JP2002343722A - Quartz glass furnace core tube for low pressure cvd - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quartz glass furnace core tube for low pressure CVD in which height dimension nearly equal to that of a furnace core tube formed of metal material can be obtained although the furnace core tube is formed of quartz glass and high strength is realized. SOLUTION: In this quartz glass furnace core tube for low pressure CVD, a ceiling part 4 having a domed shape whose radius is R1 is combined with a cylindrical part 3 whose radius is R by a combining arc part 5 whose radius is R2 . The quartz glass furnace core tube has a shape wherein R1 =1.6R-2.4R and R2 =0.2R-0.4R and is used at an internal furnace temperature of at most 900 deg.C, and compression residual stress is made to exist on an outside surface layer of the combining arc part.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a quartz glass furnace tube for low-pressure CVD, and more particularly, to improve strength by giving a specific relationship to a radius of a ceiling portion, a radius of a cylindrical portion, and a radius of a connecting arc portion. The present invention relates to a quartz glass furnace tube for low-pressure CVD.

[0002]

2. Description of the Related Art At the time of heat treatment of a semiconductor wafer or a liquid crystal panel as in LPCVD, a furnace tube is used to realize a low-pressure environment in a furnace. Conventionally, metal is used for this furnace tube.

When the pressure difference between the inside and outside of the furnace tube is a maximum of 1 atm, the stress generated in the furnace tube is smaller than the strength of the metal material. In particular, since the strength of metallic materials is almost equal in tensile and compressive stress, the stress generated in the core tube is
In absolute value, the compressive stress is maximum, and the tensile stress is smaller than the compressive stress at the joint between the ceiling and the cylinder.

However, in recent years, due to a demand for higher purity in a semiconductor process, contamination of a material to be processed by a metal core tube has become a problem, and a high-purity material has been demanded.
Quartz glass is now being used as one of the materials meeting this demand.

The strength characteristic of this quartz glass material is that the tensile strength is much smaller than the compressive strength (usually about 1/20). The tensile stress generated at the joint portion of the cylindrical portion may exceed the tensile strength of quartz glass. In order to reduce this tensile stress, it is necessary to design the dome-shaped ceiling as close as possible to a hemisphere (the radius of the dome-shaped ceiling is close to the radius of the cylinder).

[0006]

However, such a design is effective in reducing the tensile stress, but poses a problem from the viewpoint of effective utilization of the furnace space. That is, the height of the dome-shaped ceiling increases the height of the entire furnace, and increases the cost and running cost of the heat treatment furnace. Therefore, there is a demand for a quartz glass furnace tube for reduced pressure CVD in which a metal is converted into a quartz glass material while maintaining the shape of a conventional metal furnace tube.

Further, when the diameter is increased in the design of a quartz glass furnace tube as in the prior art, the tensile stress generated in the joint arc connecting the ceiling and the cylindrical portion increases in a similar manner. However, it is necessary to increase the thickness of the quartz glass. In particular, in the case of a large quartz furnace tube in which the diameter of the cylindrical portion exceeds 1 m, there is a high risk that a tensile stress of several tens MPa is generated in the joint arc portion and the tube is broken. However, considering the use of heat treatment jigs, the heat capacity is increased, the core tube price is increased due to the increase in the size of the members, the cost of the core tube is increased, and the problem of heat permeability from the heater is taken into consideration. In order to satisfy the strength, it is necessary to change the shape of the joint arc.

If the viewpoint of effective use of the furnace space as described above is not taken into consideration, the radius of the ceiling can be simply reduced to reduce the tensile stress generated therein. Therefore, there is a demand for a high-strength quartz furnace tube for reduced-pressure CVD that satisfies the height dimension even when the wall thickness is constant and has high strength.

The present invention has been made in view of the above-mentioned circumstances. Even if it is made of quartz glass, it is possible to obtain a sufficiently high height equivalent to a furnace tube made of a metal material, and to obtain a high-strength quartz for low-pressure CVD. It is intended to provide a glass furnace tube.

