WO2017198764A1

WO2017198764A1 - Device and method for measuring layer thicknesses and indices of refraction of layers on rough and smooth surfaces

Info

Publication number: WO2017198764A1
Application number: PCT/EP2017/061964
Authority: WO
Inventors: Friedrich Paul WITEK; Helge Ketelsen; Uwe Richter
Original assignee: Sentech Instruments Gmbh
Priority date: 2016-05-20
Filing date: 2017-05-18
Publication date: 2017-11-23

Abstract

The invention relates to a device for positioning a sample for measurement by means of polarimetry, ellipsometry, reflection measurement, or diffraction measurement by means of a measuring system. The sample can be positioned on a support device, in particular a contact surface of the measuring system, and the support device has at least one opening (X), through which measurement light can be fed to the side of the sample that lies on the support device.

Description

Apparatus and method for measuring layer thicknesses and refractive indices of layers on rough and smooth surfaces

description

The invention relates to a device and method for measuring layer thicknesses and refractive indices of layers on rough and smooth surfaces.

The control of coatings in the manufacture of solar cells with the

Laser ellipsometry and spectroscopic ellipsometry has to work with very low reflectivities (typically 1% and much smaller) due to the wide variety of rough silicon surfaces (microcrystalline, alkaline or acid etched, sawn and polished or even plasma etched). Furthermore, the deposited layers (e.g., Si 3 N 4 or Al 2 O 3) provide for layer stresses that occur at sample thicknesses of e.g. 0.5 mm for bulges of e.g. 2 mm height at e.g. 156 mm sample size. For the application of the ellipsometric measurement, a precise position of the sample to the measuring system is a prerequisite. Position tolerances of about 20 μηι and tilts less than 3 arc minutes are typical requirements.

The following is an apparatus based on an ellipsometer will be described, the typical problems in the application of ellipsometry on solar cells as

Desktop system of the prior art avoids:

• in rough samples with low reflectivities, ambient light is coupled in addition to the light from the transmitter of the ellipsometer,

• Samples must be adjusted in height and tumble

• Selection of measuring locations by surface detection with scatter or

diffraction patterns

In connection with the embodiments illustrated in the figures, the invention will be explained. Showing:

Fig. 1 Reflection on rough surface in ellipsometry; Fig. 2 Measurement on surface with two light sources;

Fig. 3 Spectra for measuring light and ambient light;

Fig. 4 Blockage of stray light; Fig. 5 Sample support D with curved specimen P and pressure means W;

Fig. 6 Pressing means W in the target position; Fig. 7. Blockage K of the measuring light;

Fig. 8 Mean LD and SC for surface texture assessment;

Fig. 9 Stray measurement as a sensor for the detection of the structure of the sample; Combination of scattered light measurement or diffraction measurement with ellipsometric measurement

Fig. 10 Combination with other ellipsometer assemblies for simultaneous measurement of the

Front;

Fig. 1 1 Common use of components with simultaneous measurement of front and back

Back and

Fig. 12 Arrangement for measuring pyramids.

Embodiments for a method of ellipsometry on the

Measurement of solar cells. The ellipsometer consists of a transmitter with light source and a receiver with detector (spectral or at a wavelength) which at an oblique angle of incidence (e.g., 65 ° to the sample normal) reflects the reflection from

examined polarized light. The concrete execution of the ellipsometric transmitter and receiver is not limited here.

The solar cells have a rough surface (see Fig. 1), which is illuminated by the Eilipsometer transmitter via an optional focus lens L1 with an opening angle A. Of the

Receiver of the ellipsometer detects the reflected light from the sample via an optional focus lens L2 in a solid angle B. The roughness typically reflects light in a much larger solid angle C and the proportion in B of the total light in C is much smaller.

