DEVICE AND METHOD FOR MEASURING A SUBSTRATE

Abstract

The invention relates to a method for measuring a multilayered substrate (1, 1′, 1″), particularly with at least one structure (7, 7′, 7″, 7′″, 7.sup.IV, 7.sup.V) with critical dimensions, particularly with a surface structure (7, 7′, 7″, 7′″, 7.sup.IV, 7.sup.V) with critical dimensions, characterized in that the method has at least the following steps, particularly the following procedure:

producing (110) the substrate (1, 1′, 1″) with a plurality of layers (2, 3, 4, 5, 6, 6′, 6″), particularly with a structure (7, 7′, 7″, 7′″, 7.sup.IV, 7.sup.V), particularly with a structure (7, 7′, 7″, 7″′, 7.sup.IV, 7.sup.V) on a surface (6o, 6′o, 6″o) of an uppermost layer (6, 6′, 6″), wherein the dimensions of the layers and in particular the structures are known,

measuring (120) the substrate (1, 1′, 1″), and in particular the structure (7, 7′, 7″, 7′″, 71.sup.IV, 7.sup.V)) using at least one measuring technology,

creating (130) a simulation of the substrate using the measurement results from the measurement of the substrate (1, 1′, 1″),

comparing (140) the measurement results with simulation results from the simulation of the substrate (1, 1′, 1″),

optimizing the simulation (130) and renewed creation (130) of a simulation of the substrate using the measurement results from the measurement of the substrate (1, 1′, 1″), in the event that there is a deviation of the measurement results from the simulation results, or calculating (150) parameters of further substrates, in the event that the measurement results correspond to the simulation results.

Claims

1. A method for measuring a substrate having a plurality of layers, said method comprising: producing the substrate with the plurality of layers, wherein the dimensions of the plurality of layers are known, measuring the substrate using at least one measuring technology to obtain measurement results, creating a simulation of the substrate using the measurement results from the measuring of the substrate, comparing the measurement results with simulation results obtained from the simulation of the substrate, optimizing the simulation of the substrate and renewing creation of a simulation of the substrate using the measurement results from the measuring of the substrate, in the event that there is a deviation of the measurement results from the simulation results obtained from the simulation of the substrate, or calculating parameters of further substrates, in the event that the measurement results correspond to the simulation results obtained from the simulation of the substrate.

2. The method according to claim 1, wherein the measuring technology is at least one of the following technologies: VUV/UV/VIS/NIR variable angle spectral ellipsometry (VASE) in reflection or transmission mode, wherein a measuring range extends from vacuum ultraviolet (VUV) through to near infrared (NIR), from 146 nm to 1700 nm, IR variable angle spectral ellipsometry (VASE) in reflection or transmission mode, wherein a spectral measuring range extends from 1.7 μm to 30 μm, (polarized) reflectometry, (polarized) scatterometry, UV/VIS spectroscopy, and THz spectroscopy,

3. The method according to claim 1, wherein an angle of incidence and/or a wavelength and/or a polarization state is/are varied and measured when measuring the substrate.

4. The method according to claim 1, wherein mathematical algorithms are used for the creating of the simulation of the substrate.

5. A device for measuring a substrate having a plurality of layers, said device comprising: means for measuring the substrate using at least one measuring technology to obtain measurement results, means for creating a simulation of the substrate using the measurement results from the means for measuring the substrate, means for comparing the measurement results with simulation results obtained from the simulation of the substrate, means for optimizing the simulation of the substrate and renewing creation of a simulation of the substrate using the measurement results from the means for measuring the substrate, and means for analysing and optimizing further substrates by reconstructing layer and/or structure parameters of the substrate with use of the simulation of the substrate, on the basis of measurement results from measuring the further substrates using the means for measuring the substrate.

6. The device according to claim 5, wherein the means for measuring comprises at least one optical device.

7. The device according to claim 5, wherein the device further comprises: at least one data processing unit and at least one data processing system for processing and saving data obtained from the means for measuring the substrate.

8. The device according to claim 5, wherein the means for measuring has: at least one radiation source, at least one monochromator, at least one polarizer, at least one compensator, at least one substrate holder, at least one analyser, and at least one detector, wherein the at least one polarizer enables the setting of selected elliptical polarization states.

9. The device according to claim 5, wherein the device includes a plurality of means for measuring the substrate, all of said plurality of means for measuring the substrate arranged in the device.

10. The method according to claim 1, wherein the substrate having the plurality of layers includes at least one structure.

11. The method according to claim 10, wherein the at least one structure is a surface structure.

12. The method according to claim 11, wherein the surface structure is on an uppermost layer of the plurality of layers.

13. The method according to claim 4, wherein mathematical algorithms include RCWA (rigorous coupled-wave analysis).

14. The device according to claim 5, wherein the substrate having the plurality of layers includes at least one structure.

