JPH03183689A - Device and method for pulling up single crystal - Google Patents

Abstract

PURPOSE:To control the concn. of oxygen contained in single crystal grown from the melt of a raw material and to enhance the yield of single crystal by providing a heater elevating mechanism which elevates a heater for heating the raw material of polycrystal in a crucible. CONSTITUTION:In a device for pulling up single crystal by a Czochralski process, the relative position of the liquid surface of melt Y of a raw material and a heater 6 is controlled as shown in a method described hereunder and the concn. of oxygen contained in single crystal T is controlled. (1) In an initial period for pulling up single crystal, the position of the heater 6 is highly preset for the liquid surface of melt in a crucible 5. The high-temp. part of the heater is opposed to the side face of the crucible 5. The area of the high-temp. part in the inner face of the crucible which touches melt Y is reduced and thereby the amount of SiO2 eluted into the melt is reduced. The concn. of oxygen in single crystal is lowered. (2) In the intermediate period for pulling up single crystal, the position of the heater 6 is lowered in the place lower than the case (1). The utmost part of the temp. of the heater is dislocated to the vicinity of the bottom part of the crucible 5. The amount of SiO2 eluted into the melt is increased. The concn. of oxygen contained in single crystal is enhanced by making oxygen to be easily fetched into single crystal.

Description

Detailed Description of the Invention "Industrial Application Field" The present invention relates to a single crystal pulling apparatus and a pulling method used for producing silicon single crystals for semiconductors, and in particular, to Regarding improvements to control.

"Prior Art" In pulling a silicon single crystal by the Czyoklaski method (CZ method), 5iO1 is eluted from the inner surface of a quartz crucible that holds a silicon melt, and oxygen enters the silicon melt. Most of this oxygen becomes volatile SiO and evaporates from the liquid surface, but some remains in the melt and is incorporated into the single crystal. In addition, the amount of 5iOy eluted from the inner surface of the quartz crucible is
It is proportional to the temperature of the contact surface between the crucible and the melt.

In this case, the temperature of the inner surface and inner bottom surface of the crucible in contact with the melt is high at the initial stage of pulling, and the 5i04
The oxygen concentration in the melt increases due to elution. After that, as the steady state is reached, the amount of oxygen supplied from the melt in contact with the inner surface of the crucible decreases as the single crystal is pulled, and the oxygen concentration in the single crystal decreases. The temperature at the bottom rises and 5iOy from here
The amount of elution increases, and the oxygen concentration in the single crystal increases again.

In particular, in the pulling method that uses the optical diameter control method, it is necessary to always maintain the melt fracture surface at a constant height, and as the crucible is raised as it is pulled, the heating rate of the inner surface and inner bottom of the crucible increases. It changes gradually in the early, middle, and late stages. Therefore, the single crystal obtained by this method has a high oxygen concentration at the head and reaches a steady state with an almost constant oxygen concentration from about 15% solidification rate, and a lower oxygen concentration at the tail in the pulling direction. The concentration gradient will be relatively large.

However, the oxygen concentration in a single crystal is an important factor in device manufacturing, and in particular, in the IG method, which controls the generation of microdefects with oxygen atoms in the single crystal and uses them as a getter source for impurity elements, it is necessary to obtain an appropriate and uniform Since it is essential to create a single crystal with a uniform oxygen concentration distribution, as mentioned above, a single crystal with a large concentration change has only a small portion that can be used as an element, and if the oxygen concentration is regulated within a certain narrow range, the head This method had the disadvantage that the amount of truncation was large, resulting in poor yield.

For this reason, a single crystal pulling apparatus has also been proposed in which the heater arranged around the crucible is divided into multiple stages in the vertical direction and the amount of electricity supplied to each of these divided heaters can be adjusted according to the progress of pulling.

``Problem to be solved by the invention'' However, in reality, with the above-mentioned single crystal pulling apparatus, the oxygen concentration in the melt fluctuates greatly, making it difficult to adjust the concentration steplessly and accurately, and the operation is labor-intensive, resulting in poor productivity. It had drawbacks such as low

Therefore, the present inventors investigated in detail the correlation between the temperature distribution of the heater, the crucible position, and the oxygen concentration, and as a result, by adjusting the relative position between the liquid level of the raw material melt and the heater, the following It was discovered that the oxygen concentration in the single crystal from the raw material melt could be controlled as shown in the figure.

