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Drytek2 Model 100, drytek2

The Drytek plasma etchers at SNF all use chlorine and fluorine-based chemistry for etching various Si, polysilicon, nitride, tungsten, tungsten silicide films. Drytek4 (contaminated) also has additional capabilities for oxide etching and argon sputter etching.

Picture and Location

Drytek2
 

Background

 Features:

  • Low energy etching for minimal substrate damage.
  • Excellent selectivity, e.g., 20:1 poly Si:SiO2
  • Laser interferometer for etch rate determination and end-point detection.

 (Please note that there is a two-hour limit on reservation length on this tool during prime time [8 am - 6 pm, Monday through Friday]).

 

Process Capabilities

Cleanliness Standard

 

Drytek2 is considered clean, semi-clean and contaminated.  The bottom two of six electrodes have been converted for contaminated work, while the top four are clean/semi-clean.

 

Performance of the Tool

What the Tool CAN do

Standard recipes for nitride, poly, Ti, W, and Si, resist hardening, O2 descum of patterned resist, and polymer stripping.

 

What the Tool CANNOT do

Drytek2 is not a resist stripper because of it's low power.  An alternative for semi-clean resist stripping is gasonics.

It should not be considered for oxide etching either.  Alternatives for semi-clean oxide etching are amtetcher and p5000etch.

 

Contact List and How to Become a User

Contact List

The following people make up the Team Drytek2:

  • Process and Training Staff: Nancy.  Please consult with the Training Calendar to determine scheduled sessions.
  • Maintenance:  Elmer, Cesar, Mike Dickey
  • Super-Users:  TBD

 

Training to Become a Tool User

 Please consult with the Training Calendar to determine scheduled sessions.

Contact Nancy once you have chosen a session you'd like to attend.

Operating Procedures

 

Please note: As of Sept 2011 new operating instructions are in effect;

 

Before you use drytek2 please read the new operating instructions located in the blue book and on the wiki..  They contain a new, as of 9/8/2011, RF tuning procedure.  The changes have been underlined or italicized to highlight them.

 

In addition, there is a new log form for you to fill out at the end of the etch.  You will be asked for the coil and cap settings.  They can be found by looking on the coil and cap tuning pots (the black knobs used to tune the RF).  We want to collect this information so that users of the tool can refer back to the last settings used for a given recipe and plug them in to ease the RF tuning procedure.

 

Lastly, we are requiring the labmembers turn the RF power level to zero after using the tool.  This will limit wear and tear on the RF power supply.  We also ask that users tune the RF at a much lower power (40W) before turning the RF to the full power desired.  This procedure is covered in the new operating instructions.

 

 

Function

Drytek2 is a plasma etcher for etching nitride, poly, Ti, W, and Si. It is also used for resist hardening O2 descum of patterned resist, and polymer stripping.

Overview: Drytek2 has six etch electrodes and uses SF6, CHClF2, CF4, and oxygen. See the process and etch rate chart for the processes allowed in this machine. Any process not listed, must be approved by SpecMat.

 

Special Notes or Restrictions

Non-metals and standard metals (Al, Ti, and W) are allowed in Drytek2 (See the MATERIALS section for material and equipment compatibility).

 

General Information

Pre-treatments:

  • No pre-treatment is required.
  • However, if the sample backsides cannot be exposed to the plasma (etched), the backside(s) must be coated with the standard svgcoat program (1 um of resist).

 

Post-treatments:

  • No post-treatment is required.

 

Gas Information:

Gas Switch #

Chemical Symbol

Chemical Name

Maximum Flow

1

CF4

Freon 14

84 sccm

2

SF6

Sulfur Hexafluoride

280 sccm

3

CHCIF2

Freon 22

240 sccm

4

O2

Oxygen

200 sccm

  •  The Main system electronics are ON at all times.
  • The Vacuum pumps are located in the basement and are ON.

 

Button Information

MICRO RESET

  • Resets the microprocessor memory. Always push before pushing CYCLE START. Do not push MICRO RESET at any other time. Push (the blue light comes on) and release the button. MICRO RESET does not work unless the button pops back out (the blue light goes out).

 

CYCLE START
  • Starts the microprocessor program. Always check the error message panel before pressing CYCLE START. If the LED's are red, the machine is not ready to start.


CYCLE HOLD

  • Holds the microprocessor at the current step in the program.
  • If the program is running, the timer continues timing, the plasma continues etching.
  • Press a second time to end the CYCLE HOLD. If the time is up the etch ends


CLEAR WAFER
To end a process before the timer has timed out:

  • When press a CLEAR WAFER, the plasma will stop, gases will be pumped out of the chamber, and the chamber will be vented.
  • CLEAR WAFER also allows you to end one process before the time is up and advance to the next process. 

STAND BY
  • Introduces N2 at the back of the chamber to prevent oil back-streaming.
  • To use STAND BY the drytek2 must be enabled.

