A novel fabrication technique is designed to obtain silicon crystalline flat planes. The selected silicon crystalline planes 〈110〉 are pre-obtained by deep-RIE, then EPW wet etch is used to remove the roughness after deep-RIE. Through the two etching process, a silicon mold with smooth sidewall can be got. The proposed technique is demonstrated by fabricating a solid polymer dye micro-cavity laser type filter that is replicated by the silicon mold. The experiment of simple filter confirm that the micro-cavity can work well in a filter.