If one or both focus lenses are removed, the solid angles of the transmitter and receiver change without changing the principle. The roughnesses common in prior art solar cells have feature sizes S of e.g. 10 μηι in microcrystalline Si solar cells up to e.g. 300 nm at plasma-etched surfaces. For this reason, the recognition of the surface structure for the measurement is valuable as additional information. The possibility of additional scattering and / or diffraction behavior in the

Integrating evaluation of the measurement is a claim of the invention. The measurement is typically carried out with the transmitter via a light source Q1 (integrated in or connected to the ellipsometer transmitter) (see Fig.2). Due to the high scattering behavior, however, the light detected in the receiver from the solid angle B can also contain components of other light sources Q2 (not part of the measuring system).

While the emitter of the ellipsometer uses a light source Q1 (e.g., a solar cell xenon lamp), the ambient sources Q2 are e.g. Sunlight or fluorescent tubes of the lighting of production halls above.

Since the ambient light Q2 can influence the measurement because of the rough surface in relation to the light Q1 related to the measurement, previously used methods are the complete enclosure of measuring devices. The disadvantage is that this makes the measuring systems very large and the samples must be introduced into the measuring system

(Doors / locks must be used).

The invention in one embodiment utilizes the sample itself as a means of blocking the ambient light.

The positioning of the sample on the metering device of the measuring system and the opening X in the depositing device makes it possible for the light Q1 to be guided from below onto the side of the sample lying on the depositing device. The

Storage device may be configured (e.g., as a closed container or with a shielding means) to partially or completely shield light Q2 from the environment of the measurement site and / or the light source Q1 for irradiating the sample.

The meter has a box B containing a transmitter S and a receiver E. A further embodiment can also connect the transmitter S and the receiver E to the outside of the box B (so that the ambient light Q2 is likewise shielded by the receiver E). The box is an embodiment with a storage device, here the sample support D.

The sample P is placed on the sample support surface D with the side to be measured. The sample support D has an opening X which is made large enough to allow the measuring beam T1 emanating from the transmitter S to illuminate the sample at the measuring location. The opening X must also be made large enough, the light reflected in the receiver E T2

(Opening angle B from Fig. 2).

The sample P must have sufficient absorption to adequately shield the ambient light Q2 for undisturbed ellipsometer measurement. Furthermore, the sample P must be at least so large that the opening X is completely closed. An advantageous embodiment uses, for example, a 10 mm wide slot with 40 mm in length with 8 mm thickness of the support and 156 mm solar cells made of silicon with a thickness of 500 μηι.

The sample P is brought by the support surface D without additional adjustment in the correct position to the measuring system - the usual adjustment for height and tilt is thus avoided.

The exact adjustment of the sample P with respect to the measuring system must set up the target point of the ellipsometer in height and two wobble angles. This is typically implemented on desktop devices via a height and tumble table. For rough samples P, however, the observation of the current position during adjustment is extremely complicated, since only very small and scattered reflection can be used.

In one embodiment, the sample P is placed on the support D with the side to be measured. The surface D is here aligned to Eilipsometer so that when measured surface from P to D, a measurement is correct.

The sample support D can in one embodiment also the influence of

Layer stresses that lead to a curvature of the sample, compensate.

In Fig. 5 the curved sample P is shown. In the region of the measuring location, a means W presses the sample P flat onto the support surface D. In one embodiment, the means W can be the hand of an operator who presses the sample during a measurement (typically 10 seconds). In a further embodiment, the pressure by the means W may also be automatic (e.g., motor, pneumatic, magnetic, gravity with gravity). The pressure means W may also be attached to the bridge W above the sample P in the embodiment.

In the measuring position, the sample P is pressed plane-parallel to the support D in the region of the measuring position.

Safety device Blockade of measuring light

The device can let the light of the light source Q1 through the transmitter S through the opening X without sample also upwards out of the device. An embodiment of the device with a light source of high-intensity Xe light can have a carcinogenic effect on skin contact or, in the case of eye contact, can lead to blindness. As it is not possible to ensure that a sample always shields the measuring light, In an advantageous embodiment, a bridge R above the sample is provided with a fixed blocking means K. The means K is placed at a distance so that no harmful light reaches the user. Furthermore, the means K is designed as a light trap, so that the reflection for the protective purpose is sufficiently reduced (choice of material, surface structuring).

