JPH07291783A - Silicon single crystal and production thereof - Google Patents

Abstract

PURPOSE:To provide a silicon single crystal and production method thereof by which even a FZ silicon having a low oxygen content has enough mechanical strength for the production of a device. CONSTITUTION:(1) This silicon single crystal is produced by a FZ method. The oxygen density in the peripheral part of the crystal is higher than that in the center part. (2) The silicon single crystal is produced by an FZ method by growing a single crystal 1a while a quartz plate 6 is in contact with the edge of the fused part 1b of silicon.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silicon single crystal used as a material for devices and a method for manufacturing the same.

[0002]

2. Description of the Related Art Currently, most of silicon single crystals (about 80%) used as a substrate for devices are directly pulled up from a molten liquid of raw material silicon in a quartz crucible by a rotary pulling method (hereinafter referred to as CZ method). The crystal is grown by means of a floating zone melting method (hereinafter, referred to as FZ method) in which a polycrystalline silicon rod is locally melted without using a quartz crucible and is led to a seed crystal to be a single crystal. Note)).

The most important feature of the FZ method is that the atmosphere gas in the furnace is removed before the silicon single crystal is solidified from the melt.
It is to be grown without contacting any member such as a container. Therefore, the silicon single crystal pulled by the FZ method (hereinafter, referred to as FZ silicon) is characterized by high purity. For example, the oxygen taken in the single crystal has an extremely low concentration as compared with that of a silicon single crystal pulled by the CZ method (hereinafter referred to as CZ silicon). Because of this excellent high purity property,
The resistivity of FZ silicon without addition of a dopant is 50 Ωcm or less in the case of ordinary CZ silicon,
It has a high resistivity of 300 Ωcm or more.

As described above, since FZ silicon has a high resistivity, it is mainly used for high voltage devices of 750 to 1000V.
Manufactured as a substrate for (power device) or infrared sensor.

On the other hand, when a silicon single crystal is processed into a wafer and used as a substrate for a device, a high temperature thermal process is repeated and a thin film is thermally formed on the wafer surface. A large thermal stress is locally applied to. Such thermal stress induces the generation of slip dislocations and warps the wafer surface, thus deteriorating the device characteristics and reducing the manufacturing yield. Further, if the warp of the wafer surface exceeds a certain limit, it will cause a problem in the device manufacturing process. Therefore, when processing a silicon single crystal into a wafer, it is necessary to have a predetermined mechanical strength that can withstand the device characteristics and the device manufacturing process.

Since the mechanical strength of the wafer largely depends on the oxygen concentration in the silicon single crystal, when the FZ silicon is processed into a wafer, the mechanical strength becomes insufficient as compared with the CZ silicon. .

As a means for solving the above problems, FZ
In order to increase the oxygen concentration in silicon, it has been proposed to use a ring-shaped oxygen supply material that is used in contact with the melt zone of a silicon single crystal during crystal growth (see, for example, JP-A-3-247584). ).

However, the use of the proposed oxygen supply increases the oxygen concentration over the entire region of the silicon single crystal, and even though it is FZ silicon, it has a uniform oxygen concentration similar to that of CZ silicon in the crystal. Will have. In other words, although the mechanical strength required for securing the device characteristics and the device manufacturing process can be satisfied, it can be used as a substrate material for power devices and the like that can be realized only by a wafer having high purity and high resistivity. Disappear.

[0009]

SUMMARY OF THE INVENTION An object of the present invention is to provide a silicon single crystal having a mechanical strength required for a device manufacturing process and a method for manufacturing the same even if the oxygen concentration is FZ silicon. To provide.

[0010]

DISCLOSURE OF THE INVENTION The gist of the present invention is a method for producing a silicon single crystal of (1) and a silicon single crystal of (2) below.

(1) A silicon single crystal produced by the FZ method, wherein the oxygen concentration in the peripheral portion is higher than the oxygen concentration in the central portion.

(2) A method for producing a silicon single crystal by the FZ method, wherein the single crystal 1a is grown while the quartz plate 6 is in contact with the end of the melted portion 1b of the silicon single crystal. (2) Method for producing silicon single crystal (see FIG. 1).

[0013]

In the device manufacturing process, normally, the slip dislocations in the silicon single crystal are generated from the peripheral portion of the silicon single crystal, but this peripheral portion of the silicon single crystal is not used as a substrate during device manufacturing. If the present inventor pays attention to this point and manufactures a silicon single crystal in which only the peripheral portion of the silicon single crystal has a high oxygen concentration and the central portion used as a substrate of the device has a low oxygen concentration, a power device It was found that a silicon single crystal that can be used as a substrate of, and that has excellent mechanical strength can be produced. The present invention has been completed based on this finding, and the “silicon single crystal” and the “method for producing a silicon single crystal” of the present invention will be described in detail below.

