SU1160810A1 - Ellipsometer - Google Patents

Description

The invention relates to optical polarization devices and can be used for express non-contact determination of physical parameters (layer thickness, refractive index and absorption, free carrier concentration, degree of roughness of solid surfaces, depth of the layer damaged during processing, birefringence, concentration of solutions, etc. .) solid and liquid materials in various industries, such as optical instrument making, microelectronics, optoelectronics and food processing industry,

Non-zero ellipsometers are known that contain consecutive monochromatic sources

collimated radiation, a polarizer, a sample, an analyzer, a receiving-recording system, and zero ellipsometers, in which the A / 4-plate (compensator) is additionally installed between the polarizer and the analyzer and the azimuths of the polarizer and analyzer are determined to correspond to the light of the analyzer. .

Non-zero industrial ellipsometers with manual control have low accuracy, and in zero industrial ellipsometers with manual control measurements are required in at least two zones, which leads to a significant investment of time (2-3 minutes).

The closest to the proposed ellipsometer is an ellipsometer containing a monochromatic source1160810 A1

3 1160810 4

collimated radiation and a polarizer arranged in turn along the beam, mounted for rotation, an analyzer and a receiving-recording system. ί

However, this ellipsometer has a low measurement speed and a small signal-to-noise ratio.

The aim of the invention is to increase the measurement speed and the value of the signal-to-noise ratio.

This goal is achieved due to the fact that in an ellipsometer ₅ containing a source of monochromatic radiation and a polarizer arranged in rotation along the beam, an analyzer and a receiving-recording system, the polarization beam separation element, an amplitude modulator and an element of combining rays, and the elements _{2 of} splitting and combining rays are equipped with a piezoelectric element rigidly connected to them conventional modulators *

The drawing shows schematically the proposed ellipsometer (option) /

The ellipsometer contains a source of 1 collimated monochromatic radiation (LG-126 laser providing radiation with a wavelength of 0.63, 1.15 and 3.39 μm), a polarizer 2, elements 3, 4 of the separation of polarized beams, elements similar separation beams amplitude modulator (e.g. mechanical obtyurztor 7), a phase modulator (e.g. piezoceramic modulator 8 PEP-1), the screen 9, the sample holder 10, the analyzer 11, photodetectors 12 (silicon and germanium photodiodes, fo- _ζ tosoprotivlenie PbTe) , amplifiers 13, p gistriruyuschy device 14, the reflection type polarizer and analyzer comprise two reflective mechanically polished silicon wafer _f (doped silicon KZS0,01) installed at an angle of 75 ° (near the Brewster angle), and providing a high degree of polarization in the working spectral dia- _with pazone with

The polarized beam separation element contains a transparent dividing plate (fused quartz,

CaP, Ζηδβ, or layers of films with a high refractive index on substrates with a low refractive index) and polished plates of doped silicon arranged parallel to each other at an angle. Brewster to the incident radiation.

The mechanical obturator 7 interrupts, with a frequency of 300 Hz, polarized beads A, B, and C alternately separated in space (figure 1). The modulator 8 provides a sinusoidal shift of the elements 4 and 6 in the direction perpendicular to the direction of the beam incident on the sample 10,

The ellipsometer works as follows.

A monochromatic collimated beam of radiation from the source 1 passes through the polarizer 2 and enters the beam separation element. Element 3 (figure 1) divides the radiation beam into beams A, B and B. Bundle A is reflected from silicon elements 4 and 6 installed on the modulator 8 at an angle of 76 to the incident radiation and then reflected from transparent element 5, similar to element 3, Beams B and C pass through element 5 and are combined with beam A, the equality of the optical paths of beams A and B is achieved by choosing the thickness of the transparent element and the distance between elements 3 and 4 (5 and 6),

One of the options for measuring ellipsometric parameters ψΜ Δ is as follows.

When calibrating an ellipsometer, the analyzer determines the ratio of the intensities of the beams A, B and C and their polarization state in the "To the Light" position (without a sample).

The voltage on the modulator 8

₅ is equal to zero, and the obturator interrupts beams A, B, and B with a frequency of 300 Hz. The ratio of the intensities of the beams needed to increase the accuracy is set by turning the polarizer 2

θ and related together elements of the separation and unification of the beams. In the particular case, beams A, B, and C are linearly polarized.

Setting the sample at an angle to the incident radiation, register

⁵ magnitudes of the signals on the photoreceiver Ι, ι, Ι ^ and 1 _e at the moments when beams A, B and C fall on the sample _(| respectively with azimuths of the linear polari

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* sions οί,, (Ug ^and ϊ by values

I ,, Ι ^, Ι - ,,, ος, Οί ^, (He and the analyzer's azimuth, fixed when measuring, / 3, are determined by the ellipsometric 5

cue parameters & cf.

The second measurement option "

In this embodiment, beam B overlaps, and beams A and B are interrupted by a mechanical obturator so that by 10 the sample with the interruption frequency drops either beam A or B or the beam produced at the moments when both beams A and B are open . In this case, the voltage is applied to the modulator-15 torus 8 and the desired polarization state of the beam H is set. As in the previous version, the analyzer determines the ratio of the intensities of the beams A, B and D and their state- ". This option has a greater sensitivity in measuring φ and и very thin films if circular polarization 25 of the beam is established. Measurement variant with phase modulation of the polarization state.

In this version of the ellipsometric measurement, the mechanical obturator stops, with both 30 beams A and B open. The azimuths of the orthogonal polarizations of the beams A and B οί | = 45 ° and -45 °. Azimuth Analyzer 11

β, = -45 °. In this configuration ι

'carried high 35

displacement of elements 4 and 6 with the help of modulator 8 A constant displacement on piezoceramics allows the initial phase of oscillations to be precisely determined. Turning polarizer 2 sets 40 · exact equality of beams A and B in intensity in the "To the light" position with a rotating obturator. "Harmonic components of the signal from the photodetector are measured using a selective amplifier 45 * * *

The signal-to-noise ratio, when measured on the proposed ellipsometer, is 10-30 times higher than in measurements on a known ellipsometer, due to a significant decrease in the duty cycle of the measurement intervals.

As the basic object of comparison, choose a commercially available ellipsometer with manual control e-3. The industry does not produce automatic non-zero ellipsometers. ”The main parameters of the instrument are as follows: the error in measuring the polarization angles Cp À A with reproducibility is 0.1–0.15, the error in determining absolute values and A is greater than 0.2, the measurement time and nd. more than 10 s

The measurement speed on the proposed ellipsometer is three orders of magnitude higher, and the signal-to-noise ratio is an order of magnitude higher than in the base ellipsometer E-3, due to the more effective elimination of the instability of the power of the radiation source and the reception-recording path in the high-speed measurements on the proposed ellipsometer.

Higher signal ratio /

noise makes it possible to effectively use the proposed ellipsometer for measuring cp and Δ in local areas up to 10x10 µm ² and when measuring in vacuum UV and IR spectral regions with weak radiation sources and insufficiently effective photodetectors.

A significant increase in the measurement speed makes it possible to effectively investigate the kinetics of physical phenomena on the surface of solid and liquid bodies and to control parameters, for example, layered structures in the process of their manufacture.

1160810

Claims (1)

ELLIPSOMETER containing a source of monochromatic collie2 A polarizer mounted for rotation, an analyzer and a (registering system, characterized in that, in order to increase the measurement speed and the signal-to-noise ratio between the polarizer and the analyzer, the element polarized beam separation, an amplitude modulator and a beam combining element, the beam splitting and combining elements being equipped with piezoelectric elements that are rigidly connected to them kimi modulators. (L