JPS5932428B2 - Silicon nitride jig for pulling single crystal silicon - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a silicon nitride jig used for pulling columnar or plate-shaped single crystal silicon.

The Czochralski method (CZ method) is known as a method for manufacturing columnar single crystal silicon used to cut out semiconductor wafers.

In this method, a silicon raw material is melted in a crucible, a seed crystal is immersed in the molten silicon, and the seed crystal is pulled up to produce cylindrical single crystal silicon.

In the CZ method described above, a crucible made of quartz glass has conventionally been used.

However, since the quartz glass crucible reacts with molten silicon, reaction products are incorporated into the silicon crystal ingot as oxygen impurities.

Since oxygen impurities in silicon crystal cause crystal defects, they have the disadvantage of deteriorating the characteristics of manufactured integrated circuits.

In addition, as a method for manufacturing plate-shaped single crystal silicon, the EFG method (edge defined film feed g) is used.
rowth method) is known.

This method involves melting a silicon raw material in a crucible, immersing one end of a hollow frame-shaped die in the molten silicon, and immersing a plate-shaped seed crystal in the molten silicon that has risen through the hollow part of the die due to capillary action. This method produces plate-shaped single crystal silicon by pulling the crystal.

In the EFG method described above, a crucible made of quartz glass and a die made of carbon have conventionally been used.

However, quartz glass crucibles have the same drawbacks as the CZ method, and carbon dies tend to react with molten silicon to form silicon carbide, so silicon carbide is trapped in the hollow part of the die. If a thin layer is formed around the periphery, it not only becomes difficult to pull up the silicon crystal, but also causes the disadvantage that the silicon crystal becomes polycrystalline.

Therefore, the present inventors thought of using silicon nitride jigs, such as crucibles and gouers, which are less likely to react with molten silicon, and previously proposed a silicon nitride jig for pulling single crystal silicon in Japanese Patent Application No. 56-70474. Disclosed about the ingredients.

If such a silicon nitride jig is used, in many cases, high-quality single crystal silicon with a low oxygen concentration can be pulled up.

However, it has been found that even when a silicon nitride jig is used, the silicon crystal does not become a single crystal but becomes polycrystalline depending on the properties of the jig.

The present inventors investigated various causes of polycrystallization of silicon crystals, and as a result, discovered the following.

In other words, when a silicon nitride jig has a high iron content, when this jig is used to pull up a silicon crystal, the silicon nitride in the jig dissolves into the molten silicon, and the iron also dissolves and is incorporated into the crystalline silicon ingot. The silicon crystal is then polycrystalized.

Therefore, it may be possible to reduce the iron content of the silicon nitride jig, but even if the iron content is considerably reduced, silicon crystals may become polycrystalline.

This is because there are impurities that promote the dissolution of silicon nitride in the jig into molten silicon, and even if the silicon nitride jig has a low iron content, if these impurities are large, the silicon nitride in the jig will dissolve It is thought that because the amount of iron dissolved in the molten silicon, that is, the amount of iron contained in the jig increases, crystals similar to those with a high iron content are produced.

Therefore, as a result of further research, the present inventors discovered that the impurities that promote the dissolution of silicon nitride in the jig mentioned above into molten silicon are boron or aluminum. Furthermore, by limiting the content of these impurities, we have discovered a silicon nitride jig that can pull up single crystal silicon.

That is, the silicon nitride jig for pulling single crystal silicon of the present invention has a boron content of 3 ppm or less, an aluminum content of 59I)m or less, an iron content of 10 ppm,
It is characterized by being made of crystalline silicon nitride which is under IJ.

The reason why the contents of boron, aluminum and iron are limited to below the above values is as follows.

That is, when the iron content exceeds 10 ppm, more iron is contained in the ingot when pulling the silicon crystal, and the silicon crystal becomes polycrystalline.

Also, if the boron content exceeds 3 ppm or the aluminum content! If it exceeds 5 ppm, the amount of silicon nitride in the jig that dissolves into molten silicon will increase, so even if the iron content is 10 ppm or less, more iron will be included in the ingot when pulling the silicon crystal, and silicon Crystals become polycrystalline.

The present invention will be explained in detail below.

First, five types of crucible-shaped silicon base materials subjected to purification treatment were placed in a CVD reactor, and the inside of the CVD reactor was raised to a predetermined temperature using a heater placed around the outer periphery of the CVD reactor.Next, S+C14 gas and NH3 gas to H2
The gas was supplied into the CVD reactor as a carrier gas.

These gases reacted in the CVD reactor, and crystalline silicon nitride was deposited on the inner surface of each silicon substrate (the outer surface of the silicon substrate was coated, so no silicon nitride was deposited). .

) After a predetermined period of time, the gas supply was stopped.

Subsequently, each silicon base material was removed by exposure to an HCl gas atmosphere to produce five types of silicon nitride crucibles having different contents of boron, aluminum, and iron as shown below.

The crystalline state of the silicon crystal pulled by the CZ method using the obtained silicon nitride crucible is also shown in the table below.

In addition, Comparative Examples 1 to 5 in the above table are silicon nitride crucibles obtained in the same manner as in the above Example except that a silicon base material with a high impurity content was used.

As is clear from the above table, the silicon nitride crucibles of Examples 1 to 5 all have a boron content of 3 ppm or less, an aluminum content of 5 pI)m or less, and an iron content of 10 ppm.
m or less, and all silicon crystals pulled by the CZ method using these acupuncture points were single crystals.

On the other hand, the silicon nitride crucible of Comparative Example 1 has an iron content of 1
Since it exceeds 0 ppm, the silicon crystal becomes polycrystalline.

Further, in Comparative Examples 2 and 3, since the boron content exceeded 3 ppm, the silicon crystal became polycrystalline even though the iron content was less than L Oppm.

Similarly, in Comparative Examples 4 and 5, the aluminum content was 5pp.
Since the iron content exceeds m, the silicon crystal becomes polycrystalline even though the iron content is 10 ppm.

In addition, since the single crystal silicon manufactured using the silicon nitride crucibles of Examples 1 to 5 has a low iron content, the lifetime of minority carriers could be significantly improved.

Furthermore, since the amounts of boron and aluminum mixed into the single crystal silicon from the crucible were small, the resistance value of the single crystal silicon could be well controlled.

In addition, boron content is regulated to 3 ppm or less, aluminum content is 5 ppm or less, and iron content is regulated to 10 ppm or less, and base materials, raw materials, etc. can be refined using these as indicators, so there is no significant cost increase. The above effects could be obtained without performing any ultra-high purification treatment.

As detailed above, according to the present invention, it is possible to provide a silicon nitride jig for pulling single-crystal silicon, which can pull a silicon crystal in a single-crystal state with a long minority carrier lifetime and a well-controlled resistance value. It is.

Claims (1)

[Claims] 1 In the jig used when pulling columnar or plate-shaped single crystal silicon from molten silicon, the boron content is 3 ppm or less and the aluminum content is 5 ppm.
Hereinafter, a silicon nitride jig for pulling single crystal silicon is characterized in that it is made of crystalline silicon nitride with an iron content of 10 ppm or less.