In a further embodiment, the device contains an additional means for assessing the surface structure by means of scattering and / or diffraction (see FIG. 8).

The roughness of the surface is advantageously taken into account in the ellipsometric measuring method. Depending on the manufacturing process are on a sample location or

Depending on the process different structures exist.

In one embodiment, the device includes an additional means LD and SC which assess the scattering and diffraction behavior of the sample P before the measurement and the

Result in the measurement. The means LD can e.g. be a laser diode or parallel polychromatic light. The means SC detected in one of the

Sample structure dependent distance the scattered or diffracted light as image. The characteristic of the surface structure image qualitatively and / or quantitatively assessed. The means SC can be a combination of a measuring screen with an observing camera or also directly the detector chip of a video camera.

An exemplary embodiment uses a laser light with red light (e.g., 670 nm) with a parallel beam of light to illuminate the sample P. A white shade of 5 cm

Diameter detects the scattered and diffracted image at a distance of approx. 10 cm after reflection at an angle of 45 degrees. A camera captures the image on the screen and sends it to the computer for evaluation. In the case of multicrystalline silicon as the basis of the solar cell, the different crystal orientations in the measuring field can be identified by characteristic scattering patterns as in Fig. 9.

The patterns (e.g., M1 and M2 in Figure 9) can be quickly recorded and evaluated prior to measurement. Since many surface types can occur in the solar industry, the detection algorithm is not underdeveloped.

The means LD and SC will be used to detect the surface structure by a characteristic image and to use it as follows:

• Detection if the sample location is suitable for the measurement

o Scattered light at the correct level o the image corresponds to a specification (comparison by the user with a target image or automatic comparison)

• Selection of an evaluation algorithm or adjustment of an evaluation parameter by evaluation of the image

Fig. 9 shows by way of example how a spreading pattern can be used. In the example, "tilt to the right" and "tilt to the left" are used to detect two crystal orientations. This information can then be used to evaluate the measurement (e.g., to reflect the orientation of the rough cells or their feature size into the ellipsometric model).

The angle of incidence of the light from the center LD on the sample is not limited to angles as in Fig. 9. The angle of incidence can vary between 0 and 90 degrees, the advantageous angle is selected according to the application.

The additional measurement shown in Figures 8 and 9 with the means LD and SC combines an additional measurement with the ellipsometric measurement:

1 . Combination of ellipsometry with diffraction measurement on periodic structures: from the deflection angles of the diffracted orders it is possible to deduce certain lattice parameters and this can be evaluated either subsequently or together with the ellipsometric measurement,

2. Combination Ellipsometrie with scattered light measurement on randomly rough samples: from the angle-dependent intensity distribution on the screen SC, the

Surface roughness can be determined. The ellipsometer may e.g. use the roughness so determined directly for the ellipsometric model (e.g., determine thickness of roughness, determine depolarization of the measuring light by the sample),

3. Combination of ellipsometry with the images of diffraction and scattering for

Surfaces having both of the feature sizes and the periodicity: here, both the model for ellipsometry can be selected (e.g., a distribution function of surface segments), and the scattering ratios (e.g., Rayleigh or Mie scattering) included in the analysis.

These methods are used in solar cells for the determination of additional information for

Surface structure, so that the substrate can be modeled better than only half space with roughness.

For periodic structures, eg from nanoimprint lithography, it is possible to deduce immediately from the diffraction patterns to lattice spacings (also multidimensional). In combination with Ellipsometry can then be more accurately concluded on the coating. The application of ellipsometry alone is also known as CD metrology or scatterometry. The diffraction measurement used here measures via the screen SC two-dimensional deflection angle for extended additional information.

