Optical profilometer

 

(57) Abstract:

Usage: the invention relates to measuring equipment. The technical result is to increase the accuracy of measurements as well as the opportunity to study the surfaces of large linear dimensions (of the order of 1 m). The inventive result is achieved by the fact that in the developed optical profilometer implemented a combination of optical devices using white light, namely the absence of diffraction spatial noise (speckles), and optical devices using interferention-phase measurement methods. This and achieving the required technical result is an increase in measurement accuracy to values not less than /1000 . Other achievable technical result is the ability to study surfaces substantially larger than allow other known profilometers, because the size of the investigated surface is limited only by the specific implementation used block mates. This allows the use of optical profilometer for non-contact measurements in the Metrology support subnanometric technologies. 3 C.p. f-crystals, 1 Il. for non-contact Metrology software subnanometric technologies, and can be used to control the surface profile of products in various fields of technology as when debugging technological processes, and at the Express control of the final product, as well as in scientific research.

Known class of profilometers, which are based on the principle of heterodyne interferometry. The essence of this principle is the formation of two rays that have similar frequencies, using laser radiation. Use one of the rays as the reference and measuring relative changes of phase modulated signals to obtain a profile of the surface. Known heterodyne profilometers differ in the values of the difference frequency laser beams, as well as the specific implementation of the elements of the optical circuits. As beam splitters frequency in different versions of the interferometers of this type uses a rotating quarter wave plate, the Bragg cell, rotating with constant speed splitter and Siemanowski splitter for He-Ne laser. To improve the accuracy changes often form a reference beam, averaged over the surface, which use different optical scheme of his EXT is the wavelength of the used radiation, because of the difficulty of maintaining the difference between close frequencies with high stability. One of the best heterodyne profilometers is profilometer (U.S. patent N 4,848,908, 1989), which contains He-Ne laser, acousto-optic modulator, means for expanding the reference beam, the polarizing beam splitter, a quarter-wave plate, a focusing lens and a movable table on which is located the study sample, as well as two photodiode and an electronic unit.

Known another class of profilometers, the basis of which is the method of fotomodella interferometry. Profilometers of this type include the interferometer, one of the shoulders which has the supporting plate and the other of the investigated sample. For measuring the difference of the interfering beams modulate and convert the interference pattern in the photoelectric signal, then the information about the surface profile is extracted from the phase components of the detected signal. To obtain the interference pattern using monochromatic radiation. Fotomodella profilometers are different types of interferometers (Michelson interferometer, the lens Miro and others ), using different types of modulation (Siemer of this type, providing a relatively high accuracy (/500-/1000), known, for example, Osami Sasaki, Hirokazu Okazaki, Appl. Opt. 1986, v.25, N 18, at 3,137. The Profiler includes a radiation source (laser), Michelson interferometer, one of the shoulders which you installed the sample, and the other a reference plate fixed to the piezoelectric element, and a CCD matrix for the signal.

The disadvantage of this monitor, as well as other profilometers this type, as well as profilometers heterodyne type is the high level diffractive spatial noise (speckles), associated with a high spatial coherence of monochromatic radiation and characteristic of all optical devices using a laser. Also, because this profilometer modulation is carried out by moving either the reference or the analyzed plate with a piezoelectric element, the linear dimension of the surface being examined is limited to the technical characteristics of the piezoelectric element and may not exceed 100 microns.

The third major class of profilometers this profilometers, which is based on forming a beam izlucheniya type is the degree of defocus of the image. These profilometers differ by the type of radiation source (monochromatic and white light sources), optical schemes for forming a focused beam, a method of estimating defocus, etc., for Example, by F. Quercioli, et al, Opt. Eng. 1988, v.27, No. 2, 135-known profilometer, containing a white light source, aperture, collimator, and a chromatic lens, the focus of which is the analyzed sample. The monitor also includes a monochromator, educated chromatic lens, the dispersion element and the focusing lens, the output of which is equipped with a photodiode array.

Limitations the accuracy of the measurement plane for profilometers this type are related to the fact that the evaluation of asperities is in intensity reflected from the sample surface radiation, and the measurement result depends on reflecting and scattering properties of individual sections of the sample surface, and therefore the accuracy of measurement does not exceed a few microns.

The closest analogue of the developed optical profilometer together similar essential features of an optical profilometer (U.S. patent N 4,641,971, CL G 01 B 9/02, 1987), which is difficult otnoshenie on the optical axis of the white light source and the interferometer, for the formation of the at least two beams of white light, and one of the plates of the interferometer is investigated sample, and the other of the reference plate, and a color television (TV) camera. Between the white light source and the input of the TV camera has agreed optical filter. Three entrances TV camera connected to the processing unit, the output of which is connected to the logger, which is used as a monitor. The Registrar is also linked with the TV camera.

