JPH08290995A - Silicon single crystal and its production - Google Patents

Abstract

PURPOSE: To obtain a silicon single crystal containing prescribed amounts of oxygen and carbon and giving a substrate having high IG capacity and a defect- free layer with high completeness by charging an Si raw material and carbon into a crucible and growing a single crystal under specific condition. CONSTITUTION: A crucible 1 is charged with a silicon raw material and 5.7-96.1×10<-7> pts.wt. (based on 1 pt.wt. of the silicon raw material) of carbon. The crucible is heated with a heater 2 to completely melt the silicon raw material in the crucible 1 and form a molten liquid raw material layer 6a and the lower part of the crucible 1 is cooled to form a solid raw material layer 6b at the lower part in the crucible. A seed crystal 4 is brought into contact with the molten liquid layer 6a. A silicon single crystal 3 containing 5×10<17> to 1.3×10<18> atoms/cm<3> of oxygen and 4.8×10<15> to 8.5×10<16> atoms/cm<3> of carbon is pulled up from the molten liquid layer 6a while melting the solid layer 6b from the top downward and controlling the rotational speeds of a pull-up shaft 5 and the crucible 1, the pull-up speed, etc.

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 and a method for manufacturing the same, and more particularly to a silicon single crystal used as a semiconductor material and a method for manufacturing the same.

[0002]

2. Description of the Related Art At present, most of semiconductor substrates (silicon substrates) for forming circuit elements such as LSIs are pulled from a silicon melt in a quartz crucible by a rotary pulling method, that is, a CZ method. Single crystal silicon is used. In the case of the CZ method, oxygen generated by the dissolution of a part of the quartz (SiO ₂ ) crucible is present in the silicon melt, and the single crystal silicon pulled from this silicon melt has about 1.5 × 10 ¹⁸ atoms / cm ³
It contains some oxygen impurities.

On the other hand, for example, at 1000 ° C. which is a temperature of a typical thermal oxidation process performed at the time of manufacturing an LSI, the solid solubility of oxygen in silicon is about 3.0 × 10 ¹⁷ atom.
It is about s / 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 (in the vicinity of the surface of the silicon substrate), that is, the so-called intrinsic gettering action works, and is useful for manufacturing a high quality LSI. However, if these minute defects are present in the active region of the element, they cause deterioration of the oxide film withstand voltage characteristic, increase of leakage current in the PN junction, and the like, and are harmful to the LSI.

Therefore, as a pretreatment for LSI manufacturing, a defect-free layer (Denuded Zone, hereinafter referred to as a DZ layer) is formed on the surface of the silicon substrate, and a defect layer (Intr) is formed inside the silicon substrate.
Insic Gettering, hereinafter referred to as IG layer) is performed. That is, after the pulled silicon single crystal ingot is sliced to produce a silicon substrate, the silicon substrate is sliced in a nitrogen atmosphere to, for example, 1100.
A treatment of heating to about 0 ° C. to diffuse oxygen in the vicinity of the surface outward to reduce the oxygen concentration and then performing heat treatment at, for example, about 700 ° C. to form oxygen precipitation nuclei in the silicon substrate is performed. .

[0007]

However, in recent years, the demand for the integrity of the DZ layer formed on the surface of the silicon substrate has become more stringent than ever before with the high integration and high functionality of LSIs. There is an urgent need to further improve the integrity of the DZ layer. Therefore, it is considered that the oxygen concentration in the silicon single crystal is reduced to reduce oxygen precipitates generated near the surface of the silicon substrate and secondary defects such as stacking faults and minute defects near the surface due to the oxygen precipitates. There is. However, if the oxygen concentration in the silicon single crystal is lowered, oxygen precipitates cannot be sufficiently formed inside the silicon substrate, and the IG
There was a problem of lack of ability.

On the other hand, a magnetic field application CZ (Mag) for pulling a low oxygen concentration silicon single crystal from a crucible placed in a magnetic field.
In the method of "natural field applied CZ" (hereinafter referred to as "MCZ"), there is proposed a technique for increasing the IG capability by adding carbon having an action of promoting precipitation of oxygen (Japanese Patent Laid-Open No. 60-140).
No. 716).

