JP2512340B2 - Method for producing silicon single crystal by Czochralski method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a silicon single crystal by the Czochralski method, and particularly to a graphite crucible used for the method for producing a silicon single crystal by the Czochralski method. The present invention relates to a graphite material for pulling a silicon single crystal such as a graphite heater and a graphite protection cylinder.

(B) Conventional Technology Thermal oxidation is important in the manufacturing process of semiconductor silicon electronic devices such as integrated circuits. Among them, the oxidation-induced stacking fault (OSF) generated by this thermal oxidation treatment is one of the extremely important ones. In particular, when there is an active area of a small transistor near the surface of a silicon substrate like MOSIC, leak current is generated, the lifetime is shortened, and it is considered to be unfavorable due to other influences on relaxation time. ing.

In the case of a destructive inspection, such an oxidation-induced stacking fault can be easily detected by an optical microscope by dissolving and removing the oxide film with an HF aqueous solution, and then slightly chemically etching the exposed silicon substrate surface with a diltor etch solution. However, in general, it is said that the n-type 100 surface is mainly generated in the main surface of the silicon substrate. With the progress of the semiconductor element manufacturing technology, a high-quality silicon substrate is required, and the generation is almost zero. There is also a demand for silicon substrates.

Thus, most of the silicon single crystals for semiconductors are
It is manufactured by the Czochralski method in which a silicon melt in a quartz glass crucible is solidified at the tip of a seed crystal, and at the same time, the seed crystal is crystallized and grown while being pulled up.

Since such a silicon single crystal pulling apparatus is used at a temperature higher than the melting point of silicon, the internal constituent material of the pulling furnace needs heat resistance, and quartz glass that comes into contact with quartz glass that comes into contact with silicon. Not only the high purity of the crucible but also the graphite crucible, the graphite heater, the protective cylinder made of graphite, and the like are required to be made of the high purity graphite material.

Among these constituent materials, the graphite material does not come into direct contact with the silicon melt, but during the pulling operation of the silicon single crystal at a high temperature, it is particularly heated to a high temperature or exposed to a high temperature. Therefore, when impurities are present in the graphite material, the impurities contaminate the silicon melt through outdiffusion, leaching, evaporation or chemical reaction and cause crystal defects. The graphite material of the single crystal pulling apparatus is highly purified, for example, with an ash content of 5% (see Japanese Patent Laid-Open No. 64-18986).

(C) Problems to be Solved by the Invention However, for example, even if such a highly purified graphite material is used as a graphite material used in a method for producing a silicon single crystal by the silicon Czochralski method, it is produced. Crystal defects such as dislocations often occur in a silicon single crystal,
It is inevitable to completely reduce the yield of silicon single crystals.

It is said that such crystal defects cause contamination by sodium on the surface of the silicon substrate, fine processing loss on the surface, or bulk defects such as swirl defects due to oxygen precipitation.

An object of the present invention is to solve the problem relating to impurities in the graphite material used in the method for producing a silicon single crystal by the Czochralski method.

(D) Means for Solving the Problems The inventors of the present invention paid attention to and studied oxide stacking faults caused by such bulk impurities, and found that the metal impurities in the pulled single crystal were the limit of the analytical technique. It was found that the oxidation-induced stacking faults were generated even when they were not detected by the method, and the presence or absence and the level of the generation of the graphite defects were used in the ordinary Czochralski method, particularly graphite crucibles, graphite heaters and graphite. The present invention has been completed by discovering that it correlates with the purity of the protective graphite material.

However, when specific metal impurities, vanadium, and sulfur are contained in the graphite material at a certain concentration or more, the pulled single crystal is subjected to an oxidation-induced stacking fault generation test,
Oxidation-induced stacking faults occur, and we do not have an accurate knowledge of the strong correlation between the defect generation density and the impurity concentration.

An object of the present invention is to provide a graphite material which can be used in a method for producing a silicon single crystal by the Czochralski method and which can produce a silicon single crystal having no crystal defects with a high yield.

The present invention, even if the total metal impurities content in the graphite material is 5 ppm or more, focusing on the low boiling point impurity components that are relatively easy to gasify, the content of the impurities in the graphite material and the produced silicon When the relationship of the crystal characteristics of the single crystal was investigated,
It is based on the discovery of the fact that the production yield of silicon single crystals without crystal defects can be improved by reducing the content of the impurity component in the graphite material to a predetermined value or less.

That is, the present invention, in the method for producing a silicon single crystal by the Czochralski method, the vanadium content is 2.5 to 0.30 ppm, the total metal impurity content is 50 to 14.46 pp.
m, and the maximum density of oxidation-induced stacking faults is 50 using a protective cylinder made of graphite material with a sulfur content of 1.1 to 2 ppm.
A method for producing a silicon single crystal by the Czochralski method is characterized by producing a silicon single crystal having a density of / cm ² or less.

