• PDF / 709,642 Bytes
• 4 Pages / 593.28 x 841.68 pts Page_size
• 67 Downloads / 247 Views

DOWNLOAD

REPORT

---

Crystalline perfection of chemical vapor deposited diamond films A.V. Hetherington, C. J. H. Wort, and P. Southworth Plessey Research Caswell Ltd., Towcester, Northants, NN12 8EQ, United Kingdom (Received 25 January 1990; accepted 11 April 1990) The crystalline perfection of microwave plasma assisted chemical vapor deposited (MPACVD) diamond films grown under various conditions has been examined by TEM. Most CVD diamond films thus far reported contain a high density of defects, predominantly twins and stacking faults on {111} planes. We show that under appropriate growth conditions, these planar defects are eliminated from the center of the crystallites, and occur only at grain boundaries where the growing crystallites meet.

The unique characteristics of diamond make it extremely attractive for numerous materials applications, and it has a role to play both in tribology and electronics.1"5 With the development of a technique to grow diamond films by low pressure gas activation,6'7 a new manufacturing route has evolved. Epitaxial diamond has been grown on diamond substrates,7'8 and polycrystalline films have been grown on various non-diamond substrates.9"11 However, the numerous attempts to grow diamond films on non-diamond substrates have yielded only highly defective polycrystalline films.1213 In this paper we report a significant improvement in the crystalline quality of MPACVD diamond films grown on Si substrates. The growth system is described in detail elsewhere14 and is summarized below. Prior to growth, the silicon substrates were abraded with 4 ^.m diamond powder to provide sufficient nucleation sites to form a film. The essence of the technique is a microwave frequency hydrogen discharge containing about 1% hydrocarbon (e.g., methane) above a hot silicon substrate on which the film is deposited. The discharge provides copious quantities of atomic hydrogen and sufficient energy to crack the hydrocarbon into the necessary C-H radicals for diamond nucleation and growth. It is possible for both diamond and graphite to form on the substrate; however, any graphite is removed by the hydrogen plasma to leave a growing film of pure diamond. The films were examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) with a JEOL 120CX transmission electron microscope fitted with a high resolution SEM unit. For SEM study a portion was cut from the wafer on removal from the growth chamber and examined without further preparation. For TEM study a portion of as-grown sample was polished from the substrate side, first with J. Mater. Res., Vol. 5, No. 8, Aug 1990

http://journals.cambridge.org

Downloaded: 18 Mar 2015

SiC paper, and then with alumina suspension in water, to a thickness of 30 ^tm. 3 mm disks were cut ultrasonically, mounted on copper washers, and ion-milled with 5 kv argon ions from the substrate side until perforation occurred. Observations of two films are presented here and the growth parameters are given in Table I. The main difference is that the pressure was lower for fi