JPH05221786A - Method and device for producing silicon single crystal - Google Patents

Abstract

PURPOSE:To suppress oxidation-induced stacking faults distributed annularly and easy to generate at the initial crystal growth stage and to grow a silicon single crystal excellent in the pressure withstanding characteristic when an MOS disk is mounted in a worked wafer in the CZ silicon single crystal producing device by providing a reflector to a chuck for connecting a seed crystal to its lower end in opposition to the bottom surface of a crucible. CONSTITUTION:A reflector 8 is provided to a chuck 7 in opposition to the bottom surface of a crucible 6. The reflector is not damaged or broken even under the high temp. in the furnace by specifying the quality of the reflector. Besides, a single crystal is grown in the shape corresponding to the apex angle of the reflector and mounting position by controlling the growth rate, and the efficiency in reflecting the radiant heat is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a single crystal production apparatus and method for producing a high quality silicon single crystal at high speed.

[0002]

2. Description of the Related Art Generally, in the production of a silicon single crystal by the Czochralski method, a crystal raw material is put into a quartz crucible described in a chamber, the material is heated and melted, and a seed crystal is dipped in the melt. This is performed by rotating this and pulling it upward to grow a single crystal at the lower end of the seed crystal. At first, pulling up is high speed (≧ 4.0mm /
min), a crystal (dash neck) having a diameter of about 3 mm is grown into a dislocation-free crystal, the crystal is expanded to a predetermined diameter, a shoulder is formed, and a single crystal having a constant diameter is grown. When the obtained single crystal was cut in a direction perpendicular to the growth axis, and the surface was mirror-finished into a wafer shape and subjected to wet oxidation heat treatment, a ring-shaped oxidation-induced stacking fault (hereinafter referred to as OSF) centered on the center of the wafer was applied. Called) may occur. If the OSF is generated in the heat treatment in the step of manufacturing a silicon device, it causes a leak current, so that the OSF generation density of the silicon wafer for manufacturing the device is limited. The ring-shaped OSF is likely to occur in the initial portion of the constant diameter portion of the single crystal, which causes a reduction in the production yield of silicon wafers.

In general, the ring-shaped OSF is suppressed from being generated when the growing crystal passes through a temperature near 1200 ° C. and the cooling rate is low. Conventionally, a device for providing a heater directly above the crucible or around the crystal as a means for controlling the cooling rate of the crystal (Actual Kaihei No. 2-61965, JP-A-63-60190), a device for providing a heat shield around the crystal. (Japanese Patent Publication No. 51-47153) and the like have been proposed. However, in the former case, there is a high possibility that the material of the heater is peeled off or sublimated to contaminate the melt in the crucible, the apparatus is complicated, and extra power is required.
The latter has adiabatic effect near the growth interface and slows the cooling rate near the interface, limiting the crystal growth rate and lowering the productivity, and evaporating from the melt surface to block the flow of atmospheric gas in the furnace. It is highly possible that the SiO ₂ gas will not be efficiently discharged, and SiO ₂ will be condensed on the surface of the heat shield, and this SiO ₂ will fall into the melt and adhere to the growing single crystal to become a dislocation source. There are problems such as becoming.

Next, when a MOS diode having a two-layer electrode made of polycrystalline silicon in which the upper layer is aluminum and the lower layer is doped is mounted on a silicon wafer, a polarity voltage in which majority carriers are injected from the substrate silicon is applied. When the withstand voltage characteristic of the gate oxide film is evaluated by applying the voltage, it is known that the withstand voltage characteristic is excellent in the outer region of the ring-shaped OSF and inferior in the inner region (Seiji Shinoyama, Masami Hasebe, Yamauchi). Tsuyoshi: Applied Physics 60,766 (199
1)). The breakdown voltage of the gate oxide film is required to be higher than before due to the thinning of the oxide film accompanying the miniaturization of devices. Conventionally, a method has been proposed in which the growth rate of a single crystal is limited to 0.8 mm / min or less in order to improve withstand voltage characteristics (Japanese Patent Laid-Open No. 2-267195).
issue). In addition, when the growth rate decreases, a ring-shaped OSF
It is known that the radius of becomes small and disappears at the center below a certain critical speed. Therefore, when the crystal is grown at a low speed, no ring-shaped OSF is generated and the MOS
It is possible to manufacture a silicon single crystal having excellent gate oxide film breakdown voltage characteristics when a diode is mounted. However, it cannot be said to be a sufficient technique because the productivity is reduced as long as the speed is low.