The disadvantage of this monitor is its low accuracy, due to the fact that his work is based on comparing the intensity of the interference pattern in the three portions of the spectrum with three different receivers, using the standard TV camera. Therefore, the accuracy of the monitor is probably achievable is limited by the identity of the amplitude characteristics of the channels of the receivers, which have a modern TV cameras does not exceed 1% of the Maximum dynamic range of the existing color TV camera is 252 level. Limit the accuracy of this monitor cannot exceed /200.

Problems of measurement and control with a much higher accuracy, namely, with accuracy comparable to the size of atoms and mocnych goals and to create optical devices ultrahigh spatial, and spectral resolutions. These burning issues arise in the design of instruments for remote optical sensing, in particular, optical sensing of astronomical objects. Currently, the sensitivity of the photodetectors with a score of photons allows to detect effects which cause changes in the characteristics of light emission of the order of 10-410-6from their nominal values. Simple estimates show that the implementation of these capabilities is the need to create optical elements that have the same degree of homogeneity and stability. According to experts, the establishment of the necessary technologies mainly hindered by the lack of appropriate means of measurement and control. The field of application subnanometric measuring devices currently covered not only scientific, but also a large number of practice areas. The most obvious example of the use of such devices for industrial purposes is in the area of microelectronics. With the advent of such devices link the creation of microelectronic devices of last generation, which should make, according to scientists, the revolution in electronic technology.

Task isoph technologies.

The invention consists in that the optical profilometer, as is known, contains located on the optical axis of the white light source and the measuring interferometer, capable of forming at least two beams of white light, with one of the plates of the measuring interferometer is investigated sample and the other of the reference plate, and a processing unit, a control input connected to the synchronizer, and the output connected to the data logger.

New developed optical profilometer is that it is additionally imposed on the optical axis of the collimator, interface unit, an auxiliary interferometer, the lens and the matrix Converter of the light signal into the electric and also the source of control voltages. The collimator is a source of white light, and measuring and auxiliary interferometers are installed between the collimator and the matrix Converter of the light signal into an electric. The connection unit is installed between the measuring and auxiliary interferometers, and the lens is set at the input of the matrix Converter of the light signal into an electrical matrix Converter light signals into electric. The output of the matrix Converter is connected to the processing unit. One of the plates of the auxiliary interferometer is stationary, and the other plate is configured to move the optical axis with fixed thereto a piezoelectric element, which is connected to the output of a source of control voltages. The processing unit is made in the form of multi-phase meter.

In the particular case of the measuring interferometer is made in the form of a Fabry-Perot interferometer.

In another particular case, the auxiliary interferometer is made in the form of a Fabry-Perot interferometer.

In the third special case of the measuring and auxiliary interferometers made in the form of Fabry-Perot interferometers.

It is advisable between the white light source and the matrix Converter of the light signal into an electric to establish a consistent optical filter.

In the disassembled optical profilometer introduction established on the optical axis of the collimator, the interface block, the auxiliary interferometer lens and matrix Converter light signals into electric and source of control voltages, allows realini spatial noise (speckles), and optical devices using interferention-phase measurement methods. This and achieving the required technical result of the improved accuracy of the measurements to values not less than /1000. Other achievable technical result is the ability to study surfaces substantially larger than allow other known profilometers, because the size of the investigated surface is limited only by the specific implementation used block mates. This allows the use of optical profilometer for non-contact measurements in the Metrology support subnanometric technologies.

The drawing shows a structural diagram of the developed optical profilometer.

Optical profilometer (see drawing) contains successively installed on the optical axis of the white light source 1 and the collimator 2, and mounted on the optical axis of the measuring interferometer 3, provides for the formation of at least two beams of white light, block 4 mates, auxiliary interferometer 5 and the matrix Converter 6 light signals into electric. One of the plates of the measuring interferometer 3 asetustenhallinta between the collimator 2 and the matrix Converter 6 light signals into electric, and the block 4 of the coupling is installed between the measuring and auxiliary interferometers 3, 5. In a specific implementation (see drawing) measuring interferometer 3 is a collimator 2.

