Specific Process Knowledge/Etch/DRIE-Pegasus/processA

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Effects on Process A of showerhead change in December 2014

The effects of changing of the showerhead in December 2014 was investigated. Patterned wafers were processed before and after and the profile of the etched features were inspected in SEM. Click on the numbers in the 'Runs' column below to see the profiles.

Recipe	Name	Temp.	Deposition step						Etch step							Comments
			Time	Pres.	C4F8	SF6	O2	Coil	Time	Pres.	C4F8	SF6	O2	Coil	Platen	Showerhead	Runs	Key words
Process A	Step1 11 cyc	20	4	25	200	0	0	2000	7.0	25(1.5s) 90>>150	0	350(1.5s) 550	5	2800	120>>140(1.5s) 45	Old	1
	Step2 44 cyc		4	25	200	0	0	2000	7.0	25(1.5s) 150	0	350(1.5s) 550	5	2800	140(1.5s) 45
	Step1 11 cyc	20	4	25	200	0	0	2000	7.0	25(1.5s) 90>>150	0	350(1.5s) 550	5	2800	120>>140(1.5s) 45	New	1	Profile improved
	Step2 44 cyc		4	25	200	0	0	2000	7.0	25(1.5s) 150	0	350(1.5s) 550	5	2800	140(1.5s) 45

Process A acceptance test

Process A is labelled Large trench (80μm wide) 150μm depth. In the acceptance test the process was run on a 150 mm SPTS wafer with 12-13 % etch load.

Process A specifications

Parameter	Specification	Average result
Etch rate (µm/min)	> 15	18.9
Etched depth (µm)	150	189.1
Scallop size (nm)	< 800	718
Profile (degs)	91 +/- 1	91.1
Selectivity to AZ photoresist	> 150	310
Undercut (µm)	<1.5	0.84
Uniformity (%)	< 3.5	3.0
Repeatability (%)	<4	0.43

	Process A parameters
	Step 1		Step 2
Parameter	Etch	Dep	Etch	Dep
Gas flow (sccm)	SF6 350 (1.5 s) 550	C4F8 200	SF6 350 (1.5 s) 550	C4F8 200
Cycle time (secs)	7.0	4.0	7.0	4.0
Pressure (mtorr)	25 (1.5 s) 90 >> 150	25	25 (1.5 s) 150	25
Coil power (W)	2800	2000	2800	2000
Platen power (W)	120 >> 140 (1.5) 45	0	140 (1.5) 45	0
Cycles	11 (keep fixed)		44 (vary this)
Common	Temperature 20 degs, HBC 10 torr, Short funnel, with baffle & 5mm spacers

Quality control procedure

Quality Control (QC) for DRIE-Pegasus

The QC procedure for DRIE-Pegasus The newest QC data for DRIE-Pegasus QC Recipe: Process A Step 1: 11 cycles Step 2: 44 cycles QC limits DRIE-Pegasus Etch rate in Si 21 - 28 µm/min Non-uniformity 2  %

Process A guidelines

Process A is optimized for speed and depending on feature size and etch load it will achieve etch rates up to 25-30 µm/min.

This aggressive etch has a few drawbacks - one of which is the release of energy in the etch process. In general, it is clear that

1. The higher the etch rate, the higher rate of released energy.
2. The larger an area of silicon is exposed to plasma and hence etched, the higher rate of released energy.

Given its high etch rate, Process A is very sensible to high etch load processes and substrates with reduced cooling efficiency. Therefore, users are generally advised to

1. Use Process A with precaution at high etch loads - above some 50%.
2. Avoid using Process A on bonded wafers, in particular if the etch load is more than 5-10%. The bonding reduces the heat conduction across the wafer interface so the top wafer will immediately heat up and cause the mask to erode and the bonding polymer to melt.

If you have a bonded sandwich of wafers with very poor heat conduction (typically caused by intermediate polymer layers thicker than a few microns) you are advised to use other etch processes, maybe the deepetch on the ASE.

Process A performance

The perfomance of Process A has been investigated as a function of feature size and etch load.

Experiment

A number of wafers are patterned with the Travka mask set in AZ photoresist or 600 nm oxide. The wafers are then etched (batch recipe with 5 minute TDESC interstep cleans) using two different durations of process A in the DRIE-Pegasus.

