RIE Operating Manual: Technics Series 800 Micro REACTIVE ION ETHCHER

Introduction

Safety Highlights | Pre-operational Checklist | Before You Enter the Cleanroom | Cleanroom Issues | After Entering the Cleanroom

Operating Instructions

Setup and Dry Run | Manual Operation | Subroutine 1: Automatic Operation: | Shut Down | Troubleshooting | Other RIE Manuals

Figures and Tables

Figure 1: Front View of RIE Reactor | Figure 2: Flow Control | Figure 3: Front View of Exhaust Valve Controller | Figure 4: System Control Panel | Figure 5: Top View of RIE Reactor | Table 1: Gas Factors |

Introduction

The Technics Series 800 Micro Reactive Ion Etcher (RIE) (See Figure 1) uses a radio frequency signal to generate a plasma of chemically reactive gas used to etch various materials. Because the surface to be etched is placed directly onto the cathode, momentum transfer plays a significant role in the etching process. Thus by varying the process parameters, etching may be done either isotropically or anisotropically.

The RIE has three mass flow controllers (MFCs) to assure precise control of the process gases (Figure 2). The MKS exhaust valve controller controls chamber pressure (Figure 3). The power supply provides up to 300 watts at 30KHZ (Figures 1 & 4). The unit can be run in either manual or automatic mode (Figure 4) and will hold up to three four-inch wafers or five three-inch wafers.

Safety Highlights

1. Know Your Gases. Before using any gas, become familiar with its properties. A Material Safety Data Sheet, also known as an MSDS, is available for every gas used in the lab. Both the Teaching and Research sections of the lab have sets of MSDSs. An MSDS lists all known properties of a substance including safety precautions and emergency procedures. See also Table 1 below and standard sources such as the Matheson Gas Data Book or the Handbook of Compressed Gases. For information about handling gas cylinders, see also "Compressed Gas Safety," EHS Safety Net, #60.

2. DO NOT rely on the interlocks or valve controls on this system to shut off gases. Always use the manual shut-off valves and proper purging procedures described below.

3. A plasma is a source of UV radiation. Do not look directly into the plasma for long periods.

4. If you haven't used the tool in a long time and have doubts about its operation, ask a superuser to reacquaint you with it or work together with another knowledgeable user.

5. If you have any problems contact in Kemper Hall:
superuser
lab manager

Pre-operational Checklist

Before you enter the cleanroom

1. Have you arranged training from the superuser or lab manager on the RIE? Follow the procedures below and preserve the life of the tool and its availability for your use.

2. Gas selection. Most etching in this RIE is done with two types of gas mixtures, i.e., either CF₄ premixed with four percent O₂ or a mixture of SF₆ and O₂. There are three mass flow controllers (MFCs), A, B, and C. Note that D is not used. Under normal conditions, gas A is O2, gas B is a mixture of CF₄/O₂ (4%), and gas C is SF₆. Any changes of this configuration should be done by either the superuser or the lab manager. The user should not have to make any adjustments to the MFC calibrations. If different gases are needed, follow these procedures:

• Contact the superuser or lab manager about the change.

• Determine the calibration factor for the gas you will use. (See Table 1) for calibration factors for common gases. All process gases are delivered to the system through mass flow controllers. The MFC's are all factory calibrated for N2. Each MFC has a different full scale flow and can accurately control flow within three percent of its particular full scale. When using a gas other than N2 the user must enter an ion-units calibration factor. Even in the unlikely event of using N2, check that the calibration factor is set properly.

• Depending on your intended flow rate, decide which MFC to use with a particular gas. Use the MFC with the lowest full scale flow rate possible. This will increase the accuracy and repeatability of your process. However, note that the full scale ranges apply only to gases with a calibration factor of 1.0. For instance, CF4 has a calibration factor of 0.48. Thus when you connect an MFC with a full scale flow of 100 sccm and open it all the way, you will get only a maximum 48 sccm flow.

