JPH07277891A - Method for growing crystal - Google Patents

Abstract

PURPOSE:To provide a method for growing a crystal which makes the impurity concn. in the radial direction particularly within the wafer surface uniform even of the crystal pulled up in any crystal growth bearing. CONSTITUTION:This method for growing the crystal comprises adding an impurity to a molten layer by blowing gas contg. the gaseous impurity to the surface of a melt or the molten layer 4 in a Czochralski method of growing the crystal 6 by bringing a seed crystal 3 into contact with the surface of the melt of the raw material in a crucible 1 and pulling up the seed crystal or a molten layer method of growing the crystal 6 by heating and melting the upper part of the raw material in the crucible 1 to form the molten layer 4, keeping the lower part as a solid layer 5 of the raw material, bringing the seed crystal 3 into contact with the surface of the molten layer 4 and pulling up the seed crystal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a crystal growth method by a rotary pulling method, and more specifically, a uniform distribution of crystal characteristics (especially electrical characteristics) of a silicon single crystal used as a semiconductor material in an in-plane radial direction. The present invention relates to a crystal growth method.

[0002]

2. Description of the Related Art Various methods are known for the production of semiconductor single crystals, especially high-purity silicon single crystals. Among them, the single crystal produced by the Czochralski method as the rotary pulling method is grown by pulling it from the silicon melt in the quartz crucible, so the grown crystal is supplied from the crucible quartz (SiO ₂ ). Contains a lot of oxygen that has been made. Therefore, compared to single crystals produced by other methods, IC and LS
Even if it is repeatedly heat-treated in the manufacturing process of I,
Less likely to cause slips or warpage. Furthermore, a high-density defect layer is formed on the internal oxygen precipitates by heat treatment at around 1000 ° C.,
It also has a function of reducing impurities existing in the surface area of the wafer (so-called intrinsic gettering). Due to these advantages in the manufacturing process, the Czochralski method is widely used in the industrial manufacturing of silicon single crystals.

FIG. 5 is a schematic vertical sectional view showing an implementation state of the Czochralski method, in which 1 is a crucible.
The crucible 1 has a double structure. The inner side is a crucible 1a made of quartz and the outer side is a crucible 1b made of graphite. A heater 2 for heating is arranged outside the crucible 1, and a crystal forming material melted by the heater, that is, a raw material melt 7 is accommodated in the crucible 1. The lower end of the seed crystal 3 attached to the tip of the pulling wire 13 is brought into contact with the surface of the melt 7 and the seed crystal 3 is pulled upward to grow a crystal 6 in which the melt 7 solidifies. Go.
In addition, the crucible 1 is supported by a crucible support shaft 12 which is coaxial with the pulling wire 13 and which rotates at a predetermined speed, and is surrounded by a heat insulation cylinder 11 to ensure heat retention of the crucible 1. There is. These parts and members are housed in a water-cooled chamber 14 and constitute a single crystal manufacturing apparatus as a whole.

During crystal growth, high-purity argon gas is constantly flowed from the center of the pull chamber 15 provided above the chamber 14 to form gas streams 20 and 21. The gas streams 20 and 21 are discharged from the system of the chamber 14 through a discharge port (not shown) together with silicon monoxide (SiO) evaporated from the surface of the silicon melt 7. The silicon monoxide vaporized by the gas flow is discharged by depositing silicon monoxide deposits on the inner wall of the upper portion of the chamber 14 in a layered or lump form, and the deposited fine particles or lumps of silicon monoxide form the melt 7. This is because it may fall onto the surface and be taken into the crystal growth interface, causing dislocation-free crystals to have dislocations, resulting in a defective product single crystal.

When a semiconductor single crystal is grown by the Czochralski method, an impurity element (dopant) is added to the melt before pulling in order to make the single crystal have a desired electric resistivity and electric conductivity type. Often. In this case, a phenomenon occurs in which the added impurities segregate along the crystal growth direction, which makes it difficult to obtain a single crystal having uniform electrical characteristics in the crystal growth direction.

