Solid State Microengineering Cleanroom Lab

Environmental Excursion Protocols

C. Levey 7/93

Symptom: LOW TEMPERATURE (T<65F)

It is imperative that the lab stay well above 32F to avoid freezing of water lines and water based chemicals. It is also very important to avoid condensation on cold surfaces. This is of particular concern because the surface temperatures lag that of the air as the lab warms back up. Condensation would result in contamination of all surfaces, including stock silicon wafers and experiments in progress.

Cause 1: No steam or steam valve stuck shut.

* SUMMER ONLY RESPONSE (outside T>45F): Notify one of the persons listed below so that access to the lab can be limited. Humidity may drop and static sensitive operations should be avoided in the lab. No other action is necessary as long as temperature remains well above freezing. The temperature will probably stabilize at about 50F. When steam comes back on, the temperature should be increased SLOWLY to avoid condensation on the walls. Humidity must be kept low enough to prevent condensation on room surfaces, which may remain cool well after the air temperature increases. For the conditions noted to the right, the lab walls and other surfaces must have reached at least the indicated temperature in order to avoid condensation. It is not easy to estimate how long it takes for surfaces to reach equilibrium; if the room has reached 50F, it should probably be brought up to 70F over a period of at least an hour unless the RH is well below 50%.

CONDENSATION conditions
LabRH  AirTmp WallTmp
40 %    70 F    44 F
50 %    70 F    51 F
50 %    80 F    60 F
60 %    70 F    56 F
60 %    80 F    65 F
70 %    70 F    60 F
80 %    70 F    64 F
90 %    70 F    67 F
* WINTER ONLY RESPONSE (outside T<45F): Turn off outside air damper. The resulting room pressure decrease will result in some contamination of the room, but temperature should stay well above freezing. Notify one of the persons listed below so access to the lab can be limited (to minimize contamination and for safety under reduced flow). Also see NOTE 1 at the end of this document.

Symptom: HIGH TEMPERATURE (T>75F)

The lab temperature should not exceed 75F for any extended period, and must never exceed 100F. There are processes in the lab which are very temperature sensitive (e.g. developing photoresist), and there are chemicals, gaskets, and fittings in the lab which can degrade or fail at elevated temperatures. If the temperature in the supply ducts exceeds 160F, the fire dampers will close, shutting down most of the airflow into the lab.

Cause 1: NO CONTROL LINE AIR PRESSURE

Loss of control air pressure will cause the steam valve in the lab supply to open fully.

* RESPONSE: Immediate manual shutoff of building steam is called for. [As an alternative to turning off steam to the entire building, there are two manual valves on the lines entering the AC6 McQuay handler; notify the building manager and the lab manager if these are valved off]. When temperature drops back below 65F, either continue manual control or treat as a low temperature condition. Notify one of the persons listed below so that access to the lab can be limited. NOTE: The temperature in the lab will rise much faster than that in the building. This can be a serious condition; in one recent case where the temperature reached well over 100 F, pressure lines popped off of fittings, squirt bottles dispensed solvents and caustic chemicals, containers of concentrated acid bulged and deformed (perhaps nearly bursting), and the fire dampers were tripped. We hope soon to have an automated response to this extreme condition.

Cause 2: NO COOLANT

If coolant is lost in the summer, the temperature may rise to the outside temperature. This is not a severe problem, though the resulting high humidity can be. Condensation on the lab walls must be avoided.

* RESPONSE: Notify one of the persons listed below so that access to the lab can be limited. Discontinue humidification until coolant is restored (the resulting low humidity is preferable to a high dew point).

* if temperature increases above outside temperature: follow the response to "no control line pressure" (cause 1 above).

CONDENSATION conditions
LabRH  AirTmp WallTmp
50 %	90 F	68 F
70 %	80 F	70 F
70 %	90 F	78 F
90 %	80 F	77 F
90 %	90 F	87 F
* a rapid increase in temperature without a decrease in RH could lead to condensation. For the conditions noted to the right, the lab walls and other surfaces must be above indicated temperature in order to avoid condensation. These surfaces lag the room temperature. If conditions are approaching condensation, close the outside air damper. The resulting room pressure decrease will result in some contamination of the room, but the humidity should not continue to increase. Also see NOTE 1 at the end of this document.

Cause 3: STEAM LEAK INTO ROOM

In this case both temperature and humidity may increase catastrophically, with very serious repercussions.

* RESPONSE: Immediate shutoff of steam is imperative. If remote control is not effective, manual shutoff of building steam is necessary. [As an alternative to turning off steam to the entire building, there are two manual valves on the lines entering the AC6 McQuay handler; notify the building manager and the lab manager if these are valved off]. When temperature drops back below 65F, treat as a low temperature condition. Notify one of the persons listed below so that access to the lab can be limited. We hope soon to have an automated response to this extreme condition.

Symptom: HIGH HUMIDITY (RH > 55%)

CONDENSATION conditions
LabRH  AirTmp WallTmp
50 %    90 F    68 F
70 %    80 F    70 F
70 %    90 F    78 F
90 %    80 F    77 F
90 %    90 F    87 F
It is important to avoid condensation in the lab; condensation may result in contamination of all surfaces including silicon wafers. Note that the temperature of the laboratory surfaces and walls lags behind and may be lower than the ambient lab air temperature. The chart to the right shows some conditions under which condensation will occur.

Cause 1: COOLANT CROSSOVER: Crossover from evaporative cooling to refrigeration involves a temporary increase in cooling water temperature. This limits the cooling and humidity extraction capacity of the McQuay handler, AC6. Crossover may occur more than once a day in the spring and fall.

