JPS5933553B2 - crystal growth equipment - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a crystal growth apparatus using the Czochralski method.

[Technical background of the invention and its problems]

Conventionally, the Czochralski method has been widely used for manufacturing single crystal ingots of silicon and the like.

In this crystal pulling device, polycrystalline silicon and dopants (impurities) as raw materials are placed in a quartz crucible, heated by a heater to form a melt, a seed crystal is brought into contact with this melt, and a pulling shaft is rotated. The seed crystal is gradually pulled up while being rotated, and crystals are grown one after another at the lower end of the seed crystal. However, in the conventional pulling apparatus, the dopant in the melt decreases exponentially as the crystal is pulled, so a single crystal ingot having a constant resistance value in the direction of the pulling axis cannot be produced.

Furthermore, since the polycrystalline silicon is only put into the crucible at the preparation stage of the pulling process, only the raw material equivalent to one pulling process can be melted. This is extremely uneconomical. In order to solve such problems, proposals have already been made to incorporate raw material supply means into the crystal pulling apparatus.

However, this raw material replenishment technology has not yet reached the stage where it can be put to practical use because countermeasures against an insufficient amount of melt in the crucible and countermeasures against accidents in which the melt flows out from the crucible have not yet been resolved. [Object of the Invention] An object of the present invention is to provide a crystal growth apparatus that is equipped with a means for simply and accurately detecting the height of the raw material melt surface and that enables material replenishment with good controllability. .

[Summary of the invention]

The present invention includes means for detecting the melt surface height by installing a current-carrying terminal on the crystal raw material melt in a non-contact state and detecting a change in atmospheric resistance between the current-carrying terminal and the melt.

The atmosphere around the crucible is usually Ar gas, but according to the experiments of the present inventors, a current-carrying terminal is provided on the melt without contact.
It has become clear that when a voltage is applied between the crucible and the opposing electrode, a current flows in the atmosphere, and that this atmospheric resistance increases exponentially as the melt surface height decreases.

Although it is still unclear whether the reason for this is due to the ionic conductivity of the high-temperature gas or some other mechanism, the present invention actively utilizes the knowledge obtained from this experiment. [
[Effects of the Invention] According to the present invention, the height of the crystal raw material melt surface can be detected simply and accurately, and the raw material supply can be continuously performed during crystal growth using the detection result. can.

Furthermore, when the raw material supply is excessive, it is easy to control by detecting this as information on the height of the melt surface and interrupting the raw material supply. In this case, crystal pulling does not need to be interrupted;
The melt in the crucible gradually decreases and returns to a predetermined controlled height. Further, according to the present invention, since the current-carrying terminal is installed without contacting the melt, it is possible to obtain a simple liquid level detection means with excellent durability. Although it is necessary to insulate the current-carrying terminal and its lead wire so that they do not come into contact with the crucible or heater, this can be easily achieved by using an electrically insulated tube. [Embodiment of the Invention] An embodiment of the present invention will be described with reference to the drawings.

The figure shows the schematic configuration of the device. 1 is a quartz crucible, 2 is a silicon melt, 3 is a heater, 4 is a seed crystal, 5 is a pulling shaft,
6 is a crucible axis, and 7 is a pulled silicon crystal.

This basic configuration remains the same as before. A current-carrying terminal 9 protected by a quartz tube 8 is provided above the melt 2 in the crucible 1 . The energizing terminal 9 is led to the outside of the furnace by a lead wire 10 and connected to a DC power source 11. Further, the crucible shaft 6 is grounded by an electric brush or the like, and one end of the DC power supply 11 is connected to a logarithmic operational amplifier 12 to detect the current flowing in the atmosphere between the current-carrying terminal 9 and the melt 2. . A raw material reservoir 13 and a funnel 14 for supplying the raw material to the crucible 1 are provided on the crucible 1. The raw material reservoir 13 is provided with an inclination adjustment mechanism (not shown) using, for example, a solenoid coil, and the inclination of the raw material reservoir 13 is controlled by the output of the operational amplifier 12 to replenish the raw material. The output of the operational amplifier 12 is also connected to a liquid level indicator 15. The operation of crystal growth and raw material supply by this apparatus will be explained next.