In the present invention, the total metal impurity content, among the elements other than carbon, especially aluminum, calcium, copper, chromium, boron, iron, potassium, magnesium, nickel,
It means sodium, silicon and titanium, and the total metal impurity content means the total amount of metal components corresponding to these metals contained in the graphite material.

In the present invention, in the silicon single crystal produced by the Czochralski method, in order not to cause crystal defects, the total metal impurity content in the graphite material is about 50 ppm, and even if the sulfur content is 2 ppm. The vanadium content in the graphite material should be 2.5 ppm or less.

The occurrence rate of crystal defects in a silicon single crystal relatively corresponds to the vanadium content in the graphite material, and in particular,
When vanadium is 2.5 ppm or less, no crystal defects are observed in the silicon single crystal obtained by the Czochralski method, and the yield of non-defective silicon single crystals can be increased.

In the present invention, the content of total metal impurities in the graphite material is 50 ppm or less in order to prevent crystal defects from being generated in the silicon single crystal produced by the Czochralski method.

If the total content of metal impurities in the graphite material exceeds 50 ppm, crystal defects are likely to occur in the process of forming the silicon single crystal, and the yield of the silicon single crystal having no crystal defects is significantly reduced.

In order to prevent the occurrence of crystal defects in the silicon single crystal, it is preferable that the total content of iron, nickel, and chromium is 1 ppm or less in the total content of metal impurities. iron,
When the total content of nickel and chromium exceeds 1 ppm,
Even if the total metal impurity content is 50 ppm or less, the occurrence of crystal defects is slightly observed, which is not preferable.

In the present invention, the content of sulfur in the graphite material is vanadium-containing with a total metal impurity content of 50 ppm or less in the graphite material in order to prevent crystal defects in the silicon single crystal produced by the Czochralski method. When the amount of the graphite material is 2.5 ppm or less, it is preferably 2 ppm or less.

(E) Action The present invention has a vanadium content of 2. in the graphite material used in the method for producing a silicon single crystal by the Czochralski method.
5 to 0.30ppm, total metal impurity content 50 to 14.46p
Since the pm is set and the sulfur content is set to 1.1 to 2 ppm, a good silicon single crystal having no crystal defects can be stably manufactured with a high yield in the obtained silicon single crystal product.

(F) Examples The embodiments of the present invention will be described below with reference to specific examples, but the present invention is not limited to the following examples and specific descriptions.

Among the graphite materials used in the Czochralski method silicon single crystal growth equipment, especially for the graphite protection cylinder whose purity is a problem, the impurity content in the graphite is changed to pull up and pull up the silicon single crystal. The generation density of defects in the obtained single crystal, especially the oxidation-induced stacking fault was measured, and the relationship between the content of impurities in the graphite material and the generation density of the oxidation-induced stacking fault was determined.

FIG. 1 is an explanatory view showing a schematic cross section of a main part of an example in which the graphite material of the present invention is applied to a conventional Czochralski method silicon single crystal growing apparatus, and is partially omitted. Not not.

In FIG. 1, the chamber 2 of the single crystal pulling furnace body 1 is shown.
A heater 5 is provided inside the graphite crucible 4 that holds the quartz crucible 3, and polycrystalline silicon is charged into the quartz crucible 3 and melted by heating with the heater 5. The pulling of the single crystal silicon rod 7 from 6 is performed by a conventional method.

The heater 5 is a cylinder having a plurality of slits in the upper and lower sides, and when energized, the current repeatedly flows up and down, and the whole heat is generated substantially uniformly, and the quartz crucible 3 is evenly distributed from the outer periphery through the graphite crucible 4. Heat to. The heater 5 is made of graphite, and a lower portion of the heater 2 is joined to an electrode that penetrates the bottom of the chamber 2 in an airtight and insulated state, for example, a graphite terminal (not shown) in the horizontal direction is integrally formed. ing.

Similar to the conventional Czochralski method silicon single crystal pulling apparatus 1, the graphite protective cylinder 8 is provided coaxially around the silicon single crystal rod 7 to be pulled.

In this example, the protective cylinder 8 made of graphite has a lower end 9
Is adjusted to be located about 20 mm above the silicon melt surface 10, and its upper end 11 is almost airtightly coupled to the inner wall 13 of the pull chamber 12 of the silicon pulling apparatus. Argon gas as a protective gas is fed into the upper pull chamber 12 from the gas inlet 14.

