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 test

Process A is intended as a wide trench (80μm wide) depth etched down some 150 µm. Below are the results from a run on a 150 mm 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
QC Recipe: Process A
Step 1: 11 cycles Step 2: 44 cycles
QC limits DRIE-Pegasus
Etch rate in Si 16 - 18.8 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 C01549 batch that is processed 20:10 mins.
  • Wafer C01549.01: 5 % exposed area. Some 190 nm of 600 nm oxide remains.
    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 C01549.02: 10 % exposed area. Some 122 nm oxide remains.
  • Wafer C01549.03: 20 % exposed area. In the centre some 90 nm oxide remains.
    Wafer C01549.03: 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 C01549.04: 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.
    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 10:05
  • Process time 20:10
    Process time 20:10

Results: SEM images of trench cross sections

Travkatesting2: Process A run for 55 cycles on travka 5, 10, 20, 35, 50 masks
Date Substrate Information Process Information SEM images of trenches
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



Travkatesting2: Process A run for 110 cycles on travka 5, 10, 20, 35 masks
Date Substrate Information Process Information SEM images of trenches
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, 600 nm oxide, 5% open Process A 110 cycles or 20:10 minutes, C01549.01
Trench width (µm) 2 3 4 6 8 10 15 25 40 50 75 100 150 200 300
Etched depth (µm) 175 195 209 229 247 260 289 330 370 393 428 454 488 507 523
Av. ER (µm/min) 8,7 9,7 10,4 11,3 12,3 12,9 14,4 16,3 18,3 19,5 21,2 22,5 24,2 25,2 25,9
Av. Scllp hght (nm) 1591 1772 1902 2079 2247 2359 2631 2997 3364 3569 3888 4124 4434 4614 4751
Sdwall bowing (%) 0,12 0,20 0,30 0,35 0,32 0,35 0,40 0,30 0,41 0,24 0,33 0,32 0,47 0,71 0,00
Sdwall angle (degs) 89,6 89,9 89,9 90,1 90,2 90,3 90,7 90,9 91,1 91,4 91,5 91,5 91,2 91,6 91,7
Trench width (µm) 8,5 9,5 10,8 13,2 16,0 18,4 22,6 33,0 48,0 57,5 82,7 106,8 159,0 207,0 306,8
January 2013 Travka10, 600 nm oxide, 10% open Process A 110 cycles or 20:10 minutes, C01549.02
Trench width (µm) 2 3 4 6 8 10 15 25 40 50 75 100 150 200 300
Etched depth (µm) 164 179 190 209 224 238 263 300 337 358 388 404 438 452 469
Av. ER (µm/min) 8,1 8,9 9,4 10,4 11,1 11,8 13,1 14,9 16,7 17,7 19,2 20,0 21,7 22,4 23,2
Av. Scllp hght (nm) 1489 1626 1730 1899 2034 2163 2395 2724 3063 3251 3526 3671 3978 4110 4262
Sdwall bowing (%) 0,20 0,41 0,46 0,57 0,74 0,62 0,68 0,75 0,58 0,99 0,54 0,49 0,72 0,51 0,77
Sdwall angle (degs) 89,7 90,0 89,9 90,1 90,2 90,3 90,8 91,2 91,5 91,3 92,0 92,2 92,6 92,8 93,6
Trench width (µm) 7,9 8,7 10,4 12,6 16,1 18,1 22,8 33,5 49,3 58,1 83,1 108,6 157,0 207,1 301,3
January 2013 Travka20, 600 nm oxide, 20% open Process A 110 cycles or 20:10 minutes, C01549.03
Trench width (µm) 2 3 4 6 8 10 15 25 40 50 75 100 150 200 300
Etched depth (µm) 142 153 164 181 195 206 228 258 287 303 326 342 366 380 392
Av. ER (µm/min) 7,0 7,6 8,1 9,0 9,7 10,2 11,3 12,8 14,2 15,0 16,2 17,0 18,2 18,8 19,4
Av. Scllp hght (nm) 1288 1390 1493 1647 1775 1877 2073 2342 2612 2754 2967 3108 3331 3451 3561
Sdwall bowing (%) 0,54 0,77 1,08 0,83 1,06 0,91 0,95 1,07 0,88 0,75 0,95 0,05 0,83 0,73 0,46
Sdwall angle (degs) 89,6 89,6 89,8 90,2 90,3 90,6 90,9 91,5 91,6 91,8 92,3 93,3 92,5 92,9 93,0
Trench width (µm) 7,2 8,7 9,9 12,4 14,7 16,9 22,8 31,1 48,4 58,0 81,9 108,6 160,4 209,9 311,1
January 2013 Travka35, 600 nm oxide, 35% open Process A 110 cycles or 20:10 minutes, C01549.04
Trench width (µm) 2 3 4 6 8 10 15 25 40 50 75 100 150 200 300
Etched depth (µm) 131 146 155 164 181 205 226 234 254 264 277 284 292
Av. ER (µm/min) 6,5 7,2 7,7 8,2 9,0 10,2 11,2 11,6 12,6 13,1 13,8 14,1 14,5
Av. Scllp hght (nm) 1189 1325 1408 1495 1642 1867 2050 2125 2312 2398 2523 2584 2653
Sdwall bowing (%) 1,35 1,37 1,25 1,28 1,24 1,45 1,30 1,42 1,50 1,38 1,18 0,76 0,81
Sdwall angle (degs) 89,4 89,6 89,9 90,0 90,3 91,0 91,7 91,9 92,3 92,4 93,0 93,0 93,5
Trench width (µm) 8,8 11,3 13,5 16,0 21,2 31,1 46,3 56,5 81,2 108,0 157,7 210,0 310,4
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