15. The device according to claim 6, wherein the at least one optical device includes an ellipsometer and/or reflectometer and/or scatterometer and/or spectrometer.

16. The device according to claim 8, wherein at least one radiation source includes a laser or wide-band radiation source.

17. The device according to claim 8, wherein the at least one polarizer enables the setting of selected linear or circular elliptical polarization states.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0152] FIG. 1a shows a flow chart with method steps of an exemplary embodiment of a method according to the invention,

[0153] FIG. 1b shows a flow chart with method steps of an exemplary method according to the invention,

[0154] FIG. 2a shows a cross-sectional view of a substrate with multilayer system and a surface structuring with positive periodic structures,

[0155] FIG. 2b shows a cross-sectional view of a second substrate with multilayer system and a surface structuring with negative periodic structures,

[0156] FIG. 2c shows a cross-sectional view of a third substrate with multilayer system and a surface structuring with positive trapezoidal structures,

[0157] FIG. 2d shows a plan view of four exemplary embodiments of periodic structures (7 rectangular, 7″′ linear, 7.sup.IV circular and 7.sup.V an irregular shape), and

[0158] FIG. 3 shows a schematic illustration of the optical components of a device according to the invention in an exemplary embodiment.

[0159] In the figures, the same components or components with the same function are labelled with the same reference numbers. FIGS. 2 and 3 are not illustrated to scale, in order to facilitate the illustration.

DETAILED DESCRIPTION OF INVENTION

[0160] FIG. 1a shows a flow chart of the method according to the invention. For known samples (multilayer systems with structuring), a comparison is carried out between measurement result and simulation result. In this case, the recurrent method steps of measurement 120, model production 130 or model optimization 140 and renewed simulation are necessary.

[0161] In a first method step 110, a substrate (also termed sample in the following) is produced with a plurality of thin layers and a (surface) structuring. The system to be investigated is therefore known and is used for model production and optimization. If required, a plurality of accurately known reference substrates are produced and the measurement results are used for validating and optimizing the simulation model developed.

[0162] In a second method step 120, the substrate is irradiated with electromagnetic radiation with a defined angle of incidence and the reflected radiation is measured for example as a function of the wave number and/or the angle. The measurements are not limited to reflection and can also be carried out in transmission.

[0163] A plurality of measuring technologies can be used for increasing the reliability and/or accuracy of the calculation method. The suitable measuring technologies for obtaining information are in particular scatterometry, ellipsometry, reflectometry, spectroscopy and/or diffractometry. These various measuring technologies relate, inter alia, to the measurement of light reflected or diffracted at micro- and/or (sub-)nanostructured samples as a function of a device parameter, such as for example angle of incidence or light wavelength, wherein the polarization dependence of the measured values is utilized. Analogously, the individual layers of a multilayer system are directly or indirectly detected due to reflection and/or diffraction and/or scattering of the light at the boundary surfaces.

[0164] As a function of the layer thicknesses and the refractive index of the individual layers of the known defined sample, for the development of the simulation model, either the entire multilayer system is measured after finished production or, step by step, each individual layer is produced and measured one after the other.

[0165] In a first embodiment, the individual layers of the multilayer system have a layer thickness of more than 20 nm (greater than or equal to 20 nm) and the refractive index of the individual layers is known. In this embodiment, the entire multilayer system is measured after finished production. For example, an imprint stamp for the imprint or nanoimprint lithography with a structured imprint layer.

[0166] In a second embodiment, the sample contains very thin layers with a layer thickness below 20 nm with a known refractive index. For very thin layers, particularly layers with a layer thickness in the lower nm range to sub-nm range, each individual layer is produced and measured, before the next layer is produced thereon. In this embodiment, the sample is measured after each layer application, for example an ASL layer. All measured data of the sample, which has been measured layer by layer, are taken into account for the model production.

[0167] If required, layers with a layer thickness of more than 20 nm can also be measured individually during the production process of the sample, depending on the refractive index and the available material information.

[0168] In a third embodiment, a sample contains an intermediate layer with more than 20 nm layer thickness, but with an unknown refractive index. In this embodiment, measurements are carried out after application of individual layers with a layer thickness of more than 20 nm in each case, and for the entire multilayer system after finished production.

[0169] In ellipsometry, the polarization change is described with the aid of the measurable ellipsometric characteristics—the loss angle ψ and the phase shift Δ. As the optical parameters with ψ and Δ cannot be determined directly, a parameterized model must be developed for a sample system to be investigated. To calculate the interaction of light with multilayer systems and nanostructures and microstructures, RCWA (rigorous coupled wave analysis) is preferably used according to the invention as calculation method. RCWA is used for calculating the grid diffraction, wherein the sample is divided into a plurality of individual layers. This model concept was developed and supplemented according to the invention.

