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Injection dependent measurements The minority carrier lifetime is strongly dependent on the injection (excess carrier concentration). From the shape and height of the lifetime curve information about the dominant recombination center as well as trapping center can be deduced. With MDPmap it is possible to measure not only injection dependent lifetime curves but also photoconductivity curves over a very wide range of injection. In the MDPmap and MDPingot up to 4 different lasers can be integrated and hence it is possible to measure not only injection dependent lifetime curves but also photoconductivity curves over a very wide range of injection. Figure 1 displays a comparison of the typical injection range of different known lifetime measuring methods. Because of its extraordinary sensitivity the MDPmap and MDPingot are able to measure over seven decades of injection. Due to bias light and reflection measurements a very good accuracy could be improved profoundly. With MDPmap the whole important injection range can be covered with just one method as demonstrated in figure 2 for 2 different spots on a SiNx passivated mc-Si wafer. Until now it was necessary to use several different methods, which often cannot be compared to each other. With MDP an easy excess to the important injection dependent lifetime curves is possible. For further information please read: [1] S. Rein, Lifetime Spectroscopy - A Method of Defect Characterization in Silicon for Photovoltaic Applications , Vol. 85 (Springer, Berlin Heidelberg, 2005) Bulklifetime versus injection for a varying symmetry factor and energy level Fig. 1: Comparison of typical injection ranges of different measuring methods Fig. 2: injection dependent lifetime measurements on 2 different spots on a SiNx passivated mc-Si wafer Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more MDP series MDPspot Quick and Simple Lifetime Measurement Made Easy Learn more MDP series MDPpro 850+ Advanced Solution for Quality Control of Monocrystalline Silicon Ingots, Bricks, and Wafers Learn more MDP series MDPpro Advanced Lifetime Measurement System for Quality Control and Material R&D on Semiconductors Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Investigation of defect levels in InP InP is applied in high frequency technique, for lasers, communication technique and production of integrated circuits. Hence also for this material methods for defect investigation and quality control are needed. MD-PICTS is a well suited method for the investigation of defect levels in InP. For example investigations on indium phosphide shows that the defect content changes during annealing processes, which may also have an impact on the distribution of electric properties. Whereas the defect content of as-grown samples depends on their position in the crystal, an equivalent set of defect levels is prominent in wafer-annealed samples. Figure 1 shows a comparison of Fe-doped SI-InP samples from different crystal positions. They differ in their characteristic defect levels. The observed peaks in FE-doped InP provided the first proof of iron acting as a recombination center in InP. Fig.1: Comparison of MD-PICTS spectra of as-grown Fe doped SI-InP samples from different crystal positions and thus different FE concentrations. The samples differ in their characteristic defect levels Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products MDP series HTpicts Advanced High-Temperature Lifetime Measurement System for In-Depth Material Analysis Learn more MDP series MDpicts pro High-Resolution, Temperature-Dependent Lifetime Measurement System for Precise Material Characterization Learn more MDP series MDpicts Temperature-Dependent Lifetime Measurement System for Advanced Material Analysis Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Inline metrology of mc-Si bricks Lifetime measurements are already widely used for material quality control especially in the photovoltaic industry. Taking it one step further, (Alttext zu lang) With the MDPinline ingot it is possible to measure all 4 sides of a brick in under 1 min per side with 1 mm resolution. At the same time a spatial resolved measurement of conduction type changes as well as resistivity linescans are measured. Customer defined brick cut criteria by lifetime, resistivity or conduction type change can be transmitted to the fab database, which allows a fully automated material monitoring for next generation photovoltaic fabs. Furthermore the iron density can be measured on one side of the brick, which takes about 2.5 min. Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products MDP series MDPpro 850+ Advanced Solution for Quality Control of Monocrystalline Silicon Ingots, Bricks, and Wafers Learn more MDP series MDPpro Advanced Lifetime Measurement System for Quality Control and Material R&D on Semiconductors Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Highly spatial resolved inline metrology on Multicrystalline Silicon The minority carrier lifetime is a key parameter for the performance of solar cells. Therefore it is a suitable criterion for classifying wafers by means of quality. (Alttext zu lang) Non-destructive measurements of minority carrier lifetime are well established and widely used for process control and characterization of defects in crystalline silicon. With our tool MDPinline it is possible to map the minority carrier lifetime with a so far unsurpassed combination of spatial resolution, sensitivity and measurement speed. MDP inline tools enable whole wafer maps with a resolution of 2.8 mm up to (156 x 156 mm) in less than one second When it comes to the measurement of raw wafers it has to be taken into account, that not the actual bulk lifetime, but the effective lifetime, which consists of the surface and the bulk recombination, is measured. Therefore the measured lifetime of an as-grown wafer with a thickness of 200 μm is limited to approximately 2.3 μs. However if the bulk lifetime is very small, it will dominate the effective lifetime, so that a low quality can be recognized. Figure 1 displays the lifetime map of an as-grown multicrystalline wafer from the edge of a cast. The low quality edge, due to the contact with the crucible, can be easily distinguished from the better parts. Material classification The MDP inline tool is able to classify wafers in up to 15 quality classes. For that, different characteristic parameters are taken into account, like arithmetic average, harmonic average, average according to J. Isenberg, median and standard deviation. Note that a direct correlation between the effective lifetime and the efficiency of the solar cells is not present, because of the cell process which affects single regions in ingots differently. The software equipment developed for this tool also determines a variety of process relevant parameters and low quality edge areas of the wafers. The combination