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You are here: Home / Equipment / Dry Etching / Lam Research 9400 TCP Poly Etcher, lampoly (clean) / Lampoly Operating Procedure

Lampoly Operating Procedure

Lam 9400 TCP Poly Etcher with Envision software; Clean category; for poly and Si etches; maximum etch depth 3um.

Picture and Location

Figure 1 

The tool is located at E4 on the Lab Map.

Background

This LAM Research 9400 instrument, known as a Transformer Coupled Plasma (TCP) etcher, generates a uniform, high density plasma for selective etching of silicon and polysilicon. It has two independent 13.56 MHz RF power supplies which deliver high and low power to the upper and lower electrodes, respectively.  A high density discharge is generated by the higher-power RF supply by inductive coupling of a planar source coil to the gas in the chamber. The coupling occurs through a dielectric window which forms the top of the process chamber. The discharge is produced directly above the wafer surface, providing a uniform, high density plasma without the use of external magnetic fields. The lower-power RF source which powers the lower electrode generates a DC bias voltage at the wafer surface that promotes the vertical directionality of the etch.

The substrate is mechanically clamped to the lower electrode, using back-side helium to facilitate heat transfer between the liquid-cooled electrode and substrate. The adjustable spacing between electrodes is typically set at around 5.9 cm (large compared to early plasma etch systems.) Process gases are introduced around the perimeter of the chamber. A turbo pump allows the system to operate at low process pressures with high gas flows. This combination of process settings (high density plasma, adjustable DC bias, low process pressure, high gas turnover, large electrode gap) allows gases to react with the substrate surface in a controlled fashion at a high mean free path, resulting in near-vertical wall etch profiles.

This is a single-wafer, cassette-to-cassette processing system. The plasma etch chamber is loadlocked on both the entrance and exit sides; this ensures that corrosive process gases and byproducts remain in the chamber or its exhaust system and also minimizes oxygen and moisture that will adversely affect the process.

When introduced in 1992, the LAM TCP Series of etchers quickly became an industry standard, known for high throughput, etch reproducibility/uniformity, and reliability, at an economical price over other comparable tools. 

Process Capabilities

Cleanliness Standard

 The lampoly system is in the "clean" equipment group.  Any nonstandard, non-clean materials or other nonstandard processing should be cleared through SpecMat first.

Performance of the Tool

What the Tool CAN do

  • The lampoly system is capable of etching silicon and polysilicon with high selectivity to oxide (~20:1) and photoresist (~3.8:1) and yielding structures with nearly vertical and very smooth sidewalls.  

  • In comparison with DRIE etchers, the lampoly process is much slower and not meant for deep etches (more than a few microns).  However, the smooth sidewall does not exhibit the periodicity of DRIE cycling which can be important in some applications.

  • The lampoly also incorporates a dual wavelength optical endpoint system, and can terminate process on an etch stop with minimal damage to the underlying oxide or nitride layer.

 

What the Tool CANNOT do

  • The lampoly cannot be used for deep etching of silicon.  Not only is a long etch time-consuming, but more importantly, it will accumulate excessive polymer buildup on the chamber walls, which will redeposit on wafers, resulting in black contaminant which cannot be removed.  Long etches, particularly those using HBr-only recipes, must be interspersed with cleaning cycle etches.  See Additional Operating Instructions.

 

Contact List and How to Become a User

Contact List

The following people make up the Tool Quality Circle:

  • Process Staff:  mtang, usha
  • Maintenance:  eenriquez, mdickey
  • Super-Users:

Training to Become a Tool User

 Please follow the procedure below to become a qualified user on Lampoly.

  1. Read all material on the SNF website concerning Lampoly. This includes, but is not limited to, this manual. Read enough to know your processing steps before and after using this tool.
  2. Find a Lampoly user to "shadow" while they operate the tool. You are responsible to be with that user for the full time they are operating the tool. It would be a good idea to ask questions and become as familiar as possible with Lampoly during this "shadowing."
  3. When you and the user you have shadowed both agree you are ready for your final training / certification with the process staff, send email to be added to the next training session. BE SURE TO CC THE USER YOU SHADOWED ON YOUR EMAIL.
  4. In the final training session, you will demonstrate your familiarity of normal equipment operation, as well as understand the machine status states (red, yellow, green) stated in this manual.
  5. Upon completing the final training, you have full access to use Lampoly.