As described above, the segregation of impurities in the crystal causes non-uniform characteristics in the crystal growth direction due to the impurity concentration at the start of solidification and the impurity concentration at the end of solidification at a certain point of the grown crystal. This is because the effective segregation coefficient Ke represented by the ratio is not 1. The effective segregation coefficient Ke is the ratio (C _s / C _L ) of the impurity concentration C _s in the crystal and the impurity concentration C _{L in} the melt at the interface between the melt and the crystal during crystal growth.
Also, since this Ke is not 1, the impurity concentration in the melt and thus in the crystal changes as the crystal grows. For example, when Ke <1, the impurity concentration in the melt gradually increases as the crystal grows. Therefore, the impurity concentration becomes high in the latter half of crystal growth (downward in the length direction).

Generally, the impurity concentration C _{s in} the growth direction of the pulled single crystal is the initial impurity concentration C _L0 in the melt,
In relation to the solidification rate G of the single crystal, it is represented by C _s = KeCL ₀ (1-G) ^{Ke -1} . For example, in an n-type crystal to which phosphorus (P) having a small effective segregation coefficient Ke of 0.35 is added, the phosphorus concentration in the melt increases during the growth, as compared with the case of using other impurity elements having a Ke close to 1. The degree of change is large, the change in the impurity concentration in the growth direction of the single crystal is large, and the yield of the single crystal having the desired impurity concentration is significantly reduced.

A melt layer method is used as a rotary pulling method for growing crystals while suppressing the segregation of impurities generated along the crystal growth direction.

FIG. 3 is a schematic vertical sectional view for explaining the basic constitution of the melt layer method. As shown, in the melt layer method,
By melting the upper part of the raw material filled in the crucible 1 having the same structure as described in the Czochralski method with the heater 2, the molten layer 4 is formed in the upper layer and the solid layer 5 is formed in the lower layer. There is. Then, the seed crystal 3 is brought into contact with the molten layer 4, and the crystal 6 in which the melt of the raw material is solidified is pulled up while being rotated by the pulling wire 13.

In the melt layer method, the following two methods are adopted to suppress the segregation of impurities in crystals.

One of the methods is to add impurities only to the initial molten layer, adjust the melting amount of the solid layer 5 during pulling, and change the volume of the molten layer 4, whereby the molten layer 4 is melted. Method for changing the thickness of molten layer to keep the impurity concentration in the melt
61-250691, JP-A-61-250692 and JP-A-61-21
5285). The other method is a constant melt layer method in which the solid layer 5 is continuously melted during pulling to make the volume of the melt layer 4 constant, and further impurities are continuously added to keep the impurity concentration in the melt constant. (See Japanese Patent Publication Nos. 34-8242, 62-880 and 60-32474). In any case, regardless of the value of the effective segregation coefficient Ke, the change in the impurity concentration in the melt that occurs with the growth of the single crystal is suppressed, and the impurity segregation in the crystal is suppressed.

Control of the thickness of the molten layer in these molten layer methods is performed by the heating length of the heater to be heated, that is, the heating value of the heater, the crucible size (particularly the depth), and further the circumference of the heater and the lower portion of the crucible. This is performed by appropriately selecting in advance the shape of the heat retaining tube or the material of the heat retaining tube that promotes heat transfer.

[0013]

By adopting the above method, the problem of impurity segregation in the crystal growth direction can be almost solved. However, in recent years, with the high integration and high density of wafers in the device process of the semiconductor industry,
The required quality standards have become stricter, and as one of the quality specifications, there has been a demand for uniform characteristics in the radial direction rather than in the crystal growth direction. This is due to the requirement of eliminating the characteristic variation in the wafer surface in the device process due to the increase in the diameter of the wafer, but suppressing the variation in the impurity concentration in the radial direction not only in the Czochralski method but also in the molten layer method. Became an important issue. Hereinafter, an example of the factor will be described.

