JP2562579B2 - Single crystal manufacturing method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial application] The present invention relates to the production of a silicon single crystal, as a semiconductor device material, an N-type silicon CZ single crystal having a resistivity in the practical range which is extremely uniform in the length direction. Regarding the method.

[Prior Art] As conventional silicon single crystals, FZ single crystals obtained by the floating zone melting method (hereinafter referred to as FZ method) and CZ single crystals obtained by the Czochralski method (hereinafter referred to as CZ method) are widely known. Has been.

In the FZ method, first, a polycrystalline rod having a predetermined diameter is held on the upper shaft and a seed crystal is held on the lower shaft, and the contact portion is melted by a high frequency heating coil.

After the melting is completed, the seed crystal is rotated and the vertical axis is simultaneously lowered at a slow speed to move the melting zone to the upper end of the polycrystalline rod to form a single crystal.

In the CZ method, after melting the raw material polycrystal in a quartz crucible, the tip of the seed crystal with the desired crystal orientation is attached to the melt, and the temperature is set so that the tip is slightly melted and the balance is maintained, and equilibrium is achieved. After reaching, the single crystal is pulled up while rotating the seed crystal.

In this case, for the purpose of homogenizing the temperature of the melt, for example, while rotating the seed crystal and the crucible about 5 to 20 rpm in the opposite directions respectively, while controlling the temperature and pulling rate of the melt to obtain a desired single crystal. Cultivate.

In the FZ method, since the melt does not come into contact with substances other than atmospheric gas, there is no contamination, and it is possible to manufacture crystals with high resistivity and uniform lengthwise, while advanced technology is required to obtain large diameter crystals. Become.

On the other hand, in the CZ method, it is relatively easy to increase the diameter, but since the quartz crucible and the melt are in contact with each other, contamination is likely to occur, and it is difficult to obtain a crystal having a high resistivity and a uniform resistivity in the length direction.

For example, when a high-purity quartz crucible currently on the market is used to grow a non-doped single crystal using N-type raw material polycrystalline silicon having a resistivity of about 1000 Ω · cm, the amount of trace amount contained in the quartz crucible is increased. Boron, aluminum, etc. are melted into the molten silicon, and the single crystal is converted from the crystal top portion to the P-type like the curve C in FIG. 3, and the resistivity is significantly lowered toward the bottom portion. Further, for example, when the source polycrystalline silicon having the same N type and a resistivity of about 130 Ω · cm is also used as a non-doped type, it is N type in the initial stage of the pulling, but the resistivity gradually increases due to the incorporation of acceptors.
Depending on the pulling condition, the resistivity is changed to the P type on the way, and thereafter the resistivity decreases and the resistivity distribution is shown as a curve D in FIG.

MCZ method using magnetic field (Magnetic Applied
Also in the Czochralski method), although the amount of impurity contamination from the quartz crucible is somewhat reduced, the same phenomenon as in the CZ method occurs. This state is shown in FIG.

In CZ single crystals with a resistivity of 50 Ωcm or less, which are usually used in ICs and discrete devices, phosphorus, arsenic, antimony, etc. with a small segregation coefficient, which is doped far beyond the amount of acceptor impurities from the quartz crucible, are used. Due to the donor impurity, the resistivity sharply decreases from the top part to the bottom part of the crystal as shown in FIG. In FIG. 4, E is phosphorus, F is arsenic, and G is the resistivity distribution in the crystal length direction when doped with antimony.

Since it is beneficial to make the resistivity distribution of the single crystal in the longitudinal direction uniform within the practical resistivity range from the viewpoint of device needs and improvement of the crystal acquisition rate, some improvement methods have been reported. For example, in the 1983 edition of "Solid State Technology" August issue, page 121, two crucibles were used, one of which was used to pull a single crystal.
A method of supplying a new raw material melt from the other crucible is shown.

However, these methods have not been put to practical use industrially because there are problems in terms of equipment and technology, such as enlargement of equipment and transfer of silicon melt.

As described above, as for the CZ single crystal, there is still no practical neutron-doped FZ single crystal having a practical resistivity range and a uniform resistivity over the length direction of the crystal.

[Problems to be Solved by the Invention] Since a single crystal produced by the FZ method can obtain an N-type single crystal having high resistivity when a high-purity polycrystal is used as a raw material, it has been conventionally used as a material to be subjected to neutron irradiation treatment. It has been widely practiced.

On the other hand, the single crystal by the CZ method, as described above, is an impurity from the crucible, it is difficult to obtain a high resistivity, and because the resistivity distribution has a gradient in the length direction of the crystal for neutron irradiation treatment It was never used as a material.

