A process was investigated to remove HfO 2 gate dielectric film that had been deposited and annealed under various conditions. The etch rate of HfO 2 annealed at 950°C was 0.14 Å/min in 10% HF, but increased up to 90 Å/min after Ar ion bombardment. The crystalline structure of the annealed HfO 2 films collapsed upon bombardment by Ar ions. The amorphization and rarefaction of HfO 2 by Ar ion bombardment were responsible for the dramatic increase of the etch rates. Almost no consumption of the underlying Si substrate was observed after the removal of the HfO 2 dielectric films.The quest for complementary metal-oxide-semiconductor ͑CMOS͒ integrated circuits which have a higher density and switching speed has led to the scaling of the gate length down to the nanometer level. The HfO family of materials with high dielectric constants (k) have emerged as the most promising candidates to replace SiO 2 , because they can meet the requirements with respect to bandgap, thermal stability, electrical leakage, and interface properties. However, issues related to the CMOS-compatible processing of these materials, such as dielectric deposition, postdeposition annealing ͑PDA͒, gate stack etching, and removal of the dielectric remaining, must be solved before they can be put into use in CMOS devices. 1-6 In particular, the requirements of etching and postcleaning processes include fast and complete removal of HfO 2 , minimal overetching and damage on Si substrate, and minimal notching into the dielectric layer. As etch products of HfO 2 are nonvolatile, development of an etch process that can meet all these requirements is a challenging work.Reactive ion etching ͑RIE͒ of HfO 2 was first studied to evaluate its masking properties for etching. 7 Recently, inductively coupled plasma ͑ICP͒ etching of HfO 2 as a gate dielectric was studied. 8 Results show that etch selectivity of HfO 2 over Si substrate is very low at Ͻ 1. This can result in significant consumption of Si substrate at source and drain regions. Furthermore, a significant amount of nonvolatile residues has been found, after dry etching, on the sidewalls as well as the etch-front surfaces. 7 These residues are deleterious for the subsequent processes, because they can result in undesirable sidewall formation and high contact resistance. Therefore, the etching of HfO 2 becomes a main technical barrier in developing HfO 2 -based CMOS devices.Recently, wet etching processes using HF to remove HfO 2 and HfSiO were investigated. [8][9][10][11][12] It was reported that HF at high temperature 8 or at high concentration 9 can remove the physical vapor deposited ͑PVD͒ HfO 2 prior to annealing. However, these processes are undesirable because HF of high concentration or at high temperature can etch Si substrate fast and can induce large electrical leakage. Researchers also found that, after PDA at 1000°C, HfO 2 was extremely difficult to remove in HF, at the very low etch rate at Ͻ 1 Å/min. 9-12 Therefore, neither a dry nor wet etching process appears feasible as a method to remov...
Wet etching properties of Hf based high-k dielectrics of HfO 2 , ͑HfO 2 ͒ x ͑Al 2 O 3 ͒ 1−x , Hf oxynitride and Hf silicate were investigated, using various chemicals employed for the current CMOS device fabrication. Experimental results show that fluorides species such as F − , HF 2 − HF and H 2 F 2 are very effective for dissolving Hf and HfO 2 in acids. HfF 4 is highly soluble in HF with a solubility of ϳ1.48 mol/L, which is much higher than the calculated result, and its solubility increases with reduced pH value. Etching properties of those high-k dielectrics in HF and annealing effects on their microstructure were explored. It is observed that the etch rates of Hf and HfO 2 increase with increasing HF concentration and after HF etch, Hf and HfO 2 surfaces become F terminated. Although the mechanisms responsible for the change in HF etch rates after the Hf based high-k films have undergone annealing are dependent on their chemical property, it is universally observed that the formation of the crystalline phase of HfO 2 is the primary attributor to the reduced etch rates. The HF etching of Hf based high-k films occurs via weak points in the films, e.g., Hf-N, Al-O and Si-O bonds, as well as amorphous areas of HfO 2 .
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