JP4150532B2 - Polycrystalline silicon - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a polycrystalline silicon suitable for a raw material for producing a silicon single crystal relates to a polycrystalline silicon suitable for add charge and recharge, especially in a silicon single crystal manufacturing process by the CZ method.
[0002]
[Prior art]
Conventionally, a silicon single crystal, which is a material of a semiconductor device, is industrially manufactured exclusively by the CZ method. In the production of a silicon single crystal by the CZ method, first, bulk polycrystalline silicon is heated and melted in a quartz crucible to form a silicon raw material melt. Next, a silicon seed crystal is immersed in the raw material melt, and is pulled up while rotating to grow a rod-shaped silicon single crystal below the seed crystal.
[0003]
As the raw material for producing the silicon single crystal here, polycrystalline silicon produced by the Siemens method is exclusively used. In the production of polycrystalline silicon by the Siemens method, as is well known, a rod-shaped silicon seed core is set up in a reaction furnace called a bell jar, and the inside of the furnace is replaced with a hydrogen gas atmosphere or an inert gas atmosphere such as Ar by depressurization or pressurization. Thereafter, the seed core is heated to around 1000 ° C. by energization. In this state, chlorosilanes and hydrogen gas are introduced into the reaction furnace. Thereby, polycrystalline silicon precipitates on the surface of the seed core. The seed core is usually combined in a torii type, and a large number of seed cores are set in the reactor at once.
[0004]
The rod-shaped polycrystalline silicon thus manufactured is used for manufacturing a silicon single crystal by the CZ method as follows. Normally, it is crushed into a lump, charged into a quartz crucible, and heated and melted. However, if only a lump of silicon is used, the amount of raw material charged per charge in the crucible is limited. For this reason, after melting the silicon lump loaded in the crucible, the rod-shaped polycrystalline silicon is suspended on the crucible and gradually melted into the melt in the crucible to increase the amount of melt in the crucible. The operation is performed (Japanese Patent Laid-Open No. 2000-344594). This operation is called additional charge or additional charge, and the rod-shaped polycrystalline silicon used for this operation is called additional charge polycrystalline silicon.
[0005]
In addition, the quartz crucible has been consumed at a rate of one for each pulling up to now. For this reason, the ratio of the crucible cost to the manufacturing cost of the single crystal was high. Therefore, after pulling up the single crystal, with the residual liquid left in the crucible, the rod-shaped polycrystalline silicon is suspended on the crucible, and gradually dissolved in the residual liquid in the crucible, and a predetermined amount in the crucible. An operation of forming the raw material melt again is performed (Japanese Patent Laid-Open No. 2000-344594). This operation is called recharging, and the rod-shaped polycrystalline silicon used for this operation is called recharging polycrystalline silicon.
[0006]
[Problems to be solved by the invention]
Polycrystalline silicon used for recharging and recharging is required to be used in the form of rods, unlike polycrystalline silicon used for normal crushing, and in order to connect the rods together, There is a need to perform machining at the end for forming purposes. However, when the machining is performed, cracks frequently occur. Due to this cracking, there is a problem that the yield does not increase when machining the end of the polycrystalline silicon rod. .
[0007]
Although the purpose is different, in order to prevent the polycrystalline silicon for recharging from being broken in the middle of melting and falling into the lower crucible, a technique for removing residual strain by subjecting the polycrystalline silicon after manufacture to heat treatment is It is described in WO97 / 44277. According to this, the original purpose of preventing breakage during melting is achieved. However, when the heat treatment is performed outside the reaction furnace after the production of polycrystalline silicon, a special apparatus is required so that the polycrystalline silicon is not contaminated, and when the heat treatment is performed in the reaction furnace following the deposition, there is a problem of contamination. However, there is a problem that a large-capacity power source is required for heat treatment in the polycrystalline silicon manufacturing facility and cannot be implemented depending on the facility.
[0008]
An object of the present invention is to provide polycrystalline silicon that can reliably prevent cracking due to machining for recharging or recharging without using heat treatment.
