Low-stress Silicon-rich Nitride Research Articles

Direct bonding of ALD Al2O3 to silicon nitride thin films

Direct bonding is an advanced joining technique for bonding of silicon based surfaces at low temperature without any specific surface pretreatment. The main purpose of this work is to develop new techniques to enhance the fabrication process for nanofluidic systems for in situ transmission electron microscopy (TEM) by improving low temperature annealing bonding strength when using atomic layer deposition of aluminum oxide. We have investigated and characterized bonding of Al2O3–SixNy (low stress silicon rich nitride) and Al2O3–Si3N4 (stoichiometric nitride) thin films annealed from room temperature up to 600°C without pretreatment prior to the pre-bonding. We find that bonding of Al2O3–SixNy and Al2O3–Si3N4 is favorable in a temperature range from room temperature to 600°C. We report bonding strength of 1300±150mJ/m2 comparable to and in some case even higher than that of other materials Al2O3 can be bonded to. Preliminary tests demonstrating a well-defined nanochannel system with ~100nm high channels successfully bonded and tests against leaks using optical fluorescence technique and transmission electron microscopy (TEM) characterization of liquid samples are also reported. Moreover, the current bonding method can be also used for further MEMS applications.

Thermal and mechanical analysis of a microreactor for high temperature catalytic gas phase reactions

In this contribution we describe the results of a study into the thermal and thermo-mechanical behavior of a high temperature micro gas reactor for investigation of the intrinsic reaction kinetics of rhodium-catalyzed direct catalytic partial oxidation (CPO) of methane into synthesis gas. The chip comprises a flow channel etched in silicon, capped with a thin composite membrane of heavily boron-doped silicon (p ++-Si) and low stress silicon-rich nitride (SiRN), on which thin film heaters and sensors are located. The results of analytical and numerical models, which are verified with experimental results, can be used as general guidelines for the design of membrane-based microreactors. It is found that a membrane composition of 850 nm p ++-Si and 150 nm SiRN result in time constants of 1 ms for heating up as well as cooling down, which enables the required fast control of the exothermic reaction. Thermo-mechanical analyses demonstrated that this membrane is mechanically stable for temperatures up to at least 700 °C. Although the shape of the heaters — meander or sinusoidal — does not influence the mechanical stress profiles significantly, a decrease in heater width compared to the membrane width results in a drastically improved thermal efficiency of the microreactor. Furthermore, thermal considerations showed that exact temperature distribution in the composite membrane is mainly determined by the heater width in combination with the thickness of the heavily boron-doped silicon part of the membrane and its (temperature-dependent) thermal conductivity.

Optimization of fully-implanted NPNs for high-frequency operation

With a very straightforward (low-cost) process flow as basis, fully-implanted washed-emitter-base (WEB) NPNs have been optimized for operation in the 10-30 GHz range. Above 20 GHz the best overall performance is achieved by heavy doping of the epi. A low-stress silicon rich nitride layer is proven effective as surface isolation before contact window dip-etch.

Low-stress nitride as oxidation mask for submicrometre LOCOS isolation

A large reduction in the LOCOS bird's beak is obtained by using a thick silicon nitride layer as an oxidation mask. Stress induced damage of the devices is avoided by using low-stress silicon-rich nitride. >