JP2719851B2 - Evaluation method of silicon single crystal rod - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for evaluating a silicon single crystal rod, and more particularly, to Czochralski (CZ).
The present invention relates to a method for evaluating a silicon single crystal rod, which is characterized by preparing a sample when measuring a minority carrier bulk lifetime, which is an electrical property of a silicon semiconductor single crystal rod grown from a silicon melt by a method.

[0002]

2. Description of the Related Art Heretofore, there has been known a method of measuring a minority carrier bulk lifetime as a means for evaluating the quality of a silicon semiconductor single crystal rod after pulling up the silicon semiconductor single crystal rod by the Czochralski method or the float zone method. (ASTM F28-75). According to such a method, a method for preparing a sample for measurement requires that a sample as large as possible be cut out of a silicon single crystal rod and subjected to, for example, sandblasting to avoid the influence of surface recombination of minority carriers. The heat treatment of such a sample was not specified. A rhodium plate is contacted with a p-type silicon single crystal at both end surfaces of the sample, and a nickel plate is contacted with an n-type silicon single crystal at a pressure to serve as an electrode. Is what you do.

According to ASTM-F28-75, it is required that the electrical resistance of a sample be uniform so that the minimum value is within 90% of the maximum value. Not specified as described above.

[0004]

SUMMARY OF THE INVENTION ASTM-F28-7
5 specifies the range of the maximum and minimum values of the electrical resistance value for the measurement of minority carriers, and the figure shows the actual measurement of the wafer lifetime of a silicon single crystal rod pulled by the CZ method. As shown in FIG. 3, it is possible to obtain a measured value of the minority carrier lifetime that is directly proportional to the electrical resistance value of the sample (using a p-type silicon wafer as the sample).
At this time, in order to avoid the influence of the surface recombination of minority carriers, heat treatment was performed in advance in a clean heat treatment furnace at 1000 ° C. for 1 hour in an oxygen gas atmosphere, and the minority carrier wafer lifetime was measured (for this treatment, FIG. No effect of thermal donor is seen). Therefore, it is clear that the influence of the majority carrier that contributes to the electric resistance cannot be ignored.

However, when a silicon single crystal rod is grown by the CZ method, oxygen eluted from the quartz crucible is taken into the silicon single crystal rod and becomes a thermal donor to greatly change the electrical resistance as a majority carrier. Is well known. Such an ASTM method does not specify a sample processing method, and the influence of these thermal donors has been neglected in the minority carrier bulk lifetime measurement in the past. The present invention intends to eliminate the influence of a thermal donor by preliminarily heat-treating a sample in such a measurement method. When a silicon wafer that has been subjected to such processing is shipped to a user, the heat treatment of the wafer performed by the user can stabilize the process without causing a change in the lifetime.

[0006]

Means for Solving the Problems] Evaluation method for a silicon single crystal rod according to the present invention, after growing the silicon single crystal rod of high purity silicon melt held in a quartz crucible, a single crystal rod Collect a sample for minority carrier bulk lifetime measurement and
In a method for measuring free time, the sample is treated with nitric acid.
Ammonia heated with a mixture of HF and hydrofluoric acid
Mixed solution of solution and hydrogen peroxide solution, hydrochloric acid and hydrogen peroxide solution
After alternately washing with a mixed solution of, and washing with ultrapure water, and further performing a heat treatment in a high-purity gas atmosphere of 550 ° C or more and 1400 ° C or less , measurement of the minority carrier bulk lifetime is performed.
Is performed .

That is, according to the present invention, a sample is taken from a silicon single crystal rod grown by the CZ method prior to the measurement of the minority carrier bulk lifetime, and then the sample is subjected to a heat treatment to erase the thermal donor and to be subjected to the bulk lifetime measurement. It is assumed that.

