JPH06349762A - Closed tube diffusion method - Google Patents

Abstract

PURPOSE:To avoid defects produced by contact between semiconductor substrates which are stored in a quartz ampule to be subjected to a heat treatment for impurity diffusion by a method wherein a quartz boat and the quartz ampule having a proper thickness are employed to prevent the substrates from being brought into contact with each other. CONSTITUTION:Silicon substrates 1 are arranged on a quartz boat 9 by inserting the bottom ends of the silicon substrates 1 into the slits 10 of the quartz boat 9. The quartz boat 9 is stored in a quartz ampule 2 with a reinforcing member 5 and an aluminum source 6 and, finally, a quartz cap 7 is fitted to the quartz ampule 2 and the quartz cap 7 is welded to the quartz ampule 2 along a welding part 8. The size of the quartz ampule 2 is enlarged by the size of the quartz boat. If the dimensions of the quartz ampule 2 satisfy (2d<5>+17d<4>.t)/t<2=3X10<9>, where (d) denotes the inner diameter of the quartz ampule 2 (mm) and (t) denotes the thickness of the quartz ampule 2 (mm), the quartz ampule 2 is not crushed during a diffusion process. Further, the quartz boat 9 is so designed as to be placed in the quartz ampule 2 and the pitch of the slits 10 is 3mm in order to increase the number of the substrates to be treated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a closed tube diffusion method for diffusing impurities into a semiconductor substrate by enclosing an impurity source in a quartz tube and heating the semiconductor substrate for manufacturing a semiconductor device.

[0002]

2. Description of the Related Art In addition to the above-mentioned closed-tube diffusion method, impurities are added to a semiconductor substrate by an open-tube diffusion method of heating a semiconductor substrate in a gas flow containing impurities or an ion implantation method by implanting and diffusing impurity ions. There is. In the case of adding impurities for p-type, the closed-tube method uses Ga ₂ O ₃ as an impurity source and uses Ga ₂ O gas generated by the reaction of Ga ₂ O ₃ + 2H ₂ → G ₂ O + 2H ₂ O, for example. However, the variation in gallium concentration in the plane of the semiconductor substrate is large, and it is difficult to apply to a large-diameter substrate of 4 inches or more. Further, in the ion implantation method, it is necessary to form, for example, a nitride film to prevent outward diffusion. In this respect, the closed tube diffusion method is easier than the ion implantation method, and aluminum or gallium can be diffused into the substrate more accurately than the open tube diffusion method.

FIG. 2 shows a state in which a silicon substrate 1 is enclosed in a quartz ampoule 2 for carrying out a closed tube diffusion method, and is set in a silicon tube 31, and both openings of the tube 31 are covered with a silicon thick plate 4. Press to fix the silicon substrate 1. Next, these are inserted into the quartz ampoule 2 together with the reinforcing material 5 made of quartz or silicon and the aluminum source 6, and the quartz cap 7 is fitted into the opening of the ampoule 2. In this state, the quartz ampoule 2 is evacuated, the ampoule 2 and the cap 7 are welded at the edges, and the welded portion 8 is formed, whereby the silicon substrate 1 is vacuum-sealed together with the aluminum source 6. Put this quartz ampoule in the diffusion furnace, for example 1200 ℃
Aluminum is diffused into the silicon substrate 1 by performing heat treatment for 10 hours. After the heat treatment, the quartz ampoule is broken and the silicon substrate 1 is taken out.

[0004]

However, even in the above-mentioned closed tube diffusion method, there are the following problems. 1) The silicon substrate 1 is not completely fixed in the quartz ampoule 2 and the silicon substrate 1 is set in a tilted state as shown in FIG. is there. 2) The set silicon substrates 1 may come into contact with each other and the silicon substrates 1 may not be separated one by one after the heat treatment.

For these reasons, defects are introduced into the silicon substrate 1 after diffusion from several peripheral positions, which becomes a factor of deteriorating the characteristics of the manufactured semiconductor device. It is an object of the present invention to provide a closed tube diffusion method that solves the above problems and prevents the introduction of defects into the semiconductor substrate by avoiding contact with the semiconductor substrate or the pressing plate.

