Titanium for MEMS Applications

Titanium for MEMS Applications - Dry Etching

Material Name: Titanium
Recipe No.: 8505
Primary Chemical Element in Material: Ti
Sample Type: Bulk
Uses: Etching
Etchant Name: None
Etching Method: Dry etching
Etchant (Electrolyte) Composition: Two different titanium material types were used for this set of experiments. Commercially pure Grade 1 titanium sheets with polished finish .Tokyo Stainless Grinding Co., Ltd, Tokyo, Japan. approximately 500 .m thick were purchased and used for the etch characterization and high aspect ratio etching. These substrates were sectioned into 2.5 x 2.5 cm samples using a mechanical shearing tool (24-in. Bench-Top square cut shears, McMaster-Carr, Los Angeles, CA). Titanium thin foils 2.5 x 2.5 cm, 99.6% annealed, Goodfellow Corporation, Devon, PA. were also purchased and used for the thin-foil etching experiments. These foils ranged in thickness from 10 to 100 µm and required chemical mechanical polishing (MultiPrep System, Allied High Tech Products, Inc., Rancho Dominguez, CA) prior to lithography. All samples were cleaned in acetone and isopropanol with ultrasonic agitation in preparation for processing. The general bulk titanium process flow included the following steps: (1) TiO2 mask deposition; (2) photolithographic patterning; (3) mask oxide etching; and (4) titanium deep etching. The oxide etch and titanium deep etch were both performed using the same ICP etch tool (Panasonic E640-ICP dry etching system, Panasonic Factory Solutions, Osaka, Japan). The titanium samples were mounted on a 6-in. silicon carrier wafer using diffusion pump fluid (Santovac 5, polyphenyl ether pump fluid, Santovac Fluids, Inc., St. Charles, MO), which was used to create adequate thermal conductivity between carrier wafer and sample. The lower electrode of the etching tool was held constant at 20°C, and helium backside cooling at 400 Pa was used to maintain constant carrier wafer temperature during all etches.

The TiO2 etch mask was deposited using reactive sputtering .Endeavor 3000 cluster sputter tool, Sputtered Films, Santa Barbara, CA. with a titanium target in an O2/Ar environment using the following process conditions: 10 sccm O2, 20 sccm Ar, and 2300 W power. The process pressure was approximately 5.2 mT. Each sample was sputtered for 4500 s, resulting in an average film thickness of 1.25 µm. Features were then patterned onto the TiO2 mask using 3 µm thick photoresist (SPR 220-3.0, Shipley, Marlborough, MA).

The photoresist pattern was transferred into the oxide using a CHF3 chemistry under the following conditions: 500 W ICP source power (13.56 MHz., 400 W sample rf power (13.56 MHz), 1 Pa pressure, and 40 sccm CHF3. Each sample was etched for 10 min, removed from the carrier wafer, and then cleaned in acetone and isopropanol with ultrasonic agitation. The remaining fluorinated photoresist was removed using an O2 plasma (PEII-A Plasma System, Technics) under the following conditions: 300 mT pressure, 100 W power. After cleaning, the patterned sample was remounted onto a silicon carrier wafer for the titanium deep etch. For the characterization etches, each sample was etched in a Cl2/Ar chemistry for 2 min with a specified parameter set. Only a single parameter was varied for each etch. Unless otherwise stated, all other parameters were held constant at the following values: 400 W ICP source power (13.56 MHz., 100 W sample rf power (13.56 MHz), 2 Pa pressure, 100 sccm Cl2, and 5 sccm Ar. Etch depths ranged from approximately 0.5 to 4.7 µm over the chosen parameter space. The high aspect ratio etching and titanium thin-foil etching were both performed using longer etch times at parameters within the tested characterization space.
Procedure (Condition): No data
Note: No data
Reference: E. R. Parker, et al., Inductively Coupled Plasma Etching of Bulk Titanium for MEMS Applications, Journal of The Electrochemical Society, 152 (10) C675-C683 (2005).