Methods for determining properties and / or parameters of a sample and / or at least one layer formed on a surface of a sample

Abstract

Method for determining properties and / or parameters of a sample and / or at least one layer formed on a surface of a sample, wherein with several detectors designed for spatially resolved spectral analysis of electromagnetic radiation within a wavelength interval, arranged in a row or a row and column arrangement and with connected to an electronic evaluation unit and are arranged in such a way that the electromagnetic radiation emitted by a broadband radiation source either after reflection at the surface of the sample, a layer formed on the sample or on the surface of a layer within the sample and / or after passing through a sample transparent to electromagnetic radiation onto the detectors, Measurement signals are captured with spatial and wavelength resolution within a wavelength interval, whereby The irradiation is carried out in such a way that a homogeneous intensity of the electromagnetic radiation is maintained within a simultaneously detectable area on a surface from which the electromagnetic radiation is reflected or transmitted through the surface, and with the The electronic evaluation unit compares the spatially and wavelength-resolved measurement signals of the detectors within a wavelength interval with a theoretical wavelength-dependent profile of the respective radiation intensities obtained through simulation or a profile obtained through calibration on at least one known sample, so that a statement is obtained to determine at least one property or at least one parameter of the sample or at least one layer formed on or at the sample for the recorded measurement positions and thus the spatially resolved distribution of at least one property or at least one parameter of the sample or at least one layer formed on or at the sample.

Description

[0001] The invention relates to a method for determining properties and / or parameters of a sample and / or at least one layer formed on or at a surface of a sample. A sample is understood to mean solids, solids coated with at least one layer, or elements formed from several layers arranged one above the other.

[0002] Thin films (single or multi-layer systems on defined substrates) are essential in a wide variety of applications, e.g. semiconductor films, wear-resistant films, optical films, etc. are known as such. For their functionality, compliance with specified film parameters / properties within specified tolerance ranges is required. The important parameters can be the film thickness(es), the optical refractive index(es), the absorption constant(s) at specific wavelengths or the parameters describing their progression over a specific wavelength range. Other properties of films and also of homogeneous samples can be the number of charge carriers contained per area or volume (charge carrier concentration) or the presence of inhomogeneities or defects (particles, inclusions, etc.).

[0003] Very often, it is necessary to determine these parameters reliably and quickly across the entire sample area. It should be possible to determine the distribution of the above parameters with spatial resolution across the entire sample area. This should allow for a statistically reliable statement for the entire sample.

[0004] Typically, different dedicated measurement methods are used for the above-mentioned properties and parameters. However, these are mostly single-point measurements, where a spatial resolution (x or xy) of the respective measured value can be achieved by moving a sample or sensor (mapping). A graphic representation of the recorded measured values ​​must be created separately, which is laborious.

[0005] For example, the layer thickness distribution can usually be determined interferometrically. Ellipsometry can be used for other parameters or properties mentioned above. However, this is only possible for one wavelength at a time, which reduces accuracy and / or the required time.

[0006] For example, possibilities for using hyperspectral imaging (HSI) are shown in the Fraunhofer Institute for Material and Beam Technology IWS: Annual Report 2013, Dresden, 2014, pages 30 and 31.

[0007] A method and a device for variable angle-dependent spectral detection of measured values ​​are described in WO 2013 / 157641 A1 and EP 2 840 368 A1.

[0008] It is therefore an object of the invention to provide possibilities for determining the lateral distribution of properties and / or parameters of samples or layers formed on samples or present in samples in a short time with very good accuracy, wherein preferably a graphic representation of the results should be possible with little additional effort.

[0009] According to the invention, this object is achieved by a method having the features of claim 1. Advantageous embodiments and further developments of the invention can be realized with features defined in subordinate claims.

[0010] In the method according to the invention for determining properties and / or parameters of a sample and / or at least one layer formed on a surface of a sample or present on the sample, a plurality of detectors designed for the spatially resolved spectral analysis of electromagnetic radiation within a wavelength interval are used. These detectors are arranged in a row or a row and column arrangement. The detectors are connected to an electronic evaluation unit and arranged such that electromagnetic radiation emitted by a broadband radiation source impinges on the detectors either after being reflected by the surface of the sample or a layer formed on the sample and / or after passing through a sample transparent to the electromagnetic radiation.The irradiation is carried out in such a way that a homogeneous intensity of the electromagnetic radiation is maintained on a surface from which the electromagnetic radiation is reflected or transmitted. Therefore, the area to be detected simultaneously should be irradiated with a homogeneous intensity.