Cleanroom Issues:

See the manual Introduction to the Northern California Nanotechnology Center for general reminders about clean room practice. If you have questions about where things are stored or hung, ask the lab manager or a superuser.

After entering the cleanroom:

1. Mark your use of this tool in the RIE log book. Note any problems encountered by recent users.

2. Check the oil sight glass on the side of the mechanical pump. The vacuum pump is located in the service tunnel. If you can see the oil level through the sight glass, then it is fine. If not, tell a superuser, the lab manager, or the lab technician. If the base pressure, i.e., the pressure obtained by the system when no gases are introduced, is less than 10 mTorr, then there is no need to check the pump.

Operating Instructions

Setup and Dry Run:

1. Do a dry run. Although it is certainly possible and sometimes necessary to adjust the parameters during etching, it is better to make a dry run without the sample in the chamber. This allows you to preset the parameters. Otherwise, during each run there is some unknown and unrepeatable etching in the finite period spent in adjusting the system.

2. Make sure the system is on. Check to see that the L.E.D. displays are on. Check the valve controller (Fig. 3) in particular. The toggle switch (Fig. 3, A) should be left in the "ON" position. If the controller is "OFF", turn it on and allow fifteen minutes for it to warm-up. Also confirm that the INT/EXT toggle (Fig. 3, B) is in the "INT" position, the input toggle (Fig. 3, C) is in the "IV" position, and the set-point dial is set to "0" (Fig. 3, H).

3. Check to see that the gases you want to use are connected to the system. The gas cylinders are located in a cart in the service tunnel behind the system There are three gas lines marked A, B, or C according to which MFC they are connected. Connect the appropriate lines to the gas regulators for the gas you intend to use. Open the cylinder valves.

4. Open the valve to the N2 vent gas.

5. Choose manual mode. Manual mode gives the user real- time control over the etching process. The automatic mode is most useful when you want to make mutiple runs that have the same process parameters. For automatic operation, see Subroutine 1: Automatic Operation below.

• Flip down the lower panel that covers the System Control Panel (see Fig. 4).

• Position all toggle switches in the System Control Panel down. If Gas and Power are on when you go to the next step, the system will start.

• Set the Mode Selector (Fig. 4, A) to "MAN".

• Set the Vacuum SOLN toggle (Fig. 4, B) to "OPEN" to pump down the chamber.

6. Enter the gas calibration factors.

• Open the front panel of the system to reveal the Flow Control Panel (Fig. 2).

• Set the Display Mode Selector (Fig. 2, A) to "CAL".

• Set the Channel Selector (Fig. 2, B) for the MFC you are adjusting. Check to see that your gas is hooked up to the correct MFC (either A, B, or C.

• The digital display will show the calibration factor for your gas. Below the display you will find four sets of controls, one for each MFC, with a recessed screw labeled "CAL" (Fig. 2, C). Adjust this screw until the display shows the correct calibration factor. The MFC can now accurately measure and control the flow of your chosen gas.

7. Set the flow rate for the gases.

• Turn the Display Mode Selector (Fig. 2, A) to "SET".

• Set the Channel Selector (Fig. 2, B) for the MFC you adjusting. The digital display will show the flow rate set- point for your gas.

• Rotate the Flow Control Knob (Fig. 2, D) until the display shows the desired flow rate.

• Enable the gases by flipping the Gas Enable toggle (Fig. 2, E) to the up position for each gas you want to turn on.

• Confirm that the AFC/Gas #1 switch (Fig. 2, F) is in the AFC position. This will allow the MFC's to be turned on and off by the Gas #1 switch on the lower panel (Fig. 4, C).

• Switch the Gas #1 toggle (Fig. 4, C) to the "ON" position. All gases that you enabled on the Flow Control Panel (Fig. 2) will begin to flow. In addition, the L.E.D.s near the Channel Selector (Fig. 2, B) will now show which channels are on. The pressure in the system will now rise dramatically. In about fifteen seconds the system will stabilize.

