Bulk- micromachined dielectric tunable optical filter realized with inductively coupled plasma chemical vapour deposition

Abstract

We present the characterization of silicon oxide (SiO x ) and silicon nitride (SiN x ) films deposited by inductively coupled plasma chemical vapour deposition (ICP-CVD) at low temperature (< 100 • C). A tunable optical FabryPérot (FP) -filter operating at a wavelength around 1.5µm is realized. It is hybridly assembled with two dielectric distributed Bragg reflectors (DBR). One of the DBR-mirrors is intentionally curved using the intrinsic stress inside the films. Our aim is the development of a tunable surface micromachined VCSEL with a curved dielectric mirror. Therefore ICP-CVD with a low deposition temperature is used for SiO x and SiN x films. As a first step the realization of a tunable bulk-mircomachined optical FP-filter is presented. The refractive index, deposition rate, stress and etching rate in buffered hydrofluoric acid (BHF) of thin dielectric films (<500 nm) in dependence on deposition temperature and on gas flow ratio are investigated. The knowledge of the deposition characteristics of the dielectric films is used to realize DBRs with a given curvature that are applied to electrothermally actuated, optical tunable FP-filters. The presented filter has a free spectral range of 29 nm, an insertion loss of 10 dB and a full width half maximum of 0.16 nm.

Depositon of Dielectric Films with Inductively Coupled Plasma‐CVD in Dependence on Pressure and Two RF‐Power‐Sources

“…[6,[9][10][11] Another consequential advantage by the application of nitrogen is the deposition of SiN x -films at low temperature with the same film quality as the SiN x -films deposited at 300 8C with ammonia. [4,6,10] Thereby it is possible to deposit SiN x and as well SiO x with a good film quality on temperature sensitive devices or materials. The investigated dielectric films are deposited at a temperature of 80 8C.…”

“…[4,6] The process gases (precursors) nitrogen N 2 and undiluted silane SiH 4 are used for the deposition of silicon nitride SiN x , whereas SiH 4 and nitrous oxide N 2 O are used for the deposition of silicon oxide SiO x . The main advantage of using N 2 instead of ammonia NH 3 is the lower concentration of hydrogen embedded in the deposited films.…”

“…a movable dielectric mirror can be manufactured by removing the sacrificial layer or the substrate. [4,7] The etching rate in BHF determines the film quality of the deposited dielectric films. It gives information about film composition and density, [8] but it cannot be determined which of these two characteristics have the most influence on the etching rate.…”

“…[3] Preliminary experimental results of devices with implemented dielectric films from ICP-CVD are presented elsewhere. [4,5] The PECVD with ICP-source that is also denoted as inductively coupled plasma chemical vapour deposition (ICP-CVD) deposits single dielectric films (SiO x , SiN x and SiO x N y ) or multifilm-structures. The low deposition temperature below 100 8C with a good film quality [4,6] enables the deposition of dielectric films on temperature sensitive devices and materials for antireflection-coating, passivation, insulating films, etc.…”

“…[4,5] The PECVD with ICP-source that is also denoted as inductively coupled plasma chemical vapour deposition (ICP-CVD) deposits single dielectric films (SiO x , SiN x and SiO x N y ) or multifilm-structures. The low deposition temperature below 100 8C with a good film quality [4,6] enables the deposition of dielectric films on temperature sensitive devices and materials for antireflection-coating, passivation, insulating films, etc. We investigate the influence of process parameters from the ICP-CVD in dependence on the deposition pressure and the applied power to the plasma from two RF-generators.…”