To clarify whether pattern waviness due to line-edge-roughness enhances wiggling, distortion of straight and wavy patterns was numerically analyzed by the three-dimensional (3D) elastic finite element method. Wiggling occurs only in wavy patterns but not in straight patterns at a stress or aspect ratio much lower than their buckling thresholds. More severe wiggling occurs when the wavelength of initial waviness approaches a value that is 3.3 times the pattern height. These phenomena were experimentally confirmed in the etching of amorphous carbon with a SiON mask. We consider that precise etching without wiggling is achieved by the elimination of the original line-edge roughness and the reduction in mechanical stress in an underlying film to which the pattern is transferred.
This paper describes short-gas-residence-time electron cyclotron resonance plasma etching for high etch rates, reduced contamination, and highly anisotropic etching. The new high-gas-flow-rate (high-flow) etching system is demonstrated with effective-pumping rate of 2500 ℓ/s. This method produces very high etch rate while maintaining high anisotropy at very low gas pressure below 1 mTorr. The high etch rate is due to the reduction of reaction products density because of the very short gas-residence time of 30 ms. This technique also dramatically reduces the contamination of reaction products. Etching of crystalline Si and n+ polycrystalline Si with the high-flow etching system is demonstrated. For crystalline Si etching with Cl2, a high etch rate up to 1 μm/min is achieved at a high gas flow rate of 90 sccm at 0.5 mTorr.
Reactive interactions in plasma etching have been investigated. Simple gas-phase transport of etchants and the reaction by-products in the wafer near-surface area are discussed. A new reincidence parameter, determined with a proposed near-surface model, was used to formulate metal etch rates. The experimental results obtained from an electron cyclotron resonance microwave plasma etching system revealed that the measured etching rate agreed well with those obtained by the near-surface model. It was found that reaction by-products repeatedly arrived at the surface depending on the reincidence numbers for the metal etching. The reincidence is the result of the diffusional transport in the vicinity of the wafer and is given by the expression {(one-half of the wafer radius)/(mean-free path)}. The ratio of the by-product flux is expressed by the product of the etching-rate flux times the reincidence number. Then, the resulting ratio of the reaction products in the flux becomes very high when we compare it to those obtained by the residential time model. Based on the near-surface model, the reactive interactions between the wall near-surface and the wafer near-surface make it possible to relate the etching of the wall materials to side-etching width control. The effects of wall etching on the feature profile control are clarified through the inter-near-surface mechanism in metal etching. The use of an oxygen-free reactor inner wall and a C additive to the source gas are found to be effective for enabling highly selective metal etching with fine features.
The reaction-limited etching of tungsten (W) with NF 3 plasma was performed in an attempt to achieve the uniform lateral etching of W in a deep trench, a capability required by manufacturing processes for three-dimensional NAND flash memory. Reaction-limited etching was found to be possible at high pressures without ion irradiation. An almost constant etching rate that showed no dependence on NF 3 pressure was obtained. The effect of varying the wafer temperature was also examined. A higher wafer temperature reduced the threshold pressure for reaction-limited etching and also increased the etching rate in the reaction-limited region. Therefore, the control of the wafer temperature is crucial to controlling the etching amount by this method. We found that the uniform lateral etching of W was possible even in a deep trench where the F radical concentration was low.
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