However, since the segregation coefficient of carbon with respect to silicon is smaller than 1, the carbon concentration in the silicon single crystal gradually increases according to the pulling rate of the silicon single crystal, and the silicon substrate having the carbon concentration within the desired range is obtained. Has a problem that it can be obtained only from a very small part of a silicon single crystal ingot.

The present invention has been made in view of the above problems, and it is an object of the present invention to provide a silicon single crystal having a low oxygen concentration and a high IG capability even in the axial direction of the ingot, and a method for manufacturing the same. Has an aim.

[0011]

In order to achieve the above object, a silicon single crystal according to the present invention is a silicon single crystal pulled from a raw material composed of two layers of a melt layer and a solid layer, 5.0 × 10 ^{17 to} 1.3 × 10 ¹⁸ at
at a rate of oms / cm ³ and carbon of 4.8 × 10 ¹⁵ ~
It is characterized in that it is contained at a rate of 8.5 × 10 ¹⁶ atoms / cm ³ .

In the method for producing a silicon single crystal according to the present invention, carbon is charged into the crucible at a weight ratio of 1 to 1 of silicon raw material and carbon is charged at a ratio of 5.7 to 96.1 × 10 ^-7 , and then the crucible is heated. Two layers, a raw material solid layer and a raw material melt layer, are formed therein, and the pulling shaft, the rotation speed of the crucible, the pulling speed, etc. are controlled,
Oxygen from the melt layer is 5.0 × 10 ^{17 to} 1.3 × 10
It is characterized in that a silicon single crystal containing ¹⁸ atoms / cm ³ is pulled.

[0013]

In the silicon single crystal according to the present invention, the silicon single crystal pulled from the raw material consisting of the melt layer and the solid layer has two layers of oxygen.
Carbon at a rate of 0 × 10 ^{17 to} 1.3 × 10 ¹⁸ atoms / cm ³ and carbon of 4.8 × 10 ^{15 to} 8.5 × 10 ¹⁶ atoms.
Since it is contained at a rate of ms / cm ³ , the oxygen concentration is low, so a DZ layer with high integrity can be obtained at the time of forming a silicon substrate, and carbon promotes the precipitation of oxygen inside the substrate to obtain a high IG capability. Will be done.

According to the method for producing a silicon single crystal according to the present invention, the silicon raw material 1 in the crucible in a weight ratio is
After charging carbon at a rate of 5.7-96.1 × 10 ^-7 ,
The raw material solid layer and the raw material melted liquid layer are provided in the crucible 2
A layer is formed, and the number of rotations of the pulling shaft and the crucible, the pulling speed, and the like are controlled to supply oxygen from the melt layer at a rate of 5.0 × 10 ^{17 to} 1.3 × 10 ¹⁸ atoms / cm ³ . Since the silicon single crystal containing the silicon single crystal is pulled, it is possible to control the oxygen concentration and the carbon concentration in the ingot axis direction of the silicon single crystal within a desired range, and to have a highly complete DZ layer and a high IG capability. It is possible to manufacture a silicon substrate that has been manufactured.

[0015]

EXAMPLES AND COMPARATIVE EXAMPLES Examples and comparative examples of a silicon single crystal and a method for producing the same according to the present invention will be described below with reference to the drawings. FIG. 1 is a schematic cross-sectional view showing the configuration of an apparatus for pulling a silicon single crystal according to an example, in which 1 denotes a crucible. The crucible 1 is arranged in a water-cooled chamber 8 and is composed of a quartz inner layer container 1b having a bottomed cylindrical shape and a graphite outer layer holding container 1a arranged outside the inner layer container 1b. Has been done. Crucible 1
A heater 2 is concentrically arranged around the outer periphery of the.
In addition, around the outer periphery of the heater 2, heat retaining cylinders 7 a and 7 b are arranged so as to surround the crucible 1. A support shaft 9 is connected to the center of the bottom of the crucible 1 so as to pass through the bottom of the chamber 8. The support shaft 9 causes the crucible 1 to rotate and move up and down. The pull-up shaft 5 is suspended from above the chamber 8 and is introduced into the chamber 8. The pull-up shaft 5 is rotated and pulled upward. Further, the rotation speed and the lifting speed of the lifting shaft 5 are controlled by a lifting mechanism (not shown). A seed crystal 4 is attached to the tip of the pulling shaft 5 via a seed chuck (not shown). The silicon single crystal pulling device 10 including these crucible 1, heater 2, pulling shaft 5, chamber 8 and the like. Is configured.

