Electric heating – Heating devices – With power supply and voltage or current regulation or...
Reexamination Certificate
2001-11-08
2003-09-30
Hoang, Tu Ba (Department: 3742)
Electric heating
Heating devices
With power supply and voltage or current regulation or...
C219S497000, C219S501000
Reexamination Certificate
active
06627860
ABSTRACT:
TECHNICAL FIELD
The invention relates to the field of monitoring temperature for a diffusion furnace used in the processing of semiconductor material.
BACKGROUND OF THE INVENTION
FIG. 1
shows a simplified view of a prior art diffusion furnace system used for processing semiconductor materials. The furnace
100
includes a cylindrical container
102
having a source area
104
, a center area
106
and a handle area
108
. Typically silicon wafers are positioned in the cylinder and gases are injected into the cylinder at the source end
110
of the container. A heating element
112
, which consists of a coil wrapped around the outside of the container
102
is used to heat the container
102
and its contents. A heating apparatus
114
is used to heat the coil
112
. A controller
116
is used to monitor the temperature of the container
102
and control the heating apparatus
114
driving the coils
112
. For the processing of the semiconductor material inside the container
102
to be effective the temperature must be precisely controlled. Thus, the temperature of the container
102
must be accurately monitored.
The prior art system has three temperature monitoring zones
118
,
124
and
130
which are disposed in the source area
104
, the center area
106
, and the handle area
108
, respectively. The source zone
118
includes three thermocouples positioned in the source area
104
of the container. Two of the thermocouples
120
are referred to as spike thermocouples. As shown the spike thermocouples
120
are located outside of the container
102
on opposite sides of the container
102
and positioned between adjacent windings of the heating element coil
112
. In practice however the spike thermocouples may be positioned adjacent to each other. The third thermocouple
122
in the source zone
118
is located inside the container
102
, and is referred to as the profile thermocouple. In a similar manner the center monitoring zone
124
has two spike thermocouples
126
positioned on the outside surface of the container
102
, between adjacent windings of the coil
112
, and profile thermocouple
128
positioned inside the container
102
. In a similar manner, a handle monitoring zone
130
is created in the handle area
108
. The handle zone
130
includes two spike thermocouples
132
and a profile thermocouple
134
.
A thermocouple is a heat sensing device which consists of dissimilar metals which are joined together. Other heat sensing devices which operate in manner similar to a thermocouple could also be used. The junction between the metals of the thermocouple is such that when it is exposed to heat it will generate a voltage. The more heat the thermocouple is exposed to the higher the resulting voltage. Conversely, as the temperature is lowered the voltage will decrease. In the prior system
100
, the thermocouples are coupled to a controller
116
which operates to sense the voltage for each of the thermocouples. If the voltage of the thermocouples falls below a certain threshold then the power driving coil
112
will be increased by the heating apparatus
114
, in response to signals from the controller
116
. If the voltage of the thermocouples exceeds a certain threshold then the controller
116
will cause the heating apparatus to decrease the power driving the coil
112
, thereby decreasing the generated heat sensed by the thermocouples.
In the prior art system
100
, a problem can arise when one of the thermocouples fails. Typical failures for a thermocouple are manifested in one of two ways. A thermocouple may fail to generate a voltage in response to heat. In this case the thermocouple essentially shorts out. In this situation, even if the thermocouple is exposed to a very high temperature, it will fail to generate a voltage.
A thermocouple can also fail by going to a state where it becomes an open circuit. In this situation even when the thermocouple is exposed to very little heat it will appear to be generating a high voltage relative to a thermocouple that has not failed due to an open condition.
If the thermocouple has a short failure then the controller
116
, detecting a very low voltage at the thermocouple, will process this detection as if the thermocouple were generating too little voltage as a result of the temperature being to low. Accordingly, the controller
116
will cause the heating apparatus
114
to drive the coil
112
to generate higher temperatures. Thus, increasing the temperature of the container
102
. When there is a short failure, the controller
116
will frequently cause the heating apparatus
114
to drive the coil
112
to increase temperature above desired levels, which can result in a failed process.
If one of the thermocouples has an open failure, the controller
116
will sense what appears to be a very high voltage, which would lead to less power being used to drive the coil
112
. In prior systems the thermocouple with the lower voltage was deemed to be the one on which the controller would base the control of the heating apparatus. As a result it was not uncommon to see a processes fail as a result of being overheated, where one of the thermocouples had to short failure. Further, these prior systems did not provide any easy way for a user to detect when a thermocouple failed due to a short condition.
In these prior systems, when a thermocouple failed because it was in an open condition, the operation of the furnace would likely continue successfully for a time, until a second thermocouple failed, at which point, the system operation could fail. If the second thermocouple failed as result of being open, then the controller
116
would allow the temperature to drop to low. If the second thermocouple failed as short then the system operation would fail as result to the temperature being driven to high. What is needed is a system which provides a simple and intuitive user interface which alerts a user if a thermocouple fails, and which makes optimum use of the thermocouples to increase the probability that the processing of the semiconductor material in the diffusion chamber will be successful.
SUMMARY
The heat sensing device manager system and method provided herein, offer the advantage of detecting whether a heat sensing device has failed due to an open condition or a short condition. In particular when a device is determined to have failed due to a short condition, the heat sensing manager system and method will cause the controller to not use the signal from the shorted heat sensing device as a basis for controlling the heating apparatus of the system. In addition, an embodiment of the system can provide a very simple LED user interface that conveys information about the operation of the heat sensing devices of the system. In particular the user interface can indicate which, if any, of the plurality of heat sensing devices have failed, and whether a failure of the heat sensing device is due to an open condition or a short condition.
REFERENCES:
patent: 4496940 (1985-01-01), Christel, Jr.
patent: 4937434 (1990-06-01), Nakao
patent: 5616264 (1997-04-01), Nishi et al.
patent: 5895596 (1999-04-01), Stoddard et al.
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