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Equipment Description and Operating Instructions for Plasma Therm Metal Etcher (pt-mtl)

PT-MTL is an ICP (Inductively Coupled Plasma) etch system configured for metal etching. It is a single wafer etcher with a load lock. The equipment can be configured to etch either a 4” or a 6” wafer. Thanks to superuser Usha Raghuram for these instructions.

Plasma Therm Metal Etcher Information and Operating Instructions

PT-MTL is an ICP (Inductively Coupled Plasma) etch system configured for metal etching using Cl or F chemistries.  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 interometer and optical emission endpoint.  A camera is also available for substrate observation.

Picture and Location

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

Insert fab image here.

 

Background

Overview:

The PlasmaTherm Versaline ICP Etch system is a high density plasma (HDP) etch system for metal etch applications. The most important characteristic of this system is that there are two power sources, a 2 MHz inductively coupled plasma (ICP) power and a 13.56 MHz bias power.  This allows separate control of the plasma density through the top coil (ICP) and the sheath bias through the lower electrode (bias power).  When the bias power is applied to the substrate or carrier, a self-bias DC voltage builds up on the substrate surface, independent of the substrate surface (conductive or non-conductive), thereby enabling etching of any material (conductive or non-conductive).

In the plasma processing world HDP means having at least 2 sources of plasma power. The first is used to generate the plasma, and is what is called a non-capacitive coupled source, such as inductively coupled (ICP) or ECR coupled, where power is transferred or coupled to the plasma without causing the voltage difference between the plasma and the wafer to be above about 50 V. This first source controls the plasma density (number of ions per cc) in the plasma and thus controls the ions flux (ions per sq cm per sec) bombarding the wafer. The second power source is connected through the wafer chuck/electrode and is capacitive coupled (CCP). This second source is often referred as the bias power in that it is used to control the voltage between the wafer and plasma. This voltage between wafer and plasma is important, it controls the energy and directionality of the ions bombarding the wafer surface. Thus, with high density plasmas we have the ability to control both ion flux and ion energy independently. Sometimes additional power sources are added to control the energy distribution of the ion for fine control in etching.

Plasma-Therm ICP Etcher – Power Sources:

The Plasma-Therm ICP source has a cylindrical coil configuration.  In this configuration, an inductive coil encircles a dielectric vessel.  The coil is connected to 2 MHz RF power source.  When the coil is powered, a strong RF magnetic field is generated in the center of the chamber which in turn generates a high density plasma.  The lower electrode is powered by a 13.56 MHz RF generator as in an RIE (Reactive Ion Etch) for independent control of substrate bias voltage.  A schematic is shown in Figure 1. Typical operating pressures are less than 10 mT in these systems.

 PT-MTL Chamber

Figure 1.

The Process Module: 

In addition to the two RF power sources, the process chamber (Figure 2) is supported by a gas box, vacuum system and temperature control units.  The process module is connected to a load lock by a slit valve (VAT valve). Both the process chamber and the lid are made of Al.  The chamber lid also houses the ICP coil, endpoint hardware and gas distribution hardware.  The chamber lid, chamber walls and bottom electrode are all fitted with heating and cooling coil channels. 

The system has a mechanical ceramic clamp which is used to hold the wafers down tight to the electrode.  He is used to fill the space between the wafer and the electrode  and acts as a thermal transfer media.  The electrode has no lip seal (o-ring) so the He pressure is limited to 4 Torr and requires very smooth backsides.  Due to sticking issues edge exclusion is required.  The is best achieved by using EBR (Edge Bead Removal) during resist coat.

PT-MTL System

Figure 2.

Load Lock:

Wafer/ Substrate is loaded onto the load lock module (Figure 3) and is transferred to the process chamber under vacuum.  The load lock is equipped with an automatic loading mechanism and is connected to the process chamber by a VAT valve.

PT-MTL Load Lock

Figure 3

Process Capabilities:

List to be added here.


Cleanliness Standard:

PT-MTL is a gold contaminated tool.


Performance of the Tool:

List to be added here.


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 
  • 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:

  • Process wafers with sticky surfaces.  They stick to the clamp.
  • 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, Jim Kruger
  • Maintenance: Elmer Enriquez, Cesar Baxter
  • Super-Users: Usha Raghuram

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.

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.

General Information on Plasma Therm Versaline Software

At SNF there are four Plasma Therm Versaline etch and deposition systems and they share a common software platform. Differences between them will be noted in the operating instructions. Here's a link to information about the software system.

A process sequence is a recipe that is made up of several process steps. It gives information like gases, min/max flows, set points for RF, etc. Be warned that once you change a value in a process steps that value will be changed for all the steps with the same name. To be safe, if you copy a step be sure to give it a unique name.

Operating Instructions for Plasma Therm Metal Etcher:

  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. Enable 'PT-MTL'.
  5. Make sure that there are no active alarms on the system, the modules are initialized and the chamber is empty (refer to the picture below – Figure 4).
  6. On the Jobs/Jobs Start screen load the desired recipe and click on the Go To Recipe Temps button.  This will set the tool to the temps required for the recipe, saving time.
  7. Check that the system is in PRODUCTION Mode as displayed in the Status bar (top of the screen).
  8. If it is MAINTENANCE Mode you will need to go to Maintain/Mode screen and chose PRODUCTION All Chambers.   MAINTENANCE Mode is used for manually loading and unloading wafers from the Load Lock, for loading the endpoint programs and for viewing the wafer surface using the camera.
  9. Vent the load lock by clicking the “Vent” button under “Lock” control.
  10. Once the load lock is vented, open the load lock door, remove the wafer in the arm and load your wafer. 

