Micro mirror unit and method of making the same
A micro mirror unit includes a moving part carrying a mirror portion, a frame and torsion bars connecting the moving part to the frame. The moving part, the frame and the torsion bars are formed integral from a material substrate. The frame includes a portion thicker than the moving part.
1. A method for making a micro mirror unit from a material substrate that includes a supporting silicon layer, a supported silicon layer and an intermediate layer sandwiched between these silicon layers, the supporting silicon layer being thicker than the supported silicon layer, the micro mirror unit including a mirror part, an inner frame surrounding the mirror part, an outer frame surrounding the inner frame, an inner torsion bar connecting the mirror part to the inner frame, and an outer torsion bar connecting the inner frame to the outer frame, the method comprising the steps of:
performing first etching to the supporting silicon layer of the material substrate by using a first masking pattern and a second masking pattern, the first masking pattern being arranged to mask only a region of the supporting silicon layer corresponding to the outer frame, the second masking pattern being made of a material different from the first masking pattern and masking a region of the supporting silicon layer corresponding to the inner frame without masking the region of the supporting silicon layer corresponding to the outer frame, the first etching being performed for forming the outer frame at least partially;
removing the second masking pattern while maintaining the first masking pattern; and
performing second etching to the supporting silicon layer by using the first masking pattern for forming the inner frame at least partially.
2. The method according to claim 1 , wherein the first etching is performed midway in a thickness direction of the supporting silicon layer, the second etching being performed until the intermediate layer is reached.
3. The method according to claim 1 , wherein the first etching is performed until the intermediate layer is reached, the second etching being performed midway in a thickness direction of the supporting silicon layer.
4. The method according to claim 1 , wherein the second masking pattern further includes a portion for masking a region of the supporting silicon layer that is to become a comb-like electrode.