Large Batch Etching of Gallium Nitride Using Inductively Coupled Plasma Tools as a Production Solution
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1195-B03-06
Large Batch Etching of Gallium Nitride Using Inductively Coupled Plasma Tools as a Production Solution
Zhong Ren1, Mark Dineen1, Ligang Deng1, Andrew L.Goodyear1 and Robert Gunn1 1
Oxford Instruments Plasma Technology, North End, Yatton, Bristol, BS49 4AP, UK
ABSTRACT A highly effective technique for etching large batches of GaN wafers, by means of Inductively Coupled Plasma (ICP) tools, has been developed. A variety of 27 × 2 inch wafer batch processes have been investigated and etch rates in excess of 140nm/min with selectivity of 0.9:1 to photoresist (PR) has been achieved. Particularly, a special active spacer was designed and employed in the ICP system to control plasma profile during the processes. This technique was favourable for increasing etch rates and achieving good uniformities. Using this system a wafer-to-wafer batch uniformity of ±4% was realized.
INTRODUCTION In recent years Gallium Nitride (GaN) material has become one of the most important segments of the high bright light emitting diode (HB-LED) and laser diode (LD) semiconductor industry. With its extensive application in large screen display technology and solid state lighting there is a drive for the fabrication roadmap to give dramatic acceleration in throughput. As the majority of wafer sizes remain at 2 inch this translates as increased batch sizes. In order to etch GaN it is essential to use plasma etching techniques because of the high bonding energy in the GaN lattice and lack of reliable wet etch method [1]. With higher density plasmas attainable using Inductively Coupled Plasma (ICP) etching it is possible to achieve high etch rates in comparison to parallel plate reactors, with the rates also reached at lower DC Bias levels [2].
This paper reports a highly effective technique for etching large batches of GaN wafers, by means of ICP tools as an industrial production solution. Particularly, a special active spacer was designed and employed in the ICP system to control plasma profile during the etching processes. This technique was favourable for increasing etch rates and achieving good uniformities.
EXPERIMENT The samples used for the etch tests comprised a 7 µm GaN epilayer, including an active region, grown on 2 inch sapphire substrates by metal organic chemical vapor deposition (MOCVD). Then 8 µm thick PR masks were patterned on the GaN face of the wafers by optical lithography. A pre-etched wafer was cleaved and checked by field-emission SEM (FE-SEM) tools, as shown in Figure 1 (a).
(a)
(b)
Figure 1 (a) The thickness of pre-etched PR masks was 8 µm with a near vertical profile; (b) 27 pieces of 2 inch GaN wafers, including 9 test wafers with PR masks and 18 dummy wafers which were completely covered by PR, were placed on a SiC carrier-plate in system’s load-lock.
Our etching experiments were carried out in an Oxford Instruments Plasma Technology Plasmalab133-ICP380 system using BCl3 and Cl2 as process gases. The ICP system is shown in Figure 2, the lower electrode is 330 mm in diameter and its temperature is
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