In the case of pulling up the silicon single crystal 3 according to the embodiment using the apparatus 10 thus constructed, first, the silicon raw material and carbon are charged into the crucible 1. At this time, P and carbon as impurities are added to the silicon raw material at a predetermined ratio. After that, the silicon raw material in the crucible 1 is once melted by the heater 2 to form the molten liquid layer 6a. Next, the heater 2 is moved to a predetermined position while rotating the crucible 1, the lower portion of the crucible 1 is cooled, and the solid layer 6b is formed upward from the bottom of the crucible 1. Thus, in the crucible 1, the upper portion of the crucible 1 is the melt layer 6a and the lower portion is the solid layer 6b.
After forming the seed crystal 4, the seed crystal 4 is brought into contact with the melted layer 6a to be blended, and the solid layer 6b is melted from the upper side to the lower side to be converted into the melted layer 6a, and the pulling shaft 5 is rotated at a predetermined speed. The silicon single crystal 3 is grown from the lower end of the seed crystal 4 by pulling it up (DLCZ method).

Hereinafter, the results of comparing silicon single crystals having various oxygen concentrations and carbon concentrations by the above manufacturing method and comparing them will be described.

Here, as each sample, a silicon single crystal ingot having a diameter of about 6 inches and a length of about 1100 mm was cut out, and one surface was mirror-polished to have a thickness of about 0.62.
A 5 mm silicon substrate is prepared, and about 11
Heat treatment at 00 ℃ for about 4 hours, then about 700 ℃
After heat treatment for about 4 hours at about 100 in oxygen atmosphere
The thing which formed the oxygen precipitation defect by heat-processing at 0 degreeC for 16 hours was used.

Table 1 shows the oxygen concentration (A to F) and carbon concentration (a to f) of the silicon single crystals according to the examples and comparative examples. The silicon single crystals according to the examples and the comparative examples are determined by various combinations of the oxygen concentration (A to F) and the carbon concentration (a to g).

[0020]

[Table 1]

Oxygen in a silicon single crystal enters interstitial sites in the solid solution state, while carbon replaces silicon atoms and occupies lattice points. Interstitial oxygen (Oi) and substitutional carbon (Cs) each have a wave number of 1106 cm at room temperature.
Since it is observed as an infrared absorption peak at ^-1 and 607 cm ^-1 , its concentration can be measured by an infrared absorption method. here,
The interstitial oxygen concentration and the substitutional carbon concentration were measured by using a Fourier transform infrared spectroscope (FT-IR), and the respective results were described as the oxygen concentration (A to F) and the carbon concentration (a to g). The value of As a conversion coefficient from the infrared absorption coefficient to each concentration, the oxygen concentration [Oi] is 4.81.
X10 ¹⁷ atoms / cm ² was used, and the carbon concentration [Cs] was 1.00 × 10 ¹⁷ atoms / cm ² .

FIG. 2 is a graph showing the oxygen precipitation amount (ΔOi) with respect to the interstitial oxygen concentration (hereinafter, simply referred to as oxygen concentration) [Oi], where a to g are the silicon single crystals in Table 1. Corresponding to carbon concentrations a to g, A to F in the figure correspond to oxygen concentrations (A to F) of the silicon single crystal in Table 1.

As is apparent from FIG. 2, the carbon concentration is a
In a silicon single crystal with a detection limit of 3.0 × 10 ¹⁵ atoms / cm ³ or less, the oxygen concentration is E (1.3 ×).
When the oxygen concentration is 10 ¹⁸ atoms / cm ³ ) or less, the oxygen precipitation amount is 1.0 × 10 ¹⁷ atoms / cm ³
(X in the figure) or less, and sufficient IG capability cannot be exhibited. On the other hand, when the carbon concentration is b (4.8 × 10 ¹⁵ ato
In a silicon single crystal of ms / cm ³ ) or more, the oxygen precipitation amount is 1.0 even when the oxygen concentration is a low oxygen concentration of E (1.3 × 10 ¹⁸ atoms / cm ³ ) or less.
Since it becomes more than × 10 ¹⁷ atoms / cm ³ (x in the figure), sufficient IG capability can be exhibited. From this, the carbon concentration in the silicon single crystal is 4.8 × 10 ¹⁵ atoms
It has been found that a value within the range of / cm ³ or more is desirable.
On the other hand, if the carbon concentration is 1.0 × 10 ¹⁷ atoms / cm ³ or more, as will be described later, the defect density near the surface of the silicon substrate becomes higher than the target value.

