Hydrogen cylinder change with gas manifold already purged . Nitrogen cylinder replacement with purge . Removing and replacing source bubbler .
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MOCVD Manual v1.01 2 Overview of System Operation and Features . 9Table of Contents Operational features . 9 Sources 9 Carrier gases . 9 Input gas control . 9 Gas delivery plumbing . 9 Reactor chamber 9 Exhaust gas control . 10 Operating controls .. 10 Safety features 10 Valve switching fe atures assuring safe operation .. 10 Vacuum system operational features 11 Interlock system .. 11 Control panel design criteria .. 11 Gas system criteria .. 12 Computer interface . 13 Emergency Procedures 15 Background .. 15 Action to be taken 16 Level of gas b elow TLV .. 16 Level of gas above TLV .. 16 Visible flame in Toxic Gas Cabinet .. 17 Brief summary of emergency procedures 17 Interlock System . 18 Alarm Inputs 18 Interlock Structure 19 ABORT Status . 19 A-Level Status 19 B-Level Status 19 C-Level Status 20 D-Level Status 20 Hydrogen/Nitrogen .. 21 Gas Distributi on . 21
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3 MOCVD Manual v1.01 Hazards .. 21 Precautions .. 21 Normal Operation . 22 Start of day . 22 End of day 22 Interconnections 23 Interlocks .. 23 Hydrogen purification system 23 Hydrogen purifier start -up procedure .. 23 Hydrogen purifier shut -down procedure 24 Hydrogen purifier idling procedure 25 Return from idle procedure 25 Hydrog en cylinder replacement 25 Hydrogen cylinder change with gas manifold already purged . 26 Initial connection of hydrogen cylinders. 27 Purging the hydrogen gas manifold 27 Nitrogen purification system .. 27 Purging the nitrogen purification system 28 Nitrogen cylinder replacem ent .. 28 Nitrogen cylinder replacement without purge . 28 Nitrogen cylinder replacement with purge 28 Trimethylaluminum (TMA) 29 Gas Distribution . 29 Hazards .. 29 Precautions .. 29 Normal Operation . 29 Start -of-day: 29 End of day: .. 30 Interconnections 30 Interlocks .. 30 Programming commands f or remote operation .. 31 Removing and replacing source bubbler .. 31 Bubbler removal .. 31 Bubbler installation . 32
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MOCVD Manual v1.01 4 Trimethylind ium (TMln) .. 34 Gas Distribution . 34 Hazards .. 34 Precautions .. 34 Normal Operation . 34 Interconnections 35 Interlocks .. 35 Programming commands for remote operation .. 36 Removing and replacing source bubbler .. 36 Bubbler removal .. 36 Bubb ler installation . 37 Tertiarybutylarsine (TBAs) . 39 Gas Distribution . 39 Hazards .. 39 Precautions .. 39 Normal Operation . 40 Interconnections 40 Interlocks .. 41 Programming commands for remote operation .. 41 Removing and replacing source bubbler .. 41 Bubbler removal .. 41 Bubbler installation . 42 Tertiarybuty lphosphine (TBP) .. 44 Gas Distribution . 44 Hazards .. 44 Precautions .. 44 Normal Operation . 45 Interconnections 45 Interlocks .. 46 Programming commands for remote operation .. 46 Removing and replacing source bubbler .. 46 Bubbler removal .. 46 Bubb ler installation . 47 Iron carbonyl (FE) .. 49
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5 MOCVD Manual v1.01 Gas Distribution . 49 Hazards .. 49 Precautions .. 49 Normal Operation . 49 Operation without additional hydrogen dilution: .. 50 Operation with hydrogen dilution: . 50 Interconnections 52 Interlocks .. 52 Programming commands for remote operation .. 53 Removing and replacing source bubbler .. 53 Bubbler removal .. 53 Bubbler installa tion . 54 TriMethylGallium (TMGa) .. 55 Gas Distribution . 55 Hazards .. 55 Precautions .. 55 Normal Operation . 55 Operation without additional hydrogen dilution: .. 56 Operation with hydrogen dilution: . 56 Interconnections 58 Interlocks .. 58 Programming commands for remote operatio n .. 59 Removing and replacing source bubbler .. 59 Bubbler removal .. 59 Bubbler installa tion . 60 Arsine (AsH 3) . 61 Gas Distribution . 61 Hazards .. 61 Precautions .. 61 Normal Operation . 62 Start of day . 62 End of day 62 Interconnections 62 Interlocks .. 62
