Photolithography Machine Control System RIT Computer Engineering Senior Design Project Ben ConradFebruary 13, 2004Mark Edwards User Interface Seven Executable Commands –DEV#1: Dispense developer solution –PREWET: Dispense de-ionized(DI) water –RINSE: Dispenses DI water to clean wafer –N2: Dispenses Stream of Nitrogen (N 2 ) –SPIN: Spin Dry the wafer –WAIT: Static delay option. –END PGM: End the program Parameters –Time:.1 – sec. (.1 second resolution) –Speed: 0-7,999 RPM How It Works The Solitec Model 8360 spin casting and temperature controlled positive develop bake system is used in the photolithography process of making microelectronic circuits on silicon wafers. It automates the process of applying photoresist and baking a wafer, and is fully programmable through user input. This is accomplished through a keypad and LCD display. The user enters a series of operations with parameters on the keypad, thus forming recipes for the processing of particular sets of wafers. The main modules visible to the user are the digital display and input keypad, the input wafer cartridge, the chemical application spin chuck, the bake chuck, and the output wafer cartridge. How We Did It Parts Used in System I/O Circuit (1) HCS12 Microcontroller (4) 74F675A 16-bit Serial In, Parallel Out Shift Registers (2) 74F bit Parallel In, Serial Out Shift Registers (2) LM741 Operational Amplifiers (2) DAC bit Digital to Analog Converters Design Goals Meet customer requirements – system able to hold 10 recipes for wafer processing, control wafer speed from RPM, timing accurate to 0.1 seconds. Allow use on coat and develop tracks – provide recipes general enough for controller to function on either machine Save RIT money – our total cost is $500 compared to $25,000 from industry – 98% savings Future Expandability -Software handles extra sensors which may be added later - System I/O hardware provides twice the I/O needed allowing expansion to machine with more processing stations Solitec 8360 in RITs Fab Spin Chuck Vacuum Tube Bake Chuck Vacuum Tube Wafer Output Cartridge (25 wafers) Wafer Input Cartridge (25 wafers) Top Down View ¾ Overhead View Technological Arts HSC12 Board Over 4000 lines of HCS12 assembly code was written to operate both the system and UI HCS12s. The software controlled the inputs and outputs diagrammed (left) by expanding the HCS12s input and output capabilities through the use of shift registers (below). Dual DACs provided analog signals which controlled the motor speed. Coating the wafer with photoresist or developing it by wet etching off layers after masking is an essential step in the process of creating microchips. In either track, the control system loads a wafer from the input cartridge, then moves it to the spin chuck. Once on the spin chuck, a vacuum is applied. The spin chuck is then accelerated to anywhere from RPM while various chemicals are applied to the wafer. The 8360 has the ability to dispense a main chemical (developer), de-ionized water, and an air stream of nitrogen. When finished, the system moves the wafer to the bake chuck, where the wafer is heated for a variable, user-defined length of time. Finally, the system moves the wafer to the output cartridge, and the wafer is ready to be processed by another system. Cost Breakdown A collaborative effort between RIT Computer Engineering and Microelectronic Engineering Special thanks to: John C. Nash, Dr. Alan D. Raisanen, Thomas J. Grimsley, and Dr. Roy Czernikowski The top-down diagram shows the wafer input and wafer output cartridges located on opposite ends of the line while the spin chuck and bake chuck are in the center. Vacuum tubes hold the wafers onto each chuck as they are processed. The gray rectangle represents a tray which is able to move between the input and output cartridge for wafer loading and unloading, respectively. The 3/4 th overhead view diagram shows the holes cut into the system tray to allow each chuck to move up or down to allow the tray to move to one of its three positions (at input, center, at output.) Conveyer belts move the wafer from the input assembly and to the output assembly. The black squares represent three switches used for position sensing on the system tray and two vacuum sensors on the vacuum tubes to determine if a wafer is currently making contact with the tube (and thus on the tubes chuck.) Control System Block Diagram System I/O Hardware Standby Mode Run Mode Program Mode Status Mode UI Controller The Team Digital Controller – HCS12 Analog I/O to Motor Board Motor Speed In Next Speed Out Motor Accel Out Digital Inputs Position/Level Switch Sensors Hot Plate at Temp. No more wafers to process Wafer sender ready Wafer receiver cassette full Wafer receiver ready Digital Outputs Store finished wafer Load next incoming wafer Solenoid Outputs Servo BoardMotorRPM Detect Switch Sensors Entrance Wafer Cassette Holder Exit Wafer Cassette Holder Solenoids Hot Plate HC11 SPI Interface Clk SDI/MISO SDO/MOSI LCD Panel Keypad HCS 12