■ At the beginning of the second stage, the position of the heater with respect to the surface of the raw material melt in the crucible is set higher than before, and the high ijA part of the heater is opposed to the side surface of the crucible, so that the area of the high-temperature part of the inner surface of the crucible in contact with the melt is reduced. If it is decreased, the amount of Sin eluted into the melt will be reduced, oxygen will be difficult to be incorporated into the single crystal, and the oxygen concentration in the single crystal will be reduced.

■ During the middle stage of lifting, lower the heater position than in the case of ■.
By shifting the highest temperature part of the heater to the side closer to the bottom of the crucible, the area of the high-temperature part of the inner surface of the crucible that comes into contact with the melt increases, and the amount of SiO eluted into the melt increases.
Oxygen is more easily incorporated into the single crystal, increasing the oxygen concentration in the single crystal.

The present invention has been made based on the above findings, and is a single crystal pulling device that can be commercialized with a low initial oxygen concentration and a high mid-term oxygen concentration, with a reduction rate of about 5%, and that can improve the yield of single crystals. The objective is to provide a lifting method.

"Means for Solving the Problems" Hereinafter, a single crystal pulling apparatus and a single crystal pulling method according to the present invention will be specifically explained.

FIG. 1 is a longitudinal sectional view showing an embodiment of a single crystal pulling apparatus used in the present invention.

Reference numeral l in the figure indicates a furnace body installed on the floor via a pedestal (not shown), and a lower shaft 2 vertically penetrates the bottom plate part IA of the furnace body 1 in the center of the interior of the furnace body 1. It is provided. The lower end 2A of the lower shaft 2 is connected to an elevating and rotating mechanism (not shown), and an expandable bellows 3 is hooked between the lower end 2A and the bottom plate part IA, so that the gap between the bottom plate part IA and the lower shaft 2 is Hermetically sealed.

A quartz crucible 5 is coaxially fixed to the upper end of the lower shaft 2 via a susceptor 4 made of graphite or the like, and a cylindrical heater 6 is coaxially arranged around the susceptor 4.
J-l+ l-Jw/! ? Ti
n mouth Jw y kjikh ++ ml r
rz 10 onsen 7 are provided. Further, a pulling mechanism (as shown) is provided in the upper part of the furnace body l, and a seed crystal 10 fixed to the lower end of the wire 8 via a holder 9 is melted.
The single crystal T is immersed in Y and pulled up.

The heater 6 is made of a resistor such as graphite, has a vertical length longer than the susceptor 4, and has a pair of electrode rods 11 fixed downwardly to its lower end. As shown in FIGS. 2 and 3, the heat generation distribution of the heater 6 has a semicircular shape in which the temperature is low at the upper and lower ends and high at the center.

Each electrode rod 11 passes through the bottom plate part IA and is fixed to the upper surface of a lifting plate 12 horizontally arranged below the bottom plate part IA,
Connected to the power supply (as shown). In addition, a bellows 13 that can be expanded and contracted is provided between the elevating plate 12 and the bottom plate part IA, surrounding each electrode rod 11, so that the gap between each electrode rod 11 and the bottom plate part IA is hermetically sealed. has been done.

A plurality of guide rods 15 that slidably penetrate the elevating plate 12 are vertically fixed between the lower surface of the bottom plate part IA and a base 14 installed on the floor surface, and are formed on the elevating plate 12. A screw rod 17, which is screwed into a female threaded hole 16, extends vertically so as to be rotatable about an axis. And the screw rod! 7 is a motor 18 fixed to the base 14;
The elevating plate 12 and the heater 6 move up and down accordingly.

The furnace body 1 is also equipped with an optical liquid level position sensor and an automatic diameter control sensor (both shown in the figure), and based on electrical signals from these sensors, the melt level in the crucible 5 changes as the single crystal T is pulled up. In addition to always maintaining a constant height, the growth rate of the single crystal T by a pulling mechanism is feedback-controlled to obtain a constant diameter.

According to the single crystal pulling apparatus having the above configuration, the heater 6 can be raised or lowered at an arbitrary speed without impairing the airtightness of the furnace body 1 or disturbing the flow of Ar gas within the furnace and body 1. be able to.

Next, a method for pulling a single crystal using the above-mentioned apparatus will be explained.