As a measuring interferometer 3 can be used any interferometer that meets the above requirements. In the specific implementation shown in the drawing, the measuring interferometer 3 is made in the form of a Fabry-Perot interferometer. As an auxiliary interferometer 5 can be used any interferometer. In the specific implementation shown in the drawing, the measuring interferometer 3 is also made in the form of a Fabry-Perot interferometer. Plate 9 auxiliary interferometer 5 is stationary, and the plate 10 is arranged to move along the optical axis by the fixed thereto piezoelectric element 11, which is connected to the output of source 12 operating voltage. The control input of the matrix Converter 6 light signal into an electrical connected to the synchronizer 13, which is connected also to the input source 12 operating voltage and with a control input multi meter 14 phase. The output mnogocennaja the white light source 1 and the matrix Converter 6 has a coherent optical filter 17. In a specific implementation according to the drawing, a coherent optical filter 17 is installed between the output of the auxiliary interferometer 5 and the lens 16.

Unit 4 mate is designed for coupling light measuring diameters and auxiliary interferometers 3, 5 and can be made in the form of a lens system.

As a matrix Converter 6 can be used a standard CCD camera.

The distance between the plates 7,8 measuring interferometer 3 and between the plates 9, 10 of the auxiliary interferometer 5 when coherent optical filter 17 in the optical profilometer is missing, are multiples of each other with an accuracy of the order of the wavelength of the Central part of the visible spectrum. With the introduction of a coherent optical filter 17 in the optical profilometer specified limit on the distance between the plates 7, 8 and 9, 10 are missing, however, bandwidth coherent optical filter 17 must be coordinated with the distance between the plates or measuring, or auxiliary interferometers 3, 5.

The lens 16 is designed to generate images of the sample surface on photocast made in the form of an interference filter.

The source 12 of control voltages is to change the optical gap of the auxiliary interferometer 5.

The synchronizer 13 is designed to provide synchronous operation of the matrix Converter 6, the source 12 operating voltage and the processing unit 14. As a synchronizer 13 can be used, for example, the generator type G6-15.

As a multi-meter 14 phase can be used in any computing device that computes a phase of the first Fourier harmonic of the signal from its values at three points, in particular computers.

As recorder 15 may be used any two-coordinate recording device (plotter, two-coordinate recorder, printer, and so on).

Optical profilometer according to the drawing operates as follows.

Diverging radiation beam from the white light source 1 impinges on the collimator 2. A parallel beam of radiation formed by the collimator 2, illuminates the plates 7, 8 of the measuring interferometer 3. The interferometer 3 forms a W-shaped radiation spectrum corresponding to its own transmission functions, while the position of the maxima of the spectrum) is therefore profile of the study sample surface 7. The radiation output of the measurement interferometer 3 through the block 4 pair without changing the spectral composition falls on the auxiliary interferometer 5. Plate 10 of the auxiliary interferometer 5 using the piezoelectric element 11, controlled by source 12, is moved along the optical axis according to the law of the control voltage. Because the same law changes the path difference of the interfering beams in the auxiliary interferometer 5, respectively, changing the position of the maxima of the function of the transmittance spectrum of the auxiliary interferometer 5. On the photosensitive surface of the matrix Converter 6 lens 16 forms an image of the surface. In each point of the image the emission maximum occurs at the time of coincidence to the extent of the short distance between the plates 9, 10 with the distance between the plate 8 and the corresponding point on the sample surface 7. Because, as you know, the phase of the first harmonic signal corresponds to the position of its maximum, when the movement of the plate 10 along the optical axis at the output of the matrix Converter 6 are formed signals, the phase of which is therefore the profile of the surface. The multi-phase meter 14 provides a measurement of the phases of the signals at the output of each element of the matrix Converter 6. The 15 Registrar registers the obtained values of the phases of the signals, which correspond to the profile of the surface.

1. Optical profilometer, containing a white light source and mounted on the optical axis of the measuring interferometer formed investigated surface and the reference plate and capable of forming at least two beams of white light series-connected optical signal Converter in electrical and processing unit of the signal, the synchronizer is connected to its control input, and a recorder connected to its output, characterized in that it has installed on the optical axis of the collimator, located behind a white light source, an auxiliary interferometer, a connection unit and a lens installed on the inverter input optical signal into an electrical executed matrix, while measuring and auxiliary interferometers are installed between the collimator and the optical signal Converter in electric, alausa stress the inlet of which is connected to the synchronizer, also connected with the control input of the Converter of the optical signal into an electric, one of the plates of the auxiliary interferometer is stationary, the other can move along the optical axis and is provided with a piezoelectric element connected to the output of the source of control voltages, and the block of signal processing executed in the form of a multi-meter phase.

2. Optical profilometer under item 1, characterized in that the measuring interferometer is made in the form of a Fabry-Perot interferometer.

3. Optical profilometer under item 1 or 2, characterized in that the auxiliary interferometer is made in the form of a Fabry-Perot interferometer.

4. Optical profilometer under item 1, or 2, or 3, characterized in that it additionally introduced a coherent optical filter installed between the white light source and a matrix Converter light signals into electric.

 

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