在半导体激光诱导扩散实验中,用连续波CO2 10.6 μm激光聚焦后照射基片表面。为实现局部区域的选择扩散,激光光斑半径仅数十微米。要使曝光区温度达到扩散实验要求,必须使曝光区功率密度很高。另一方面,Si、InP等半导体材料对10.6 μm波长激光的吸收系数随温度的升高而增大,这导致实验时容易产生热致破坏,损伤基片。在分析热致破坏的产生机理后,提出了在聚焦激光束照射下,曝光区温度的数值计算方法。计算结果表明,在半导体基片初始温度为室温时,以恒定功率的激光束照射基片,曝光区温度不能稳定在扩散试验需要的温度范围。在此基础上,提出了预热基片及对曝光区温度进行实时控制等抑制热致破坏的方法,有效地克服了这一困难。这对于用激光微细加工制作出高性能的单片光电集成电路(OEICs)器件有重要意义。

In the experiment of 10.6 μm continuous wave CO2 laser induced diffusion, the substrate is irradiated by a focused laser beam. To realize selective diffusion in local region, the diameter of the laser beam spot on the surface of the semiconductor substrate is only about dozens of microns. Because temperature rise of the exposed region must meet the requirement of diffusion experiment, high power density of the incident laser beam is necessary. On the other hand, the 10.6 μm light absorption coefficient of semiconductors such as Si, InP increases with the rising of temperature. The above two factors can easily lead to a thermal runaway phenomenon. The mechanism of thermal runaway was analyzed, then a numerical method was proposed to calculate the relation between the temperature of the exposed region and the power density of the incident laser beam. When the semiconductor substrate is kept at room temperature before the laser irradiation, it is shown that the temperature of the exposed region cannot be induced steadily to the value required in the diffusion experiment by using irradiation of laser beam with constant power. This problem can be avoided by preheating the substrate and real-time controlling the temperature of the exposed region.