JPH0688865B2 - Doping equipment - Google Patents

Description

TECHNICAL FIELD The present invention relates to a doping apparatus used for a single crystal pulling apparatus by the CZ method, for doping impurities, particularly Sb, into a melt in a crucible.

[Prior Art] When pulling an N-type single crystal for an epitaxial wafer by the CZ method, Sb is generally added as a dopant to the Si melt in the crucible before pulling. Conventionally, for example, a method has been performed in which Sb is put together with polycrystalline Si in a crucible and heated and melted under a low pressure. However, the melting point of Si is 1,410 °
However, since the melting point of Sb is as low as 630 ° C,
Sb dissolves before melting, and Sb evaporates and scatters in the low-pressure furnace, so that doping cannot be performed sufficiently. In order to solve this, a doping device equipped with a thin tube with a diameter of about 3 mm that communicates with the lower part of the Sb holding container is used, and
It has been proposed to lower the doping device by dipping the lower end of the thin tube into the Si melt, and then pouring it into the Si melt while melting Sb with the heat in the furnace (Jikkou 1-7730). Gazette).

[Problems to be solved by the invention] However, in this doping apparatus, it is difficult to completely drop Sb into the Si melt because the heating of the thin tube and the Sb holding container is not uniform, or As a result, Sb was evaporated and the quantitative doping could not be performed. In addition, the doping operation was not easy because the temperature at the upper end of the thin tube had to be equal to the melting point of Sb.

In view of such problems, an object of the present invention is to provide a doping apparatus that can perform accurate and accurate doping and that can be easily doped.

[Means for Solving the Problems] In order to achieve this object, in a doping apparatus according to the present invention, a dope tube having open ends, a suspending wire, and a lower end of the wire are attached to the dope tube. A bottom lid that opens and closes a lower end opening of the dope, a cap attached to an upper end opening of the dope tube, in which a hole through which the wire and an inert gas are formed, and the dope tube or the cap are provided to project. And a locking member for locking the dope tube at a predetermined position above the crucible.

[Operation] While supplying an inert gas, usually Ar gas, into the chamber of the pulling apparatus, the inside of the chamber is decompressed by a vacuum pump to heat and melt the polycrystalline Si in the crucible. Next, close the gate valve, make the sub chamber above the main chamber normal pressure,
The doping device is suspended and an appropriate amount of dopant, for example Sb, is placed in the doping tube.

Next, the inside of the sub chamber is decompressed to the same level as the inside of the main chamber, the gate valve is opened, and the doping apparatus is lowered while supplying Ar gas into the sub chamber. A portion of this inert gas enters the dope tube through the holes in the cap and cools the dopant to keep it in the solid state. When the hooking member comes into contact with a part of the chamber and is hooked, the dope tube stops. In this state, the bottom lid continues to descend, the lower end opening of the dope tube is opened from the peripheral portion, and the dopant drops along the slope of the bottom lid and is poured into the melt.

The pressure in the chamber is adjusted so that one or both of the supply amount and the discharge amount of the inert gas can be adjusted to prevent the scattering of the inert gas during the dropping.

According to the present invention, since it is not necessary to hold the dopant at the position of its melting point, the same doping apparatus can be used regardless of the temperature distribution in the furnace, and the doping operation is easy.

In addition, since the temperature of the dopant can be maintained at a relatively low temperature, it is possible to prevent the evaporation of the dopant before adding the dopant, and therefore, it is possible to add the entire amount of the dopant into the Si melt, and thus it is possible to perform reproducible quantitative analysis. Doping can be done.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings.

(1) First Embodiment FIG. 1 shows a usage state of the doping apparatus.

A sub-chamber 14 is connected to an upper end opening of the main chamber 10 via a gate valve 12, and the gate valve 12 connects the inside of the main chamber 10 with the inside of the sub-chamber 14.
It can be shut off.

