Chapter 6.30

Plasma Quest ECR PECVD System

(pqecr)

1.0 Title

Plasma Quest ECR PECVD System

2.0 Purpose

This document describes the proper procedure for operating the Plasma Quest Model 347 ECR PECVD system.

3.0 Scope

This is a state-of-the-art CVD tool. It has a turbo pumped load lock with a shuttle mechanism that graphite carrier. Substrates up to 100 mm in diameter can be processed. An optical sensor prevents system damage by verifying the location of the shuttle at transfer. The process chamber has water cooling channels and it is constructed out of stainless steel. The chamber is used to deposit silicon dioxide in the Cryogenic Research Group’s superconductive IC process. Pressure is maintained with a throttling gate valve. RF substrate etch is available (13.56 MHz) and could be used in a planarization process. The substrate chuck has broad thermal range (LN2 to 350C), and is normally cooled with water to maintain a temperature of 25ºC. Substrate temperatures other than room temperature are possible but you must disconnect the water cooling lines, blow out the water, and then change the temperature range. This procedure only takes about 15 minutes to do. A quartz disk shields the chamber top plate to prevent the possibility of stainless sputtering at low ECR pressures. It should be noted that no stainless was observed in oxide films by SIMS when no quartz shield was in place when oxide had been deposited at very low pressure (e.g. 3 mTorr) at maximum ECR power (i.e. 1000 Watts). The Model 357 uses an AsTex 4400 (i.e. 6 inch) ECR source.

A 1000 lps turbo backed by a roots blower and mechanical pump provide adequate throughput of the process gas: 10% silence in argon. The roots blower reduces the foreline pressure to improve hydrogen pumping efficiency of the turbomolecular pump. Deposition rates of over 0.25um/min are possible using as little as 200 Watts of microwave power (i.e. 2.4 GHZ) with out causing the substrate temperature to exceed 100 degrees C. High deposition rate/low temperature oxides tend not to be dense as determined by a comparison to the wet etch rate of thermal oxide in 5:1 buffered oxide etch. For example, thermally grown silicon dioxide will etch at about 500 A/min and the undense ECR films will etch at about 30 kA/min. However, the undense films appear nevertheless to be good electrical insulators. It is possible to deposit dense silicon dioxide, with a 5:1 BOE etch rate of 1500-2000 A/min using ECR with out causing the substrate temperature to get above 130 degrees C. Such a process requires at least 350 Watts of microwave power at a lower pressure (e.g. 4mTorr vs 15mTorr) and a pulsed process mode to allow the wafer to cool down during deposition. In a pulsed process mode, the deposition rate is reduced to about 110 A/min, similar to what one would expect in an LPCVD process however without the economy of batch processing available in a typical LPCVD process. All system control is though a PC 386 with software that is very user friendly. The software also includes tolerance checking should the user deem this to be necessary.

4.0 Applicable Documents

5.0 Definitions and Process Terminology

6.0 Safety

6.1 Never use the system in diagnostics mode (i.e. “DIAG” on the screen). “DIAG” is a manual system control mode for maintenance only. If you are not familiar enough with the machine, you can easily damage it in this mode because the system does NOT check interlocks at this level of operation. It assumes that YOU KNOW WHAT YOU ARE DOING!

6.2 Always pump/purge any gas line after a gas bottle has been changed. It is especially important that you convince yourself that there is no leak in the silene line BEFORE introducing gas after a bottle change. One way to do this is to pump out the silane line to chamber base pressure, close the MFC, and let the system idle overnight. The next morning, open the silane MFC (with the bottle closed) and watch the MFC readout to see if ther is any detectable gas flow flow. If there is there may be a leak. Convince yourself that the leak is a virtual leak before opening the silane bottle. Helium leak check the gas line if you suspect a leak in the silane line. An air leak in a silane line can damage gas delivery hardware, especially MFC’s.

6.3 If you choose the use escape (i.e. “ESC”) to abort a process run, an error message will be displayed and you will need the key operator to proceed. NEVER reboot the computer to override this message. If you were to do so, the system probably will not be able to tell the state that it was left in and damage could occur if you try to run another process.

6.4 Make sure that the chamber and substrate carrier have been cleaned and recoated BEFORE depositing silicon dioxide on your substrate.

