Effect of annealing on the structural and electrical properties of d.c. multipolar plasma deposited a-C : H films

The changes upon annealing in C-H and C-C bonding in relation to the struct ural and electronic properties have been investigated in two different seri es of a-C:H samples prepared in a direct current (d.c.) multipolar plasma s ystem from pure methane at quite different substrate bias (-40 and -600 V). Using a combination of infrared absorption, elastic recoil detection analy sis, high resolution transmission electron microscopy and electrical resist ance measurements, we fully characterize the samples in their as-deposited state as well as after successive annealing cycles at increasing temperatur es up to 700 degrees C, The results show clearly that the two types of seri es exhibit quite different microstructures and hydrogen incorporation in th eir as-deposited state. The low bias (-40 V) series exhibits a highly disor dered structure, while the high bias (-600 V) one already contains well ord ered regions. They also have a completely different behavior upon annealing C ones occurs in the temperature range to high temperature. A microstructu re conversion such as from hydrogenated as well as non-hydrogenated sp(3) C sites to sp(2) C ones occurs in the temperature range 400-500 degrees C in all cases. However, a more efficient graphitization is observed in the hig h bias series (-600 V) for annealing temperatures as high as 700 degrees C, Quite surprising results are obtained for the low bias series (-40 V): con trarily to what is usually observed for this type of sample, this series is found to be more thermally stable for high annealing temperature (> 400 de grees C) than the high bias one (-600 V). These results are discussed and e xplained in terms of the relaxation process in the local microstructure. (C ) 2000 Elsevier Science S.A. All rights reserved.