449 LASER CHEMICAL ETCHING OF METALS IN NEUTRAL SALT SOLUTIONS M. Datta, L. T. Romankiw, D. R. Vigliotti and R. J. von Gutfeld IBM T.J. Watson Research Center, Box 218, Yorktown Heights, NY 10598. ABSTRACT: We report the first results of experiments using a focused argon ion laser to locally induce chemical etching of steel and stainless steel in neutral salt solutions for maskless pat- terning. The solutions include sodium chloride, sodium nitrate and potassium sulfate. Vertical etch rates up to 4 microns/s are observed. INTRODUCTION: The advantage of neutral salt solutions is their relative safety both for the manufacturing environment and for safe disposal as opposed to the more commonly used strong acids and bases normally employed today for chemical micromachining. In the present study we have used neutral salt solutions for laser chemical etching of steel and stainless steel. Etch rates and metallurgical data have been obtained as a function of solution concen- tration, laser power density and laser on-time. We find etch rates as high as 4 microns/second resulting from the etching of stainless steel in sodium nitrate. In our experiments we used all lines of an argon ion laser focused into a quartz cell containing the salt solution and the steel and stainless steel samples. The samples varied in thickness from between 0.075-0.150 cm with an area of approximately 2 cm 2 The samples were attached to the arm of a computerized table which provides micron resolution move- ment. Laser on-time was also controlled by the same computer. We estimate the gaussian radius of the laser beam to be 65 microns based on a series of laser intensity measurements using apertures of varying radii. Thus for an incident laser power of 22 watts, the power density at the center of the gaussian is estimated to be approximately 3.3 x 10 5 W/cm 2 Here we have used the relation, P = I 0 exp-2(r/r 0 ) 2 , with P, total laser power, I0, power density at the center of the beam, r, the distance from the center and r 0 , the gaussian radius. RESULTS AND DISCUSSION: The use of neutral salt solutions for electrochemical machining is well known [1, 2]. The present work reports the first data on micromachining of steel and stainless steel without the use of an externally applied current. No etching occurs without laser irradiation for these samples submerged in any of the three salt solutions under study. However, the intense local heating of the substrate provided by the absorption of the laser by the steel gives rise to local etching. The mechanisms responsible for the rapid etching are believed to be due to a competition between metal dissolution and the formation of a passivating oxide layer, hence a dependence on the particular salt solution and its concentration. For cases in which a passivation layer readily forms, etching occurs mainly via thermal breakdown of the passivating film due to the heat supplied by the focused laser. This Mat. Res. Soc. Symp. Proc. Vol. 101. ' 1988 Materials Research Society