Atomic Layer Deposition (ALD) of Metal Gates for CMOS

Abstract

The continuous down-scaling of complementary metal oxide semiconductor (CMOS) field effect transistors (FETs) had been suffering two fateful technical issues, one relative to the thinning of gate dielectric and the other to the aggressive shortening of channel in last 20 years. To solve the first issue, the high-κ dielectric and metal gate technology had been induced to replace the conventional gate stack of silicon dioxide layer and poly-silicon. To suppress the short channel effects, device architecture had changed from planar bulk Si device to fully depleted silicon on insulator (FDSOI) and FinFETs, and will transit to gate all-around FETs (GAA-FETs). Different from the planar devices, the FinFETs and GAA-FETs have a 3D channel. The conventional high-κ/metal gate process using sputtering faces conformality difficulty, and all atomic layer deposition (ALD) of gate stack become necessary. This review covers both scientific and technological parts related to the ALD of metal gates including the concept of effect work function, the material selection, the precursors for the deposition, the threshold voltage (Vt) tuning of the metal gate in contact with HfO2/SiO2/Si. The ALD of n-type metal gate will be detailed systematically, based mainly on the authors’ works in last five years, and the all ALD gate stacks will be proposed for the future generations based on the learning.

Advanced Atomic Layer Deposition Technologies for Micro-LEDs and VCSELs

“…The most important application of ALD is in the field of semiconductors [ 18 – 22 ], such as the preparation of high-k dielectrics, metal thin films, copper barrier films, and etch stop layers for fin field-effect transistors (FinFETs) [ 23 – 28 ], oxide passivation layers, and anti-reflection layers for LEDs and VCSELs. The very uniform coverage and high-density film characteristics of ALD make it suitable for devices that are sensitive to water and oxygen.…”

The role of atomic oxygen in the decomposition of self-assembled monolayers during area-selective atomic layer deposition

“…Atomic Layer Deposition (ALD) has greatly enhanced the capability to deposit very uniform and conformal thin films on high aspect ratio structures allowing for the continued downscaling of feature sizes in nanoelectronic devices. ALD is largely compatible with semiconductor device fabrication processes and has many other advantages that make it an attractive deposition method [1][2][3]. One main drawback for ALD is that the same conformality that leads to uniform deposition across large substrates, leads to increased process complexity when patterning of the surface is required.…”

Alternative Surface Reaction Route in the Atomic Layer Deposition of Titanium Nitride Thin Films for Electrode Applications

“…1−5 TiN films have especially been regarded as an electrode material of capacitors in the dynamic random access memory (DRAM) because of its low resistivity (13 μΩ•cm at 298 K), moderate work function, and high thermal stability. 4,6 For the application of electrode materials in next-generation DRAM capacitors having an extremely high aspect ratio, atomic layer deposition (ALD) is the only feasible deposition technique to grow the electrode films in the DRAM capacitors, owing to its highly conformal deposition characteristics. 7−13 Extensive research has been conducted to deposit highquality TiN films via ALD.…”

“…Titanium nitride (TiN) has gained considerable attention for the applications in diffusion barriers, metal gates in CMOS, protecting layers in tungsten CVD, and electrodes in DRAMs, owing to its chemical inertness, thermal stability, and low resistivity. − TiN films have especially been regarded as an electrode material of capacitors in the dynamic random access memory (DRAM) because of its low resistivity (13 μΩ·cm at 298 K), moderate work function, and high thermal stability. , For the application of electrode materials in next-generation DRAM capacitors having an extremely high aspect ratio, atomic layer deposition (ALD) is the only feasible deposition technique to grow the electrode films in the DRAM capacitors, owing to its highly conformal deposition characteristics. − …”