[0006]

In order to achieve the above object, in the closed tube diffusion method of the present invention, the lower end of each semiconductor substrate is fitted into the groove of a quartz boat having a plurality of parallel grooves,
When the inner diameter is dmm and the wall thickness is tmm, (2d ⁵ + 17d ⁴
・ T) / t ² ≦ 3 × 10 ^{9 The} quartz boat and the impurity source were housed in a quartz ampule, the inside of the quartz ampule was evacuated, and the edge of the quartz cap was welded to the edge of the opening of the quartz ampule. After that, it shall be heated from the outside. Alternatively, each one may be placed in the groove of a quartz boat having a plurality of parallel grooves.
Insert the lower ends of the semiconductor substrates, and set the inner diameter to dmm and the wall thickness to t.
mm, (2d ⁵ + 17d ⁴ · t) / t ² ≦ 3 × 10
Insert the quartz boat into a quartz tube that satisfies ⁹ and further store the quartz tube and the impurity source in the quartz ampoule, evacuate the inside of the quartz ampoule, and weld the edge of the quartz cap to the edge of the opening of the quartz ampoule. After that, it shall be heated from the outside. Then, it is effective that the impurity source is made of aluminum or gallium by these methods.

[0007]

It is obvious that tilting of the semiconductor substrate or contact between the semiconductor substrates can be prevented by inserting the semiconductor substrate into the grooved quartz boat used in the normal processing step of the semiconductor substrate, but the quartz boat has a volume corresponding to that of the quartz boat. When it is housed in a silicon tube, the silicon tube having a large diameter must be used, but such a silicon tube becomes expensive. So we have to exclude silicon tubes. However, the quartz ampoule 2 accommodating the quartz boat on which the semiconductor substrate is mounted is formed by the ampoule 2 and the cap 7 when heated in the diffusion furnace 12 as shown in FIG.
Due to the pressure difference between the internal space 13 that is evacuated to about 10 ^-6 Torr and the internal space 14 at the atmospheric pressure of the diffusion furnace 12, the pressure indicated by the arrow 15 is applied, and the quartz ampoule 2 heated to 1200 ° C. has a hardness. Since it has decreased, it is crushed like the dotted line 16. The collapse speed V at this time is expressed by the following equation.

V∝wD ⁴ / t ³ ────── (1) where, w: weight of unit length of quartz tube, D: outer diameter of quartz tube, t: thickness of quartz tube, When the inner diameter of the quartz tube is d, D = d + 2t and w = 2.2π (2d + t) t. If d >> t, the equation (1) can be approximated by the following equation (2). V∝ (2d ⁵ + 17d ⁴ · t) / t ² ─────── (2) In the conventional path, d = 102.5mm and t = 3mm are required. In order to guarantee, it is understood that the following conditions must be satisfied by including the values of d and t in the equation (2).

(2d ⁵ + 17 · d ⁴ · t) / t ² ≦ (2 × 102.5 ⁵ + 17 × 102.5 ⁴ × 3) / 9 ────── (3) (2 × 102.5 ⁵ + 17 × 102.5 ⁴ × 3) / 9≈3 × 10 ⁹ That is, assuming that the wall thickness is t when the inner diameter is d, (2d ⁵ +
If a quartz ampoule with a value of 17 · d ⁴ · t) / t ² of 3 × 10 ⁹ or less is used, it will not be crushed during diffusion.
However, if there is a problem that it is difficult to weld when the thickness of quartz becomes thick, it is sufficient to accommodate a quartz tube satisfying the above conditions in a thin quartz ampoule to support the collapsing quartz ampoule.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG. 1 in which parts common to those in FIG. Figure 1
In this embodiment, the silicon substrates 1 are arranged with their lower ends inserted into the slits 10 having a width of 1 to 2 mm in the quartz boat 9 having an inverted trapezoidal cross section. It is housed together with the aluminum source 6, and finally the quartz cap 7 is fitted, the inside of the quartz ampoule 2 is evacuated, and the quartz ampoule 2 and the quartz cap 7 are welded at the welding portion 8. If the vacuum is rapidly evacuated to high vacuum, the silicon substrate 1 inserted in the slit 10 of the quartz boat 9 may pop out, so it is necessary to gradually reduce the pressure. The quartz ampoule 2 has an inner diameter (d) of 117.5 mm for accommodating a 4-inch diameter silicon substrate 1, and the wall thickness (t) is calculated to be 4.33 mm by the formula (3). Use thick ones. The quartz boat 9 is designed to have a size that fits in this quartz ampoule, and the pitch of the slits 10 is set to 3 mm in order to increase the number of treatments in one batch. The diffusion was performed by heat treatment at 1200 ° C. for 10 hours as in the prior art, but no crushing of the quartz ampoule 2 was observed after the completion of the diffusion. Moreover, when the silicon substrate 1 was evaluated, Al on the surface
In-plane variation of density is less than 1%, same as before,
No defects were detected by X-ray topography.

