Difference between revisions of "STS Pegasus 4/Processes/LNF Recipe 3"

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<!-- Make sure to add any other relevant categories -->
 
<!-- Make sure to add any other relevant categories -->
[[Category:Processes]]
+
[[Category:Processes]]{{Infobox process
{{warning|This page has not been released yet.}}
 
{{Infobox process
 
 
|technology = DRIE
 
|technology = DRIE
 
|material = [[Silicon|Si]]
 
|material = [[Silicon|Si]]
|mask = [[Photoresist|PR]], [[Silicon Dioxide|SiO2]]
+
|mask = [[Photoresist|PR]], [[Silicon dioxide|SiO2]]
|gases = [[Sulfur_Hexafluoride|SF<sub>6</sub>]], [[Octafluorocyclobutane|C<sub>4</sub>F<sub>8</sub>]], [[Oxyegen|O<sub>2</sub>]]
+
|gases = [[SF6|SF<sub>6</sub>]], [[C4F8|C<sub>4</sub>F<sub>8</sub>]], [[O2|O<sub>2</sub>]]
 
|created = Jan 1, 2011
 
|created = Jan 1, 2011
 
|modified =  
 
|modified =  
 
|authors = Kevin Owen
 
|authors = Kevin Owen
 
}}
 
}}
Recipe 3 is designed for deep and through wafer etching particularly on masks with a large exposed area (>20%). Undercut and scalloping is larger than LNF Recipe 1, but etch rates are higher (4-16 μm/min).
+
'''{{SUBPAGENAME}}''' is designed for deep and through wafer etching particularly on masks with a large exposed area (>20%). Undercut and scalloping is larger than LNF Recipe 1, but etch rates are higher (4-16 μm/min).
  
 
==Procedure==
 
==Procedure==
Line 18: Line 16:
  
 
==Recipe Parameters==
 
==Recipe Parameters==
{| class="wikitable" border="1"
+
{| class="wikitable" border="1" style="text-align: center"
 
|-
 
|-
! Parameter
+
! rowspan="2"|Parameter
! Dep
+
! rowspan="2"|Dep
! Etch
+
! colspan="2"|Etch
 +
|-
 +
! Boost
 +
! Main
 
|-
 
|-
 
| ICP Power
 
| ICP Power
| W
+
| 2000 W
| W
+
|colspan="2"| 4000 W
 
|-
 
|-
 
| Bias Power
 
| Bias Power
| W
+
| 0 W
| W
+
| 100 W
 +
| 50 W
 
|-
 
|-
 
| Bias Pulsing
 
| Bias Pulsing
|  
+
| N/A
|  
+
|colspan="2"| 40 Hz 80%
 
|-
 
|-
 
| Pressure
 
| Pressure
| mTorr
+
| 25 mTorr
| mTorr
+
| 30 mTorr
 +
| 100 mTorr
 
|-
 
|-
| C4F8 Flow
+
| C<sub>4</sub>F<sub>8</sub> Flow
| sccm
+
| 200 sccm
| sccm
+
|colspan="2"| 0 sccm
 
|-
 
|-
| SF6 Flow
+
| SF<sub>6</sub> Flow
| sccm
+
| 0 sccm
| sccm
+
|colspan="2"| 600 sccm
 
|-
 
|-
| O2 Flow
+
| O<sub>2</sub> Flow
| sccm
+
| 0 sccm
| sccm
+
|colspan="2"| 60 sccm
 
|-
 
|-
 
| Time
 
| Time
| s
+
| 4 s
| s
+
| 2 s
 +
| 6.5 s
 +
|-
 +
| Chuck Temperature
 +
|colspan="3" | 10°C
 +
|}
 +
 
 +
==Capabilities==
 +
This process, as is true with all Bosch processes, varies depending on feature size and density, due to [[:Category:DRIE#Aspect ratio dependent etching|RIE lag]]. The below table contains typical results for 2 µm, 10 µm, and 100 µm trenches and the following sections expand on these results. It is strongly recommended that the process is tested with any new mask.
 +
 
