Titanium Nitride (TiN) is a wear resistant and complementary metal oxide silicon (CMOS) compatible material that is increasingly being investigated for MEMS applications. Incorporating any new material into a MEMS device requires the development of a processing strategy. This paper discusses a wet-etching strategy for patterning and releasing TiN features on Cr sacrificial layers. Filtered arc TiN films were deposited onto Cr coated Si (100) substrate. A Cr contact mask was sputtered over the TiN and patterned using UV photolithography. Patterned TiN features were examined using scanning electron microscopy (SEM). Rutherford Backscattering Spectroscopy (RBS) was carried out to investigate the selective etching of TiN and Cr in their respective etchants, which consisted of SC-1 for etching the TiN and a commercial chromic acid solution for etching the Cr. The results showed that Cr was not etched by SC-1 and that TiN was not etched by the Cr etchant.
This paper presents the results on single-shot laser micromachining of filtered arc deposited TiN films and compares the machining characteristics of the films deposited under partially and fully filtered conditions. Machining performance was evaluated in terms of patterning quality and the ability to perform selective removal of top TiN film with minimal interference to an underlying layer. TiN was arc-deposited onto silicon substrate with a chromium layer on the top. These films were analysed for their composition and microstructure using Rutherford Backscattering Spectroscopy (RBS) and Scanning Electron Microscopy (SEM) before and after laser machining. Under single shot conditions the effect of fluence on the machined features has been investigated. The results showed selective removal of TiN films with a single shot from the underlying Cr layer. Further, this work clearly shows a distinction between the laser machining characteristics of the films deposited under different filtering conditions and substrate temperatures.
A pulsed excimer laser (248 nm) based LIGA-like process is presented for the fabrication of Ni serpentine microstructures, such as those that might be used for micro-heaters. The structures were produced on both Cu (60 micrometers ) clad PCB and on Cu/Ti (up to 4 micrometers /15 nm) sputtered Si (100) substrates. The substrates were coated with a Laminar dry film (35 micrometers ) photoresist, which was then patterned by laser ablation to produce the mould for Ni electroforming. The optimal ablation conditions were identified for laser patterning to prepare the micro polymer mould. Beam fluence (~ 1 J/cm2) and number of shots (~ 60 pulses) for 50 micrometers wide features on this photoresist were established, and it was observed that an increased number of shots and increased fluence were needed for features less than 20 micrometers wide. Additionally, the Cu layer surface was cleaned by the use of 5 -10 laser pulses at the same fluence. Ni electroforming has been carried out using standard Ni sulfamate bath at a current density of ~ 10 mA/cm2. After Ni electroforming, both the Laminar dry film and the Cu layers around the electroformed Ni patterns were removed using a combination of acetone, laser and Cu selective etching. Finally, a series of Ni microstructures were fabricated consisting of up to 50 micrometers wide and 35 micrometers thick serpentine tracks. The devices were measured using a scanning confocal microscope and it was found that using the excimer laser to remove the remaining dry film laminate also smoothed the electroplated Ni surfaces from a pre-laser treated Ra of 1.20 micrometers to 0.19 micrometers . Laser ablation also released the finer features from the substrate.
In this work, the relative performance of patterning TiN film from metal sacrificial layers using a 248nm excimer laser is presented. Patterning performance was determined by investigating etching behavior in terms of edge quality, film delamination and layer selectivity. Using <100> silicon as a substrate, TiN was arc deposited onto sputtered Cr and Cu sacrificial layers and silicon in a partially Filtered Arc Deposition (FAD) system at 150 degree(s)C. The TiN films were directly patterned into matrixes of fluence verses number of shots. The results show excellent patterning of TiN from Cr sacrificial layers in terms of pattern quality and film selectivity. The TiN ablated from a Cu sacrificial layer produced poor patterning and no layer selectivity. The experimental results are presented and discussed in relation to the explosion mechanism of ablation.