Step distance measuring device based on femtosecond optical-frequency comb and measuring method thereof

Abstract

Disclosed are a step surface topography measuring device based on a femtosecond optical-frequency comb and a measuring method thereof. The measuring method includes steps of utilizing the femtosecond optical-frequency comb with repetition frequency and offset frequency which are locked to reach the microwave frequency reference as a light source; interfering measuring light with reference light, which is delayed by a certain light path, of split light beam; scanning repetition frequency of the femtosecond optical-frequency comb and acquiring positions of coherent peak value of light strength received by corresponding pixels of each step surface; and working out the absolute distance of steps according to the corresponding repletion frequency and light path delay of the coherent peak value. The measuring method overcomes the defects that light path is difficult to be regulated and precision is limited by motion precision of piezoelectric ceramic machinery when in use of the conventional measuring method, and has the advantages of high longitudinal resolution ratio and wide measuring range. Besides, the repetition frequency and offset frequency of the femtosecond optical-frequency comb are locked to reach the microwave frequency reference so that measuring results are traceable.

Description

technical field [0001] The present invention relates to a step-type surface topography measuring device and method, in particular to a step distance measuring device and method based on a femtosecond optical frequency comb. Background technique [0002] In the field of precision metrology, it is often necessary to measure the step distance with high precision. At the same time, step-type absolute distance precision measurement also has important requirements in modern industry, such as the measurement requirements for the height of micro-nano steps in semiconductor technology. [0003] Traditional non-contact step measurement methods are usually based on the principle of white light interferometers. When white light is used as the light source for interference, because white light contains a wide spectral range, it can only obtain interference fringes with better contrast when the optical path difference is zero. Using this feature of white light interference, construct a ...

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Problems solved by technology

[0004] Using the above white light interference method to accurately measure the step distance has the following limitations: 1) Because the temporal coherence of white light is small, interference fringes can only be obtained in a small range near the equal optical path, so it is difficult to adjust the optical path. The two light beams are adjusted to the position of equal optical path

2) The interference pattern is obtained by mechanical scanning motion of piezoelectric ceramics, and the hysteresis characteristics of piezoelectric ceramics will affect the measurement resolution and accuracy, and the range of motion of piezoelectric ceramics also limits the measurement range of step height

3) The measurement results of this method cannot be linked with the current metrological benchmarks, and do not meet the requirements of traceability of measurement results in metrology

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