However, if a large-diameter CZ single crystal can be used as a material for neutron irradiation treatment, the number of elements produced from one wafer will increase and productivity will improve. from now on,
While it is expected that the diameter of wafers will become larger and larger, it is difficult for the FZ method to do so due to the limitations of the equipment. Therefore, the use of large diameter single crystals by the CZ method has been desired.

The present invention, which was not realized from the technical difficulties as described above, makes it possible to pull a single crystal by the CZ method or the MCZ method at a high resistivity without inclination in the crystal length direction,
Further, this single crystal is subjected to neutron irradiation treatment to give an N-type silicon CZ single crystal having a uniform resistivity in the crystal length direction within the practical resistivity range as a material for semiconductor devices.

[Means for Solving Problems] The present invention is composed of two large steps as described below.

That is, in the method for producing a silicon single crystal in which the silicon single crystal is left in a nuclear reactor and subjected to neutron irradiation doping, when the silicon single crystal is pulled up by the CZ method or the MCZ method as the first step, the conductivity type N type Polycrystalline silicon, for example, N-type polycrystalline silicon having a resistivity of 90 Ω · cm or more is used as a raw material and is pulled up without doping. From the resistivity distribution from the top side to the bottom side of this single crystal and its distribution slope, The amount of the acceptor impurities mixed is obtained, and then, a segregation coefficient that is slightly larger than that for compensating the mixed acceptor impurities and that offsets the distribution gradient of the resistivity distribution in the length direction of the single crystal by the acceptor. A high resistivity N-type silicon single crystal having a very uniform resistivity in the length direction by doping the donor impurity with Then, as a second step, by subjecting this N-type silicon single crystal to neutron irradiation treatment, N-type silicon having a very uniform resistivity in the length direction in the practical resistivity range as a material for semiconductor devices is obtained. CZ single crystal is obtained.

The N-type dopant used in the present invention includes
Examples include phosphorus, antimony, and arsenic.

However, antimony and arsenic are not always practical when they are subjected to neutron irradiation treatment, because their isotopes have a long half-life, which poses a safety problem due to residual radioactivity.

[Operation] The fact that a CZ single crystal having an extremely uniform resistivity in the practical resistivity range can be obtained by the present invention is due to the following action and principle.

That is, when high purity N-type polycrystalline silicon is melted in a commonly used quartz crucible and a single crystal is pulled up by non-doping by the usual CZ method or MCZ method, boron and aluminum contained in the quartz crucible are eluted. As a result, it acts as a so-called acceptor impurity on silicon, and the obtained single crystal becomes a P-type single crystal having a resistivity gradient in the longitudinal direction as shown in FIG. As it is in the form, it becomes a single crystal that is converted to P type on the way.

When the MCZ method is used, the amount of impurities eluted from the quartz crucible is reduced, but there is no change in the tendency that these acceptors mixed in the crystal length direction increase from the crystal top to the bottom.

The inclination of the resistivity distribution is caused by the elution and segregation of impurities from the quartz crucible.

As is well known, the equilibrium segregation coefficient of boron with respect to silicon is 0.8 and that of phosphorus is 0.35.
When phosphorus is used as a dopant in order to obtain N-type single crystal silicon in the resistivity range for discretes and discretes, the length of the pulled single crystal increases due to the difference between the segregation of acceptor impurities from the crucible and the segregation of phosphorus as the dopant. The resistivity distribution in the depth direction is inclined as shown by the curve E in FIG.

As for the elution of impurities from the crucible, the inventors of the present invention have studied in more detail.Since it always occurs from the early stage of pulling to the latter stage, the acceptor incorporated into the single crystal from the crucible along with the progress of pulling is segregated. It became clear that the concentration increased rapidly. This state is shown in FIG. FIG. 6 shows the concentration distribution of acceptor impurities in the crystal length direction, which is obtained by subtracting the donor impurity amount from the impurity amount in a single crystal, which is pulled up undoped using N-type 500 Ω · cm polycrystalline silicon.

Since constant elution of impurities occurs, it was actually measured (curve K in FIG. 6) from the theoretical concentration increase (curve L in FIG. 6) in the acceptor single crystal calculated from the segregation coefficient based on the initial concentration. ) Is higher, and the difference is larger on the single crystal bottom side, that is, in the latter stage of pulling.

According to the present invention, first, in the first step, the concentration increase ratio of this eluted acceptor impurity, especially boron in the crucible, is
The fact that the rate of concentration increase due to segregation of donors, especially phosphorus, is used is utilized.