General Description of Lampoly (Lam 9400 with Envision controller):

The Lam 9400 Envision controller screens have the standard layout as shown below.

Figure 2

The machine status and any alarms will appear at the top header. 

The footer menu bar lists the different “page groups” available, with the current one highlighted.  Within each “page group” are several related “pages” which are selected from the Menu button box at the far right of the menu bar.  To navigate between pages, select the “page group” and then use the Menu button to select the individual page.  The name of the specific page will appear just under the Help button at the top right.

Figure 3

Operating Procedure 

  1. Check machine status on Badger. Note any problems and comments.

  2. Enable lampoly on Badger.

  3. Clear the ALARM. Go to the Alarm (page group) and select Clear.  The lampoly is interlocked on Badger through the gas box, so alarm 00-0314 will appear whenever the machine has been disabled on Badger.
  4. Login (top right corner of the Operate Screen) - 
    1. Username: process
    2. Password (no password; just press enter):
  5. Check your recipe.  Go to the Recipe (page group), menu page Editor. The current recipe appears on the “Recipe Name” bar near the top.  To select a different recipe, select from one of the “Open Recipes” box on the right.  Or, if it does not appear there, select “Open” option just above and select the recipe to open.  If you wish to create your own recipe, use the “Save as” option and enter a filename.  Make sure it is correct, as someone may have saved over it.  DO NOT save over the standard recipes.

  6. Load your Recipe. Go to the Operate (page group), menu page Control Panel PM1.  Click Select Recipe to choose and load your recipe.  Make sure it appears in the “Current Recipe” window.

  7. Warmup the chamber.  Blank silicon dummy wafers are used to warm up and condition the chamber. This is not necessary, but recommended. This allows you to check the machine to ensure it is functional. Warm up can be done either using the “Condition” recipe or the recipe to be used for processing the wafers.

  8. Place wafers in a metal cassette and place on the sender (left-side) stage. It is not necessary to align the flats. Make sure the H-Bar of the cassette is down and hits the switch on the loading stage. It is best to tilt the cassette back slightly, align the two edges of the back of the cassette with the red pins on the loading stage, then gently drop the cassette forward. When the switch is tripped, the stage will drop down.

  9. Place a metal cassette on the receiving stage (right-side).  It should drop down automatically. If a cassette is on the stage, but all the way up, no wafers will be received. Just tilt the cassette back and gently drop it forward so that the H-Bar hits the stage switch. The receiver stage should drop down.

  10. Start load and process by selecting the "START" button on Operate (page group), menu page Control Panel PM1.  After a couple of minutes of system self-checks, a wafer will load.

  11. Monitor your process.  Go to the Process (page group), menu page Main Chamber PM1 page. You can monitor the progress of your wafers through the system and in the processing chamber from this page.  Green buttons indicate parameters are within control limits.  Red buttons indicate parameters are outside control limits, which occurs when parameters are undergoing change from one step to another (normal) or if there’s a problem.

  12. Place your wafers in the sender cassette after dummy wafers have been processed, Make sure the output cassette is indexed down and ready to accept processed wafers.

  13. Monitor the process frequently. Make sure to note any alarms, if they occur, particularly the yellow warnings.  Make sure to note the alarm number.

Additional Operating Instructions

To avoid excessive HBR-polymer deposit on the etch chamber walls, deep etching of silicon or polysilicon is limited to a single session of about 2.5 microns in depth. Immediately after each session, run a "Clean" recipe on a SiO2 or a sapphire wafer.   

Process Recipes

Some of the recipes set up in Lampoly are given below.  Use these recipes as starting points to create your own recipes.   DO NOT save over these recipes. It is recommended to check any recipe before running your wafers.

Altering/Writing a New Recipe

Any time you wish to change gas flows or the chamber pressure, you must have a stabilization step before you turn on the RF power. A stabilization step runs until either 1) the process conditions stabilize and fall within a tolerance level of the set point, or 2) the time allotted (e.g. 20 sec) runs out. Realize that the second case is indicative of some error in the recipe or the machine parameters and will result in a“yellow” alarm state.

The He Clamp must be off during step 1. If you turn the backside He on before the wafer is clamped, it will fly off the chuck. There should also be an unclamp step after processing. The last step is always END.

After altering a recipe, you may save it. Do not save over standard or user recipes.

