JPH0834698A - Single crystal pulling method - Google Patents

Abstract

(57) [Summary] [Structure] Step A of normal speed and 6 of normal speed
A single crystal pulling method of pulling the single crystal silicon 20 while alternately repeating the pulling step B at a speed of 0% or less. [Effect] Since the temperature of the single crystal silicon 21b, 22b, ... Near which the pulling speed is 60% or less of the normal speed can be maintained within a predetermined temperature range of 1300 ° C. or more for a predetermined time each time, the vicinity of these single crystal silicons can be maintained. It is possible to reduce the number of atomic vacancies in a portion to a predetermined amount or less, and the layer 21 containing a large amount of oxygen precipitates is pulled in the pulled single crystal silicon 20.
, and a small number of layers 21b, 22b, ... Can be formed alternately, and when sliced at the division points 22c, 23c, ..., Oxygen precipitates do not exist in the surface layer portion serving as the active region of the element. A silicon substrate can be formed, and a silicon substrate having excellent oxide film withstand voltage characteristics can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal pulling method, and more specifically, a single crystal pulling method for pulling single crystal silicon for manufacturing a semiconductor substrate by the Czochralski method (hereinafter referred to as CZ method) or the like. Regarding

[0002]

2. Description of the Related Art At present, most of the manufacturing of semiconductor substrates for forming circuit elements such as LSIs is carried out by a rotary pulling method,
That is, single crystal silicon pulled from the silicon melt in the quartz crucible by the CZ method is used. CZ
In the case of the method, quartz (SiO ₂ ) is contained in the silicon melt.
Oxygen generated by melting a part of the crucible exists, and the single crystal silicon pulled up from the silicon melt contains oxygen impurities of about 1 × 10 ¹⁸ atoms / cm ³ .

On the other hand, for example, at 1000 ° C. as a temperature of a typical thermal oxidation process performed in manufacturing an LSI, the solid solubility of oxygen in silicon is about 3 × 10 ¹⁷ atoms /
It is about cm ³ . Therefore, during heat treatment for manufacturing LSI, oxygen contained in the silicon substrate is always in a supersaturated state, and oxygen is likely to precipitate in the silicon substrate.

The function of oxygen in a silicon single crystal is complicated and diverse. When oxygen exists between crystal lattices, it has the effect of fixing dislocations and suppresses the warpage of the silicon substrate that occurs during heat treatment. On the other hand, when oxygen precipitates and changes to SiO ₂ , silicon atoms are released due to volume expansion to form stacking faults, or when the strain is large, minute defects such as punch-out dislocations are formed.

When these minute defects are generated only in the interior sufficiently distant from the surface of the silicon substrate, contaminants such as heavy metals adhering to the surface of the silicon substrate are adsorbed on the surface of the silicon substrate during the LSI manufacturing process. The action of removing from the active region (near the surface of the silicon substrate), that is, the so-called gettering action works, and is useful for manufacturing a high-quality LSI. However, if these minute defects exist in the active region of the device, they cause an increase in leak current, which is harmful to the LSI.

Therefore, as a pretreatment for LSI manufacturing, a defect-free layer (Denuded Zone) is formed on the surface of the silicon substrate, and a defect layer (Intrinsic Getterin) is formed inside the silicon substrate.
g) is being formed. That is, after the pulled single crystal ingot is sliced to manufacture a silicon substrate, the silicon substrate is sliced in a nitrogen atmosphere to, for example, 1
The temperature is heated to about 100 ° C., oxygen near the surface is diffused outward to reduce the oxygen concentration, and then heat treatment is performed at, for example, about 700 ° C. to form a precipitation nucleus of oxygen in the silicon substrate. .

Further, a method has been proposed in which a single crystal is passed through a heater disposed above the crucible and is pulled up while being heated at 900 to 1100 ° C. for 3 hours or more (JP-A-61-2).
No. 01692).

[0008]

In the single crystal silicon pulled by the conventional CZ method, oxygen precipitates stable at high temperature formed during the pulling of the single crystal already exist, and the above-mentioned For example, 11 for forming a defect layer
It is difficult to form a solid solution of the oxygen precipitate in the single crystal by heat treatment at about 00 ° C. As a result, there is a problem in that defects due to the precipitates are likely to exist near the surface of the silicon substrate that becomes the active region of the device, and the withstand voltage characteristic of the oxide film formed on the substrate is poor.

Also in the method of heating the entire single crystal during the above-mentioned single crystal pulling, the heating temperature is 900 to 11
It was as low as 00 ° C., and there was a problem that it was difficult to form a solid solution of the oxygen precipitate.

