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Unless otherwise stated, all content in this section was done by Berit Herstrøm, DTU Nanolab

SiO2 trench etching with Cr mask

Start parameters, variations noted in the gallery headline	Recipe name: no 10 with lower platen power
Coil Power [W]	2500
Platen Power [W]	200
Platen temperature [^oC]	20
H2 flow [sccm]	25.6
C₄F₈ flow [sccm]	25.6
He flow [sccm]	448.7
Pressure	Fully open APC valve (8-9 mTorr)
Electromagnetic coils (EM) 'outer coil' / 'inner coil'	'2 A' / '30 A' (PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN)

100 nm Cr mask etched in ICP metal with 500nm DUV neg resist (NUV 2300-0.5) and 65 nm barc.

Cr mask before SiO2 etch 800 nm pitch 50% duty cycle. The The Cr linewidth is clearly less than designed

Results

Temporary conclusions on how the process parameters affect the results in this study:

What process parameters affect the results?

Going from full wafer to small piece on Si carrier:
- Seemed to give more sidewall passivation
Platen power: lowering the platen power gives
- more sidewall passivation
- lower etch rate
- Less trenching
Removing the H2 gave:
- less sidewall passivation
Adding O2 gave:
- less sidewall passivation
Process pressure/total gasflow rate
- Reducing total gasflow rate which reduced the pressur inside the chamber gave:
  - less sidewall passivation
  - Reduced the CD (Critical Dimensions)
Coil power: Reducing coil power
- less CD loss
- more sidewall passivation
Increasing process time:
- less sidewall passivation
- more sidewall bow
- CD loss due to larger mask faceting

Sidewall passivation↑
- Sample size↓
- Platen power↓
- Coil power↓
- H2 flow↑
- O2 flow↓
- Total gas flow rate/pressure↑

