Diamond and Related Materials 8 (1999) 220–225 The eﬀect of nitrogen on the growth, morphology, and crystalline quality of MPACVD diamond ﬁlms J. Asmussen *, J. Mossbrucker, S. Khatami, W.S. Huang, B. Wright, V. Ayres Department of Electrical Engineering, Michigan State University, East Lansing, MI 48824, USA Received 27 July 1998; accepted 22 October 1998 Abstract The inﬂuence of varying nitrogen concentrations (5–1000 ppm) on the conventional CH 4 /H 2 diamond ﬁlm deposition process using a microwave plasma disk reactor is investigated. This reactor has important diﬀerences, such as reactor volume, power density, gas ﬂow, from the common tubular microwave reactors. The experimental behavior indicates, that similar to the tubular reactors, the addition of small amounts of a nitrogen stabilizes the growth of high quality, {100} faceted ﬁlms. However, the actual threshold nitrogen concentrations and the variation of these threshold concentrations versus other independent experimental variables diﬀers considerably from tubular reactor performance. This suggests that reactor design has an important inﬂuence on the deposition process in the presence of impurities. © 1999 Elsevier Science S.A. All rights reserved. Keywords: MPACVD diamond ﬁlms; Nitrogen; Morphology; Crystalline quality 1. Introduction play an active role in the chemical reactions occurring in the bulk plasma as well as on the deposition surface. The inﬂuence of nitrogen is a complex function of many The addition of nitrogen (N ) to the conventional CH 4 /H 2 input diamond ﬁlm synthesis gases has been experimental variables such as methane concentration, pressure, power, substrate temperature, etc. The changes shown to have an important inﬂuence on the CVD synthesis of diamond ﬁlms [1–6 ]. For example high in morphology, texture, ﬁlm quality and growth rate are also reactor dependent. Thus diﬀerent CVD reactor N-concentrations result in nanocrystalline and black ﬁlms containing graphite or amorphous carbon [1–3], designs synthesize diﬀerent ﬁlms under similar input conditions. Earlier investigations have made use of and very high N-concentrations, i.e. 20%, can completely inhibit diamond growth [2]. In contrast, the addition of similar tubular and vertical ﬂow microwave reactors [1–6 ]. In this paper the inﬂuence of nitrogen gas on only 20–100 ppm of nitrogen can have a beneﬁcial eﬀect. At deposition pressures of 20–60 Torr N-concentrations diamond deposition using a microwave cavity plasma reactor is investigated. of only a few 10 ppm stabilize the formation of smooth, 100 textured diamond ﬁlms [4], and at higher depos- ition pressures and higher input power densities the deposition rate is increased by factors of 3–5 with the addition of only 25 ppm of nitrogen [5]. Despite nitro- 2. The experimental system and procedures gen’s important impact on diamond ﬁlm synthesis it has been noted that even at high input concentrations, 2.1. The microwave reactor and vacuum system N-incorporation in the ﬁlms is low [2]. These observed changes in ﬁlm synthesis and properties suggest that The deposition experiments were performed using a atomic nitrogen and other N-containing radicals may microwave plasma disk reactor [7]. A cross-sectional view of the reactor is displayed in Fig. 1. As has been described in detail earlier [8], the impressed TM 013 * Corresponding author. Fax: +1 517 353 1980; e-mail: asmussen@egr.msu.edu microwave electromagnetic ﬁeld creates a discharge 0925-9635/99/$ – see front matter © 1999 Elsevier Science S.A. All rights reserved. PII: S0925-9635(98)00371-9