If only due to the segregation effect, the segregation coefficient of boron is 0.8 and that of phosphorus is 0.35 as described above, so that the rate of increase in concentration with each other will never be equal. The continued elution of boron results in a rate close to the increase rate of phosphorus concentration.

Therefore, when an N-type silicon single crystal is obtained by the CZ method or the MCZ method, a slightly larger amount of donor impurities than the amount of acceptor impurities taken into the single crystal from the crucible that has been grasped in advance, for example, is used. If phosphorus is added and pulled up, the concentration increase due to the eccentricity of the added donor impurity becomes closer to the concentration increase caused by the constant elution and segregation of acceptor impurities from the crucible, and the resistance in the single crystal length direction The slopes of the distribution of the rates cancel each other out,
Finally, an N-type silicon single crystal having a very uniform resistivity distribution is first obtained.

By the way, according to the method of adding a slightly larger amount of dopant than compensating for the acceptor impurities from the quartz crucible as described above, the N-type CZ single crystal in the practical resistivity range is doped by doping the donor which is generally widely used. The amount of doping must be smaller than that in the case of obtaining. Even if the resistivity distribution of the pulled single crystal is uniform, it becomes higher than the practical resistivity as a material for semiconductor devices. Therefore, if the single crystal thus obtained is subjected to neutron irradiation treatment aiming at the target resistivity, finally an N-type silicon single crystal having a very uniform practical resistivity range can be obtained.

 Next, the present invention will be described in detail with reference to examples.

[Example 1] In the present example, when pulling a single crystal according to the present invention, the non-doped pulling single crystal was mixed with impurities from the quartz crucible, so that the conductivity type, the impurity concentration distribution, etc. This was done to understand whether or not it has characteristics.

A 14-inch quartz crucible manufactured by T Co. was loaded with 25 kg of raw material polycrystalline silicon having a resistivity of 500 Ω · cm N, and a 5-inch φ single crystal was pulled by a normal MCZ method.

Curve C in FIG. 3 shows the conductivity type of the single crystal obtained in this example and the resistivity distribution in the length direction.

Further, in FIG. 5, the solid line shows the impurity concentration distribution quantitatively analyzed by the photoluminescence method in the length direction of the single crystal obtained in this example, and the broken line shows spontaneous solidification based on the initial pulling concentration. The impurity concentration distribution calculated from the above theory is shown.

 H represents boron, I represents aluminum, and J represents phosphorus.

As can be seen from this example, when the raw material polycrystalline silicon having N type resistivity of 500 Ω · cm is used, the curve C in FIG. 3 is used.
As described above, the obtained single crystal is P-type and has a gradient in the resistivity distribution in the crystal length direction due to the segregation of impurities.
As described above, the reason why the N-type compound is converted to the P-type compound is that the acceptor impurities are eluted from the crucible and taken into the single crystal. According to FIG. 5, not only acceptors such as boron and aluminum but also phosphorus as a donor is an impurity that is eluted from the crucible and taken into the single crystal. However, as shown in FIG. Since the amount exceeds the donor amount, the resulting single crystal becomes P-type.

A curve K in FIG. 6 is a concentration distribution curve measured by a photoluminescence method in which the donor concentration is subtracted from the acceptor concentration in the length direction of the silicon single crystal obtained in this example, and the curve L is the initial concentration. It is a concentration distribution curve theoretically drawn from.

Table 1 shows the impurity concentration distribution in the length direction of the crystal, that is, in each solidification rate. Further, pulling was similarly performed by the CZ method, and the impurity concentration distribution in the crystal length direction is shown in Table 2.

In addition, "solidification rate" described in Tables 1 and 2 and the drawings indicates the weight of the single crystal pulled up with respect to the total weight of the raw material melt in%.

Example 2 A 14-inch quartz crucible manufactured by T Co. was loaded with 25 kg of raw material polycrystalline silicon having a resistivity of 130 Ω · cm N, and a 5-inch φ single crystal was pulled by a normal MCZ method.

Curve D in FIG. 3 shows the conductivity type of the single crystal obtained in this example and the resistivity distribution in the length direction.

According to this embodiment, the raw material polycrystalline silicon is N type 130Ω.
・ For the cm type, the resistivity remains N type for a while in the early stage of pulling up, and the resistivity increases, but as the pulling progresses, it eventually changes to P type, and then the resistivity gradually decreases.

As in Example 1, this indicates that the acceptor was eluted from the quartz crucible.

[Example 3] Next, from this result, the slope of the resistivity distribution in the single crystal in Example 1 was canceled to obtain a uniform 500 Ω · c in the length direction.
Regarding the amount of phosphorus doped, 25 kg of N-type polycrystalline silicon having a resistivity of 500 Ω · cm was doped with 3.12 × 10 ¹⁷ atom of phosphorus atoms by calculating the doping amount of phosphorus as follows so as to give an N-type single crystal of m. MC loaded in the quartz crucible used in Example 1
It was pulled up by the Z method.

