CN102912424A - Method for improving uniformity of axial resistivity of czochralski silicon and obtained monocrystalline silicon - Google Patents

Abstract

The invention discloses a method for improving the axial resistivity uniformity of Czochralski monocrystalline silicon, which comprises the following steps: (1) melting polycrystalline silicon raw materials and solid dopant under an argon atmosphere to obtain stable molten silicon; 2) Introduce the seed crystal in the stable molten silicon, and the crystal growth enters the equal-diameter growth stage through the process of necking and shouldering; (3) in the equal-diameter growth stage, the conductive type of the solid dopant is opposite to that of the solid dopant. Doping gas until the growth of Czochralski single crystal silicon is completed. In the method for improving the axial resistivity uniformity of Czochralski single crystal silicon in the present invention, the type and dosage of doping gas are conveniently controlled, and various required impurity concentration distributions can be obtained; the utilization rate of Czochralski single crystal silicon is improved; significantly The resistivity uniformity of Czochralski monocrystalline silicon is improved.

Description

Method for Improving the Uniformity of Axial Resistivity of Czochralski Single Crystal Silicon and the Obtained Single Crystal Silicon

technical field

The invention relates to the field of semiconductor materials, in particular to a method for improving the axial resistivity uniformity of Czochralski single crystal silicon through a gas phase doping method and the obtained single crystal silicon.

Background technique

In the foreseeable future, photovoltaic power generation is the most important renewable energy technology. According to the forecast of the European Photovoltaic Industry Association (EPIA), photovoltaic power generation will meet nearly 10% of the world's electricity demand in 2030.

Current solar cells are mainly manufactured based on boron-doped single crystal silicon materials, but because single crystal silicon contains boron and oxygen at the same time, boron-oxygen complexes will be formed during use, resulting in lower photoelectric conversion efficiency of solar cells. With a drop of more than 10%, the performance of the solar cell is significantly reduced. To solve this problem, researchers invented gallium-doped monocrystalline silicon solar cells.

Although gallium-doped monocrystalline silicon solar cells have no light attenuation phenomenon, they have great defects. Due to the extremely low segregation coefficient of gallium in silicon (about 0.008), this leads to the growth of gallium-doped Czochralski monocrystalline silicon. During the process, the axial resistivity varies greatly, and the resistivity of the last grown monocrystalline silicon in the Czochralski monocrystalline silicon cannot meet the requirements, so that the actual utilization rate of gallium-doped Czochralski monocrystalline silicon is only about 80%.

In addition, the resistivity distribution of gallium-doped Czochralski monocrystalline silicon is wide, resulting in a wide distribution of solar cell efficiency, which seriously affects the consistency of power output of solar cell modules.

These defects lead to high cost of gallium-doped solar cells and difficulties in large-scale application in the industry. So far, no effective method has been announced at home and abroad to obtain gallium-doped Czochralski single crystal silicon with uniform distribution of axial resistivity.

In the field of microelectronics, antimony-doped Czochralski single crystal silicon is also an important material. The n/n+ epitaxial wafer made of it has the advantages of narrow transition zone, steep junction gradient, and small diffusion coefficient of antimony at high temperature. Antimony single crystal silicon becomes an important substrate.

However, similar to gallium-doped single crystal silicon, the equilibrium segregation coefficient of antimony in silicon is also very small (about 0.023), which also leads to poor axial resistivity uniformity of antimony-doped Czochralski single crystal silicon.

Contents of the invention

The invention provides a method for improving the uniformity of the axial resistivity of Czochralski single crystal silicon. Through the gas phase doping method, the uniformity of axial resistivity of Czochralski single crystal silicon is greatly improved, which is simple and practical, and has good Industrial application prospects.

A method for improving the axial resistivity uniformity of Czochralski single crystal silicon, comprising the steps of:

(1) Melting the polysilicon raw material and solid dopant under an argon atmosphere to obtain stable molten silicon;

(2) The seed crystal is introduced into the stable molten silicon, and the crystal growth enters the equal-diameter growth stage through the necking and shouldering process;

(3) In the equal-diameter growth stage, a doping gas having a conductivity type opposite to that of the solid dopant is introduced until the growth of the Czochralski single crystal silicon is completed.