Profile SEM images

Recipe settings	Comments	SEM gallery
On 6" wafer Coil Power [W]:2500 Platen Power [W]: 200 Platen temperature [^oC]: 20 H2 flow [sccm]:25.6 C₄F₈ flow [sccm]: 25.6 He flow [sccm]:448.7 Pressure:Fully open APC valve (8-9 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'2 A' / '30 A' PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN	text	SiO2 etch with Cr mask on full wafer 6 min etch
Piece on Si carrier Coil Power [W]:2500 Platen Power [W]: 200 Platen temperature [^oC]: 20 H2 flow [sccm]:25.6 C₄F₈ flow [sccm]: 25.6 He flow [sccm]:448.7 Pressure:Fully open APC valve (8-9 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'2 A' / '30 A' PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN	More sidewall passivation on chip than on full wafer	SiO2 etch with Cr mask on wafer piece on Si carrier 6 min etch
Coil Power [W]:2500 Platen Power [W]: 200 Platen temperature [^oC]: 20 H2 flow [sccm]:0 C₄F₈ flow [sccm]: 25.6 He flow [sccm]:448.7 Pressure:Fully open APC valve (8-9 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'2 A' / '30 A' PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN	Less sidewall passivation from removing the H2	SiO2 etch with Cr mask on wafer piece on Si carrier 6 min etch, H2:0sccm
Coil Power [W]:2500 Platen Power [W]: 200 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 5 C₄F₈ flow [sccm]: 25.6 He flow [sccm]:448.7 Pressure:Fully open APC valve (8-9 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'2 A' / '30 A' PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN	Not a large effect from adding a little O2	SiO2 etch with Cr mask on wafer piece on Si carrier 6 min etch, H2:0sccm, O2:5sccm
Coil Power [W]:2500 Platen Power [W]: 200 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 0 C₄F₈ flow [sccm]: 13.0 He flow [sccm]:225 Pressure:Fully open APC valve (3.35 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'2 A' / '30 A' PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN	Reducing total flow rate and thereby the pressure gives less passivation/redeposition. Sidewall roughness not so bad.	SiO2 etch with Cr mask on wafer piece on Si carrier 6 min etch, H2:0sccm, C4F8:13sccm He:225sccm, Pressure:3.35mTorr
Coil Power [W]:1200 Platen Power [W]: 150 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 0 C₄F₈ flow [sccm]: 13.0 He flow [sccm]:225 Pressure:Fully open APC valve (3.35 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'2 A' / '30 A' PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN	Reducing the coil power a lot and platen power a little gives more sidewall passivation/redeposition	SiO2 etch with Cr mask on wafer piece on Si carrier 6 min etch, H2:0sccm, C4F8:13sccm He:225sccm, Pressure:3.35mTorr; platen power 150W, coil power:1200W
Coil Power [W]:1200 Platen Power [W]: 150 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 10 C₄F₈ flow [sccm]: 13.0 He flow [sccm]:215 Pressure:Fully open APC valve (3.35 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'2 A' / '30 A' PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN	Adding oxygen reduces the passivation/redeposition	SiO2 etch with Cr mask on wafer piece on Si carrier 6 min etch, H2:0sccm, C4F8:13sccm He:215sccm O2:10sccm, Pressure:3.6mTorr; platen power 150W, coil power:1200W
Coil Power [W]:1200 Platen Power [W]: 150 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 20 C₄F₈ flow [sccm]: 13.0 He flow [sccm]:205 Pressure:Fully open APC valve (3.35 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'2 A' / '30 A' PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN	Adding more oxygen reduces further the passivation/redeposition but some trenching appears.	SiO2 etch with Cr mask on wafer piece on Si carrier 6 min etch, H2:0sccm, C4F8:13sccm He:205sccm O2:20sccm, Pressure:3.6mTorr; platen power 150W, coil power:1200W
Coil Power [W]:1800 Platen Power [W]: 150 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 10 C₄F₈ flow [sccm]: 13.0 He flow [sccm]:215 Pressure:Fully open APC valve (3.35 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'2 A' / '30 A' PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN	Increasing coil power reduces trenching but increases passivation/redeposition	SiO2 etch with Cr mask on wafer piece on Si carrier 6 min etch, H2:0sccm, C4F8:13sccm He:215sccm O2:10sccm, Pressure:3.6mTorr; platen power 150W, coil power:1800W
Coil Power [W]:1800 Platen Power [W]: 150 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 20 C₄F₈ flow [sccm]: 13.0 He flow [sccm]:205 Pressure:Fully open APC valve (3.6 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'2 A' / '30 A' PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN	Adding more O2 reduces the sidewall passivation/redeposition	SiO2 etch with Cr mask on wafer piece on Si carrier 6 min etch, H2:0sccm, C4F8:13sccm He:205sccm O2:20sccm, Pressure:3.6mTorr; platen power 150W, coil power:1800W pitch 800 nm Top 461 nm @edge 437 nm bottom 402 nm height 916 nm height from edge 827 nm Cr left 83.5 nm selectivity 55.5 156 nm/min
Coil Power [W]:1200 Platen Power [W]: 100 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 20 C₄F₈ flow [sccm]: 13.0 He flow [sccm]:205 Pressure:Fully open APC valve (3.6 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'2 A' / '30 A' PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN	Running with the lower coil power and reducing the platen power also seems to reduced the sidewall passivatin/redeposition, but etch rate goes down	SiO2 etch with Cr mask on wafer piece on Si carrier 6 min etch, H2:0sccm, C4F8:13sccm He:205sccm O2:20sccm, Pressure:3.6mTorr; platen power 100W, coil power:1200W pitch 800 nm Top 444 nm bottom 374 nm height 718 nm Cr left 85 nm selectivity 48
Coil Power [W]:1200 Platen Power [W]: 100 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 20 C₄F₈ flow [sccm]: 13.0 He flow [sccm]:205 Pressure:Fully open APC valve (3.6 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'2 A' / '30 A' PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN	Repeating with longer etch time to etch 1500 nm down. Unfortunately this damaged the hardware due to the EM coils getting too hot.	SiO2 etch with Cr mask on wafer piece on Si carrier 14 min etch (PLEASE DO NOT REPEAT THIS LONG TIME), H2:0sccm, C4F8:13sccm He:205sccm O2:20sccm, Pressure:3.6mTorr; platen power 100W, coil power:1200W Etch on none patterned wafer, Uniformity: +- 6.4%
