AUTOMATED SINGLE SLICE CASSETTE LOAD LOCK PLASMA REACTOR

Abstract: A plasma etch system that processes one slice at a time is disclosed. The system is comprised of an entry loadlock 21, an exit loadlock 49, a main chamber 37, vacuum pumps 29,31, RF power supply 51, heat exchanger 63, control gas flow distribution system 45 and microprocessor controller in cabinet 23. A multiple slice cassette full of slices is housed in the entry loadlock 21 and after pumping to process pressure, a single slice at a time is moved from the cassette to the main processing chamber 37. The slice is etched and transferred to the exit loadlock 49. This process is repeated until all of the slices in the cassette have been processed.

Description: BACKGROUND OF THE INVENTION This invention relates to a semiconductor manufacturing apparatus and in particular to a semiconductor manufacturing apparatus in which circuit patterns are etched on a semiconductor wafer by a plasma reaction. The manufacturing of semiconductor devices such as a 256K RAM or even up to a 1 megabit RAM device require precision dry etching with high repeatability, low particulate levels, reliable endpoint detection, multiple process capability and reliable feedback control to a microprocessor controller for reliable systems execution. An example of a prior art plasma reactor system is described in U.S. Patent 3,757,733 which is assigned to the assignee of the present invention. In the prior art systems, the transportation of silicon wafers through a plasma reactor required an opening in the reactant chamber that is large enough for the wafer to pass through. The mechanisms that are typically used create particles that potentially reduce the yield of devices of the semiconductor wafers that are processed. Chlorine and bromine gases which are typically used in the process during plasma etching are highly corrosive to the components that are used to build the plasma reactors. Over a long term operation, reactor components exposed to the plasma must be constructed of materials that are resistant to the corrosive effects of the plasma. Aluminum is an excellent material for construction for a plasma reactor, especially when it is protected by anodization. However, during etching, when a semiconductor or silicon wafer is placed on a substrate assembly that is anodized and used as an electrode, the substrate is protected from the plasma by the silicon wafer. However, each silicon wafer has a slice or flat to allow for crystallographic orientation. If the slice is placed on the substrate with random orientation of the flat, an annulus of equal width of the flat width plus the placement tolerance will in general be exposed to the plasma. Anodizing the whole substrate is impractical in that it is conductive of the RF electrical power used in the plasma reactor. However, it is an insulator to DC. It is known that electrically floating objects such as silicon wafers covered with oxides exposed to a plasma will acquire an electrical potential, the floating potential, above the ground of the system. It has been observed in production that an electrostatic repulsion develops between the wafer and the semiconductor substrate causing the wafer to randomly drift off its alignment position on the substrate. Although several commercially available automatic wafer etch reactors use a confined plasma, none of the known systems provide a small gap which will not support a plasma and therefore confine the plasma within the small gap, use the same gap for both pumping the exhaust of gases from the reactors and for transporting the semiconductor wafers into the reaction chamber and thus keeping the reaction chamber simple and free of poorly controlled dead space within the reaction chamber. Additionally, it has been determined that the gap between the collimator or electrode and substrate during process should be approximately around 1 mm (0.040 inch) for oxide processing. With a non-load locked system, the process chamber is vented to atmosphere which allows the electrode and collimator to move up to between 0.75 and 1 mm (0.030 and 0.040 inch) and the semiconductor wafer passes under the collimator. This is unreliable due to the fact that an inconsistent gap can now be achieved and the slice levitation varies, also, an automatic transportation system is impractical with the above operation. And in particular, the single slice dioxide and oxide etch processes have historically used the highest possible density to remove silicon dioxide. This elevated power density is far more difficult to control than any other type of etching operation. Also, highly selective etch processing often builds up deposits in the reactors. For this reason, these processes have tended to be limited in commercial applications. In US-A-4 318 767, there is described an apparatus for the treatment of semiconductor wafers by plasma reaction. An entry load lock and an exit load lock are provided on opposite sides of the plasma chamber. Both load locks can hold a cassette of wafers and can be evacuated. Wafer transport means are provided for conveying wafers between the cassettes and the plasma chamber without exposing them to the atmosphere. It is an object of the present invention to provide an improved apparatus for processing semiconductor wafers by plasma reaction. According to the present invention there is provided apparatus for processing semiconductor wafers having a main plasma chamber containing main support means for supporting a wafer to be processed, with means for feeding reacting gases to the chamber and means for generating a plasma in the chamber to process the wafer, an entry load lock having means enabling it to be evacuated, being coupled to the main plasma chamber through an entry port, and including first elevator means (156) supporting first cassette means having a plurality of slice openings for holding a wafer, first wafer transporting means having first wafer support means effective to transport wafers from the first cassette means to the main plasma chamber, and an exit load lock having means enabling it to be evacuated, being coupled to the main plasma chamber through an exit port, and including second elevator means supporting second cassette means having a plurality of slice openings for holding a wafer, second wafer transporting means having second wafer support means effective to transport wafers from the main plasma chamber to the second cassette means, the main plasma chamber including means for transferring wafers between the first wafer transporting means and the wafer main support means and the main wafer support means and the second wafer transporting means, control means for operating the components of the apparatus so that wafers are passed from the first cassette means in the entry load lock to the second cassette means in the exit load lock through the main plasma chamber and undergo a particular process when in the main plasma chamber, CHARACTERISED IN THAT the first transporting means comprises a first slice transport arm that rotates about a vertical axis to convey a wafer between the first cassette means and the main