1. Field of the Invention
The present invention relates to a method of manufacturing a micro machine member and the like from a silicon wafer according to a semiconductor process, and, more particularly to a silicon processing method for manufacturing a silicon structure from a wafer, a silicon substrate with etching mask, and the like. The structure is used as, for example, an elastic member and configures a micro oscillator that performs oscillation. The oscillator can be used for optical apparatuses such as a light deflector and an image forming apparatus using the light deflector, sensors such as an acceleration sensor and an angular velocity sensor, and the like.
2. Description of the Related Art
Conventionally, micro machine members manufactured from a wafer according to a semiconductor process can be processed in a micrometer order. Various micro functional elements are realized by using the micro machine members (see, Japanese Patent Application Laid-Open No. H06-232112). As one of such methods of finely processing silicon, there is a method of performing anisotropic etching with an alkali solution after forming an etching mask on a wafer. The anisotropic etching is a method of forming, making use of the fact that an etching rate of a (111) surface of silicon and a crystal surface equivalent thereto (these are collectively referred to as (111) equivalent surface as well) is lower than other crystal surfaces, a structure mainly including the (111) surface and the crystal surface equivalent thereto. This is a simple processing method of immersing wafers in the alkali solution. A large number of wafers can be collectively processed. Therefore, inexpensive micro-order processing is possible. More specifically, the anisotropic etching is etching performed by using etchant having a characteristic that the etching does not proceed in a specific crystal orientation. A microstructure with a specific crystal surface set as a reference, i.e., a structure specified by the crystal surface can be created at extremely high processing accuracy. Examples of anisotropic etchant include KOH (potassium hydroxide), TMAH (tetramethyl ammonium hydroxide solution), EDP (ethylene diamine pyrocatechol+water), NaOH (sodium hydroxide) and hydrazine.
In a silicon micro functional element, a structure subjected to stress is often used. With the anisotropic etching, a member having a smooth processed surface can be obtained. In particular, when the structure subjected to stress is formed, since the smooth surface can avoid stress concentration, a structure having satisfactory durability can be manufactured.
A light deflector that performs optical scanning by torsionally oscillating a reflection surface with a micro oscillator formed by such a technique (see U.S. Pat. No. 4,317,611) has, for example, the following characteristics compared with an optical scanning optical system that uses a rotary multisurface mirror such as a polygon mirror: the light deflector can be reduced in size and power consumption is small. In particular, power consumption can be further reduced by driving the light deflector near a resonant frequency of the torsional oscillation of the micro oscillator.
However, as one of problems of the method of manufacturing a structure from a wafer according to the anisotropic etching, an error occurs in a processing dimension between a formed etching mask and a crystal axis direction of the wafer because of an alignment error. For example, when such a structure is used as a spring to manufacture a micro oscillator, a spring constant error occurs because of the processing dimension error. This is likely to lead to a manufacturing error of a resonant frequency of the micro oscillator.