Many new surfaces (e.g., polymer brushes, embedded nanoparticles) exhibit both scattering and diffraction. With the combination of ellipsometry with the means LD and SC in this case, the surface at least one

Fingerprint method are classified. In such cases, the assignment between the intensity profile in the image with a mathematical structural model is application specific.

An embodiment may also be used with another device for simultaneous measurement of the other sample side.

Modern solar cells (such as the PERC type) are coated on both the front and the back. It is advantageous if you can measure the coatings on both sides of the sample simultaneously.

As shown in FIG. 10, the device according to the above illustrations can be equipped with further ellipsometer assemblies S2 and E2 as well as further light source Q1b and a further detector in or connected to module E2.

A further advantageous embodiment (see Fig. 1 1) can share the light source Q1 and the detectors SP via optical fibers LL1 to LL4 between the two devices, which is particularly advantageous when designed as a spectroscopic ellipsometer.

The measuring box B can also be integrated into an automatic transport system for an inline measurement in a further embodiment. The sample storage, the measurement start and the result storage are fully automatic in this case.

The invention can also be used for the measurement of samples with pyramidal structure. This embodiment applies the sample at an angle (e.g., 55 degrees) in the same manner:

The sample shields the ambient light,

• The sample support D is slanted by one (optional depending on the embodiment)

Supplement D2 supplemented, the positional relationship to Eilipsometer is also made by placing and pressing.

Claims

claims

1 . Device for positioning a sample for measurement by polarimetry,

Ellipsometrie, reflection measurement or diffraction measurement by a measuring system, characterized in that the sample on a storage device, in particular a contact surface of the measuring system can be positioned and the storage device has at least one opening (X) through which measuring light on the side of the sample can be guided on the storage device is located.

2. Device for adjustment-free attachment of a sample for surveying means

Polarimetry, ellipsometry, reflectance measurement or diffraction measurement, characterized in that the sample surface to be measured is placed directly on a contact surface of the measuring system and the contact surface has an opening (X) through which the measuring light falls on the sample and is reflected there.

3. Device for measuring with polarimetry, ellipsometry or reflection measurement, in which for the measurement of a structured sample additionally the scattered light of an angle (E) incident light beam is evaluated.

4. Device according to one of claims 1, 2 or 3, characterized in that the diffraction is evaluated.

5. Device according to at least one of the preceding claims, characterized

in that the additional scattering is used to select the measuring location.

6. Device according to at least one of the preceding claims, characterized

in that the measurement is carried out with polarimetry, ellipsometry or reflection measurement only if the scattered light contains certain characteristic information.

7. Device according to at least one of the preceding claims, in particular for adjustment-free attachment of the sample for measurement by means of polarimetry, ellipsometry or Reflection measurement, characterized in that the contact surface against the

Incidentally inclined by an angle Y is.

8. The device according to at least one of the preceding claims, in which the contact surface is mounted inclined to the plane of incidence to be measured samples in addition to a contact surface for perpendicular to the plane of incidence to be measured samples.

9. Device according to at least one of the preceding claims, characterized by a pressure piece (K), which presses curved samples on the contact surface.

10. The device according to claim 9, characterized in that the pressure piece (K) is replaced by the pressure with the hand of the user at least for the period of a measurement.

1 1. Device according to at least one of the preceding claims, characterized by a shield (Z) in order to absorb the light emerging from the opening (X) of the contact surface without applying a measuring sample.

12. The device according to at least one of the preceding claims, characterized in that the storage device itself or by means of a separate

Abschirmmittels can keep light from the environment of the measuring point.

13. A method for measuring by means of polarimetry, ellipsometry, reflection measurement or diffraction measurement by a measuring system, characterized in that the sample is positioned on a storage device, in particular a contact surface of the measuring system, wherein the storage device has at least one opening (X) through which subsequently measuring light falls on the side of the sample lying on the storage device.