<Calculation of Dope Amount> From Table 1, for example, the impurity concentration in the case of non-doping at the solidification rate of 74.7% is phosphorus 4.64 × 10 ¹² atom / cm ³ boron 10.8 × 10 ¹² atom / cm ³ aluminum 14.5. × 10 ¹² atom / cm ³ Therefore, the acceptor that contributes to the resistivity is [boron concentration] + [aluminum concentration] − [phosphorus concentration], that is,
2.07 × 10 ¹³ atom / cm ³ .

Here, in order to compensate for this 2.07 × 10 ¹³ atom / cm ³ acceptor and give a resistivity of N-type 500 Ω · cm, from the Irvin curve, an additional amount of 9 × 10 ¹² atom / cm ³ Phosphorus is needed.

Therefore, when the solidification rate is 74.7%, 2.07
In order to obtain × 10 ¹³ + 9 × 10 ¹² = 2.97 × 10 ¹³ atom / cm ³ , the initial phosphorus concentration is the theoretical formula of spontaneous solidification, Here, Cg: impurity concentration taken into the crystal when the solidification rate is g (atom / cm ³ ) Ko: equilibrium partition coefficient (0.35 because of phosphorus) C _LO : initial impurity concentration (atom / cm ³ ) Now, Cg = Since 2.97 × 10 ¹³ , g = 0.747, Ko = 0.35, C _LO ＝ 3.47 × 10 ¹³ .

Since the density of Si is 2.33, dividing this C _LO by 2.33 gives 1.489.
× 10 ¹³ (atom / cm ³ ) is calculated.

Therefore, phosphorus required in 25 kg of N-type raw material polycrystalline silicon having a resistivity of 500 Ω · cm is 3.72 × 10 ¹⁷ atoms. The doping amount was slightly adjusted from the theoretical formula depending on the pulling conditions, and thus the doping amount was finely adjusted by experiment (the doping amount after the fine adjustment is 3.22 × 10 ¹⁷ atoms).

The resistivity distribution in the length direction of the N-type silicon single crystal obtained in this example is as shown by a straight line A in FIG.

The resistivity distribution in the length direction of this single crystal was extremely uniform, and was approximately 500 Ω · cm, which was higher than that of the pulling single crystal by phosphorus doping which is usually practiced.

 Similarly, the CZ method was also used for similar pulling.

 In this case, the results of non-doping are shown in Table 2.

For example, in order to obtain 300 Ω · cm at a solidification rate of 73%, the same calculation as above is performed to obtain N of resistivity 500 Ω · cm.
The phosphorus atom is 7.04 × 10 ¹⁷ atom in 25 kg of the mold raw material polycrystalline silicon
Will be needed.

 The dope amount was finely adjusted in the same manner as described above.

As a result of this pulling up, as shown by the straight line B in FIG. 2, the resistivity distribution in the length direction of the obtained N-type silicon single crystal is extremely uniform and approximately 300 Ω · cm.

[Example 4] Similar to Example 3, the resistivity distribution gradient of the single crystal in Example 2 was canceled to obtain a uniform resistivity of 500Ω in the longitudinal direction.
When the phosphorus doping amount is calculated so as to give an N-type single crystal of cm, a resistivity of 130 Ω · cmN-type polycrystalline silicon of 25 kg requires 1.08 × 10 ¹⁷ atoms of phosphorus atoms. After finely adjusting the dope amount, the quartz crucible used in Example 1 was loaded with MC
It was pulled up by the Z method.

The pulling result was almost the same as the straight line A in FIG.

Example 5 The single crystal obtained in Example 3 and Example 4 by the MCZ method was subjected to thermal neutron flux density of 6.65 × 10 ¹³ n / cm ² · sec and irradiation time of 6
The neutron irradiation treatment was performed for 770 seconds.

As a result, the obtained single crystal has conductivity type N type and a resistivity of 45.
It was extremely uniform in the practical resistivity range along the length of Ω · cm.

 The result is shown by the straight line X in FIG.

Regarding the single crystal obtained by the CZ method in Example 3, the thermal neutron flux density was 6.65 × 10 ¹³ n / cm ² · sec, and the irradiation time was 522.
The neutron irradiation treatment was performed for 0 seconds.

As a result, the obtained single crystal has conductivity type N type and a resistivity of 40
It was extremely uniform in the practical resistivity range along the length of Ω · cm.

 The result is shown by the straight line Y in FIG.

