Properties of Aluminum Thin Films Prepared by Targets Facing Type of Sputtering System
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PROPERTIES OF ALUMINUM THIN FILMS PREPARED BY TARGETS FACING TYPE OF SPUTTERING SYSTEM T. HIRATA, S. KAKU* AND M. NAOE Tokyo Institute of Technology, Fac. of Engineering, Dept. of Electrical and Electronic Engineering, 2-12-1 O-okayama, Meguro-ku, Tokyo 152, Japan *Osaka Vacuum, Ltd., 3-6 Kitahama, Higashi-ku, Osaka 541, Japan
ABSTRACT
The Targets Facing Type of Sputtering (TFTS) system can deposit very dense films on substrates at a high rate without undesirable influences of the plasma. Using this system, Al films 0.7 r 1.5 pm thick were deposited in an argon gas pressure PAr of 9.7 x 10-2 Pa. The grains with irregular shape grew as PAr became high. However, the number of grains per unit area decreased and their size became small when the bias voltage to the substrate Vb was -40 V. Consequently, the film surfaces became smooth. The Al films became hardest at Vb of about -40 V and were twice as hard as ones prepared without the bias voltage. The step coverage of these Al films was very satisfactory to the wiring of the integrated circuit (IC) by adjusting Vb and PAr at the proper values.
INTRODUCTION
Nowadays, aluminum thin films play important roles in various fields of electronic engineering. They also are very useful as reflecting layers in optical and magneto-optical recording media. Concerning the production of the integrated circuit (IC), 6-inch Si wafers have been advanced in practical use and 8-inch wafers will be used in the near future. Usually, Al thin films for electrodes and wires in IC are prepared by electron beam evaporation and DC magnetron sputtering methods. The DC magnetron sputtering method is more convenient for in line production and produces better quality films than electron beam evaporation. However, the film quality is still not satisfactory since hot particles such as yelectrons and negative ions attack and damage the growing films. Especially, in the case of the Al sputtering, the dicharge current concentrates on the narrow area of the target surface and melts material in the area due to the locally extreme heating. Consequently, many splinters may be ejected from the target and hillocks may deposit on the growing film. On the other hand, the TFTS system hardly exposes the growing films to the plasma'). In addition, the TFTS system can effectively apply the bias voltage to the substrate for control of the structure and properties of films, since the substrates are free from the plasma and are not attacked by energetic particles such as y-electrons and negative ions. In the range of 9.7 x 10-2 n 2.0 Pa of PAr, the surface appearances of the films on the lower side of PAr are very smooth and lustrous, while ones on the higher side of PAr are rough with the formation of larger grains. In grains of the bias sputtered films, the number of the grains per unit area decreased and the film surfaces became smooth. In addition, those became hardest at Vb of -40 V. The TFTS is also excellent for step coverage because it has two facing targets and no dead regions exist in the groove of the wafe
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