The present invention has been made in view of the above problems, and it is possible to manufacture a silicon substrate in which a stable oxygen precipitate does not exist at a high temperature in the surface layer portion which is the active region of the device, and the withstand voltage of the oxide film can be manufactured. An object of the present invention is to provide a single crystal pulling method capable of obtaining a silicon substrate having excellent characteristics.

[0011]

In order to achieve the above object, a single crystal pulling method according to the present invention is a single crystal pulling method for pulling a single crystal from a melt in a crucible,
The single crystal is pulled while alternately repeating the pulling process at the normal speed and the pulling process at a speed of 60% or less of the normal speed (1).

The method for pulling a single crystal according to the present invention is
A single crystal pulling method for pulling a single crystal from a melt in a crucible is characterized by pulling a crystal by alternately repeating a pulling step and a pulling stopping step (2).

[0013]

According to the single crystal pulling method (1) of the present invention, the single crystal is pulled by alternately repeating the pulling step at the normal speed and the pulling step at a speed of 60% or less of the normal speed. In the pulling step at a speed of 60% or less of the normal speed, the vicinity of the single crystal can be kept in a predetermined temperature range of 1300 ° C. or higher for a predetermined time each time by heating from a high temperature melt or the like. Therefore, in this step, atomic vacancies contained in supersaturation during solidification of the crystal decrease due to the solid-liquid interface, diffusion to the crystal surface, and recombination with interstitial silicon, and become close to the thermal equilibrium concentration. On the other hand, atomic vacancies are included in supersaturation in the portion of the single crystal pulled at the normal speed. Therefore, in the pulled single crystal ingot,
A layer having a relatively large number of atomic vacancies and a layer having a relatively small number of atomic vacancies are alternately formed at a predetermined pitch along the pull-up axis direction. Then, since the atomic vacancies promote the formation and growth of oxygen precipitates, when the single crystal ingot produced by the method of the present invention is sliced at a predetermined interval in the pulling axial direction, the inside has a relatively small size. While large and stable oxygen precipitates exist at high temperature, a silicon substrate that does not exist in the surface layer that will be the active region of the device will be obtained, and a silicon substrate with excellent oxide film withstand voltage characteristics will be obtained. .

Further, according to the single crystal pulling method (2) of the present invention, the crystal is pulled up while alternately repeating the pulling step and the pulling stop step. It is possible to keep the vicinity of the single crystal in a predetermined temperature range of 1300 ° C. or higher for a predetermined time by heating from 1. Therefore, the same effect as in the case of the single crystal pulling method (1) can be obtained.

[0015]

EXAMPLES AND COMPARATIVE EXAMPLES Examples of the single crystal pulling method according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing an apparatus used in a method for pulling a single crystal according to an example and a single crystal to be pulled.
Reference numeral 1 indicates a chamber. Chamber 11 is container 1
2 and is kept at a low pressure by using a vacuum pump (not shown).
r gas is introduced. Chamber 11
A cylindrical crucible 13 having a bottom is provided at a substantially central portion of the crucible, and the crucible 13 is rotatably supported. A heater 14 is arranged on the outer periphery of the crucible 13 concentrically with the outer periphery of the crucible 13, and a heat retaining cylinder 14 a is arranged on the outer periphery of the heater 14. The crucible 13 is filled with a molten liquid 15 obtained by melting a silicon crystal raw material with a heater 14, and a pulling shaft 16 is arranged on the central axis of the crucible 13. The pulling shaft 16 is adapted to be pulled upward while rotating, and the rotational speed and the pulling speed can be controlled. A seed crystal 16a is attached to the tip of the pulling shaft 16, and the single crystal pulling apparatus 10 is configured including the chamber 11, the crucible 13, the heater 14, the pulling shaft 16 and the like.

In the case of pulling a silicon single crystal using the apparatus 10 thus constructed, first, a silicon raw material is charged into the crucible 13 and the heater 14 melts the silicon raw material to form a molten liquid 15. Next, after the seed crystal 16a is immersed in the melt 15, the crucible 13 and the pulling shaft 16
While rotating, the pulling shaft 16 is pulled up by a predetermined distance M for a predetermined distance M to grow the single crystal silicon 21a. Next, while the crucible 13 and the pulling shaft 16 are being rotated, the pulling shaft 16 is pulled up by a predetermined distance N at a predetermined speed of 60% or less of the normal speed to grow the single crystal silicon 21b, or the pulling is stopped. . Then, the pull-up shaft 16 is pulled up again at a normal predetermined speed for a predetermined distance M to grow the single crystal silicon 22a. Thereafter, the pulling shaft 16 is pulled up by a predetermined distance N at a predetermined speed of 60% or less of the normal speed to grow the single crystal silicon 22b, or the pulling is stopped. Less than,
Similarly, single crystal silicon 23a, 23b, 24a, ...
Are continuously or intermittently pulled to form the single crystal silicon 20.