During the normal equal-diameter growth process of Czochralski silicon single crystal, doping gas is continuously and uniformly introduced to realize gas phase doping, and the distribution of gas phase impurities introduced by doping gas in silicon single crystal obeys the following equation:

${\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; ak</span>}}{\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; [</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

in,

C _s is the doping concentration of impurities in the silicon single crystal;

a is the doping rate of the doping gas;

V is the growth rate of Czochralski monocrystalline silicon;

k is the segregation coefficient of impurities introduced by the doping gas;

g is the coagulation fraction.

If there is co-doping of p-type impurities and n-type impurities, the distribution of carriers in the silicon crystal obeys the following equation (taking p-type gallium and n-type phosphorus co-doping as an example):

$\mathrm{<span\; class="notranslate">\; p</span>}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\frac{{\mathrm{<span\; class="notranslate">\; ak</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; V</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; [</span>{<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; g</span>}<span\; class="notranslate">\; )</span>}^{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; ]</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

in,

p is the concentration of carriers in the silicon crystal;

C ₀ is the initial melt concentration of gallium;

k ₁ is the segregation coefficient of gallium;

g is the solidification fraction;

a is the doping rate of the doping gas (the amount of impurities introduced per unit time, controlled by the flow rate of the doping gas);

V is the growth rate of Czochralski monocrystalline silicon;

k ₂ is the segregation coefficient of phosphorus;

表示固体掺杂剂引入的杂质浓度；

Indicates the impurity concentration introduced by the solid dopant;

Indicates the impurity concentration introduced by the doping gas.

By adjusting the concentration and flow rate of the doping gas, the optimal gas phase doping amount can be obtained, so that the axial resistivity of the Czochralski silicon single crystal can be kept uniformly distributed.

The optimum gas doping amount is:

$\frac{\mathrm{<span\; class="notranslate">\; a</span>}}{{\mathrm{<span\; class="notranslate">\; V</span>}}_{\mathrm{<span\; class="notranslate">\; optim</span>}<span\; class="notranslate">\; .</span>}}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; C</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

in,

C ₀ is the initial melt concentration of solid dopant;

k ₁ is the segregation coefficient of the solid dopant;

a is the doping rate of the doping gas;

V is the growth rate of Czochralski monocrystalline silicon;

k ₂ is the segregation coefficient of impurities in the dopant gas.

According to this formula, in the compensation crystal of gallium and phosphorus, the suitable doping amount of phosphine is 0.0268C ₀ (C ₀ is the initial melt concentration of gallium), and it should not exceed 0.0326C ₀ , and a small part will appear if it exceeds 0.0404C ₀ Inversion type; for antimony and boron compensation crystals, the appropriate doping amount of borane is 0.0463C ₀ (C ₀ is the initial melt concentration of antimony), and should not exceed 0.0569C ₀ , and a small amount of antimony will appear if it exceeds 0.0775C ₀ type. In practice, the optimal gas doping amount can vary within a range up and down from the appropriate value.

During the manufacturing process of Czochralski silicon single crystal, the polycrystalline silicon raw material is placed in a quartz crucible, and a corresponding amount of solid-phase dopant is put in according to the target resistivity. The resistivity of the long part) and the tail (the part where the crystal growth ends) will be different, resulting in uneven axial resistivity distribution.

In order to improve the axial resistivity of the Czochralski silicon single crystal, during the equal-diameter growth stage of the Czochralski silicon single crystal, the dopant gas with the conductivity type opposite to that of the solid dopant is continuously fed at a uniform speed. Inject the dopant gas, continue the process of finishing and cooling under the protection of argon, and complete the growth process of the entire silicon crystal. The doping amount of the doping gas is 0.001-0.1 times of the initial melt concentration of the solid dopant. The specific value is calculated according to formula (3).

Preferably, when the solid dopant is gallium, the dopant gas is phosphine, and the doping amount of phosphine is 0.025-0.03 times the initial melt concentration of gallium.

The utilization rate of the produced Czochralski silicon single crystal is close to 100% (removing the crystal head and tail), which is significantly improved compared with the 80% Czochralski silicon single crystal without doping gas, and the resistivity of the area above 90% is controlled In the range of 0.5 ~ 3Ω.cm.

