Specific Process Knowledge/Etch/DRIE-Pegasus/processB

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Process B

Process B was run on a 150 mm 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 mask set in 4 microns of AZ photoresist. The wafers are then etched using two different durations of process B in the DRIE-Pegasus.

Wafers Wafer number Mask Process B duration 2 Travka 05 17 cycles, 3:07 mins 3 Travka 05 34 cycles, 6:14 mins 5 Travka 10 17 cycles, 3:07 mins 6 Travka 10 34 cycles, 6:14 mins 8 Travka 20 17 cycles, 3:07 mins 9 Travka 20 34 cycles, 6:14 mins

Wafers Wafer number Mask Process B duration 11 Travka 35 17 cycles, 3:07 mins 12 Travka 35 34 cycles, 6:14 mins 14 Travka 50 17 cycles, 3:07 mins 15 Travka 50 34 cycles, 6:14 mins 17 Travka 65 17 cycles, 3:07 mins 18 Travka 65 34 cycles, 6:14 mins

After etching each wafer is cleaved in two places: Both cleavage lines run across the A-line fields. This produces three sites on each wafer where the depth of the trenches can be determined using an SEM.

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