[0010]

Means for Solving the Problems According to the first aspect of the present invention, which has been made to achieve the above object, the present invention is used in a reduced pressure heat treatment furnace, and has an outwardly convex ceiling provided at an upper portion thereof. the reduced pressure CVD for the quartz glass furnace tube of cylindrical bottom is opened, the ceiling portion forms a dome shape with a radius R _1,
The cylindrical portion of the ceiling portion and the radius R are combined in coupling arcuate portion of radius _{R 2, R 1 = 1.6R~2.4R,} R 2 = 0.2R
A quartz glass furnace tube for reduced-pressure CVD, having a shape of ~ 0.4R, used at a furnace temperature of 900 ° C or less, and having a compressive residual stress in the outer surface layer of the joint arc. It is a gist.

The invention according to claim 2 of the present invention is a cylindrical quartz glass furnace tube for low-pressure CVD, which is used in a low-pressure heat treatment furnace and has an upper portion provided with an outwardly convex ceiling portion and an open lower portion. in the ceiling part forms a dome shape with a radius R _1, is coupled by coupling arcuate portion of radius R ₂ between the cylindrical portion of the ceiling portion and the radius R, the radius R of the cylindrical portion is not less than 300 mm, and, 0.6R ≧ R ₂ ≧ 0.2R, 2.4R ≧ R ₁
The gist is a quartz glass furnace tube for reduced pressure CVD characterized by having a curvature of ≧ 1.2R and 9 ≧ R ₁ / R ₂ ≧ 3.8.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, reduced pressure CVD according to the present invention will be described.
An embodiment of a quartz glass furnace core tube for use will be described with reference to the accompanying drawings.

FIG. 1 is a conceptual view of an embodiment of a quartz glass furnace tube for reduced pressure CVD according to the present invention.

As shown in FIG. 1, a quartz glass furnace tube 1
Is a cylindrical portion 3 in which a storage portion 2 for storing a wafer boat on which a semiconductor wafer is mounted and which is made of transparent quartz glass is formed.
And a ceiling part 4 provided on the upper part of the cylindrical part 3 and having a convex shape outward, a connecting arc part 5 connecting the ceiling part 4 and the cylindrical part 3, and an opening part 6 provided on the lower part. Have.

The cylindrical portion 3 is a cylindrical portion having a radius R which is large enough to form the storage portion 2 for storing the wafer boat.

The ceiling part 4 forms a dome shape with a radius _{R 1,} and has a relationship of R 1 = 1.6R~2.4R.

The coupling arcuate portion 5, the cross-sectional shape of radius _{R 2} is an arc _shape, and has a relationship of R 2 = 0.2R~0.4R. In addition, a compressive residual stress exists in the outer surface layer 5s of the connecting arc portion 5.

The quartz glass furnace tube 1 has a structure in which the inside gas pressure of the quartz glass furnace tube 1 is used in the vertical heat treatment furnace at a higher gas pressure than the outside gas pressure.
Are outwardly convex.

The determination of the shapes of the ceiling portion 4 and the connecting arc portion 5 is based on the knowledge obtained by the present inventors described below, and aims at improving the strength devised by the present inventors. The shape design method of the quartz glass furnace tube is used, and in particular, based on the designed shape according to the use conditions of the quartz glass furnace tube.

That is, as a method of improving the strength of the quartz glass, a specific relationship is given to the radius R ₁ of the ceiling portion 4, the radius R of the cylindrical portion 3, and the radius R ₂ of the connecting arc portion 5.
The presence of a compressive residual stress in the outer surface layer 5s of the joint arc 5 enhances the strength of the quartz glass furnace tube 1, particularly the strength of the joint arc 5.

Generally, the stress state of a furnace tube used in a heat treatment furnace such as LPCVD is as follows. Tensile stress occurs at the joint between the ceiling and the cylindrical portion, and compressive stress occurs at other portions. This stress state depends on the structure (shape and size) of the furnace tube, but is not related to the material of the furnace tube.

Here, while using the same structure as the metal core tube in the quartz glass core tube, a compressive residual stress is generated in a portion where a tensile stress is generated during use of the heat treatment, so that it is generated during use. A method of partially or completely canceling out the tensile stress is adopted. The formation of the residual compressive stress includes a method of direct temperature quenching or a chemical method by diffusion of atoms other than Si and O. This stress state is compression on the surface layer and tensile stress on the inside.