In the main chamber 10, a table 18 is fixedly attached to the upper end of an elevating and lowering rotary shaft 16 which can be moved up and down and rotated.
A graphite crucible 20 is placed on top of the graphite crucible
A quartz crucible 22 is fitted in 20. Graphite crucible
The periphery of 20 is surrounded by a heater 24, and the periphery of the heater 24 is surrounded by a graphite heat insulating wall 26. When polycrystalline Si is put in the quartz crucible 22 and electric power is supplied to the heater 24, the Si is melted and becomes a melt 28.

A pulling shaft 30 which is vertically moved along the center line of the sub chamber 14
A seed holder 32 is fixed to the lower end of the seed holder 32, and a pseudo seed 34 is held by the seed holder 32. An upper end of a tungsten wire 36 is connected to the pseudo seed 34, and a doping device 38 is hung on the tungsten wire 36.

As shown in FIG. 3, the doping device 38 includes a cylindrical tube 40a.
And a quartz dope tube 40 including a taper tube 40b welded to the lower end of the quartz dope tube 40. The tapered tube 40b has an upper end opening diameter equal to that of the cylindrical tube 40a, and linearly expands toward the lower end.

On the outer peripheral surface of the upper end of the cylindrical tube 40a, a quartz ring plate 4
2 is welded on its inner peripheral surface. As shown in FIG. 2, on the upper edge of the ring plate 42, a quartz hooking piece 441 protruding radially from the center of the ring plate 42.
~ 443 are conformally arranged and welded. This hook 4
Reference numerals 41 to 443 are for engaging with a ring plate 14a provided at the lower end of the sub chamber 14.

The upper end of the cylindrical tube 40a projects above the ring plate 42, and a Teflon (registered trademark) cap 46 is fitted to the upper end as shown in FIG. As shown in FIG. 4, a hole 46a through which the tungsten wire 36 is passed is formed in the center of the cap 46, and an Ar is formed around the hole 46a.
A plurality of holes 46b are provided for passing the gas into the dope tube 40.

At the lower end of the tungsten wire 36, a quartz bottom cover 48 that opens and closes the lower end opening of the tapered tube 40b is suspended. As shown in FIG. 5, the bottom lid 48 is composed of a hollow cone portion 48a and a solid cone portion 48b fitted to the upper end of the hollow cone portion 48a. At the lower end of the hollow cone 48a, a short cylinder 4
8c is formed. Further, the tungsten wire 36 is provided at the upper end of the hollow cone portion 48a and the center of the solid cone portion 48b.
A hole through which the
A stopper pin 50 is fixed to the lower end of the.

Next, the operation of this embodiment configured as described above will be described.

The inside of the main chamber 10 and the sub chamber 14 is
The pressure is reduced to about 25 to 30 mbar, and electric power is supplied to the heater 24 to melt the polycrystalline Si in the quartz crucible 22.

Next, the gate valve 12 is closed, the inside of the sub-chamber 14 is returned to normal pressure, the pseudo seed 34 is attached to the seed holder 32, and the doping device 38 in which an appropriate amount of Sb51 has been previously put is suspended.

Next, the pressure inside the sub chamber 14 is reduced to the same level as that inside the main chamber 10, the gate valve 12 is opened, and
The pulling shaft 30 is lowered while supplying Ar gas. A part of this Ar gas passes through the hole 46b of the cap 46 and the doping tube 4
It goes into 0 and cools Sb51 and keeps it in the solid state. The locking pieces 441 to 443 are the ring plate 14 at the lower end of the sub chamber 14.
When it comes into contact with a, the doping device 38 is hooked on this ring plate 14a. Even in this state, the pulling shaft 30 continues to descend, the lower end opening of the taper tube 40b is opened from the peripheral edge portion, and Sb51 falls along the slope of the bottom lid 48 and is poured into the melt 28. The pressure in the chamber 10 is adjusted to 10 or 10 by adjusting either or both of the supply amount and the discharge amount of Ar gas.
Hold it at about 0 mbar to prevent it from scattering when Sb51 falls.