[0005]

SUMMARY OF THE INVENTION An object of the present invention is to produce a silicon single crystal which is free of ring-shaped OSF in the initial stage of growth and has excellent gate oxide film withstand voltage characteristics at a high speed without using the slow growth method. It is to provide the means to produce.

[0006]

According to the present invention, in order to solve the above-mentioned problems, when a crystal passes around 1200 ° C.,
0.8m even at a growth rate of 0.8mm / min or more
An installation and method is provided that achieves about the same cooling rate as at a growth rate of m / min or less.

The results of calculating the temperature distribution of the growing crystal by computer simulation with respect to the growth rate of the two-level silicon single crystal, and the cooling rate at around 1200 ° C. (temperature gradient in the growth direction × growth rate) Is shown in FIGS. 3 and 4. From this, it can be seen that the cooling rate near the central axis of the crystal is higher than that at the outside, and the difference is smaller as the growth rate is smaller. Due to the fact that the radius of the ring-shaped OSF becomes smaller as the growth rate is made smaller and the gate oxide film breakdown voltage is better on the outside of the ring than on the inside, the ring-shaped O
SF occurs in a certain cooling rate range. At that speed, it was found that the gate oxide film breakdown voltage was poor in the high speed region and the gate oxide film breakdown voltage was excellent in the low speed region. From this knowledge, if the cooling rate in the vicinity of the central axis is suppressed so that the overall cooling rate becomes lower than the critical rate, a single crystal with excellent withstand voltage characteristics of the gate oxide film can be obtained without generation of ring-shaped OSF. Be done. The prior art heater directly above the crucible and the heat shield around the crystal reduce the cooling rate by applying heat from the outside of the crystal, and have the problems already mentioned above.

FIG. 1 shows an apparatus for producing a silicon single crystal provided with a reflector of the present invention. The conical portion (10) immediately after the dash neck of the single crystal has a larger angle facing the main chamber (2) cooled by the cooling water than the side surface of the straight body of the single crystal, and quartz heated to a higher temperature The angle of the crucible (6) and the surface of the raw material melt is small. This is in contrast to the conical portion 10, in which the side surface of the straight body of the crystal faces the quartz crucible, the angle facing the main chamber is small, and the angle facing the quartz crucible is large. Especially in the initial stage of crystal growth, the surface area of the cone occupies a large proportion of the total surface area of the crystal, so heat is removed from the crystal mainly from the cone, and as a result, the cooling rate near the central axis of the crystal is increased. growing. Therefore, if the heat removal from the conical portion is suppressed, the cooling rate of the single crystal decreases, especially near the central axis, and the cooling rate becomes lower than the critical cooling rate as a whole.