(1) Silicon Single Crystal The silicon single crystal of the present invention is manufactured by the FZ method. The oxygen concentration in the peripheral portion of the silicon single crystal of the present invention is higher than the oxygen concentration in the central portion.
The oxygen concentration in the central portion is 2.0 × 10 ¹⁶ atoms / cm ³ or less. On the other hand, the oxygen concentration in the peripheral area is 2.0 × 10 ¹⁶ to 1.0
Is a × 10 ¹⁸ atoms / cm ³ or so, more preferably the oxygen concentration is ^{1.0 × 10 17 ~ 1.0 × 10} 18 atoms / cm 3. This is because the mechanical strength of the silicon single crystal containing oxygen at this concentration is dramatically improved.

The peripheral part in the present invention means a region which is not used as a device substrate and its vicinity when processed into a wafer. Therefore, the range of the peripheral portion varies depending on the diameter of the silicon single crystal and the device manufacturing region, and may be set appropriately. For example, the range of the peripheral portion when a silicon single crystal having a diameter of 5 inches (127 mm) is processed into a wafer may be set to a range of 5 to 10 mm from the outer peripheral edge.

The silicon single crystal of the present invention has a high purity in a region where a device is processed by processing it on a wafer, that is, the central portion of the wafer has a resistivity of 300 Ωcm or more, which is used for power devices and infrared sensors. Suitable for substrates. On the other hand, since the oxygen concentration in the peripheral portion of the wafer is high, even if a large thermal stress is applied in the device manufacturing process and a slip dislocation is induced, a large amount of oxygen fixes the movement of the slip dislocation, so that the wafer surface warp Can be prevented and the device characteristics and the manufacturing yield are not reduced.

(2) Method for Manufacturing Silicon Single Crystal FIG. 1 is a diagram for explaining the outline of the process for manufacturing a silicon single crystal using the method of the present invention.

The method for producing a silicon single crystal according to the present invention comprises:
It is based on the Z method. The furnace used for manufacturing does not require a special configuration and may have a furnace structure normally used for the FZ method. Regarding the atmosphere in the furnace, after the inside of the furnace is evacuated, an inert gas atmosphere is created. Next, the tip of the polycrystalline silicon ingot 2 as a raw material is melted by a high-frequency current supplied from a high-frequency oscillator (not shown) to the high-frequency coil 5 to form the melted portion 1b. Next, the melted portion 1b is welded to the seed crystal 7 and the melt is squeezed to produce the squeezed portion 3. Thereafter, while rotating the silicon polycrystal 2 and the narrowed portion 3 in opposite directions and pulling the narrowed portion 3 downward, the silicon single crystal 1a to be manufactured is adjusted to have a predetermined diameter (for example, 5 inches). .

After this adjusting step, the silicon single crystal 1a
Grow. At that time, the quartz plate 6 is replaced with the silicon single crystal 1
A silicon single crystal is grown while being fixed so as to be in contact with a position of about 1 to 5 mm from the end of a.

The quartz plate 6 used is made of SiO ₂ as a raw material, and its shape may be rectangular, circular, elliptical, or the like as long as it does not hinder the contact with the silicon single crystal 1a. . By bringing the quartz plate 6 into contact with it to grow a silicon single crystal, oxygen is introduced from the melted portion of the quartz plate 6 to the end portion of the silicon single crystal, and the end portion has a high oxygen concentration, but the central portion is It is possible to manufacture a silicon single crystal having a low oxygen concentration and a high purity by utilizing the characteristics of the FZ method.

As a method for heating the polycrystalline silicon ingot 2, in addition to the high frequency coil 5 described above, a method using an infrared lamp, a carbon heater, a method using a laser beam, an electron beam or the like can be used. There is no restriction on the heating method in carrying out.

The oxygen concentration at the end of the silicon single crystal can be adjusted by adjusting the rotation speed and pulling down speed of the silicon single crystal 1a.

The silicon single crystal produced by the method of the present invention has a high oxygen concentration at the edges, but has a high purity with a low oxygen concentration at the center. Therefore, when processing a silicon single crystal into a wafer, even if thermal stress is applied during device manufacturing, the slip dislocations generated at the edge of the wafer are fixed and the warp of the wafer surface is prevented. On the other hand, the central portion of the wafer used for device processing has high purity and is suitable for manufacturing power devices.

[0024]

EXAMPLES The method of the present invention will be described in detail based on examples.

The silicon single crystal produced by the method of the present invention is shown in FIG.
It is manufactured by the manufacturing process shown in. As shown in the figure, in the method of the present invention, a high-purity polycrystalline silicon ingot 2 is attached to a crystal supporting jig 4, the inside of the furnace is evacuated, and then argon gas is supplied to supply an inert gas atmosphere of 5 Torr. And After that, a high-frequency current is supplied to a high-frequency coil 5 from a high-frequency oscillator (not shown) to heat the lower end of the polycrystalline silicon ingot 2 to form a molten portion 1b, which is welded to the seed crystal 7. After that, in order to extract the generated slip transition to the surface of the single crystal, the melted portion 1b was squeezed (diameter: about 3 mm, length: about 30 mm). Check.