In the case of forming a silicon substrate from the single crystal silicon 20 thus pulled up, first, the vicinity of the upper portion of the single crystal silicon 20 is cut off, and the thickness is about 2 mm so as to include the central axis along the pulling axis 16 direction. A sample having a substantially triangular shape is cut out, and both surfaces of this sample are mirror-polished. Next, this sample is subjected to a cleaning treatment and then subjected to a heat treatment in an oxygen atmosphere at about 1000 ° C. for about 16 hours. Next, by observing with an X-ray topography, for example, after confirming the positions of the upper and lower end surfaces of the single crystal silicon 22b having a low oxygen content, the substantially middle point is set as a starting point 22c, and a predetermined distance (M
The single crystal silicon 20 is sliced at the divided portions 23c, 24c, ... For each + N). Then, for example, sandwiching single crystal silicon pulled at a normal speed, 60% of the normal speed
A silicon substrate is formed opposite to the single crystal silicon pulled at the following speed.

A single silicon substrate 20 having a diameter of about 6 inches and a length of about 1 m grown by the single crystal pulling method according to the embodiment is used to form a silicon substrate having a thickness of about 0.625 mm. Then, the results of investigating the withstand voltage characteristics of the oxide film formed on the silicon substrate will be described. The normal speed raising step A according to the embodiment and the normal speed 6
The pulling condition in the pulling step B at a speed of 0% or less is usually a constant speed of about 1.0 mm / min, and in Example 1, the pulling distance M in the step A is about 1.09.
The pulling rate in step B was set to 0 mm and the pulling rate in step B was set to zero (the pulling stop time was about 26 seconds). In Example 2, the pulling distance M in the process A is about 0.990.
mm, pulling speed in step B is about 0.3 mm / m
in (the pulling distance N is about 0.1 mm). Further, in Example 3, the pulling distance M in the process A
Is about 0.990 mm, and the pulling rate in step B is about 0.5 mm / min (pulling distance N is about 0.1 mm).
Set to each. In Example 4, the pulling distance M in the step A was set to about 0.990 mm, and the pulling rate in the step B was set to about 0.6 mm / min (the pulling distance N was about 0.1 mm).

As Comparative Example 1, all steps were continuously pulled up at a normal speed of about 1.0 mm / min, and as Comparative Example 2, the pulling distance M in Step A was about 0.990.
mm, pulling speed in step B is about 0.8 mm / m
The one set to in (the pulling distance N is about 0.10 mm) was used.

When the interstitial oxygen concentration in the single crystal silicon thus pulled up was measured by using a Fourier transform infrared spectroscope, it was about 1.5 × 10 5 over the entire length of the crystal.
¹⁸ atoms / cm ³ (conversion factor = 4.81 × 10 ¹⁷ a
toms / cm ² : old ASTM).

Next, silicon substrates were cut out from the single crystal silicon ingots pulled by the methods according to Examples 1 to 4 and Comparative Examples 1 and 2, and one surface of each substrate was mirror-polished to have a thickness of about 0. It was 625 mm. Next, after cleaning each of the silicon substrates, it was placed in a diffusion furnace and subjected to a heat treatment at 950 ° C. in an oxygen atmosphere to form an oxide film having a thickness of 250 Å on the surface of each of the silicon substrates. Next LPC
Using a VD (Low Pressure Chemical Vapor Deposition) device, 20% He-based SiH at about 630 ° C
₄ gas is flowed, and the film thickness is about 400 on each silicon substrate.
A polycrystalline silicon layer as a 0Å electrode was formed. Next, heat treatment was performed at 900 ° C. while flowing POCl ₃ , O ₂ , and N ₂ gas to diffuse phosphorus into the polycrystalline silicon layer, and then an etching solution of HF (50%): H ₂ O = 1: 10. The oxide film formed on the back surface of each silicon substrate was removed by etching. After that, 254 electrode elements made of a polycrystalline silicon layer were formed on each of the silicon substrates by the photolithography technique.

2 to 7 are views showing the in-plane distribution of the oxide film withstand voltage characteristics on the silicon substrate, and FIGS. 2 to 5 are silicon from single crystal silicon pulled by the methods according to Examples 1 to 4, respectively. When a substrate is formed, FIGS. 6 to 7 show cases of the methods according to Comparative Examples 1 and 2, respectively. Note that the breakdown voltage characteristics of the oxide film are considered to be breakdown when a current of 1 mA flows between the electrode elements, and the electric field strength (E _bd ) at that time is 0 to 2 MV / cm, with a black square mark, Two
The evaluation was carried out by expressing x when ˜5 MV / cm, / when 5-8 MV / cm, and □ when 8 MV / cm or more.