A feature of the single crystal pulling method according to the present invention is that the position of the heater 6 is determined according to the desired oxygen concentration, as shown in a and b below.

a. To reduce the oxygen concentration in the single crystal T, raise the heater 6 as shown in FIG. 7
Set to the center of the surface. As a result, the temperature of the inner surface of the crucible that comes into contact with the melt Y, especially the inner bottom surface, decreases relatively, and the area of the high-temperature part of the inner surface that comes into contact with the melt Y decreases, reducing the amount of S r O eluted into the melt. decreases, and the concentration of oxygen taken into the single crystal T decreases.

b. On the other hand, in order to increase the oxygen concentration contained in the single crystal T, the heater 6 is lowered as shown in FIG. 3 so that the highest temperature point of the heater 6 faces the bottom of the susceptor 4. As a result, the temperature of the inner bottom surface of the crucible 5 becomes relatively high,
The area of the high-temperature part of the inner surface that comes into contact with the melt Y expands, and SiO! The amount of elution increases, the oxygen concentration in the melt Y increases, and the oxygen concentration in the single crystal T increases.

To give a specific example, the oxygen concentration is about the same as that of regular products (1, 5
In order to obtain a longitudinally uniform single crystal with a density of ~1.7 x 10 ''atoms/C1), the heater 6 is turned off as shown in Fig. 2 at the initial stage of pulling when the oxygen concentration is high in the normal pulling method. It is positioned higher than in the conventional method, and the highest temperature point of the heater 6 is opposed to the side surface of the crucible 5 that is in contact with the melt, and the shoulder T1 of the single crystal is formed while heating. Reduces oxygen concentration.

Next, when the formation of the shoulder part of the single crystal T is completed and the formation of the straight body part begins (the position of the melt surface is always kept constant by the upward movement of the crucible 5), the motor 18 is activated to move the screw rod. 17, the elevating plate 12 and the heater 6 are gradually lowered at a constant speed so that the highest temperature point is at the bottom of the raw material melt Y in the crucible 5. This offsets the decrease in oxygen concentration due to the growth of the straight body, reaching a nearly constant oxygen concentration early in the pulling process, and thereafter maintaining a gradual decreasing trend in oxygen concentration due to the decrease in the crucible wall surface of the melt. can do.

Note that the optimum moving amount and moving speed of the heater 6 should be determined experimentally because they vary depending on the dimensions of each part, the temperature distribution of the heater 6, the desired oxygen concentration, etc.

On the other hand, depending on the use of single crystal T, the oxygen concentration may be lower than usual (1.2 to 1.4 x 10" atoms).
/cm3), but in that case, the heater 6 is set at a high position at the beginning of the pulling process, and then the heater 6 is further raised at a constant speed as the lifting process progresses. Thereby, the temperature of the contact surface between the crucible wall surface and the bottom surface of the melt Y can be lowered, and a single crystal with a small oxygen concentration in a steady state can be obtained.

Note that the present invention can be used not only for the purpose of making the oxygen concentration in the single crystal uniform in the longitudinal direction, but also for the purpose of increasing the gradient of the oxygen concentration.

"Experiment example" Next, the effects of the present invention will be demonstrated by giving experimental examples.

(Experiment Example 1) In the equipment configuration shown in Fig. 1, 30 kg of silicon raw material was filled into a quartz crucible with a diameter of 14 inches, and the furnace internal pressure was 25 Torr%, and the Ar gas flow rate (converted to normal pressure) was 30Q/min. A single crystal was pulled.

Note that the crucible was gradually raised from the start to the end of pulling, and the melt surface position was always kept constant.

The upper ends of the heater and the susceptor were aligned from the time of soaking the seed crystal until the shoulder of the single crystal was grown.

Next, the growth of the straight body part with a diameter of 1105x was started, and the heater was started to be lowered, and the heater was lowered by 401111 times while the straight body part was growing to 100x* (solidification rate 7%). After that, keep the heater off and run the entire length! A 300μ silicon single crystal was pulled.

(Comparative Example 1) Using the same apparatus as in Experimental Example 1, the upper end of the heater was set 50 x m below the upper end of the susceptor at the time of growing the shoulder of the single crystal from dipping the seed crystal, and was fixed at this position until the pulling was completed. . Other conditions were the same as in Experimental Example I, and the total length was l.
A 300μ silicon single crystal was pulled.

FIG. 3 shows the results of measuring the oxygen concentration distribution for the single crystals obtained in Experimental Example 1 and Comparative Example. Experimental example! In comparison with Comparative Example 1, the oxygen concentration at the head was reduced and averaged out. As a result, the range of oxygen concentration was narrowed by about 30% compared to the single crystal obtained in the comparative example.

