JPH0686353B2 - Seed crystal contact detection method - Google Patents

Description

The present invention relates to a method for growing a semiconductor single crystal by the Czochralski method.

[Conventional Technology] As a conventional technology for growing a compound semiconductor, there is a liquid-encapsulated Czochralski method. In this method, as shown in FIG. 1, a crucible 1 capable of rotating and moving up and down is placed in a pressure vessel 9.
Is used, and a means 2 for heating is provided around it, and an upper shaft 3 which can rotate and move up and down is arranged above the crucible.

The raw material 4 is put into the crucible, and the raw material is melted by a heating device. However, since the raw material contains components such as P and As that are gasified at a low temperature, the sealing material 5 is further placed in the crucible to melt the raw material. The surface of the liquid is covered with this to prevent the composition of the raw material from changing.

A seed crystal 6 is attached to the tip of the upper shaft 3, and the seed crystal 6 is brought into contact with the raw material melt surface adjusted to an appropriate temperature by a thermocouple 7 embedded in the crucible bottom or on the side of the heating device and slowly pulled up. , Grow a single crystal while adjusting the temperature environment for crystal growth.

In the conventional pulling, the contact and separation of the seed crystal 6 of the raw material melt 4 are performed by detecting the change in the resistance value between the seed crystal and the raw material melt, or the change in the electrical property such as the change in capacitance. Alternatively, the operator observes the inside of the furnace and visually judges the appearance or disappearance of the meniscus formed when the seed crystal 6 and the raw material melt 4 come into contact with each other.

[Problems to be Solved by the Invention] Visual contact and separation can be judged by checking the inside of the furnace. When the viewing window becomes dirty and cloudy with volatile components of the raw material melt, or inside the pressure vessel. If it is necessary to close the observation window to maintain the symmetry of the thermal environment, there is a problem that the judgment cannot be made.

Further, in the case of making a judgment of contact or separation by changing the electric characteristics, periodic noise due to the rotation of the seed crystal or the crucible is overlapped with the observed signal, and it may be judged that the signal is observed as it is. This noise needs to be removed because it is difficult. In addition, the electrical characteristics during contact may not be constant because the electrical characteristics such as the resistance value of the crucible used depend on the temperature when the temperature conditions inside the furnace are changed, and the signal level for each operation is reproduced. Since it is difficult to unify the electrical characteristics due to the structure inside the furnace, the reality is that it is difficult to accurately detect contact.

Therefore, in order to make a more accurate contact / separation judgment,
It is necessary to judge by the change rate of this signal level.

However, as mentioned above, it is necessary to perform the smoothing process of the signal in order to calculate the change rate of the signal that originally contains noise.However, the smoothing process slows down the ability to detect the change rate of the signal. , Which may result in malfunction.

If the judgment of contact or separation is not performed properly, the seed crystal varies in the amount immersed in the raw material melt, the initial growth conditions of the grown crystal vary, and finally the crystal shape, It also causes variations in quality.

Therefore, by using the method of extracting a change rate that is strong against noise, by accurately capturing the change in the electrical characteristics between the seed crystal and the raw material melt at the moment when the seed crystal and the raw material melt contact, the seed at the start of growth can be obtained. It is necessary to enhance the reproducibility of the relative positions of the crystal and the raw material melt and to accurately align the environment for starting the crystal growth.

[Means for Solving the Problem] First, the apparatus is provided with means capable of detecting a change in electrical characteristics due to contact and separation between the seed crystal and the crucible. In particular,
As shown in FIG. 2 as an example of the outline of the configuration, an AC voltage device 10 is attached to apply an AC voltage between the mounting axis of the seed crystal and the crucible shaft, and the space between the seed crystal and the raw material melt is attached. An alternating current ammeter 11 is attached to measure the current flowing through.

The current value observed by this ammeter shows a change as shown in FIG. 3 (A) when the seed crystal comes into contact with the raw material melt.

Further, in order to remove the noise of the captured signal and eliminate the artificial variations such as the operator's judgment, the noise removal and contact / separation judgment by the computer are performed.

Although smoothing processing is performed in order to reduce noise, the response of the processed data to the input data is reduced by the processing, so that the signal change becomes dull and the detection capability deteriorates as indicated by 1 in FIG. 3 (B). In order to deal with this, a smoothed value (2 in FIG. 3 (B)) of data past a certain fixed time is used as a reference value.