According to the present invention, in order to suppress heat removal from the conical portion of the single crystal immediately after the dash neck, the diameter of the bottom surface is the inner diameter of the pull chamber (1) on the body side surface of the chuck (7) for mounting the seed crystal. The device has a hollow conical shape that does not exceed 5 cm, and the hollow portion is provided with a reflecting plate facing the bottom surface of the crucible. As for the method of joining the reflector and the chuck, for example, the hole 13 shown in FIG. 2 is passed through the shaft 14, and the concave portion 15 is engaged with the convex portion 16 for insertion. However, the insertion method is not limited to the one shown here. The material of the reflector should be a material that does not break or break even at high temperature (about 1200 ° C) in the furnace and has high reflectance of radiant light. Graphite coated with molybdenum or silicon carbide, or semi-transparent Use quartz. The reflectance of quartz changes depending on the volume ratio of bubbles in meat, and the volume ratio of bubbles in meat is 4 × 10 in order to obtain sufficient heat removal suppression efficiency.
^{-Must be -3} or higher. Further, it is desirable that the side surface of the reflecting plate be parallel to the conical surface of the single crystal, and the apex angle (θ) of the reflecting plate should be approximately equal to the apex angle (φ) of the conical surface in normal operation. While growing the conical portion, while controlling the crystal diameter, the growth rate is controlled so that φ becomes substantially equal to θ. Further, the larger the angle at which the conical surface of the crystal faces the reflector, the higher the heat removal suppression efficiency, and in FIG. 5, x is preferably 0.5 times or more the length of the generatrix of the conical surface. That is, the distance L between the joint portion (12) and the single crystal dash neck end position (9) is L ≦ 2R / sin.
(Θ) -r / 2 / sin (φ / 2) / cos (θ / 2)
It suffices to satisfy [Equation 1]. In order to satisfy this condition, the position of the bonded portion and the length of the seed crystal are adjusted to appropriate values in advance, and the length of the dash neck satisfies the formula 1 during the crystal growth. The minimum value of L is determined by the structure and manufacturing conditions of the single crystal manufacturing apparatus.

[0010]

By providing the reflecting plate of the present invention, heat removal from the conical portion (10) after the dash neck of the single crystal is suppressed at the initial stage of growth of the silicon single crystal, and especially the cooling rate is near the center axis of the crystal. Becomes smaller. As a result, even when the growth rate is 0.8 mm / min or more, the cooling rate when the crystal passes through a temperature near 1200 ° C. becomes lower than the critical rate at which the ring-shaped OSF is generated. Also, the material of the reflector is molybdenum or graphite coated with silicon carbide,
Alternatively, by using semi-transparent quartz with a volume ratio of bubbles in meat of 4 × 10 ^-3 or more, radiant heat can be efficiently reflected, and even if the temperature inside the furnace is high, there is no breakage and breakage, which hinders the growth of single crystals. There is nothing to do. Further, the growth rate is controlled so that the conical surface (10) is parallel to the reflection plate, and the joint (1
By setting the distance L between the 2) and the dash neck end position (9) to satisfy the expression 1, the angle at which the conical surface (10) faces the reflecting plate becomes large, and the radiant heat is efficiently reflected. Further, since only the conical portion after the dash neck of the single crystal of the reflector of the present invention is insulated, the influence on the vicinity of the growth interface is small and the growth rate is not limited. Further, since it has a conical shape, the flow of the atmospheric gas is hardly disturbed, and the SiO gas is smoothly discharged.

[0011]

EXAMPLES The present invention will be specifically described below with reference to Examples of the present invention and Comparative Examples. In addition, both of the present invention example and the comparative example are shown in Table 1.
Single crystals were grown under the common conditions shown in. An example of the obtained single crystal is shown in FIG. The sample for evaluation was taken from a position at a distance S = 50 mm from the shoulder of the crystal, and processed into a mirror-finished wafer having a diameter of 150 mm through a process in normal industrial production. Table 2 shows common implementation conditions of the present invention example and the comparative example. Further, FIG. 7 shows the shape of the reflection plate of each embodiment, and FIG. 8 shows an embodiment in which the mounting position of the reflection plate is changed.

