JP4273793B2 - Single crystal manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for producing a single crystal, and more particularly to a method for producing a silicon single crystal in which nitrogen and boron are added as dopants.
[0002]
[Prior art]
Conventionally, the Czochralski method (CZ method) and the floating zone method (FZ method) are known as methods for producing a single crystal such as a silicon single crystal.
In order to produce a silicon single crystal by the CZ method, polycrystalline silicon is contained as a raw material in a crucible, and a seed crystal is fused to a raw material melt obtained by heating and melting the single crystal. Crystals are grown. In recent years, the size of single crystals has increased, and so-called MCZ method is often used in which single crystals are grown while applying a magnetic field to the melt.
[0003]
The grown silicon single crystal is then processed into a mirror surface wafer through processes such as slicing, chamfering, and polishing, and an epitaxial layer may be further grown thereon. In such an epitaxial wafer, if heavy metal impurities are present on the silicon wafer serving as a substrate, the semiconductor device will have poor characteristics. Therefore, it is necessary to reduce the heavy metal impurities as much as possible.
[0004]
Therefore, the importance of gettering technology as one of the technologies for reducing heavy metal impurities is increasing, and as a substrate for an epitaxial wafer, it has a high gettering effect and a low resistivity (for example, 0.1Ω · cm or less). ) P-type silicon wafers are often used.
In addition, nitrogen doping is increasingly used for the purpose of increasing the BMD and controlling the grown-in defect size.
Therefore, in recent years, the MCZ method (or CZ method) is used to grow a large-diameter P-type silicon single crystal having a diameter of 200 mm or more, particularly 300 mm, and nitrogen-doped for resistance to gettering. A lot is happening.
[0005]
For example, in order to grow a P-type silicon single crystal by the CZ method, boron is generally used as a dopant for controlling the resistivity. As the boron dopant, specifically, there are a case where a metal boron element is used and an alloy which is once dissolved in silicon.
[0006]
On the other hand, regarding the method of doping nitrogen, there are cases where a solid such as a nitride is used and a nitrogen-containing gas is used.
As a method of using a solid nitrogen dopant, a method of mixing a nitride such as a sintered product of silicon nitride powder in a silicon melt (see Patent Document 1), forming a nitrogen-doped FZ silicon or silicon nitride film There has been proposed a method of adding a silicon wafer to a raw material (see Patent Document 2).
As a method using a nitrogen-containing gas, a method of melting polycrystalline silicon as a raw material in a nitrogen atmosphere (see Patent Document 2), a method of growing a single crystal in a nitrogen-containing atmosphere (see Patent Document 5), and the like It has been known.
In addition, about the case where a silicon single crystal is grown by FZ method, the method of growing a silicon single crystal in nitrogen-containing atmosphere is disclosed (refer patent document 3 and patent document 4).
[0007]
By the way, when a single crystal is grown by the CZ method, dislocation may occur during the growth (dislocation formation). When such dislocations occur, the grown single crystal is melted again (remelted), and the single crystal is grown again. However, when nitrogen doping is performed in a nitrogen-containing atmosphere, a nitride film grows on the surface of the grown crystal. When the crystal is disturbed, it will be remelted and grown again, and the nitrogen concentration in the crystal will be controlled. Almost impossible to do. For this reason, in the CZ method, doping is generally performed using a solid dopant such as silicon nitride.
[0008]
[Patent Document 1]
JP-A-60-251190 [Patent Document 2]
JP-A-5-294780 [Patent Document 3]
JP-A-57-17497 [Patent Document 4]
JP-A-8-91993 [Patent Document 5]
JP 2000-53489 A
[Problems to be solved by the invention]
As described above, when a nitrogen-doped P-type single crystal is grown by the CZ method, a solid nitrogen dopant and a boron dopant are often used, and a boron dopant together with a polycrystalline silicon raw material is contained in a quartz crucible. And a nitrogen dopant, and after melting together, the crystal is grown.
