JIPElec Rapid Thermal Proccessor model 150

The JIP Elec Rapid Thermal Processor uses powerful lamps to rapidly heat 4"-6" wafers with accurate control of temperature and time. The range of temperatures runs from ambient to about 1100 C, the time span can be from seconds to many minutes. Below 200 C temperature measurement is via a thermocouple contacting the back side of the wafer, above 200 an optical pyrometer can be used for improved response time.

The cooling of the specimen is dominated by the thermal conductivity of the atmosphere in the process chamber, which can be either air, inert gas or vacuum (tens of millitorr), although the vacuum performance is not wholly reliable. At present the inert gas is nitrogen, but any other gas can be connected easily. Four separate gas channels are available, with manually adjustable flowmeters.

Specimens are supported on slender fused quartz pins to minimize thermal contact with the chamber. Thus, fragments must be supported on a handle wafer and thermometry is on the handle, not the specimen.

Safety considerations

The tool is relatively harmless to the operator apart from obvious hazards such as pinching fingers while closing the chamber or picking up a hot specimen too quickly after a process run completes.

However, the operator can easily damage the instrument, in several ways. Probably the most imminent danger is damaging the fused quartz pins which support the wafer. They're easily replaced, but custom made and expensive.

A more catastrophic threat is introduction of a sample which, when heated, contaminates the chamber or, more specifically, the window to the lamphouse.

Any material placed inside must be non-volatile and non-reactive to temperatures well above the process range. Some thought should be given to mishaps in which the specimen becomes hotter than intended, especially in the early stages of recipe development. Dirt on the window is labor-intensive to remove, the window is fused silica and therefore costly to replace. Any contaminant will result in excessive heating of the window, some contaminants (sodium, for example) will attack the quartz and impair its mechanical and thermal integrity.

The instrument is self-protected against gross malfunctions (loss of cooling water or compressed air) and overtemp. However, the overtemp protection will not activate until the sample is well over 1000 C, so the sample's behavior is of paramount importance.

Process gases are restricted to inerts. There is no provision for dealing with reactive gases.

Process cycle

Processing is initiated by opening the chamber and carefully placing a wafer on the three quartz pins which support and center the wafer. The lid is closed and latched, and the control computer is told to run the recipe. At termination, the operator opens the chamber and removes the specimen. Typically, the cycle begins with a nitrogen purge, perhaps alternating with partial evacuation to displace adsorbed moisture, followed by heating at a controlled rate to a set temperature and finally cooldown.

Recipe

Recipes are stored on the control computer and consist of commands to evacuate, heat or backfill. Parameters set in software include temperature, valve state and time. Flow rates are set manually using needle valves prior to running. Note there is no quantitative pressure control and very limited control once temperature exceeds setpoint; the only cooling control is to backfill the chamber and use convection/conduction of heat to the water-cooled chamber. A small library of recipes is provided, which can be edited and saved under a new name to support custom processes.

A recipe contains a series of steps. Each step contains ten parameters:

1. final temperature
2. step duration
3. timer resolution
4. temperature control or power control
5. temperature signal source, pyrometer/thermocouple
6. vacuum valve open/closed
7. gas 1 on/off
8. gas 2 on/off
9. gas 3 on/off
10. gas 4 on/off

The temperature parameter is satisfied at the end of the step, all others are applied at the beginning.

Startup

The tool is normally left in a state of complete shutdown. To start it: check the water level in the heat exchanger; must be above float. Turn heat exchanger on, use bypass to set delivery pressure to 20-25 psi; water will leak into lamphouse when chamber is evacuated at higher pressure.

Start the computer, allow it to boot Windows 95 and turn on the RTP. When the RTP starts a menu appears on the display, press F4 to put the machine under remote control via the computer.

Start the Jet First 150 program on the control computer. A menu appears. Recipes are batched, so they must be edited using the JetFirst 150 program and then downloaded to the RTP for execution; there is no interactive mode. To make any change, edit the recipe and download it again. "Run Process" runs the recipe on the RTP, not the recipe displayed on the computer.

Load the specimen making sure the thermocouple just touches the back of the wafer. Close and latch the lid. Click Run Process. Noisy cooling air jets will turn on to prevent the lamp terminals from overheating, a water valve will open to keep the lamphouse and window from overheating, the vacuum and gas valves will take on the desired state and finally the lamps will turn on to drive the specimen to the step temperature desired.

The second step will implement any parameter changes at its outset and drive the sample temperature to the target temperature at the end.

Following the last step power to the lamps will be terminated and the cooling air and water will remain on to protect the lamp terminals and lamphouse from residual heat in the lamps. However, the specimen can be removed immediately.

Data Logging

Input power, measured temperature, and valve states are recorded, temperature and power can be plotted. The system offers to save process logs at the end of each run, logs are accessed using the "Historicals" button on the main menu.

Power control versus temperature control

It will be discovered that there is considerable lag and some overshoot in temperatures, aggravated by high heating rates. Large temperature excursions can be more accurately achieved by using more than one recipe step to accomplish them. Early in the ramp, when measurements are relatively certain to be inaccurate, power control can be used to limit overshoot until temperature measurement becomes meaningful, which may take several seconds.

Operators are cautioned that power control must be used sparingly; The RTP is capable of achieving temperatures over 1300 C in just a few seconds if run at 100% power. It is very easy to destroy specimens and start fires.

Thermocouple versus pyrometer measurement

Thermocouples offer relatively good amplitude accuracy but poor time response, pyrometers have fast response but no absolute calibration and a relatively high minimum temperature, around 200 C. In some cases it will be found advantageous to switch between the two during a single recipe.

Shutdown

1. Close the JetFirst 150 program on the control computer, then call Shutdown from the Start menu as usual for Windows 95. The computer will power down.
2. Press the square red button on the front panel of the RTP to turn off the controls
3. Go into the chase and turn off the heat exchanger.
4. You're done!