STUDY OF ULTRA-HIGH-SPEED CMOS USING FULLY SELF-ALIGNED METALLIZATION

在亚0.1um MOSFET中，互连寄生效应严重限制了性能的提高。具有宽栅极宽度的MOSFET对于诸如字线驱动器、门阵列器件和模拟RF器件等高电流驱动能力器件的应用是必不可少的。为了降低寄生电阻，本文提出并研究了采用传统硅化物和选择性Al-CVD工艺的全自对准金属化（FSAM）MOSFET，其特点是：（1）TiSi_2/Si接触电阻低，（2）TiSi_2表面等离子体氮化形成自对准阻挡层，（3）CVD-Al层薄层电阻低。首先，我们发展了一种利用氮气电浆氮化传统矽化表面的自对准阻障层形成方法。证实了10 nm氮化阻挡层为Ti-Si-N三元非晶层。此外，还发现Ti-Si-N层在450 ℃热处理后仍起到扩散阻挡层的作用，在自对准阻挡层上，在不破坏真空的情况下，在同一工艺室中成功地沉积了铝膜。结果表明，铝膜选择性地沉积在导电阻挡层上，并应用于模拟RF-CMOS，对宽栅FSAM MOSFET的高频性能进行了RF模拟评估。模拟结果表明，FSAM器件的跃迁频率f_T在栅长小于0.2 μ m时仍有提高，而传统硅化物器件由于寄生电阻高，栅长减小到0.2 μ m时，跃迁频率f_T反而下降.此外，本文还研究了移动的手机射频CMOS功率放大器的电路设计，提出了GHz波段高效率CMOS推挽放大器的设计方案.

In sub-0.1um MOSFETs, interconnect parasitics are drastically limiting the performance improvement. MOSFETs with wide gate width are essentially required for an application to high current-drivability devices such as word-line drivers, gate array devices and analog RF devices. In this work, in order to reduce the parasitic resistances, fully-self-aligned-metallization (FSAM) MOSFET using conventional salicide and selective Al-CVD techniques are proposed and investigated.FSAM technology features ; (1) low contact resistivity of TiSi_2/Si, (2) self-aligned barrier layer formed by plasma nitridation of TiSi_2 surface, and (3) low sheet resistance of CVD-Al layer. At first, we have developed a self-aligned barrier layer formation method using N2 plasma nitridation of conventional silicided surface. It is confirmed that the 10-nm nitrided barrier layer is Ti-Si-N ternary amorphous layer. Furthermore, it is found that the Ti-Si-N layer acts as a diffusion barrier even after the 450ﾟC thermal treatment.On the self-aligned barrier layer, aluminum films are successfully deposited in the same process chamber without breaking the vacuum. It is found that the aluminum films are selectively deposited on the conductive barrier layer.For an application to analog RF-CMOS, high-frequency performance of wide-gate FSAM MOSFETs has been evaluated using RF simulation. Simulation results have shown that a transition frequency f_T of FSAM devices increases even below 0.2um gate length, while that of conventional silicide devices decrease with shrinkage of gate length down to 0.2um because of high parasitic resistances.Furthermore, circuit design of RF-CMOS power amplifier for mobile phone has been investigated, and GHz-band high-efficiency CMOS push-pull amplifier has been proposed.