(Experimental example 2) Under the same conditions as experimental example 1, 1000 JIx (solidification rate 7
After the single crystal was grown to a length of 0%), at this point the heater was started to descend again and was further lowered by 40ix until it reached 1300 zm, yielding a single crystal with a total length of 1300 cm.

FIG. 4 is a graph comparing the oxygen concentration distributions of Experimental Example 2 and Comparative Example 1. In Experimental Example 2, as compared to Experimental Example 1, a decrease in oxygen concentration in the stationary region was prevented and further uniformity was achieved.

(Experimental Example 3) A single crystal with a low oxygen concentration was produced. Using the same apparatus as in Experimental Example 1, the upper ends of the heater and susceptor were made to coincide with each other at the time when the shoulder of the single crystal was grown from immersion of the seed crystal.

Next, the growth of a straight body portion having a diameter of 105zz was started, and the heater was started to rise, and while the straight body portion was growing by 100yi (solidification rate: 9%), the heater was raised 30xx at a constant speed. Thereafter, a silicon single crystal with a total length of 1,100 Ox was pulled while the heater was stopped. Other conditions are Experimental Example 1
I did the same thing.

(Comparative Example 2) Using the same equipment and conditions as in Experimental Example 3, the top end of the heater was set 25jIjI below the top end of the susceptor from the immersion of the seed crystal to the point where the shoulder of the single crystal was grown, and the top end of the heater was kept at this level until the pulling was completed. A silicon single crystal with a total length of 1000 cm and a straight body portion with a diameter of 105xx was pulled up while being fixed at a certain position.

FIG. 6 is a graph showing the results of Experimental Example 3 and Comparative Example 2. The single crystal obtained in Experimental Example 3 had a low oxygen concentration over its entire length, and the range of oxygen concentration was about 30% compared to Comparative Example 2.
Narrowed down.

"Effects of the Invention" As explained above, according to the single crystal pulling apparatus and the pulling method according to the present invention, when lowering the oxygen concentration in the single crystal, the highest temperature part of the heater is set to the side surface of the crucible. By reducing the area of the high-temperature portion of the inner surface of the crucible, the amount of 5iO7 eluted into the melt is reduced, and the amount of oxygen incorporated into the single crystal is reduced.

On the other hand, when increasing the oxygen concentration in the single crystal, iZ
Compared to case J, the highest temperature part of the heater is moved closer to the bottom of the crucible, increasing the area of the high-temperature part of the inner surface of the crucible that comes into contact with the melt, and reducing the amount of SiO into the melt.
The elution amount of x is increased, and the amount of oxygen taken into the single crystal is increased.

Therefore, according to the apparatus and method of the present invention, it is possible to accurately control the oxygen concentration in a single crystal, and it is possible to improve the productivity of a single crystal having a desired oxygen concentration.

[Brief explanation of drawings]

FIG. 1 is a longitudinal cross-sectional view showing an embodiment of a single crystal pulling device according to the present invention, and FIGS.
4 to 6 are graphs showing the results of experimental examples of the present invention. 1... Furnace body, 2... Lower shaft, 3... Bellows, 4...
・Susceptor, 5... Crucible, 6... Heater, 7...
・Heating cylinder, 8... Pulling wire, IO... Seed crystal, 11... Electrode rod,! 2... Elevating plate, 13...
-Bellows, 15...Guide rod, 17...Screw rod (essential part of heater lifting mechanism), 18...Motor, 19...Recelerator, T-Single crystal, Y...Melten liquid.

Claims (2)

[Claims] (1) A crucible fixed via a susceptor to the upper end of a lower shaft that is operated to move up and down and rotate, a heater placed around the crucible to heat the polycrystalline raw material in the crucible, and a heater that heats the raw material melt in the crucible. What is claimed is: 1. A single crystal pulling apparatus comprising a pulling mechanism for immersing a seed crystal and pulling the single crystal, comprising: a heater lifting mechanism for lifting and lowering the heater. (2) Single crystal pulling by heating the polycrystalline raw material held in the crucible with a heater placed around the crucible to generate a raw material melt, and growing a single crystal by immersing a seed crystal in this raw material melt. In the method, a. When decreasing the oxygen concentration in the single crystal, the highest temperature part of the heater is opposed to the side surface of the crucible; b. When increasing the oxygen concentration in the single crystal, the above step a.
A single crystal pulling method characterized by shifting the highest temperature part of the heater to a side closer to the bottom of the crucible than in the case of.