8. Set the Display Mode Selector (Fig. 2, A) to "READ". This will reveal the actual flow rate for the selected channel.

9. Set the Valve Controller. The MKS Downstream Exhaust Valve Controller (Fig. 3) drives a variable butterfly valve between the plasma chamber and the vacuum pump. See #2 above for beginning settings.

• Adjust the Set-point dial on the valve controller to the </a> pressure desired tuning will be done automatically. DO NOT adjust the control parameters. Contact the superuser if manual control is necessary or if the system becomes unstable.

• Do not adjust the control parameters unless you have contacted the superuser. To adjust the automatic response of the valve controller, set the Mode Selector to AUTO, the Phase Lead dial to 1.5 seconds, and the Gain dial (Fig. 3, G) to 100%. The Set- point dial (Fig. 3, H) corresponds roughly to the system pressure. Turn on your gas to the desired flow and set the Set-point dial to the desired pressure. The controller will begin to adjust the valve to reach that pressure. However, you may have to fine tune the Set-point dial to get the exact pressure. Now change the set-point about 15 mTorr and watch the pressure response. If the pressure oscillates, lower the gain. If the pressure is slow in approaching the correct setting, decrease the phase lead. If the pressure overshoots but then settles on the correct value, increase the phase lead. Once you have tuned the controller, adjust the Set-point to the correct pressure. You may have to retune the controller for different flow rates, gases, and pressures.

• To operate the valve controller manually, set the Mode Selector (Fig. 3, D) to Manual (directly towards the "OPEN/CLOSE" toggle (Fig. 3, E)). Toggle the "OPEN/CLOSE" switch between the two positions until you get the desired pressure reading on the RIE.

10. Set the desired power.

• When you have reached the desired pressure and flow, switch the Power toggle on the System Control Panel (Fig. 3, D) to "ON". A plasma should begin immediately.

• Adjust the Power Level knob (Fig. 4, E) until you have the desired power level (maximum = 400 watts). Flow, rate, and pressure are all interrelated. Therefore you may need to adjust them all a few times in sequence to get all three to read correctly.

11. Everything is now set.

Manual Operation

1. Assuming you have calibrated the RIE in a dry run in steps #2-#10 above, TURN OFF the Power toggle (Fig. 4, D). DO NOT adjust the power level (Fig. 4, E).

2. TURN OFF the Gas #1 toggle (Fig. 4, C).

3. After noting the position of the Set-point dial (Fig. 3, H) that gave the correct pressure, TURN the dial to zero.

4. WAIT until the chamber pressure is dropping no faster than about 0.5 mTorr/sec. Under normal conditions the system pressure should drop below 10 mTorr.

5. TURN OFF the Vacuum SOLN toggle (Fig. 4, B) and then turn on the Vacuum Vent toggle (Fig. 4, F). This isolates the chamber from the vacuum pump and allows the N2 to vent to the chamber.

6. After about fifteen seconds the chamber will be at atmospheric pressure and may be opened. Open the chamber lid and TURN OFF the Vacuum Vent toggle (Fig. 4, F).

7. Insert your samples on the platen. Etch uniformity is best when the sample is placed midway between the outer edge and the center of the chamber. Close the chamber lid.

8. TURN ON the Vacuum SOLN toggle (Fig. 4, B). Allow the chamber to pump down until the pressure is dropping no faster than 0.5 mTorr/sec.

9. TURN ON the Gas #1 toggle and adjust the Set-point dial on the valve control (Fig. 3, H) to the setting you noted in operating step #3 above.

10. When the flow rates and pressure stabilize, you are ready to etch. Simply TURN ON the Power toggle (Fig. 4, D) and start timing. All the process parameters should be the same as the ones you set in the dry run.

11. When you're ready to stop etching, REPEAT steps #1-#6.

12. Remove your sample.

Subroutine 1: Automatic Operation:

1. Prepare system by going through the setup described in the section Setup and Dry Run above.

2. Set the timer for the desired amount of etch time. (Fig. 4) Make sure the timer switch is set to TIME ONLY.

3. With the system in MANUAL mode turn off the SOLN switch and open the VENT switch to bring the chamber up to atmospheric pressure. When the chamber is open turn off the VENT valve.