 +
{| class="wikitable" border="1" style="text-align: center"
 +
|-
 +
! Parameter
 +
! 2 µm Trench
 +
! 10 µm Trench
 +
! 100 µm Trench
 +
|-
 +
| Etch Rate
 +
| 7 µm/min
 +
| 10.5 µm/min
 +
| 15.8 µm/min
 +
|-
 +
| Undercut
 +
| 0.83 µm
 +
| 1.13 µm
 +
| 1.13 µm
 +
|-
 +
| Scallop height
 +
| 1.8 µm
 +
| 2.5 µm
 +
| 2.9 µm
 +
|-
 +
| Scallop depth
 +
| 0.5 µm
 +
| 0.7 µm
 +
| 0.8 µm
 +
|-
 +
| Sidewall angle
 +
| 90.1°
 +
| 90.1°
 +
| 90.2°
 
|}
 
|}
  
==Characterization==
 
 
===Etch Rate===
 
===Etch Rate===
 
The etch rate will vary with the size of the trench being etched.  Larger trenches tend to etch faster, this trend can be seen below.
 
The etch rate will vary with the size of the trench being etched.  Larger trenches tend to etch faster, this trend can be seen below.
<gallery mode="packed" heights="300px">
+
 
File:STS_Pegasus_4_Recipe_3_Etch_Rate.jpg|Recipe 3 Etch Rate vs. Feature Size
+
{{#widget:Iframe
</gallery>
+
|url= https://docs.google.com/spreadsheets/d/193-swCgAFeAuUAq5m6ewOFA-0r8uqdhZmkqVTSbZDwk/pubchart?oid=1796971608&amp;format=image   
 +
|width= 503.5
 +
|height= 311.3308333333333
 +
|border= 0
 +
|scrolling= no
 +
}}
  
 
===Mask Selectivity===
 
===Mask Selectivity===
 
* Photoresist Etch Rate
 
* Photoresist Etch Rate
** [[SPR 220]]: 770 A/min  
+
** [[SPR 220]]: 770 Å/min  
* [[Silicon Dioxide|SiO2]] Etch Rate: Unknown
+
* [[SiO2|SiO<sub>2</sub>]] Etch Rate
 +
** Thermal oxide: 222 Å/min
 +
** HTO: 219 Å/min
 +
** LTO: 230 Å/min
 +
** PECVD: unknown
 +
* [[Silicon nitride]] Etch Rate
 +
** LPCVD Nitride: 321 Å/min
 +
** LPCVD Low Stress Nitride: 223 Å/min
 +
 
 +
===Sidewall Profile===
 +
Mask undercut, scalloping, and sidewall angle are shown below.
 +
 
 +
{{#widget:Iframe
 +
|url= https://docs.google.com/spreadsheets/d/193-swCgAFeAuUAq5m6ewOFA-0r8uqdhZmkqVTSbZDwk/pubchart?oid=992129259&amp;format=image   
 +
|width= 503.5
 +
|height= 311.3308333333333
 +
|border= 0
 +
|scrolling= no
 +
}}
 +
 
 +
{{#widget:Iframe
 +
|url= https://docs.google.com/spreadsheets/d/193-swCgAFeAuUAq5m6ewOFA-0r8uqdhZmkqVTSbZDwk/pubchart?oid=76533524&amp;format=image   
 +
|width= 503.5
 +
|height= 311.3308333333333
 +
|border= 0
 +
|scrolling= no
 +
}}
 +
 
 +
{{#widget:Iframe
 +
|url= https://docs.google.com/spreadsheets/d/193-swCgAFeAuUAq5m6ewOFA-0r8uqdhZmkqVTSbZDwk/pubchart?oid=1310380588&amp;format=image   
 +
|width= 503.5
 +
|height= 311.3308333333333
 +
|border= 0
 +
|scrolling= no
 +
}}
  
===Side Profile===
 
 
====Trench====
 
====Trench====
 
Running recipe 3 for 20 minutes with 3 µm of [[SPR 220]] on a silicon wafer with our standard DRIE characterization mask can produce a profile like this.
 