When the diameter of the silicon single crystal 1a grew to 5 inches, the quartz plate 6 was brought into contact with the fused portion 1b at a position 5 mm from the end thereof. While adjusting the downward moving speed, rotating speed and high frequency power of the polycrystalline silicon ingot 2,
A silicon single crystal 1a having a diameter of 5 inches and an ingot length of 1100 mm was manufactured.

In order to measure the interstitial oxygen concentration (radial distribution) of the manufactured silicon single crystal 1a, the single crystal silicon ingot 1a was sliced to a thickness of 0.6 mm, and then one surface was mirror-polished. Then, the measurement wafer was processed.

FIG. 2 is a diagram showing the radial distribution of the interstitial oxygen concentration of a wafer (diameter 5 inches) manufactured by the method of the present invention. A Fourier transform infrared spectroscope (FT-IR) was used for this measurement, and the interstitial oxygen concentration ([O _i ]) was calculated using the absorption coefficient (α) at 1106 cm ⁻¹ and the conversion coefficient (f). Was calculated as 4.81 × 10 ¹⁷ atoms / cm ³ from the following equation.

[O _i ] = fα ₁₁₀₆ (atoms / cm ³ ) ... (A) As is apparent from FIG. 2, the interstitial oxygen concentration is high at the outer peripheral portion of the wafer, and is about 15 mm from the edge of the wafer. 1.0 × in area
10 ¹⁷ atoms / cm ³ or more, from the center of the wafer
In the region of 40 mm, it is below the detection limit (1.0 × 10 ¹⁶ atoms / cm ³ ).

On the other hand, for comparison, when a silicon single crystal is manufactured, a wafer is prepared from a silicon single crystal grown without contacting the quartz plate 6, and the distribution of interstitial oxygen concentration in this wafer in the radial direction. Was measured. As a result, the concentration of interstitial oxygen was below the detection limit over the entire surface of the wafer.

Next, in order to measure the state of slip dislocations generated on the wafer, the manufactured silicon single crystal is processed into a wafer, washed, and then heat-treated by holding it at a temperature of 1200 ° C. for 1 hour in an oxygen atmosphere. It was However, the loading and unloading of the wafer into and out of the diffusion furnace were carried out for 2 minutes in order to minimize the influence.

FIG. 3 shows the results of measuring the number of occurrence of slip dislocations by the X-ray topography (lang) method. The number of dislocations indicated by ● in FIG. 3 is the measurement result of 25 wafers processed from the silicon single crystal manufactured by the method of the present invention, and the average of the generated slip dislocations was 32 per wafer. . On the other hand, the circles in FIG. 3 indicate the number of slip dislocations generated in the comparative example. In the comparative example, a wafer is processed from a silicon single crystal grown without contacting the quartz plate 6 when manufacturing the silicon single crystal, washed, and then subjected to the same heat treatment. Also in the comparative example, when evaluation was performed using 25 wafers, the average of the slip dislocations generated was 144 per wafer.

Since the silicon single crystal of the present invention contains a high concentration of oxygen in the outer peripheral portion thereof, the number of dislocations generated by the induction of thermal stress can be reduced, and the warp of the wafer during device manufacturing does not occur. . Further, since the silicon single crystal of the present invention has a high purity in a region used as a substrate of a device, it can exhibit excellent performance as a substrate for a power device or the like.

[0034]

The silicon single crystal of the present invention has the mechanical strength required in the device manufacturing process, and can satisfy the high purity required for substrates for power devices and the like. Further, according to the method of the present invention, it is possible to easily manufacture the above silicon single crystal having a high oxygen concentration in the peripheral portion, a low oxygen concentration in the central portion, and a high purity.

[Brief description of drawings]

FIG. 1 is a diagram illustrating an outline of a process for producing a silicon single crystal using the method of the present invention.

FIG. 2 is a wafer manufactured by the method of the present invention (diameter: 5 inches).
FIG. 3 is a diagram showing a distribution state of interstitial oxygen concentration in the radial direction.

FIG. 3 is a diagram showing the results of measuring the number of occurrences of slip dislocations in silicon single crystals of Examples of the present invention and Comparative Examples.

[Explanation of symbols]

1a, silicon single crystal 1b, melting part 2, polycrystalline silicon ingot 3, narrowing part 4, crystal support jig 5, high frequency coil 6, quartz plate 7, seed crystal

Claims (2)

[Claims] 1. A silicon single crystal produced by a floating zone melting method (FZ method), wherein the oxygen concentration in the peripheral portion is higher than the oxygen concentration in the central portion. 2. A method for producing a silicon single crystal by a floating zone melting method (FZ method), wherein the single crystal is grown while a quartz plate is in contact with the end of the silicon melting portion. 1. The method for producing a silicon single crystal according to 1.