About the Process

The standard etch process was designed for etching polysilicon over thin gate oxide although many lampoly users use this and variations of this for a wide variety of applications. The typical CMOS polysilicon Lam etch consists of three parts:

  1. Breakthrough Etch: The purpose is to remove native oxide on the silicon. Because of the selectivity of the Main and Overetch steps, even native oxide may prevent etching of underlying silicon by micromasking subsequent etching.
  2. Main Etch: This is a fast, selective, highly anisotropic etch which is responsible for the bulk etching of polysilicon. The mechanism of the Main Etch involves a fine balance in chemistry between bulk etching of silicon and preferential by-product deposition (and protection) on the sidewall of etch trenches to yield the anisotropic profile. Because the Main Etch is quite selective, any contaminant and even native oxide can lead to micromasking of the Main Etch (apparent as tiny speckles under dark field microscopy); thus, the short, lower selectivity “Breakthrough Etch” is run before the Main Etch.
  3. Overetch: This etch process has even greater selectivity of polysilicon to silicon oxide. Because the Main Etch strongly depends on the diffusive transport of reactants to, and byproducts from of the wafer surface, there are local variations in etch rate. What results is a “rainbow” of colors outlining the etched areas as the poly film begins to clear (over an underlying oxide etch stop) with smaller areas showing more fringes than larger open areas. To ensure that all areas of poly are clear with minimum attack of underlying oxide (usually a thin gate oxide in a CMOS process), an “Overetch” is performed after the Main Etch.

For an excellent series of tutorials on plasma etching – and Cl2/HBr etching in particular, visit the Clarycon website at: http://www.clarycon.com.

Poly_etch_timed: (Standard poly etch recipe with break through main and overetch steps) 

STEP

 

1

2

3

4

5

6

7

8

9

Description

 

Stabilize

Clamp wafer to chuck

Etch

Stabilize

Main

Stabilize for overetch

Over-etch

Unclamp wafer

End

gap adjust

native oxide

for main etch

etch

Pressure

mT

13

13

13

10

10

15

15

 

 

RF Top

W

 

 

250

 

250

 

250

 

 

RF Bottom

W

 

 

45

 

60

 

45

 

 

Gap

cm

5.9

5.9

5.9

5.9

5.9

5.9

5.9

5.9

5.9

Cl2

sccm

 

 

 

40

40

 

 

 

 

HBr

sccm

 

 

 

100

100

50

50

 

 

O2 (20%)

sccm

 

 

 

5

5

5

5

 

 

CF4

sccm

 

 

 

 

 

 

 

 

 

He

sccm

 

 

 

 

 

 

 

50

 

C2F6

sccm

100

100

100

 

 

 

 

 

 

O2

sccm

 

 

 

 

 

 

 

 

 

N2

sccm

 

 

 

 

 

 

 

 

 

He Clamp

T

 

6

6

6

6

6

6

 

 

Completion

 

stab

stab

time

stab

time

stab

time

time

end

Time

sec

20

20

10

20

60

20

30

10

 

Channel

 

 

 

 

 

 

 

 

 

 

Delay

sec

 

 

 

 

 

 

 

 

 

Norm

sec

 

 

 

 

 

 

 

 

 

NormValue

 

 

 

 

 

 

 

 

 

 

Trigger

%

 

 

 

 

 

 

 

 

 

Slope

cs/s

 

 

 

 

 

 

 

 

 

 




Poly Etch Rate

Oxide Etch Rate

Selectivity (Poly/Oxide)

Breakthrough

1066 Å/min

177 Å/10 sec

1

Main Etch

3200 Å/min

150 Å/min

21

Overetch

2325 Å/min

26 Å/min

89

 

Poly_etch_endpoint: (Standard poly etch recipe with end point)

STEP

 

1

2

3

4

5

6

7

8

9

Description

 

Stabilize

Clamp wafer to chuck

Etch

Stabilize

Main

Stabilize for overetch

Over-etch

Unclamp wafer

End

gap adjust

native oxide

for main etch

etch

Pressure

mT

13

13

13

10

10

15

15

 

 

RF Top

W

 

 

250

 

250

 

250

 

 

RF Bottom

W

 

 

45

 

60

 

45

 

 

Gap

cm

5.9

5.9

5.9

5.9

5.9

5.9

5.9

5.9

5.9

Cl2

sccm

 

