Yuden Teraoka

Anisotropic Si(100) etching induced by high translational energy Cl2 molecular beams

Si(100) has been etched by high speed Cl2 molecular beams, generated by seeding in He. The translational energy dependence for etch rates has been measured by changing the gas mixing ratio and nozzle temperature. The two methods provided the same results. A 2.1 eV energy threshold was observed at 530u2009°C substrate temperature. The Cl+/Cl+2 intensity ratio, directly monitored by a quadrupole mass spectrometer, was independent of the nozzle temperature. These facts indicate that the etch rate enhancement is not attributed to Cl radicals or vibrationally excited Cl2 molecules. Owing to the translational energy induced etching, anisotropic etching profiles are realized at 670u2009°C substrate temperature.

Native oxides on Si surfaces of deep‐submicron contact‐hole bottoms

The effects of cleaning and treatment on the characteristics of contact‐hole‐bottom Si surfaces are investigated in order to reveal the origin of the increased contact resistance and to find treatment processes that can be used to obtain low contact resistance. Contact‐hole‐bottom Si surfaces were analyzed by using thermal desorption spectroscopy, transmission electron microscope, and energy‐dispersive x‐ray spectroscopy. Nonpatterned Si surfaces, which roughly simulate the properties of the contact‐hole‐bottom Si surfaces, were also analyzed by using x‐ray photoelectron spectroscopy. It is revealed that suboxide‐rich native oxide layers are formed on dry‐etch‐damaged Si surfaces. The oxide layer persists after the samples are cleaned with a mixture of NH4OH, H2O2, and H2O, and with a mixture of HCl, H2O2, and H2O, and even after dipping in diluted HF. The roughly 1.3‐nm‐thick oxide layer remains at the plugging‐poly‐Si/Si–substrate interface, increasing the contact resistance. The carbon contamination in...

SI(100) ETCHING BY TRANSLATIONAL ENERGY CONTROLLED ATOMIC CHLORINE BEAMS

Si(100) etching was investigated using a translational energy controlled atomic chlorine beam. The results were compared with translational‐energy‐induced molecular beam etching and conventional gas etching. The etch rate was enhanced by increasing the translational energy of the chlorine atoms up to 0.98 eV. The reaction yield of the atomic beam etching was several hundred times greater than that of translational‐energy‐induced molecular beam etching. The activation energy of the atomic beam etching at a 0.28 eV translational energy was determined to be 0.76±0.16 eV from an Arrhenius plot. It decreased to 0.62±0.09 eV when the translational energy was increased to 0.98 eV. These values were smaller than those for translational‐energy‐induced molecular beam etching (1.2±0.3 eV) and conventional gas etching (2.7±0.3 eV).

Stimulated etching of Si(100) by Cl2 molecular beams with hyperthermal translational energies

Etching reaction of Si(100) is investigated by using Cl2 molecular beams with a hyperthermal translational energy up to 3.0 eV. The reaction rate is clearly enhanced by translational energy, and the threshold energy is 2.1 eV. The translational-energy-induced reaction rates are measured as a function of substrate temperature; the results closely fit Arrhenius plots as the sum of two components having activation energies of 2.7 and 1.2 eV. The higher energy, derived from the fit of the high-temperature region, agrees well with the pure thermal reaction, i.e., low-translational-energy reaction. The lower energy, which is observed here, is determined as the activation energy of the translational-energy-induced reaction. This energy is not affected by the translational energy from the threshold to 3.0 eV, whereas the etch rate increases with translational energy. These findings suggest that the translational energy contributes to the formation of a new chlorinated Si surface from which silicon chloride desorb...

Influence of Halogen Plasma Atmosphere on SiO2 Etching Characteristics

The influence of halogen plasma atmosphere on SiO2 dry etching characteristics has been investigated using various halogen gases (SF6, Cl2, HBr and HI). It was found that in Cl2 and HBr plasma atmospheres, when Si and SiO2 are etched simultaneously, the SiO2 etch rate increases to more than 4 times larger than the SiO2, etch rate obtained when only SiO2 is etched. It was also found that the SiO2 etch rate increases linearly in proportion to the total amount of silicon halide produced by etching Si. Low-order silicon halides such as SiX and SiX2 (X=Cl or Br) connect with oxygen atoms in solid SiO2 by Coulomb force since both silicon halide and SiO2 are electrically polarized. Silicon oxyhalide (e.g., SiOX) as an etching product of SiO2 is produced and desorbed by ion sputtermg or thermal evaporation. This is because that the Si-O bond strength in solid SiO2 (108 kcal/mol) is weaker than that in a diatomic molecule (191 kcal/mol) composed of a Si atom from silicon halide and an O atom from SiO2. Consequently, SiO2 etching progresses when silicon chloride or silicon bromide is contained in the plasma, which drastically decreases the etching selectivity of n+ poly-Si to SiO2.

After-Corrosion Suppression Using Low-Temperature Al-Si-Cu Etching

The authors investigated the low-temperature etching effect on Al-Si-Cu after-corrosion. The after-corrosion extent was evaluated from the corrosion point density generated on the rinsed Al-Si-Cu stripes after dry etching. As the etching temperature was reduced, after-corrosion was suppressed. In order to study the low-temperature etching effect, the authors analyzed the Cl compounds remaining on the Al-Si-Cu film by thermal desorption spectroscopy (TDS). TDS revealed that the Cl concentration remaining on the Al-Si-Cu film etched at -60°C after rinsing in water was smaller than that remaining on the film etched at 30°C. Consequently, suppression of after-corrosion by low temperature etching could be attributed to the smaller number of Al-Cu bonds remaining in the Al-Si-Cu etch surface after removal of the AlClx layer by rinsing with water. This fact is due to the reduction of chemical reaction and diffusion rate by lowering the substrate temperature.

Anisotropic Si Etching by a Supersonic Cl 2 Beam

Perpendicular etching profiles of n + -Si(100) are obtained with a supersonic Cl 2 beam at substrate temperature of 900°C. Although small undercuts are observed just below the SiO 2 mask, the side wall etching caused by the background Cl 2 is almost negligible. An aspect ratio of greater than 6 and selectivity of greater than 8000 are obtained with 0.5 μm line & space mask pattern. From Arrhenius plots of etch rates, an effective activation energy of the nozzle beam etching is determined to 0.53 eV. Assuming that the reaction product is SiCl 2 , the reaction probability is estimated to be 19% at 900°C. Highly anisotropic etching of the Si(100) obtained here is due to the large reaction probability.

Dependence of Residual Chlorine Amount on Al Grain Size

From the investigation of the thermal desorption spectroscopy (TDS) results, it was found that the amount of residual chlorine on Al films increased with increasing Al grain boundary length after 60°C etching and rinsing. The aluminum surface morphology, which was observed by atomic force microscopy (AFM) after etching, indicated that the Al surface was etched along grain boundaries. Consequently, residual chiorine was trapped at the ditches of grain boundaries which were engraved by etching. In the case of -10°C etching, residual chlorine was hardly trapped at the ditches of grain boundaries because engraving along grain boundaries by etching was suppressed at low temperature.