磷通过热生长二氧化硅层在硅中的扩散

用四探针测量薄层电导方法及阳极氧化去层技术,测定了磷在硅中扩散的具体分布,在恒表面浓度下,它们偏离余误差函数分布。如认为这是由于扩散系数是杂质浓度的函数,实验得到了当杂质浓度大于10¹⁹原子/厘米³时,扩散系数随杂质浓度增加而增大的强烈依赖关系。用同样方法测定了磷通过二氧化硅层后在硅中扩散的具体分布,研究了这些杂质分布的特性,实验表明,不同厚度的氧化层在1300℃高温下仍具有掩蔽效应,在完全掩蔽失效时间附近,杂质分布的共同特点是表面浓度较低(～10¹⁷原子/厘米³)、结较浅(～1微米)。对不同厚度的氧化层,经过足够的时间后,硅中表面浓度不受氧化层厚度的影响,而只由扩散源的蒸气压决定。磷通过氧化层后扩散的具体分布情况还与扩散源的性质、条件等密切相关。扩散过程中观察到的氧化层厚度增长有可能影响表面附近杂质的具体分布情况。

DIFFUSION OF PHOSPHORUS INTO SILICON THROUGH SILICON DIOXIDE FILM GROWN BY THERMAL OXIDATION

Detailed distributions of diffusion of phosphorus into silicon have been measured by the four-point probe method. During the measurement, each successive layer is removed by the anodic oxidation technique. These impurity distributions are found to deviate from the error function complement even with the surface concentration kept constant during diffusion. If it is assumed that this is due to a concentration denpendence of the diffusion coefficient, the experimental results would indicate that the diffusion coefficient rises very rapidly when the concentration exceeds 10¹⁹/cm³.Detailed distributions of diffusion of phosphorus into silicon through silicon dioxide films of different thicknesses grown by thermal oxidation have also been measured by the method described above. The experimental data indicate that the silicon dioxide films remain effective for masking at a diffusion temperature as high as T_d = 1300℃. With diffusion time close to masking failure time, the surface concentration is found to be close to l0¹⁷/cm³ and the diffusion depth is found to be very small (～1 μ). However, for sufficiently long diffusion times, the surface concentrations apparently reach an ultimate value not influenced by the thickness of the oxide film, it remains a constant as long as the vapour pressure of diffusont source is kept constant. Detailed distributions of diffusion of phosphorus through a silicon dioxide film are also found to be strongly dependent on the nature and the condition of the diffusing source. An increase of the thickness of the oxide film during diffusion has been observed; it might affect the impurity distribution especially in the region near the surface.