JPH04243995A - Production of semiconductor crystal - Google Patents

Abstract

PURPOSE:To provide the title production by pull method using a crucible in such a way that the second impurities to compensate the effects of the increase in the concentration of the first impurities in a melt is melted in the melt along with the dissolution of the crucible's inner wall, thereby obtaining crystal with uniform resistivity distribution. CONSTITUTION:The production of the objective semiconductor single crystal (1) by pull method from a melt (3) containing the first impurities contributing to the first electrically conductive type. The process is as follows: the second impurities in the inner wall of a crucible (2) is dissolved in the melt (3) and incorporated into said crystal (1), and the decline in the resistivity of said crystal(1) due to the increase in the first impurities with the solidification of the melt (3) is compensated by the increase in the second impurities. And, the concentration distribution for the second impurities for the depth of said inner wall is so designed that the ratio of the rate of increase in the concentration of the first impurities in the melt (3) to that of increase in the concentration of the second impurities in said melt (3) due to the dissolution of said inner wall and solidification of said melt (3) come to 0.5-1.5 times the ratio of the segregation coefficient of the second impurities to that of the first impurities.

Description

Description: [0001] The present invention relates to a semiconductor manufacturing method for manufacturing a single crystal by a pulling method using a crucible. With the recent miniaturization of semiconductor devices and the increase in the size of their chips, there is a demand for semiconductor substrates whose electrical characteristics are precisely controlled. However, single crystals produced by the pulling method have a distribution of electrical resistivity due to the segregation of impurities when the melt solidifies, and for this reason only a portion of the produced single crystal can be used. . [0003]Therefore, there is a need to produce crystals that have a uniform distribution of electrical resistivity even when there is segregation of impurities. 2. Description of the Related Art The production of semiconductor crystals by a conventional pulling method will be explained with reference to FIG. FIG. 4 is an explanatory diagram of an embodiment of the prior art, and FIG. 4(a) is a sectional view showing the main part of a semiconductor crystal manufacturing apparatus using a pulling method. [0005] The melt 3 held in the crucible 2A contains a predetermined amount of the first impurity. This first impurity melt 3
The concentration of impurities in crystal 1A is due to segregation of impurities when melt 3 solidifies, so impurities that were not incorporated into crystal 1A are
The first impurity increment 4 flows into the melt from the interface between the first impurity and the melt 3, and therefore increases continuously during the crystal production process. As a result, the electrical resistivity of the crystal 1A changes continuously in accordance with the impurity concentration distribution from the initial stage of manufacture to the final stage of manufacture. This change in impurity concentration depending on the solidification rate is expressed as follows. Let the volume of the melt at the beginning of crystal production be V0, and the initial impurity concentration of the melt be C0, and when the melt volume VG solidifies per unit time at a constant rate during the growth period, from the start of the growth Impurity concentration C1 in the melt after t time (t
), using the impurity segregation coefficient k1, [Formula 1]C1 (t)=C0(1-VG t/V0)k
It is known that the ratio is 1-1. [0009] Therefore, the impurity concentration CC (t) of the part that grows after t hours from the start of growth of crystal 1A follows the segregation during solidification of the melt, and is expressed as follows: [Equation 2] CC (t) = k1 Since ×C1(t), the impurity concentration in the crystal 1A changes according to the fluctuation of C1 shown in Equation 1. FIG. 4(b) shows the distribution of electrical resistivity in the direction of the pulling axis of the crystal 1A produced by the conventional technique. Note that silicon was used for the crystal 1A, B was used as an impurity, and quartz was used for the crucible 2A. The distribution of electrical resistivity in the figure matches the distribution obtained from Equations 1 and 2, and in the conventional technology, the segregation of impurities causes the electrical resistivity of the semiconductor crystal to become non-uniform. It has been clearly shown that this is a contributing factor. [0013] In order to solve this inconvenience, a continuous charging method or a double crucible method was devised in which the same amount of raw material as the solidified melt is continuously added with the same impurity concentration as the impurity concentration in the crystal. . However, in both cases, the devices are complicated and therefore expensive. [0015] As mentioned above, in the prior art, since the segregation coefficient of impurities added to determine conductivity type and electrical resistivity is usually smaller than 1,
As crystal production progresses, impurities are concentrated in the melt, and as a result, the impurity concentration in the crystal becomes non-uniform, resulting in a problem in that the electrical resistivity in the crystal becomes non-uniform. Furthermore, the continuous charging method and the double crucible method have the disadvantage that they require complicated and expensive equipment. The purpose of the present invention is to easily grow crystals with a uniform electric resistivity distribution by melting impurities into the melt as the crucible melts to compensate for the increase in impurity concentration in the melt. It is an object of the present invention to provide a method for manufacturing a semiconductor crystal that can be used to produce a semiconductor crystal. [Means for Solving the Problems] FIG. 1 is an explanatory diagram of the principle of the present invention, and is a sectional view showing the main parts of a semiconductor crystal manufacturing apparatus using a pulling method. Referring to FIG. 1, in the semiconductor manufacturing method of the present invention, a melt 3 containing a first impurity that makes a semiconductor crystal 1 have a first conductivity type and held in a crucible 2 is extracted by a pulling method. In a semiconductor crystal manufacturing method for manufacturing a single crystal,
In the method for producing a semiconductor crystal having the above structure, the inner wall of the crucible 2 contains a second impurity that makes the crystal 1 of the second conductivity type. The rate at which the second impurity concentration C2 in the melt 3 increases due to melting of the inner wall of the crucible 2 and solidification of the melt 3 is dC2 /dt. However, using the rate of increase of the first impurity concentration C1 in the melt 3, dC1 /dt, the segregation coefficient k1 of the first impurity, and the segregation coefficient k2 of the second impurity, 0.5 ×k2/k1<(dC1/dt)/(d
C2/dt)<1.5×k2/k1. [Operation] The operation of the structure of the present invention will be explained with reference to FIG. In crystal production by the pulling method from melt 3 containing impurities, when melt 3 solidifies to become crystal 1,
Since the segregation coefficient of impurities is smaller than 1, impurities that are not incorporated into the crystal flow into the melt 3 from the interface between the melt 3 and the crystal 1 as an impurity increment 4, increasing the impurity concentration in the melt 3. . For this reason, non-uniform impurity concentration, ie non-uniform resistivity, occurs in the crystal 1. On the other hand, in the present invention, since the inner wall of the crucible 2 that comes into contact with the melt 1 melts,