FIG. 2 shows a furnace tube 1 used in an LPCVD furnace.
FIG. 3 is a schematic diagram of a core tube used to determine the shape of the core tube.

When the pressure difference between the inside and outside of the furnace tube 1 is p, the maximum compressive stress of the dome-shaped ceiling 4 is

Σ = R ₁ p / 2t (1) Maximum compressive stress of the cylindrical portion 3

Σ = Rp / t (2) and the relationship between R1, R2 and R, the ceiling part 4 and the cylindrical part 3
Coupling unit tensile stress caused by (normal arc of coupling the arc portion of the R ₂₎ in 5 bending occurs in.

Here, t is the wall thickness of the furnace tube. FIG. 3 shows an analysis result of the state of occurrence of tensile stress in the furnace core tube 1 when using a vacuum. In a general core tube structure, the effect is negligible because the tensile stress is smaller than the compressive stress.
Thus, from the viewpoint of the compressive stress, it is easily imagined that the design condition of R1 = 2R is appropriate for the metal core tube (the stress values of the equations (1) and (2)). Are equal). Such a design condition is usually adopted for a metal pressure vessel, and is also used for the structure of a furnace tube. That is,
A structure in which the space of the dome-shaped ceiling portion 4 is sufficiently small is obtained.

However, quartz glass is a material having a characteristic that its tensile strength is lower than its compressive strength, and the quartz glass manufactured by the present inventors has a compressive strength of 1130 MPa and a tensile strength of 48 MPa. For this reason, in a quartz core tube, the tensile stress cannot be ignored.
It becomes a bottleneck in structural design.

A practical core tube structure falls within the range indicated by the following conditions.

[0028]

(Equation 3)

Under these structural conditions, the tensile stress important for quartz glass is about 40 MPa in the worst case when the pressure difference p is about 1 atm. In general,
As R ₁ is greater than R is smaller, and as the R ₂ is large, the tensile stress generated is small. Further, as the thickness t increases, the tensile stress decreases.

When such a structure is realized and used with quartz glass, a compressive residual stress of a maximum of about 40 MPa may be formed on the outer surface of the connecting arc portion 5 connecting the ceiling portion 4 and the cylindrical portion 3. The formation of the residual compressive stress may be performed by a high-temperature quenching method or a chemical method by diffusion of atoms other than Si and O. FIG. 4 shows the residual stress along the section AA of the connecting arc portion 5 having the radius R2 in FIG. The required maximum compressive stress of the outer surface layer 5s differs depending on the structure (shape and size). The required maximum compressive stress of the outer surface layer 5s is calculated by a known stress analysis method.

Further, such a quartz glass furnace tube 1
When used at a high temperature, the residual stress is gradually reduced due to viscous deformation, and the reinforcing effect is lost.

FIG. 5 shows the half-life of the residual stress under the condition of the operating temperature. However, the quartz glass of FIG. 5 has the viscosity coefficient of the quartz glass manufactured by the inventors.
Considering the practical life of the quartz glass furnace tube 1, it is considered that if the use temperature is 900 ° C. or less, the strengthening effect of the quartz glass can be sufficiently maintained (about 3700 use hours). Therefore, the quartz glass furnace tube of the present invention has a temperature of 900 ° C.
It is desirable to use it below.

Next, a method for heat-treating a semiconductor wafer using a quartz furnace tube according to the present invention will be described. An example in which the inner pressure of the quartz furnace core tube is always kept higher than the outer pressure will be described.