 

Operating Procedures

Check Standby Conditions:

  • Check the Reservation page and the machine status (problems, shutdowns) on the computer lab management system.
  • Enable “Drytek2”.
  • Check the top panels.
  • White PROCESS select buttons (1, 2, 3) – OFF.
  • Pressure ~200 mT.
  • CYCLE START, CYCLE HOLD, and CLEAR WAFER buttons – OFF.
  • Green STANDBY light - ON.
  • Pull lightly on the Chamber door (it should not open).
  • Check the lower left panels.
  • Machine button – ON.
  • System button – ON.
  • Mechanical Pump button – ON.
  • Blower button – ON.
  • If any of these 4 buttons are not on, DO NOT proceed. Notify the maintenance technician via coral.
  • RF Power Supply toggle – OFF.
  • RF power level pots (the black knobs above the timers) should all be set to Zero.
  • Cooling water flow should be ~ 1 GPM
  • Check behind the machine: Gas Whitey valves - OFF.

 

Setup and system check:

Always run a test process before loading your wafers. There are two reasons for this. First, you need to set up the matching network so the rf generator does not see excessive reflective power, which will shorten it life. The second reason to “season” the chamber is that seasoning brings the chamber surface chemistry to equilibrium with the process being run so your process stabilizes quickly after the plasma is turned on. Seasoning leads more repeatable etching results.

 

  • In the process logbook find a recent listing of the setup parameters for the process you want to run. The parameters you want are the process step number ( 1, 2 or 3), the gas flow settings, the pressure, the coil and cap setting and the rf power. If you are developing  a new process, find a similar processs listing so you have initial valves for the coil and cap settings.
  • Push the STANDBY button to vent the chamber. (Green light off)
  • Look at the DRYTEK2 PROCESSES WITH ETCH RATES sheet in the binder or on the website and choose the appropriate process.
  • Select the appropriate white PROCESS button(s).
  • Select the gases to be used for each process.
  • Push the DIP rocker switches (located in the center of the control panel), for each gas needed; to the right (OPEN) (Left = Process 1; Middle = Process 2; Right = Process 3).
  • Turn the desired gases ON at the wall behind drytek2. Rotate the gas Whitey valve of the desired gas from the OFF position toward the chosen gas label.
  • Set the mode toggle switches to "time."
  • Set the time in minutes (left two digits) and seconds (right two digits).
  • Unlatch the chamber door. Make sure inside the chamber is clean.
  • Turn on the RF power supply (the black box on the load station will light up).
  • Set RF power level pot to 0.40 (40w) for each process step to be used. 
  • Check that the sensing element for the Bird meter (located above the tuning pots) is turned to the correct direction to measure reflected power and that the element is the correct size, which is 50W.
  • There is a RF Network Matching Box located at the lower right panel. Make sure the Toggle switch in manual mode. The purpose of the matching box is to transform the plasma impedence to 50 ohms so we get the maximum power transferred efficiency from the rf generator to the plasma.
  • Run a system check with no wafers in the chamber to verify that gas flow(s), pressure, power, and RF tuning are correct.
  • Make sure CYCLE HOLD, CLEAR WAFER, and STANDBY buttons are off.
  • Make sure the door is latched.
  • Push MICRO RESET.
  • Push CYCLE START.
  • Check for stabilization of gas flows and chamber pressure. Adjust as necessary.
  • The plasma should light when the timer counter starts. If the turning/matching is way off, the plasma may not light, which is ok at this point.
  • Use the bird meter (located above the tuning pots) to monitor the reflected power.
  • Start the turning process by first very very slowly adjusting the coil pot for the process step being run.  Slowly move the pot in the direction that lowers the reflected power. If you turn the pot too fast, the coil rotation will not keep up and you will overshoot the minimum.  You actually want to go slightly past the minimum so you will not end up at a local minimum.  If you can get below 5 w of reflected power,  you can increase the forward power level using the power level pot  for the the process step you are in.  You can monitor the power level using the top readout on the black box. When increasing the power keep the reflected power below 15w on the Birdmeter.
  • After the first adjustment of the coil pot go to the cap pot for your process step. Again move the pot in the direction which reduces the reflected power. Again you want to go slightly pass the minimum to avoid ending upm at a local tuning minimum.
  • Continue going back and forth between the coil and cap pots to lower reflected power. Everytime to go below 5w you can increase the forward power until you get the power level needed for your process.
  • Note the final RF pot set points on the logsheet.
  • If more than one process is to be used, adjust the flows and pressure and power during those steps. Push "CLEAR WAFER" while RF is on to advance to the next process or to end a process before the time is up.
  • Check that plasma color is correct for gas flowing.
    • a) O2 - silver
    • b) Freon 14 (CF4) and O2 - light blue
    • c) Freon 22 (CHClF2) and O2 - light blue
    • d) Freon 22 (CHClF2) and SF6 - light blue
    • e) N2 - pink (indicates a possible leak)
    • f) SF6 - deep purple

 

Etch Procedure:

  • Push CLEAR WAFER to abort the process.
  • Open the chamber door and place the samples on the electrode plate(s). The 4 pins should prevent the samples from sliding off the plate.
  • Close and latch the chamber door.
  • Set the desire process time.
  • Push MICRO RESET.
  • Push CYCLE START.
  • Monitor the gas flows, pressure, and RF power during the etching process.
  • When the process is complete, the system will evacuate the gases and purge the N2 to vent the chamber. The door will pop out once it’s vented. Open the door and remove the sample.
  • Repeat the etch procedure until all samples are etched.