The distance between the lower end of the dope tube 40 and the surface of the melt 28 is preferably as short as possible, but under the worst possible conditions, unless Sb51 is held in a solid state until the lower end opening of the tapered tube 40b is opened. Be restricted not to be. The conditions for holding Sb51 in a solid state are the descending speed of the doping device 38, the flow rate of Ar gas, and the main chamber.
It also depends on the pressure within 10.

(2) Experimental Example Next, an experimental example will be described. The experimental conditions are as follows.

Cylindrical tube 40a: Diameter 60 mm, length 250 mm Tapered tube 40b: Bottom diameter 80 mm, length 200 mm Distance between the lower end of the tapered tube 40b and the surface of the melt 28: 150 mm Ar gas flow rate: 40 l / min Many in the crucible 22 Crystal Si charge amount: 18 kg Sb51: 140 g Under the above conditions, 16.5 kg of single crystal Si having a crystal orientation <111> and a diameter of 4 inches was pulled up. When Sb51 was charged for each charge and this was repeated a number of times, there was almost no evaporation and scattering when Sb51 dropped, and no contamination in the main chamber 10 was observed.

When this type of doping apparatus was used to pull up N-type single crystal Si 10 times, the average resistivity of the pulled single crystal Si was 0.
It was 0122 Ωcm, and the resistivity could be within ± 10% from the average value.

(2) Second Embodiment In this second embodiment, as shown in FIG. 6, a hood 52 made of quartz is attached to the lower end of the dope tube 40. Hood 52
The upper end opening of the cone-shaped shoulder portion 52a is welded to the outer peripheral surface of the lower end portion of the dope tube 40, and the upper end of the cylindrical body portion 52b is welded to the lower end of the shoulder portion 52a.

According to the second embodiment, when the lower end opening of the dope tube 40 is opened and Sb51 slides down the slope of the bottom lid 48 and falls, Sb51
Can be prevented from hitting the inner wall of the hood 52 and scattering far away from the center line of the dope tube 40. Further, immediately after the dope tube 40 is opened, the cooling argon gas in the dope tube 40 enters the hood 52, so the temperature condition becomes better than in the case of the first embodiment.

[Effects of the Invention] As described above, according to the doping apparatus of the present invention, since it is not necessary to hold the dopant at the position of its melting point, the same doping apparatus can be used regardless of the temperature distribution in the furnace. , The doping operation becomes easier, and
Since the temperature of the dopant can be kept relatively low, it is possible to prevent the dopant from evaporating before the dopant is added and to add the entire amount of the dopant into the Si melt, and to perform reproducible quantitative doping. It has an excellent effect that it is possible to contribute to improving workability and stabilizing the quality of Si single crystal.

[Brief description of drawings]

1 to 5 show the first part of the doping apparatus according to the present invention.
1 is a schematic vertical sectional view for explaining a use state of a doping apparatus, FIG. 2 is a plan view of the doping apparatus shown in FIG. 1, and FIG. 3 is a front view in which a middle portion of the doping apparatus is omitted. 4 and 5 are plan views of the cap 46 shown in FIG. 1, and FIG. 5 is a longitudinal sectional view of the bottom lid 48 shown in FIG. FIG. 6 is a bottom vertical sectional view of a doping apparatus according to a second embodiment of the present invention. 12 is a gate valve 22 is a quartz crucible 24 is a heater 28 is a melt 30 is a pulling shaft 32 is a seed holder 36 is a tungsten wire 38 is a doping device 40 is a dope tube 42 is a ring plate 441-443 is a hook 48 The lid 52 is a hood

Claims (1)

[Claims] 1. A dope tube (40) having both ends open, a suspending wire (36), a bottom lid (48) to which a lower end of the wire is attached and which opens and closes the lower end opening of the dope tube, A cap (46) attached to the upper end opening of the dope tube and having a hole (46a) through which the wire passes and a hole (46b) through which an inert gas passes, and a cap (46) protruding from the dope tube or the cap. A hooking member (42, for locking the dope tube at a predetermined position above the crucible.
441 to 443), and a doping device.