As shown in FIG. 6, a large number of semiconductor wafers W are mounted on a wafer boat 11 and
1 is placed on a furnace support 13 via a heat insulating stand 12, and further, the wafer boat 11 on which the furnace support 13 is mounted is covered with the quartz glass furnace tube 1, and the wafer boat 11 is placed on the quartz glass furnace tube 1. To store. In this state, the furnace support 13 is raised, and the quartz glass core tube 1 and the wafer boat 11 are stored in the heat treatment furnace 14. Thereafter, the inside of the furnace is heated to a furnace temperature of 900 ° C. or lower by the heater 15, and the quartz glass furnace tube 1 and the semiconductor wafer W in the quartz glass furnace tube 1 are heated. In this state, a processing gas 16 is supplied from outside the quartz glass furnace tube 1 to perform a heat treatment on the semiconductor wafer W. In the heat treatment step of the semiconductor wafer W, the radius R ₁ of the ceiling portion 4 is R ₁ = 1.6R to 2.4R. Quartz glass furnace tube 1
The semiconductor wafer W is stored in the quartz glass core tube 1
And the maximum tensile stress is generated in the outer surface layer 5s of the joint arc portion 5 of the quartz glass furnace core tube 1.
Radius R of the cylindrical portion 3, between the radius _{R 2} of the radius _{R 1} and coupling the arc portion 5 of the ceiling portion 4 _R 1 = 1.6R~2.4R, _R
2 = 0.2R to 0.4R, and a compressive residual stress is present in the outer surface layer 5s of the joint arc 5 so that the compressive residual stress and the generated tensile stress cancel each other. , Ceiling part 4 due to tensile stress, joint arc part 5
Can be prevented from being deformed. The compressive residual stress of the outer surface layer 5s has a half-life when the use temperature is 900 ° C. as shown in FIG. 5, and the reinforcing effect of the quartz glass core tube 1 can be sufficiently maintained even for about 3700 use hours, and the Becomes possible.

Further, according to the method of the present invention, the quartz glass furnace tube has the following structure and dimensions, and can be safely used in a low pressure CVD furnace without generating residual stress in the quartz glass.

[0036] That is, the radius R of the cylindrical portion is not less than 300 mm, coupled arcs 2.4R ≧ _{R 1} ≧ 1.2R, the cylindrical portion radius R between the radius _{R 1} of the cylindrical portion radius R and the ceiling portion between the radius _{R 2} parts have relation 0.6R ≧ _{R 2} ≧ 0.2R, further between the radius _{R 2} of the coupling arcuate portion with a radius _{R 1} of the ceiling portion, 9 ≧ _{R 1} / R ₂ ≧ 3.8.

In the quartz furnace core tube 1 having such a structure, when used in a heat treatment furnace, a maximum tensile stress is generated in the joint arc 5 and the tensile stress applied to the joint arc 5 is 10%.
Since it is less than MPa, there is no problem in strength considering the tensile strength of general quartz glass of 40 to 50 MPa. The quartz furnace tube having such a structure has a wider usable temperature range than the furnace tube with residual stress, and can generally be used up to 1200 ° C.

[0038]

Test 1: With respect to the quartz glass furnace tube according to the present invention shown in FIG. 1, a computer was used to perform a structural analysis simulation on the state of occurrence of tensile stress in the furnace tube when vacuum was used. The radius of the cylindrical portion R = 600
mm, the radius R _{1 of the} ceiling portion was 1200 mm, and the radius R ₂ of the joint arc portion was 150 mm.

Result: shown in FIG.

It was found that the tensile stress generated in the core tube was minimum at the cylindrical portion and maximum at the joint arc. Since residual stress exists in the furnace tube, the maximum tensile stress actually generated is within the strength range of quartz glass.

Test 2: A quartz glass furnace core tube having the structure of the quartz glass furnace tube according to the present invention as shown in FIG. 1 was changed to various dimensions as shown in Table 1, and a computer was used for vacuum bonding. The maximum tensile stress at the arc was calculated.

Results: shown in Table 1.

[0043]

[Table 1]

0.6R ≧ R2 ≧ 0.2R, 2.4R ≧ R
If the curved surface design satisfies 1 ≧ 1.2R and 9 ≧ R1 / R2 ≧ 3.8, the tensile stress generated in the joint arc becomes 10 MPa or less, and a quartz glass furnace tube with no problem in strength is manufactured. I knew I could do it.

Test 3: The relationship between the half-life of the residual stress and the temperature of the quartz glass used for the quartz glass furnace tube according to the present invention is examined.

Result: shown in FIG.

At 900 ° C., it was found to be 3700 hours.

[0048]

According to the quartz glass furnace tube for low-pressure CVD according to the present invention, even if it is made of quartz glass, a sufficient height can be obtained as high as that of a furnace tube made of a metal material, and a high-strength low-pressure CVD tube can be obtained. A quartz glass furnace tube for use can be provided.