plasma chamber, and that the first elevator means is operated when the first slice transport arm is in the first cassette means to lower the first cassette means so as to transfer a wafer from the first cassette means to the first slice transport arm and the second transporting means comprises a second slice transport arm that rotates about a vertical axis to convey a wafer between the second cassette means and the main plasma chamber, and that the second elevator means is operated when the second slice transport arm is in the second cassette means to raise the second cassette means so as to transfer a wafer from the second slice transport arm to the second cassette means. SUMMARY OF THE INVENTION A plasma etch system that processes one slice at a time is disclosed. The system is comprised of an entry loadlock, an exit loadlock, a main chamber, vacuum pumps, RF power supply, RF matching network, a heat exchanger, throttle valve and pressure control gas flow distribution and a microprocessor controller. A multiple slice cassette full of slices is housed in the entry load lock and after pumping to process pressure, a single slice at a time is moved by an articulated arm from the cassette through an isolation gate to the main process chamber. The slice is etched and removed from the main process chamber through a second isolation gate by a second articulated arm into a cassette in the exit loadlock. The process is repeated until all semiconductor wafers have been etched. The cassette loadlock system is able to evacuate a whole cassette of semiconductor wafers for processing which lowers the particulate environment for the slices and, provides a more stable environment for the slices by removal of moisture and preventing static discharges and additonally provides a safety feature that protects the operators from harsh or toxic gases that are traditionally used in semiconductor type plasma reactors. This novel feature enables clean slice handling and eliminates the problem that traditionally occurs in the manufacturing of semiconductor devices in that there are no airtracks on the devices, no rubbing of the parts or semiconductor wafers. The semiconductor wafers are lifted off the cassette slot before movement and all belts, pulleys or drives are either external to the chamber or shielded within the main reactor chambers. The movement of the slices through the process is tracked with sensors. The cassette loadlock apparatus according to the invention is a closed loop feedback process control system which ensures that adequate pressure within the entry loadlock, the exit loadlock and the main chamber are controlled by microprocessor. The RF power during the reaction of the manufacturing process is monitored and controlled by a microprocessor . Gas flows are monitored and controlled by the microprocessor through mass flow controllers. The end of etch is monitored and controlled by the microprocessor through a novel endpoint detection scheme. The invention provides a multiple process capability by which multiple menus can be applied to a single slice in situ to achieve special etch profiles and other special processing requirements such as high selectivity of the etch films to the substrate and the etching of multiple stacked films. These features provide a high etch rate with high resist survival through the use of a refrigerated liquid cooling on the top and bottom electrodes, thus allowing high power with good photoresist preservation during the operation. These and other advantages and features of the invention will be more apparent from reading of the specification in conjunction with the figures in which: BRIEF DESCRIPTION OF THE FIGURES Figure 1 is a front elevation of a cassette load lock plasma reactor according to the invention; Figure 2 is top view of the cassette load lock plasma reactor according to the invention; Figure 3 is a block diagram of the control system for the plasma reactor according to the invention; Figure 4 is a block diagram for the RF circuit; Figure 5 is a block diagram for the endpoint detection logic; Figure 6 is a flow diagram of the endpoint detection process; Figure 7 are waveforms illustrating the detection of an endpoint; Figures 8 and 9 are the gas and vacuum flow diagrams; Figures 10 and 11 are different views of the cassette load lock plasma reactor; Figures 12 through 13 illustrate the wafer transport system; Figures 14 through 17 are drawings illustrating the slice transport arm; Figure 18 is a view of the entrance port of the plasma reactor; Figures 19 and 20 are views illustrating the operation of the gate valves; Figure 21 is a sectional view of the reactor chamber; Figure 22 is a top view of the plasma plate illustrating an anodized ring; Figures 23 and 24 illustrate the substrate assembly; Figure 25 is a cross sectional view of another embodiment of the reaction chamber; Figures 26 through 28 are illustrations of the power load lock reactor, which is not claimed; Figures 29 and 30 are illustrations of the power load lock slice handler arm; and Figures 31 through 34 are diagrams of the power load lock chambers. DESCRIPTION OF THE PREFERRED EMBODIMENTS In Figure 1 there is shown a front elevation of a cassette load lock plasma reactor. The cassette of semiconductor wafers having photoresist patterns printed on them is placed in an entry load lock 21. A process is entered into a microprocessor that is contained within the cassette load lock reactor 23 by a keyboard 25 and a display 27. The menu is loaded in memory of the microprocessor and the process sequence begins. The entry load lock 21 is pumped down to a predetermined pressure or process pressure by a vacuum pump 29. The process pressure is maintained by feedback control circuit via a manometer that provides information to the microprocessor within the cassette load lock reactor 23 to control a throttle valve that is used to control the pump rate of the entry load lock 21. At the time that the entry load lock 21 is being pumped down to a process pressure and maintained there, the main chamber is either pumped down to main process pressure or is maintained at process pressure by a main chamber pump 31. A cassette elevator that is contained within the entry load lock 21 positions a first semiconductor wafer or slice that is to be processed by the cassette load lock reactor 23 and in the embodiment shown in Figure 1, a cassette that is a handling device that stores a plurality of, in the case of Figure 1 25, semiconductor wafers. Each wafer has patterns for semiconductor circuits printed on them by a photoresist process. The first semiconductor wafer is, as shown in Figure 2, positioned by the cassette elevators located generally at 33. The semiconductor wafer is moved from the entry chamber 21 through an isolation gate valve 35 into a main process chamber 37 and placed on the main chamber bottom electrode 39 for etching by an articulating arm 41. The position of the semiconductor wafer 143 is controlled by a feedback system and capacitive sensors that monitor the movement of the semiconductor wafer from the load lock chamber into the main chamber. After the slice