Wafers Wafer number Mask Mask material Process A duration C01548.01 Travka 05 AZ photoresist 55 cycles, 10:05 mins C01548.02 Travka 10 AZ photoresist 55 cycles, 10:05 mins C01548.03 Travka 20 AZ photoresist 55 cycles, 10:05 mins C01548.04 Travka 35 AZ photoresist 55 cycles, 10:05 mins C01548.05 Travka 50 AZ photoresist 55 cycles, 10:05 mins

Wafers Wafer number Mask Mask material Process A duration C01549.01 Travka 05 600 nm oxide 110 cycles, 20:10 mins C01549.02 Travka 10 600 nm oxide 110 cycles, 20:10 mins C01549.03 Travka 20 600 nm oxide 110 cycles, 20:10 mins C01549.04 Travka 35 600 nm oxide 110 cycles, 20:10 mins

Results: Optical images

• Optical images of the C01548 batch that is processed 10:05 mins.
• 
  Wafer C01548.01: 5 % exposed area
• 
  Wafer C01548.02: 10 % exposed area
• 
  Wafer C01548.03: 20 % exposed area
• 
  Wafer C01548.04: 35 % exposed area
• 
  Wafer C01548.05: 50 % exposed area
• File:Without pre-etch measurements of the thicknesses of the photoresist it is not possible to determine the resist etch rate. However, it looks very uniform.

• Optical images of the C01549 batch that is processed 20:10 mins.
• 
  Wafer C01549.01: 5 % exposed area. Some 190 nm of 600 nm oxide remains.
• 
  Wafer C01549.02: 10 % exposed area. Some 122 nm oxide remains.
• 
  Wafer C01549.03: 20 % exposed area. In the centre some 90 nm oxide remains.
• 
  Wafer C01549.04: 35 % exposed area. In the centre some 90 nm oxide remains.
• 
  Wafer C01549.05: 35 % exposed area (close-up). The oxide has disappeared leaving the Si exposed.

The etching of silicon releases energy. This means that the faster the etch is, the more heat needs to be dissipated. The consequence is the same if a larger percentage of the wafer is etched. Process A is the fastest etch and as seen above, the exposed area plays an important role. As the exposed area increases the oxide mask erosion is more and more pronounced.

If a larger area is to be etched, the cooling must be made more efficient, either by lowering the platen temperature or with increasing the pressure of He on the backside of the wafer. This will be investigated soon.