[0009]
[Means for Solving the Problems]
In order to achieve the above object, the present inventors have investigated in detail the cause of the end crack in machining in the manufacture of the polycrystalline silicon rod for additional charge. As a result, it was found that the quality at the boundary between the seed core portion and the deposited silicon portion of the polycrystalline silicon rod produced in the bell jar furnace has a great influence on the above-mentioned machining crack.
[0010]
That is, in the production of polycrystalline silicon by the Siemens method, the silicon seed core is set to an electrode in a reaction furnace, the furnace interior is replaced with a hydrogen atmosphere or an inert gas atmosphere, and the seed core is energized and heated in the furnace. Is supplied with a gas of chlorosilanes to deposit polycrystalline silicon on the surface of the seed core. When the seed core is incorporated into the reactor, the boundary between the seed core portion and the deposited polycrystalline silicon portion due to a small amount of oxide film or moisture adhering to the surface of the seed core, or a small amount of oxygen remaining in the reactor. An oxide is formed in the part.
[0011]
There is no problem when this oxide is in a very small amount, but if it is produced in a large amount, a phenomenon of a core failure in which the boundary portion between the seed core portion and the deposited silicon portion of the manufactured polycrystalline silicon rod is easily separated occurs. Then, it was found that if the polycrystalline silicon rod with a poor core is subjected to machining for additional charging, processing cracks are very likely to occur. The reason for this is that, after the polycrystalline silicon is deposited, the residual stress generated during cooling is added to the stress concentration that accompanies the machining, so that separation easily occurs at the boundary between the seed core portion and the precipitated silicon portion. It can be considered that the rod progresses to crack.
[0012]
As described above, according to the knowledge of the present inventors, the polycrystalline silicon rod in which a relatively large amount of oxide is generated at the boundary portion between the seed core portion and the deposited silicon portion is cracked by machining for additional charging. On the contrary, in the polycrystalline silicon rod in which the generation of the oxide is suppressed, this crack is effectively suppressed. In other words, if the generation of oxide is suppressed at the boundary between the seed core portion and the deposited silicon portion of the polycrystalline silicon rod, the machining for additional charging is possible without removing the stress by heat treatment and leaving the residual stress. This prevents cracks in And the production | generation suppression of the oxide in the boundary part of a seed core part and a deposited silicon part can be easily implemented by adjustment of the furnace atmosphere at the time of the energization start to a seed core, adjustment of heating temperature, etc.
[0013]
The present invention has been made on the basis of such findings, and is polycrystalline silicon manufactured using chlorosilanes by the Siemens method. The cross-section of the present invention includes a 50% hydrogen fluoride aqueous solution and a 70% nitric acid aqueous solution. Polycrystal with an etching recess depth of 200 μm or less formed at the boundary between the seed core portion and the deposited silicon portion in the cross section when an etching treatment of 15 μm is performed with a mixed acid solution having a ratio of 1:50 The gist is silicon.
[0014]
The method for producing the polycrystalline silicon of the present invention is as follows. In the method for producing polycrystalline silicon by the Siemens method, in which energization of the seed core is started after the seed core is incorporated in the reaction furnace and then chlorosilanes are supplied to start precipitation, silicon is added to the surface of the seed core. when precipitating, to suppress the formation of an oxide film on its surface. More specifically, the oxygen concentration in the furnace gas when starting energization to the seed core is 50 ppm or less, and the surface temperature of the seed core when starting to precipitate silicon is 1100 to 1250 ° C., which is higher than the steady temperature. The surface temperature is lowered to the steady temperature after the elapse of the precipitation start period .
[0015]
The amount of oxide produced at the boundary between the seed core part of polycrystalline silicon produced by the Siemens method and the precipitated silicon part is a mixed acid solution of a hydrogen fluoride aqueous solution and a nitric acid aqueous solution when a predetermined amount of etching treatment is performed. It can be evaluated from the etching depth at the boundary portion.
[0016]
That is, when a wafer-like target sample cut from a polycrystalline silicon to be evaluated is etched, if a mixed acid solution of a hydrogen fluoride aqueous solution and a nitric acid aqueous solution is used as an etching solution, the silicon portion on the surface of the sample first becomes nitric acid. Is oxidized to SiO ₂ and then dissolved with hydrogen fluoride. On the other hand, the oxide generated at the boundary between the seed core portion and the deposited silicon portion is dissolved directly by hydrogen fluoride without undergoing an oxidation reaction with nitric acid. For this reason, the larger the amount of oxide at the boundary portion, the larger the etching depth at the boundary portion, and the amount of oxide is quantitatively estimated from the depth.