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MOCVD Manual v1.01 6 Programming commands for remote operation .. 63 Purging of AsH 3 Lines .. 63 Regulator and low -pressure delivery lines . 63 Cylinder Replacement 63 Phosphine (PH3) . 65 Gas Distribution . 65 Hazards .. 65 Precautions .. 65 Normal Operation . 66 Start of day . 66 End of day 66 Interconnections 66 Interlocks .. 67 Programming commands for remote operation .. 67 Purging of PH3 Lines 67 Regulator and low -pressure delivery lines . 67 Cylinder Replacement 68 N-Dopant 69 Gas Distribution . 69 Hazards .. 69 Precautions .. 70 Normal Operation . 71 Start -of-day: 71 Operation of bubbler source without additional hydrogen dilution: 71 Operation of bubbler source with additional hydrogen dilution: .. 72 Operation of gaseous source without additional hydrogen dilution: .. 73 Operation of gaseous source with additional hydrogen dilution: .. 74 End of day: .. 75 Interconnections 75 Interlocks .. 75 Programming commands for remote operation .. 76 Removing and replacing source bubbler .. 76 Bubbler removal .. 76 Bubbler installation . 77
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9 MOCVD Manual v1.01 A MetalOrganic Chemical Vapor Deposition (MOCVD) system has been constructed at SDS M&T for the growth of epitaxial layers of semiconducting compounds formed from elements in groups III and group V of the periodic table. The alloys which can be grown include those containing indium, aluminum, gallium, arsenic and phosphorus. The potential exists for the grown layers to be doped with impurities to form either n -type or p -type layers. The system is housed in Room 240 of the Electrical Engineering/Physics Building. Overview of System Operation and Features Sources Operational features 1. The group V sources are provided in the form of gases by the hydrides AsH 3 and PH 3. Quantities are limited to 0.21 cu. ft. cylinders to reduce the consequences of a catastrophic release of the contents. These sources may also be provided by alkyl bubblers of Te rtiary Butyl Arsine (TBAs) or TertiaryButylPhosphine (TBP) 2. Group III sources are provided by alkyl bubblers of E thyl DiMethyl Indium (EDMln), Tri MethylG allium ( TMGa a), and Tri Tethy Aluminum (TMA). 3. N-dopants can be provided either by silane diluted to 10 percent in hydrogen or by a Terta Ethyl Tin 4. (TESn) bubbler. 5. P-dopants can be provided either by DiMethyl Zinc (DMZ) diluted to 0.1 percent in hydrogen or by a carbon tetrachloride bubbler. 6. The dopant for growing semi -insulating material is iron provided by a ferrocene bubbler. Carrier gases 1. Hydrogen from a palladium purifier is used as the carrier for all the alkyl sources and as the primary diluent for the reactor gases. 2. Nitrogen purified by a Nanochem purifier is used as an alternative diluent and purge gas for displacement of hydrogen in the reactor. Input gas control 1. Gas flows are controlled by precision Mass Flow Controllers from Vacuum General. 2. Gas valving is with Nupro BNV series, low -dead space bellows valves. No rmally closed valves provide fail -safe operation. 3. Ven t/run valving to the chamber is performed with a Thomas Swann ten -port, low -dead -space manifold. 4. The vapor pressure of the alkyl sources is controlled by constant temperature Lauda/Brinkman cooling baths . Gas delivery plumbing 1. All -welded, electropolished, pre -cleaned, semiconductor grade stainless steel tubing is used in the gas system. 2. All tubing connections are with Nupro VCR metal gasket fittings. 3. Some Nupro bellows valves have been modified by adding ports to eliminate dead space in critical gas lines. Low dead -space tee connections are within the valve bodies. Reactor chamber 1. The circular cross section reaction chamber is part of a vertical flow system in which gases enter from the top and impinge on a horizontal substrate supported on a graphite susceptor which is heated by inductive coupling from an RF magnetic field.
