After the discovery of high Tc superconductivity in LaBaCuO by Bednorz and Muller and the subsequent discovery of the superconductivity above liquidnitrogen temperature in YBaCuO system by Wu et al, it became clear that this new material will be important in superconducting electronics. In order to fabricate integrated superconducting devices (e.g.,dc SQUID's) using these materials, the thin films have to be patterned by ㎛ scale. In the case of the thin film made by MOCVD, the superconducting phases were very stable. After the etching process, there was some residual phases which were formed at high deposition temperature. These phases are not superconducting but have high resistivity at liquid nitrogen temperature. The etching rate of the film using strong acid etchant was too high to control the etching process, but phosphoric acid solution is a good candidate because of its lower etching rate. Etching rate was very sensitive to the concentration for the phosphoric acid solution. Because the water in the etchant solution damages the film, etching time must be short. In the case of plasma etching, photoresist could not survive due to high etching rate. Therefore new etching mask have to be developed.