Coil Power [W]:1800 Platen Power [W]: 150 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 20 C₄F₈ flow [sccm]: 13.0 He flow [sccm]:205 Pressure:Fully open APC valve (3.6 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'2 A' / '30 A' PLEASE DO NOT RUN WITH THESE SETTINGS FOR MORE THAN 6 MIN	Running 1800W/150W at increased time to etch down to 1500 nm.	SiO2 etch with Cr mask on wafer piece on Si carrier 10 min etch, H2:0sccm, C4F8:13sccm He:205sccm O2:20sccm, Pressure:3.6mTorr; platen power 150W, coil power:1800W
Coil Power [W]:1200 Platen Power [W]: 100 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 20 C₄F₈ flow [sccm]: 13.0 He flow [sccm]:205 Pressure:Fully open APC valve (3.9 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'0 A' / '0 A'	Repeating the 1200W/100W recipes at 14 min but without the EM coils. For this recipe the uniformity over the wafer improved from removing the EM coils, so no need for those and now the recipe could run 14 min without damaging the hardware. The profile looked as before. After removing the Cr I looked from the top and with a tilted view and saw the the sidewall roughness was very bad.	SiO2 etch with Cr mask on wafer piece on Si carrier 14 min etch, EM:0/0 H2:0sccm, C4F8:13sccm He:205sccm O2:20sccm, Pressure:3.9mTorr; platen power 100W, coil power:1200W Etch on none patterned wafer, Uniformity: +-1.7% tilt 30 degrees tilt 30 degrees tilt 20 degrees tilt 20 degrees
Coil Power [W]:2500 Platen Power [W]: 100 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 20 C₄F₈ flow [sccm]: 13.0 He flow [sccm]:205 Pressure:Fully open APC valve (3.9 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'0 A' / '0 A'	Tried high coil power and low platen power. This seemed to give som undercutting,especially on the narrow lines. The smallest has been etched away. The etch rate was very low	SiO2 etch with Cr mask on wafer piece on Si carrier 14 min etch, EM:0/0 H2:0sccm, C4F8:13sccm He:205sccm O2:20sccm, Pressure:3.9mTorr; platen power 100W, coil power:2500W
Coil Power [W]:2500 Platen Power [W]: 200 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 0 C₄F₈ flow [sccm]: 13.0 He flow [sccm]:225 Pressure:Fully open APC valve (3.9 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'0 A' / '0 A'	Increasing the platen power and and removing the oxygen helped on the under cutting but the lines are still very narrow at the bottom. It also increased the etch rate	SiO2 etch with Cr mask on wafer piece on Si carrier 14 min etch, EM:0/0 H2:0sccm, C4F8:13sccm He:225sccm O2:0sccm, Pressure:3.9mTorr; platen power 200W, coil power:2500W
14 min Coil Power [W]:2500 Platen Power [W]: 200 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 20 C₄F₈ flow [sccm]: 13.0 He flow [sccm]:205 Pressure:Fully open APC valve (3.9 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'0 A' / '0 A'	Adding the oxygen again further increased the etch rate and reduced the CD (Critical Dimension) of the Cr mask.	SiO2 etch with Cr mask on wafer piece on Si carrier 14 min etch, EM:0/0 H2:0sccm, C4F8:13sccm He:205sccm O2:20sccm, Pressure:3.9mTorr; platen power 200W, coil power:2500W
Back to start setting without EM coils - 14 min Coil Power [W]:2500 Platen Power [W]: 200 Platen temperature [^oC]: 20 H2 flow [sccm]:25.6 O2 flow [sccm]: 0 C₄F₈ flow [sccm]: 25.6 He flow [sccm]:448.7 Pressure:Fully open APC valve (8-9 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'0 A' / '0 A'	I repeated the start setting but without the EM coils. This gives a very none uniform etch over the wafer where in some parts it deposites instead of etching. The profile of 800 nm oitch look fairly good but a closer look reveals the the sidewall is very rough from either redeposition or polymerization. this cannot be removed with a O2 plasma.	SiO2 etch with Cr mask on wafer piece on Si carrier 14 min etch, EM:0/0
Coil Power [W]:600 Platen Power [W]: 50 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 10 C₄F₈ flow [sccm]: 6.5 He flow [sccm]:100 Pressure:Fully open APC valve (<2 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'0 A' / '0 A'	Due to the large sidewall roughness I decided to try and run at lower powers because it looked at some images like an ionbonbardment effect. First try with 600W/50W. The profile looks fairly good but still with some sidewall roughness. there is also some trenching and the Cr mask looks has a facet all the way down to the SiO2. The is also some bowing.	C10751: SiO2 etch with Cr mask on wafer piece on Si carrier 20 min etch, EM:0/0 H2:0sccm, C4F8:6.5sccm He:100sccm O2:10sccm, Pressure:?mTorr; platen power 50W, coil power:600W
Coil Power [W]:300 Platen Power [W]: 25 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 10 C₄F₈ flow [sccm]: 6.5 He flow [sccm]:100 Pressure:Fully open APC valve (<2 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'0 A' / '0 A'	Even lower powers: 300W/25W. The profiles looks better with less roughness but also mush slower etch rate, so not as deep as the previous.	C10752: SiO2 etch with Cr mask on wafer piece on Si carrier 30 min etch, EM:0/0 H2:0sccm, C4F8:6.5sccm He:100sccm O2:10sccm, Pressure:?mTorr; platen power 25W, coil power:300W
45 min Coil Power [W]:300 Platen Power [W]: 25 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 10 C₄F₈ flow [sccm]: 6.5 He flow [sccm]:100 Pressure:Fully open APC valve (<2 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'0 A' / '0 A'	Repeating with longer etch time. Low sidewall roughness, less faceting of the Cr mask. Still some trenching and bowing or negative tapering of the profile.	C10834: SiO2 etch with Cr mask on wafer piece on Si carrier 45 min etch, EM:0/0 H2:0sccm, C4F8:6.5sccm He:100sccm O2:10sccm, Pressure:?mTorr; platen power 25W, coil power:300W
Coil Power [W]:300 Platen Power [W]: 20 Platen temperature [^oC]: 20 H2 flow [sccm]:0 O2 flow [sccm]: 10 C₄F₈ flow [sccm]: 6.5 He flow [sccm]:100 Pressure:Fully open APC valve (<2 mTorr) Electromagnetic coils (EM) 'outer coil' / 'inner coil':'0 A' / '0 A'	Decreased the platen power a little to see if this could remove the trenching. Not much different from the last.	C10844: SiO2 etch with Cr mask on wafer piece on Si carrier 50 min etch, EM:0/0 H2:0sccm, C4F8:6.5sccm He:100sccm O2:10sccm, Pressure:?mTorr; platen power 20W, coil power:300W