is sensed to be safe in the main chamber 37 and the articulating arm 41 is sensed to be moved back into the entry load lock 21, the isolation gate 35 is closed and appropriate gases are applied from the gas distribution system 43 of Figure 1 through the filtering systems generally at 45 and applied to the main chamber 37 by flow controllers 845 that are contained within each gas line 45. In the embodiment of Figure 1, up to four gases may be applied to the main chamber for the process. Additionally, in Figure 1, a nitrogen line 47 provides nitrogen gas for purging of the system when it is necessary to open up the main chamber, the entry load lock or the exit load lock 49. As prescribed by the menu that was entered on the keyboard 25, pressure established by a throttle valve that is connected to the main chamber vacuum pump 31 and a manometer pressure sensor and the feedback loop process control is maintained by the microprocessor within the cassette load lock reactor 23. The cassette load lock reactor 23, in the embodiment of Figure 1, is a plasma reactor and a plasma is formed by applying RF energy between the two electrodes that are contained within the main chamber 37 which ionizes the gases to form reactant gases that include ions, free electrons and molecular fragments. The gases are provided by the gas distribution 43 and the filters 45. RF power is provided to the main chamber 37 by an RF generator 51 and is applied to an RF matching network 53 by a conductor 55. The RF matching network controls and adjusts the energy that is applied between the electrodes that are contained within the main chamber by sensing the reflected power and converting this information to the digital signal that the microprocessor within the cassette load lock 23 will respond to. In either etching or deposition process, the processing is automatically terminated by the microprocessor within the cassette load lock reactor 23. When in the etching mode, an endpoint is detected by an endpoint detector in the cassette load lock 23 which measures change in the optical emissions at a specific wavelength. The cassette load lock reactor 23 that is shown in Figure 1 and 2 provide multiple menus to be run on the same slice by the proper selection during the menu entry to the keyboard 25. After the process is complete, the slices or semiconductor wafers are automatically removed from the main chamber by a second articulated arm 57 that is located within the exit load lock 49 and is passed through a second isolation gate 61 and placed in an empty cassette whose position is positioned by the exit load lock elevators 33A. At the completion of the processing of each semiconductor wafer , the process is repeated until all of the semiconductor wafers have been processed by the cassette load lock reactor after which the entry load lock 21 and the exit load lock 49 are brought up to atmospheric pressure by applying nitrogen through line 47 to purge the entry 21 or the exit load lock 49. The cassette is then removed and a new cassette is loaded for processing. Heat transfer from the slice during etching is accomplished through a refrigerated system that is contained within a refrigerator controller 63 that refrigerates, in the embodiment of Figure 1, an ethylene glycol - water mixture flowing through the top and bottom electrodes that are contained within the main chamber 37. A thermocouple sensor element is used to monitor the temperature so that the process may be controlled by the microprocessor that is contained within the cassette load lock reactor 23. Additionally, the oil that is used by the main chamber vacuum pump is re-circulated and filtered by a filter system 65. Figure 3 is a block diagram of a microprocessor control system 10 that is used to control the operation of the cassette load lock reactor 23. In particular, a central processing unit 17, in the embodiment of Figure 1, is manufactured with a 9900 microprocessor that is manufactured by Texas Instruments Incorporated of Dallas, Texas or can be any central processing unit known in the art that has similar specifications as to speed, word length and operation. The central processing unit 17 has an EPROM and RAM memory 19 which stores data and program instructions that are used to control the I/O devices that are connected to data bus 6. A language translator 15 is provided which is used to convert SECS 11 protocol into internal protocol that the CPU 17 will recognize. SECS II is an industry standardized interface for semiconductor equipment communication. The central processing unit or CPU 17 is connected to a data bus 6, which interfaces to the I/O devices. In particular, a battery memory RAM 13 stores menu data that is provided to the processor system 10 of Figure 3 by the keyboard 25 and the display terminal 27. A digital I/O 3 provides digital controls to control the process to include the gate valves and other controllable devices that are contained within the cassette load lock reactor 23 or the power load lock reactor 523 of Figure 26 and receives status from these devices indicating the initiation of operation or the completion of operation. The status and control signals that are used to control the operation of the devices of Figure 1 are listed in Table 1. An analog I/O device 5 provides analog control signals on its output by converting digital commands that are provided to it to analog signals by digital to analog converters. It additionally receives analog signals back from the cassette load lock plasma reactor 23 and the power load lock reactor 523. Table II provides a listing of the signals that are either analog signals converted from digital commands provided to the analog I/O device 5 by the microprocessor 17 or analog signals received by the analog I/O device and converted to digital signals by the converters that are contained within the analog device 5. It should be noted that the analog I/O is just a parallel combination of digital to analog converters or analog to digital converters that are connected to the data bus 6 and the digital I/O 3 is a plurality of line drivers and receivers. Control is provided by the analog controller 7 which is a microprocessor such as a Texas Instruments 9900. Any microprocessor that is capable of meeting similar specifications may be used however, in lieu of the Texas Instruments 9900. The data terminal is controlled by data terminal controller 9 which interfaces the display 27 and the keyboard 25 to the microprocessor 17 as well as displaying the voltage representation that is provided from the RF generator 51 and the analog control unit 7 by a data line 12. The movement of the semiconductor wafers from each cassette into the reactor chambers and from the reactor chambers into the exit chamber is controlled by a slice handler 11 through the operation of stepper motors 4 and responding to sensors 2. The slice handler 11 is a microprocessor which provides digital commands on its output and receives digital inputs from the sensors. The microprocessor is a device such as the TI9900. The program that is used to control the central processor unit 17 is a complex program and in