EFFECTS OF THE INVENTION According to the present invention, pulling can be performed without adding any new mechanism to the pulling device. Moreover,
The result is that a single crystal with a high resistivity, which is extremely uniform in the length direction, is first obtained as compared with the conventional single crystal by the CZ method or the MCZ method.

In the CZ method, the purity of the quartz crucible, the main material such as raw material polycrystalline silicon, the melting temperature of the auxiliary material and the raw material polycrystalline silicon, the melting time, the loading amount and the size and shape of the quartz crucible,
The pull-up speed, the number of rotations of the crucible, and other crystal pull-up conditions such as the suppression of thermal convection of the silicon melt by the MCZ method can control the amount of acceptor impurities taken into the single crystal to some extent, thus reducing the inclusion of acceptor impurities. When the present invention is carried out under such conditions, a single crystal having a high resistivity of several hundred Ω · cm to 1000 Ω · cm, which is uniform in the length direction, can be obtained before the neutron irradiation treatment.

Therefore, for use as a semiconductor device material, if the degree of neutron irradiation treatment is changed in accordance with the target resistivity, a single crystal having a target resistivity can be freely obtained.

In the conventional method such as the CZ method or the MCZ method, in which the target resistivity is obtained by the amount of the dopant, it is inevitable that the distribution of the resistivity in the single crystal length direction is inclined.
As a result, the usable portion per single crystal is limited.

According to the present invention, for example, the one using phosphorus as a dopant has no problem of residual radioactivity after neutron irradiation, and its resistivity distribution is also extremely uniform, so that the portion usable as a device material is significantly increased. , Yield and productivity are improved.

Further, since the target resistivity is lowered by the neutron irradiation treatment under a constant condition, the applicable range of the single crystal after the pulling is widened, and the pulling process is unified so that the efficiency is improved.

Is the present invention extremely suitable for a quartz crucible that should be pure in the first step? Since the acceptor impurities existing as trace impurities are used in reverse to the phenomenon of being eluted during the pulling process of the single crystal, if the physical properties of the crucible are different, the amount of dopant can be correspondingly changed.

Further, from the present invention, a method is conceivable in which a dopant impurity is positively mixed in the crucible at the time of manufacturing the crucible and the elution phenomenon is utilized.

[Brief description of drawings]

FIG. 1 is a distribution diagram of resistivity with respect to solidification rate in the length direction of a single crystal obtained by the present invention. FIG. 2 is a distribution diagram of the resistivity with respect to the solidification rate in the length direction of the single crystal after the first step of the present invention. FIG. 3 is a diagram showing the conductivity type of a single crystal pulled up undoped by the MCZ method and the resistivity distribution with respect to the solidification rate in the length direction. FIG. 4 is a distribution diagram of resistivity with respect to solidification rate in the length direction of a conventional single crystal obtained by pulling phosphorus, boron, and arsenic as doping agents by the MCZ method. FIG. 5 is a diagram showing the concentration distribution of impurities and the types of the impurities with respect to the solidification rate in the length direction of a single crystal pulled undoped by the MCZ method. FIG. 6 is a diagram showing an acceptor impurity concentration distribution obtained by subtracting donors from acceptors with respect to the solidification rate in the length direction of a single crystal pulled up by the MCZ method.

Claims (3)

(57) [Claims] 1. In a method for producing a silicon single crystal in which a silicon single crystal is left in a nuclear reactor and subjected to neutron irradiation doping, when a silicon single crystal is pulled by the CZ method or the MCZ method, a conductivity type N type is used. Conducting non-doping with polycrystalline silicon as a raw material, and determining the amount of acceptor impurities mixed in the crucible from the resistivity distribution and the distribution gradient from the top side to the bottom side of this single crystal,
Doping with a donor impurity having a slightly larger amount than compensating for this mixed amount and having a segregation coefficient that cancels out the slope of the distribution of resistivity in the lengthwise direction of the single crystal by the acceptor is pulled up. To obtain a high-resistivity N-type silicon single crystal having extremely uniform resistivity in the length direction, and then subjecting this N-type silicon single crystal to neutron irradiation treatment, a practical resistance as a material for semiconductor devices is obtained. N-type silicon CZ single crystal having a resistivity range and an extremely uniform resistivity in the longitudinal direction is obtained.
-Type silicon CZ single crystal manufacturing method. 2. The method for producing an N-type silicon CZ single crystal according to claim 1, wherein the donor impurity is phosphorus. 3. The method for producing an N-type silicon CZ single crystal according to claim 1, wherein the raw material polycrystalline silicon used for the pulling is N-type and has a resistivity of 90 Ω · cm or more.