JPH0442890A - Apparatus for growing crystal - Google Patents

Abstract

PURPOSE:To suppress evaporation of oxygen from the surface of a melt layer, enhance the oxygen concentration taken into a single crystal and improve quality of the single crystal by providing a cap made of quartz in contact with the surface of the melt layer in a crucible in growing the single crystal by a melt layer method. CONSTITUTION:A required amount of polycrystal silicon is filled in a crucible 11 and melted from the upper side with a heater 12 to form a melt layer 17. A cap 25 made of quartz is simultaneously provided in contact with the surface of the melt layer 17. A solid layer 18 is then melted while keeping the surface of the melt layer 17 always at the position of the cap 25 by temperature control and position control of the heater 12 and position control of the crucible 11 to control the thickness of the melt layer 17. The lower end of a seed crystal 15 is subsequently dipped in the melt layer 17 to pull up and grow a single crystal 16. Thereby, the single crystal 16 having an oxygen concentration required as a gettering source can be produced.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crystal growth apparatus, and more particularly to an apparatus for growing a crystal such as a silicon single crystal used as a semiconductor material.

There are various methods for growing single crystals, one of which is a pulling method called the Czochralski method (CZ method). FIG. 5 is a schematic vertical cross-sectional view of a crystal growth apparatus used in the conventional pulling method, and 11 in the figure indicates a crucible. The crucible 11 is composed of an inner layer holding container 11a made of quartz and having a cylindrical shape with a bottom, and an outer layer holding container 11b made of graphite and having a cylindrical shape with a bottom fitted on the outside of the inner layer holding container 11a. A resistance heating type heater 12 is arranged in a concentric cylindrical shape on the outside. The crucible 11 is filled with a molten liquid 13 of the raw material melted by the heater 12, and a pulling shaft 14 made of a pulling rod, wire, etc. is disposed on the central axis of the crucible 11. A seed crystal 15 is attached to the tip of the pulling shaft 14, and when growing a single crystal, the seed crystal 15 is brought into contact with the surface of the melt 13 and the pulling shaft 14 is pulled up. A single crystal 16 formed by solidifying the melt 13 is grown.

When growing a semiconductor single crystal using this method, the single crystal 16
The electrical resistivity and electrical conductivity type of the single crystal 16 should be adjusted (impurity elements are often added to the melt 13 before pulling. For this reason, it is said that the added impurities segregate along the crystal growth direction of the single crystal 16. As a result, there was a problem in that a single crystal 16 having uniform electrical characteristics in the direction of crystal growth could not be obtained.

This segregation is determined by the ratio of the impurity concentration at the start of solidification to the impurity concentration at the end of solidification at a certain point in the single crystal, that is, the impurity concentration Cs in the single crystal that occurs at the interface between the melt and the single crystal during solidification. Ratio Cs/Cj to impurity concentration CQ in the liquid
This occurs because the (effective segregation coefficient Ke) is not 1. For example, when Ke<1, as the single crystal 16 grows, the impurity concentration in the melt naturally increases, causing segregation in the single crystal 16.

A method for growing crystals while suppressing the segregation of impurities is a molten layer method. As shown in FIG. 6, the molten layer method uses a crucible 11 constructed similarly to the one shown in FIG.
By melting only the upper part of the raw material inside with the heater 12, the upper part becomes the molten liquid layer 17 and the lower part becomes the solid layer 18, and seeds are added to the molten liquid layer 17 while keeping the impurity concentration in the molten liquid layer 17 constant. In this method, the single crystal 16 is grown by bringing the crystal 15 into contact with each other and pulling up the pulling shaft 14. As methods for keeping the impurity concentration in the molten liquid layer 17 constant, a constant molten layer thickness method and a varying molten layer thickness method have been proposed.

For example, the constant molten layer thickness method is disclosed in Japanese Patent Publication No. 34-8242, Japanese Utility Model Publication No. 61-150862, Japanese Patent Publication No. 62-880, and Japanese Patent Application Publication No. 63-252989. 18 to form a molten liquid layer 17
In this method, the volume of the melt layer 17 is kept constant, and impurities are continuously added during pulling of the single crystal 16, thereby keeping the impurity concentration in the melt layer 17 constant.