Next, the density of defects generated in the vicinity of the surface of the silicon substrate formed of the silicon single crystal according to the example and the comparative example is determined by selective etching (Wrig) of 20 μm on each side.
It was made visible by an HT etching) and evaluated by an optical microscope. FIG. 3 is a graph showing the defect density near the surface of the silicon substrate with respect to the oxygen concentration of the silicon single crystal, and the vertical axis (defect density) is represented by a logarithmic memory. A- in the figure
g and A to F in the figure are the same as in the case of FIG.

As is apparent from FIG. 3, the oxygen concentration is A
(5.2 × 10 ¹⁷ atoms / cm ³ ) to E (1.3 ×
In a silicon single crystal of 10 ¹⁸ atoms / cm ³ , the carbon concentration is a (detection limit of 3.0 × 10 ¹⁵ atoms).
ms / cm ³ or less) to f (8.5 × 10 ¹⁶ atoms /
cm ³ ), the defect density in the vicinity of the surface of the silicon substrate is 1.0 × 10 ³ cm ² (y in the figure) or less. No extreme increase in defect density was observed. This is because the addition of carbon reduced the size of the oxygen precipitates, and some of the oxygen precipitates near the surface of the silicon substrate shrank and disappeared during the heat treatment step in the above-described 1000 ° C. oxygen atmosphere. Conceivable. However, in a silicon single crystal having a carbon concentration of g (1.0 × 10 ¹⁷ atoms / cm ³ ), the defect density near the surface of the silicon substrate was larger than 1.0 × 10 ³ cm ^-2 (y in the figure). .

On the other hand, when the oxygen concentration is F (1.5 × 10 ¹⁸ at)
In a silicon single crystal of oms / cm ³ ), the defect density in the vicinity of the silicon substrate surface is larger than 1 × 10 ³ cm ² (y in the figure) regardless of the carbon concentration having any of the above values. became. It is considered that this is because a large amount of oxygen precipitates were deposited on the surface of the silicon substrate due to the addition of carbon. From this, the oxygen concentration is changed to A (5.
0 × 10 ¹⁷ atoms / cm ^{3 to} E (1.3 × 10 ¹⁸ a
When the value is within the range of (toms / cm ³ ), the carbon concentration is a (detection lower limit of 3.0 × 10 ¹⁵ atoms / cm ³ or less) to f (8.5 × 10 ¹⁶ atoms / cm ³ ). It was found that a highly perfect DZ layer was formed with the silicon single crystal.

As can be seen from the above description, in the silicon single crystal 3 according to the example, oxygen was added at 5.0 × 10 ¹⁷
˜1.3 × 10 ¹⁸ atoms / cm ³ and carbon 4.8 × 10 ^{15 to} 8.5 × 10 ¹⁶ atoms / cm 3.
^Since it is contained in a ratio of ^3, a DZ layer having high integrity can be obtained at the time of forming a silicon substrate, and a high IG capability can be provided.

Next, the carbon distribution in the ingot axial direction of the silicon single crystals according to the examples and comparative examples was evaluated. FIG. 4 is a graph showing the distribution of carbon concentration in the ingot axis direction in both the silicon single crystal 3 according to the example and the silicon single crystal grown by the MCZ method as a comparative example. In FIG. 4, the vertical axis represents the carbon concentration [Cs], and the horizontal axis represents the position in the ingot axis direction. As is apparent from FIG. 4, the target range value of the carbon concentration is, for example, 4. In order to precisely control the amount of precipitation of oxygen.
When it is set to 5 to 6.5 × 10 ¹⁶ atoms / cm ³ (q in the figure), in the silicon single crystal 3 according to the example, 900 is obtained from a position 100 mm in length from the top of the ingot.
The area (mm in the figure) reaches the target range over the area of mm, and most of the ingot length of 1000 mm falls within the target range. On the other hand, in the silicon single crystal according to the comparative example, the length from the top of the ingot is 240 mm.
The target range can be entered only from the point to the point of 540 mm (p in the figure). That is, when the case of the silicon single crystal according to the example is set to 100%, [(540-240) /
(900-100)] × 100 = 37.5% only falls within the target range.

