单晶硅的完整 3D蚀刻轮廓分析

We have developed an anisotropic-chemicaletching process simulation system, MICROCAD, which is equipped with a database of  orientation dependent etching rates of single  crystal silicon. When crystallographic orientation of the wafer, mask pattern, etching  media and etching conditions such as its concentration and temperature are given, it calculates 3D etching profiles according to the  etching time increments.

Etching profiles of anisotropic etcliing of single crystal silicon depends on etching media and etching conditions. The three dimensional shape calculating system, which  is equipped with etching rates in complete  orientation, is able to predict an anisotropic  etching profile. The system of MICROCAD  has a database of etching rates in complete  orientation and can simulate 3D etching profiles from the mask pattern only. The calculation is continued after a concave hole penetrates a wafer. For an etchant, the etching  rate of each direction at arbitrary temperatures or concentrations is interpolated with  measured data in the database. The simulation system is distinguished from other previous works , regarding the following issues.

The method of analyzing geometrical  change of 3D profile was previously reported by Sequin. However, he did  not calculate actual etching profiles because of lacking in etching rate data.  Nor could he calculate after the etching fronts penetrated through the wafer.  Our newly developed system can deal  with actual problems such as occurrence  of penetration.

The database of etching rates for KOH  solution is provided. This allows interpolation of the etching rates under arbitrary etching conditions in terms of etching temperature and etchant’s concentration. Arrhenius equations are applied  for the temperature dependence. That  will be described later. The database is  ready to be expanded further for other  etchants like TMAH.

Three dimensional etching profiles are expected by the etching rate distribution. The  fact is illustrated using simulation results.  Fig.3 shows etching rate distributions measured at 70°C for 30%, 40%, and 50% KOH  aqua solution. Fig.4 shows the cross sections  calculated by the simulation system using the  etching rate distributions of Fig.3. The silicon wafers of (110) have a mask of an opencross pattern which is a rectangle of 80 x 5pm.  One side is aligned to < 111 > and another  side is aligned to < 112 >. The grooves are  etched to a depth of about 15pm. The etching profiles differ in bottom shape, because  the etching rates whose directions are perpendicular to the groove, are different due to  the etchant’s concentration.

Fig3

The masks of square open-cross patterns are  symmetrically patterned on the upper and  lower sides of (100) planes. The etching proceeds from both sides. Robustness of the system is proved by the fact that the calculations continued even after the penetration of  the wafer have occurred. Fig.5 shows the 3D  etching profiles and the cross sections along  < 110 > direction (A-A’) and along < 100 >  direction (B-B’). Fig.6 shows a photograph  of the actual etching profile compared with  the simulation result. The simulation result  is very close to the actual etching profile.  In particular, planes which are etched slower  than (110) planes, appear at the four inside  corners in both results. One of them is shown  in Fig.5 (b) in the circle.

We have newly developed a 3D etching profile simulation system of MICROCAD. It is  equipped with a database, useful GUI, and  an output module which describes 3D etching  profiles using the IGES format. In this paper,  the simulation results of the etching profiles  with respect to the change of the etchant’s  concentration, the penetration of the wafer  by concave holes, and the square compensation mask are discussed. The prediction of  3D etching profiles calculated from the arbitrary mask patterns are available at arbitrary  etching temperatures and etchant’s concentrations using MICROCAD.