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PT-MTL - Capabilities, Specifications and Operation

Additional information specific to PT-MTL is given in this section.

Picture and Location

PT_MTL

The tool is located in the C area next to Innotec.

Equipment Locations (gif)

 

Background

 PlasmaTherm Metal Etcher (PT-MTL) is an ICP (Inductively Coupled Plasma) etch system configured for metal etching using Cl or F chemistry.  It is a single wafer etcher with a load lock.  The equipment can be configured to etch either a 4” or a 6” wafer.  It has both laser interferometer and optical emission endpoint.  A camera is also available for substrate observation.

 

Process Capabilities

Cleanliness Standard

PT-MTL is a flexible tool belonging to the "contaminated" group.


Performance of the Tool

What the Tool CAN do

  • System is mainly used for metal etch applications. It has both fluorine (CF4) and chlorine (Cl and BCl3) source gases.
  • Can etch 4” or 6” wafer – make sure the equipment is in the correct configuration for processing.  Conversion between substrate sizes take approximately 3 hours.
  • Can be used for processing pieces – make sure the pieces are attached to a carrier wafer; ensure that pieces do not extend into the clamp region (5 mm from edge of the wafer).

 

What the Tool CANNOT do

  • Wafers with resist or particles on the back of the wafer are not allowed as it will cause wafer breakage/ backside He errors.
  • Wafers with no EBR are not allowed in the etcher.  2mm EBR for thin resist (<2um) and 5mm EBR for thicker resist is required to prevent wafers from dropping in the chamber.
  • Transparent wafers are currently an issue for processing.  Here is a procedure on How to Process Transparent Wafers.

 

Contact List and How to Become a User

Contact List

The following people make up the Tool Quality Circle:

  • Process Staff: Nancy Latta, Jim McVittie, Usha Raghuram
  • Maintenance: Elmer Enriquez
  • Super-Users: Jim Kruger

 

Training to Become a Tool User

  • Consult the training calendar for a training session that is convenient to attend.  
  • Contact the appropriate staff member or super user.
  • Read the training materials.

**Shadowing a qualified user prior to the training session is highly recommended and will speed up your understanding of the tool.

 

Operating Procedures

Process Parameters/Limits

·        Process pressure, Max = 100 mTorr

·        Backside He Pressure, Max = 10 Torr

·        Bias Power, Max = 600 Watt

·        ICP Power, Max = 1200 Watt, min 200W

·        Electrode Temp, Max = 60°C, Min = 10°C

·        Lid Temp, Max = 180°C

·        Liner Temp., Max = 180°C

·        Spool Temp., Max = 180°C

·        Cl2, Max Flow = 114.2 sccm

·        BCl3, Max Flow = 119.55 sccm

·        O2, Max Flow = 96.6 sccm

·        SF6, Max Flow = 103.6 sccm

·        Ar, Max Flow = 98.1 sccm

·        CF4, Max Flow = 101.8 sccm

·        CH4, Max Flow = 135.7 sccm

·        N2 , Max Flow = 194.0 sccm

More parameter information for the PT-MLT system can be found here.  This is a link to the default Process Step page in WIKI.

 

System Components

  • Load Lock.
  • Reaction Chamber.
  • Process Monitor/Control Computer.
  • Mechanical Pumps – located in basement.
  • Heat exchanger – located next to the tool.
 

Additional Operating Instructions

Specifics to PlasmaTherm are in this section:
  1. PT-MTL can be used to process either 4” or 6” wafers. 
  2. Both the bottom electrode chuck and the transfer arm have to be set to the correct wafer size configuration. 
  3. Verify the tool configuration and status in Badger before running your process. 
  4. Follow the link for general operating procedure for all PlasmaTherm etchers: Plasma Therm Etchers - General Operating Procedure
  5. Note that Recipe Sequence is a combination of several Recipe Steps and that in the Plasma Therm Versaline systems the Sequence as well as recipes Steps are stored separately. If a recipe step is modified and saved, the changes are effective in all the sequences the recipe step is used even if the sequence is not edited.
  6. Always make sure that the recipe parameters are correct before running any process.


Recipe Sequence Example:  Al Etch Recipe

Process Parameter Units Stab Light1 Light2 Main Etch Post Etch 
Corrosion
Time seconds 10 3 3 60 180
Pressure mTorr 5 5 5 7 10
Cl2 sccm 50 50 50 70 0
BCl3 sccm 50 50 50 20 0
N2 sccm 10 10 10 10 40
Bias W 0 200 200 150 10
ICP W 0 0 1000 1000 500
Electrode Temp C 20 20 20 20 20
Lid Temp C 90 90 90 90 90
Liner Temp C 70 70 70 70 70
Spool Temp C 90 90 90 90 90
He backside P Torr 4 4 4 4 4

 

Endpoint Detection

Chamber Plasma Clean and Warm Up / Conditioning

Etch processes may be impacted by chamber condition and previous processing.  In a R&D facility where the type of materials etched in the tool and the chemistry changes significantly from run to run, it is important to be aware of potential impact on process deliverables and condition the chamber to ensure some level of reproducibility.  Please note that the procedure described below is only a guideline and procedure may have to be optimized for different applications.

1.  Run chamber clean with a bare Si dummy wafer using the recipe “Cham_Clean_Def_Cl2_SF6_O2”.  The recipe has the following steps:

       a.  Chlorine based chemistry.  As metals are typically etched in PT-MTL and most metal chlorides are volatile while metal oxides are not.  Hence a chlorine based clean will be more effective in cleaning the chamber.

        b. The next step is a SF6 based one – to remove materials such as tungsten, which form volatile fluorides.

        c.  The last step is a O2 clean to remove organics.