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MOCVD Manual v1.01 10 2. A high velocity air stream flows over the walls of the quartz upper deposition chamber to keep the walls cool and prevent deposition o n the quartz. The lower portion of the chamber which is constructed of stainless steel is water cooled. 3. The system is operated at pressures in the range 7.6 -76.0 Torr . Exhaust gas control 1. The chamber exhaust passes through a Vacuum General AdapTorr pressu re controlling valve before it enters the vacuum pump. This allows constant chamber pressure to be maintained regardless of the gas flow rate. 2. The source gas vent lines are connected downstream of the chamber at the inlet to the pressure control valve to provide the same pressure on both the “vent” and “run” gas routes. 3. A particle filter on the pump inlet and a recirculating oil filter system on the pump are used to remove solid and corrosive contaminan ts fro m the exhaust gas to promote long pump life. 4. Con tinuous nitrogen gas -ballast through the pump is used to control condensation of condensable vapors and to scrub dissolved toxic vap ors from the pum p oil between runs. 5. Exhaust ga s from the pump is scrubbed by a charcoal filter to remove arsine and phosphin e vapors before the exhaust is vented to air. Operating controls 1. The reactor can be operated by manual controls on the reactor panel. All valving is done with switches, and the gas flow of the individual gas source is digitally displayed. 2. Alternatively , the reactor can be computer operated. Interfacing of the valve and flow controllers is provided via a Hewlett Packard Multiprogrammer controlled by a PC running LabView. 1. Normally closed bellows valves a re used for fail -safe protection from toxic gases. Safety features 2. Pneumatic valve operation assures positive, leak -tight shut -off. 3. All -welded stainless steel plumbing with Nupro VCR compression gasket fittings meets requirements for hazardous production gases. 4. A ventilated reactor cabinet with separate secti ons for the chamber, toxic gases, gas control , and the electronics contains all of the hazardous gas components. 5. Flow reducing orifices are used on all the gas cylinders. 6. The reactor will shut down for: a. Failure of cabinet exhaust. b. Detection of PH3 or AsH 3 leaks. c. Detection of hydrogen leaks. d. Loss of pneumatic valve air pressure. e. Low hydrogen pressure. f. Low nitrogen pressure. g. Power failure. h. Loss of chamber vacuum. Valve switching features assuring safe operation 1. Computer operation of the valves is set individually for each valve; only those switched to remote operation can be computer activated.
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11 MOCVD Manual v1.01 2. All interlocking of valves to assure that certain combinations do not occur, or conversely that certain combinations occur together, is hard -wired and not depen dent on operator performance or soft ware . The interlocking operates the sam e for both m anual and computer operation. 3. The interlock system , when in abort status , removes power from the solenoid valves to return them to their normally closed position. The ab ort mode overrides all valve settings under either manual or computer control for fail -safe shut down of the gas flows. 4. The system abort mode applies a va lve close signal to the mass flow controllers and sounds an audio alarm. Vacuum system operational features 1. The reactor exhaust system is vacuum tight. 2. The vacuum pump is sealed from the atmosphere to contain all process gases. 3. Nitrogen gas us used to provide ballast to the vacuum pump. This helps to purge the pump of gases trapped in the pump oil. 4. A so lenoid valve introduces nitrogen only when the pump is on (this prevents pressurizing the pump case and forcing oil up the inlet). 5. The gas ballast flow is controlled by a manual metering valve and measured with a rotameter to limit the flow and provide the pressure drop from the 15 psi delivery pressure to the pump case. 6. The pump exhaust lines are gas tight to prevent leakage of toxic gas. 7. Continuous gas flow (from the combined gas ballast and the inlet flow) keep air out of the pump case and the exhaust li nes to prevent explosive mixtures of H2 and air . 8. Loss of N2 supply pressure is interlocked to close the valve on the gas ballast input to the vacuum pump. 9. Catastrophic loss of vacuum during reactor operation closes vacuum exhaust valve EXPV2 to the pump in let to prevent pumping of air. 10. Loss of vacuum during reactor operation puts the interlock system in abort mode which terminates all gas flows. Interlock system The system is shut down and latched -off if any of the conditions listed below arise. 1. Power failu re (system power must be reset to operate any sources; only N2 flow can turn on when power is resumed). 2. AsH 3/PH 3 monitor alarm (set to monitor for the TLV level in both the gas cabinet exhaust and in the adjacent lab space). 3. H2 at 20% of the explosive limi t alarm. 4. Exhaust ventilation failure alarm. 5. Low H2 supply pressure alarm. 6. Low N2 supply pressure alarm. 7. Low of vacuum in chamber alarm. 8. Loss of pneumatic valve air supply pressure. 9. Emergency stop button activated. 1. Controls for each source input are organized in individual blocks on the reactor front panel. During manual operation, the operator’s attention is thus focused on one block at a time minimizing the possibility of error. Control panel design criteria 2. The control layout for each source is in a left -to right sequence according to a normal sequence of operating steps. This keeps the operator aware of the gas circuit function.
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