In addition, in the molten layer thickness change method, the crucible 11 or the heater 12 is raised and lowered as the single crystal 16 grows, and the molten liquid layer 1 of the crucible 11 is
By changing the volume of 7, impurities can be removed from the single crystal 16.
This is a method of keeping the impurity concentration in the melt layer 17 constant without adding any impurities during the pulling process (Japanese Patent Laid-Open No. 61-2056).
No. 91, JP-A-61-205692, JP-A-61-2
No. 15285).

By the way, in the CZ method, in addition to the above-mentioned impurity elements, the pulled single crystal 16 usually contains 1017 to 1 O
” Contains atoms-cm-3 of oxygen.

Oxygen in the single crystal 16 is essential for increasing the mechanical strength of the wafer and as a gettering source for adsorbing contaminants such as heavy metals. This is supplied by the elution of oxygen. The eluted oxygen then undergoes thermal convection (a), forced convection due to the rotation of the crystal (b), as shown in Figure 7.
It is transported throughout the melt 13 by forced convection (C) caused by the rotation of the crucible 11, Marangoni convection (d) caused by the difference in surface tension, and the like. At this time, the oxygen concentration in the melt 13 can be controlled by convection control by rotating the crucible 11 or crystal rotation, or by applying a magnetic field (Electronic Materials, September 1987).
p, pH 1 to 115), thermal convection and oxygen dissolution by heating control of the heater 12 are performed by controlling the amount of discharge.

However, in the molten layer method, since the solid layer 18 exists at the bottom of the crucible 11, the contact area between the crucible 11 and the molten liquid layer 17 is smaller than in the C2 method, and the pulling single crystal 1
There was a problem in that the concentration of oxygen taken into 6 was low.

Therefore, the mechanical strength is weaker than that of the single crystal 16 formed by the C2 method, and contaminants such as heavy metals are not removed from the device active region of the wafer, reducing the characteristics of the devices formed on the wafer. This was a contributing factor.

The present invention has been made in view of the above-mentioned problems, and provides a crystal growth apparatus that can increase the concentration of oxygen taken into a single crystal and improve the quality of the single crystal in the fused layer method. The purpose is to

To solve the problems, a crystal growth apparatus according to the present invention includes a crucible in which a solid layer and a molten liquid layer are formed, and a heater for melting the solid layer in the crucible. In the crystal growth apparatus, which is arranged around the crucible and has a pulling shaft above the crucible, a cap made of quartz is arranged in contact with the surface of the molten liquid layer in the crucible. It is characterized by a crucible in which a solid layer and a molten liquid layer are formed, and a heater for melting the solid layer in the crucible is disposed around the crucible, and above the crucible there is a The crystal growth apparatus equipped with a shaft is characterized in that an oxygen supply piece is immersed in the melt layer in the crucible.

Normally, oxygen is taken into the single crystal from the melt layer through the following processes (1) to (3).

That is, (1) oxygen is eluted due to the dissolution of quartz at the interface between the molten liquid and the quartz crucible. SiO□→Si+20
1 (2) Oxygen moves within the melt layer due to convection, and (3) oxygen becomes S at the interface between the melt layer and the atmosphere (melt layer surface).
It evaporates as iO (Si+0 → 5iOT) or is incorporated into the single crystal at the interface between the melt and the single crystal (growth interface) (0 (in Melt) - +0 (i
nCrystal)).

According to the above-mentioned apparatus, since the quartz cap is disposed in contact with the surface of the molten liquid layer in the crucible, the quartz in the cap is dissolved in the molten liquid, and the quartz in the process (1) shown above is dissolved. The dissolution of oxygen promotes the elution of oxygen. At the same time, evaporation of oxygen from the surface of the melt layer in process (3) is suppressed. Therefore, the concentration of oxygen contained in the melt layer increases, and the concentration of oxygen in the pulled single crystal increases. Further, when the oxygen supply piece is immersed in the molten liquid layer in the crucible, the quartz of the oxygen supply piece dissolves in the molten liquid, and the oxygen is removed by dissolving the quartz in the process (1) shown above. Elution is promoted and the concentration of oxygen incorporated into the single crystal increases.

Embodiments of the crystal growth apparatus according to the present invention will be described below with reference to the drawings. Note that components having the same functions as those of the conventional example are given the same reference numerals.