Preferably, when the solid dopant is antimony, the doping gas is diborane, and the doping amount of diborane is 0.045-0.055 times the initial melt concentration of antimony.

The axial resistivity variation of more than 80% of the produced Czochralski silicon single crystal is controlled within the range of 25%.

Preferably, an inert gas is mixed in the doping gas in the step (3).

The inert gas is used to dilute the dopant gas, and the gas that does not affect the crystal growth should be selected, such as argon, which is usually used as a protective gas for crystal growth, or nitrogen with stable properties.

The mixed dopant gas can be directly passed into the crystal growth chamber, as shown in Figure 1, or the inert gas source 2 and the dopant gas source 4 can be respectively set, and the inert gas flowmeter 1, doping gas can be adjusted. The gas flowmeter 3 and the flowmeter 5 of the mixed gas pass into the crystal growth chamber 6 through the high-purity quartz glass pipeline 7 after obtaining the mixed gas with a certain ratio.

Preferably, the volume percentage of the inert gas in the doping gas is 1-99.9%. The volume percentage of the inert gas in the dopant gas is not strictly limited. The inert gas dilutes the dopant gas, avoiding the excessive concentration of the dopant gas, which may be caused by the excessive concentration of the local dopant gas in the Czochralski silicon single crystal. anti-type.

Preferably, the flow rate of the dopant gas into the growth chamber is 1-1000 sccm (standard milliliter per minute).

The flow rate of the doping gas depends on the type and concentration of the doping gas and the type and concentration of the solid dopant in the crystal. It is necessary to ensure that the doping rate of the doping gas is compatible with the growth rate of the crystal, so that doping with the opposite conductivity type The impurity gas compensates the solid-phase dopant, and a Czochralski silicon single crystal with uniform axial resistivity is obtained.

The axial resistivity of more than 90% of the region of gallium-phosphorus compensated Czochralski monocrystalline silicon for solar cells prepared by the method for improving the uniformity of axial resistivity of Czochralski single crystal silicon according to the present invention is 0.5-3Ωcm, The axial resistivity variation of more than 80% of Czochralski monocrystalline silicon compensated by heavily doped antimony boron for microelectronics is less than 25%.

The Czochralski monocrystalline silicon manufacturing method provided by the present invention has the following advantages:

(1) The type and amount of doping gas are convenient to control, and various required impurity concentration distributions can be obtained;

(2) Improve the utilization rate of Czochralski silicon single crystal;

(3) Remarkably improve the resistivity uniformity of the crystal.

Description of drawings

Fig. 1 is the device schematic diagram that implements the method of the present invention to manufacture Czochralski silicon single crystal;

Fig. 2 is the resistivity distribution diagram of the Czochralski silicon single crystal prepared in embodiment 1;

FIG. 3 is a resistivity distribution diagram of the Czochralski silicon single crystal prepared in Example 2. FIG.

Detailed ways

Example 1

Add 60kg of high-purity polysilicon raw material into the quartz crucible, and at the same time add 2.982g of high-purity gallium (the target resistivity of the control head is 1.8 ohm.cm).

Under the protection of argon, the temperature is gradually raised to above 1420°C to completely melt the high-purity polysilicon. According to the conventional crystal growth parameters, the seeding and shouldering are carried out to enter the equal-diameter growth stage, and the crystal pulling rate is controlled to 1.2 mm/min, and the crystal diameter is 150 mm.

The furnace pressure is controlled to 20 Torr, and the argon gas flow rate is 70 slpm (standard liter per minute).

Set the parameters for the dopant gas:

1) Phosphine diluted with argon is used as the doping gas, and the volume ratio of phosphine to argon is 1:1000;

2) Assuming that the doping efficiency is 100% (the impurities introduced by the doping gas can all enter into the Czochralski silicon single crystal), the flow rate of the doping gas is set to 21.14 sccm.

After the equal-diameter growth, close the doping gas, finish normally, and cool down.

Samples were taken from different parts of the grown Czochralski silicon single crystal, and the resistivity distribution was tested using a four-probe resistivity meter. The results are shown in Figure 2.