[0049] That is, the ceiling portion forms a dome shape with a radius _{R 1,} the cylindrical portion of the ceiling portion and the radius R are combined in coupling arcuate portion of radius _{R 2, R 1 = 1.6R~2.4R,} R ₂ =
Since it is a quartz glass furnace tube for reduced pressure CVD which has a shape of 0.2R to 0.4R, is used at a furnace temperature of 900 ° C. or less, and has a compressive residual stress in an outer surface layer of a joint arc portion, the heat treatment furnace The useless space can be reduced, and a large number of semiconductor wafers can be heat-treated at one time. Further, even if the semiconductor wafer is used for a long time, it is not deformed, and the safety in use is improved.

[0050] Further, the ceiling portion forms a dome shape with a radius R _1, is coupled by coupling arcuate portion of radius R ₂ between the cylindrical portion of the ceiling portion and the radius R, the radius R of the cylindrical portion is at least 300mm And 0.6R ≧ R ₂ ≧ 0.2R, 2.4R ≧ R ₁
Since it is a quartz glass furnace tube for reduced pressure CVD having a curvature of ≧ 1.2R and 9 ≧ R ₁ / R ₂ ≧ 3.8, a large number of semiconductor wafers W having a large diameter can be heat-treated at one time and can be used for a long time. Furthermore, even with a large core tube used under reduced pressure, a core tube with satisfactory strength can be realized without changing the wall thickness, and the problem of cost increase due to the increase in the size of the core tube and the problem of height limitation are reduced. Can be eliminated, and
Safety during use can be improved.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram of a quartz furnace tube for a vertical heat treatment furnace according to the present invention.

FIG. 2 is a schematic view of a furnace tube used for determining the shape of a quartz furnace tube for a vertical heat treatment furnace according to the present invention.

FIG. 3 is an analysis result diagram of a tensile stress generation state of the furnace core tube when the vacuum furnace core tube for a vertical heat treatment furnace according to the present invention is used in vacuum.

FIG. 4 is an explanatory view of a residual stress along a cross section AA of a joint arc portion in FIG. 1;

FIG. 5 is a test result diagram showing a half-life of residual stress under conditions of a use temperature of quartz glass used in the present invention.

FIG. 6 is a conceptual diagram showing a use state of a quartz furnace core tube for a vertical heat treatment furnace according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Quartz glass furnace tube for low-pressure CVD 2 Storage part 3 Cylindrical part 4 Ceiling part 5 Joining arc part 5s Outer surface layer 6 Opening R Radius of cylindrical part R ₁ Radius of ceiling part R ₂ Radius of joining arc part t Thickness of furnace tube

Continued on front page F term (reference) 4G014 AH00 4K030 CA04 FA10 KA04 KA09 LA15 4K061 AA01 AA05 BA11 CA08 CA14 DA05 EA10 FA07 5F045 AA06 BB14 DP19 DQ05 EB03 EC01

Claims (2)

[Claims] Claims: 1. An upper part used in a reduced pressure heat treatment furnace.
Is a circle with a convex ceiling on the outside and an open bottom
In the tube-shaped quartz glass furnace tube for low-pressure CVD, the ceiling has a radius R₁The dome shape of this ceiling and half
The cylindrical part of diameter R is radius R ₂Are joined at the joining arc of₁= 1.6R to 2.4R, R₂= 0.2R-0.4R
It is used at a furnace temperature of 900 ° C or less and has compressive residual stress on the outer surface layer of the joint arc.
A quartz glass furnace tube for reduced pressure CVD characterized by the following. 2. A cylindrical quartz glass furnace tube for low-pressure CVD, which is used in a low-pressure heat treatment furnace and has an upwardly projecting ceiling at an upper portion and an open lower portion, wherein the ceiling has a radius. No dome shape of R _1, is coupled by coupling arcuate portion of radius R ₂ between the cylindrical portion of the ceiling portion and the radius R, the radius R of the cylindrical portion is not less than 300 mm, and, 0.6R ≧ R
₂ ≧ 0.2R, 2.4R ≧ R ₁ ≧ 1.2R, 9 ≧ R ₁ /
Low pressure CVD characterized by having a curvature of R ₂ ≧ 3.8
Quartz glass furnace tube.