Control of the light power at different wavelengths for photoelectric measurements of MOS structures

In this work, the method of the light power control by width of the slit at different wavelengths (λ) was described. The method is applied for photoelectric measurements of metal oxide semiconductor structures in the characteristic range of wavelengths (220÷480 nm). Two algorithms setting the light power (P) by means of slit width (d) control at given wavelengths are necessary for implementation of the method. The first algorithm allowed determination of the P(λ,d) relationship. According to assumptions for given wavelengths, different P(d) relationships was carried out for which polynomial of the second order was fitted. Next, polynomial factors in the dependence of wavelength was found. Such obtained relationships were implemented in the second algorithm assuring the light power control. The final controlling program had the correcting mechanism of the slit widths. Additionally, in order to obtain sufficiently high light powers at smaller wavelengths (in UV range) the program was modified in such way that in some wavelength range the second diffraction grating with higher resolution and blaze angle should be used. It is connected with the installation of the nitrogen purging system. The good points of the mentioned solution are efficiency and simplicity. The slit width control occur directly without the need of the additional drivers.