When crystal-growing silicon as a semiconductor material, typical growth directions are [100] and [11].
1], the growth rate of the pulled crystal depends on the growth direction. This is because the in-plane atom density in each growth direction is different, but especially when the crystal growth direction is [111], the crystal growth rate is significantly slower than the [100] direction and other directions. And form facets at the solidification interface of the crystal. When the facets are formed in this way, the facet portion changes in characteristics as compared with other portions. For example, the effective segregation coefficient of impurities becomes large as compared with other parts. Therefore, when the crystal is grown by the rotary pulling method,
At the same time, there is a difference in the amount of impurities taken into the crystal between the facet portion and the other portion, so that the electrical characteristics differ depending on the crystal growth position, that is, the crystal radial direction.

In FIG. 4, phosphorus is contained as an impurity,
It is the figure which shows the change situation of the resistivity in the radial direction when the 4 ″ diameter silicon crystal grown in the crystal growth direction is [111] is processed into a semiconductor wafer. The resistivity is low in the facet part of the part, but it is high in other peripheral parts, so that it becomes the variation in the radial direction of the wafer as it is.Since such a silicon single crystal causes a difference in electrical characteristics, It cannot be used for semiconductors.

The present invention overcomes the problems of the above-mentioned conventional methods and can be applied to any crystal grown in any crystal orientation.
In particular, it is an object to establish a crystal growth method in which the impurity concentration in the radial direction of the wafer is uniform.

[0017]

The present invention provides the following (1),
The crystal growth method (2) is the gist of the invention.

(1) In the Czochralski method of growing a crystal 6 by bringing a seed crystal 3 into contact with the surface of a melt 7 of a raw material in a crucible 1 and pulling it up, an impurity gas is added to the surface of the melt 7. A crystal growth method characterized in that an impurity is added to a molten liquid by blowing a contained gas (see FIG. 1).

(2) The upper part of the raw material in the crucible 1 is heated and melted to form a molten layer 4, the lower part is a solid layer 5 of the raw material, and the seed crystal 3 is brought into contact with the surface of the molten layer 4 to pull up the crystal. In the melt layer method of growing No. 6, a crystal growth method characterized in that a gas containing an impurity gas is blown onto the surface of the melt layer 4 to add impurities to the melt layer (see FIG. 2).

[0020]

The present inventors have made detailed investigations on the concentration distribution of impurities in the Czochralski method and the melt layer method and the behavior of the impurities melting into the pulled crystal, and as a result, the following findings have been obtained.

Even when a silicon single crystal having a crystal growth orientation of [111] is grown by the rotary pulling method, by adjusting the concentration distribution of impurities in the melt near the crystal growth interface or the entire surface of the melt, The impurity concentration in the radial direction in the pulled crystal can be controlled. For example, when phosphorus is used as the impurity, the impurity concentration becomes high in the facet portion of the crystal center, as described above,
It becomes lower in other peripheral areas. Therefore, a gas containing phosphorus is blown onto the surface of the melt corresponding to the peripheral portion of the crystal to add phosphorus as an impurity to the melt. By this operation, the impurity concentration of the melt corresponding to the peripheral portion of the crystal can be adjusted to be high, and the impurity concentration in the radial direction of the grown crystal can be made uniform.

In particular, in the melt layer method, the depth of the melt layer is shallower and the temperature difference between the upper part and the lower part of the melt layer is smaller than that in the Czochralski method, so that convection in the melt layer due to the temperature difference in the melt is caused. Will be suppressed. Therefore, the melt in the vicinity of the crystal growth interface where the impurity concentration is increased by blowing gas is not transferred by convection,
It reaches the crystal growth interface in the state of having the same concentration distribution. So to implement this method,
The melt layer method is a particularly effective crystal growth method.

The present invention is based on a crystal growth method completed on the basis of the above findings, but the method of adding an impurity gas to a melt is not limited to a particular method, and for example, an impurity gas may be used. May be added to the melt by spraying on the surface of the melt near the crystal growth interface by introducing a gas containing the gas into the melt, or by adding an impurity gas to the atmosphere gas in the furnace to melt the melt. It may be added to the liquid surface.

[0024]

The effects of the crystal growth method of the present invention will be described in detail below based on the Czochralski method (Example 1) and the melt layer method (Examples 2 and 3).

