Abstract:
A heat sensing device manager system and method for processing signals from heat sensing devices used to monitor the semiconductor processing environment. The system includes a circuit for determining if a heat sensing device has failed. Where a heat sensing device has failed the system can switch control of the system such that it relies on signals generated by operational heat sensing devices. The system also provides the user with an intuitive LED interface that provides the user with information regarding the operation of the heat sensing elements of the system, and where a heat sensing device has failed the user interface can convey information regarding the nature of a particular heat sensing device failure.

Description:
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. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a simplified view of the of the diffusion furnace system of the prior art. 
     FIG. 2 is a view of a LED user interface of the invention. 
     FIG. 3 is a functional diagram of a portion of the thermocouple manager system. 
     FIGS. 4A-4B are detailed schematics of a portion of the circuitry which embodies the thermocouple manager system. 
     FIGS. 5A-5D are detailed schematics of a portion of the circuitry which embodies the thermocouple manager system. 
     FIGS. 6A-6D are detailed schematics of a portion of the circuitry which embodies the thermocouple manager system. 
     FIGS. 7A-7B are detailed schematics of a portion of the circuitry which embodies the thermocouple manager system. 
    
    
     DETAILED DESCRIPTION 
     A thermocouple manager system and method have been developed which can be used in conjunction with prior art systems as shown in FIG.  1 . Specifically, the thermocouple manager system can be designed to interface with the existing temperature control systems of the prior art. In one embodiment the thermocouple manager system has a user interface  200  as shown in FIG.  2 . The user interface includes LEDs  204  which corresponds to the different thermocouples described above. As shown there is a first area “Spike T/C”  202  where information is shown for the spike thermocouples. As discussed in more detail below, the operation of the interface is such that if an open circuit condition is sensed for the one of the spike thermocouples, which is identified as Source (A), then a red LED will light for the Source (A) LED. Similarly, if a short circuit condition is detected for the Center spike thermocouple (referred to as Centre (A) on the interface) then a green LED will light for the Center (A) LED. For the profile thermocouples, note that there is only one thermocouple per zone, the LEDs operate in similar manner. As shown in FIG. 2, in the “Profile T/C” area  206 , a green LED is lit for the center profile thermocouple indicating a short failure. The torch LED can also be used to indicate information regarding the torch, which is an optional element of the heating apparatus. The interface  200  also provides a blue fault LED  208  which lights and latches when a fault is detected, and an audible alarm sounder can also be activated. The reset button  220  is available to reset the thermocouple manager system. 
     A simplified operational diagram of a portion of the thermocouple manager system  300  is shown in FIG.  3 . Address decode/select circuitry  302  is used to identify which thermocouple voltage is being detected. When a voltage is detected that indicates that a particular thermocouple has failed due to an open or short condition, either a red LED  304  or a green LED  306  corresponding to the failed led will be lit by closing either the open circuit fault detect switch  308  or the short circuit fault detect switch  310 . Upon the closing either of these switches a signal will also be sent to the alarm detect circuitry  312 . 
     FIGS. 4A-4B to FIGS. 7A-7B show a detailed embodiment of a thermocouple manager system circuit. In this embodiment the circuitry can be thought of in two parts. One part is primarily analog (shown in FIGS. 4A-4B) and can be directly connected via a ribbon cable  414  to a control board, which is part of the prior art controller  116  shown in FIG.  1 . The analog circuitry  400  can utilize signals from existing control boards of the controller  116  to detect the voltages generated by the different thermocouples. 
     In one embodiment the circuitry  400  shown in FIGS. 4A-4B is implemented on a printed circuit board (PCB), and relevant control and power signals are derived from the existing temperature control circuitry of the controller  116 . In some cases it is beneficial to enclose the circuitry  400  in a RF protection casing to prevent noise. 
     The comparators U 20  and U 21  of FIG. 4A, form a window comparator circuit which monitors the value of the analog voltage  402  detected at the thermocouples. The voltages at the different thermocouples are sequentially input to the window comparator circuit. The comparators operate to detect if either an open circuit or short circuit thermocouple condition is present. The window comparator threshold voltages  404  and  406  are provided by R 3  and R 4  shown in FIGS. 5A-5B. As shown in FIGS. 5A-5B the short circuit threshold voltage is 0.06 volts and the open circuit threshold voltage is 2.2 volts. When a thermocouple failure is present the relevant comparator, U 20  or U 21  of the window comparator, output voltage changes state and outputs  410  and  412  are transmitted to the circuitry shown in FIGS. 6A-6D. 
     FIGS. 5A-5D to FIGS. 7A-7B show the primarily digital circuitry of the thermocouple manager  300 . This circuitry can be implemented on a PCB which is located remotely from the circuitry shown in FIGS. 4A-4B. The power and control signals are transferred from the analog PCB  400  to the digital control circuitry shown in FIGS. 5A-5D to FIGS. 7A-7B via a 26-way ribbon cable  408 . The fact that these threshold resistors R 3  and R 4  are remotely located from the analog PCB board  400  can simplify the set-point adjustment for threshold voltages  404  and  406 . 