 

 

40

40

 

 

 

 

HBr

sccm

 

 

 

100

100

50

50

 

 

O2 (20%)

sccm

 

 

 

5

5

5

5

 

 

CF4

sccm

 

 

 

 

 

 

 

 

 

He

sccm

 

 

 

 

 

 

 

50

 

C2F6

sccm

100

100

100

 

 

 

 

 

 

O2

sccm

 

 

 

 

 

 

 

 

 

N2

sccm

 

 

 

 

 

 

 

 

 

He Clamp

T

 

6

6

6

6

6

6

 

 

Completion

 

stab

stab

time

stab

Endpt

stab

time

time

end

Time

sec

20

20

10

20

60

20

30

10

 

Channel

 

 

 

 

 

 A

 

 

 

 

Delay

sec

 

 

 

 

 20

 

 

 

 

Norm

sec

 

 

 

 

 10

 

 

 

 

Norm Value

 

 

 

 

 

 

 

 

 

 

Trigger

%

 

 

 

 

 95

 

 

 

 

Slope

cs/s

 

 

 

 

 

 

 

 

 

 

There are five parameters which must be set for endpoint detection.

Parameter

Description

Recommended

Delay (sec)

A delay in the beginning of the main etch, before data is sampled. This delay allows the plasma to stabilize before capturing a normalized signal reference.

20s (depends on poly thickness)

Norm (sec)

Time interval over which signal will be averaged and normalized to 100%

10s

 

 Clean: Chamber Clean Process

STEP

 

1

2

3

6

7

 

 

Stabilize

Clamp wfr to chuck

Clean Process

Unclamp wafer

End

gap adjust

Pressure

mT

15

15

15

 

 

RF Top

W

 

 

600

 

 

RF Bottom

W

 

 

0

 

 

Gap

cm

5.9

5.9

5.9

 

 

Cl2

sccm

20

20

20

 

 

HBr

sccm

 

 

 

 

 

O2 (20%)

sccm

 

 

 

 

 

SF6

sccm

100

100

100

 

 

He

sccm

 

 

 

50

 

C2F6

sccm

 

 

 

 

 

O2

sccm

20

20

20

 

 

N2

sccm

 

 

 

 

 

He Clamp

T

 

6

6

 

 

Completion

 

stab

stab

time

time

end

Time

sec

20

20

300

10

 

Channel

 

 

 

 

 

 

Delay

sec

 

 

 

 

 

Norm

sec

 

 

 

 

 

Norm Value

 

 

 

 

 

 

Trigger

%

 

 

 

 

 

Slope

cs/s

 

 

 

 

 

 

Condition: Chamber Conditioning Process

STEP

 

1

2

3

4

5

 

 

Stabilize

Clamp wfr to chuck

Chamber Condition

Unclamp wafer

End

gap adjust

Pressure

mT

10

10

10

 

 

RF Top

W



800

 

 

RF Bottom

W



0

 

 

Gap

cm

5.9

5.9

5.9

 

 

Cl2

sccm

50

50

50

 

 

HBr

sccm

150

150

150

 

 

O2 (20%)

sccm



 

 

 

SF6

sccm



 

 

 

He

sccm



 

50

 

C2F6

sccm



 

 

 

O2

sccm



 

 

 

N2

sccm



 

 

 

He Clamp

T

6

6

6

 

 

Completion

 

stab

stab

time

time

end

Time

sec

20

20

120

10

 

Channel

 

 

 

 

 

 

Delay

sec

 

 

 

 

 

Norm

sec

 

 

 

 

 

Norm Value

 

 

 

 

 

 

Trigger

%

 

 

 

 

 

Slope

cs/s

 

 

 

 

 

 

Nitride_etch: Silicon Nitride Etch

STEP

 

 

1

2

3

4

5

6

7

 

Stabilize

Clamp wfr to chuck

Main

Stabilize

Main

Unclamp wafer

End

gap adjust

Etch

for main etch

etch

Pressure

mT

20

20

20

20

20

 

 

RF Top

W

 

 

600

 

600

 

 

RF Bottom

W

 

 

60

 

0

 

 

Gap

cm

5.9

5.9

5.9

5.9

5.9

5.9

5.9

Cl2

sccm

 

 

 

 

 

 

 

