ETCHING OF COPPER AND COPPER-OXIDE AT HIGH-RATES VIA GENERATION OF VOLATILE COPPER SPECIES

Two new chemical approaches to etching copper have been identified recently. The first involves oxidizing copper films with halogens and then generating various Lewis base adducts of CuX where X = Cl or Br (L(n)CuX, where n = 1 or 2). The second approach involves the reaction of Cu films with Cu(hfac)2 (where hfac = 1,1,1,5,5,5-hexafluoro-2,4-pentanedione) and various Lewis bases to form two equivalents of (hfac)CuL (L = ligand). Spontaneous etching experiments have been carried out in a hot-wall reactor which showed that etch rates up to 1 mum min-1 can be achieved at temperatures below 420 K. The high etch rates are the result of the high vapor pressures of the L(n)CuX and (hfac)CuL which are on the order of 0.1-1 Torr at 330-370 K. The interaction of Cl2 and triethyl phosphine (PEt3) with a single-crystal copper surface was studied under ultrahigh vacuum conditions to provide a better understanding of the etching process. At temperatures above 320 K, PEt3 reacts rapidly with a heavily chlorinated copper surface (10 000 L exposure (1 L = 1 langmuir = 1 x 10(-6) Torr s) of Cl2 at 300 K). The mass spectrum of the desorbing product is similar to that of CuCl(PEt3)2, suggesting that etching of copper occurs by reaction with Cl2 and PEt3 to form gaseous CuCl(PEt3)2. Subsequent examination of the substrate by Auger electron spectroscopy showed removal of chlorine (and presumably copper). Finally, the reactions of copper oxide with hfacH were investigated as a method for etching copper oxide films. Etch rates of up to 1 mum min-1 at an hfacH partial pressure of 1 Torr and temperature of 540 K were obtained in a differential cold-wall reactor.