As is clear from FIGS. 2 to 7, 8 MV /
In the case of the methods according to Examples 1 to 4, the number of elements that does not break down with an electric field strength of cm is 20 out of 254 elements.
4 elements (80% yield rate), 174 elements (69% yield rate)
%), 160 elements (non-defective rate 63%), and 124 elements (non-defective rate 49%). On the other hand, in the case of the methods according to Comparative Examples 1 and 2, 98 out of 254 elements (non-defective rate 39
%) And 106 elements (non-defective rate 42%).

As is clear from the above results, in the single crystal pulling method according to the embodiment, the single crystal silicon 21b, 22b, which is pulled at a rate of 60% or less of the normal rate, by heating from the high temperature melt 15 or the like, 23b, ... The temperature in the vicinity can be kept in a predetermined temperature range of 1300 ° C. or more for a predetermined time each time, and it is included in supersaturation at the time of crystal solidification due to diffusion to a solid-liquid interface or crystal surface and recombination with interstitial silicon. It is possible to reduce the number of atomic vacancies that are generated and to approach the thermal equilibrium concentration. Therefore, in the pulled single crystal silicon 20, it is possible to alternately form a layer having a relatively large number of atomic vacancies and a layer having a relatively small number of atomic vacancies along the pulling axis 16 direction at a predetermined pitch. Since the atomic vacancies promote the formation and growth of oxygen precipitates, when the single crystal silicon 20 is sliced along the pulling axis 16 direction by 22c, 23c, 24c, ..., The size formed during crystal growth is relatively large. It is possible to form a silicon substrate that has stable oxygen precipitates inside at high temperature and does not exist in the surface layer portion that is the active region of the device, and obtain a silicon substrate with excellent withstand voltage characteristics of the oxide film. it can.

Further, since the pulling step and the pulling stopping step are alternately repeated, the pulling step is performed. Therefore, while pulling is stopped, the single crystal silicon 21b, 22b, ... Therefore, it is possible to obtain substantially the same effect as in the case where the speed is raised alternately by the normal speed and the normal speed of 60% or less.

[0026]

As described above in detail, in the single crystal pulling method (1) according to the present invention, the size is relatively large along the pulling axis direction, and the number of oxygen precipitates stable at high temperature is relatively large. Layers and relatively few layers can be alternately formed at a predetermined pitch, and when this single crystal is sliced at predetermined intervals in the pulling axial direction, oxygen precipitates are present inside, and the active region of the device is formed. It is possible to form a silicon substrate that does not exist in the surface layer portion to be formed, and it is possible to obtain a silicon substrate having excellent withstand voltage characteristics of the oxide film.

Further, in the single crystal pulling method (2) according to the present invention, substantially the same effect as in the single crystal pulling method (1) can be obtained.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing an apparatus used for a single crystal pulling method according to the present invention and a single crystal silicon to be pulled.

FIG. 2 is a diagram showing an in-plane distribution of oxide film withstand voltage characteristics in a silicon substrate using single crystal silicon pulled up by the method according to Example 1.

FIG. 3 is a diagram showing an in-plane distribution of oxide film withstand voltage characteristics in a silicon substrate using single crystal silicon pulled up by the method according to Example 2;

FIG. 4 is a diagram showing an in-plane distribution of oxide film withstand voltage characteristics in a silicon substrate using single crystal silicon pulled up by the method according to Example 3;

FIG. 5 is a diagram showing an in-plane distribution of oxide film withstand voltage characteristics in a silicon substrate using single crystal silicon pulled up by the method according to Example 4;

FIG. 6 is a diagram showing an in-plane distribution of oxide film withstand voltage characteristics in a silicon substrate using single crystal silicon pulled by the method according to Comparative Example 1.

FIG. 7 is a diagram showing an in-plane distribution of oxide film withstand voltage characteristics in a silicon substrate using single crystal silicon pulled by the method according to Comparative Example 2.

[Explanation of symbols]

 13 Crucible 15 Melt Liquid 20 Single Crystal Silicon

Claims (2)

[Claims] 1. In a single crystal pulling method for pulling a single crystal from a melt in a crucible, a crystal is pulled by alternately repeating a pulling step at a normal speed and a pulling step at a speed of 60% or less of the normal speed. A method for pulling a single crystal characterized by the above. 2. A single crystal pulling method for pulling a single crystal from a melt in a crucible, wherein the pulling step and pulling stopping step are repeated alternately to pull the crystal.