* RESPONSE: Watch to ensure the transient humidity and temperature rise are not extreme; the temperature of the lab surfaces (assumed here to be at 70 F) must remain above the dew point of the lab air. If dew formation is imminent, shut outside damper and notify one of the persons listed below so that sensitive surfaces can be protected and access limited. The resulting room pressure decrease will result in some contamination of the room, but condensation will be avoided. Also see NOTE 1 at the end of this document.

Cause 2: COMPLETE COOLANT LOSS

* RESPONSE: Notify one of the persons listed below so that access to the lab can be limited. Watch to ensure transient humidity and temperature rise are not extreme; the temperature of the lab surfaces (assumed here to be at 70F) must remain above the dew point of the lab air. If dew formation is imminent, shut outside damper, and notify one of the persons listed below so that sensitive surfaces can be protected and access limited. The resulting room pressure decrease will result in some contamination of the room, but condensation will be avoided.

Cause 3: STEAM LEAK INTO ROOM

In this case both temperature and humidity may increase catastrophically, with very serious repercussions.

* RESPONSE: Immediate shutoff of steam is imperative (if remote control is not effective, manual shutoff of building steam is necessary). When temperature drops back below 65F, treat as a low temperature condition. Notify one of the persons listed below so that access to the lab can be limited. We hope soon to have an automated response to this extreme condition.

Symptom: LOW HUMIDITY (RH <30%)

The major concern here is with devices sensitive to static electricity and with photoresist spin-on. Lab users need to be notified so they can take appropriate precautions.

Cause 1: LOSS OF STEAM

* RESPONSE: Notify one of the persons listed below so that access to the lab can be limited, sensitive processes avoided.

Symptom: LOW PRESSURE (room to building < 0.04 inches for > 5 min.)

The concern here is with contamination. A pressure below that of the building is especially bad, as it draws airborne contamination into the lab. If such an under pressure condition exists for several hours, it may take a day or longer to recover clean conditions. A low pressure condition may also be an indication of other serious problems.

Cause 1: OUTSIDE DAMPER CLOSED

* RESPONSE: Notify one of the persons listed below so that access to the lab can be limited. If the damper has been closed to solve another problem condition, continue to follow the protocol for that condition. Otherwise check the computer control and investigate for damper malfunction. Also see NOTE 1 at the end of this document.

Cause 2: FIRE DAMPERS CLOSED

This may happen if there is a temperature extreme well in excess of 100 F in the lab (and in excess of 160F at the damper).

* RESPONSE: Notify one of the persons listed below so that access to the lab can be limited. The dampers must be reset. Also see NOTE 1 at the end of this document.

Symptom: POWER LOSS

Power loss results in the loss of pressure, temperature, and humidity control, and the loss of fume hood venting. All persons should leave the lab immediately. Toxic and/or corrosive fumes may be present in the lab. The lab is susceptible to contamination from building air, and no lab entries should be made while power is off.

* RESPONSE: Notify one of the persons listed below so that the lab may be evacuated and access limited. Continue with the instructions below when power is restored.

* POWERUP RESPONSE FOR MOMENTARY OUTAGE: If the power outage is reasonably short (say less than 10 minutes), startup should be straight forward. Check that the cooling water is restored and all blowers start up (watch for a tripped breaker in the wall box near AC6).

* POWERUP RESPONSE FOR EXTENDED OUTAGE: When power is restored after being off for more than a few minutes, the proper sequence of events is essential in order to avoid further problems (overheating, condensation and contamination). The problem is that cooling water will not be immediately available (after the lubricating oil is up to temperature, it takes 16 minutes to restart the system, but if the power has been off for an extended period, it can take a couple of hours for the oil to reheat). The lack of cooling can cause overheating and/or condensation, depending on the outside conditions and how much outside air is drawn in.

* If the outside temperature is below about 95 F

AND

* if the outside dew point is below about 65 F,

then ordinary startup is OK. The blowers will start as soon as power is restored; if not, check for a tripped breaker in the wall box near AC6. Cooling water may not be available for several hours, and the lab temperature may rise, but the pressure will be normal, and contamination controlled.

* If the outside temperature is above about 95 F

OR

* if the outside dew point is above about 65F,

then the outside damper should be shut until cooling water is restored. This will keep hot and moist outside air out of the cool room, and thus limit the temperature rise an risk of condensation. However, this is at the expense of loss in room pressure. Entry to the lab must be limited until cooling has been restored the outside damper opened, and pressure returned to normal. The blowers will start as soon as power is restored; if not, check for a tripped breaker in the wall box near AC6. Also see NOTE 1 at the end of this document.

NOTE 1: WHEN OUTSIDE DAMPER MUST BE SHUT:

If the fume hood and service corridor exhaust fans continue to run while the outside "makeup air" damper is shut, the room pressure will go below building pressure (in the long run, the best solution to this problem would be to add another source of makeup air). Under special circumstances (for example, when contamination would be catastrophic for an important experiment), the solid state lab manager may decide to power down the fume hood and service corridor exhaust fans until the outside damper can be reopened. With these fans off, the room will remain at building pressure rather than going below building pressure. While this is advantageous, it is not to be standard practice because it compromises safety--without the fume hood exhaust fans, if there are open containers in the hoods, fumes may enter the lab. Thus these fans should be powered back up as soon as possible; were the exhaust fans to be forgotten and left off, subsequent lab users would have no protection in the hoods. This would be a very serious breach of safety. It is the responsibility of the person who turns them off to verify that they have been powered back up. During the time these fans are off and for an hour after that, there must be a sign posted on the doors : "Fume hood and lab exhaust disabled--DO NOT ENTER" .

CONTACT LIST (in order of prefered attempt):

Chris Levey x2071 (office) x2618 (lab) (802) 785-4121 (home)

Gary Durkee x3457 (office) (802) 785-4084 (home)