In the present invention, first, after growing a silicon single crystal rod held in a quartz crucible, for example,
A sample for measuring the minority carrier bulk lifetime of a predetermined size is collected from both ends of the single crystal rod to a predetermined size using a device such as a diamond saw. Then, when measuring the minority carrier bulk lifetime of this sample, this sample is subjected to a heat treatment in a high purity gas atmosphere of 550 ° C. or more and 1400 ° C. or less. Heat treatment temperature is 550
If the temperature is lower than ℃, the progress speed of the heat treatment is small, which is not preferable. On the other hand, at a temperature exceeding 1400 ° C., the melting point of silicon is 14
Since it is 20 ° C., it is not preferable from the viewpoint that heat treatment is performed without melting. The processing temperature is preferably 600 ° C. or higher in order to increase the speed of the heat treatment, and 800 ° C. from the viewpoint of avoiding contamination from the heat treatment environment.
The following is preferred.

In the present invention, before a sample cut from a single crystal rod is subjected to the above-mentioned heat treatment, the sample is etched with a chemical solution.
Cleaning with chemical solution and cleaning with ultrapure water.
U. This makes it possible to prevent distortion when cutting out samples,
Remove impurities adhering to the surface and remove impurities
Prevent the spread of materials and the resulting reduction in lifetime
Can be. That is, the lifetime is
Very sensitive to crystal defects and contamination by heavy metals, etc.
The invention takes this into account and considers the effect of thermal donors.
Samples should be heat treated at high temperatures as described above to eliminate
External contamination (such as heavy metals) on the sample surface.
Impurities) are minimized from diffusing into the bulk,
A reliable bulk lifetime assessment
There are advantages. In the present invention, it is preferable to measure the minority carrier bulk lifetime after lapping the surface of the sample after the heat treatment.
This eliminates the effects of the sample surface
You. In the present invention, the interior (bulk) excluding the influence of the crystal surface
To evaluate the lifetime of Generally rifta
In the measurement of the im
Need to be separated because it contains
To measure only the lifetime, a sample table
The surface recombination must be zero or conversely infinite.
You. Wrapping the sample surface is a shadow of surface recombination
The sound approaching infinity, and as a result
The acoustics are eliminated and the lifetime inside the bulk is more accurate
Can be evaluated.

Thus, the silicon single crystal according to the present invention
In the rod evaluation method, a sample is cut out from a single crystal rod,
Etching, cleaning with chemicals, and ultrapure water
After treatment in the order of cleaning and heat treatment (preferably,
After further lapping after the heat treatment), it is supplied to a bulk lifetime measuring device having a pulsed light emitting diode , for example , so that the minority carrier bulk lifetime can be reduced.
Measurement is performed.

The present invention particularly relates to the bulk lifetime, but the thermal donor must be erased when measuring the so-called wafer lifetime using a silicon wafer as a sample. In order to eliminate the influence of surface recombination of minority carriers, oxidation is generally performed at 1000 ° C., and such a value is measured. At this time, the thermal donor is erased, and there is no problem. As another means to eliminate the effect of surface recombination of minority carriers, a silicon wafer may be immersed in a dichromic acid solution to perform surface treatment.In this case, however, thermal donor erasure must be performed prior to lifetime measurement. Processing must be done on the sample. The reason why the same surface treatment as the wafer lifetime is not performed prior to the bulk lifetime measurement is that it is possible to easily eliminate the influence of surface recombination of minority carriers by giving mechanical damage such as sandblasting to the surface. by. Since the bulk lifetime can be easily measured simply by performing a process such as pressure bonding of electrodes to both end surfaces of the ingot, no consideration has been given to thermal donor erasure until now.

[0012]

By subjecting a sample for minority carrier bulk lifetime measurement to a heat treatment in a high-purity gas atmosphere of 550 ° C. or more and 1400 ° C. or less, a single crystal eluted from a quartz crucible when growing a single crystal rod by the CZ method. Thermal donors based on oxygen incorporated into the bar can be eliminated. When the minority carrier bulk lifetime is measured on the sample after the heat treatment, there is no thermal donor that hinders the measurement as a majority carrier,
The minority carrier bulk lifetime can be measured accurately and with good reproducibility. In addition, before the heat treatment,
Etching of sample, cleaning with chemical solution, cleaning with ultrapure water
By applying each treatment of purification, distortion at the time of cutting out the sample,
Remove impurities adhering to the sample surface and heat-treat
Prevents diffusion of impurities and associated reduction in lifetime
And, as a result, minority carrier bulk life
Time can be measured with high accuracy.