the embodiment of Figure 3 has a pascal compiler. Listings of the microcode and pascal programs used in operation of the apparatus are contained in US-A-4,654,106 as a microfiche appendix. Figure 4,to which reference should now be made,shows a block diagram of the control circuit that is used to control the radio frequency energy that is applied to the load lock reactors 23 and 523. As was indicated in conjunction with Figures 1 and 3, the microprocessor 17 provides an output command to the RF generator 51 by a control line 32. The RF generator 51 includes an RF interface 26 and a generator 28. This is a commercially available unit as manufactured by Plasma Therm Inc. or can be a device such as that manufactured by Ortec Incorporated of Oak Ridge, Tenn. Status of the operation is provided back to the digital I/O 3 by a data bus 34. The RF output is applied from the RF generator 51 and in particular, the generator section 28 of the RF generator 51 to the matching network 53 by a conductor 55. The matching network includes a Bird Watt meter 22, manufactured by Bird Electronics of Columbus, Ohio, which monitors power that is applied to the upper electrode 30 that is contained within the main chamber 37 by an impedance matching circuit 53. The output of the Bird watt meter 22 is applied by an isolation amplifier 24 to the analog to digital converter contained within the analog I/O 5 and to the analog control microprocessor 7. Adjustment of the RF energy that is applied to the cassette load lock reactor 23 and power load lock reactor 523 is provided by the microprocessor 17 of Figure 3. A digital to analog converter that is a part of the analog I/O 5 and an isolation amplifier 20 in the RF interface 26 will cause the RF generator 51 to adjust its energy in response to the analog signal that is applied to it. This of course, provides a feedback loop for the host microprocessor 17 to control the plasma operation according to the prescribed menu that is entered by the keyboard 25. Figure 5 is a block diagram of the control system that is used to detect the endpoint of the operation. In the embodiment shown in Figure 5, there are dual channels used in the endpoint detection process. Quartz windows 58 and 60 provide an optical opening into the main chamber 37. Adjustable filters 62 and 64 can be selected to ensure that only light having the proper wavelength is applied to the endpoint detector 70. There are, as described earlier, two channels, an A channel and a B channel. The A channel has a light detector 54 which is a device such as a photomultiplier or silicon detector. The B channel detector 56,of course,is a similar device. Each channel has an automatic gain control circuit 50 or 52. The gain of the automatic gain control circuits 50 and 52 is controlled by the analog controller 7 and the analog I/O 5. In particular, the output of the automatic gain control circuit 50 for channel A is applied to an analog to digital converter 40 that is contained within the analog I/O 5 and applied to the analog controller 7 where the data is processed and passed on the host microprocessor 17. Adjustment of the automatic gain control circuit 50 is provided by either the host microprocessor 17 and/or the analog controller 7 by providing a digital command to a digital to analog converter 42 that is contained within the analog I/O 5. The digital to analog converter 42 provides an analog signal to adjust the gain on the automatic gain control circuit 50. The output of the channel B automatic gain control circuit 52 is converted to a digital signal by an analog to digital converter 44 that is contained within the analog I/O 5 and is processed by the analog controller 7 for averaging of data to be used by the central processor 17. An output to set the automatic gain control circuit 52 is provided by a digital command provided by the analog controller 7 whether originating from the analog controller 7 or from the CPU 17 and is converted to an analog signal by the digital to analog converter 46 and applied to set the automatic gain control of the channel B automatic gain control circuit 52. Additionally, the display at 27a provides display of the setting up of the automatic gain control circuits 50 and 52. An auxillary display is provided from the analog controller 7 and a digital to analog converter 48. These provide meter displays of the endpoint detector circuit. The operation of the endpoint detector allows the user through the keyboard entry 25 to define parameters which fall into two classes, the detection mode parameters and the detection parameters. The detection mode parameter is selected by the users and provides the following modes of operation. In the No endpoint mode the endpoint detector does not operate. Either channel A or channel B detector outputs can be monitored and applied to a strip chart recorder via the display outputs 27a. Channel A endpoint selects a signal from channel A detector to be used to determine the endpoint. The channel B mode selects the signal to be used as the endpoint detection from channel B. The a-b endpoint detection subtracts the output of B from channel A. In this mode, the signal used for endpoint detection is formed by subtracting the detector B signal 56 from that of the A detector 54. The purpose of this mode is to allow the signal to noise ratio of the combined signals to be increased by removing correlated noise during the subtraction process. The final mode of operation is the a+b mode in which the detector outputs from channel B are added to the detector outputs from channel A. This mode is useful to increase the available amount of total signal for the detection process. Figure 6 provides a flow diagram of the adjusting of the automatic gain control circuits 50 and 52 and the operation of the endpoint detector circuit as is programmed by the analog controller 7. The endpoint detector of Figure 5 is designed to detect the endpoint when the following parameters are set. The window length, T(w) is the time interval during which endpoint signal after signal process must remain greater than its selected threshold value for the endpoint to be determined. The filter factor T(k) determines the time interval used to perform the digital differentiation of the endpoint signal by the microprocessor 7. The +/- threshold V(t). is the percent of voltage of an upper limit, such as eight volts in the embodiment of Figure 5 and is said to correspond to either positive or negative slope endpoint signal. This threshold is selected as a percent of the maximum voltage. The delay to detector time T(d) is in units of seconds as the time interval from the application of RF energy to the main chamber 37 to the start of endpoint detection. For example, entering of a number 40 to the keyboard 25 means that the endpoint detector will not start looking for the endpoint until after 40 seconds has expired after the RF energy is applied to the main chamber 37 by the RF generator 51. Figure 6 is a flow diagram of the process in which the microprocessor 7 is used to perform all the signal processing for the endpoint detectors. After the initialization of turning