JPS5950626B2 - Container for pulling silicon single crystals - Google Patents

Description

[Detailed description of the invention] The present invention relates to a container for pulling silicon single crystals.

The CZ method is generally known as a method for manufacturing silicon single crystals used as wafers and the like for semiconductor devices.

Among these, the CZ method is a method in which silicon is melted in a container (such as a crucible), and a cylindrical silicon single crystal is pulled up while rotating it using a seed crystal.

A silicon melting container used in such a CZ method has conventionally been made of quartz glass.

However, if the container is made of quartz glass, silicon will react with the quartz glass even at the melting temperature of silicon, and oxygen components will be incorporated into the molten silicon, resulting in a solid solution of approximately 2 x 101018ato/m in the crystallized silicon. Inevitable.

When oxygen is dissolved in silicon in this way, it becomes the nucleus of various crystal defects and deteriorates the crystallinity of the silicon single crystal. Therefore, when a semiconductor device is manufactured by processing this, the electrical characteristics of the silicon are significantly deteriorated. deteriorate.

On the other hand, as a result of intensive research by the present inventors in order to overcome the above-mentioned drawbacks, we focused on the fact that silicon nitride does not easily react with silicon. The container was made of silicon.

However, the reactive sintering method uses a binder such as polyvinyl alcohol, while the hot pressing method uses MgO, AIN,
Since sintering accelerators such as Y2O3 are used, these are mixed into silicon nitride as impurities.

Therefore, it has been found that when silicon is melted in a container made of silicon nitride and a silicon single crystal is pulled, the impurities in the silicon nitride dissolve into the silicon single crystal and significantly deteriorate its crystallinity. .

As a result of studies based on the above knowledge, the inventors of the present invention focused on the fact that silicon nitride produced by the CVD method has high purity and high density. A container was constructed by coating the body (base material).

However, if this container is used to pull a silicon single crystal, the high purity of the silicon nitride film will be impaired due to the diffusion of impurities in the silicon nitride sintered body, and impurities will be mixed into the molten silicon from the container. It was discovered that this resulted in a fatal drawback of reducing the purity of the resulting silicon single crystal.

Therefore, the present inventors conducted further studies based on the above investigation results, and noticed that among the impurities in the silicon nitride sintered body, Fe and Cu have high diffusivity. If the Fe content is 250
Using a silicon nitride sintered body whose Cu content is regulated to 50 ppm or less, and whose porosity is regulated to a predetermined range,
It has been found that by coating this with a silicon nitride film deposited from the gas phase to form a container, it is possible to prevent impurities from entering the molten silicon due to impurities of silicon nitride.

As a result, unlike when using a conventional silica glass crucible, solid solution of oxygen can be prevented, resulting in high purity and an oxygen concentration of 2.
It was possible to pull a good silicon single crystal with a very low X of 101016ato/ClTl3 or less.

Moreover, since the silicon nitride film is made of a base material, it does not peel off due to thermal shock.

In other words, the present invention does not particularly purify the silicon nitride sintered body, but takes into consideration diffusion into the silicon nitride film, and at least Fe
By regulating the content limit of impurities of Cu and Cu, we have achieved a container for pulling silicon single crystals that has the above-mentioned effects at a relatively low cost without incurring the high costs associated with ultra-high purification processing. It is.

That is, the present invention provides FFe in a container used for pulling a silicon single crystal from molten silicon using a seed crystal.
250pp or less, Cu50ppm or less, porosity 10-4
The structure is characterized in that a 0% silicon nitride sintered body is used as a base material, and at least the surface in contact with molten silicon is coated with a silicon nitride film deposited from the gas phase.

The reason why the content of Fe and Cu in the silicon nitride sintered body in the present invention is limited to the above range is because of these Fe.

This is because when Cu exceeds 250 ppm and soppm, respectively, the purity of the silicon nitride film coated by these diffusions deteriorates, and the purity of the silicon single crystal obtained by these impurities during pulling of the silicon single crystal decreases.