[0170] The development according to the invention advantageously makes it possible, using the simulation model from method step 130, to simultaneously analyse the diffraction of incident (planar) waves at the multilayer system and at the structures. Multilayer systems and non-planar layers, i.e. structures, are advantageously determined with very high reliability and accuracy due to the use of polarized light with ellipsometry.

[0171] In a third method step 130, the data records of the selected measurement variables are used for the model production, so that a simulation of a multilayer system with (surface) structuring can be calculated. In this case, the deviation between the experimental data and the simulated data should be as low as possible (140). For a complex system according to the invention, as for example illustrated in FIG. 2a, with a plurality of layers and a surface structuring, the model developed in the method according to the invention may physically describe the sample correctly. Thus, a simulation with high reliability is enabled.

[0172] For known samples, which were produced in step 110, in a fourth method step 140, a comparison is carried out between measurement result and simulation result. In this case, the recurrent steps of measurement, model production or model optimization (model fitting) and renewed simulation are required. The aim of the adjustment is that the model, i.e. the generated data records fit the measured data records (i.e. experimental data) in the best possible manner. If this is not (yet) the case, the model is optimized further in method step 130. If this is the case, the model developed can be used in method step 150 for the determination of the desired parameters.

[0173] A mathematical analysis of the developed model systems can, if required, additionally be called upon specifically during the development of generic model systems.

[0174] FIG. 1b shows a flow chart of the method according to the invention when applying a finished simulation model according to the invention for a multilayer system with (surface) structuring. Here, after system optimization, a developed model for routine simulations is available. The system parameters are determined. A known sample—i.e. the number of planar and/or non-planar (i.e. structured) layers and the layer materials are known—is measured according to the invention in method step 120 and, after the comparison of experimental and generated data records (140), the desired parameters are determined (150).

[0175] FIG. 2a shows a cross-sectional view of a substrate 2 according to the invention, with a plurality of thin coatings 3-6 and a surface structuring 7. The number and the thickness of the coatings is not limited to the embodiments from FIGS. 2a to 2c. The thickness of the coatings is not illustrated to scale, in order to improve the illustration. FIGS. 2a to 2c show similar embodiments with different surface structurings 7, 7′, 7″. The last coating 6, 6′, 6″ can for example include a photoresist or an imprinting compound, which was structured by means of lithography or nanoimprint lithography. The structures 7, 7′, 7″ have dimensions in the nanometre range. The surface 6o, 6′o, 6″o of the structured coating defines the residual layer thickness.

[0176] FIG. 2a shows a multilayer system 1 with surface structuring with positive periodic structures 7.

[0177] FIG. 2b shows a further embodiment of a multilayer system 1′ with surface structuring with negative periodic structures 7′.

[0178] FIG. 2c shows a third embodiment of a multilayer system 1″ with a surface structuring with positive periodic trapezoidal structures 7″.

[0179] If the surface is structured with micro- and/or nanostructures and/or subnanometre structures, the incident light impinges onto these (for the most part) periodic, extensive structures, which may represent an optical diffraction grid. The critical dimensions of the investigated structures 7, 7′, 7″ include the height or depth of the structures, the width and the length of the structures, the angles, for example the side wall angle, residual layer thickness(es) and the surface roughness.

[0180] FIG. 2d shows by comparison, in a plan view of a plurality of cutouts, further possible surface structurings 7, 7′″, 7.sup.IV and 7.sup.V according to the invention of a sample. According to the invention, models are developed, which allow a reliable characterization of complex multilayer systems with a (surface) structuring according to the structures from FIGS. 2a to 2d. The structures 7 are quadrilaterals, particularly squares. The structures 7′″ are periodic extensive linear structures. In a further embodiment according to the invention, the structures 7.sup.IV are circular. Also, structures with more complex or irregular structural forms, such as for example the structures 7.sup.V from FIG. 2d, do not constitute a problem for the method according to the invention and are detected and correctly reproduced in the model production. The structuring is not limited to the embodiments shown.

[0181] According to the invention, the non-planar layer with a structuring is the uppermost layer 6, 6′, 6″ of a multilayer system 1, 1′, 1″. In an alternative embodiment, the non-planar layer with a structuring is located between two layers in the multilayer system. For example, a structured imprinting compound is coated with an ASL coating after imprinting for an application as working stamp. In a further alternative embodiment, a multilayer system contains more than one non-planar layer with a structuring.

[0182] FIG. 3 shows the optical components of a first embodiment of a device 13 according to the invention. A polarizer (P) 9 converts the non-polarized light of a radiation source 8 into linearly polarized light. After reflection at the sample 1, the radiation passes through an analyser (A) 10. The electromagnetic radiation is elliptically polarized upon reflection at the sample 1. The analyser 10 again changes the polarization of the reflected electromagnetic radiation, which then impinges on a detector (D) 11. In a first preferred embodiment, a polychromatic radiation source is used, so that a selected wavelength range is used in the measuring method. In an alternative embodiment, a monochromatic radiation is used, wherein a laser is preferably used as radiation source. A plurality of radiation sources may be present in the device at the same time and/or be exchanged if required.