However, according to the investigation by the present inventors, when a nitrogen-doped P-type (boron-doped) single crystal is grown as described above, the frequency of dislocations is higher than in the case of single crystal growth without adding nitrogen. It has been found that there is a problem that the number of times of re-growing by dissolving the dislocated single crystal is increased, resulting in a decrease in productivity.
[0010]
The present invention has been made in view of such a problem. A nitrogen-doped P-type (boron-doped) single crystal having high gettering ability can be produced at high cost with low productivity. An object is to provide a manufacturing method.
[0011]
[Means for Solving the Problems]
In order to achieve the above object, according to the present invention, a polycrystalline raw material is accommodated in a crucible, and a seed crystal is fused from a raw material melt obtained by heating and melting the single crystal and then pulled up to grow a single crystal. A method for producing a crystal, wherein when nitrogen and boron are added as dopants to the single crystal, a solid nitrogen dopant and boron dopant are used as the dopant, respectively, and either one of the dopants is the polycrystalline Provided is a method for producing a single crystal characterized in that it is housed in a crucible together with a raw material and melted, and then the other dopant is added to the raw material melt and melted, and then the single crystal is grown. (Claim 1).
[0012]
As will be described later, analysis by the present inventors revealed that one of the causes of dislocation formation when producing a single crystal by the CZ method is boron nitride (BN) formed in the melting process. did. Therefore, if the nitrogen dopant and boron dopant are melted separately as described above, the solid state nitrogen dopant and boron dopant do not coexist in the raw material melt, and the reaction between nitrogen and boron is suppressed. It was found that the formation of boron nitride can be suppressed. Therefore, if a single crystal is grown after separately melting the solid dopant as described above, dislocation due to boron nitride is prevented, so that productivity can be improved and high getter can be achieved. A nitrogen-doped P-type silicon single crystal having a ring capability can be manufactured at low cost.
[0013]
In this case, after melting one of the dopants together with the polycrystalline raw material, the surface of the raw material melt is solidified, the other dopant is added to the melt with the solidified surface, and the surface is solidified. It is preferable to melt together with the liquid (claim 2).
When adding the dopant to be added later, if the surface of the raw material melt is solidified, the melt can be prevented from splashing and safety can be improved, and the dopant can be surely secured together with the solidified surface. The number of dislocations of the single crystal can be reduced.
[0014]
The boron dopant is preferably added so that the resistivity of the single crystal to be grown becomes a boron concentration that is 0.001 Ωcm or more and 1000 Ωcm or less (Claim 3).
When the resistance is higher than 1000 Ωcm, the amount of boron added is small, which is not a problem. When the resistance is less than 0.001 Ωcm, the boron is close to the solid solution limit, and the crystal is difficult to be made into a single crystal. On the other hand, the present invention is particularly effective because dislocations due to BN are likely to occur during the growth of boron-doped single crystals in the above resistivity range.
[0015]
On the other hand, the nitrogen dopant is preferably added so that the nitrogen concentration in the single crystal to be grown is 1 × 10 ¹⁰ / cm ³ or more and 5 × 10 ¹⁵ / cm ³ or less.
The nitrogen concentration in the single crystal grown can be adjusted by the amount of nitrogen dopant added to the raw material melt, but if the nitrogen crystal is added to grow the single crystal so that the nitrogen concentration is in the above range, Thus, it is possible to reliably produce a single crystal that has no adverse effect on the single crystallization, sufficiently exhibits the control effect of BMD and grow-in defects, and has further excellent gettering ability.
[0016]
It is preferable to grow a silicon single crystal as the single crystal. Silicon single crystals are in high demand, and high-quality nitrogen-doped P-type silicon single crystals can be produced at a lower cost if manufactured by applying the present invention.
[0017]
In growing a single crystal, it is preferable to grow a single crystal by applying a magnetic field of at least 0.03 Tesla ( 300 gauss ) or more to the raw material melt.
