Jiashen Wei

Low stress PECVD—SiNx layers at high deposition rates using high power and high frequency for MEMS applications

The paper reports a new fabrication method for low stress SiNx layers at high deposition rates in a PECVD reactor using high power and high frequency (13.56 MHz) and their MEMS applications. By increasing the deposition power at 600 W in high frequency mode, a decrease of the tensile residual stress to values between 0 and 20 MPa was noticed. Meanwhile, the high power, which promotes a high dissociation of gases, generates a high deposition rate (in the range 250 to 350 nm min−1). In addition, the paper presents the influence of other important parameters that affect the residual stress and deposition rate such as pressure and SiH4, NH3 and N2 flow rates. SiNx layers fabricated at high power in high frequency mode were successfully used in two classical MEMS applications: fabrication of the masking layer for anisotropic wet etching in KOH solution and fabrication of a low stress cantilever.

A new fabrication method for low stress PECVD - SiNx layers

This paper presents a new method of depositing low stress silicon nitride (SiNx) with high deposition rate using a plasma-enhanced chemical vapour deposition (PECVD) system (STS, Multiplex Pro-CVD). By increasing the operating power of the PECVD system at the high frequency mode (13.56MHz), the deposition rate also increases while that the level of intrinsic stress within the SiNx film decreases. The relationships between some of the key deposition parameters of the experiment such as chamber pressure, silane (SiH4), ammonia (NH3) and nitrogen (N2) flow rates and the two important response variables namely the level of intrinsic stress and deposition rate are established within this investigation.

Low Stress PECVD SiNx Process for Biomedical Application

This paper presents a development in producing low residual stress PECVD SiNx layers at high deposition rates and their biomedical. The key factor in the novel process is the employment of up to 600 W high powers in high frequency (13.56 MHz). In conjunction with the adjustment of the reactant gases composition, the residual stress can he tuned to 4MPa and high deposition rate up to 320 nm/min can be achieved. Moreover, by using this optimized process, an 11 mum thick low stress SiNx layer was produced, which will be used to fabricate large area windows for cell culture. Finally, a cell culture test by cultivating mouse stem cells onto porous membrane by the low stress PECVD SiNx layers also indicated that these layers are biocompatible and are suitable for biomedical applications.

Transdermal drug delivery: Microfabrication insights

The paper presented an enhancement solution for transdermal drug delivery using microneedles array with biodegradable tips. The microneedles array was fabricated by using deep reactive ion etching (DRIE) and the biodegradable tips were made to be porous by electrochemical etching process. The porous silicon microneedle tips can greatly enhance the transdermal drug delivery in a minimum invasion, painless, and convenient manner, at the same time; they are breakable and biodegradable. Basically, the main problem of the silicon microneedles consists of broken microneedles tips during the insertion. The solution proposed is to fabricate the microneedle tip from a biodegradable material - porous silicon. The silicon microneedles are fabricated using DRIE notching effect of reflected charges on mask. The process overcomes the difficulty in the undercut control of the tips during the classical isotropic silicon etching process. When the silicon tips were formed, the porous tips were then generated using a classical electrochemical anodization process in MeCN/HF/H2O solution. The paper presents the experimental results of in vitro release of calcein and BSA with animal skins using a microneedle array with biodegradable tips. Compared to the transdermal drug delivery without any enhancer, the microneedle array had presented significant enhancement of drug release.

Low-stress PECVD amorphous silicon carbide (α-SiC) layers for biomedical application

A detailed characterization of PECVD to produce low stress amorphous silicon carbide (α-SiC) layers at high deposition rate has been done and the biomedical applications of α-SiC layers are reported in this paper. By investigating different working principles in high-frequency mode (13.56MHz) and in low frequency mode (380KHz), it is found that deposition in high-frequency mode can achieve low stress layers at high deposition rates due to the structural rearrangement from high HF power, rather than the ion bombardment effect from high LF power which results in high compressive stress for α-SiC layers. Furthermore, the effects of deposition temperature, pressure and reactant gas ratios are also investigated and then an optimal process is achieved to produce low stress α-SiC layers with high deposition rates. To characterize the PECVD α-SiC layers from optimized process, a series of wet etching experiments in KOH and HF solutions have been completed. The very low etching rates of PECVD α-SiC layers in these two solutions show the good chemical inertness and suitability for masking layers in micromachining. Moreover, cell culture tests by seeding fibroblast NIH3T3 cells on the monocrystalline SiC, low-stress PECVD α-SiC released membranes and non-released PECVD α-SiC films on silicon substrates have been done to check the feasibility of PECVD α-SiC layers as substrate materials for biomedical applications. The results indicate that PECVD α-SiC layers are good for cell culturing, especially after treated in NH4F.

Microneedles array with biodegradable tips for transdermal drug delivery

The paper presented an enhancement solution for transdermal drug delivery using microneedles array with biodegradable tips. The microneedles array was fabricated by using deep reactive ion etching (DRIE) and the biodegradable tips were made to be porous by electrochemical etching process. The porous silicon microneedle tips can greatly enhance the transdermal drug delivery in a minimum invasion, painless, and convenient manner, at the same time; they are breakable and biodegradable. Basically, the main problem of the silicon microneedles consists of broken microneedles tips during the insertion. The solution proposed is to fabricate the microneedle tip from a biodegradable material - porous silicon. The silicon microneedles are fabricated using DRIE notching effect of reflected charges on mask. The process overcomes the difficulty in the undercut control of the tips during the classical isotropic silicon etching process. When the silicon tips were formed, the porous tips were then generated using a classical electrochemical anodization process in MeCN/HF/H2O solution. The paper presents the experimental results of in vitro release of calcein and BSA with animal skins using a microneedle array with biodegradable tips. Compared to the transdermal drug delivery without any enhancer, the microneedle array had presented significant enhancement of drug release.