4. Load the materials to be etched. Close the chamber lid.

5. Switch the system to AUTO mode. Turn on the SOLN, Gas #1, and POWER switches at the same time. These systems are now controlled by the timer.

6. Press START (Fig 1). Wait until the gas begins to flow, then adjust the MKS valve controller set point to the desired setting. At this point the system will continue to control the etch and may be left unattended. The system will automatically pump down to below 60 mTorr, before turning on the gas. Once the gas is on, the system will be given some time to stabilize before the power is turned on. When the power is turned on the pressure will tend to rise and settle slowly, particularly at low working pressures. For this reason, it is best to do short runs less than 10 minutes using manual mode.

7. After the etch time is complete, the gas and the power are shut down and an alarm will sound. The alarm will continue until the Start button is pressed again. The system will remain pumped down.

8. Switch the POWER, GAS #1, and SOLN off.

9. Switch the mode back to MANUAL.

10. Vent system as described in step 3 above.

Shut Down

1. Close the chamber lid.

2. TURN ON the Vacuum SOLN toggle (Fig. 4, B). Allow the chamber to pump down until the pressure is dropping no faster than 0.5 mTorr/sec. Now TURN OFF the toggle. It is very important that the RIE be left under vacuum, but with the vacuum switch off. This keeps the chamber free of contamination from the air and from "back streaming" vacuum pump oil. DO NOT leave the system "pumping down all the time" or "not pumped down."

3. Close the cylinder valves to all the gases you used including the N2 vent gas. DO NOT adjust the pressure regulators or the valves downstream from the regulators.

4. Leave the valve controller, power toggle switch "ON" (see Figure 3, A).

5. Complete your notes in the RIE logbook. Record the information on the material etched, the gases used, the gas flow rates, the operating pressure, the power, and any etch rates measured.

6. You're finished!

Troubleshooting

1. Check the logbook for any problems on prior runs.

2. If the chamber is dirty, clean it with an O2 plasma (8 sccm, 120 mTorr, 300 Watts, for 30 minutes) followed by a wipe down with isopropyl alcohol.

3. If the main power is off, turn it back on with the button located on the upper right corner (as viewed from the front) of the back of the system.

4. If a base pressure of less than 10 mTorr is not reached, check the vacuum pump oil level and inform one of the contacts.

5. For other problems consult with the lab technician or the Technics Micro-RIE Manual located in 2136 EUII or next to the RIE itself.This is not the Manufacturer's Manual and Schematics but rather an ad hoc collection of materials .