In recent years, a single crystal is often produced by the MCZ method. However, when a magnetic field is applied with a magnetic field strength of 0.03 Tesla ( 300 gauss ) or more, the effect of suppressing convection of the melt is increased and a temperature gradient is likely to occur. . Therefore, the crucible temperature becomes high and boron nitride is easily generated. However, in the present invention, since formation of boron nitride is suppressed, dislocation formation is prevented when growing a single crystal by the MCZ method. A single crystal having a large diameter and high gettering ability can be produced with high productivity.
[0018]
It is preferable to grow a single crystal having a diameter of 200 mm or more as the single crystal.
When growing a large-diameter single crystal having a diameter of 200 mm or more, since the distance from the crucible to the crystal is increased, the temperature of the crucible tends to be high, and boron nitride is easily generated. Therefore, by applying the present invention, formation of boron nitride is suppressed, and a large-diameter single crystal can be manufactured with high productivity.
[0019]
Hereinafter, the present invention will be described in more detail.
The present inventors verify various dislocations using various analytical methods (IR, X-ray diffraction, Raman spectroscopy, fluorescent X-rays, etc.), and the boron-doped low-resistance silicon single crystal undergoes dislocations. One of the causes could be identified as boron nitride (BN) formed by the reaction of nitrogen and boron. Boron nitride is generated at a temperature of about 1500 ° C., but once generated, it is a substance that does not melt unless it is pressurized at 3000 ° C., and causes dislocations. When such boron nitride adheres to the growing single crystal, it is considered that dislocation occurs in the growing single crystal.
[0020]
Therefore, in order to suppress the formation of such boron nitride, the present inventors have finished melting the nitrogen dopant so that the solid state nitrogen dopant and boron dopant do not coexist in the silicon melt. Boron nitride formation is suppressed by melting separately by adding boron dopant later, or by melting separately by adding nitrogen dopant after melting the boron dopant. As a result, it has been found that productivity can be improved and costs can be reduced, and the present invention has been completed.
[0021]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, as a preferred embodiment, a case where a silicon single crystal to which boron and nitrogen are added as dopants is manufactured by the CZ method in the present invention will be described with reference to the drawings.
FIG. 1 shows an outline of an example of a single crystal manufacturing apparatus (pulling apparatus) used when manufacturing a silicon single crystal by the CZ method. This single crystal manufacturing apparatus 20 contains a main chamber 1 equipped with a crucible 5 and a heater 7 for containing a raw material melt 4, and a single crystal rod 3 pulled up from the raw material melt 4, and a pull for taking it out. Chamber 2.
[0022]
The crucible 5 is composed of an inner quartz crucible 5a and an outer graphite crucible 5b. The crucible 5 is placed on the pedestal 15 and rotated through a rotating shaft 16 by a crucible control means (not shown) provided below. It can be moved up and down. A heater 7 is provided around the crucible 5, and a heat insulating member 8 is provided outside the heater 7.
[0023]
A gas flow straightening cylinder 11 is provided between the main chamber 1 and the pulling chamber 2 and close to the melt surface, and a heat shield member 12 is provided at the tip of the flow straightening cylinder 11. Further, an optical system device (not shown) for measuring and observing the diameter and state of the growing single crystal rod 3 is provided above the main chamber 1.
[0024]
The pulling chamber 2 is configured to be open so that the grown single crystal 3 can be taken out, and above the crystal pulling, the single crystal 3 is pulled up while rotating through a wire (or shaft) 13. Means (not shown) are installed.
[0025]
When growing the single crystal 3, the wire 13 is gently lowered from above, and a cylindrical or prismatic seed crystal 14 suspended on the holder 6 at the lower end of the wire 13 is deposited (fused) on the melt surface. Let Next, after necking to gently pull up the seed crystal 14 while rotating the seed crystal 14 to gradually reduce the diameter, the pulling portion is expanded by adjusting the pulling speed and temperature, and the cone portion of the single crystal rod 3 Shift to training. After the cone portion is expanded to a predetermined diameter, the pulling speed and the melt temperature are adjusted again, and the straight barrel portion having a desired diameter is grown.