The argon gas sent into the pull chamber 12 flows downward in the void 15 formed between the protective cylinder 8 and the pulled silicon single crystal rod 7, contacts the silicon melting surface 10, and then melts the silicon. It flows laterally along the surface 10, rises upside down along the inner wall 16 of the quartz crucible 3, and further over the end of the quartz crucible 3 to the inner wall 17 of the main chamber 2 of the pulling furnace body 1 below the pull chamber 12. It flows so as to face, then flows downward, and is discharged from the discharge port 18 of the pulling furnace 1.

The inspection of oxidation-induced stacking faults is made by cutting a 2 mm thick disc at a right angle to the length from the straight body near the shoulder of the pulled single crystal rod, and after mirroring the surface, It was performed by observing a stacking fault generated on the surface by thermal oxidation with a microscope.

The thermal oxidation conditions and measurement conditions for the oxide stacking faults are as follows. That is, heat at 1200 ° C for 2 hours in an oxygen atmosphere saturated with water at 95 ° C in a quartz tube, take it out, and cool it.
The oxide film was removed in an aqueous solution 1, and then the film was immersed in a Zirtor etching solution for 2 minutes to selectively develop the oxide stacking fault portion. The observation was performed by counting with an optical microscope at a magnification of 10 × 5 for an area of 0.09 cm ² , and converted into a unit per square centimeter. The crystal quality evaluation based on the stacking fault density was based on the maximum value on the sample surface.

Next, Table 1 shows the analytical values of the graphite materials used in Examples 1 to 7 and Comparative Examples 1 to 6.

Iron (Fe), nickel (Ni), chromium (C) in graphite materials
r), vanadium (V), and sulfur (S) were controlled by adjusting the blending ratio of the raw materials or the heating temperature, time, and the graphitization conditions of the atmosphere gas.

Next, in the pulling apparatus equipped with the protective cylinders of Examples 1 to 7 and Comparative Examples 1 to 6 in Table 1, the diameter was 152.4 mm each time.
A (6 inch) single crystal having an n-type resistivity of 1 to 10 Ωcm was pulled up with its pulling direction set to (100), and a silicon single crystal of about 25 kg was obtained from 30 kg of the silicon melt. The production of the silicon single crystal by this pulling was repeated 10 times. As a result, when a product having a maximum density of oxidation-induced stacking faults of 50 / cm ² or less was regarded as a good product, the relationship between the graphite material of the protective cylinder and the good product ratio of the silicon single crystal was obtained as shown in Table 2. .

Comparing the non-defective rate in the pulling examples of the silicon single crystals of Examples 1 to 7 and Comparative Examples 1 to 6, the total metal impurity content, the vanadium content, and the sulfur content affect the non-defective rate of the silicon single crystal. Shows to give.

(G) Effect of the Invention The present invention provides a vanadium content of 2. in the graphite material used in the method for producing a silicon single crystal by the Czochralski method.
5 to 0.30ppm, total metal impurity content 50 to 14.46p
pm and the sulfur content was 1.1 to 2 ppm, so the yield rate of the obtained silicon single crystal products was significantly improved compared to the conventional method of producing silicon single crystals by the Czochralski method using graphite materials. Can be
Moreover, a stable yield rate can be provided.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a schematic cross section of a main part of an example in which the graphite material of the present invention is applied to a conventional Czochralski method silicon single crystal growing apparatus, and is partially omitted. Not not. Regarding the reference numerals, 1 is a single crystal pulling furnace body, 2 is a chamber, 3 is a quartz crucible, 4 is a graphite crucible, 5 is a heater, 6 is a silicon melt, 7 is a single crystal silicon rod, 8 is a protective cylinder, 9
Is the lower end of the protective cylinder, 10 is the silicon melt, 11 is the upper end of the protective cylinder, 12 is the pull chamber, 13 is the inner wall of the pull chamber, 14 is the gas inlet, 15 is a void, 16 is the inner wall of the quartz crucible, 17 is the inner wall of the main chamber, and 18 is the outlet.

Claims (2)

(57) [Claims] 1. A method for producing a silicon single crystal by the Czochralski method, wherein the vanadium content is 2.5 to 0.30 p.
pm, the total metal impurity content is 50 to 14.46 ppm, the sulfur content is 1.1 to 2 ppm using a protective cylinder made of graphite material, the maximum density of oxidation-induced stacking faults is 50 pieces / cm ²
A method for producing a silicon single crystal by the Czochralski method, which comprises producing the following silicon single crystal. 2. The total amount of iron, nickel and chromium in the protective cylinder made of graphite material is 1 to 0.49 pp.
The method for producing a silicon single crystal by the Czochralski method according to claim 1, wherein m is m.