CN104897076A - Three dimensional shape measurement method for micro nanoscale - Google Patents

Abstract

The invention discloses a three dimensional shape measurement method for micro nanoscale. The three-dimensional shape measurement method for micro nanoscale is mainly used for the three-dimensional shape measurement for the micro nanoscale measurement surfaces of the semiconductor integrated circuit, MEMS members, etc. The three dimensional shape measurement method for the micro nanoscale comprises steps of performing the scanning measurement on the surface of a sample through femtosecond laser, adopting a measurement optical path to realize cross-scale micro nano measurement, wherein the an interference pattern which is obtained in measurement is detected by a high-speed CCD, obtaining surface three dimensional shape characteristic parameters after processing and analyzing and thus resorting surface three dimensional shape of the surface of the sample.

Description

A method for micro-nano scale three-dimensional shape measurement

technical field

The invention relates to a method for measuring surface three-dimensional topographic features by using a femtosecond laser frequency comb. The method is mainly used for measuring the three-dimensional topographic features of micro-nano scale surfaces such as semiconductor integrated circuits and MEMS devices.

Background technique

With the further development of semiconductor integrated circuit manufacturing technology and micro-nano ultra-precision processing technology, the emergence of large-scale, nano-scale large-scale integrated circuits and miniaturized and precise micro-electromechanical systems, the detection capabilities of related measurement methods and measuring instruments Detection accuracy poses new requirements and challenges.

At present, the existing methods for measuring the three-dimensional topography characteristics of micro-nano scale surfaces have many limitations, such as the small horizontal field of view for a single measurement, the slow speed of scanning field and fast scanning for longitudinal measurement, and the measurement accuracy is related to the mechanical scanning device, etc. , can no longer meet the requirements of large visual velocity measurement of the three-dimensional surface features of micro-nano scale.

Femtosecond laser frequency comb has unique time and spectral characteristics in precision spectroscopy, optical frequency metrology and absolute distance measurement. The characteristic method of femtosecond laser pulse with low temporal coherence and high spatial coherence is a new type of measurement method. It has the advantages of large measurement field of view and fast measurement speed. It has unprecedented advantages in the measurement of three-dimensional topography of large-scale surfaces in semiconductor integrated circuit manufacturing, MEMS device processing and other micro-nano manufacturing. The surface three-dimensional surface measurement based on femtosecond laser frequency comb It has important application value in fields such as shape feature measurement.

Contents of the invention

The invention adopts femtosecond laser frequency comb as the light source, utilizes its characteristics of low temporal coherence and high spatial coherence to realize large-scale micro-nano measurement, and the repetition frequency of the frequency comb can be adjusted, and the scanning of the sample surface can be completed by changing the repetition frequency Measurement. In the present invention, the measurement optical path is an unbalanced and asymmetric optical path, which is composed of an optical fiber optical path, a frequency doubling system and a beam expanding optical path, so as to realize cross-scale micro-nano measurement. The measured interference pattern is detected by a high-speed CCD. After processing and analysis, the characteristic parameters of the three-dimensional topography of the sample surface can be obtained, and the three-dimensional topography of the sample surface can be restored through three-dimensional model reconstruction.

Compared with the traditional measurement method, the present invention uses a femtosecond laser frequency comb as the light source, which expands the measurement field of view; uses the electronic scanning method to scan, improves the scanning speed, and avoids the influence of mechanical scanning on the measurement accuracy; Scale micro-nano measurement.

Description of drawings

In order to more clearly and accurately illustrate the technical solutions in the embodiments of the present invention, the following will briefly introduce the drawings that need to be used in the embodiments or the description of the prior art. Obviously, the drawings in the following description are only the present invention. For the embodiment of the present invention, those of ordinary skill in the art can also obtain other drawings according to the provided drawings on the premise of not paying creative efforts.

Figure 1 is a block diagram of the femtosecond laser frequency comb three-dimensional surface shape measurement method

Figure 2 is a schematic diagram of the structure of the femtosecond laser frequency comb three-dimensional surface measurement system

Figure 3 is a flow chart of the femtosecond laser frequency comb three-dimensional surface measurement method

Among them, 21: fiber coupler; 22, 23: single-mode fiber; 24: dispersion compensation fiber; 25, 33, 34: lens; 26: dichroic mirror; 27: frequency doubling crystal; 31: plane mirror; 32: beam splitting prism ;35: Tested sample; 41: High-speed CCD camera

Detailed ways

The technical solutions in the embodiments of the present invention will be accurately and completely described below in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some, not all, embodiments of the present invention. Based on this, all other embodiments obtained by persons of ordinary skill in the art without making creative efforts belong to the protection scope of the present invention.