6.5 The system is dedicated to silicon dioxide deposition in the Cryo Group low Tc IC process. Other materials are forbidden from the chamber.

6.6 Do NOT put photoresist coated substrates in the ECR system.

6.7 The magnetic fields generated by the upper and lower electro-magnets are capable of erasing magnetically recorded data (e.g. mag strips on credit cards; floppy disks; hard disks; etc), Keep all such items at least 3 feet away from the process chamber when running the system.

6.8 The system should be checked annually to verify that microwave leakage is within acceptable limits for this type of equipment(e.g. <3mWatts/sqcm at any point 3 inches or more away from the chamber).

6.9 Persons with pace makers should not be in the room where the ECR system is located while the system is running.

7.0 Statistical/Process Data

8.0 Available Process, Gases, Process Notes

8.1 High Deposition Rate/Low Substrate Heating SiO2 (Not Dense)

Process I.D.: 1019A. ECR

STEP 1

O2 FLOW: 60 sccm

N2 FLOW: 70 sccm

SiH4 FLOW: 200 sccm

PRESSURE: 15 mTorr

CHUCK T: 24ºC

UPPER MAG (Amps): 170

Lower MAG (Amps): 120

Use STEP 1 parameters, but MW PWR on at: 250 Watts

Deposition Rate: 2325 A/min

Max 100 mm Wafer Temp: < 99ºC for a 0.5 µm continuous deposition.

8.2 Low Deposition Rate/Low Substrate Heating SiO2 (Dense)

Note: Uses “pulsed process mode” to keep the substrate cool.

PROCESS I. D: 1117 .ECR

STEP 1

O2 FLOW: 100 sccm

SiH4 FLOW: 75 sccm

PRESSURE: 4 mTorr

CHUCK T: 24ºC

UPPER MAG (Amps): 170

LOWER MAG (Amps): 75

TIME: 60 sec

STEP 2

Use STEP 1 parameters, but MW PWR on at: 350ºC

Deposition Rate: 10.2 A/sec

Nf: 1.46

Uniformity: +/- 3.0% (100 mm dia wafer)

Max 100mm Wafer Temp (pulsed mode ONLY!); >99C<138C

TIME: 10 sec

PLUSED MODE OPERATION: Run STEP 1 and STEP 2. Do NOT reduce the STEP 1 time. This will cause the substrate to get very hot! Reducing STEP2 time to 5 sec will reduce the wafer temp to 99-110ºC.

Note: Pulsed mode not required before Nb/AlOx/Nb trilyer deposition.

8.3 Amorphous Silicon

STEP 1

SiH4 FLOW: 300 sccm

PRESSURE: 15 mTorr

CHUCK T: 24ºC

UPPER MAG (Amps): 170

LOWER MAG (Amps): 120

TIME: 60 sec

STEP 2: Same as STEP1, but MW on at 250 Watts

Deposition Rate: -40 A/sec

8.4 CF4/O2 Chamber Cleaning Cycle

STEP 1

CF 4 FLOW: 80 sccm

O2 FLOW: 20 sccm

PRESSRE: 10 mTorr

CHCK T: 24ºC

PPER MAG (Amps): 170

LOWER MAG (Amps): 120

TIME: 60 sec

STEP 2: See STEP 1 conditions with MW PWR set at 350 Watts.

Note: Be sure to clean graphite carrier AND the chamber!

9.0 Equipment Operation

9.1 Getting started and Programming Instructrions

9.1.1 Enable the system via the wand. An error message will be displayed if you try to use the system without having it enabled. The message reads: “ERROR! Access Denied! You must login first.”

9.1.2 Users are only permitted to access “RUN” and “EDIT.” These allow you to run a program, create a new program, and edit an existing without being in run mode. To create or delete a program, you must access “EDIT” directly.

9.1.3 Use the mouse and click on “RUN.” Enter the user password that you obtained from the superuser and press “ENTER” on the key board.

9.1.4 Select the program that you want to run. WARNING: If you are using a “pulsed mode” Process and use “ESC” to abort out of the deposition you will introduce a bug to that process file. The file will have to be deleted and rewritten entirely as a new process if you do this. Also, using “ESC” to abort out of any process will require that the key operator enter their password to reset the system. If you ever need to abort a process that is in progress, use “STOP” in the “RUN” menu instead! Then use “UNLOAD” to remove the substrate carrier from the process chamber.