As described above, according to the method for producing a silicon single crystal according to the embodiment, the solid layer 6b is gradually melted, so that the carbon concentration in the melt layer 6a can be kept substantially constant, and the ingot axial direction can be maintained. The carbon concentration can be made substantially constant over a wide range.

As described above, according to the method for producing a silicon single crystal according to the embodiment, the oxygen concentration and the carbon concentration in the ingot axis direction of the silicon single crystal 3 can be controlled within a desired range, and the silicon concentration can be controlled. If the single crystal 3 is used, it is possible to manufacture a silicon substrate having a highly complete DZ layer and having a high IG capability.

[0031]

As described above in detail, the silicon single crystal according to the present invention is a silicon single crystal pulled from a raw material composed of two layers, a melt layer and a solid layer, and contains oxygen of 0.
Carbon at a rate of 5 × 10 ^{18 to} 1.3 × 10 ¹⁸ atoms / cm ³ and carbon at 4.8 × 10 ^{15 to} 8.5 × 10 ¹⁶ atoms.
Since the content of ms / cm ³ is contained, the oxygen concentration is low, so that a DZ layer with high integrity can be obtained at the time of forming the silicon substrate, and carbon promotes the precipitation of oxygen inside the substrate, which has a high IG capability. Can be obtained.

According to the method for producing a silicon single crystal according to the present invention, the silicon raw material 1 in the crucible in a weight ratio is
After charging carbon at a rate of 5.7-96.1 × 10 ^-7 ,
Two layers of a raw material solid layer and a raw material melt layer are formed in the crucible,
By controlling the number of rotations of the pulling shaft and the crucible, the pulling speed, etc., oxygen was added from the melt layer to 0.5 × 10 ^{18 to} 1.3.
Since the silicon single crystal contained at a rate of × 10 ¹⁸ atoms / cm ³ is pulled, the oxygen concentration and the carbon concentration in the ingot axis direction of the silicon single crystal 3 can be controlled within a desired range, and the DZ layer having high integrity can be obtained. And a silicon substrate having high IG capability can be manufactured.

[Brief description of drawings]

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

FIG. 2 is a diagram showing a relationship between an oxygen concentration and a carbon concentration and an oxygen precipitation amount in a silicon substrate formed of a silicon single crystal according to an example and a comparative example.

FIG. 3 is a diagram showing a relationship between oxygen concentration and carbon concentration and a defect density near the surface of a silicon substrate in a silicon substrate formed of a silicon single crystal according to an example and a comparative example.

FIG. 4 is a diagram showing a carbon concentration distribution in the ingot axis direction of a silicon single crystal pulled by a method for manufacturing a silicon single crystal according to an example and a comparative example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Crucible 3 Silicon single crystal 5 Pulling shaft 6a Melt liquid layer (raw material melt liquid layer) 6b Solid layer (raw material solid layer)

Claims (2)

[Claims] 1. A silicon single crystal pulled from a raw material composed of two layers, a melt layer and a solid layer, and having a rate of oxygen of 5.0 × 10 ^{17 to} 1.3 × 10 ¹⁸ atoms / cm ³ . And carbon of 4.8 × 10 ^{15 to} 8.5 × 10 ¹⁶ a
A silicon single crystal containing at a rate of toms / cm ³ . 2. A crucible is charged with carbon at a ratio of 5.7 to 96.1 × 10 ⁻⁷ with respect to 1 of silicon raw material in a weight ratio, and then a raw material solid layer and a raw material melt layer are formed in the crucible. 2 layers are formed, and the number of rotations of the pulling shaft and the crucible, the pulling speed, etc. are controlled to supply oxygen from the melt layer to 5.0 × 10 ¹⁷ to
A method for producing a silicon single crystal, which comprises pulling a silicon single crystal contained at a rate of 1.3 × 10 ¹⁸ atoms / cm ³ .