[0017]
As a result of detailed investigations by the present inventors, a 15 μm etching process was performed on the deposited silicon portion using a mixed acid solution having a ratio of 50% hydrogen fluoride aqueous solution and 70% nitric acid aqueous solution of 1:50 as an etchant. When the etching depth at the boundary portion between the seed core portion and the deposited silicon portion is 200 μm or less, the cored state is good enough to prevent processing cracks even if machining for recharging or recharging is performed. Turned out to be. The liquid temperature of the mixed acid here is 25 ° C.
[0018]
The indentation due to this etching formed at a position just outside the seed core can be accurately measured by a commercially available handy type surface roughness measuring instrument. Moreover, it can be easily measured with a dial gauge. Then, the measured depth of the dent is a reference for easily determining the amount of oxide generated.
[0019]
For the measurement of the etching amount, a polycrystalline silicon wafer-like sample (reference sample) capable of calculating the surface area is prepared, and the weight is measured in advance. A wafer-like target sample cut from a polycrystalline silicon to be evaluated by cutting is etched together with the sample. After etching, the sample weight is measured, the volume is obtained from the reduced weight, and the value divided by the surface area is the etching amount.
[0020]
As a method of suppressing the formation of oxide at the boundary between the seed core portion and the deposited silicon portion of the polycrystalline silicon, an oxide film is formed on the surface of the seed core at the start of the deposition of polycrystalline silicon. The operation for suppressing the above is effective, and the condition setting at that time is important. Specifically, the oxygen concentration in the in-furnace gas when starting energization to the seed core and the surface temperature at which chlorosilanes are supplied into the reaction furnace and silicon starts to precipitate on the seed core surface are determined. is important.
[0021]
That is, in the production of polycrystalline silicon by the Siemens method, the inside of the reaction furnace is replaced with a hydrogen gas atmosphere or an inert gas atmosphere by depressurization or pressurization, heating of the seed core is started, and after raising the temperature to a predetermined temperature, The supply of the kind is started. In order to suppress the etching depth at the boundary portion between the seed core portion and the deposited silicon portion to 200 μm or less, first, the oxygen concentration in the furnace gas is suppressed to 50 ppm or less at the start of energization to the seed core, It is effective to suppress it to 30 ppm or less. As a result, the oxidation reaction on the seed core surface is suppressed, and the amount of oxide produced at the boundary portion is reduced.
[0022]
In order to reduce the oxygen concentration in the furnace gas at the start of energization, after the seed core setting, the number of times of pressure replacement when replacing the interior of the furnace with inert gas or hydrogen gas, the degree of vacuum reached during vacuum replacement, The gas purge amount of the active gas or hydrogen gas may be manipulated. The lower limit of the oxygen concentration is not particularly specified because it is better from the viewpoint of suppressing oxidation, but an extremely low concentration makes the operation complicated, and is practically about 40 ppm.
[0023]
It is also effective to set the surface temperature of the seed core at the start of silicon deposition to 1100 ° C. or higher, preferably 1160 ° C. or higher, more preferably 1210 ° C. or higher, along with the decrease in oxygen concentration. As a result, oxygen sources that form an oxide film on the surface of the seed core such as adsorbed moisture and natural oxide film on the surface of the seed core are sufficiently removed, and the amount of oxide at the boundary portion is reduced. However, the seed core is a thin rod having a thickness of several millimeters, a length of 1000 mm or more, and if the temperature is raised too much, the seed core softens and bends, and in the worst case, breakage occurs. For this reason, upper limit temperature shall be 1250 degreeC.
[0024]
Incidentally, the oxygen concentration in the in-furnace gas at the start of conventional energization is about 90 ppm, and the surface temperature of the seed core at the start of silicon deposition is about 1000 ° C. As a result, the etching depth at the boundary portion when the etching treatment with a mixed acid solution having a ratio of 50% hydrogen fluoride aqueous solution and 70% nitric acid aqueous solution of 1:50 is 15 μm is about 300 μm. If no measures to prevent bursting are taken, processing cracks occur with a probability of several percent.