9.1.5 If the program needs to be reviewed and/or edited, click on “EDIT” and enter your password. The program may now be edited. Make sure that all deposition parameters are correct and that the deposition time is what you will need to get film thickness that you want. It is a good idea to run a test wafer through the system to verify that the ECR match condition is correct and to verify the deposition rate before depositing on your actual device substrate. If you are concerned about substrate heating during process, you can use the pulsed process mode to help minimize the degree to which the substrate is heated by the plasma. The manual slug tuner works best if you minimize reflected power and then off tune a little (e.g. reflected power reads about 9 to 11 Watts). This increases the voltage at ignition and makes ignition of the plasma more reliable.

9.1.6 If the program looks OK, click on “SAVE” and edit the process description text if you want to. This is a good place to comment on your measured deposition rate and the date of the test to assist other users.

9.1.7 Click on “START” if you are ready to deposit a film. Otherwise, click on “EDIT” if further editing is required or click on “EXIT” to get out of run mode. If you are starting a process, you will be prompted “Do you want ot load a wafer before running?” If you answer “no” the process will run without transferring the wafer carrier to the chuck. If you answer “yes.” You will be asked if you want to vent the load lock to load a substrate. If you answer ”no,” the graphite carrier will be transferred to the process chamber as soon as the transfer pressure setpoint is reached (REF: HPS 412 cold cathode (Load Lock) setpoint 1 should be set to 5*10E-5 Torr for all processes run in this system). If you answer “yes, “ the load lock will vent. Upon venting, load your substrate and press “ENTER.”.

9.1.8 When the transfer pressure setpoint is reached the substrate will be loaded onto the chuck in the process chamber.

9.1.9 The process will run automatically and unload the substrate when the process is complete. The load lock will vent automatically so that you can unload the substrate. Pressing “EXIT” will pump out the load lock and leave the system in a safe idling mode.

9.2 Chamber Cleaning

9.2.1 The graphite carrier and chamber need to be cleaned frequently to prevent particulates from getting on the substrate during process. It is recommended that the clean process be run for 30 minutes for ever micron of material that has been deposted.

9.2.2 You will be able to tell if the chamber is clean by looking at the gas injectors just above the chuck while a plasma is running. The injectors will appear as shinny stainless streel if they are clean. When they are coated, they appear to be covered with a white powdery material.

9.2.3 The graphite carrier can be removed and wiped down with methanol to remove the coating more quickly.

9.2.4 Always coat the chamber and graphite carrier after a clean cycle. Coat with about 0.2 um of silicon dioxide before processing through any device substrates.

9.3 System Set-up Information

9.3.1 If you develop a process that ses high gas flows or gases that are not already installed on the system (e.g. N2; O2; CF4; SiH4; and Ar), you may have to “relearn” the throttle valve. The throttling gate valve needs to “learn” the new gas dynamics and how the throttle valve plate needs to be adjusted to get the pressure setpoint you’ll need. This “learning cycle” allows the valve controller to adjust to the pressure you want more quickly. To “relearn” the valve, have the key operator turn on the gasses you’ll need in “DIAG” mode. Put the VAT valve controller in “LOCAL” and press “LEARN.” The controller will close down the valve slowly and measure pressure versus valve position and store this information in memory.. When finished, return to “REMOTE” and have the key operatior adjust the gas pressure at a couple of different pressures in the regime that you intend to work in. The pressure control should be quick and smooth. If not, repeat this procedure. The valve will probably have to be “relearned” again for other processes before they can be run.

9.3.2 The MFC’s can be zero’s remotely via the key board by accessing “CONFIG” on the main men. Only the key operator has access to this program. To zero remotely, program all gases to full open flow while in “DIAG,” but do not open the gas lines. Write down the values that appear in “Readings” next to each gases “Settings.” Remember, the gas lines are not open so the “Readings” should be zero indicating on flow. “EXIT” from “DIAG” and select “CONFIG” at the top of the screen select “MFC.” Enter the flow that was recorded for each gas “Reading” and with the opposite magnitude in the column labeled “Zero Offset.” Click on “SAVE”. Access “DIAG” once more, program the gas flows as before without opening the gas line, and the “Readings” for each should be very close to zero.

10.0 Troubleshooting Guidelines

11.0 Figures and Schematics

12.0 Appendices