The reason why the porosity of the silicon nitride sintered body in the present invention is limited to the above range is that when the porosity is less than 10%, the adhesion of the silicon nitride film deposited from the gas phase to the sintered body decreases. On the other hand, if the porosity exceeds 40%, the quality of the silicon nitride film deposited from the gas phase becomes rough and pinholes are likely to occur. It is from.

The thickness of the silicon nitride film in the present invention is preferably 5 μm or more.

The reason for this is that if the film thickness is less than 5 μm, pinholes are likely to occur locally, and molten silicon may invade the silicon nitride body during pulling of the silicon single crystal, leading to a decrease in purity.

Next, the present invention will be explained in detail.

Example First, polysilicon for semiconductors was pulverized, polyvinyl alcohol was added as a binder to the silicon powder, and the mixture was molded and then nitrided at 1400° C. for 5 hours in a nitrogen atmosphere.

(Crucible No. 1. 2) This is further heated to 1400℃
Purification treatment was performed in C12 gas.

(Crucible No., 3.4s 5) These are the five types of silicon nitride sintered bodies (substrates) with purity and porosity shown in the table below.

Next, these base materials were introduced into a vapor deposition furnace, and SIC14 gas was supplied at 260 cc/min and H2 gas was supplied at 2000 cc/min.
A silicon nitride film with a thickness of 80 to 130 μm was deposited on the entire surface of the substrate using the CVD method under a temperature condition of 1380° C. while supplying NH3 gas at a rate of 80 cc/min and maintaining 20 TOrr. We built a crucible for pulling silicon single crystals.

The resulting crucibles are used to melt silicon, and the seed crystal is pulled up while rotating from the liquid surface of the molten silicon to pull up the silicon single crystal. The concentration, crystal state, etc. were investigated.

The results are also listed in the same table.

As is clear from the above table, crucibles (No. 1. When using 2), impurities in the molten silicon increase due to impurity diffusion into the silicon nitride film coated on the base material, and the pulled silicon becomes polycrystalline instead of single crystal. Ta.

Furthermore, even if a silicon nitride sintered body whose content of Fe and Cu is below the specified value is used, a crucible (No. ,
When 4') was used, the silicon nitride film peeled off during silicon pulling, making it difficult to pull a predetermined silicon single crystal.

On the other hand, the crucible of the present invention (No. 3゜5) is made of a silicon nitride sintered body in which the content of both Fe and Cu is below the specified value and the porosity is in the range of 10 to 40%. When using , the silicon nitride film coated on the base material does not peel off,
Moreover, by maintaining a predetermined level of high purity, it was possible to suppress the incorporation of impurities into the molten silicon, and it was possible to pull high quality silicon single crystals.

Moreover, the amount of oxygen in the silicon single crystal pulled using the crucible of the present invention (No. 3.5) is 2 x 10101
6ato/CI+13, which is higher than that in a silicon single crystal obtained using a conventional quartz glass crucible (I x 10
1018ato/ClTl3), it was possible to significantly reduce the oxygen concentration.

As described in detail above, according to the present invention, it is possible to pull a silicon single crystal with high purity and a very low oxygen concentration of 2×101016 atO/cm3 or less, and also with excellent electrical properties. It is possible to provide a container for pulling silicon single crystals that has remarkable effects such as being able to obtain silicon single crystals that are effective for wafers and the like suitable for manufacturing semiconductor devices.

Claims (1)

[Claims] 1. In a container used for pulling a silicon single crystal from molten silicon using a seed crystal, the porosity is 1 when FFe is 250 ppm or less and Cu is 50 ppm or less.
A container for pulling a silicon single crystal, characterized in that it has a structure in which a silicon nitride sintered body containing 0 to 40% is used as a base material, and at least the surface in contact with molten silicon is coated with a silicon nitride film deposited from a gas phase.