[0025]
Incidentally, refer to _{SiCl 4, SiHCl 3, SiH 2} Cl 2, SiH 3 Cl and chlorosilane compounds, it is possible to use them alone or mixed.
[0026]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a conceptual diagram of a method for producing polycrystalline silicon by the Siemens method.
[0027]
In the production of polycrystalline silicon by the Siemens method, the reaction furnace 10 called a bell jar is opened, and a predetermined number of seed cores 20 are set on the furnace bottom. The seed core 20 is made of thin rectangular bar-shaped polycrystalline silicon, and is combined in a gate shape to be connected to a pair of electrodes at the bottom of the furnace. When the seed core 20 is set, the reaction furnace 10 is closed and the inside of the furnace is evacuated. Thereafter, the inside of the furnace is pressurized and replaced with hydrogen gas or inert gas. At this time, the oxygen concentration in the furnace gas after completion of the substitution is controlled to 50 ppm or less, preferably 30 ppm or less.
[0028]
When the atmosphere replacement in the furnace is finished, a predetermined number of seed cores 20 set in the furnace are energized and heated simultaneously. The heating temperature is 1100 to 1250 ° C., preferably 1160 to 1250 ° C., more preferably 1210 to 1250 ° C. in terms of surface temperature. In this state, a mixed gas of chlorosilanes and hydrogen is supplied into the furnace as a raw material gas. Thereby, precipitation of polycrystalline silicon on the surface of the seed core 20 is started. Regarding the surface temperature after the elapse of the deposition start period, the amount of electric power is adjusted to a steady temperature condition of around 1000 ° C.
[0029]
When the deposited silicon 30 reaches a predetermined amount, the supply of the source gas into the furnace is stopped. Also, the power supply to the polycrystalline silicon is stopped. In this way, a rod-shaped polycrystalline silicon product is manufactured.
[0030]
The manufactured polycrystalline silicon product is taken out of the furnace, and both ends are cut off to form a recharging rod. A wafer-like target sample is collected from the rod by round cutting. An etching process of 15 μm is performed on the surface of the target sample using a mixed acid solution having a ratio of 50% hydrogen fluoride aqueous solution and 70% nitric acid aqueous solution of 1:50. The liquid temperature of the mixed acid is 25 ° C. After etching, the etching depth at the boundary portion between the seed core portion and the deposited silicon portion is measured, and a measured value of 200 μm or less is a non-defective product that is less likely to be cracked by end face machining for additional charging, exceeding 200 μm. The product is a defective product that is prone to cracking.
[0031]
By setting the oxygen concentration in the furnace gas when starting energization to the seed core to 50 ppm or less and setting the surface temperature of the seed core when starting to deposit silicon to 1100 to 1250 ° C., the product is generally good. Generation of defective products is avoided. Then, end face machining for recharging is performed on the non-defective product.
[0032]
【Example】
Next, examples of the present invention will be shown, and the effects of the present invention will be clarified by comparing with comparative examples.
[0033]
Example 1
When producing polycrystalline silicon by the Siemens method, a 9 mm square seed core made of polycrystalline silicon was assembled in a torii type and set in a reaction furnace. The inside of the reaction furnace was depressurized to 0.03 kPaabs by evacuation. Thereafter, the inside of the reactor was pressurized and replaced to 220 kPaabs with high-purity hydrogen gas. At this time, when the oxygen concentration in the atmosphere gas in the furnace was measured using a trace oxygen concentration meter, it was 29 ppm.
[0034]
The seed core in the reaction furnace was energized and heated, and the surface temperature of the seed core was measured using a radiation thermometer from a monitoring window provided in the reaction furnace. After confirming that the surface temperature was 1160 ° C., a raw material gas in which trichlorosilane and hydrogen were mixed at a ratio of 1: 6.5 was supplied into the reaction furnace to start precipitation. After 10 minutes from the start of supply of the raw material gas, the surface temperature of the seed core was changed from 1160 ° C. to 1000 ° C. over 120 minutes by adjusting the amount of energization, and then the precipitation was continued at 1000 ° C. Thus, a polycrystalline silicon rod having an outer diameter of about 135 mm was manufactured.