[0026]
As the single crystal 3 grows, the raw material melt 4 is reduced and the melt surface is lowered. Therefore, the level of the melt surface is kept constant by raising the crucible 5 so that the single crystal rod 3 being grown has a predetermined level. It is adjusted to be the diameter.
Further, during operation, argon gas is introduced into the chambers 1 and 2 from the gas inlet 10 and discharged from the gas outlet 9 in an argon gas atmosphere.
[0027]
In order to manufacture a nitrogen-doped P-type silicon single crystal according to the present invention using such an apparatus 20, first, a solid nitrogen dopant and a boron dopant are prepared, and either one of the dopants is prepared. The polycrystalline silicon raw material is housed in a crucible 5 and melted by a heater 7.
For example, if the nitrogen dopant is to be melted first, solid nitrogen dopant such as silicon previously doped with nitrogen, silicon nitride formed on the surface of silicon wafer, sintered product of silicon nitride powder, etc. It puts in the quartz crucible 5a together with the polycrystalline silicon raw material.
[0028]
The amount of the nitrogen dopant that melts simultaneously with the polycrystalline silicon is reflected in the nitrogen concentration in the single crystal to be grown. Therefore, the amount of the dopant may be determined according to the nitrogen concentration of the target silicon single crystal. However, if the nitrogen concentration in the single crystal is too small, a sufficient effect on BMD and grow-in defects cannot be obtained. Therefore, it is preferably set to 1 × 10 ¹⁰ / cm ³ or more that sufficiently causes heterogeneous nucleation.
[0029]
On the other hand, if the nitrogen concentration in the melt exceeds the solid solution limit in silicon, it becomes difficult to form a single crystal, so that the nitrogen concentration in the grown single crystal is 5 × 10 ¹⁵ / cm ³ or less. It is preferable to add a dopant.
After a predetermined amount of nitrogen dopant is accommodated in the crucible 5 together with polycrystalline silicon, it is heated by a heater to completely melt the polycrystalline silicon and nitrogen dopant.
[0030]
After confirming that the nitrogen dopant and polycrystalline silicon have been melted, a boron dopant is added to the melt. As the boron dopant, for example, a metal boron element, boron-containing silicon, or the like can be used.
[0031]
These boron dopants may be added to the melt as they are, but when the boron dopant is added, the raw material melt may be splashed. Therefore, before the addition, it is preferable to lower the temperature of the melt surface by solidifying the surface by lowering the output of the heater or the like, and to add the boron dopant there. If the addition is performed in this manner, the melt can be prevented from scattering. Then, if the solidified melt surface and the additive dopant are melted together, the dopant can be reliably melted without generating BN. In addition, although the melting time becomes longer due to the solidification of the surface once, since the number of dislocations of the single crystal after the addition of the dopant is reduced, the total operation time including the growth of the silicon single crystal is shortened. Become efficient.
[0032]
The amount of the boron dopant to be added is reflected in the boron concentration in the grown single crystal, that is, the resistivity, and therefore may be determined according to the resistivity of the target silicon single crystal. In general, when growing a P-type silicon single crystal of 1000 Ωcm or less by doping boron for resistance control, boron nitride is likely to be formed. However, in the present invention, a nitrogen dopant and a boron dopant are used. By separately melting, formation of boron nitride can be suppressed, and occurrence of dislocation can be suppressed. However, when a single crystal having a resistivity smaller than 0.001 Ωcm is grown, the boron concentration in the melt becomes extremely high, exceeding the solid solution limit of boron in silicon, and difficult to be crystallized. Therefore, it is preferable to add a boron dopant so that the resistivity of the grown single crystal becomes a boron concentration of 0.001 Ωcm or more and 1000 Ωcm or less.
