Pulse-Modulated Plasma Etching of Copper Thin Films via CH3COOH/Ar.

Pulse-modulated plasma etching of copper masked using SIO2 films was conducted via a CH3COOH/Ar. The etch characteristics were examined under pulse-modulated plasma. As the duty ratio of pulse decreased and the frequency of pulse increased, the etch selectivity and etch profile were improved. X-ray photoelectron spectroscopy and indicated that more copper oxides (Cu2O and CuO) and Cu(CH3COO)2 were formed using pulse-modulated plasma than those formed using continuous-wave (CW) plasma. As the concentration of CH3COOH gas in pulse-modulated plasma increased, the formation of these copper compounds increased, which improved the etch profiles. Optical emission spectroscopy confirmed that the active ingredients of the plasma increased with decreasing pulse duty ratio and increasing frequency. Therefore, the optimized pulsed plasma etching of copper via a CH3COOH/Ar gas provides better etch profile than that by CW plasma etching.

Etch Characteristics of Nanoscale Patterned Magnetic Tunnel Junction Stacks Using Pulse-Modulated Radio Frequency Source Plasma.

Magnetic tunnel junctions (MTJs) patterned with 70 × 70 nm² square arrays were etched in a CH4/O2/Ar gas mixture by pulse-modulated inductively coupled plasma reactive ion etching (ICPRIE). A good etch profile of MTJs with etch slope of approximately 82° was achieved by adjusting the on-off duty ratio of the plasma and pulse frequency. Langmuir probe analysis and optical emission spectroscopy confirmed that the balance between the formation of the passivation layer as an etch byproduct and sputtering effect is responsible for the etch selectivity and etch profile with a high degree of anisotropy. It is concluded that the application of pulse-modulated plasma on ICPRIE can be an effective method to obtain the anisotropic etch profile of nanometer-scale MTJs.

Etch Characteristics of Micrometer-Scale Masked Cu Thin Films Using Inductively Coupled Plasma of H2/Ar.

Inductively coupled plasma reactive ion etching (ICPRIE) of copper thin films masked with photoresist (PR) and SiO2 thin films was performed in H2/Ar gas. As the H2 concentration increased, the etch rates of copper films significantly decreased. The etch profiles show heavy redeposition on the sidewall of the etched films in low H2 concentration but steep etch profiles without redeposition and etch by-product were obtained in high H2 concentration. The systematic variation of the etch parameter such as ICP source power, dc-bias voltage to substrate, and process pressure was carried out to characterize the copper etching in H2/Ar gas. Based on the etch characteristics of copper films, Langmuir prove analysis, and X-ray photoelectron spectroscopy, it was revealed the physical sputtering by ions and the formation of the volatile copper compound and the protection layer had great influence on achieving a good etch profile.

Characterization of Zn(O,S) Buffer Layers for Cu(In,Ga)Se2 Solar Cells.

Zn(O,S) thin films were deposited using a ZnS target under Ar/O2 gases by radio-frequency magnetron sputtering. As the O2 concentration increased, the deposition rates of the Zn(O,S) films decreased due to increase of O-. The crystalline structure of Zn(O,S) was maintained at up to 0.6% O2, while the films became unstable at the condition exceeding 0.8% O2. This was attributed to incomplete nucleation and film growth on the substrate at the room temperature. Additionally, optical emission spectroscopy analysis indicated that an increased O- intensity at high O2 concentration was responsible for the slow deposition rate and increased oxygen concentration of the films. X-ray diffraction and scanning electron microscopy revealed the formation of a Zn(O,S) crystal structure with partial substitution of O for S and uniform and dense grains of the films. X-ray photoelectron spectroscopy showed that the Zn(O,S) films have a uniform composition of each element and consisted of a mixed crystal structure of Zn(O,S) with Zn-O bonding. Overall, the results of this study confirmed that Zn(O,S) films deposited by radio-frequency sputtering using Ar/O2 gas at room temperature can be applied to Cu(In,Ga)Se2 solar cells as a buffer layer.

Growth mechanism of CdS nanofilms prepared by chemical bath deposition.

Deposition of CdS nanofilms was performed using the chemical bath deposition method, as a function of the concentration ratio of [S] to [Cd] (S/Cd) and of deposition temperature. As the S/Cd ratio and deposition temperature increased, the deposition rate of the films increased, and the transmittance was improved. With increasing S/Cd ratio, the crystallinity of the CdS nanofilms decreased due to the formation of small grains therein. Atomic force microscopy revealed that the surface morphology of the films became smooth with increasing S/Cd ratio and deposition temperature. The evolution of the grain formation showed that the slow deposition rate of the films leads to a small number of grains at the initial stage of the deposition, followed by fast grain growth, resulting in a rough surface. On the other hand, a fast deposition rate initially causes the formation of many grains on the entire surface as well as slow grain growth, making the films smooth. It is evident that the deposition rate affects the physical and optical properties of the films due to their different growth mechanisms.

Investigation on etch characteristics of nanometer-sized magnetic tunnel junction stacks using a HBr/Ar plasma.

The etch characteristics of CoFeB magnetic films and magnetic-tunnel-junction (MTJ) stacks masked with Ti films were investigated using an inductively coupled plasma reactive ion etching in a HBr/Ar gas mix. The etch rate, etch selectivity, and etch profile of the CoFeB films were obtained as a function of the HBr concentration. As the HBr gas was added to Ar, the etch rate of the CoFeB films, and the etch selectivity to the Ti hard mask, gradually decreased, but the etch profile of the CoFeB films was improved. The effects of the HBr concentration and etch parameters on the etch profile of the MTJ stacks with a nanometer-sized 70 x 100 nm2 pattern were explored. At 10% HBr concentration, low ICP RF power, and low DC-bias voltage, better etch profiles of the MTJ stacks were obtained without redeposition. It was confirmed that the protective layer containing hydrogen, and the surface bombardment of the Ar ions, played a key role in obtaining a steep sidewall angle in the etch profile. Fine-pattern transfer of the MTJ stacks with a high degree of anisotropy was achieved using a HBr/Ar gas chemistry.