High Density Plasma Etching Damage Effects on Contacts to n -GaN
- PDF / 168,034 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 78 Downloads / 204 Views
High Density Plasma Etching Damage Effects on Contacts to n-GaN Rajwinder Singh, C. R. Eddy, Jr. 1 and T.D. Moustakas Boston University, Department of Electrical & Computer Engineering, & Photonics Center 8 St. Mary’s Street Boston MA 02215, USA. H.M. Ng Bell Laboratories, Lucent Technologies, 600 Mountain Avenue, Room 6H-424 Murray Hill 07974 NJ, USA ABSTRACT The effects of inductively-coupled plasma etching on the quality of ohmic contacts to etched nGaN are reported. A high density chlorine plasma and a range of rf bias power levels (incident ion energies) are employed to etch n-GaN films with varying doping levels. Resulting plasma damage degrades contact ohmicity in all cases examined. At moderate levels of rf bias power the extent of this degradation for nitride layers with lower doping levels (mid-1017 cm-3) is similar to the degradation for nitride layers with higher doping levels. With increased rf bias, the degradation becomes more severe in films with higher carrier concentration. Annealing at 700 oC rapidly improves the contact quality. Studies of cumulative annealing time, up to 160 seconds, show that the improvement in contact quality takes place within the first twenty seconds of annealing. INTRODUCTION GaN and related compound semiconductors have attracted much interest in recent years due to their suitability in a range of applications including blue and ultraviolet light emitters and detectors, and high temperature, high power, and high frequency electronics [1]. The properties of GaN and alloys incorporating Al and In, responsible for their suitability in these applications include a wide range of bandgaps, high electron-saturation velocity, good thermal conductivity, and good resistance to device degradation with time [2]. The high bond energy of the bonds between N and the group III elements is a major contributor to these desirable characteristics of the nitride semiconductors [3]. At the same time, the high bond energy of the group III-N bonds makes it difficult to etch structures into the nitride films using the conventional wet etching schemes common in semiconductor processing. Due to its ability to give sufficiently high etch rates, plasma etching by various techniques is the leading candidate for etch processing of nitride semiconductors [4]. Among the various plasma etching techniques, high density plasma etching gives some of the fastest etch rates, with lower etch damage levels [4].
1 [email protected]
G6.61.1
Inductively coupled plasma etching, like other high density plasma etching techniques, allows independent control over ion energies and ion flux, giving flexibility in controlling the etch process [5]. A wide range of gases and gas mixtures can be employed to obtain optimal results in terms of etch rates, selectivity, surface morphology and electrical properties. While some investigations of metal contacts to high density plasma etched nitride semiconductors have been reported [6-8], much work remains to be done. This paper reports the results of experimental work conducted in the
Data Loading...