In the embodiment shown in FIG. 5, the silicon substrate 1 was erected in the slit 10 of the quartz boat 9 and placed in the quartz tube 3 having an inner diameter of 140 mm, as in the embodiment shown in FIG. Calculating with equation (3), t = 6.985 when d = 140 mm, so t =
A 7.5 mm quartz tube 3 is used. Quartz tubes of such dimensions are easier and cheaper to obtain than silicon tubes. This quartz tube 3 was inserted into a quartz ampoule 2 together with a quartz boat 9, and a quartz cap 7 was vacuum-sealed together with an aluminum source 6 and a reinforcing material 5. Quartz ampoule 2 has an inner diameter of 157 m
m, wall thickness 3.5 mm was used. The weldability between the quartz ampoule 2 and the quartz cap 7 was better than that in the case of FIG. 1 because the thickness of the ampoule was thinner than that of the embodiment shown in FIG.

After the diffusion, the crushing of the quartz ampoule 2 is not observed, and the surface Al concentration and the X-ray topography observation result also show that
It was as good as the example shown in FIG. In the above-mentioned both embodiments, the case of Al diffusion was described, but Ga diffusion can be similarly carried out.

[0013]

According to the present invention, when a semiconductor substrate is housed in a quartz ampoule and a heat treatment for impurity diffusion is performed,
In order to prevent the substrates from touching each other, the substrates are fitted into the grooves of the quartz boat, and the crushing of the quartz ampoule, which increases the inner diameter by the size of the boat, is prevented by using a quartz ampoule or quartz tube with an appropriate thickness. To prevent. As a result, the occurrence of defects due to the contact of the semiconductor substrate is eliminated, and it is possible to obtain a semiconductor device in which the characteristics are not deteriorated due to the defects.

[Brief description of drawings]

FIG. 1 is a sectional view of a quartz ampoule used in a closed tube diffusion method according to an embodiment of the present invention.

FIG. 2 is a sectional view of a quartz ampoule used in a conventional closed tube diffusion method.

FIG. 3 is a sectional view showing a problem in the conventional closed tube diffusion method.

FIG. 4 is a cross-sectional view of the collapse phenomenon of a quartz ampoule in the closed tube diffusion method.

FIG. 5 is a sectional view of a quartz ampoule used in a closed tube diffusion method according to another embodiment of the present invention.

[Explanation of symbols]

 1 Silicon Substrate 2 Quartz Ampoule 3 Quartz Tube 5 Reinforcing Material 6 Aluminum Source 7 Quartz Cap 8 Welding Part 9 Quartz Boat 10 Slit

Claims (4)

[Claims] 1. When the lower end of each semiconductor substrate is fitted into the groove of a quartz boat having a plurality of parallel grooves and the inner diameter is dmm and the wall thickness is tmm, (2d ⁵ + 17d ⁴ · t) / t ² ≦ 3
A quartz boat and an impurity source are stored in a quartz ampule that satisfies × 10 ⁹ , a vacuum is applied to the inside of the quartz ampule, the edge of the quartz cap is welded to the edge of the opening of the quartz ampule, and then heating is performed from the outside. Characteristic closed tube diffusion method. 2. When the lower end of each semiconductor substrate is inserted into the groove of a quartz boat having a plurality of parallel grooves and the inner diameter is dmm and the wall thickness is tmm, (2d ⁵ + 17d ⁴ · t) / t ² ≦ 3
Insert a quartz boat into a quartz tube that satisfies × 10 ⁹ , further store the quartz tube and the impurity source in the quartz ampoule, make a vacuum inside the quartz ampoule, and attach the edge of the quartz cap to the edge of the opening of the quartz ampoule. A closed tube diffusion method characterized by heating from the outside after welding. 3. The impurity source comprises aluminum.
Alternatively, the closed tube diffusion method described in 2. 4. The closed tube diffusion method according to claim 1, wherein the impurity source is gallium.