[0011] The electronic evaluation unit is designed to compare the spatially and wavelength-resolved measurement signals of the detectors within a wavelength interval with a theoretical wavelength-dependent profile of the respective measured radiation intensities obtained by simulation or with a profile obtained by calibration on at least one known sample in order to obtain information for determining at least one property or at least one parameter of the sample or at least one layer formed or present on the sample. The wavelength interval in which the evaluation is carried out should be at least a subset of the wavelength interval of the electromagnetic radiation used for irradiation.

[0012] At least 30, preferably at least 100 detectors should be arranged in a row.

[0013] The area should be irradiated at an angle of at least 0° to < 90° relative to the normal to the sample surface. When irradiating a sample that is transparent to electromagnetic radiation, the angle should be at least almost 0° to the sample normal, i.e. the radiation should be directed as perpendicularly as possible to the sample surface in order to keep the reflected portion as small as possible. Irradiation and detection can also be carried out with a variable angle of incidence of the electromagnetic radiation. As already stated, angles of incidence in the range 45° to a maximum of 89° can be selected. Angles of incidence in the range 60° to 80° are preferred if reflected radiation is to be detected, regardless of whether a constant angle of incidence or various angles of incidence are to be used.

[0014] Irradiation or detection can also be performed with polarized electromagnetic radiation. In this case, the orientation of the polarization plane can be changed, and the electromagnetic radiation can be emitted and / or detected with different polarizations.

[0015] The invention can be used to determine the layer thickness(es), the optical refractive index(es), their wavelength-dependent profiles, the absorption constant(s), their wavelength-dependent profiles, the surface quality of the sample or at least one layer formed on the sample, the charge carrier concentration, and / or the number and / or size of defects / particles or inhomogeneities in the sample or at least one layer. For example, thickness and surface quality can be determined simultaneously. In this process, the surface roughness can be determined. The size of individual defects or inhomogeneities (differences in the material composition) and / or their number per area can also be determined.

[0016] Particularly for large-area samples, the detectors and the sample can be moved relative to each other along at least one axis, preferably at a constant distance from each other. For example, with statically fixed detectors and radiation sources, a sample can be moved along one axis. This can be achieved in an x- and, if necessary, a y-direction using a suitable movable table on which a sample is mounted. However, unwinding from roll to roll is also possible if the sample is made of a flexibly deformable material, for example, in the form of a film.

[0017] The radiation source can contain elements that shape the electromagnetic radiation. In a simple design, the radiation source can be a microscope. However, the radiation source can also be arranged in a hollow body, from which the electromagnetic radiation can emerge diffusely and be directed onto the surface to be irradiated. The hollow body can be a sphere or cylinder. It should be possible to irradiate a surface to be detected simultaneously and homogeneously. For a radiation source with beam-shaping optical elements, the wavelength range used should be considered when selecting the optical elements used for beam shaping.

[0018] Preferably, a diaphragm preventing the incidence of scattered electromagnetic radiation can be arranged in front of the detectors in the beam path of the electromagnetic radiation.

[0019] The radiation source can emit electromagnetic radiation whose wavelengths begin with UV radiation and end with IR radiation. Radiation from the NIR and IR ranges, i.e., from 700 nm to 10,000 nm, is particularly preferred. Within a used wavelength range, it should be possible to use as many wavelengths as possible within the respective interval for irradiation. The limits should be determined solely by the sensitivity range of the detectors used and the optical properties of the beam delivery components. For very thin layers, wavelengths in the UV / VIS range (from 250 nm) are preferred.

[0020] There may also be at least one element present or integrated therein that allows a targeted selection of the polarization of the electromagnetic radiation.

[0021] A sample can also be a multilayer structure, consisting of several layers made of different materials. This can, for example, be a substrate on which layers are formed that are at least partially transparent to the electromagnetic radiation used. The substrate can also be correspondingly transparent. The transparency can relate to a portion of the wavelength spectrum of the emitted electromagnetic radiation and / or a non-absorbed portion of the entire wavelength spectrum of the radiation.

[0022] The detectors used and the electronic evaluation unit as well as, if applicable, the radiation source can represent a so-called hyper-spectral image system, which can be used in the arrangement according to the invention.

[0023] The simultaneously spatially resolved spectra detected (at each recorded position) can be evaluated as follows with regard to the material or material parameter of interest or its property.

[0024] In a first variant (A), the entire setup can be physically described using a parameterized optical model. The sample parameters to be determined can be determined by regression (fitting) a spectrum simulated based on the optical model to the measured spectrum, which can be achieved, for example, by linear or nonlinear curve fitting or by minimizing the sum of the squares of the errors (least squares fit). If a sufficient fit is not possible, the measurement results should be discarded or they can be considered as a disturbance in the layer or sample surface.

