Sep 28 2004
Researchers at theUniversity of Illinois at Urbana-Champaignhave developed a technique that uses surface chemistry to make tinier and more effective p-n junctions in silicon-based semiconductors. The method could permit the semiconductor industry to significantly extend the life of current ion-implantation technology for making transistors, thereby avoiding the implementation of difficult and costly alternatives.
为了使基于硅的晶体管更快，科学家在P-N连接中大大收缩了活性区域，同时增加了电活性掺杂剂的浓度。目前，对于下一代设备，这些活性区域的厚度约为25纳米，这些活性区域必须降低至约10纳米，或大约40个原子。
传统的过程，离子植入，将掺杂剂原子射入硅晶片中，就像shot弹枪将颗粒送入靶标一样。为了有用，掺杂原子必须靠近表面并替换晶体结构中的硅原子。然而，在植入植入的原子尺度混乱中，许多掺杂原子和硅原子最终以间隙 - 在晶体中的原子之间笨拙地扎住。
Ion implantation also creates defects that damage the crystal in a way that degrades its electrical properties. Heating the wafer – a process called annealing – heals some of the defects and allows more dopant atoms to move into useful crystalline sites. But annealing also has the nasty effect of further diffusing the dopant and deepening the p-n junction.
伊利诺伊州化学和生物分子工程教授埃德蒙·西鲍尔（Edmund Seebauer）表示：“我们开发了一种使用表面化学来获得较浅的活性区域并同时获得掺杂剂激活的方法。”“通过修改硅表面从底物吸收原子的能力，我们的技术可以控制和纠正植入过程中诱导的缺陷。”
在活动区域内，坐在晶格位点的原子与四个邻居具有键合，这使硅原子的粘结能力饱和。坐在地面上的原子的邻居较少，导致未使用或“悬空”纽带。氢，氧或氮等气体的原子可以使悬挂键饱和。
“These dangling bonds can also react with interstitial atoms, and remove them from the crystal,” Seebauer said. “The process selectively pulls silicon interstitials to the surface, while leaving active dopant atoms in place. The preferential removal of silicon interstitials is exactly what is needed to both suppress dopant diffusion and increase dopant activation.”
Seebauer及其同事 - 化学和生物分子工程教授Richard Braatz和研究生研究助理Kapil Dev和Charlotte Kwok - 使用氨和其他含氮气的气体，以使某些悬挂式粘合物饱和，并控制表面的能力，以去除整体式。
“The amount of surface nitrogen compound formed, and therefore the number of dangling bonds that become saturated, can be varied by changing the type of gas and the degree of exposure,” Seebauer said. “As an added benefit, nitrogen compounds are also quite compatible with conventional chip manufacturing processes.”
Through computer simulations and experimental verification, the researchers have shown that “defect engineering” by means of surface chemistry can extend the life of current ion-implantation technology and create smaller, faster electronic devices. Seebauer will present the team’s latest findings at the 51st International Symposium of the AVS Science and Technology Society, to be held Nov. 14-19 in Anaheim, Calif.
Funding was provided by International SEMATECH and the National Science Foundation. The researchers have applied for a patent.
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