The Effect of Bias Voltage Application to Metals to Promote Their Nitriding and Carburizing in High-Density Inductively Coupled Plasma

采用N_2-H_2（90: 10）电感耦合等离子体（频率：4 MHz，压力：240 mtorr）对厚度为1mm的纯铁样品进行处理，温度为550℃，处理时间为120min。在不施加偏置电压的情况下，从样品表面向样品内部出现脱氮层（厚度：-20mum）。可以估计，氢自由基加速了这种反硝化作用。对样品施加200V的负偏置。观察到氮化铁层（厚度为-25mum）和铁扩散层（厚度为200mum）的生长。这一事实意味着负偏压对样品的影响超过氢自由基的影响。在对sus304样品进行氮化处理时，与铁氮化处理相比，负极合金对样品的表面硬度有显著的提高。在Ti的氮化和碳氮化过程中，氮或碳扩散层和氮化物或碳氮化物层在去年得到了显著的增加。今年，一种非常高密度的等离子体（13.56MHz）被用于Ti的氮化，其电子密度约为8 × 10^<13>/cm^3。Ti样品（厚度为0.8mm）在总压8-60mtorr，气体流量N_2, 0-7 sccm, H_2, 18- 70sccm，功率70W和350W，时间120min，衬底温度300-600 C条件下的等离子体中进行处理。用负偏压等离子体处理Ti样品，证实了Ti的氮化和氮化Ti的形成。这是一个非常有趣的现象，因为这意味着只有在大量自由基参与氮化过程的情况下，氮离子才能促进氮化。

Pure iron sample (the thickness : 1mm) was treated at 550ﾟC and for 120min under N_2-H_2 (90 : 10) inductively coupled plasma (frequency : 4 MHz, pressure : 240 mtorr). Without the application of bias voltage to the sample, denitrification layr (the thickness : -20mum) appeared towards the inner part of the sample from its surface. It can be estimated that hydrogen radical accelerates such denitrification. With the application of negative bias of 200V to the sample. the growth of iron nitride layr (the thickness : -25mum) and 200mum iron diffusion layr was observed. This fact means that the effect of negative bias supply to the sample exceeds that by hydrogen radical. In nitriding of SUS 304 sample, the increase of surface hardness was remarkable under the application of negative bais to the sample, comparing with the case of iron nitriding.In nitriding and carbo-nitriding of Ti, the remarkable increase of nitrogen or carbon diffusion layr and nitride or carbonitride layr were confirmed last year. This year, a very high density r. f. (13.56MHz) plasma which has about 8 x 10^<13>/cm^3 in electron density, was used for nitriding of Ti. Ti sample (the thickess : 0.8mm) was treated in the plasma generated under the next experimental conditions, total pressure : 8-60mtorr, gas flow rate : N_2, 0-7 sccm, H_2, 18-70sc cm, power input : 70W and 350W, time : 120min, substrate temperature : 300-600ﾟC.The nitriding of Ti and the formation of Ti nitride were confirmed by using a plasma with negative bias application to Ti sample. It is a very interesting phenomena, because it means that the nitriding can be only promoted by nitrogen ion in presence of plenty of radicals taking part in nitriding process.