[0183] Further optical components are for example, optical filters, a compensator (e.g. a λ/2 plate), monochromator, and different optical variable attenuators, which, if required, can be used depending on the measuring technology and/or wavelength range. These components are known to the person skilled in the art and are not described in more detail.

[0184] The measuring technologies according to the invention differ due to the arrangement and the type of the optical components. The analyser 10 may for example be constructed such that it can rotate.

[0185] In variable angle spectral ellipsometry (VASE), there is a broad coverage of wavelengths, in contrast to monochromatic ellipsometry. As a result, information content of the measured data and the accuracy of the simulations increase. A goniometer enables variable angular measurements. The combination of wavelength-resolved and angle-resolved measurements is the preferred embodiment and leads according to the invention to a higher reliability of the simulations. According to the invention, this combination is carried out with VASE as preferred measuring technology.

[0186] Furthermore, depending on the sample type and measuring method, the measurements may be carried out not only in reflection mode, but also in transmission mode, in order to obtain additional information and data, if required.

[0187] The device 13 according to the invention comprises optical devices and a data processing unit 12 for processing and saving the data, which are obtained from the optical devices.

[0188] A work-holding device (not illustrated) is used for holding and fixing the sample or the substrate. The work-holding device may, in a particular embodiment, be moved in a z direction, if required. Furthermore, a rotation and/or tipping over of the work-holding device is possible.

[0189] The work-holding device can be heated and its temperature controlled in a temperature range between 0° C. and 1000° C., preferably between 0° C. and 500° C., more preferably between 0° C. and 400° C., most preferably between 0° C. and 350° C. The work-holding device can alternatively be cooled using a cooling device. For example, in a first embodiment, the work-holding device may be cooled in a temperature range between −196° C. and 0° C. The temperature of the work-holding device may be adjusted using a temperature control arrangement.

[0190] The work-holding device may additionally have sensors (not illustrated), with the aid of which, physical and/or chemical properties can be measured. These sensors may be temperature sensors for example.

[0191] In a further preferred or else independent embodiment of the work-holding device, the work-holding device contains a liquid cell, which allows measurements under liquids. In a special embodiment, the liquid cell is a through-flow cell. Thus, multilayer systems with or without (surface) structuring can be measured in a liquid environment. According to the invention, in a special application, the electrochemical response of a multilayer system can be characterized using the liquid cell. The liquid cell can therefore also be constructed as an electrochemical cell, with reference electrode, counter-electrode and optical windows for the spectroscopically ellipsometric measurements.

[0192] The device 13 according to the invention can advantageously also be operated in a vacuum or at ambient pressure under a gas atmosphere. Preferably, the gas atmosphere is an inert gas atmosphere, for example nitrogen (N.sub.2). Thus, multilayer systems with structuring, which are sensitive to liquid or to oxygen for example, can be investigated.

[0193] The device 13 according to the invention can preferably be evacuated and heated. The device has means for introducing one or more gaseous components. A loading device, preferably a sluice, allows the loading of the samples. In an alternative embodiment, the device can be built such that in situ measurements can be carried out.

[0194] Instead of the embodiment shown in FIG. 3, alternative embodiments are conceivable, which allow combinations of spectrometric and/or ellipsometric or scatterometric measuring methods, inter alia. All measuring technologies previously mentioned according to the invention are conceivable.

[0195] A computer-assisted data processing system 12 saves and processes the data, which are obtained from the optical devices, for simulating the multilayer systems (with or, if appropriate, without structuring) according to the invention using the simulation algorithms developed according to the invention. The simulation models according to the invention make it possible for the first time and using the suggested method to detect and to characterize a plurality of thin layers and a (surface) structuring at the same time and with high reliability.

REFERENCE LIST

[0196] 1, 1′, 1″ Substrate/multilayer system with (surface) structuring [0197] 2 Substrate base material with refractive index n.sub.s [0198] 3 First layer with refractive index n.sub.1 [0199] 4 Second layer with refractive index n.sub.2 [0200] 5 Third layer (nth layer) with refractive index n.sub.3 or n.sub.n [0201] 6, 6′, 6″ Uppermost layer with surface structuring and refractive index n.sub.o [0202] 6o, 6′o, 6″o Surface of the uppermost layer [0203] (7, 7′, 7″, 7′″, 7.sup.IV, 7.sup.V) [0204] Radiation source [0205] Polarizer [0206] Analyser [0207] Detector [0208] Control and computing unit [0209] Optical device [0210] 110 Method step [0211] 120 Method step [0212] 130 Method step [0213] 140 Method step [0214] 150 Method step