First, polycrystalline silicon 200y and dopant boron are placed in a crucible 1 and then melted by a heater 3 to form a silicon melt 2. After attaching the seed crystal 4 to the seed crystal chuck portion of the pulling shaft 5 provided above the crucible 1, the pulling shaft 5 is lowered and the lower end of the seed crystal 4 is placed on the silicon melt inside the crucible 1.
Then, while rotating the pulling shaft 5, the crystal 7 is gradually pulled up to grow the crystal 7 at the lower end of the seed crystal 4. The rotation speed is optimally 6 to 10 revolutions per minute, and the pulling speed is preferably 2 mm per minute. At this time, the crucible shaft 6 is also rotated at the same time, but the crucible shaft 6 is grounded with an electric brush. Before the diameter of the pulled crystal 7 becomes constant, the inclination adjustment mechanism of the raw material reservoir 13 is operated so that granular polycrystalline silicon is continuously introduced into the crucible 1 from the raw material reservoir 13. Then, around the time when the diameter of the pulling crystal 7 becomes constant, the switch of the DC power supply 11 is turned on to apply a DC bias to the energizing terminal 9, the energizing current is amplified by the logarithmic operational amplifier 12, and the output signal is converted to the liquid level. It outputs to the display 15 that displays the height, and at the same time outputs to the solenoid coil of the inclination adjustment mechanism of the raw material reservoir 13. According to experiments, the surface of the melt 2 and the current-carrying terminal 9
When the distance between them is Xc7rL, the resistance R (Ω
/Cnl) is expressed by the following equation. Therefore, according to the embodiment, by detecting the amount of decrease in the melt 2 due to crystal growth and automatically controlling the amount of raw material replenishment, it is possible to stably pull the crystal for a long time.

Moreover, the length of the ingot becomes extremely large due to continuous growth, so the working efficiency is greatly improved. Since additives such as impurities can be prepared and placed in the raw material reservoir 13 in advance, it is possible to arbitrarily correct the exponential impurity concentration change, which was difficult with conventional techniques, and to continuously produce homogeneous crystals. I can do it. As a modification of the present invention, the present invention can be applied not only to a crystal pulling apparatus but also to a semiconductor casting method.

Further, the detection of the melt surface height using the current-carrying terminal of the present invention can be used not only for controlling the supply of raw materials but also for controlling the diameter using the ordinary Czyochralski method.

In this case, it is necessary to install the current-carrying terminal in a non-contact manner near the solid-liquid interface where the rod-shaped ingot comes into contact with the melt. As a result, the degree of mounding of the melt changes in proportion to the change in diameter, and this can be detected.

[Brief explanation of the drawing]

The figure is a schematic diagram of a crystal pulling apparatus according to an embodiment of the present invention. 1... Crucible, 2... Silicon melt,
3... Heater, 4... Seed crystal, 5...
... Pulling shaft, 6 ... Crucible shaft, 7 ...
...pulled crystal, 8...quartz tube, 9...
...Electricity terminal, 11...DC power supply, 12...
... Logarithm, operational amplifier, 13 ... Raw material reservoir, 1
4...funnel, 15...liquid level height indicator.

Claims (1)

[Claims] 1. In an apparatus that forms a crystal raw material melt in a crucible and performs crystal growth by bringing a seed crystal into contact with this melt and pulling it up, a current-carrying terminal is installed on the crystal raw material melt in a non-contact state, and this 1. A crystal growth apparatus comprising means for detecting a level of a crystal stock solution by detecting a change in atmospheric resistance between a current-carrying terminal and a crystal raw material melt.