[0025] In variant B, the relationship "spectrum - the target parameter(s)" can be calibrated using samples with known target parameter value(s). Using this calibration model, the target parameter(s) can be determined from each measured spectrum (at each location). Methods of multivariate mathematical-statistical data analysis, such as principal component analysis (PCA) and partial least square analysis (PLS), can be used for calibration.

[0026] The entire sample area to be examined should be homogeneously illuminated. Otherwise, lateral intensity fluctuations caused by the irradiation will overlap with the intensity fluctuations caused by the sample (and to be evaluated), leading to errors. To create a laterally homogeneous light field for irradiating a small area on samples, a microscope optics with homogeneous microscope illumination can be used. For larger samples, a "diffuser setup" can be used for irradiation, in particular at least one radiation source arranged within a hollow body (e.g., an integrating sphere or a hollow cylinder).

[0027] When recording spectra at a defined angle of incidence of the electromagnetic radiation, one or more angles of incidence in the range 0° - 85° can be used for a reflection setup.

[0028] A combination of different measurement conditions can be used. This includes transmission / reflection measurements, combinations of different angles of incidence, and the use and combination of different polarization planes of electromagnetic radiation in a variety of ways.

[0029] It is also possible to use multiple rows or rows and columns of detectors, which can then be arranged one after the other in the direction of movement, for example. These detector arrangements can each detect under different measurement conditions.

[0030] With arrays of detectors whose row / line is formed by using different optical arrangements (different optical elements) or which can be modified, detection can be carried out under different measurement conditions.

[0031] With the invention, a rapid characterization of an entire sample with respect to a target parameter can be achieved in a short time.

[0032] For example, the user can immediately obtain a "layer thickness image" of the sample. It is also possible to visualize defects, the local charge carrier concentration, or the chemical composition.

[0033] The information obtained can be used for monitoring coating processes (inline control), the development of coating systems and also quality control (lateral distribution of relevant coating parameters).

Claims

[1] Method for determining properties and / or parameters of a sample and / or at least one layer formed on a surface of a sample, in which with several detectors designed for the spatially resolved spectral analysis of electromagnetic radiation within a wavelength interval, arranged in a row or a row and column arrangement and with connected to an electronic evaluation unit and are arranged so that the electromagnetic radiation emitted by a broadband radiation source either after reflection from the surface of the sample, a layer formed on the sample or hits the detectors at the surface of a layer within the sample and / or after passing through a sample transparent to electromagnetic radiation, Measurement signals are recorded spatially and wavelength-resolved within a wavelength interval, whereby the irradiation is carried out in such a way that on a surface from which the electromagnetic radiation is reflected or transmitted through the surface, a homogeneous intensity of the electromagnetic radiation is maintained within a surface to be detected at the same time and with the electronic evaluation unit, the spatially and wavelength-resolved measurement signals of the detectors within a wavelength interval are compared with a theoretical wavelength-dependent curve of the respective radiation intensities obtained by simulation or with a curve obtained by calibration on at least one known sample, so that a statement for determining at least one property or at least one parameter of the sample or at least one layer formed on or at the sample for the recorded measurement positions and thus the spatially resolved distribution of at least one property or at least one parameter of the sample or at least one layer formed on or at the sample is obtained. [2] Method according to claim 1, characterized by that the irradiation of the surface is carried out at least at an angle in the range 0 ° to < 90 ° with respect to the normal of the surface of the sample. [3] Method according to claim 1 or 2, characterized by that the angle of incidence of the electromagnetic radiation is changed or adjusted, preferably in the range 60° to 80°, whereby the detection and evaluation is preferably carried out at several different angles of incidence. [4] Method according to one of the preceding claims, characterized by that the detection and evaluation is carried out using a polarizer with a defined, known plane of polarization with respect to the plane of incidence. [5] Method according to one of the preceding claims, characterized by that the lateral distribution of the layer thickness(es), the optical refractive constant(s), or their wavelength-dependent course, the absorption constant(s), or their wavelength-dependent course, the surface or interface quality (roughness) of the sample or at least one layer formed on the sample, the charge carrier concentration and / or the number and / or size and / or shape of defects and / or particles in the sample or at least one layer is determined. [6] Method according to one of the preceding claims, characterized by that the detectors and the sample are moved relative to each other along at least one axis and preferably at a constant distance from each other. [7] Method according to one of the preceding claims, characterized by that the electromagnetic radiation is shaped by optical elements or electromagnetic radiation is emitted diffusely onto the surface by the radiation source which is arranged inside a hollow body and, particularly preferably, the incidence of scattered electromagnetic radiation onto the detectors is avoided by means of an aperture arranged in front of the detectors in the beam path of the electromagnetic radiation. [8] Method according to one of the preceding claims, characterized bythat a multi-layer structure, consisting of several layers made of different materials, is used as a sample.