Specific Process Knowledge/Etch/ICP Metal Etcher

The ICP Metal Etcher

The ICP Metal Etcher allows you to dry etch a small set of metals that includes aluminium, titanium, chromium, titanium tungsten and molybdenum (along with the related oxides and nitrides). It is, despite its name, strictly forbidden to etch (or expose to plasma) other metals. In order to do so use the IBE/IBSD Ionfab 300.

The gasses available for etching include flourine, chlorine and bromine.

Process information

• Etch of aluminium
• Etch of titanium
• Etch of chromium

An overview of the performance of the ICP Metal Etcher and some process related parameters

Purpose	Dry etch of	Metals such as aluminium, chromium and titanium and the related oxides and nitrides Metals such as molybdenum, tungsten, titanium tungsten
Performance	Etch rates	Alumninium : ~350 nm/min (depending on features size and etch load)
	Anisotropy	Good
Process parameter range	Process pressure	~0.1-95 mTorr
	Gas flows	SF6: 0-100 sccm O2: 0-100 sccm C4F8: 0-100 sccm Ar: 0-100 sccm CF4: 0-100 sccm H2: 0-30 sccm CH4: 0-50 sccm BCl3: 0-100 sccm Cl2: 0-100 sccm HBr: 0-100 sccm
Substrates	Batch size	1 6" wafer per run 1 4" wafer per run 1 2" wafer per run Or several smaller pieces on a carrier wafer
	Substrate material allowed	Silicon wafers with layers of silicon oxide or silicon (oxy)nitride Quartz wafers
	Possible masking material	Photoresist/e-beam resist PolySilicon, Silicon oxide or silicon (oxy)nitride Aluminium, titanium or chromium

Recipes on the Metal Etcher

Aluminium etch

The aluminium etch has two steps:

Breakthrough

The breakthrough step is designed to break through the native aluminium oxide layer that is present on all aluminium surfaces. The duration of this step should remain fixed.

Main

The main step etches bulk aluminium.

Al etch

Parameter	Process step
	Breakthrough	Main
Time (secs)	20	40 (variable)
HBr (sccm)	-	15
Cl2 (sccm)	20	25
Pressure (mTorr)	2, Strike 3 secs @ 15 mTorr???	1
Coil power (W)	600	500
Platen power (W)	125	100
Temperature (oC)	20	20
Spacers (mm)	30	30

Titanium etch

Ti etch

Parameter	Process 1	Process 2
Cl2 (sccm)	30	30
HBr (sccm)	-	-
Pressure (mTorr)	3, Strike 3 secs @ 15 mTorr???	3
Coil power (W)	800	900
Platen power (W)	100	50
Temperature (oC)	20	20
Spacers (mm)	30	30
Etch rate (nm/min)	152	64
AZ resist selectivity	0.67	0.83

Chromium etch

The Chromium etch has ONLY been carried out on the following substrate stack: The Chromium is sputter deposited onto a 2" quartz wafer and pattered by e-beam with Zep520A resist. This 2" QZ wafer is bonded with crystal bond to a 65mmx65mm quartz plate with the thickness: 6.35mm. This QZ plate is bonded to a Si wafer.

Cr etch

Parameter	Cr etch
Cl2 (sccm)	65
O2 (sccm)	15
Pressure (mTorr)	15
Coil power (W)	300
Platen power (W)	15
Temperature (oC)	50 (no back side cooling)
Spacers (mm)	100
Etch rate (nm/min)	~14
Zep520A resist selectivity	~0.9
Comment	.

Etching of nanostructures in silicon

A series of experiments with etching nanostructures in silicon has been carried out. The common process parameters are:

Substrates

A pattern containing 30 nm, 60 nm, 90 nm, 120 nm and 150 nm wide lines has been transferred using E-beam lithography onto three separate batches of 2" wafers (with three different thicknesses of zep resist). In order to make sure that the narrowest features are fully opened they are intentionally over-exposed in the E-beam writer (400 muC/cm2) causing the lines to widen. The resist profiles of the three batches are:

• The 180 nm zep resist profiles (Wafer WF_2B1_feb06_2011)
• The 340 nm zep resist profiles (Wafer WF_2C1_feb2011)
• The 211 nm zep resist profiles (Wafer WF_2E02_mar23_2011)

The exposed area is very small. The 211 nm batch has the same lines distributed in a different way that allows you monitor the progress of the etch in three different durations by cleaving off a piece of the wafer 3 times. After E-beam exposure the wafers have been developed: N50 for 2 minutes followed by 30 seconds of IPA.

Substrate mounting

The 2" wafers are mounted with crystalbond in the center of 4" Si carriers that have an oxide layer facing the plasma.

Conditioning the process chamber

Recipe Sinano	3.0	3.1	3.2	3.3	3.4	4.0	3.5	3.6	3.3	3.7	3.31	3.31	3.32
Cl2 (sccm)	0	0	0	0	0	20	15	15	0	0	0	0	0
BCl3 (sccm)	5	3	5	5	5	0	5	5	5	5	5	5	5
HBr (sccm)	15	17	15	15	15	0	0	0	15	15	15	15	15
Coil power (W)	900 L	900 F	900 F	900 F	900 F	900 L	900 L	900 F	900 F	900 L	900 F	900 F	900 F
Platen power (W)	50	50	60	75	90	60	60	60	75	60	75	75	30
Pressure (mtorr)	2	2	2	2	2	2	5	10	2	10	2	2	2
Temperature (oC)	20	20	20	20	20	20	20	20	20	50	50	50	50
Spacers (mm)	100	100	100	100	100	100	100	100	100	100	100	30	100
Process time (s)	150	180	120	180	120	90	120	180	300	180	180	180	180
Etch rates (nm/min)
Averages	311	104	92	105	116	169	108	79	101	66	91	98	59
Std. Dev	44	15	15	21	22	9	11	31	29	4	28	18	12
Zep etch rate (nm/min)
		30	40	51	67			45	59		53	36	19
Sidewall angle (degrees)
Averages	82	82	82	82	82	84	81	83	83	85	80	83	79
Std. Dev	2	2	1	1	1	1	1	2	2	1	3	2	2
CD loss (nm pr edge)
Averages	65	-11	-15	-2	-11	67	63	-29	-5	-29	10	-14	-17
Std. Dev	30	5	2	4	3	29	27	6	5	8	7	8	10
Bowing (nm)
Averages	31	31	15	6	5	22	12	15	28	13	25	1	-2
Std. Dev	6	7	3	6	4	5	2	6	9	7	5	2	2
Bottom curvature
Averages	-9	-6	-9	-11	-9	9	-4	-8	-24	-2	-9	-13	-10
Std. Dev	22	19	19	11	7	17	15	15	12	15	13	17	18

• Nanoetch on DRIE-Pegasus
• 1 - the first nanoetch