on RF energy at circle 100, the unit waits for the delay to detect time to expire at diamond 101. The adjustments of the AGC units 50 and 52 is performed at block 102 and in the embodiment of Figure 5, the AGC is adjusted to provide an output of five volts. The AGC is then sampled and in the embodiment of Figure 5, the sample rate is every one-tenth second. This is illustrated by the control loop at 103 and includes the steps of reading the signal level at block 105, converting the signal level to a digital signal by the analog digital converter 40 or 44 at block 106 computing the average signal over a period of time at block 107, computing the difference using the filter factor at block 108 and comparing to see if the difference or sum, i.e., a-b, a+b,or either a or b, is greater than or equal to the threshold voltage at block 109. This loop continues until, as detected by the block 109, the difference is greater than or equal to the voltage threshold, in which case the rendered length is incremented to ensure that the window length has expired as indicated by control loop 110. If the window length has expired, then an endpoint detection is indicated at block 111 and the operation is complete and exited from at circle 112. It should be noted that in performance of the AGC operation, the analog controller 7 reads a data word, interprets it as a voltage, and compares it with a reference such as 5 volts. It then computes a gain adjustment word and sends it to the digital to analog converter, either 42 or 46, which converts a digital word into a voltage level. This voltage is applied to the automatic gain control circuit, either channel A AGC 50 or channel B AGC 52, of the circuit which acts as a multiplier. In this matter, the gain is adjusted by successive approximations until the output of either or both of the channel A AGC 50 and the channel B AGC 52 is at a predetermined voltage level,which in the embodiment of Figure 5 is five volts. Figure 7 illustrates the operation of the control loop of Figure 6 graphically. In particular, Figure 7a is a curve that illustrates the signal level output from either the A detector 54 or the B detector 56 by waveform 114. In Figure 7b, waveform 116 illustrates the output from the analog controller 7 as is displayed on the auxiliary 1 output of the display 27 A in which at point 118 the RF power is turned on. The window T(w) is represented by dimension lines 115. At point 119, the threshold voltage V(t) is exceeded and the endpoint is detected. When an endpoint is detected, a square wave output as illustrated by waveform 116 is produced. GAS AND VACUUM CONTROL SYSTEM The vacuum and gas control system for the cassette load lock plasma reactor 23 is illustrated in Figure 8 to which reference should now be made. The gas from the gas distribution 43 of Figure 1 is applied to a manifold 750 by mass flow controller 721 through 724. The mass flow controllers are controlled by the analog inputs from the control system 10 and additionally valves 710 through 713 are controlled by the status I/O 3 of the control system 10 and are on/off valves. The gases are mixed in the manifold 750 and applied to the main chamber 37 where the temperature of the reaction within the main chamber is monitored by a thermocouple 751. The thermocouple 751 feeds an analog input to the analog I/O 5 of the control system 10. A vacuum pump 31 pulls a vacuum in the main chamber 37 when the block valve 709 is open. The flow rate is controlled by a throttle valve 708 the position of which is fed into the analog input and is set by the output from the analog input of the control system 10. Sensor 2 senses the position of the silicon wafer within the main chamber 37. The vacuum of the entry load lock 21 and the exit load lock 49 is provided by pump 29 as was discussed in conjunction with Figure 1. Gate valves 705 and 707 are set open and the pump rates are controlled by throttle valves 704 and 706. The gate valves are interfaced in the control system 10 at the digital I/O 3 and the throttle valves 704 and 706 are controlled by the analog I/O card 5. Additionally, the positioning of the semiconductor wafers within the entry load lock 21 and the exit load lock 49 is provided by the sensor 2 and motors 4. Figure 9 to which reference should now be made shows the gas and vacuum flow diagram for the power load lock 523. The difference between the power load lock 523 and the cassette load lock 23 is due to the fact that the entry load lock can have a plasma reaction as well as the exit load lock 49. In this case there are 2 vacuum pumps required, 29A and 29B. The entry load lock has a gas manifold 760 which mixes three gases from three mass flow control valves 725 through 727 which are controlled by the analog inputs and outputs from the control system 10 and are activated by setting of gate valves 714, 715, 716. The exit load lock 49 can have a plasma reaction based upon the mixture of up to three gases in a manifold 761 that are controlled by mass control valve 728, 729 and 730. The on/off operation of the gas flow into the manifold 761 is provided by the digital I/O 3 of the control system and controls the valves 717, 718, 719 as is the case with the gas valves into the entry load lock 21. In Figure 10, to which reference should now be made, there is shown a front view of the cassette load lock reactor 23 in which the keyboard 25 provides, as discussed earlier, a data entry point, the information of which is displayed on a display 27. Figure 10 also illustrates a quartz window covered with plexiglass or other plastic 120 for viewing by the operator of the plasma reaction that is going on within the main chamber 37. This also enables the operator to ensure that the semiconductor wafer is in the proper position between the electrodes during the reaction process. Additionally, the tuning of the RF generator 51 is illustrated by tuning meter 123 and the DC voltage that develops across electrodes is displayed by the DC voltage meter 122. In Figure 3 that is provided by the analog control 7 to the terminal controller 9 via data line 12. Figure 11 is a top view of the cassette lock load plasma reactor 23 in which the keyboard 25 is illustrated showing switches 133, and keypads 135. The cassette that contains the semiconductor wafers to be processed is placed within the entrance load lock 21 by lifting a vacuum tight lid 137 and rotating it around hinges 124 to place the cassette into the entrance chamber 21. Glass window 128 provides for visual inspection of the placement and the transfer of the semiconductor wafers from the entrance load lock 21 to the main chamber 37. Similarly, at the completion of the processing of a cassette of semiconductor wafers, the lid 139 of the exit load lock 49 is lifted by rotating the lid 139 around the hinges 126 for removal of a cassette of processed semiconductor wafers. SEMICONDUCTOR WAFER HANDLING INCLUDING TRANSPORT ARM Figure 12, to which reference should now be made, shows a cassette 141 containing a plurality of semiconductor wafers or slices 143. A slice transport arm 145 is placed into the cassette 141 and the cassette 141 is