Kenji Harafuji

Magnesium diffusion at dislocation in wurtzite-type GaN crystal

The behavior of interstitial Mg atoms at an edge dislocation is studied in the wurtzite-type GaN crystal by molecular dynamics (MD) simulation. Parameters for a two-body interatomic potential are determined by the Hartree–Fock ab initio method. First, an edge dislocation extending to the [0001] direction is generated in an MD basic cell composed of about 11,000 atoms. Second, Mg atoms are placed at substitutional and interstitial positions in the MD basic cell, and the Mg atoms are traced. It is found that the diffusivity of Mg atoms at a dislocation is enhanced along the dislocation. At 1000 K, the diffusivity of interstitial Mg atoms inside the dislocation core is approximately three orders of magnitude larger than that of interstitial Mg atoms located outside the dislocation. The enhanced diffusion along the dislocation originates from unbalanced atomic forces between the Mg atom and surrounding atoms.

Determination of proximity effect parameters in electron‐beam lithography

A new empirical method for determining proximity parameters in electron‐beam lithography is introduced on the assumption that the proximity function is composed of two Gaussians. This method is based on the clearance of resist after development in the nonexposed square region surrounded by the latticed exposed one. Since there are many identical patterns arranged two dimensionally, statistically averaged data of proximity parameters is obtained without undertaking scanning electron microscopy for linewidth measurements. Theoretical considerations are combined with the experimental observations in order to calculate proximity parameters by the use of the design pattern.

On the image brightness of the trench bottom surface in a scanning electron microscope

Trajectories of secondary electrons (SEs) as an image signal in scanning electron microscopy are studied analytically in high‐aspect‐ratio submicron wide infinite trenches. It is found that the SE collection efficiency ξ, which is defined as the ratio of the number of SEs exiting the trench top surface divided by that emitted from the trench bottom surface, has the following dependencies on magnetic flux density Bz generated by an objective lens and electric field Ez. Here, Bz and Ez are the components perpendicular to the wafer surface. For a low Bz region corresponding to a usual operation condition, ξ decreases gradually but is almost constant at about 0.15 with increasing Bz for trenches 0.5 μm wide and 5 μm deep. For a high Bz region over 3 T, ξ increases with increasing Bz, since the cyclotron radius is fairly small compared with the trench width. A special superconducting magnet is necessary to reach the high Bz region. An external electric field Ez brings about the larger increase of ξ for the sma...

Hierarchical proximity effect correction for e-beam direct writing of 64-Mbit DRAM

A high-speed proximity effect correction system with two-level cell hierarchy processing has been developed to realize an accuracy-assuring electron beam (EB) direct-writing for high density VLSI. The system has two distinct advantages. First, a new hierarchial zoning algorithm is introduced to realize a data compaction for the total pattern transactions. Zone data or assemblies or patterns to be proximity-corrected are created by the zoning procedure. Frame region is associated with each zone in order to incorporate the effect of back-scattered electrons into the zone data. Second, a fast iterative technique is introduced for the proximity effect correction calculation based on a dos modulation method. A double Gaussian proximity function is used for describing the electron scattering. The present correction system was applied to 64 Mbit DRAM pattern with a 0.4 micrometers design rule. The total correction processing for the layer with maximum data volume was completed within four hours in CPU time. The patterns after delineation and development were successfully obtained by combining the present proximity effect correction with tri-layer resist process.