添加剂对化学沉积速率的影响

基于化学镀Ni-W-P和Ni-P体系中,添加剂LaCl3、乳酸、Fe2(SO4)3、硫脲和2,2’-联吡啶的浓度对沉积速率的影响表现出较为一致的变化规律,即随添加剂浓度的增加,出现最大沉积速率的实验事实,建立了一种吸附模型并导出添加剂加速化学沉积的公式.根据该公式和实验结果进行曲线拟合,得到相当吻合的结果.由拟合结果可得到一些参数值,如吸附平衡常数等.添加剂在基体上的吸附平衡常数(K1)大于已吸附了还原剂的表面上的吸附平衡常数(K2). K1值大表明添加剂在基体表面吸附能力更强. LaCl3、硫脲和2,2’-联吡啶的K1、K2值远大于乳酸、Fe2(SO4)3的K1、K2值,这表明LaCl3、硫脲和2,2’-联吡啶的吸附能力远强于乳酸、Fe2(SO4)3的, 因此,LaCl3、硫脲和2,2’-联吡啶所引起的沉积速率峰值的浓度远小于乳酸、Fe2(SO4)3的.

Effect of Additives on Electroless Deposition Rate

It has been known experimentally that, additives, such as LaCl3, lactic acid, Fe2(SO4)3, thiourea and 2,2’-bipyridine, regularly influence the electroless deposition rate, that is, there is a maximum deposition rate with increasing additives concentration. In order to explore this regularity, an adsorption model is proposed and a deposition rate formula is deduced. The deposition rate formula is used to operate nonlinear curve fitting. The fitting curves obtained, correspond with the experimental results. Some parameters can be obtained from the fitting results, such as adsorption equilibrium constants of additives. It is found that the adsorption equilibrium constant on the naked surface (K1) is larger than that on the adsorbed reductant (K2). The larger K1 means that additives adsorb on the naked surface more easily than on the adsorbed reductant. The adsorption ability of different additives also can be illustrated through K1 and K2. For example, the K1, K2 of LaCl3, thiourea and 2,2’-bipyridine are greater than that of lactic acid and Fe2(SO4)3. The comparison indicates that the adsorption ability of LaCl3, thiourea and 2,2’-bipyridine is stronger than that of lactic acid and Fe2(SO4)3. Thus the concentration of LaCl3, thiourea and 2,2’-bipyridine, which corresponds to maximum deposition rate, is smaller than that of lactic acid and Fe2(SO4)3.