Improved Adhesion of P-doped SiO 2 -Interface Layers on InP by Low-Temperature Damage-Free Plasma-CVD
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ABSTRACT The deposition of thin films on III-V compound semiconductors is encountered with various interfacial problems. We present a new approach using a modified plasma technique in a phosphorous ambient at substrate temperatures ranging from 250 to 350 *C which covers two import aspects: Firstly, a good insulator quality due to the plasma process. Secondly, an appropriate surface pre-treatment and defect passivation by a phosphine-like cleaning process using a solid phosphorous source. The analysis of the film adhesion yields improved adhesive properties due to the high activation energy of a plasma process for surface reactions, and by preventing a phosphorus-related defects. The phosphorous concentration in the SiO 2 films has to be adapted in order to prevent electrical degradation of the SiO2-InP interface. The influence of phosphorous deficiency and excess phosphorous will be discussed.
INTRODUCTION InP is an attractive III-V compound semiconductor material for optoelectronic applications by virtue of its large bandgap, high electron mobility, low surface recombination velocity and low surface state density. However, III-V compounds in general suffer from a non-stable native oxide. Thus, various deposition techniques have been employed in order to replace the native oxide by other non-native dielectrics like SiO 2 , Si 3N 4 etc. High temperatures which occur in the fabrication of opto- electronic-integrated circuits ( OEICs), tend to alter the stoichiometry of the InP surface [1,2]. The deposition of thin films therefore is essential in OEIC technology for surface encapsulation during diffusion, contact alloying, implantation annealing or for passivation purposes [3]. Owing to the heteromorphic nature of the insulator-InP interface, considerable research efforts have been directed to achieve a reliable interface, providing sufficient electrical and physical properties. Major interest has emerged in photo CVD for the deposition of SiO 2 at 100 - 200 *C owing to its advantage of a damage-free process [1,4]. Nevertheless, uniformity and reliability problems become increasingly important in the case of this low-energy process [5]. Although plasma-enhanced CVD (PECVD) has made possible a deposition at low temperatures ( in the range of 200 400 OC ) providing high quality films, the bombardment by high-energetic
231 Mat. Res. Soc. Symp. Proc. Vol. 318. @1994 Materials Research Society
ions in the plasma process causes physical and chemical damage of the substrate [6-9]. However, we have developed a modified-plasma technique which keeps the high quality of the deposited films as known from conventional PECVD, and provides also a considerable reduction of the ion bombardment during the deposition [5,10]. Furthermore, dramatic changes in surface state densities can be obtained by chemical modification of the InP surface prior to the deposition using elements like 5, P, Si or As [1,11-15]. Although hydrogenation of InP by H2-plasma treatment is known to remove the native oxide and to passivate non-radiative recom
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