In-Process Measuring System for U1tra-Precision Diamond Turned Surface

研究了几种用于测量微小表面粗糙度的非接触式光学技术。这些技术的缺点是：(1)测量存在系统误差，(2)很难应用于在线测量，(3)测试需要很长的时间。本文的主要研究成果如下：(1)基于夫琅和费衍射的理论分析，推导出了一种通过测量三阶衍射光强来精确估算金刚石车削表面粗糙度的传统公式。对应于表面粗糙度(Rmax)的夫琅和费衍射粗糙度R可以从以下公式中确定。其中I_0-I_3是以0-3个衍射的数量级的主极大值的强度，λ是光波长。(2)通过对磁记忆盘以及通过钻石车削产生的各种工件的表面粗糙度的测量，所提出的夫琅和费衍射法使得能够在10%的误差范围内测量从1 nm到最大200nmRmax的表面粗糙度。(3)可以从旋转过程中的平均夫琅和费衍射粗糙度的分布图来评估磁存储盘表面的纹理，因此，该方法可用于车削加工过程中超细表面粗糙度的在线测量。(4)该方法可用于定量估计硅片等镜面上小于亚微米的细小划痕的深度和宽度。

Several non-contact optical techniques have been investigated for the measurement of fine surface roughness. Disadvantages of these techniques are (1) systematic errors of measurements occur, (2) it is rather difficult to apply to in-process measurement and (3) it requires a long time to perform the test.A new optical method based on the Fraunhofer diffraction theory is proposed, in which it is possible to estimate quantitatvely the fine surface roughness on the order of nanometeres of the surfaces generated by ultra-precision diamond turning without disadvantages mentioned above.The results obtained in this paper are summarized as follows :(1) A conventional equation which can accurately estimate the fine diamond turned surface roughness of less than 200nmRmax by measuring the intensity values of Oth-3rd order diffractions is derived from theoretical analysis based on the Fraunhofer diffraction. The Fraunhofer diffraction roughness R corresponding to the surface roughness (Rmax) can be determined from the following equation<<numerical formula>>where I_0-I_3 are intensities of the principal maximum in order of 0-3 diffractions, lambda is light wavelength.(2) From the measurements of surface roughness of a magnetic memory disk as well as various workpieces produced by diamond turning, this proposed Fraunhofer diffraction method makes it possible to measure the surface roughness from 1nm to the maximum 200nmRmax within an error range of 10%.(3) It is possible to evaluate the texture of a magnetic memory disk surface from the distribution map of the average Fraunhofer diffraction roughness during rotation, so that this method will be applied to in-process measurement of the ultra-fine surface roughness during turning operation.(4) This method can be applied to estimate quantitatively both the depth and the width of fine scratches of less than submicron in mirror surfaces, such as a silicon wafer surface.