[0035]
The surface of the wafer-like sample collected from the manufactured polycrystalline silicon rod was etched by 15 μm with a mixed acid solution (liquid temperature 25 ° C.) having a 1:50 ratio of 50% aqueous hydrogen fluoride and 70% aqueous nitric acid. The dent in the boundary part between the seed core part and the precipitated silicon part could not be confirmed visually. When the depth of this dent was measured using a surface roughness meter, it was confirmed that the centering was good with a width of 100 μm and a depth of 50 μm.
[0036]
Since the manufactured polycrystalline silicon rod was used as an additional charge raw material in the production of a silicon single crystal by the CZ method, the rate of occurrence of work cracks was 0.5% when grooves were formed on the rod end face by machining.
[0037]
Example 2
In Example 1, the surface temperature of the seed core at the start of the reaction was 1210 ° C. Other conditions were the same as in Example 1.
[0038]
After the same etching treatment as in Example 1, a dent at the boundary between the seed core portion and the deposited silicon portion was visually observed, but the dent could not be confirmed. When the depth of this dent was measured using a surface roughness meter, it was confirmed that the centering state was even better with a width of 50 μm and a depth of 20 μm.
[0039]
In order to use the manufactured polycrystalline silicon rod as an additional charge raw material in the manufacture of a silicon single crystal by the CZ method, the rate of occurrence of work cracks was 0% when grooves were formed on the rod end face by machining.
[0040]
Comparative Example 1
In Example 1, the pressure after evacuation in the reaction furnace was set to 0.1 kPaabs, and then the pressure in the reaction furnace was increased to 220 kPaabs with high-purity hydrogen gas. At this time, when the oxygen concentration in the atmosphere gas in the furnace was measured using a trace oxygen concentration meter, it was 85 ppm. Other conditions were the same as in Example 1.
[0041]
After the same etching treatment as in Example 1, the dent at the boundary between the seed core portion and the deposited silicon portion was visually observed. Although the dent could not be confirmed by visual observation, when the depth of the dent was measured using a surface roughness meter, the width was 150 μm and the depth was 250 μm, and the manufactured polycrystalline silicon had a poor cored state. confirmed.
[0042]
In order to use the manufactured polycrystalline silicon rod as an additional charge raw material in the production of a silicon single crystal by the CZ method, the rate of occurrence of work cracks was 5% when grooves were formed on the end face of the rod by machining.
[0043]
Comparative Example 2
In Example 1, the surface temperature of the seed core at the start of the reaction was 1000 ° C. Other conditions were the same as in Example 1.
[0044]
After the same etching treatment as in Example 1, the dent at the boundary between the seed core portion and the deposited silicon portion was visually observed. Although the dent could not be confirmed by visual observation, when the depth of the dent was measured using a surface roughness meter, the width was 300 μm and the depth was 250 μm, and the manufactured polycrystalline silicon had a poor cored state. confirmed.
[0045]
In order to use the manufactured polycrystalline silicon rod as an additional charge raw material in silicon single crystal manufacturing by the CZ method, the rate of occurrence of processing cracks was 6% when grooves were formed on the rod end face by machining.
[0046]
【The invention's effect】
As described above, the polycrystalline silicon according to the present invention suppresses the generation of oxide at the boundary between the seed core portion and the deposited silicon portion, and has a good core state, so that it can be recharged or recharged. There is an effect that cracks in machining can be reliably prevented without depending on heat treatment.
[Brief description of the drawings]
FIG. 1 is a conceptual diagram of a method for producing polycrystalline silicon by a Siemens method.
[Explanation of symbols]
10 reactor 20 seed core 30 precipitated silicon

Claims (2)

Polycrystalline silicon produced using chlorosilanes by the Siemens method. Etching treatment of 15 μm with a mixed acid solution having a ratio of 50% hydrogen fluoride aqueous solution and 70% nitric acid aqueous solution to the cross section of 1:50. Polycrystalline silicon having a depth of an etching recess formed at a boundary portion between a seed core portion and a deposited silicon portion in the cross section of 200 μm or less. The polycrystalline silicon according to claim 1, wherein the depth of the etching recess is 50 μm or less.

Images