FIG. 1 is a cross-sectional view schematically showing an embodiment of a crystal growth apparatus according to the present invention, and numeral 21 in the figure indicates a chamber. The chamber 21 is a vacuum container having a substantially cylindrical shape with its axial direction perpendicular, and the crucible 11 is disposed approximately at the center of the chamber 21 . The crucible 11 is composed of an inner layer holding container 11a made of quartz and having a cylindrical shape with a bottom, and an outer layer holding container 11b made of graphite and also having a cylindrical shape with a bottom and fitted on the outside of the inner layer holding container 11a. A shaft 22 for rotating and raising and lowering the crucible 11 is provided at the bottom of the outer layer holding container 11b of the crucible 11, and on the outer periphery of the crucible 11, a heater 12 composed of a resistance heating type or the like is installed so that it can be raised and lowered. It is arranged. Furthermore, a heat insulating cylinder 23 is provided around the outside of the heater 12, and by adjusting the relative vertical position of the crucible 11 and the heater 12, the molten liquid layer 1 in the crucible 11 is heated.
7. The thickness of each of the solid layers 18 can be adjusted relatively. In addition, a cap 25 made of quartz is disposed in contact with the surface of the melt [17], and the cap 25 has a main body having a substantially annular shape as shown in Fig. 2 fa) and (b). 25a and three supports 25b connected to its periphery at approximately equal intervals. The support body 25b has an inverted cross-section, and the end portion of the support body 25b is fixed to the upper part of the heat retaining cylinder 23, so that the cap 25 is disposed on the surface of the melt layer 17. Note that even if the thicknesses of the molten liquid layer 17 and the solid layer 18 change as the single crystal 16 is pulled, the inside of the crucible 11 can be adjusted by adjusting the relative vertical positions of the crucible 11 and the heater 12 as described above. Since the surface position of the melt layer 17 is constant, the cap 25 is always held in contact with the surface of the melt layer 17.

On the other hand, above the crucible 11, a pulling shaft 14 is vertically installed so as to be rotatable and movable up and down through a small, generally cylindrical pull chamber 24 formed in series with the upper part of the chamber 21, and the lower end of the pulling shaft 14 A seed crystal 15 is removably attached to the holder. After the lower end of the seed crystal 15 is immersed in the melt layer 17, it is rotated and raised to grow the single crystal 16 from the lower end of the seed crystal 15.

When operating the apparatus configured in this way, first, a necessary amount of lump or granular polycrystalline silicon is filled as a solid raw material into the crucible, which is calculated backward from the volume of the single crystal 16 to be pulled. . Next, this solid raw material is melted from above using the heater 12 to form a melt layer 17. Heater 12. After adjusting the position of the crucible 11 and adjusting the thickness of the melt layer 17 to a predetermined thickness, phosphorus is introduced as an impurity and the phosphorus is diffused. Next, the heater 12
The temperature control and position control of the crucible 11 and the position control of the crucible 11 prevent the surface position of the molten liquid layer 17 from moving, that is, the surface of the molten liquid layer 17 is maintained at the position of the cap 25 while the solid layer 18 is melted to control the thickness of the melt layer 17. Then, the lower end of the seed crystal 15 is immersed in the molten liquid layer 17, and pulled up while rotating the pulling shaft 14. At this time, since the cap 25 is always placed in contact with the surface of the melt layer 17, the evaporation of oxygen as SiO from the surface of the melt layer 170 (Si+0-5iOT)
It also acts to promote the dissolution of quartz (SiO2-+Si+20) at the interface between the molten liquid layer 17 and the cap 25 and to elute oxygen. Therefore, melt layer 1
The oxygen concentration in the seed crystal 7 is increased, and from the lower end of the seed crystal 15, a single crystal 16 having an oxygen concentration necessary as a gettering source is grown.
can be grown.

The crucible 11 of the above-mentioned apparatus is filled with 70 kg of raw silicon, and a silicon single crystal 1 with a diameter of 6 cm and a length of about 50 cm is prepared.
6 was pulled up and the oxygen concentration at the center at a crystal length of 20 cm was measured. As a result, the oxygen concentration in the single crystal 16 grown using conventional equipment is about 10'' to 10
” atoms-cm bow, whereas with the above device it was about 1017 to 1019 atoms
-cm-30') Oxygen concentration was obtained. From this, it was confirmed that the above device is effective in increasing the oxygen concentration in the single crystal 16.