The femtosecond laser frequency comb method of the present invention for measuring surface three-dimensional topography features includes: femtosecond laser frequency comb system 1 with adjustable repetition rate, optical path system 2 composed of optical fiber optical path and frequency doubling system, Michelson interference optical path and expansion The measurement system 3 composed of the optical beam path and the signal receiving system 4 composed of the high-speed CCD camera are shown in Fig. 1 . The femtosecond laser frequency comb three-dimensional surface measurement system involved in the present invention is shown in Figure 2. The femtosecond pulse generated by the femtosecond laser frequency comb is divided into two beams of light by the fiber coupler 21 and enters the optical fiber optical path composed of the reference optical path and the measurement optical path. . The reference optical path is composed of a long single-mode optical fiber 23, and at the same time, the dispersion compensation optical fiber 24 is used in combination to compensate the dispersion caused by long-distance transmission. The measurement optical path consists of a short single-mode optical fiber 22 . At the same time, a large optical path difference is designed between the reference optical path and the measurement optical path. The femtosecond pulse emitted from the optical fiber path enters the frequency doubling crystal 27 through the plane mirror 25 and the dichroic mirror 26 for frequency doubling, and only the frequency multiplied femtosecond pulse can be reflected by the dichroic mirror 26 and enter the measurement system. The measurement system is composed of a Michelson interference optical path composed of a plane mirror 31, a dichroic prism 32, lenses 33 and 34, and a measured sample 35, wherein the lenses 33 and 34 form a beam expanding optical path to better detect the surface of the sample. By adjusting the repetition frequency of the femtosecond laser frequency comb, the scanning of the sample to be tested is completed, and the corresponding interference pattern is obtained on the high-speed CCD camera 41 .

The flow chart of the measurement method of the present invention is shown in Figure 3. First, the repetition frequency adjustment step is determined according to the actual sample, and then starting from the initial repetition frequency, the repetition frequency after each step is adjusted to complete a measurement of the sample surface and obtained on the CCD. One frame of corresponding images, repeating this cycle until the scanning of the surface of the tested sample is completed. After scanning, through the analysis and processing of the interference pattern obtained on the CCD, the characteristic parameters of the three-dimensional topography of the sample surface can be obtained, and the three-dimensional topography of the sample surface can be restored through three-dimensional model reconstruction.

The foregoing description of the disclosed embodiments enables those skilled in the art to make or use the invention, and various modifications to these embodiments will be apparent to those skilled in the art. The general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (3)

1., for a method for micro/nano-scale measuring three-dimensional morphology, comprise,

The femtosecond laser frequency comb system 1 that repetition frequency is adjustable, the light path system 2 of optic fibre light path and frequency doubling system composition, the receiving system 4 that michelson interferometer optical path forms with the measuring system 3 and high-speed CCD camera that expand light path formation.

2. according to claim 1, draw the femtosecond laser frequency comb tri-dimensional facial type measuring system related to, the femtosecond pulse that femtosecond laser frequency comb produces is divided into two-beam by fiber coupler 21 and enters the optic fibre light path be made up of reference path and optical path.Wherein reference path is made up of segment length's single-mode fiber 23, is combined dispersion compensating fiber 24 to compensate the dispersion because long range propagation causes simultaneously.Optical path is made up of one section short single-mode fiber 22.Be designed with larger optical path difference between reference path and optical path simultaneously.Incided frequency-doubling crystal 27 by the femtosecond pulse after optic fibre light path outgoing carry out frequency multiplication through level crossing 25, dichronic mirror 26, and only have the femtosecond pulse after frequency multiplication can enter measuring system by dichronic mirror 26 reflection.The michelson interferometer optical path that measuring system is made up of level crossing 31, Amici prism 32, lens 33 and 34, sample 35 forms, and wherein lens 33 and 34 composition expands light path better to detect sample surfaces.Complete the scanning to sample by the repetition frequency adjusting femtosecond laser frequency comb, high-speed CCD camera 41 obtains corresponding interference pattern.

3. according to claim 2, draw actual sample determination repetition frequency adjustment step-length, then from initial repetition frequency, repetition after each step by step modulating completes and once on CCD, obtains the corresponding image of a frame to the measurement of sample surfaces, so goes round and begins again until complete the scanning on sample surface.By the analyzing and processing to gained interference pattern on CCD after having scanned, sample surfaces three dimensional topography parameter can be obtained, and sample surfaces three-dimensional appearance can have been reduced by reconstructing three-dimensional model.