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PT-OX Capabilities, Specifications and Operation

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

 Picture and Location

PT-OX

The tool is located in the C area next to Pt-MTL.

Equipment Locations (gif)

 

Background

PlasmaTherm Oxide Etcher (PT-OX) is an ICP (inductively Coupled Plasma) etch system configured for dielectric etching.  Etch chemistry is mainly fluorine based.  It has both optical and laser endpoint systems.

 

Process Capabilities

Cleanliness Standard 

PT-OX is a flexible tool and so can process materials belonging to "Contaminated" group.

 

Performance of the Tool:

What the Tool CAN do:

  • Etch SiO2, SiN and other dielectrics.
  • Etch high aspect ratio features.
  • Pattern quartz wafers.
 

What the Tool CANNOT do

  • Process sticky wafers.  Wafers will stick to the clamp and cause clamping as well as unloading issues.

 

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 (jimkruger@yahoo.com)

 

Training to Become a Tool User 

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

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

 

General Information about Plasma Therm Versaline Software

PT-Ox Rules of Engagement- Is this the right tool for you?

Here is information that may be used to determine if PT-Ox is the best tool for you work.

  • No metal etching or sputtering is allowed.  One concern is that sputtered metals may coat and hence short out the chamber.
  • Due to the mechanical clamp and the possibility the wafer sticking to it Edge Bead Removal (EBR) is required.  Please refer to the General Operating Procedure for more details.
  • Many users want to etch oxide which will be used as an etch mask for the PlasmaTherm DRIE system (PT-DSE).  Selectivity for various oxides are; ccp SiO300-1 = 200 : 1, ccp SiO350-1 = 400 : 1 (almost as good as Thermal Oxide).
  • For the standard ox etch recipe (jkPRmask OxSTD) the selectivity of photoresist is 1.5 : 1.  The recipe can be modified to achieve 3.5 : 1 but polymer deposition increases and a post etch polymer clean  (seO2Clean-1) is needed to clean the chamber.  Polymer may need to etched off the sample, too.
  • The software that runs the pt-ox is the same as runs three other systems.  It is described here.
  • Here is a typical process sequence step for the pt-ox system.  It contains ranges and min/max for various parameters.

 

 

Process Parameters/Limits

  • Process pressure, Max = 100mT
  • Backside He cooling pressure, max = 10 Torr
  • ICP (3-turn coil) power, max = 3500 W; min = 400 W
  • Bias power, max = 600 W
  • Electrode temp, max = 40 C; min = -40 C
  • Lid temp, Max = 180 C
  • Liner temp, max = 180 C
  • Spool temp, max = 180 C
  • Process gases, max flow
      • C4F8 = 201.8 sccm
      • H2 = 98.4 sccm
      • Ar = 97.3 sccm
      • CF4 = 102.1 sccm
      • O2 = 95.4 sccm
      • CHF3 = 103.5 sccm
      • He = 97.8 sccm
      • N2 = 191.8 sccm

 

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

Purpose

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-OX qual is to monitor SiO2, PR, and Si etch rates, selectivity of those materials, and within-a-wafer uniformity of etch. 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.

 

Frequency 

Quals are run monthly by SUMO. The SUMO member in charge of the tool is Gabriela Lomeli (glomeli4@stanford.edu). 

Quals are also run by labmembers periodically, especially under the following circumstances:

After major repairs to the system. 

When a labmember reports a variance from normal results.


Qual Process Overview

The PT-OX qual runs two wafers through a 1 minute process of the standard etch program - one wafer with a 1.6um 3612 Photoresist pattern, and one wafer with 10,000A SiO2 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)
35   10,000A SiO2 -
85  -  1.6um 3612 PR pattern, 1-2 min bake @ 110C 

 

Process

Use 1 blank Si wafer with 1.6um layer of SPR3612 photoresist with 5 mm EBR and 120sec post bake and 1 wafer with 10,000A SiO2, unpatterned. The Si wafer is 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.

  2. Season the chamber for 10 minutes using the O2 Clean Recipe (00:10:00), running with a blank Si wafer.  Be sure to check the program parameters before starting. Use the step editor to edit the etch time if needed.

  3. Condition the chamber with the OX_ER_TEST Recipe for 5 minutes.

  4. Etch one of the qual wafers (Si or SiO2, order does not matter) with OX_ER_TEST for 1 minute (change etch time in step 3).

  5. Repeat the same etch with the other qual wafer.

  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.

  7. Calculate the amount of photoresist etched from the Si measurements. Record

  8. Strip the Si wafer of photoresist via Matrix.

  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.

  10. 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.

  11. Repeat with the SiO2 wafer.

  12. Record results on the Monitor Log. Record results in data file to get within-a-wafer uniformity.

 

Recommendation to users with critical processes

It would be wise to run the qual before committing valuable samples to the deposition. 

 

Reported Data

Qual data may also be found on the Badger comment log. The following data is reported for the PT-OX qual:

  • SiO2 Etch Rate
  • Si Etch Rate
  • PR Etch Rate (3612)
  • SiO2:Si Selectivity
  • SiO2:PR Selectivity
 

Qualification Results 

Recipe Conditions

  • Recipe Name: Oxide_ER_Test
  • Etch Conditions: 600W ICP/ 50W BP/ 45 CHF3/ 2 O2/ 5mT/4T BSHe/Electrode 10C/ Lid 90C/ Liner 70C/ Spool 90C/ 60sec

 

Etch Rate Data (7/30/2014)

Etch rate and selectivity data on 4" wafers:

    • Silicon dioxide ER = 2010A/min; Uniformity = 6.0% (NanoSpec; 5 points; Thermal oxide - Patterned wafer)
    • Si ER = 803A/min; Uniformity = 2.7% (Step height; AlphaStep; 5 points; Patterned wafer)
    • Photo resist ER = 1009A/min; Unif = 2.7% (NanoSpec; 5 points; SPR3612; Si wafers pattered with 3612 resist)
    • SiO2:PR Selectivity = 2.0
    • SiO2: Si Selectivity = 2.5

 

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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