2.  Condition the chamber with a bare Si wafer and the recipe to be used for processing device wafers (~ 5min plasma on time).

3.  Process device wafers.

 

Special Considerations

Transparent Wafers (quartz, pyrex, sapphire or glass) present unique loading issues.  A procedure for the loading of these substrates can be found here.


Process Monitoring and Machine Qualification

Each month, tool qualification runs are performed on most tools in the SNF to monitor variations in each tool’s performance. The purpose of the PT-MTL qual is to monitor Si, PR, and SiO2 etch rates and selectivity of those materials.  The qual is performed by SUMO members, but users may perform the specified qual process before tool use if more recent qual data is desired for reference.

For more information on the SNF tool performance monitoring system and SUMO, please see the Monthly Tool Monitoring page under the Equipment tab on the SNF wiki.

 

Qual Process Overview

The PT-MTL qual runs three wafers through a 1 minute process of the standard etch program - one wafer with a 1.6um 3612 Photoresist pattern, one wafer with 10,000A SiO2 coating, and one wafer with a 10,000A Al coating. Nanospec measurements are taken before and after etching to calculate the PR and SiO2 etch rate respectively. To calculate Si etch rate and selectivities, the wafer coated in photoresist is then stripped of resist so that the Silicon step height may be measured via Alphastep.

 

Procedure

Wafers for Processing

SUMO Wafer #
(all Si 4" wafers)
Coating Pattern
(using SUMO mask)
1 10,000A Al -
41   10,000A SiO2 -
78  -  1.6um 3612 PR pattern, 1-2 min bake @ 110C 

 

Process

Use one blank Si wafer with 1.6um layer of SPR3612 photoresist with 5 mm EBR and 120sec post bake, one wafer with 10,000A SiO2 unpatterned, and one 10,000A Al on Si wafer with 1.6um layer of SPR3612 photoresist with 5 mm EBR and 120sec post bake. The Si and Al wafers are patterned with the SUMO MASK 2.0.

  1. Measure photoresist thickness of the Si wafer and the SiO2 thickness on the oxide wafer using Nanospec.  Be sure to use the reference wafer before testing to calibrate the tool.  Take readings for the Top, Flat, Center, Left, and Right positions of the wafers.  Readings should be taken about 20mm from the edge. For the Si wafer, measure on the Pos Resist on Silicon program. For the SiO2 wafer, measure on the Oxide on Silicon program.  Record. You do not need to measure the Al wafer as Nanospec does not have a good PR on Al recipe.
  2. Season the chamber for 5 minures using the O2_Clean1 Recipe (00:05:00), running with a blank Si test wafer. Be sure to check the program parameters before starting. Use the step editor to edit the etch time if needed (set the time of the last step, O2_clean_na to 300).
  3. Condition the chamber with the Al-HiPrSel-ERTest Recipe for 5 minutes (set time to 300 like above).
  4. Etch the Si and SiO2 wafers with the Al-HiPrSel-ERTest for 1 minute (change etch time in step 4 to 60).
  5. Etch the Al wafer for 30 seconds with the same recipe (change etch time in step 4 to 60).
  6. Measure post-etch thicknesses using the same Nanospec.  Be sure to use the reference wafer before testing to calibrate the tool. Again, take readings for the Top, Flat, Center, Left, and Right positions of the wafers. Readings should be taken in more-or-less identical spots as the pre-etch measurements. Again, for the Si measure, measure on the PR. For the SiO2 wafer, measure on the SiO2 directly. Record in the Log. You do not need to measure the Al wafer.
  7. Calculate the amount of photoresist and oxide etched. Record.
  8. Strip the Si and Al wafers of photoresist via Matrix (put the Al wafer through a spin/rinse cycle if you are delaying this step--Al corrodes).
  9. Now measure the depth of the etches into the Si (on the Si wafer) using Alphastep. Find a place that has been etched and measure across it. Make sure to LEVEL if the trace is not horizontal. Take readings in about the same 5 places as you took readings from step 1. Once you get consistent readings in each spot, record the measurement in the Log. Repeat with the Al wafer.
  10. Record results on the Monitor Log. Record results in data file to get within-a-wafer uniformity.

 

Qualification Results

Recent qual results will be posted on the lab management system (Badger) and on the Recent Qual Results page


Recipe Conditions

1000W ICP/ 150W BP/ 70 Cl2/ 20 BCl3/ 10N2/ 7mT/4T BSHe/ Electrode 20C/Lid 90C/Liner 70C

To view the full process sequence of the qual recipe click here.

 

Etch Rate Data (3/9/2013)

 Please note; Etch rate and selectivity data is based on etching six inch wafers.  Four inch results should be slightly different.

·         Al Etch Rate = 6208A/min; Uniformity = 10.7%

·         (based on 9 pt Rs measurements; 10mm edge excl; Al  Resistivity = 2.86E-02 ohm-cm)

·         Oxide ER = 964A/min; Uniformity = 6.85% (NanoSpec; Thermal oxide; 9 pt)

·         Photo resist ER = 4727A/min; Unif = 11.9% (SPR3612; 9 pt; NanoSpec)

·         Al:PR Selectivity = 1.31

·         Al: Oxide Selectivity = 6.44

 

Machine Status States

  • Red: Tool is in shutdown due to serious hardware or software issues.  Maintenance staff has been notified.
  • Yellow: Tool has an issue that will allow for the running of some but not all recipes.  For example, a gas not common to all recipes is under repair/observation.
  • Green: All recipes and processes may be run.
 

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