Device for measuring surface defects

#The invention relates to a device for measuring surface defects.

#In view of the miniaturization of semiconductor components, the prevention of particles and other defects on the wafer surface during production is of great importance. Since a particle grain can by now be larger than an entire circuitry, even the smallest defects lead to a large amount of waste.

#In general, scattered light is used for measuring defects on smooth surfaces. For this purpose, the surface of, for example, a wafer is illuminated with a laser beam. The scatter characteristics of different particle sizes are shown in FIG. 1. A small particle 2 as well as a large particle 3 are illuminated with a laser beam 1. ‘Small particle' means that the particle diameter is much smaller than the wavelength used. 'Large particle’ means that the particle diameter is approximately of the same size as the wavelength or a little larger. As shown in FIG. 1, small particles scatter in isotropic manner into the space. Large particles, on the other hand, generate strong backscattering; see also scatter ellipse 4.

#The invention is described in detail with the aid of the following drawings:

#FIG. 1 shows the different scatter characteristics of particles;

#FIG. 2 shows an optical measuring system for the detection of large particles;

#FIG. 1 shows the differing scatter characteristics of particles of differing sizes. Incident light 1 falls on a small particle 2 as well as on a large particle 3. A particle is considered small when its size is much smaller than the wavelength of the incident light 1. A particle is considered large when its size is comparable to the wavelength of the incident light 1 or even greater. The scatter characteristics of small particles 2 and large particles 3 differ in so far as the small particle 2 scatters in isotropic manner into the space, while the large particle 3 generates strong backscattering.

#FIG. 2 shows an optical measuring system for the detection of large particles in the form of a measurement block 10 for measuring samples such as wafers 16. The wafer 16 is supported by a sample holder (wafer chuck) 17 which is caused by a rotation motor 18 to rotate around the axis 27 perpendicularly to the wafer surface 16. The arrows indicate the possible directions of movement of the optical measurement block 10. Due to the overlap of the translational movement of the measurement block 10 and the rotational movement of the wafer surface 16, each spot on the wafer surface 16 can be measured.

#A laser 11 serves as light source. The light beam first traverses a beam-shaping optical system 12 and a diaphragm 13, before hitting the laser deflection mirror 14 and being reflected onto the sample surface. Not only the incident beam, but also the reflected beam pass the signal deflection mirror 19 and the diaphragm 15 by traversing the respective openings. The isotropic scattered light generated by any possible small particles is blanked out by the diaphragm 15. Only the back scatter caused by large particles traverses the diaphragm 15 and is deflected at the signal deflection mirror 19 onto the photo multiplier 22. In order to focus the scattered light and to improve the signal-to-noise ratio, the scattered light traverses the lens 20 and the third diaphragm 21. The incident beam is not projected onto the sample surface exactly vertically, but rather at a very small angle to the surface normal line so that the reflected beam, as well, can be monitored with the aid of the photo detector 53. Furthermore, this allows the reflectivity of the sample surface also to be measured.