Example 1 FIG. 1 is a schematic vertical sectional view showing an example of an apparatus for carrying out the crystal growth method of the present invention by the Czochralski method. The basic structure of the apparatus is the same as that of the conventional apparatus shown in FIG. 5 described above, but in order to carry out the method of the present invention, a gas injection pipe 17 for adding an impurity gas to the melt near the crystal growth interface. Is provided.

As the crystal growth by the Czochralski method, using the apparatus shown in FIG. 1, phosphorus was used as an n-type dopant and a silicon single crystal was grown under the following conditions.

1. Filling of Silicon Raw Material A quartz outer crucible was fitted with a quartz inner crucible (inner diameter 400 mm × depth 350 mm) to form a crucible, and 60 kg of silicon polycrystal as a raw material for crystals was filled in the crucible.

Further, phosphorus-silicon alloy is used as an impurity.
0.6 g was added.

2. Pretreatment After the inside of the chamber was made to have an argon atmosphere of 10 Torr, the heat input amount of the heater was set to 60 kw to melt all the raw materials.

3. Initial stage of crystal growth After stabilizing the melt in the crucible, in order to start pulling the crystal, the rotation speed of the crucible was set to 10 rpm, while rotating the pulling wire in the reverse direction at 10 rpm, the seed crystal ( The lower end of the crystal orientation [111]) was immersed in the molten layer.

4. Crystal Growth and Gas Spraying After the initial stage of single crystal growth (end of neck process-formation of shoulder (shoulder) -changing shoulder (shoulder)), the stage was changed to pulling up of single crystal (body process).

After the transition to the pulling stage (body process), gas was blown from the gas injection pipe onto the surface of the melt. The gas supplied to the gas injection tube was an argon gas containing 1% of PH ₃ (phosphine), and its flow rate was 1 liter / min. While adding gas, a single crystal with a crystal diameter of 6 "
It was grown to a pulling length of 1000 mm without defects.

For comparison, crystal growth was carried out even under the condition that gas was not blown.

(Embodiment 2) FIG. 2 is a schematic vertical sectional view showing an example of an apparatus for carrying out the crystal growth method of the present invention by the melt layer method. The basic structure of the device is the same as that of the device for carrying out the Czochralski method described with reference to FIG. 1, but on the outer periphery of the crucible 1, a short heat generation length, for example, 90 mm.
A resistance heating type heater 2 having a heat generation length of the order of magnitude is arranged coaxially with the pulling shaft as a center. Then, during the crystal growth, by adjusting the relative positions of the heater and the crucible in the vertical direction or adjusting the heat input amount, the amounts of the molten layer 4 and the solid layer 5 in the crucible can be adjusted. It has become.

In addition, in order to carry out the crystal growth method of the present invention, the gas injection pipe 17 for blowing the gas containing the impurity gas to the molten layer 4 which becomes the crystal growth interface is arranged. The same as in the Czochralski method.

As crystal growth by the melt layer method, phosphorus was used as an n-type dopant to grow a single crystal of silicon under the following conditions.

1. Filling of silicon raw material A quartz outer crucible is fitted with a quartz inner crucible (inner diameter 400 mm x depth 350 mm) to form a crucible, and a high-purity silicon polycrystal with a weight of 65 kg is used as a raw material for the crystal in this crucible. Was filled.

As an n-type dopant, 0.4 g of phosphorus-silicon alloy was added to the above raw material.

2. Pretreatment After the inside of the chamber was made to have an argon atmosphere of 10 Torr and the heater was set to 75 kw of heat input to melt all the raw materials, the heat input of the heater was reduced to 60 kw, and a solid layer was grown under the molten layer.

3. Initial stage of crystal growth After the solid layer is sufficiently grown to stabilize the molten layer, the rotation speed of the crucible is set to 1 rpm in order to start pulling the crystal,
The lower end of the seed crystal (crystal orientation [111]) was immersed in the molten layer while rotating the pulling wire at a constant rotation speed of 10 rpm in the opposite direction.

4. Crystal Growth and Gas Addition Similar to Example 1, after shifting to the pulling stage (body process), gas was blown from the gas injection pipe. The supplied gas was an argon gas containing 1% of PH ₃ (phosphine), and the flow rate was 1 liter / min.