After the desired amount of boron dopant is added, the boron dopant is melted together with the melt whose surface is solidified, for example, by increasing the heater output.
[0033]
Note that the order of melting the dopant is not limited to the above order, and the boron dopant may be melted again after the boron dopant is completely melted together with the polycrystalline silicon. In any case, the formation of boron nitride due to the reaction between nitrogen and boron is suppressed by completely dividing and melting the nitrogen dopant and the boron dopant.
[0034]
After both the dopants are melted separately as described above, a seed crystal is fused to the raw material melt and slowly pulled up while rotating to grow a single crystal.
The size of the single crystal to be grown is not particularly limited, but when growing a large-diameter silicon single crystal having a diameter of 200 mm or more, particularly 300 mm, a magnetic field application device is provided outside the main chamber 1. In many cases, the growth is performed by the MCZ method using an apparatus. At this time, if a magnetic field is applied with a central magnetic field strength of 0.03 Tesla ( 300 gauss ) or more, the effect of suppressing the convection of the melt is increased, and the crucible temperature becomes high and boron nitride is easily formed. Since the formation of boron nitride is suppressed by separately melting the agent, a single crystal having a large diameter and high gettering ability can be grown with high productivity by the MCZ method.
[0035]
In this way, when growing a single crystal rod by the Czochralski method, if the solid nitrogen dopant and boron dopant are separately melted so as not to coexist in the raw material melt, Since the formation of boron nitride in the melt is suppressed, the frequency of occurrence of dislocations in the single crystal by boron nitride can be reduced, and productivity can be improved. Moreover, since it can implement easily using the conventional manufacturing apparatus, it is advantageous also in the point which does not require the addition of a manufacturing apparatus newly.
[0036]
And the silicon single crystal manufactured as described above has a high gettering ability by promoting oxygen precipitation by nitrogen doping. From this single crystal, processes such as slicing, chamfering, lapping, etching, polishing, etc. The low resistivity wafer obtained through the above process is particularly excellent in gettering ability and can be advantageously used as a substrate for an epitaxial wafer.
[0037]
【Example】
Examples of the present invention and comparative examples will be described below.
<Example 1>
Using a single crystal manufacturing apparatus 20 (crucible diameter: 800 mm) schematically shown in FIG. 1, a P-type (boron doped) silicon single crystal doped with nitrogen having a diameter of 12 inches (300 mm) by the Czochralski method (CZ method) I grew up. Here, the nitrogen concentration in the crystal was in the range of 2 to 8 × 10 ¹³ / cm ³ and the resistivity was in the range of 1 to 10 Ωcm.
In the melting step, 320 kg of polycrystalline silicon raw material was charged in the crucible, and at the same time, silicon nitride for nitrogen doping was added. After all of this was melted by heating with a heater, the output of the heater was lowered to solidify only the melt surface, and resistance control boron was added on the solidified surface and melted again.
[0038]
In the crystal growth step, a horizontal magnetic field having a central magnetic field strength of 0.35 Tesla ( 3500 gauss) was applied, and a crystal having a straight body length of about 100 cm was grown from the melt.
When the crystal has undergone dislocations on the way, the crystal is again melted and grown again, and remelting and regrowth are repeated until a single crystal that can be used as a product is obtained. Under such conditions, a total of 6 crystals were produced.
[0039]
<Comparative example>
In the crucible, 320 kg of silicon polycrystalline raw material, silicon nitride for nitrogen doping, and boron for resistance control were charged at the same time, and were melted at one time by heating with a heater. The other conditions were the same as in the example, and the single crystal was grown. Also in the comparative example, remelting and regrowth were repeated until a single crystal that could be used as a product was obtained, and a total of 12 silicon single crystals were manufactured.
[0040]
<Result>
2 to 4 show the results of comparison with respect to melting time, number of dislocations, and productivity in Examples and Comparative Examples.
