Specific Process Knowledge/Etch/DRIE-Pegasus/processB

Process B

Process B is labelled Via (30μm diameter) 100μm depth. In the acceptance test the process was run on a 150 mm SPTS wafer with 12-13 % etch load.

Process B specifications

Parameter	Specification	Average result
Etch rate (µm/min)	> 10	10.7
Etched depth (µm)	100	107
Scallop size (nm)	< 800	685
Profile (degs)	91 +/- 1	90.7
Selectivity to AZ photoresist	> 100	183
Undercut (µm)	<1.5	0.89
Uniformity (%)	< 3.5	2.7
Repeatability (%)	<4	0.47

Process B recipe

Main etch (D->E)	Etch	Dep
Gas flow (sccm)	SF6 350 O2 35	C4F8 200
Cycle time (secs)	7.0	4.0
Pressure (mtorr)	20 (1.5 s) 100	25
Coil power (W)	2800	2000
Platen power (W)	130 (1.5) 40	0
Cycles	55 (process time 10:05)
Common	Temperature 10 degs, HBC 10 torr, Short funnel, with baffle & 5mm spacers

Experiment with process B performance

Purpose

Perhaps the most commonly occuring question posed by users of the dry etch tools is something like ' I want to etch my trenches down to a depth of 40 microns, how long should I etch?'. The answer is that it depends on the width of the trench and on the etch load of your design (that is how many percent of the wafer it etched).

An experiment has been set up to investigate the etched depth of a number of different trenches (with widths ranging from 2 microns to 300 microns) as a function of etch load (the exposed area ranges from 5 % to 65 %)

Results

A number of wafers are patterned with the travka masks in 4 microns of AZ photoresist. The wafers are then etc

Wafers

Wafers Wafer number Mask Process B duration 2 Travka 05 17 cycles or 3:07 mins 3 Travka 05 34 cycles or 6:14 mins 5 Travka 10 17 cycles or 3:07 mins 6 Travka 10 34 cycles or 6:14 mins 8 Travka 20 17 cycles or 3:07 mins 9 Travka 20 34 cycles or 6:14 mins
Wafer number	Mask	Process B duration
11	Travka 35	17 cycles or 3:07 mins
12	Travka 35	34 cycles or 6:14 mins
14	Travka 50	17 cycles or 3:07 mins
15	Travka 50	34 cycles or 6:14 mins
17	Travka 65	17 cycles or 3:07 mins
18	Travka 65	34 cycles or 6:14 mins

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Travka 05: A-line 2 µm to 25 µm fields Trench width (µm) Ridge width (µm) Period width (µm) Total periods Width of array (µm) 2 38 40 2 80 3 57 60 3 180 4 76 80 2 160 6 114 120 1 120 8 152 160 1 160 10 190 200 1 200 15 285 300 1 300 25 475 500 1 500

Travka 05: A-line 40 µm to 300 µm fields Trench width (µm) Ridge width (µm) Period width (µm) Total periods Width of array (µm) 40 760 800 1 800 50 950 1000 1 1000 75 1425 1500 1 1500 100 1900 2000 1 2000 150 2850 3000 1 3000 200 3800 4000 1 4000 300 5700 6000 1 6000

• The results of process B after 17 and 34 cycles of etching
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  The 60 nm trenches