PT-MTL Process Module

Figure 4: Process Chamber Status Description

PT-MTL Process Start Screen

Figure 5: Job Start Screen

  1.  Align the flat parallel to the line marked on the arm (away from the chamber). Ensure that the wafer is touching the pins near the flat area.
  2. Close the load lock door.
  3. In 'Jobs/Jobs Start' double check that the correct recipe has been selected from the Recipe list (Figure 5).
  4. Make sure the recipe sequence and recipe steps are correct and have the desired settings.  Instructions on creating/editing the recipe are in a separate section.
  5. Make sure “Process in PM. No Transfer” box is unchecked and “Vent after Job” is selected.
  6. Click on the “Start Job” button to start the processing.
  7. Once the processing begins, details of the process recipe and the process parameters, set points and actuals, will appear on the right side of the Jobs screen.
  8. Click the Jobs/Adjust button to monitor your process.  You have a choice of monitoring three parameters in a real time plot.  Typically, RF forward, reflected and power are plotted.
  9. Monitor the process.
  10. In case the processing has to be aborted, click the command button “Next Step” in the Jobs/Adjust screen.
  11. When processing is completed, wafers will be transported back to the load lock and the load lock will be vented if “Vent after Job” is selected.
  12. Continue with next wafer or if you are finished pump LL.
  13. Fill out log sheet and Disable tool in Badger.

PT-MTL Alarm Screen

Figure 6.  Alarm Screen?

If you get an Alarm During Processing:

<to be written>

Additional Information

Recipe Set Up:

1.      Recipe Sequence is the combination of several Recipe Steps.

2.      In the Plasma Therm Versaline systems the Sequence as well as recipes Steps are stored separately. 

3.      Use “Editors” menu to create/edit/delete recipe sequences and steps.

4.      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.

5.      Always make sure that the recipe parameters are correct before running any process.


Step Editing:

a.       “Step Editor” screen can be accessed directly by choosing the “Step Editor” tab in the editors Menu (Figure 7) or by choosing edit this step in the Sequence Editor screen.

PT-MTL Step Editor

      Figure 7.  Step Editor Screen Editor Menu (Example)

b.      The items that can be set/ changes are Set points, Soft and Hard tolerances for the process parameters.  Min, Max and Units represent tool configuration and cannot be changed.

c.       Steps that are open are listed in the “Open Steps” field.  The step that is highlighted in the “Open Steps” field is the step that is being displayed in the “Editor” and can be edited.

d.      Edit the steps by changing the desired set point or tolerance limits.

e.       Once the changes are completed, the modified recipe step can be saved under the same name (use “Save” command) or under a different name (use Save As command).

f.        If the hard tolerance limit is reached during process, processing will stop and alarm will be posted.

g.       In case of a soft tolerance error, an alarm will be posted, but processing will continue.

Editing a Sequence:

a.       Sequence Editor is used to combine process steps, create new process sequences, edit or delete existing sequences.

b.      “Sequence Editor” screen is accessed from the “Editors” menu by clicking on the “Sequence Editor” tab.

c.       As in the case of “Step Editor” page, the commands (such as Open, Save, Save As, Delete) are at the top right portion of the screen while ate bottom right has Open Sequences.

d.      Sequences display step names as well as the set points in each step.

e.       In order to create a new sequence, one can start with the new command or load an existing sequence and save it under a new name and modifying.

f.        Once a sequence is loaded, click and hold on the cell at the head of process step you want to edit and choose the desired option from the pull down menu.  The options in the pull down menu are:

                                                              i.      Replace this step

                                                              ii.      Insert a new step

                                                             iii.      Remove this step

                                                             iv.      Edit this step

g.       Choose the appropriate option from the pull down menu as shown in the following example (Figure 8).

PT-MTL Sequence Editor

Figure 8:  Replacing a Process Step in a Sequence

h.       In case, edit this step option was chosen, then the step editor screen opens up for editing the chosen step.  Make the desired changes and either save the step under the same name or a different name.

i.         If a new name is chosen for the modified step, then make sure that the original step name has to be replaced with the new step name in the sequence.

j.        Once the changes are made save the sequence either using the “Save” command or “Save As” command depending on whether the same sequence name is retained or a new sequence name is desired.

Recipe Sequence Example:  Al Etch Recipe

 Process Parameter

 Units

Stab

Light1

Light2

Main Etch

Post Etch
Corrosion

Time

seconds

10

3

3

1800

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:

<to be written>


Pre and Post Etch Conditioning of the tool:

<to be written>

 

Special Considerations for use of the Tool

 

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

Tool Qualification Run

Frequency

Quals are run after major repairs to the system, when a labmember reports a variance from normal results and on a routine basis.

Procedure <work in progress>

Description of test wafers- Al on ox, patterned ox, patterned bare Si.

Description of recipe using timed etch and using endpoint etch.

Description of measurement procedures- nanospec, woollam, alpha step, prometrix

Description of recording of results- badger, wiki, MES Enterprise

Responsibility

Quals may be run by concerned labmembers before running critical processes or as a measure of tool functionality. Staff members will run quals routinely or as needed or requested.

Recommendation to users with critical processes

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

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.

Process Monitoring 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



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