Specifically, this signal is input to the input 1 as it is, and the other input 2 delays the output of the signal for a certain period of time.
After being input to the computer 14 via 12 or subjected to input delay processing by the computer, the signals of these two systems are each smoothed and the difference U: U = (smoothing processing of input 1) − (input 2 Smoothing treatment), a large positive value is obtained when the seed crystal and the crucible are in contact with each other, and a small negative value is separated when the crucible is in contact, as shown in FIG. 3C, and this value U is a preset threshold value. When U ₀ is exceeded, contact or separation can be judged. Threshold
U ₀ may be set based on the noise level of the smoothed signal.

[Operation] The present method reliably detects the change in the signal by comparing the contact signal of the noisy seed crystal with the smoothed data and the delayed and smoothed data.

[Example] An example of the present invention in pulling a single crystal by the liquid sealed Czochralski method of GaP will be described.

Fill the crucible with GaP polycrystal, heat it with a heating device to melt the raw material, and apply an AC voltage of 13 V between the seed crystal and the crucible to obtain the value of the alternating current between the crucible axis and the seed crystal axis. Was taken into the computer every 10 seconds.

Before the raw material melt and the seed crystal contacted each other, the current flowing between these two points was in the range of 0.30 ± 0.02mA. Here, when the seed crystal was lowered and brought into contact with the raw material melt, the current between these two points increased to 0.34 ± 0.02 mA, and the maximum value of the current before contact and the minimum value of the current after contact were the same. It was a level. When this signal was moving averaged in the range of 5 samples and the difference from the moving average value of the 5 samples in the past 80 seconds was calculated, the change in the value at the time of contact was 0.04 mA, and this change amount was observed continuously for 30 seconds. did it.

Subsequently, when the temperature of the raw material melt was raised to melt the seed crystal and separate from the raw material melt, the current, which was 0.34 ± 0.02 mA at the time of contact, changed to 0.30 ± 0.02 mA. At this time, the change in the calculated value by the computer was −0.04 mA, and it was observed that the value was maintained for 30 seconds.

After that, the raw material melt and the seed crystal were contacted in the same manner, and when the contact with the computer was detected, the crystal growth was started after stopping the descending of the seed crystal and maintaining the temperature for a certain time. There was no possibility that the amount of immersion in the raw material melt was too large, or conversely, the contact with the raw material melt was erroneously judged to stop the drop of the seed crystal before making contact.

[Effects of the Invention] By this signal processing, the amount of change can be extracted with good reproducibility from a noisy signal, and contact of the seed crystal with the raw material can be accurately detected.

By improving the reproducibility of the seed crystal immersion amount in the raw material melt at the start of crystal growth, the reproducibility of the angle of the cone part is improved, and the reproducibility of the shape of the necking part at the start of crystal growth is also improved. Improved.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of a single crystal growth apparatus for a liquid semiconductor Czochralski method of a compound semiconductor, FIG. 2 is a diagram showing an outline of a processing configuration by a signal processing method of the present invention, and FIG. 3 (A).
Is a signal diagram of the contact path between the seed crystal and the raw material melt, 1 in FIG. 3 (B) is the data after the smoothing treatment in FIG. 3 (A), and FIG. 3 (B)
No. 2 is data that is smoothed after delay processing,
FIG. 3C shows signal processing data according to the present invention. 1 ... crucible, 2 ... heating device, 3 ... upper shaft, 4 ... raw material melt, 5 ... liquid sealant, 6 ... seed crystal, 7 ... thermocouple, 8 ... crucible shaft, 9 ... … Pressure vessel 10 …… AC power supply, 11 …… AC ammeter 12 …… Delay device, 13 …… Smoothing device 14 …… Arithmetic device, 15 …… Drive device 16 …… Temperature control device

Claims (1)

[Claims] 1. In single crystal growth by the Czochralski method, an AC voltage is applied between a seed and a raw material melt at the start of crystal growth, and the change with time of the AC current is taken into a computer as electric signal data. The rate of change of the electric signal taken in is calculated from the difference between the smoothed value of the electric signal and the smoothed value of the electric signal through the delay processing, and the contact between the seed result and the raw material melt is detected from the rate of change. A method for detecting the contact of a seed crystal, which is characterized in that