     The analog PCB  400  provides a voltage injection  418  to the prior art controller  116  via a tri-state buffer U 22 . The short circuit bypass enable signal  416  switches the tri-state buffer U 22  on and raises the ‘short circuit bypass” voltage  418  to  5  volts via R 1  pull up resistor. This signal ‘fools’ the prior art controller  116 , by sending a signal  418  which makes the prior art controller  116  operate as if the shorted thermocouple is actually an open thermocouple. Thus, the controller  116  will operate to control the heating apparatus  114  based on a signal which corresponds to the thermocouple which is not shorted. This prevents the uncontrolled thermal runaway condition which short circuit thermocouples can initiate. (As previously discussed the prior art controller  116  operates to control the heating apparatus based the information generated by the thermocouple which corresponds to the lowest apparent detected temperature.) 
     U 4 , U 5 , U 6  and U 10  shown in FIGS. 5A,  5 C and  5 D perform address decoding based on signals  502 ,  504  and  506  from a negative edge triggered control board thermocouple multiplexer circuit of a control board of the controller  116 . The U 7  inverters convert the negative edge triggered signals  502 ,  504  and  506  to positive edge triggered signals suitable for address decoding. The output of the U 4  BCD to decimal decoder is fed to U 5 , U 6  and U 10  BCD to decimal decoders to provide ten thermocouple channel select signals; six for the spike thermocouples, and three for the profile thermocouples; and one for the torch thermocouple. These outputs are shown as lines from U 5 , U 6  and U 10  to inverters U 8 ( a-f ) and U 9 ( a-d ). The inverters operate to invert the signals and provide ground potential signals for a user interface circuit  600 . The output from the inverters U 8 ( a-f ) and U 9 ( a-d ) are labeled to show the corresponding thermocouple. 
     These signals from U 5 , U 6  and U 10  provide a ground connection to the common cathode of a particular bi-color LED(LED  1 - 10 ) shown in FIGS. 6A-6B, where the particular bi-color LED corresponds to the thermocouple whose voltage  402  is being input to the comparators U 20  and U 21 . If a fault condition is detected by the U 20 /U 21  window comparator circuit of FIG. 4A the output signal ( 410  and  412 )is buffered by U 14   a /U 14   d  and is used to drive analog switches DG 1  and DG 2 . If an open circuit condition is detected via signal  412  then the open circuit switch DG 2  will send a driving voltage to the anodes of the of the red LEDs, and the red LED corresponding to thermocouple which is indicated as selected via the signals from the inverters U 8 ( a-f ) and U 9 ( a-d ) will be driven. Thus, the red LED, which corresponds to the failed thermnocouple, will light on the user interface  200 . Similarly, when a short is detected the green LED corresponding to the failed thermocouple will be lit. 
     When the analog switches are enabled the voltage at pin  1  on DG 1  or DG 2  drops from 5 Volts to approximately 3 volts due to the voltage drop created by the current drawn through the LED. Specifically, when there is a voltage resulting from an open or short detection input to pin  6  of DG 1  or DG 2  a short is created between pin  1  to pin  8  which causes current to flow through the resistor R 2  or R 5 . This voltage drop is detected by comparator circuits U 12  or U 13 . The U 12  and U 13  threshold voltage  602  is set using R 6 . 
     The open circuit and short circuit voltage drop output signals  604  and  606  from U 12  and U 13  are OR&#39;d (U 14   b ) as shown in FIG. 7A to provide a single fault detect signal  702 . This signal  702  can be used to latch the audible alarm sounder and also the Alarm LED (LED  11 ). This latch can be reset by pressing the alarm latch reset switch (SW 1 ). U 15  provides power for the sounder and LED via R 7  and R 3  pull-up resistors. 
     U 23  and related components constitute a delay timer, having an approximately 2 minute delay, which prevents the thermocouple manager circuit from intervening when the diffusion furnace is cold at power up. This circuit uses the output  704  from the handle profile thermocouple to determine if the furnace is below 250° C. if so, the thermocouple manager system audio alarm and short circuit bypass signals are disabled allowing the furnace to reach standby temperature. Once the temperature is above 250° C. the thermocouple manager system is enabled and becomes fully operational. 
     The benefits of using the system and method of the present invention can be illustrated by considering different thermocouple failure scenarios. In the prior systems when the spike thermocouples are being used to control, if a spike thermocouple failed due to a short situation, the controller would cause the temperature to increase, based on the assumption that the low voltage reading at the shorted thermocouple was due to low temperature. Using the thermocouple manager system described herein, the detection circuitry will determine that the thermocouple is shorted and will cause the controller to ignore the voltage detected at the shorted thermocouple, and instead use the voltage reading from the other spike thermocouple. Additionally, the thermocouple manager system will cause the user interface to indicate exactly which thermocouple failed and the nature of the failure. 
     Because the thermocouple manager system is able to determine if a thermocouple has failed due to either an open or short condition, the thermocouple manager system offers the advantage of being able to identify a situation where both spike thermocouples have a short failure, and where such a situation has been identified, existing software can be utilized to cause the system to switch from spike control to profile thermocouple control. Similarly, if the system is operating under profile thermocouple control and the thermocouple system manager detects a failure due to either an open or a short then existing software can be utilized to cause the system to switch over to spike thermocouple control. 
     While the method and apparatus of the present invention has been described in terms of its presently preferred and alternate embodiments, those skilled in the art will recognize that the present invention may be practiced with modification and alteration within the spirit and scope of the appended claims. The specifications and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense. Further, even though only certain embodiments have been described in detail, those having ordinary skill in the art will certainly understand that many modifications are possible without departing from the teachings thereof. All such modifications are intended to be encompassed within the following claims.