Results: Etched depths in trenches of different widths

• Graphs
• 
  Process time 10:05
• 
  Process time 20:10

Travkatesting2: Process A run for 55 cycles on travka 5, 10, 20, 35, 50 masks

Date	Substrate Information	Process Information	SEM images of trenches															Numbers
			2 µm	3 µm	4 µm	6 µm	8 µm	10 µm	15 µm	25 µm	40 µm	50 µm	75 µm	100 µm	150 µm	200 µm	300 µm
January 2013	Travka05, AZ 5214, 5% open	Process A 55 cycles or 10:05 minutes, C01548.01																Trench width 2 3 4 6 8 10 15 25 40 50 75 100 150 200 300 Etched depth (µm) 92 106 113 126 136 146 161 181 200 208 222 230 238 243 248 Av. ER (µm/min) 9,2 10,5 11,2 12,5 13,5 14,4 16,0 18,0 19,9 20,7 22,0 22,8 23,6 24,1 24,6 Av. ER (nm/cyc) 1679 1918 2054 2294 2473 2648 2933 3299 3641 3786 4038 4184 4324 4409 4507 Sdewll bowing (%) 0,3% 0,2% 0,2% 0,3% 0,3% 0,2% 0,0% 0,2% 0,2% -0,3% 0,1% 0,1% 0,2% 0,2% -0,1% Sdewll angle(degs) 90,4 90,3 90,5 90,8 90,6 90,9 91,0 90,9 90,9 91,0 90,9 90,9 91,1 91,2 91,4 Trench width (µm) 4,8 7,1 7,7 9,7 12,6 14,1 20,0 30,3 46,3 56,4 82,5 107,3 156,9 206,7 308,6
January 2013	Travka10, AZ 5214, 10% open	Process A 55 cycles or 10:05 minutes, C01548.02																Trench width (µm) 2 3 4 6 8 10 15 25 40 50 75 100 150 200 300 Etched depth (µm) 90 101 108 121 130 138 152 171 189 198 210 218 228 232 239 Av. ER (µm/min) 8,9 10,0 10,7 12,0 12,9 13,7 15,1 16,9 18,8 19,6 20,9 21,6 22,6 23,1 23,7 Av. Scllp hght (nm) 1639 1834 1964 2192 2356 2508 2772 3103 3441 3601 3825 3961 4143 4227 4346 Sdwall bowing (%) 0,40 0,19 0,25 0,16 0,04 0,12 0,16 -0,18 -0,04 0,00 0,04 -0,08 -0,20 -0,05 -0,05 Sdwall angle (degs) 90,2 90,3 90,5 90,5 90,6 90,7 90,8 91,1 91,1 91,1 91,1 91,2 91,2 91,3 91,6 Trench width (µm) 5,2 7,2 8,2 10,9 13,2 15,5 20,6 31,3 46,5 56,1 81,2 107,2 158,9 211,1 306,2
January 2013	Travka20, AZ 5214, 20% open	Process A 55 cycles or 10:05 minutes, C01548.03																Trench width (µm) 2 3 4 6 8 10 15 25 40 50 75 100 150 200 300 Etched depth (µm) 75 85 92 103 111 117 130 148 164 170 181 188 194 199 203 Av. ER (µm/min) 7,5 8,4 9,1 10,2 11,0 11,6 12,9 14,7 16,2 16,8 17,9 18,6 19,3 19,7 20,1 Av. Scllp hght (nm) 1371 1543 1676 1874 2019 2133 2368 2692 2978 3086 3286 3412 3533 3619 3686 Sdwall bowing (%) 0,46 0,59 0,40 0,42 0,40 0,28 0,35 0,18 0,36 0,36 0,26 0,58 0,40 0,31 0,05 Sdwall angle (degs) 90,1 90,4 90,4 90,5 90,8 90,6 91,1 91,3 91,4 91,5 91,5 91,7 91,8 91,8 92,2 Trench width (µm) 4,9 6,1 7,8 10,4 12,2 14,9 19,9 30,5 46,3 57,4 82,3 106,6 158,1 209,0 309,7
January 2013	Travka35, AZ 5214, 35% open	Process A 55 cycles or 10:05 minutes, C01548.04																Trench width (µm) 2 3 4 6 8 10 15 25 40 50 75 100 150 200 300 Etched depth (µm) 61 70 76 86 94 100 111 126 139 143 153 158 163 165 168 Av. ER (µm/min) 6,1 6,9 7,6 8,6 9,3 9,9 11,0 12,5 13,8 14,2 15,2 15,6 16,2 16,4 16,7 Av. Scllp hght (nm) 1117 1267 1390 1568 1704 1810 2014 2287 2526 2602 2786 2868 2967 3007 3054 Sdwall bowing (%) 0,22 0,31 0,30 0,46 0,39 0,55 0,41 0,20 -0,04 -0,33 -0,25 -0,19 -0,13 -0,13 -0,21 Sdwall angle (degs) 89,7 90,1 90,2 90,4 90,5 90,4 90,2 89,9 90,0 89,9 90,2 90,4 90,8 90,9 91,3 Trench width (µm) 4,5 5,4 6,7 9,0 11,4 13,4 19,1 30,0 45,0 56,2 82,3 108,4 156,3 207,5 308,3
January 2013	Travka50, AZ 5214, 50% open	Process A 55 cycles or 10:05 minutes, C01548.05																Trench width (µm) 2 3 4 6 8 10 15 25 40 50 75 100 150 200 300 Etched depth (µm) 62 67 75 81 86 94 105 113 118 123 125 129 131 133 Av. ER (µm/min) 6,2 6,7 7,5 8,0 8,5 9,3 10,4 11,2 11,7 12,2 12,4 12,8 13,0 13,2 Av. Scllp hght (nm) 1132 1223 1370 1472 1565 1706 1906 2061 2142 2234 2277 2355 2379 2412 Sdwall bowing (%) 0,42 0,61 0,39 0,36 0,41 0,38 0,39 0,52 0,24 0,36 0,47 0,63 0,59 0,32 Sdwall angle (degs) 89,9 89,8 90,0 90,1 90,5 90,7 91,1 91,3 91,6 91,8 92,1 92,3 92,4 92,6 Trench width (µm) 5,1 6,7 9,3 11,4 13,7 18,6 29,0 44,5 54,4 80,5 106,7 156,9 207,4 310,1

Process A variations May-June 2016

Process A may overpassivate producing grass. To investigate the results

Recipe	Temp.	Deposition step				Etch step						Comments
		Time	Pres.	C4F8	Coil	Time	Pressure	SF6	O2	Coil	Platen	SEM images	Key words
PrA-0	20	4	25	200	2000	7.0	25(1.5s) 150	350(1.5s) 550	5	2800	140(1.5s) 45	4	Step 2 original recipe
PrA-1	20	3.5	25	200	2000	7.0	25(1.5s) 150	350(1.5s) 550	5	2800	140(1.5s) 45	4	Shorter dep cycle
PrA-2	20	4	25	150	2000	7.0	25(1.5s) 150	350(1.5s) 550	5	2800	140(1.5s) 45	4	Lower C4F8 flow in dep cycle

Process Log entries