Auxiliary heat-insulating jig

Details Auxiliary heat-insulating jig Auxiliary heat-insulating jig

2002-01-24

2003-08-19

Wilson, Gregory (Department: 3749)

Heating

Accessory means for holding, shielding or supporting work...

Support structure for heat treating ceramics

C211S041180, C427S255120

Reexamination Certificate

active

06607381

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to an auxiliary heat-insulating jig, and more specifically, it relates to an auxiliary heat-insulating jig improved to be capable of increasing an adiabatic effect. The present invention also relates to a method of manufacturing an auxiliary heat-insulating jig improved to increase an adiabatic effect. The present invention further relates to a vertical heat treatment apparatus having such an auxiliary heat-insulating jig.
2. Description of the Prior Art
A semiconductor device such as a MOS-LSI or a bipolar LSI is fabricated through a number of heat treatment steps such as an oxidation step, a CVD step and a diffusion step. Following the recent progress of the semiconductor device fabrication technique, a general process apparatus is mainly formed by a single wafer processing apparatus. On the site of production, about 25 silicon wafers for forming semiconductor devices are generally treated as a single lot. Thus, the single wafer processing apparatus treats and physically distributes silicon wafers lot by lot.
On the other hand, a vertical heat treatment apparatus requiring a long treatment time generally treats and physically distributes at least 100 silicon wafers, i.e., at least four lots of silicon wafers at a time, while a vertical heat treatment apparatus called a high-temperature heat treatment furnace capable of reducing the treatment time can treat and physically distribute a lot of silicon wafers at a time.
When a vertical heat treatment apparatus such as a vertical transformation CVD (chemical vapor deposition) furnace is employed in heat treatment steps, silicon wafers for forming semiconductor devices are loaded on a vertical heat treatment wafer boat of quartz or SiC and inserted into a reaction tube of the vertical heat treatment apparatus. A number of silicon wafers can be vertically loaded on the vertical heat treatment wafer boat at proper intervals in a horizontally kept state. In this case, the vertical heat treatment wafer boat is generally set on a heat-insulating jig referred to as a heat-insulating cylinder.
This heat-insulating jig is set between the vertical heat treatment wafer boat and a cap (a component serving as the lid of the reaction tube during heat treatment). The heat-insulating jig prevents heat in the reaction tube from escaping from a throat by thermal conduction while preventing a sealing member for the cap and a rotation mechanism of the wafer bat from deterioration or breakage caused by radiant heat. Therefore, a heat-insulating cylinder having large thermal capacity is employed in a high-temperature vertical heat treatment furnace.
The heat-insulating cylinder may be provided in various shapes. Referring to
FIG. 37
, for example, an opaque quartz cylinder
324
stores an insulator
323
prepared by deairing a quartz capsule
321
and sealing the same with flocculently rounded quartz wool
322
. This opaque quartz cylinder
324
is generally applied to a furnace of a relatively high-temperature specification.
Referring to
FIG. 38
, a heat-insulating jig formed by vertically arranging several opaque quartz discs of about 5 mm in thickness at intervals of several cm is also known.
Referring to
FIG. 39
, an opaque quartz cylinder
392
storing several vertically arranged opaque quartz discs
391
is also proposed.
Referring to
FIG. 40
, a large cylinder
401
storing alternately stacked discs
7
and cylinders
36
(not welded) is also known.
FIG. 41
shows a low-temperature heat-insulating cylinder set on a boat.
FIG. 42
shows a high-temperature heat-insulating cylinder set on a boat. The heat-insulating cylinder shown in
FIG. 41
is applied to a furnace employed at a relatively low temperature, and the heat-insulating cylinder shown in
FIG. 42
, prepared from that shown in
FIG. 37
, is applied to a furnace employed at a relatively high temperature.
While opaque quartz is the optimum material for the heat-insulating cylinder, transparent quartz may be additionally employed as an auxiliary material.
A material prepared by storing a silicon wafer in a deaired or nitrogen-sealed quartz glass member for preventing the silicon wafer from oxidation is also proposed as an insulator. This material, proposed on the basis of such a supposition that the silicon wafer having a mirror-finished surface may reflect approximately 100% of radiant heat, reflects visible light. However, the material absorbs infrared light and the silicon wafer is immediately heated to cause heat radiation again, and hence this material is improper for application to an insulator.
Some materials of silicon carbide (hereinafter referred to as SiC) are proposed as ideas. However, it is to be noted that the thermal conductivity of SiC is 45 to 125 W/m.k, i.e., at least 20 to 60 times that of quartz glass. SiC must be regarded as a remarkably excellent thermal conductor, and an expression “insulating or heat-shielding plate of SiC” means “heat-shielding plate having excellent thermal conductivity” in other words. This expression is unsubstantial and misleading wording confusing users similarly to “insulator excellently conducting electricity”, since SiC has no heat-shielding effect in practice. A thin plate of SiC used in any of the aforementioned ideas may be used not for heat shielding but for a purpose of attaining an effect of rectifying reaction gas, for example, and must have a more proper name than a heat-shielding plate. For example, the thin plate of SiC may be properly referred to as a rectifying plate or a dummy wafer. In a vertical heat treatment apparatus, SiC having excellent thermal conductivity is mainly employed as the material for a soaking pipe.
Recently, a general vertical heat treatment apparatus having a track temperature increase speed of not more than 8° C./min. and a track temperature reduction speed of not more than 3° C./min. is being replaced with a vertical heat treatment apparatus, referred to as a high-speed temperature-control furnace, having a track temperature increase speed of at least 45° C./min. and a track temperature reduction speed of at least 15° C./min.
Such a high-speed temperature-control furnace employs a heat-insulating jig having small thermal capacity so that the temperature control speed is not reduced.
When such a heat-insulating jig is employed, heat escapes from a bottom area of a wafer boat in a temperature region exceeding 1000° C. Therefore, the heat-insulating jig requires a long time for reaching a target temperature exceeding 1000° C. and entering a stable state.
Also in a range where the heat-insulating jig can reach the target temperature, heat escapes from a portion around the bottom, and hence a heater for the bottom portion is regularly in a state substantially at full power. Therefore, thermal stress is applied to a wafer treated in the vicinity of the bottom, to cause crystal defects called slips in the wafer.
For example, Japanese Patent Laying-Open No. 9-74071 (1997) proposes a heat-insulating jig formed by arranging a plurality of thin heat-shielding plates as a heat-insulating jig capable of reducing thermal capacity. The material for this heat-insulating jig is SiC. As to employment of quartz, the gazette shows such a negative view that quartz may be selected if the thickness of a quartz member can be technically reduced.
As described above, SiC absorbing infrared rays and having excessively small thermal capacity has a small adiabatic effect. Therefore, SiC cannot be used as a heat-shielding material even in a furnace of a relatively low-temperature specification such as a CVD furnace. In other words, radiant heat (transmitted radiant heat and re-radiation) and heat conduction from a material referred to as a heat-shielding plate of SiC disadvantageously deteriorate or disappear a sealing member of a heat treatment furnace or break down a rotation mechanism of a wafer boat.
The inventors have reached an idea of adding an auxiliary heat-insulating jig to a heat-insulating jig employed in a general furnace

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