The second impurity contained in the inner wall of the crucible 2 dissolves into the melt. Therefore, in addition to the first impurity, the second impurity also increases in the melt 3, and in the crystal 1 solidified from the melt 3, the above two types of impurities increase with the solidification rate. The distribution will be as follows. [0022] In the present invention, these two types of impurities are said to generate carriers that bring about mutually opposite conductivity types in the crystal 1, and therefore are impurities that compensate for each other as donors or acceptors. Therefore, the increase in carriers due to the increase in the first impurity, which is the main impurity, is compensated for by the increase in the second impurity, which is a smaller amount, resulting in a change in resistivity caused by the increase in the first impurity. is alleviated. [0024] Therefore, a crystal with uniform resistivity can be manufactured. Note that the increase in impurity concentration in the melt 3 due to segregation occurs for both the first and second impurities, but since the first impurity has a higher concentration than the second, in many cases the absolute amount is The first impurity increases faster. For this reason, if no impurities are added to the melt 3, the difference between the first and second impurity concentrations will always be large, and in order to compensate for this difference, the structure of the present invention has Thus, the supply of the second impurity from the inner wall of the crucible 2 is essential. [0026] In the second configuration of the present invention, a concentration distribution in the depth direction of the second impurity contained in the inner wall of the crucible is formed so that the difference in the concentration of the two types of impurities in the crystal is constant. It is something. The operation of the second configuration will be explained below with reference to FIG. The inner wall of the crucible 2 in contact with the melt 3 usually melts at a substantially constant rate. Therefore, if the thickness to be melted per unit time is vc, then after t hours from the start of crystal production, the inner wall of the crucible having a thickness of vct will be melted. [0028] Therefore, when the second impurity concentration distribution in the crucible material at the position of depth d from the initial crucible inner wall surface is n(d), the inner wall of the crucible 2 contacts the melt 3 and melts. The second impurity concentration in the melt 3 increases as a result of this, where S is the contact area with the melt 3 and V is the volume of the melt 3. t) increases by S/V per unit time. In addition, crucible 2 with radius R
When using, [Equation 4] S=πR2 +2V/R, V=V0 (1−vg t)
is given by Furthermore, the segregation coefficient k2 accompanying the solidification of the melt 3
The increase in the concentration of the second impurity in the melt 3 is VG /V
When 0 = vg, per unit time, 003
2] [Equation 5] Since C2 V0 (1-k2)vg /V, the rate of increase in the concentration of the second impurity in the melt 3 is dC
2/dt is obtained by adding Equation 3 and Equation 5, [Equation 6] dC2/dt=vc n(vc t)S/V+
C2 V0 (1-k2)vg/V. On the other hand, the increasing rate dC1/dt of the concentration of the first impurity in the melt 3 can be calculated by differentiating the equation 1 as follows: dC1/dt=vg C0 (1-k1) (1- vg
t) k1-2=C1 V0 vg (1-k1)/
It is V. Here, V=V0 (1-vg t) was used. In the second configuration of the present invention, the rate of increase in both impurity concentrations at any time during crystal production is
7] n(d) is determined so that (dC1/dt)/(dC2/dt)=k2/k1 approximately holds true. At the above ratio, the difference D between the concentrations of both impurities in the crystal 1 becomes constant, taking into account the effect of segregation: D=k1.C1 -k2.C2 =. [0040] Therefore, in the second configuration of the present invention,
Since the concentration difference of impurities that compensate for each other is always a constant value D in the crystal 1, the carrier concentration is constant, and therefore it is possible to manufacture a crystal having a constant resistivity for the entire crystal 1. The concentration distribution n(d) of the second impurity in the inner wall of the crucible 2 to achieve this effect can be determined so that Equations 8 and 9 hold. For example, by substituting numbers 9, 6, and 7 into equation 8, we get
vc )(C1 V0 /S)(1-k1)×[1-
(1-D/(k1 C1))(1-k2)/(1-k
1)] by replacing it with t=d/vc. Here, C1 is determined from Equation 1 and S is determined from Equation 4. [Embodiment] FIG. 2 is an embodiment of the present invention, and shows an example of the second impurity concentration distribution in the inner wall of the crucible. The present invention will be explained based on an embodiment with reference to FIGS. 1 and 2. A semiconductor material such as silicon is charged in a crucible 2, a first impurity is added thereto, and the material is heated and melted. For example, quartz can be used as the crucible material, and B, P, As, or Sb can be used as the first impurity. Next, a seed crystal whose pulling axis direction is, for example, <100> is immersed in the melt 3 and pulled up to grow a semiconductor single crystal 1. Here, in an example using a quartz crucible 2 with a diameter of approximately 35 cm, a charge amount of 20 kg, and an initial concentration of B in the melt 3 of 7 x 1014 atoms/g, the dissolution rate of the inner wall of the quartz crucible 2 is 7 μm/g. It is h. As the second impurity, for example, P, As or Sb can be used. When the specific resistance of the crystal is 10 Ωcm, the concentration distribution of P, As or Sb in the inner wall of the quartz crucible 2 is calculated from the equation 10 as shown in FIG. are determined as shown as P, As, and Sb, respectively. In order to manufacture a quartz crucible 2 having such an impurity concentration distribution, for example, CVD is applied onto the inner wall of the quartz crucible 2.
This is achieved by depositing SiO2 doped with impurities. [0048] When P is the second impurity, the above distribution is
For example, under the conditions of a growth temperature of 800°C and a growth rate of 90 nm/min, TEOS (Tetraethyl Orthos)
Initially, the partial pressure ratio of
3 and then gradually increasing the partial pressure ratio to 104 when the SiO2 film has a thickness of 100 μm. FIG. 3 is an explanatory diagram of an embodiment of the present invention, and shows an example of the resistivity distribution of a silicon crystal manufactured using the above crucible. As shown in FIG. 3, a crystal with uniform resistivity can be manufactured according to the present invention. [0050] Here, in order to keep the resistivity from 10 Ωcm to within 10%, it is necessary that the impurity concentration distribution on the inner wall of the crucible be within 10% of several tens of values. Furthermore, the present invention is particularly useful when the absolute amount of impurities is small and there is little risk of producing defects that are considered to be obstacles during device formation, and in such cases, the resistivity of the crystal can be reduced to within 10%. In order to make the ratio k2/k1 0.5 to 1.
5 times was sufficient. [0051] Therefore, since a large permissible value can be taken for the impurity concentration distribution on the inner wall of the crucible, there is an effect that manufacturing of the crucible becomes easier. Note that As, B, and Sb can also be provided with a desired concentration distribution by the same CVD method, and the present invention can be applied to these as second impurities. B in FIG. 2 is the B concentration distribution on the inner wall of the crucible calculated from equation 10 when P is the first impurity and B is the second impurity. This is an example applied to the production of crystals. Furthermore, it goes without saying that the present invention is equally applicable to materials other than silicon, such as compound semiconductors. Furthermore, even if the impurity distribution in the inner wall of the quartz crucible is constant,
It goes without saying that the present invention has the advantage of being able to produce more uniform crystals than conventional techniques. [0054] According to the present invention, impurities that compensate for the increase in impurity concentration during crystal production due to segregation are melted into the melt at the same time as the crucible is melted, thereby improving electrical conductivity. Since fluctuations in the carrier concentration in the crystal that contribute to
It greatly contributes to improving the performance of semiconductor devices.

