{"id":1116,"date":"2013-07-10T15:59:48","date_gmt":"2013-07-10T15:59:48","guid":{"rendered":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/?p=1116"},"modified":"2013-08-05T17:57:56","modified_gmt":"2013-08-05T17:57:56","slug":"nano-scale-metal-contacts-for-iii-v-fets","status":"publish","type":"post","link":"https:\/\/mtlsites.mit.edu\/annual_reports\/2013\/nano-scale-metal-contacts-for-iii-v-fets\/","title":{"rendered":"Nano-scale Metal Contacts for III-V FETs"},"content":{"rendered":"

In the last few years, III-V compound semiconductors have emerged as a promising family of materials to replace silicon in logic applications[1<\/a>]<\/sup>. Novel III-V MOSFET prototypes with superior electron-transport properties have been recently demonstrated[2<\/a>]<\/sup>. One of the challenges to obtain high performance is to achieve a very low ohmic contact resistance. As transistor scaling continues, it is important to fabricate and characterize high-quality ohmic contacts with nanometer-scale contact length. In this project, a nano-scale transmission line model (nano-TLM) structure is being developed to study and optimize metal contacts for III-V field-effect transistors.<\/p>\n

This works builds on prior research in our group on the fabrication and characterization of nanoscale contacts to III-V FET structures[3<\/a>]<\/sup>. Our nano-TLM structure comprises a Mo contact on an InGaAs heterostructure, with various contact lengths (Lc<\/sub>) and spacings (Ld<\/sub>). The Mo contact is patterned by electron beam lithography, followed by reactive-ion etching (RIE). The mesa isolation and contact pads are fabricated by a series of lithography, RIE, and lift-off processes. The ohmic contact is annealed at 400 \u00b0C for 40 s. Figure 1 shows a nano-TLM with Lc <\/sub>= 19 nm, the smallest contacts we have fabricated at present. The finished test structures are characterized using Kelvin 4-terminal measurement.\u00a0 We developed a 2-D circuit model to extract the contact resistivity, semiconductor sheet resistance, and metal sheet resistance. Figure 2 shows resistance measurements on Mo-n+<\/sup>-InGaAs structures with 80-nm contact length and various contact spacings. From measurements of this kind in several structures, an average contact resistivity of 0.6 \u03a9\u2219\u03bcm2<\/sup> is obtained.<\/p>\n

Our research will continue to optimize the contact fabrication to achieve lower contact resistance and further scaling. We will also investigate the contact resistance to a buried channel. We will further explore metals contacts on p-type Sb-based heterostructures, which are as critical as the n-type counterpart but in great need of a high-quality ohmic contact.<\/p>\n\n\t\t