Running recipe 3 for 20 minutes with 3 µm of [[SPR 220]] on a silicon wafer with our standard DRIE characterization mask can produce a profile like this.
<gallery mode="packed-hover"  heights="200px">
+
<gallery mode="packed-hover"  heights="180px">
 
File:STS Pegasus_4_Recipe_3_2_um.jpg|Recipe 3 for 20 min, 2 µm Trench
 
File:STS Pegasus_4_Recipe_3_2_um.jpg|Recipe 3 for 20 min, 2 µm Trench
 
File:STS Pegasus_4_Recipe_3_10_um.jpg|Recipe 3 for 20 min, 10 µm Trench
 
File:STS Pegasus_4_Recipe_3_10_um.jpg|Recipe 3 for 20 min, 10 µm Trench
Line 78: Line 158:
 
</gallery>
 
</gallery>
  
====Scallop====
+
==Limitations==
* 0.46 µm wide X 2.2 µm tall
+
LNF Recipe 3 is known to work under a range of conditions. Outside of these conditions, etch performance is not guaranteed. Etch rates will vary depending on feature size, etch length, open area, etc. We strongly recommend testing the process prior to running device wafers.
  
====Undercut====
+
<!--One common problem seen when running outside of these conditions is [[Grass|grassing]]. This occurs when the C4F8/SF6 ratio is unbalanced causing micromasking. This creates tiny pillars of un-etched Si and teflon on the surface of the feature. An example of grassing can be seen below.
* 483 nm
 
  
====Grassing====
+
[[File:STS_Pegasus_4_Recipe_1_grass.jpg|Height:200px| Grass (brown area) on perimeter of wafer|thumbnail]]-->
An example of grassing can be seen below.  This can happen if there is too much exposed area  (>25%) on the mask.
 
<gallery mode="packed-hover"  heights="200px">
 
File:STS_Pegasus_4_Recipe_1_grass.jpg| Grass (brown area) on perimeter of wafer
 
File:Temp_Image.jpg| XXX find some SEM of grass XXX
 
</gallery>
 
  
==Limitations==
 
 
===Etch Length===
 
===Etch Length===
 +
*Generally 30 sec - 30 minutes is known to work well.
 +
*Recipe 3 is tested for 10 min monthly to verify performance.
 +
*Etches longer than 35 min are not well tested, since this is typically deeper than a standard thickness wafer.
  
 
===Feature Size===
 
===Feature Size===
 +
*This recipe is designed for large (>10 μm) features.
 +
*Smaller features often exhibit re-entrant (widening) sidewalls.
 +
*The standard characterization pattern used to qualify Recipe 1 has open lines, trenches, and grating patterns from 1 μm - 100 μm.
  
 
===Aspect ratio===
 
===Aspect ratio===
 +
*Aspect ratio limitations vary depending on feature size. For instance, 2 μm features have an aspect ratio limit of around 50:1. For larger features, aspect ratio is typically limited to the thickness of the wafer.
  
 
===Open area===
 
===Open area===
 +
*This recipe will not produce grass up to 100% open area
 +
*Large open areas (>50%) may require an SiO<sub>2</sub> mask, as excessive heating can cause photoresist to reticulate.
 +
*Small (<20%) open area may cause an undesirable increase in etch rate or shift in sidewall profile due to excess Fluorine.
  
 
===Multi-step etching===
 
===Multi-step etching===

Latest revision as of 10:43, 26 March 2021

About this Process
Process Details
Equipment STS Pegasus 4
Technology DRIE
Material Si
Mask Materials PR, SiO2
Gases Used SF6, C4F8, O2
Date Created Jan 1, 2011
Authored By Kevin Owen


LNF Recipe 3 is designed for deep and through wafer etching particularly on masks with a large exposed area (>20%). Undercut and scalloping is larger than LNF Recipe 1, but etch rates are higher (4-16 μm/min).