[Brief explanation of the drawing]

[Figure 1] Diagram explaining the principle of the present invention

[Figure 2] Example of the present invention

[Figure 3] Illustration of an embodiment of the present invention

[Figure 4] Illustration of an example of conventional technology

[Explanation of symbols]

1,1A crystal 2,2A Crucible 3 Melt liquid 4 Increment of first impurity 5 Increment of second impurity

Claims (2)

[Claims] Claim 1: A semiconductor crystal in which a single crystal is produced by a pulling method from a melt (3) containing a first impurity that makes the semiconductor crystal (1) a first conductivity type and held in a crucible (2). A method for manufacturing a semiconductor crystal, characterized in that the inner wall of the crucible (2) contains a second impurity that causes the crystal (1) to have the second conductivity type. 2. The method for manufacturing a semiconductor crystal according to claim 1, wherein the second impurity concentration in the thickness direction in the inner wall of the crucible (2) is determined by melting the inner wall of the crucible (2) and melting the melt. The melt (3) increases due to solidification of (3).
) the rate of increase in the second impurity concentration C2 dC2
/dt is the first impurity concentration C in the melt (3)
1 using the increasing rate dC1/dt and the segregation coefficient k1 of the first impurity and the segregation coefficient k2 of the second impurity, 0.5 × k2/k1<(dC1/dt)/
A method for manufacturing a semiconductor crystal, characterized in that it is formed in a distribution such that (dC2/dt)<1.5×k2/k1.