[0013]

EXAMPLE After 60 kg of polysilicon was charged into a quartz crucible, boron was doped, and a silicon single crystal rod with a growth direction <100> and a diameter of 150 mm and a length of 90 cm was pulled up. After cutting off the cone-shaped portion of the crystal head and crystal tail with a diamond saw, cut out a rectangular parallelepiped with a square cross section with a side length of 10 mm perpendicular to the growth direction from the crystal head end face with a diamond saw, The samples were used for lifetime measurement. The bulk lifetime of the sample containing the thermal donor was measured by a bulk lifetime measuring device equipped with a pulsed light emitting diode. The electric resistivity value was measured with a four-probe electric resistance measuring device. Further, the sample was etched with a mixed solution of nitric acid and hydrofluoric acid to remove dirt and strain on the surface, and washed alternately with a heated mixed solution of ammonia solution and hydrogen peroxide solution and a mixed solution of hydrochloric acid and hydrogen peroxide solution. Thereafter, a rinsing heat treatment was added well with ultrapure water.

The heat treatment was performed at 650 ° C. for 30 minutes in a nitrogen atmosphere. After the heat treatment, the side surface of the rectangular parallelepiped sample was wrapped with lapping powder of silicon carbide so as to avoid the influence of surface recombination at the time of measuring the lifetime, and then the bulk lifetime was measured. Further, the electric resistivity value was measured with a four-probe electric resistance measuring device. The amount of thermal donor was determined from the change in electrical resistivity before and after the heat treatment. FIG.
Fig. 3 shows the results of plotting the bulk lifetime in the as-grown state and the lifetime value after erasing the thermal donor for each sample.

The electrical resistivity of the sample subjected to the measurement is 5Ω.
・ Because it is widely taken from cm to 50Ω ・ cm ,
Bulk lifetime from 100μsec to 500μsec
c, but the bulk lifetime is reduced after erasing the thermal donor. This thermal donor acts on p-type samples before the heat treatment, MiKakeue electric
Because the resistivity increased, the majority carrier did not contribute to the decay of the minority carrier, and it can be explained that the bulk lifetime was longer in the as-grown state. FIG. 2 shows the amount of thermal donor erased (reduced) after heat treatment.
The relationship between the small amount) and the degree of decrease in the bulk lifetime was shown. The greater the amount of decrease in the thermal donor, the greater the degree of decrease in the bulk life time. It was confirmed that bulk lifetime measurement was possible.

Next, heat treatment in a nitrogen atmosphere was performed at each temperature between 300 ° C. and 1400 ° C. as shown in Table 1, and the bulk lifetime was measured in the same manner as above except for the above. The results are also shown in Table 1.

[0017]

[Table 1] As is clear from Table 1, the heat treatment temperature was 550 ° C. or higher,
By setting the temperature within the range of 400 ° C or less, the lifetime
Can be measured accurately.

[0018]

As described in detail above, according to the present invention, CZ
The thermal donor based on oxygen taken into the single crystal rod during the growth of the single crystal rod by the method can be eliminated, and the minority carrier bulk lifetime can be measured accurately and with good reproducibility.

[Brief description of the drawings]

FIG. 1 is a graph showing the values of the bulk lifetime of a p-type silicon single crystal rod before and after heat treatment.

FIG. 2 is a graph showing the relationship between the erasure amount of a thermal donor and the degree of reduction in bulk lifetime.

FIG. 3 is a graph showing the relationship between the electrical resistivity of a p-type silicon single crystal rod and the wafer lifetime.

Claims (2)

(57) [Claims] 1. Silico grown by the Czochralski method
A sample is taken from a single crystal rod and a small number of
In a method for measuring a carrier bulk lifetime,
Etching the sample with a mixture of nitric acid and hydrofluoric acid,
A mixed solution of a heated ammonia solution and a hydrogen peroxide solution,
Wash alternately with a mixed solution of hydrochloric acid and hydrogen peroxide solution,
After washing with water, it was subjected to further heat treatment under a high-purity gas atmosphere at 550 ° C. or higher 1400 ° C. or less, minority carriers Bal
A method for evaluating a silicon single crystal rod , comprising measuring a lifetime . 2. The method for evaluating a silicon single crystal rod according to claim 1 , wherein the minority carrier bulk lifetime is measured after wrapping the surface of the heat-treated sample.