Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
1999-03-15
2001-02-27
Paik, Sang (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C392S419000, C374S121000, C374S124000, C250S338100
Reexamination Certificate
active
06194691
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method for manufacturing a heating furnace to be used when a thin film, such as silicon semiconductor single crystal thin films, is deposited on a surface of a wafer such as silicon semiconductor single crystal substrates.
For a deposition of a thin film such as a silicon semiconductor single crystal thin film on a surface of a wafer such as a silicon semiconductor single crystal substrate, there has been employed a so-called lamp heating furnace using radiant heating which is equipped with a light source for radiating light for use of heating, a lamp house having a wall surface that reflects light derived from the light source, and the like.
FIG. 1
shows an example of the arrangement of the heating furnace. This heating furnace comprises a reaction furnace
14
made of quartz glass
15
for holding a wafer
1
therein, and a lamp house
10
provided above the reaction furnace
14
and having a light source
11
such as a plurality of infrared lamps placed therein. The lamps of the light source
11
are arranged circumferentially in a plural number, and a mirror reflecting plate
12
for reflecting light emitted from the lamps of the light source
11
is mounted on the inside-wall surface of the lamp house
10
. Besides, as required, a mirror reflecting cylinder
13
whose inner and outer surfaces depicted by broken line are mirror surfaces is also mounted. This mirror reflecting cylinder
13
, which is removable, can be mounted for the control of heating distribution based on heating calculations.
Conventionally, design and manufacture of such a heating furnace has been carried out in a manner in which trials and errors are iterated through steps of, with respect to a trial-manufactured heating furnace prototype, first, measuring a heating temperature distribution of a wafer
1
in a heating experiment using thermocouples
2
as shown in
FIG. 1
, then making improvements on the heating furnace prototype based on results of the experiment, and further performing temperature measurement again in another heating experiment. In brief, the heating furnace has hitherto been designed and manufactured empirically. As a result, quite a large number of times of trials and errors have been involved before the completion.
This being the case, an attempt to reduce the number of times of trials and errors has also been made by performing temperature prediction with numerical calculation. This attempt is implemented by simulations based on the presumption that light emitted from the light source is all irregularly reflected.
However, since a mirror-surfaced reflecting plate has been used in recent years as the wall surface of the lamp house of the heating furnace for heating the wafer, such as a silicon semiconductor single crystal substrate, correct temperature predictions cannot be achieved without regarding the light reflection occurring at the wall surface of the lamp house as regular reflection, i.e., mirror reflection rather than irregular reflection. Besides, since the wafer to be heated is a mirror-surfaced wafer, the main surface of which has been mirror finished, there is a need for taking into consideration about the light reflection occurring at the wafer surface. Therefore, with such a simulation method as would be applied to a conventional heating furnace comprising radiant heating and an irregularly reflecting plate, it has been difficult to perform temperature prediction in the case where the mirror-surfaced wafer is heated by a heating furnace in which a mirror-surfaced reflecting plate is used as the mirror surface of the lamp house.
More specifically, in the heating process by the heating furnace of recent years' use, in which a mirror-surfaced wafer and a mirror reflecting plate are included as component members, light emitted from the light source imparts energy to the wafer while undergoing a great many number of times of reflections, thus making it difficult to predict the energy distribution on the wafer, unlike heating furnaces characterized principally by irregular reflection. Due to this, with simulations based on the assumption that all of light is irregularly reflected, insufficient prediction of temperature distribution or the like would result so that only a heating furnace low in the degree of completeness could be obtained. Thus, in order to solve such issues as low heating efficiency, excessive trials and errors would be involved inevitably. This would lead to losses of not only time and expense but also earth resources.
SUMMARY OF THE INVENTION
Under these circumstances, there has been a desire for development of a method for predicting heating distribution and then, base on results of this prediction, designing and manufacturing a heating furnace. The invention has been accomplished in view of these and other problems, with an object to provide a heating furnace and a manufacturing method which allows a heating furnace having a desired heating distribution with less trial and error by predicting heating distribution in advance before heating the wafer.
In order to achieve the above object, the invention provides a method of manufacturing a heating furnace for use of wafer heating which has a light source and a lamp house surrounding the light source, the method comprising: a calculating process for determining heating distributions on a wafer on a presumption that a light flux emitted from the light source is mirror reflected by a wall surface of the lamp house while the light flux is mirror reflected also by a surface of the wafer, tracing a path of the light flux attributable to the reflection on the wall surface of the lamp house as well as the reflection on the surface of the wafer, performing a calculation of converting an absorption of the light flux into thermal energy occurring together with the reflection at least on the surface of the wafer with respect to a plurality of light fluxes emitted from the light source and a structure determining process of the light source and the lamp house based on a result of the calculation.
Preferably, the structure is determined so as to make a difference between a first heating distribution by light fluxes incident that come for the first time on said wafer and a second heating distribution by light fluxes incident that come for the second and following times after the first-time reflection on the wafer surface.
Preferably, said light source is presumed to be a set of a plurality of point light sources, and results of the calculation performed for each of a plurality of light fluxes emitted from said individual point light sources at different angles are totaled for all the angles and all said point light sources.
The invention also provides a heating furnace which has a light source and a lamp house surrounding the light source for use of heating a wafer, characterized in a structure in which there is a difference between a first heating distribution attributable to light fluxes incident for the first time on the wafer, and a second heating distribution attributable to light fluxes incident on the second and following times after the first-time reflection on the wafer surface.
Preferably, the structure is such a structure that peripheral portions of the wafer are heated more intensely by the light fluxes incident for the first time on the wafer, while central portions of the wafer are heated more intensely by the light fluxes incident for the second time on the wafer.
The inventors of the invention, focusing on characteristics in heating with light, have developed a method for manufacturing a heating furnace based on results of a prediction about the heating distribution through a numerical calculation in which straight traveling property and reflecting property of light as shown in
FIG. 2
are described plainly. In a case that a light flux
11
a
emitted from a light source
11
toward a mirror-finished wafer
1
is mirror reflected according to a reflectivity R (where 0<R<1) on the surface of the wafer
1
, it was presumed that a part of
Habuka Hitoshi
Otsuka Toru
Paik Sang
Shin-Etsu Handotai & Co., Ltd.
Snider Ronald R.
Snider & Associates
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