FIG. 3 is a cross-sectional view schematically showing another embodiment of the crystal growth apparatus according to the present invention. This point is immersed in the liquid layer 17. As shown in FIGS. 4(a) and 4(b), the oxygen supply piece 30 includes a main body 30a formed into a substantially cylindrical shape in order to obtain symmetry in oxygen distribution;
It is composed of three supports 30b connected to its periphery at approximately equal intervals, and the supports 30b have an inverted cross-section. As in the case of the cap 25, the end of the support body 30b is fixed to the upper part of the heat retaining cylinder 23, so that the oxygen supply piece 30 is held in a state immersed in the molten liquid layer 17.

In this device, similarly to the device shown in FIG. 1, the lower end of the seed crystal 15 is immersed in the molten liquid layer 17 in the crucible 11,
When the pulling shaft 14 is raised while rotating, the quartz oxygen supply piece 30 immersed in the molten liquid layer 17 promotes the dissolution of the quartz (Si02-eSi+20). Therefore, the oxygen concentration in the melt layer 17 is increased, and the seed crystal 1
A single crystal 16 having a desired oxygen concentration can be grown from the lower end of the crystal 5.

Then, the crucible 11 of the above-mentioned device was filled with 70 kg of raw silicon, and the silicon single crystal 16 with a diameter of 6 cm and a length of about 50 cm was pulled up, and the oxygen concentration in the center at a crystal length of 20 cm was measured. Approximately 1 in
It was possible to obtain an oxygen concentration of 017 to 1 O18 atoms -cm-''.

As is clear from the above description, the crystal growth apparatus according to the present invention includes a crucible in which a solid layer and a molten liquid layer are formed, and a heater that melts the solid layer in the crucible. is arranged around the crucible, and a pulling shaft is arranged above the crucible. In the crystal growth apparatus, a cap made of quartz is arranged in contact with the surface of the molten liquid layer in the crucible. Therefore, evaporation of oxygen from the surface of the molten liquid layer can be suppressed, and elution of oxygen due to dissolution of quartz can be promoted. Therefore, the oxygen concentration taken into the single crystal can be increased, and the quality of the single crystal can be improved. Furthermore, it becomes possible to manufacture high-quality elements with good yield.

The present invention also includes a crucible in which a solid layer and a molten liquid layer are formed, a heater for melting the solid layer in the crucible is disposed around the crucible, and a pulling shaft is disposed above the crucible. In a crystal growth apparatus, if an oxygen supply piece is immersed in the molten liquid layer in the crucible, the elution of oxygen due to the dissolution of quartz can be promoted, and the oxygen taken into the single crystal can be accelerated in the same manner as described above. The concentration can be increased.

[Brief explanation of the drawing]

FIG. 1 is a sectional view schematically showing an embodiment of the crystal growth apparatus according to the present invention, FIG. 2(a) is a plan view schematically showing an embodiment of the cap, and FIG. ) is a sectional view taken along line II in FIG. 2(a), FIG. 3 is a sectional view schematically showing another embodiment of the crystal growth apparatus according to the present invention, and FIG.
l is a plan view schematically showing an example of an oxygen supply piece;
Fig. 4 fb) is a cross-sectional view taken along the line II-II in Fig. 4 (al), Fig. 5 and Fig. 6 are cross-sectional views schematically showing an example of a conventional crystal growth apparatus, and Fig. 7 is a It is an explanatory view showing the state of oxygen transport by liquid convection. 1... Crucible 4... Pulling shaft 8... Solid layer 5a... Main body 0... Oxygen supply piece ob... Support body 12... Heater 17... Melt liquid layer 25... Cap 25b... Support body 30a... Main body

Claims (2)

[Claims] (1) A crucible is provided in which a solid layer and a molten liquid layer are formed, a heater for melting the solid layer in the crucible is disposed around the crucible, and a pulling shaft is disposed above the crucible. A crystal growth apparatus characterized in that a cap made of quartz is disposed in contact with the surface of the molten liquid layer in the crucible. (2) A crucible in which a solid layer and a molten liquid layer are formed, a heater for melting the solid layer in the crucible is disposed around the crucible, and a pulling shaft is disposed above the crucible. A crystal growth apparatus characterized in that an oxygen supply piece is immersed in the melt layer in the crucible.