Thereafter, a single crystal having a crystal diameter of 6 ″ was grown without defects with a pulling length of 1000 mm while adding gas.

For comparison, crystal growth was carried out even under the condition that gas was not blown.

(Embodiment 3) As another method of crystal growth by the melt layer method, an impurity gas is contained in the argon gas for the atmosphere in the chamber, and the gas flow 21 in FIG.
A silicon single crystal was grown by a method of constantly contacting the surface of. The apparatus used in this method has the same structure as the apparatus shown in FIG. 2, but the gas injection pipe 17 for supplying the gas containing the impurity gas was not used.

The conditions for crystal growth are 1% of PH ₃ (phosphine) in argon gas for atmosphere (flow rate of 1 liter / min).
The conditions for filling the silicon raw material, pretreatment, and crystal growth other than the above were the same as those in the second embodiment.

For comparison, crystal growth was carried out even under the condition that the atmosphere argon gas did not contain the impurity gas.

After processing the single crystal grown in (Example 1) to (Example 3) as a semiconductor wafer, the radial resistivity distribution in the wafer surface was measured by the four-point probe method. Here, the resistivity distribution is represented by (maximum resistivity-minimum resistivity) / (maximum resistivity + minimum resistivity). The measurement part in the crystal growth direction of the single crystal is the upper part (100 mm from the top),
The central part and the lower part (100mm from the bottom)
The results are summarized in Table 1.

[0048]

[Table 1]

As is clear from Table 1, the wafer manufactured by the method of the present invention is sprayed with a gas containing an impurity gas during crystal growth at any of the upper, middle and lower parts during crystal growth. The radial resistivity distribution in the plane of the wafer is more uniform than in the case of no wafer.

In the examples, only the case of using phosphorus as an impurity to be added has been described, but it has been confirmed that the present invention can be applied to other impurity elements such as boron (B).

Furthermore, the method of the present invention is applied not only to the production of silicon single crystals for semiconductors, but also to the production of single crystals other than silicon.

[0052]

According to the present invention, when a single crystal for a semiconductor is grown by the Czochralski method or the melted layer rotation pulling method, even if the crystal is pulled in any crystal growth direction, It is possible to grow a crystal having a uniform impurity concentration. As a result, it is possible to obtain a semiconductor wafer having excellent electrical characteristics in the processed wafer surface.

[Brief description of drawings]

FIG. 1 is a schematic vertical cross-sectional view showing an example of an apparatus for carrying out the crystal growth method of the present invention by the Czochralski method.

FIG. 2 is a schematic vertical sectional view showing an example of an apparatus for carrying out the crystal growth method of the present invention by the melt layer method.

FIG. 3 is a schematic vertical cross-sectional view illustrating the basic configuration of the melt layer method.

FIG. 4 is a diagram showing changes in the radial resistivity of a 4 ″ diameter silicon crystal grown with [111] crystal growth direction containing phosphorus as an impurity.

FIG. 5: Conventional rotation pulling method (Czochralski method)
It is a schematic longitudinal cross-sectional view showing an implementation state of.

[Explanation of symbols]

1 ... crucible, 1a ... quartz crucible, 1b ... graphite crucible, 2 ... heater,
3 ... Seed crystal 4 ... Molten layer, 5 ... Solid layer, 6 ... Crystal, 7 ... Molten liquid 11 ... Insulating cylinder, 12 ... Crucible supporting shaft, 13 ... Pulling wire, 14
… Chamber 15… Pull chamber, 17… Gas injection pipe, 20, 21… Gas flow

Claims (2)

[Claims] 1. A Czochralski method for growing a crystal by bringing a seed crystal into contact with the surface of a melt of a raw material in a crucible to pull it up, and blowing a gas containing an impurity gas onto the surface of the melt. And then adding impurities to the melt. 2. A melt layer method in which an upper part of a raw material in a crucible is heated and melted to form a molten layer and a lower part thereof is a solid layer of the raw material, and a seed crystal is brought into contact with the surface of the molten layer to pull up a crystal to grow a crystal. 2. The crystal growth method according to, wherein the surface of the molten layer is blown with a gas containing an impurity gas to add impurities to the molten layer.