Procedure

Run LNF Recipe 3 for up to 20 minutes with the 1 minute automated clean recipe, longer etches should be run with the 3 minute automated clean recipe.

Recipe Parameters

Parameter Dep Etch
Boost Main
ICP Power 2000 W 4000 W
Bias Power 0 W 100 W 50 W
Bias Pulsing N/A 40 Hz 80%
Pressure 25 mTorr 30 mTorr 100 mTorr
C4F8 Flow 200 sccm 0 sccm
SF6 Flow 0 sccm 600 sccm
O2 Flow 0 sccm 60 sccm
Time 4 s 2 s 6.5 s
Chuck Temperature 10°C

Capabilities

This process, as is true with all Bosch processes, varies depending on feature size and density, due to RIE lag. The below table contains typical results for 2 µm, 10 µm, and 100 µm trenches and the following sections expand on these results. It is strongly recommended that the process is tested with any new mask.

Parameter 2 µm Trench 10 µm Trench 100 µm Trench
Etch Rate 7 µm/min 10.5 µm/min 15.8 µm/min
Undercut 0.83 µm 1.13 µm 1.13 µm
Scallop height 1.8 µm 2.5 µm 2.9 µm
Scallop depth 0.5 µm 0.7 µm 0.8 µm
Sidewall angle 90.1° 90.1° 90.2°

Etch Rate

The etch rate will vary with the size of the trench being etched. Larger trenches tend to etch faster, this trend can be seen below.

Mask Selectivity

  • Photoresist Etch Rate
  • SiO2 Etch Rate
    • Thermal oxide: 222 Å/min
    • HTO: 219 Å/min
    • LTO: 230 Å/min
    • PECVD: unknown
  • Silicon nitride Etch Rate
    • LPCVD Nitride: 321 Å/min
    • LPCVD Low Stress Nitride: 223 Å/min

Sidewall Profile

Mask undercut, scalloping, and sidewall angle are shown below.

Trench

Running recipe 3 for 20 minutes with 3 µm of SPR 220 on a silicon wafer with our standard DRIE characterization mask can produce a profile like this.

Limitations

LNF Recipe 3 is known to work under a range of conditions. Outside of these conditions, etch performance is not guaranteed. Etch rates will vary depending on feature size, etch length, open area, etc. We strongly recommend testing the process prior to running device wafers.


Etch Length

  • Generally 30 sec - 30 minutes is known to work well.
  • Recipe 3 is tested for 10 min monthly to verify performance.
  • Etches longer than 35 min are not well tested, since this is typically deeper than a standard thickness wafer.

Feature Size

  • This recipe is designed for large (>10 μm) features.
  • Smaller features often exhibit re-entrant (widening) sidewalls.
  • The standard characterization pattern used to qualify Recipe 1 has open lines, trenches, and grating patterns from 1 μm - 100 μm.

Aspect ratio

  • Aspect ratio limitations vary depending on feature size. For instance, 2 μm features have an aspect ratio limit of around 50:1. For larger features, aspect ratio is typically limited to the thickness of the wafer.

Open area

  • This recipe will not produce grass up to 100% open area
  • Large open areas (>50%) may require an SiO2 mask, as excessive heating can cause photoresist to reticulate.
  • Small (<20%) open area may cause an undesirable increase in etch rate or shift in sidewall profile due to excess Fluorine.

Multi-step etching

  • Multi-step processing (i.e. running two or more etches with overlapping features) with the Bosch process is known to cause undesirable results. Please contact the tool engineers if you wish to run such a process so we can help reduce or eliminate issues.

Qualification

Every third Friday Recipe 3 is run for 10 minutes on a Si wafer with our standard DRIE characterization mask, with 3 µm of SPR 220. This is performed after the weekly clean, and a 100 µm trench is measured in 5 locations with the Zygo NewView 5000. This etch rate is reported in the chart below.