lowered by an elevator 156 that includes lead screw 152, stepping motor 4, and sensor 2, until the semiconductor wafer 143 rests on the slice transport arm 145 in the middle of the slice opening 147. Because the slice is not touching any part of the cassette as it leaves during the rotation of the slice transport arm, there is no friction between the semiconductor wafer 143 and the slice handling arm 145. This feature minimizes particulate generation as the slice leaves the cassette 141. The position of the slice transport arm 145, the cassette 141 are controlled by the slice handler 11 of Figure 3 and the motors 4 and sensors 2. The cassette platform 154 provides a reference position for the cassette 141 and thus the exit position of the cassette can be determined by the sensor 2 and the precise control of the elevator 156. After the semiconductor wafer leaves the input cassette 141, it may be placed over a primary staging platform 149 or on the reactor substrate as is illustrated in Figure 13. The semiconductor wafer 143 is lowered to the staging platform 149 by a lifting assembly 150 which provide a plurality of lift pins 153 that lift the semiconductor wafer 143 off of the slice transport arm 145. The unloaded arm is then removed from under the semiconductor wafer 143. When the unloaded slice transfer arm 145 is clear, the semiconductor wafer 143 is lowered onto the staging platform 149 which centers the semiconductor wafer 143 through the action of the centering pins 155. When the entrance slice handling arm 145 is moved under the platform 149, the slice after being raised by the pins 153 is lowered onto the slice transport arm 145 as the pins 153 are retracted. When the main chamber 37 is ready to accept a semiconductor wafer 143, the entry load lock slice transport arm 145 moves into the main process chamber 37 through the gate valve 35 (Figure 2). The semiconductor wafer 143 is then lifted off the slice transport arm 145 and the slice transport arm is then removed from the main process chamber. The semiconductor wafer 143 is then lowered onto the substrate within the main process chamber for processing The semiconductor wafer 143 is removed from the main process chamber to the output chamber 49 by reversing the above described sequences and using the output chamber slice transport arm. Figures 14 through 17 illustrates the slice transport arm 145 as is used on the entrance chamber transport arm 41 or the exit chamber transport arm 57. A fork 151 is designed with touch pads 158 for balancing of the semiconductor wafers 143 thereon. The fork is rotatable around shaft 157 which is adjustable through the setting of set screws 159. A main arm 161 rotates around shaft 163 and is driven by a stepping motor 4 as shown in Figure 17 which is coupled to the slice transport arm 145 via coupling means 165 and feed through 180 which forms a vacuum tight seal with load lock walls 181. The wafer transport arm is mounted to the chamber by mounting bracket 164 and through holes 166 and 167. The arm assembly 161 contains a sealed chain drive mechanism which is driven by a chain 172 of Figure 16 which rotates causing sprocket 174 to rotate the fork 151 after being driven by sprocket 176 which is connected to the shaft 163 and coupling 165 of Figure 15. As illustrated in Figure 15, the slice transport arm is very narrow to facilitate it sliding under the semiconductor wafers 143 and entering the gate port between the load locks and reaction chamber. GATE VALVES Figure 18 is a side-view showing the entrance or the exit into the main chamber 37. A gate port 184 allows the slice transport arms 145 to transfer semiconductor wafers 143 into and out of the reactor chamber 37. Gate valves 35 and 61 which are identical devices are shown in Figures 19 and 20 and each includes a gate plate 183 which presses against the sides 182 of the main chamber 37 to provide a seal thereto. It is important to keep particulate emissions at a minimum and this is achieved through a camming action on the gate valves. Guide rails 192 and 194 guide the gate valves 35 and 61 up to the gate plate 183 until they contact with stops 187 and 186. At this point, the camming action that is precipitated by the linkage 190 that includes a first arm 191 and second arm 193 going into place and locking as shown in Figure 20 pressing the gate plate 183 against the gate stop 186 and 187 and transferring the gate carrier 189 into the up position. A spring bias provided by spring 195 holds the gate carrier 189 in the position shown in Figure 19 until the bias provided by the spring 195 is overcome by the camming action through the rotation of the arms 191 and 193 via the rotation of a drive shaft 197 that is controlled by an air cylinder. Figures 26 to 28, to which reference should now be made, illustrate a power load locks plasma reactor unit 523 in which a cassette 141 contains a plurality of slices and is housed outside of the entry load lock 21. A process menu is entered into the microprocessor that is contained within the power load locks plasma reactor and the process sequence begins. A single slice that is housed within the entry cassette 141 is moved from the entry cassette 141 through the isolation gates 435 which are devices such as that disclosed in conjunction with figures 19 and 20 and is carried to the power entry load lock with articulated arm 441. The power load lock 21 is pumped down to the desired pressure through a throttle pressure controller and the pre-etch process is begun within the entry load lock 21. The first semiconductor wafer at the completion of the pre-etch process is moved from the entry load lock 21 through a second isolation gate 35 into the main chamber 37 and placed on a main chamber bottom electrode for etching. This is accomplished in the same manner as was discussed in conjunction with Figures 1-18. Feedback of the slice movement is accomplished by capacitive sensors in the load lock chambers and main chamber. After the semiconductor is sensed to be safe in the main chamber and the articulated arm is sensed to have been moved back from the main chamber into the entry load lock 21, the isolation gates are closed and the appropriate gases,up to 4, are provided from the gas distribution 43. It should be noted that the gas distribution also provides up to 3 gases to the entry load lock 21 for the pre-etch reaction and up to 3 gases to the exit load lock 49 for post-etching,and of course all of these are in addition to the purge gas,which in the embodiments of Figures 1 and 26 to 28 is nitrogen. As prescribed by the menu that has been entered by the keyboard 25, pressure stabilized by a throttle valve capacitor manometer feedback to the microprocessor, RF power is activated and applied from the RF generator 51 and automatically tuned by the RF matching network as was discussed in conjunction with Figure 4, with control feedback from the reflected power to the microprocessor 7. Etching of the film is automatically terminated by the microprocessor 7 via the feedback from the endpoint detector,as was discussed in conjunction with Figure 6, seeing a major change in the optical emission