Kyusaku Nishioka

Cold and Low-Energy Ion Etching (COLLIE)

It is shown that a new cold and low-energy ion etching system (COLLIE) is effective as a dry etching technique for fabrication of VLSI devices. In the COLLIE system, plasma instabilities are suppressed by an MHD stable magnetic field consisting of a solenoid coil and multicusp magnets. The ion temperature, which is strongly related to plasma instabilities, is lowered below 2 eV in this system. Etched profiles show a strong anisotropic feature without applying any external electrical bias. As small angular distribution of incident ions to a sample is realized, the microloading effect is greatly improved.

ECR Plasma Etching with Heavy Halogen Ions

It is shown that the ECR plasma, which contains heavy halogen ions and other light ions, is effective as a dry etching technique for fabrication of VLSI devices. The ion temperature, which is one of the most important parameters for etching fine features, is greatly reduced by using a Cl2/He mixture gas and by controlling the pressure. By this method, strong anisotropic etching of poly-Si is realized with high selectivity to SiO2. Hydrogen halide gases are suitable gases for the ECR plasma etching process, because they produce heavy halogen ions and protons. In particular, using HBr or HI gas produces a strong anisotropic feature with no micro-loading effects. The ion temperature of Br+ ions and I+ ions is 1.0~1.1 eV, which is about half that of Cl+ ions.

Microfabrication of Anti-Reflective Chromium Mask by Gas Plasma

Gas plasma etching and photoresist removal techniques were successfully applied to the microfabrication of the anti-reflective chromium masks, in which the chromium oxide films are formed on the reflective chromium films. Four kinds of gas plasmas are examined to etch the chromium and the chromium oxide films of the total thickness of about 700 A. The etch rates are measured as a function of gas pressure and also RF power. They becomes maximum at a certain value of gas pressure and RF power. Generally, the etch rate of the chromium oxide film is smaller than that of the chromium film. The gas plasma technique simplifies the fabrication process and make the process clean because of the eliminations of the hard baking of the photoresist and also sequential treatment of etching and removal steps. The masks produced with gas plasma process showed little pattern shifts and the high quality finer patterns because of little undercutting of gas plasma etching. The pattern defect densities are reduced by using gas plasma process. The high quality fine patterns of a few to submicron meter widths are fabricated.

High Performance Electron Cyclotron Resonance Plasma Etching with Control of Magnetic Field Gradient

It is shown that high-performance Electron Cyclotron Resonance (ECR) plasma (hyper-ECR) is effective as a dry etching technique for fabrication of VLSI devices. The gradient of the magnetic field is one of the most important parameters for a uniform high etch rate. The Si etch rate and the ion current density can rise with decreasing magnetic field gradient. The high uniformity of the etch rate is achieved with highly uniform distribution of the magnetic field gradient. The density distribution of plasma is also improved by the hyper-ECR, so the drift instability is stabilized and a no-microloading etching process is produced.

Prevention of Cu degradation using in situ N2 plasma treatment in a dual-damascene process

The surface state of copper after an etching process using CF4 gas has been analyzed. Copper surface stability against corrosion is evaluated through a storage test performed under high-humidity conditions after the etching process. The storage test reveals that the copper surface suffered from both corrosion and oxidation. The copper degradation is caused by a postreaction between moisture and residual fluorine, wherein the resulting oxygen-containing copper film features a rough surface morphology. We examined in situ plasma treatments with several gases to reduce corrosive reactions. Results indicate that in situ N2 plasma treatment removes fluorine residue from the copper surface, and that this treatment effectively stabilizes the copper surface against corrosive conditions.

Highly Selective AlSiCu Etching Using BBr3 Mixed-Gas Plasma

The effect of selectivity to photo resists when exposed to gas plasma containing Br is studied in AlSiCu etching. The magnetron enhancement reactive ion etching reaction of AlSiCu employs a BBr3/Cl2 gas mixture in comparison with the conventional Cl-containing gas process of SiCl4/Cl2. Selectivity to photo resists increases with increase in the magnetic field when the BBr3/Cl2 process is employed, but not when the SiCl4/Cl2 process is employed. Further, selectivity to photo resists peaks at the concentration of 10% to 20% BBr3. The mechanism behind the highly selective etching is the production of a C-Br compound on the photo resist during AlSiCu etching. This C-Br compound strongly protects the surface of the photo resist. This deposit on the film restrains the etching rate of the photo resist, and high selectivity to the photo resist is obtained by using the gas process containing Br.

Effects of plasma parameters on etching characteristics with ECR plasma

Abstract In order to realize submicron patterns for VLSI devices, it is necessary to form patterns having anisotropic profiles, without damage and contamination. In this paper, we report the results of the study on etching characteristics of poly-Si and parameters of Electron Cyclotron Resonance (ECR) plasma. The relationships between the etching characteristics and the plasma parameters are investigated. It has been found that there is a strong relationship between the etching characteristics and the plasma parameters. Etch rate depends linearly on both ion current and ion energy. These two parameters can be controlled independently by microwave power and gas pressure.

Reactive Ion Beam Etching Using a Selective Gallium Doping Method

A maskless process has been realized by combining reactive ion beam etching (RIBE) with focused ion beam (FIB) technology. Si patterns of 0.3 µm with no undercutting can be obtained using RIBE with electron cyclotron resonance (ECR) plasma. A Ga compound is formed as an in situ etching mask.

Effect of Electric Field on Electron Cyclotron Resonance Plasma Etching

Recent studies of etching technology using plasma indicate that serious problems are induced by a charge build-up. The charge build-up causes radiation damage and distortion of etched profiles. These problems are induced by a non-neutrality of charge supply to the surface. By controlling the electric potential of surface material with a dc power supply, dependences of damage and pattern distortions on charge-up are investigated. Keeping the net current to the wafer zero is effective for reducing the radiation damage. The profile distortions occur due to the potential difference between mask and etched material. The profile is improved by setting the applied dc potential equal to floating potential.

Low energy ECR plasma etching with a hybrid magnetic field

Abstract It is shown that a new cold and low-energy ECR ion etching system is effective as dry etching technique for fabrication of VLSI devices. In this system, plasma instabilities are suppressed by MHD stable magnetic field consisting solenoid coil and multicusp magnets. The ion temperature, which is strongly related to plasma instabilities, is lowered below 2eV in this system. Etched profiles show a strong anisotropic feature without applying any external bias. The plasma density is also enhanced by using a minimum-B field.