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**
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

**Wafers**
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

**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
The 60 nm trenches