at a given wavelength. Of course, multiple menus can be run on the same slice by appropriate selection during menu entry. At the completion of the process, the semiconductor wafer is automatically removed from the main chamber 37 by an articulated arm 57 in the exit load lock 49 and placed in the exit load lock for the post-etching process. After processing in the post-etching load lock, the semiconductor wafer is moved to the exit elevator cassette 401 by articulated arm 541. Additionally, cooling is provided to the main chamber as well as the post chamber and the entry chamber via temperature controller 63. Viewing windows 461, 462 allow viewing of the post-etch and pre-etch operation respectively. Figures 29, 30 and 33 are mechanical illustrations of the articulated arm 441 and 541 in which each has a fork 551. The articulated arms are mounted on the power load lock assembly by pedestal 553 and include a central arm section 161 which rotates around shaft 163 as was discussed in conjunction with Figures 14 to 17, ELECTRODE AND COLLIMATOR ASSEMBLY Figure 21 is a sectional view of the main chamber 37 as seen from section lines XXI of Figure 18. Initial input of the semiconductor wafer 143 is through the opening 184 onto a substrate or wafer plate 206. The wafer plate is in position to allow clearance for the semiconductor wafer 143 and the fork 151 to position the semiconductor wafer over the wafer plate 206. Pins 153 will lift the semiconductor wafer off of the fork 151 and after its removal, lower the semiconductor wafer onto the substrate or wafer plate 206. The embodiment shown in Figure 25 provides a two position substrate. It is generally accepted that during processing in the power load lock the substrate should be at different positions for different modes of operation, such as 1 mm (0.040 inch) for oxide processing.In the case of the cassette load lock, the substrate position is varied only for oxide processing, in all other etching modes the substrate is stationary. To achieve this, the wafer plate 206 has two positions, a low position, and a process position. In the embodiment of Figure 25, two stainless steel bellows an inner bellows 220 and an outer bellows 221 form a chamber between the bellows at 224. By introducing compressed air into lines 211, pressure is built up in the chamber between the bellows and this causes the movement of the substrate 206 to be implemented. Under initial operation, air is introduced into an air cylinder, not shown, which raises the pins 153 for removal of the semiconductor wafer 143 from the fork 151. The centering pins 155 are raised by introducing air into air cylinder, not shown, which brings the guides 155 into position to center the semiconductor wafer 143 onto the wafer plate 206. The wafer plate 206 is in position for the process which is defined by the opening as indicated by dimension lines 228 between the cathode 230 and the substrate or top of the wafer plate 206. A consistent process gap between the cathode 230 and the substrate 206 is maintained during processing. A consistent opening for movement of the semiconductor wafer 143 between the collimater 430 and the substrates 206 is also maintained during slice movement. A constant low pressure 133.3 Pa (1 TORR) is maintained in the main chamber 37 during slice handling, this eliminates the slice contamination caused by lifting of the main chamber to the atmospheric pressure and facilitates the use of the slice transport arm 441, 541. Line 212 (Figure 21) is connected to the gas distribution 43 via filters 45 (Figure 1) and provides for the entrance of gas to be processed in between the cathode 230 and the substrate 206. Lines 210 allow for cooling of the process reaction by the temperature controller 63 controlling coolant flow through channels 232 and 242 to cool the semiconductor wafer 143 when placed on the wafer plate 206. Ring 205 is an isolation substrate ring that is isolated from the substrate 206 via isolation assembly 207. The ring consists of the body of the ring itself, 205, a retractible slice centering lip 209, isolation mechanism 207 which is made of a metal but with small thermal contact or with an insulator such as teflon which more completely isolates the ring 205 thermally and electrically with a possible ring extension shown at 231. The ring extension 231 is of course to increase the surface area of the top of the ring which increases the area of the overlap between the ring and the collimator itself in the electrode assembly 240. This extension has been found to improve the effectiveness of the collimator in eliminating plasma expansion beyond the outside ring. The ring 205 is used to provide isolation and to aid in the control of plasma discharge which occurs during the reactor process between the cathode 230 and the substrate 206. The electrode assembly includes an electrode or cathode 230 to which RF voltage is applied via attachment to the plate 250. The electrode or cathode 230 is surrounded by a coillmator 430, which includes insulator 251, which is in turn surrounded by a grounded plate 252, all of which have a cylindrical symmetry about an axis through the center of the electrode as indicated by line 256. When placed a small distance above a flat grounded substrate 206, the electrode assembly creates a volume as indicated by dimension lines 228 which can effectively confine a high power density plasma, while maintaining a sufficient channel for flowing gas through the lines 212 in the direction as indicated by arrows 258 and for observing the plasma optically through the window 120. As discussed earlier, the chamber can be widened for automatic transport of the semiconductor wafers from outside of the main chamber 37. By having a confined high power density plasma, high rate uniform anisotropic etching, especially for silicon dioxide and silicon nitrides, can be achieved. The ring 208 has an annulus of a width equal to the distance between the placement pins 155 and lip 209, which is an area which is generally exposed to plasma due to the fact that most semiconductor wafers have a flat portion that is used for alignment. The reacting plasma will attack the semiconductor wafer plate 206 or substrate and cause damage . In Figure 22, anodizing an area 208 around the substrate 206, an area in width as indicated by dimension lines 270, will prevent etching of the substrate 206 when , as shown in Figure 21, a semiconductor wafer 143 is placed on the substrate 206. In general, the substrate 206 is manufactured of aluminum which is highly corrodible if not protected by anodization. The cathode assembly 230 of Figure 21 is shown in Figures 23 and 24 and includes a top plate 269 and a bottom plate 268. The top plate 269 has a gas inlet 305 to allow the cooling gas to enter via from line 212 and a water cooled line which removes heat from the plate 268. Recessed gas flow channels are provided at 307 and areas 306 provide for thermal contact between the bottom plate 268 and the top plate 269. The top plate 269 is illustrated in Figure 23 and the bottom plate 268 is illustrated in Figure 24. The thermal contact area must be maximized