The total melting time is about 20% longer than that of the comparative example in which all of the dope was melted at one time as shown in FIG. However, the number of dislocations was 40% less in the example than in the comparative example as shown in FIG. Therefore, as shown in FIG. 3, the productivity of the example was slightly more than 10% higher than the comparative example.
[0041]
The present invention is not limited to the above embodiment. The above embodiment is merely an example, and the present invention has the same configuration as that of the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.
For example, although the case where a silicon single crystal is manufactured has been described in the above embodiment, the present invention can also be applied to a case where another single crystal to which nitrogen and boron are added as dopants is manufactured by the CZ method.
[0042]
【The invention's effect】
As described above, in the present invention, when growing a single crystal to which nitrogen and boron are added as dopants by the Czochralski method, a solid nitrogen dopant and a boron dopant are used as dopants, respectively. Boron nitride by melting each dopant separately, such as adding boron dopant after melting and melting or adding nitrogen dopant after melting boron dopant. The formation of can be suppressed. Therefore, the frequency of occurrence of dislocations in the single crystal due to boron nitride can be greatly reduced, and a nitrogen-doped P-type silicon single crystal having high gettering capability can be produced with high productivity. In particular, a reduction in manufacturing cost can be achieved.
[Brief description of the drawings]
FIG. 1 is a schematic view of an example of a single crystal production apparatus.
FIG. 2 is a graph comparing time taken for melting raw materials in Examples and Comparative Examples.
FIG. 3 is a graph comparing the number of occurrences of dislocations in Examples and Comparative Examples.
FIG. 4 is a graph comparing productivity in examples and comparative examples.
[Explanation of symbols]
1 ... Main chamber, 2 ... Pulling chamber, 3 ... Single crystal rod,
4 ... Raw material melt, 5 ... Crucible, 5a ... Quartz crucible, 5b ... Graphite crucible,
6 ... Seed crystal holder, 7 ... Heater, 8 ... Heat insulation member,
DESCRIPTION OF SYMBOLS 9 ... Gas outflow port, 10 ... Gas introduction port, 11 ... Rectification cylinder, 12 ... Heat insulation member, 13 ... Wire, 14 ... Seed crystal, 15 ... Pedestal,
16 ... crucible rotating shaft, 20 ... single crystal manufacturing apparatus.

Claims (7)

  A method for producing a single crystal by the Czochralski method, in which a polycrystalline material is contained in a crucible, and a seed crystal is fused and pulled up from a raw material melt obtained by heating and melting the crystal, and the single crystal is grown. In the case of adding nitrogen and boron as a dopant, a solid nitrogen dopant and a boron dopant are used, respectively, and after either one of the dopants is housed in a crucible together with the polycrystalline raw material and melted, A method for producing a single crystal, comprising adding the other dopant to the raw material melt and melting it, and thereafter growing the single crystal.   After melting the one dopant together with the polycrystalline raw material, solidify the surface of the raw material melt, add the other dopant to the melt with the solidified surface, and melt with the melt with the solidified surface The method for producing a single crystal according to claim 1, wherein:   The single crystal production according to claim 1 or 2, wherein the boron dopant is added so that the resistivity of the grown single crystal becomes a boron concentration of 0.001 Ωcm or more and 1000 Ωcm or less. Method. The nitrogen dopant is added so that a nitrogen concentration in a single crystal to be grown is 1 × 10 ¹⁰ / cm ³ or more and 5 × 10 ¹⁵ / cm ³ or less. 4. The method for producing a single crystal according to any one of 3 above.   The method for producing a single crystal according to any one of claims 1 to 4, wherein a silicon single crystal is grown as the single crystal. 6. The single crystal is grown by applying a magnetic field of at least 0.03 Tesla ( 300 gauss ) or more to the raw material melt when the single crystal is grown. The manufacturing method of the single crystal of description.   The method for producing a single crystal according to claim 1, wherein a single crystal having a diameter of 200 mm or more is grown as the single crystal.

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