silicon substrate used is 1 ×
10 ¹⁵ cm ^-3 . As the applied voltage was increased, the minority carrier recombination lifetime was prolonged. From 50 microseconds at the beginning to 200 microseconds, the carrier was saturated.
Therefore, it is expected that the silicon substrate has a high concentration of contaminants near the surface in a depth range of up to 1 micrometer, which significantly deteriorate the recombination lifetime. In fact,
SIMS (Secondary Ion Mass Sp
As a result of electron scopy (secondary ion mass spectrometry), it was confirmed that iron (Fe) atoms were present near the surface of the silicon substrate.

[0011]

As described above, according to the present invention, a voltage is applied to a silicon substrate through an electrode covered with an insulator and a transparent electrode covered with a transparent insulator.
Since a depletion layer is created in the silicon substrate to prevent recombination of minority carriers on the surface of the silicon substrate, recombination on the true silicon substrate is not affected by recombination on the front and back surfaces of the silicon substrate. Lifetime can be measured.

Then , by measuring the minority carrier recombination lifetime while changing the thickness of the depletion layer by changing the voltage applied to the electrode, the measurement in the depth direction is possible.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a reference example of the present invention.

FIG. 2 is a schematic cross-sectional view showing, on an enlarged scale, a silicon substrate and electrode portions in the configuration shown in FIG. 1 to explain the operation of the present invention.

FIG. 3 is a diagram showing an example of an observed waveform of reflected microwave intensity in a reference example of the present invention.

FIG. 4 is a diagram showing a configuration of one embodiment of the present invention .

In the embodiment of Figure 5 the present invention, showing an example of the relationship between the silicon substrate in the depth and minority carrier recombination lifetime.

FIG. 6 is a diagram showing a configuration of a conventional minority carrier recombination lifetime measuring device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Microwave generation part 2 Circulator 3 Silicon substrate 4 Reflection microwave detection part 5 Amplification part 6 Laser diode 7 Pulse generation part 8 Oscilloscope 9 Vacuum suction table 10 Rotary pump 11A, 11B Insulator 12A, 12B Electrode 13 Depletion layer 14 Minority carrier 15, 17 Power supply 16 Laser pulse

Claims (1)

(57) [Claims] 1. A minority carrier is generated by irradiating a laser pulse from one surface of a silicon crystal substrate to generate a minority carrier. A minority carrier recombination lifetime measuring device of the type for determining the recombination lifetime of at least,
An electrode coated with an insulator that supports the silicon crystal substrate on the other surface, a transparent electrode coated with a transparent insulator that contacts one surface of the silicon crystal substrate, and one of the silicon crystal substrates Minority carrier recombination with a power supply to create a depletion layer inside one side and the other side
In lifetime measuring apparatus, the minority carriers, characterized in that the voltage of the power supply is variable
Recombination lifetime measurement device .