[0012]

[Table 1]

[0013]

[Table 2]

A) Comparison of OSF generation density After each sample was heat-treated in a wet oxidation atmosphere at 1100 ° C. for 80 minutes, the surface oxide film was removed with dilute hydrofluoric acid and corroded with a Wright etching solution for 90 seconds to form a pit. The crystal defects that appeared were observed with an optical microscope, and the number of pits that could be determined as stacking faults was counted. Table 3 shows the results of counting the number of OSFs in the diameter direction of the wafer with a microscope magnification of 200 times. In addition, the influence of θ-φ and L on the number of OSFs is shown in FIG.
And shown in FIG. In the present invention example and the comparative example, OSF
Is 0 to 2 per wafer, but in Comparative Examples 9 to 16, OSFs distributed in a ring shape were observed. In particular, FIG. 11 shows the OSF density distribution in the wafer surface of the crystal of Comparative Example 9.
In this sample, a high-density OSF having a peak around 55 mm from the axis is ring-shaped. Comparative Example 1
No ring-shaped OSF was observed in the sample No. 3, but OSF was generated on the entire surface of the wafer. It is considered that this is because carbon was mixed into the silicon melt from the reflector. Further, according to FIG. 9, when the difference between the apex angle φ of the reflector and the apex angle θ of the conical portion of the crystal is large, the number of OSFs increases, and from FIG.
It can be seen that the number of OSFs is large even when does not satisfy the formula of claim 6 of the present invention.

A) Comparison of breakdown voltage of gate oxide film The breakdown voltage characteristic is that many MOSs mounted on a silicon wafer.
An electric field was applied to the gate electrode of the diode by the voltage ramping method, and evaluation was made by the electric field in which the oxide film caused dielectric breakdown. M
A method of mounting the OS diode will be described with reference to Table 4. First, the wafer is washed (process No. 1 and subsequent numbers are shown only), gate oxidation is performed to form a SiO ₂ layer (2), and polycrystalline silicon is deposited (3). Doping by ion implantation (6). Pre-oxidation cleaning (4) and polycrystalline silicon oxidation (5) are pre-treatments for ion implantation (6). Then, cleaning before annealing (7)
Then, drive annealing is performed to solidify the dopant in the polycrystalline silicon (8), the polycrystalline silicon oxide film is removed by etching (9), and aluminum is deposited to form an aluminum layer (10). Next, a polyresist film is coated by lithography (11) to mount a two-layer gate electrode having a diameter of 5 mm, and after patterning, the aluminum layer is etched (12) and the resist film is removed (14). Then, by hydrogen annealing, S
After stabilizing the i / SiO ₂ interface (15), a resist film is applied to the surface to protect the MOS diode (1
6) The surface polycrystalline silicon film is removed by plasma etching (17). A protective resist film is applied again on the surface (18), the backside oxide film is removed by etching (19), and gold is deposited for p-type and gold-antimony alloy is deposited for n-type. A back electrode is formed (20).
Finally, the protective resist film was removed (21).

The voltage ramping method is as shown in FIG.
In this method, a DC voltage having a polarity in which majority carriers are injected from the substrate silicon is applied between the aluminum layer (21) and the back surface current (20), and the voltage is increased stepwise with respect to time. In the example of the present invention, the voltage increase per step of this voltage ramping method is converted into an electric field of 0.25.
MV / cm, protection time is 200 ms / step, and critical electric field (Eb) at which insulation film breakdown occurs is 8.0 MV / cm.
The ratio of the number of the MOS diodes described above (C mode acceptance rate) was calculated.

[0017]

[Table 3]

The results are shown in Table 4. 13 and 14 show the relationship between the C mode acceptance rate and θ−φ and L.
In the single crystals of the present invention example and the comparative example 8 (without a reflector), C was used.
The mode pass rate is 90% or more. On the other hand, in the crystals of Comparative Examples 9, 13, and 14, the C mode acceptance rate is 70% or less. FIG. 15 shows distributions of pass / fail of C mode in the plane of the wafer for the crystals of Inventive Example 1 and Comparative Example 8. In Comparative Example 8, the number of rejects increases in the area inside the ring-shaped OSF. Further, as shown in FIG. 13, when the difference between the apex angle φ of the reflection plate and the apex angle θ of the conical portion of the crystal is large, the pass rate becomes low. It can be seen that the pass rate is low.