HBr

sccm

30

30

30

75

75

 

 

O2 (20%)

sccm

10

10

10

 

 

 

 

SF6

sccm

 

 

 

25

25

 

 

He

sccm

 

 

 

50

50

50

 

C2F6

sccm

75

75

75

30

30

 

 

O2

sccm

 

 

 

20

20

 

 

N2

sccm

 

 

 

 

 

 

 

He Clamp

T

 

6

6

6

6

 

 

Completion

 

stab

stab

time

stab

time

time

end

Time

sec

20

20

60

20

20

10

 

Channel

 

 

 

 

 

 

 

 

Delay

sec

 

 

 

 

 

 

 

Norm

sec

 

 

 

 

 

 

 

Norm Value

 

 

 

 

 

 

 

 

Trigger

%

 

 

 

 

 

 

 

Slope

cs/s

 

 

 

 

 

 

 

 


LPCVD Nitride Etch Rate

Uniformity

Main Etch

3200 Å/min

<5%

Overetch

1300 Å/min

~5%

 

Endpoint Monitoring:

The lampoly has two optical sensors used in endpoint detection. Very simply, the change in the color of the plasma is an indication of the atomic species present. Channel A detects at a wavelength of 405 nm, which is sensitive to the presence of silicon in gaseous etch by-products and Channel B detects at 520 nm which is sensitive to CO. Thus, if you are etching poly or silicon on top of oxide, you would expect during the Main Etch that the Channel A signal would quickly reach a high plateau level during the bulk poly etch and then drop off steeply as the poly cleared. In contrast, Channel B would be pretty flat for bulk poly etching during the Main Etch step, but increase rapidly in intensity as the poly begins to clear. The steepness of the signal change can be viewed as some measure of etch uniformity (although dependent on loading effect) and you can get a pretty good idea of the etch rate of the Main Etch from the endpoint signal change. The change in signal, however, is dependent on the amount of open area being etched; for mask layers with very small open area, the signal change may not be easily observed. You can increase the signal intensity by monitoring both channels at once using the ratio of Channel A/Channel B. Remember, presuming the process is in control, that the endpoint signal will depend on the film you are etching (composition, thickness, uniformity) and the mask used (total open area, large versus small structures on the mask) and substrate (plasma is an electronic process so changes in capacitance of the substrate will affect etch). So, automatic endpoint is not recommended for processes, films, substrates, and masks that are not well characterized, as you risk over- or under- etching.

In order to set up endpoint plotting, you will need to run test wafers with as similar a film and mask pattern as on your device wafers. To set up and view the endpoint plots, go to the “datalog” page and follow the instructions below.

1.      Up to four parameters (signals) can be tracked at the same time in the Datalog screen. Parameter/ signal value is plotted in the Y axis and the time in the X-axis.  Each tracked signal has a different color.

2.      The plot parameters are identified by the channel numbers A-D. 

3.      Click on the box next to the channel and choose from the list of parameters/ signals for monitoring.

4.      Adjust the Y-scale for that parameter as needed.  Typical full scale for endpoint monitoring is 0-32000units (Y-scale).  Some factors that will affect the signal intensity are: exposed area, endpoint detector gain set up, condition of the endpoint window etch conditions etc.

Datalog Screen

Figure 4


Post-Etch Cleanup Tips

Cl2 and HBr leave a sidewall polymer residue containing halogens and silicon oxide. Depending on your process margin, this residue has been known to cause problems, so standard industry practice is to remove the polymer immediately after processing. The sidewall polymer is not always completely removed using standard resist stripping piranha, so post-processing usually consists of: a 10 second 50:1 HF dip, rinse, and dry, followed by plasma O2 ash, and then piranha clean.

Depending on your application, the complete stripping process may not be required. However, it is possible that the -Cl and -Br present in the sidewall polymer can cause corrosion over time, as moisture is absorbed and local acid concentration becomes high. This reaction can be passivated by cycling wafers in the dump rinse tank and spin drying afterwards. 

Process Monitoring and Machine Qualification:

Tool Qualification Run:

  •  Tool qualification run will be done periodically by Staff (roughly once a quarter or as needed to troubleshoot) using the recipe “Poly_etch_timed"
  • Si loss loss and selectivity to oxide and photo resist will be monitored during this qualification
  • Users are advised to run their own quals prior to their processing.
  •  

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