without restricting the gas flow. This is illustrated in the bottom plate where there are many drilled holes in area 301 and the lines in 302 allow for gas flow channels for the bottom plate 268. Figure 25 is alternate embodiment in which the substrate 206 has dual positions. The alignment pins 155 and lift off pins 153 are controlled by lifting of the carriage assembly 312 which is guided into place by wheels 316. The carriage assembly 312 is lifted by the levers 311 being raised by compressed air applied to a cylinder contained within a housing 313. The positioning of the substrate 206 is accomplished by feeding air in between an inner bellows 220 and an outer bellows 221 into a chamber 224 at air ducts 211 which causes the wafer plate 206 to be raised or lowered depending upon the air pressure that is contained within the air chamber 224. Insert E - Powered Load Lock Reaction Figure 31 through 34 illustrate the load lock chambers which provide for pre-etch processing in the entry load lock through a plasma assisted reaction, and post-etch processing in the exit load lock through a plasma assisted reaction. In Figures 31 and 32 the gas from the gas distribution manifold 760 is applied by line 781. The feedthrough 886 as shown in Figure 32 provides for movement of tubing 781 to provide for adjustable spacing of the electrode assembly 987 to control the volume of reactant area 988. This is illustrated in Figure 32. In addition to the tubing 781, the electrode assembly 987 includes feedthrough 886 and O ring seals 981 and includes a gas distribution assembly 889, and a retainer 888 that holds the electrode 890 onto the gas distribution assembly 889. The retainer 888 also seals the electrode assembly 987 to the walls of the collimator 891, which is made of insulating material . The gas is distributed through the electrode 890 by means of plurality of distribution holes 991. The slice handling mechanism which is shown at 882 has a fork 873 which lifts a slice from outside of the load lock chamber and centers it on ring 876 and then rotates around axis 877 to position the slice over the bottom electrode 875. The spacing 871 and 872 is 3 mm (1/8th of an inch) so as to minimize its effect on the plasma that is contained within volume 988. The slice handler 441 was discussed in conjunction with Figures 29 and 31. The substrate 875 has cooling channels 874 to facilitate the cooling of its semiconductor slice that is mounted to the substrate during its reaction. Function 870 is designed and positioned so as to ensure that the gaps 871 and 872 are minimum. Figure 34 illustrates the bottom electrode in which the reactant gases are removed from via line 896 which goes to vacuum pumps 29a or 29b and includes a mechanical housing 885 and a bellows chamber 884. Within the bellows chamber 884 is a bellows assembly 878 which moves the bottom substrate 875 by the operation of an air cylinder pressing shaft 978 to an upper or a lower position. The compressing of the bellows 878 positions the substrate 875 to ensure the proper reaction as was discussed in conjunction with the main chamber.

Claims: Apparatus for processing semiconductor wafers having a main plasma chamber (37) containing main support means (149) for supporting a wafer to be processed, with means (45) for feeding reacting gases to the chamber and means (51, 53) for generating a plasma in the chamber to process the wafer, an entry load lock (21) having means enabling it to be evacuated, being coupled to the main plasma chamber through an entry port, and including first elevator means (156) supporting first cassette means (141) having a plurality of slice openings (147) for holding a wafer, first wafer transporting means having first wafer support means effective to transport wafers from the first cassette means to the main plasma chamber, and an exit load lock (49) having means enabling it to be evacuated, being coupled to the main plasma chamber through an exit port, and including second elevator means (156) supporting second cassette means (141) having a plurality of slice openings (147) for holding a wafer, second wafer transporting means having second wafer support means effective to transport wafers from the main plasma chamber to the second cassette means, the main plasma chamber including means (150) for transferring wafers between the first wafer transporting means and the main wafer support means and the main wafer support means and the second wafer transporting means, control means (10) for operating the components of the apparatus so that wafers are passed from the first cassette means in the entry load lock to the second cassette means in the exit load lock through the main plasma chamber and undergo a particular process when in the main plasma chamber, CHARACTERISED IN THAT the first transporting means comprises a first slice transport (145) arm that rotates about a vertical axis to convey a wafer between the first cassette means and the main plasma chamber, and that the first elevator means is operated when the first slice transport arm is in the first cassette means to lower the first cassette means so as to transfer a wafer from the first cassette means to the first slice transport arm and the second transporting means comprises a second slice transport (145) arm that rotates about a vertical axis to convey a wafer between the second cassette means and the main plasma chamber, and that the second elevator means is operated when the second slice transport arm is in the second cassette means to raise the second cassette means so as to transfer a wafer from the second slice transport arm to the second cassette means. Apparatus according to claim 1, characterised in that the wafer transferring means (150) includes a plurality of retractable pins (153) which can project through a support plate (206) forming part of the main wafer support means and are operated to lift off a wafer from a slice transport arm and lower it on to the support plate for processing, and lift off a wafer from the support plate and lower it on to a slice transport arm after processing. Apparatus according to claim 2, characterised in that the main wafer support means further includes a second set of retractable pins (155) for aligning a wafer on the support plate. Apparatus according to claim 2 or 3, characterised in that means (211, 220,221) are provided for enabling the support plate to be raised and lowered to alter the distance between a wafer to be processed and a radio-frequency electrode. Apparatus according to any preceding claim characterised in that the slice transport arm (145) comprises a main arm (161) which rotates about a fixed axis (163) and a fork (151) for carrying a wafer and which is pivotable about an axis (157) at the free end of the main arm. Apparatus according to claim 5 characterised in that the fork (151) is provided with three pads (158) for supporting a wafer.

Inventors: BROWN, FREDERICK W., DAVIS, CECIL J., JOHNSON, RANDALL E., JUCHA, RHETT B., KOHAN, STANFORD P., SPENCER, JOHN E.
Applicants: TEXAS INSTRUMENTS INCORPORATED
Application year: 1985
Main classification: H01J37
IPC codes: H01J37