 

Shutdown Procedure:

  • Turn all the rf power level pots to zero.
  • Turn all white PROCESS buttons OFF.
  • Push STAND BY button (green light goes on; you will hear no sound).
  • Push MICRO RESET
  • Push CYCLE START (you will hear a hissing sound).
  • Pull lightly on the chamber door (it should not open).
  • Turn off whitey gas select valves in the back of the system.
  • Turn the RF Power OFF (white toggle down; the red light goes OFF).
  • This leaves the system in the standby condition.
  • Close all three doors.
  • Disable "drytek2"

 

Drytek2 Etcher Training Check list

This check list represents the basic knowledge of the tool that new users should have.

 

  • Know the contamination level of the specific drytek etch system.
  • Know stand-by conditions.
  • Know the functions of the various buttons.
  • Understand gas manifold and be able to turn on desired gases.
  • Know how to turn on RF power supply.
  • Know how to set and readout process timer.
  • Know how to select correct gases to flow into chamber using dip switches.
  • Know how to adjust gas flows.
  • Know how to adjust chamber pressure.
  • Know how to set RF power level and be able to read out power.
  • Know how to tune RF matching network.
  • Know how to stop an etch before it has timed out.
  • Know how to drain a gas if you are using a shared line.
  • Know how to put the system back into stand-by mode.

 

Drytek2 Recipes and Etch Rates

 Standard Recipes and Etch Rates for Drytek2

Additional Information About Recipes 

  • ASML First Layer Targets- Use the Poly Etch for 30 seconds to create ASML targets (1200A)

 

Process Monitoring and Machine Qualification

Tool Qualification Run

Purpose: to provide verification and trend of the poly program including etch rates of poly and photoresist, selectivity of those materials, and wafer-to-wafer and within-a-wafer uniformity of etch.

 

Frequency of the test: to be completed after major maintenance such as cleaning or gas line replacement or on a set schedule to be determined or as needed based on user feedback.  Users of the tool should perform the process qual before committing critical wafers to the tool.

 

Documentation of results: to be posted on the log sheet located in the assigned book at the tool, posted in the equipment archive for drytek2 on the SNF website and in a file or webpage available to users in data or chart format.

 

Procedure: Use six wafers, one for each electrode.  Patterned Si line-width test wafers may obtained from the photolithography area.  The should have the resolution mask in 3612 resist.

  1. Season the chamber for 10 minutes using the poly etch program.  Be sure to check the program parameters while seasoning.
  2. Measure photoresist thickness using one of the Nanospecs.  Be sure to use reference wafer before testing to calibrate the tool.  Take readings for the Center, Top, Flat, Right and Left positions of the wafer.  Use the statistics option to get averages. Readings should be taken about 15mm from the edge.  See Fig. 2.  Record results on the Process Qualification Log Sheet.
  3. Place the wafers on the electrodes.  See Fig. 1.
  4. Etch for 10 minutes.  Monitor gas flows, RF power and reverse power.
  5. Measure  photoresist thickness using the same Nanospec.  Be sure to use reference wafer before testing to calibrate the tool.  Take readings for the Center, Top, Flat, Right and Left positions of the wafer.  Readings should be taken in roughly the same place as the first measurements.
  6. Record results on the Monitor Log.  Record results in data file to get wafer-to-wafer and within-a-wafer
    • Subtract the second average reading from the first average reading for poly and for photoresist to get total material etched
    • To get the etch rate per minute divide the average total material etched measurements by 10. 
    • To get the selectivity for Si vs photoresist divide the Si etch rate by the photoresist etch rate
  7. Strip the resist off the wafer using either the Gasonics of Matrix ashers.  Use the Zygo system to determine the amount of Si etched.  Divide the results by 10 to get the Si etch rate.

 

<insert picture of electrodes with wafers>

<insert picture of reading placement>

 

Machine Status States

Red:  A major sub-system of the tool (RF power supply, Mass Flow Controller, vacuum pump, etc...) is not functioning up to standard or a process qual is out of specification.

Yellow: A sub-system or component of the tool not common to all recipes is not at specification, for example, RF tuning for 2 plasma is out, or a gas is being replaced.

Green:  System has past process qual and tool is running at specification.

 

Process Monitoring Results

 

For recent process qualification results click here.

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