Figures and Tables

Figure 1: Front View of RIE Reactor

Figure 2: Flow Control

Figure 3: Front View of Exhaust Valve Controller

Figure 4: System Control Panel

Figure 5: Top View of RIE Reactor

Table 1: Gas Factors

GAS FACTORS

CHEMICAL NAME	SYNONYM	FORMULA	F
Acetylene	Ethyne	C2H2	.66
Air			1.00
Allene	Propadiene	C3H3	.47
Ammonia		NH3	.77
Argon		AR	1.40
Arsine		AsH3	.76
Boron Trichloride	Boron Chloride	BCl3	.39
Boron Trifluoride	Boron Fluoride	BF3	.58
Bromine		Br	.88
1,3 Butadiene	Biethylene,	C4H6	.38
	Erythrene,
	Vinylethylene
Butane		C4H10	.29
Butene	Alpha-Butylene	C4H8	.33
Carbon Dioxide		CO2	.74
Carbon Monoxide		CO	1.00
Carbon Tetrachloride		CCl4	.35
Carbonyl Fluoride		COF2	.62
Carbonyl Sulfide	Carbon Oxysulfide	COS	.68
Chlorine		Cl2	.84
Chlorine Trifluoride		ClF3	.46
Chloroform	Trichloromethane	CHCl3	2.02
Cyanogen	Dicyan,	C2N2	.50
	Oxalonitrile
Cyclopropane	Trimethylene	C3H6	.52
Deuterium		D2or	1.00
		2H2
Diborane		B2H6	.50
Dichlorosilane		SiH2Cl2	.47
Dichloro Methyl Silane		SiHCl2CH3	.27
1.1 Difluoroethlene	Genetron 1132A	H2C:CF4	.48
Dimethylamine		(CH3)2NH	.42
Dimethyl Ether	Methyl Ether	(CH3)2O	.44
Ethane		C2H6	.55
Ethyl Chloride	Chlorethane	C2H5Cl	.41
Ethylene	Ethene	C2H4	.67
Ethylene Oxide	Epoxyethane	C2H4O	.61
Fluourine		F2	.93
Fluoroform	Freon 23,	CHF3	.57
	Trifluoromethane
Freon 11	Trichlorofluoromethane	CCl3F	.35
Freon 12	Dichlordifluoromethane	CCl2F2	.36
Freon 13	Chlorotrifluoromethane	CClF3	.42
Freon 13Bl			.40
Freon 14		CF4	.48
Freon 22	Chlorodifluoromethane	CHClF2	.43
Freon 114	Dichlorotetrafluorethane	C2Cl2F4	.22
Freon 116	Hexafluoroethane,	C2F6	.28
	Perfluoroethane
Genetron 21			.46
Genetron 115	Chloropentafluoroethane	C2ClF5	.27
Germane	Germanomethane	GeH4	.63
Helium		He	1.43
Hydrogen		H2	1.03
Hydrogen Bromide		HBr	.98
Hydrogen Chloride		HCl	.99
Hydrogen Cyanide	Formonitrile	HCN	.79
Hydrogen Fluoride		HF	1.00
Hydrogen Iodide		HI	.94
Hydrogen Selenide	Selenium Hydride	H2Se	.81
Hydrogen Sulfide		H2S	.82
Isobutane	2-Methylpropane,	CH(CH3)3	.30
	Trimethylmethane
Isobutylene	Isobutene,	(CH3)2C:CH2	.32
	2-Methylpropene
Krypton		Kr	1.39
Methane	Methylhydride	CH4	.69
Methanol		CH3OH	.58
Methyl Acetylene	Allylene, Propyne	C3H4	.49
Methylamine	Aminomethane,	CH3NH2	.56
	Monomethylamine
Methyl Bromide	Bromomethane	CH3Br	.64
Methyl Chloride	Chloromethane	CH3Cl	.68
Methyl Fluoride	Fluoromethane	CH3F	.75
Methyl Mercaptan	Methanethiol	CH3SH	.58
Methyl Trichlorosilane		SiCl3CH3	.25
Neon		Ne	1.39
Nitric Oxide		NO	.99
Nitrogen		N2	1.00
Nitrogen Dioxide		NO2 or	.44
		N2O4
Nitrogen Trioxide		N2O3	-
Nitrogen Trifluoride		NF3	.55
Nitrous Oxide		N2O	.75
Oxygen		O2	.99
Pentaborane	Bornhydride	B5H9	.18
Pentane		C5H12	.22
Phosgene	Carbonyl Chloride	COCl2	.50
Phosohine		PH3	.79
Propane		C3H8	.32
Propylene	Propene	C3H6	.45
Silane		SiH4	.68
Silicon Tetrachloride		SiCl4	.33
Silicon Tetrafluoride		SiF4	.39
Sulfur Dioxide		SO2	.71
Sulfur Hexafluoride		SF6	.28
Tetrafluoroethylene		F2C:CF2	.36
Titanium Tetrachloride		TiCl4	.28
Trichlorosilane		SiHCl3	.39
Trimethylamine		(CH3)3N	.30
Tungsten Hexafluoride		WF6	.23
Uranium Hexafluoride		UF6	.24
Vinyl Bromide	Bromoethene	C2H3Br	.51
Vinyl Chloride	Chloroethene	C2H3Cl	.54
Vinyl Fluoride	Fluoroethene	C2H3F	.62
Water Vapor		H2O	.79
Xenon		Xe	1.37