[0019]

[Table 4]

[0020]

By providing the reflecting plate of the present invention,
0.8 mm / m even at a growth rate of 0.8 mm / min or more
A cooling rate similar to that in the case of less than or equal to in can be realized, a ring-shaped OSF, which was easily generated in the initial stage of growth, is not generated, and a silicon single crystal having excellent gate oxide film high-voltage characteristics can be manufactured.

[Brief description of drawings]

FIG. 1 is a view showing a silicon single crystal production apparatus of the present invention,

FIG. 2 is a diagram showing an example of a structure of a joint portion between a reflector and a chuck for mounting a seed crystal of the present invention,

FIG. 3 is a diagram showing a temperature distribution of a silicon single crystal at an early stage of growth obtained by computer simulation,

FIG. 4 is a diagram showing a cooling rate when a single crystal passes through a temperature near 1200 ° C.,

FIG. 5 is a diagram showing a positional relationship between a reflector and a single crystal of the present invention,

FIG. 6 is a view showing an example of a grown silicon single crystal,

FIG. 7 is a diagram showing the shape of a reflector in each example,

FIG. 8 is a diagram showing a mounting position of a reflection plate in each embodiment,

FIG. 9 is a diagram showing the relationship between the number of OSFs and θ-φ;

FIG. 10 is a diagram showing the relationship between the number of OSFs and L;

11 is a diagram showing an in-plane OSF density distribution of Comparative Example 9, FIG.

FIG. 12 is a partial cross-sectional view of a mounted MOS diode,

FIG. 13 is a diagram showing a relationship between a C mode acceptance rate and θ-φ;

FIG. 14 is a diagram showing a relationship between a C mode acceptance rate and L;

FIG. 15 is a diagram showing gate oxide film breakdown voltage characteristics (in-plane distribution of wafer) of Inventive Example 1 and Comparative Example 9.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Pull chamber 2 Main chamber 3 Heat insulating material 4 Heating means 5 Graphite crucible 6 Quartz crucible 7 Seed crystal mounting chuck 8 Reflector plate 9 Dash neck end position 10 Single crystal cone portion 11 Silicon single crystal 12 7 Joint portion of 7 and 8 13 hole Part 14 Shaft 15 Recess 16 Protrusion 17 Single crystal shoulder 18 Substrate silicon 19 SiO ₂ film (thickness about 250 ohm strong) 20 Polycrystalline silicon layer (thickness about 5000 ohm strong) 21 Aluminum layer (thickness 2000 to 5000) Ohm Strong) 22 Double-layer gate electrode

Claims (6)

[Claims] 1. A device for producing a single crystal by the Czochralski method, wherein a chuck (7) for connecting a seed crystal at a lower end thereof is provided with a reflection plate facing the bottom surface of the crucible (6). Characteristic silicon single crystal manufacturing equipment. 2. The silicon single crystal manufacturing apparatus according to claim 1, wherein the material of the reflector is molybdenum. 3. The silicon single crystal manufacturing apparatus according to claim 1, wherein the material of the reflector is graphite coated with silicon carbide. 4. The apparatus for producing a silicon single crystal according to claim 1, wherein the reflector is semitransparent quartz and the volume ratio of bubbles in the meat is 4 × 10 ⁻³ or more. 5. The production of a silicon single crystal, wherein the crystal growth rate is controlled so that the apex angle (θ) of the reflector and the apex angle (φ) of the conical surface (10) of the single crystal are equal. Method. 6. The distance L between the joint (12) between the reflector and the chuck for mounting the seed crystal and the dash neck end position (9) of the single crystal is L ≦ 2R / sin (θ) -r / 2 /
A method for producing a silicon single crystal, characterized in that the single crystal is pulled so as to satisfy sin (φ / 2) / cos (θ / 2) (R: radius of circumference of lower end of reflector, r: radius of single crystal). ..