If the resistivity of silicon wafers for solar cells is controlled at 0.5-3 ohm.cm, the utilization rate of silicon single crystal doped with gallium is only 75%; Gas monocrystalline silicon), its utilization rate can be increased to 93%, which means that after removing the head and tail, gallium phosphorus co-doped single crystal silicon can be fully utilized. At the same time, the resistivity distribution of gallium-doped silicon single crystal is very uneven. For silicon single crystals co-doped with gallium and phosphorus, most of the resistivity is very uniform, and only a small part of the resistivity decreases at the end, and these obtained silicon wafers can be used to prepare high-efficiency solar cells without light attenuation. Battery.

Example 2

Add 60 kg of high-purity polysilicon raw material into the quartz crucible, and at the same time add 416.64 g of high-purity antimony (the target resistivity of the control head is 0.016 ohm.cm).

Under the protection of argon, the temperature is gradually raised to above 1420°C to completely melt the polysilicon. According to the conventional crystal growth parameters, the seeding and shouldering are carried out to enter the equal-diameter growth stage, the crystal pulling rate is controlled to 0.8mm/min, and the crystal diameter is 150mm.

The furnace pressure is controlled to 20 Torr, and the argon gas flow rate is 70 slpm.

Set the parameters for the dopant gas:

1) Diborane diluted with argon, the volume ratio of diborane to argon is 1:100;

2) Assuming that the doping efficiency is 100%, the flow rate of the doping gas is set to 97.58 sccm.

After the equal-diameter growth is completed, the dopant gas is turned off, finished normally, and cooled.

Samples were taken from different parts of the grown single crystal silicon, and the resistivity distribution was tested using a four-probe resistivity meter. The results are shown in Figure 3.

According to the requirements of microelectronics manufacturers for the change of resistivity to fluctuate by 25%, the utilization rate is only about 40% for monocrystalline silicon doped with antimony only, and for monocrystalline silicon co-doped with antimony and boron (that is, the dopant gas is introduced Single crystal silicon), the utilization rate can reach about 80%, nearly doubled, significantly improving the utilization rate of single crystal silicon, and significantly improving the uniformity of resistivity, and the quality control of integrated circuits.

Claims (9)

1. A method for improving the uniformity of the axial resistivity of Czochralski silicon comprises melting a polycrystalline silicon raw material and a solid dopant in an argon atmosphere to obtain stable molten silicon; introducing seed crystals into the stable molten silicon, and leading the crystal growth to enter an isodiametric growth stage through necking and shouldering processes; the method is characterized in that doping gas with the conductivity type opposite to that of the solid dopant is introduced in the equal-diameter growth stage until the growth of the czochralski silicon is finished.

2. The method of improving the axial resistivity uniformity of czochralski silicon as claimed in claim 1 wherein the doping gas is doped in an amount of 0.001 to 0.1 times the initial melt concentration of the solid dopant.

3. The method of claim 2 wherein when the solid dopant is gallium, the dopant gas is phosphane in an amount of 0.025 to 0.03 times the initial melt concentration of gallium.

4. The method for improving the axial resistivity uniformity of czochralski silicon as claimed in claim 2, wherein when the solid dopant is antimony, the doping gas is diborane, and the doping amount of the diborane is 0.045-0.055 times of the initial melt concentration of the antimony.

5. The method for improving the axial resistivity uniformity of czochralski silicon as claimed in any one of claims 1 to 4, wherein the doping gas in the step (3) is mixed with an inert gas.

6. The method of improving the axial resistivity uniformity of czochralski silicon as claimed in claim 5, wherein the volume percent of the inert gas in the dopant gas is 1 to 99.9%.

7. The method of improving the axial resistivity uniformity of czochralski silicon as claimed in claim 6 wherein the dopant gas is introduced into the growth chamber at a flow rate of 1 to 1000 sccm.

8. The Czochralski silicon produced by the method for improving the uniformity of the axial resistivity of Czochralski silicon as claimed in claim 3, wherein the axial resistivity of 90% or more of the regions is 0.5 to 3 Ω cm.

9. The Czochralski single crystal silicon produced by the method of improving the uniformity of the axial resistivity of the Czochralski single crystal silicon of claim 4, wherein greater than 80% of the regions have an axial resistivity variation of less than 25%.

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