of lifetime averages and standard deviation enables a very good classification of the material quality. Figure 2 showcases an exemplary classification of three wafers from the bottom, middle and top part of an ingot. It is even possible to distinguish wafers of the bottom from those of the top part of the ingot. Wafer of the bottom often have higher oxygen and defect concentration, which results in a lower average lifetime. Wafers from the top often have a low lifetime, because of metallic impurities, a high nitrogen and carbon concentration and segregations of SiC, Si3N4 and other crystallization defects. Monitoring and recognition of crystal defects For the monitoring and recognition of crystal defects an extensive study was carried out, where specific wafers with special defect constellations were measured. In this study characteristic results for different crystallographic defects were determined. One of the most abundant defects are Si3N4 and SiC segregates, which lead to shunts in the solar cell. In the MDP lifetime maps these defects lead to a very high inhomogeneity and a high percentage of pixels with a lifetime under 0.2 μs. The second most abundant crystal defects are microcrystalline structures in the wafer. These structures lead to a very low lifetime, together with a low inhomogeneity. In combination with a crack tester these microcrystalline wafers can be recognized and distinguished from the wafers with segregates. Furnace monitoring Another useful application is the monitoring of furnace properties. Complications in the growth process can be detected and furnace properties can be optimized. Figure 4 and 5 show two examples of the above mentioned possible applications. In figure 4 the average of 5 ingots, which were grown in different furnaces, were plotted versus the ingot height. It becomes obvious, that different furnace properties lead to different slopes in the bottom and top part of the ingots. For example furnace 2 and 5 differ by about 30 % in the bottom slope and furnace 2 and 4 by about 50 % in the top slope. With this information an optimization of the furnace is possible. Figure 5 displays the abundance of a crystallographic parameter, which is characteristic for the material quality. A high value indicates a low quality and vice versa. The abundance of this parameter is displayed for the wafers of different weeks of production. Several thousand wafers were analyzed. Week 4 shows a higher percentage of wafers with a high crystallographic parameter. Apparently there have been contaminations in the feedstock or something influences the growth process, which can be detected with the MDP measurements. In such a way problems can be traced back to their origin and thus can be eliminated efficiently. Further applications especially for ingots are shown in other case studies. Inline mappings of as-grown wafers and ingots are a versatile tool for the detection of e.g. crystallization defects early in the production process. With the MDP tools MDPingot and MDPinline a full electrical wafer characterization at up to one wafer per second is possible. Along with the effective minority carrier lifetime also the resistivity is measured. With these investigations of each individual wafer, a huge variety of applications are possible like process control, yield and process improvement as well as a fast ramping up of any new production line or process. In inline applications, this opens an entire spectrum of new possibilities towards a highly efficient optimization of products and production processes together with an improvement of yield. For more information read: [1] K.Dornich, N.Schüler, D. Mittelstrass, A. Krause, B. Gründig-Wendrock, K.Niemietz, J.R. Niklas, Conferenceproceedings 24th PVSEC Hamburg (2009) in press Lifetime map of a mc-Si wafer from the edge of a cast ingot Exemplary classification of three wafers of bottom (a), the middle (b) and top(c) of an ingot. Si3N4 and SiC segregates (a); microcrystalline wafer (b) average versus ingot height for 5 ingots grown in different furnaces | histogram of the crystallographic parameter of different weeks Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products MDP series MDPlinescan Versatile OEM Unit for Lifetime Measurements on Silicon Samples, from Bricks to Processed Wafers Learn more MDP series MDPspot Quick and Simple Lifetime Measurement Made Easy Learn more MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more MDP series MDPpro Advanced Lifetime Measurement System for Quality Control and Material R&D on Semiconductors Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Determination of passivation homogeneity and surface recombination velocity For a lot of applications a well passivated surface is necessary e.g. in solar cells. With MDPmap and MDPingot it is possible to investigate the quality and homogeneity of the passivation with a high resolution. The measured or effective lifetime consists of the bulk lifetime and the surface lifetime, via: \(\cfrac{1}{\tau_{eff}} = \cfrac{1}{\tau_{bulk}} + \cfrac{1}{\tau_{surface}}\) That‘s why the surface properties, especially the surface recombination velocity S, has a huge influence on the measured lifetime. This can be used to investigate the surface properties of a sample. Thermal silicon oxide or SiN x are often used to passivate the surface of Cz- , Fz- or mc-Si, which means that the surface recombination velocity is minimized strongly. The homogeneity of this passivation layer can be investigated by lifetime measurements. The aim is to measure the homogeneity of a passivation layer with a high resolution. With MDPmap , MDPingot or MDPinline it is possible to investigate the homogeneity of a passivation layer with a very high resolution (only limited by the diffusion length of the carriers), which is exemplary shown in figure 1. Especially in high quality material with a high bulk lifetime the surface recombination is very dominant, so that every difference in a lifetime map has its origin in passivation inhomogeneity. By a measurement with different wavelength or different sample thickness even a good estimation of the surface recombination velocity can be made. If the sample quality is very high as in FZ-Si the surface recombination velocity can be determined from the measured lifetime by assuming that the bulk lifetime is only dependent on the Auger recombination. MDPmap , MDPingot or MDPinline enables to measure the homogeneity of a passivation layer with a very high resolution even inline. With this an optimization of the passivation process is possible. To approximate the bulk lifetime from the measured lifetime on unpassivated bricks, the following equation is used: \(\tau_{eff, \lambda} = \cfrac{\tau_{bulk}}{1-\alpha ^2L^2} \Biggl \lfloor 1-\alpha L\cfrac{\alpha L + \frac{SL}{D} coth \frac{\alpha d}{2}}{1 L + \frac{SL}{D} coth \frac{d}{2 L}} \Biggr]\) With d - sample thickness α - 1/penetration depth α = a/s (s – skin depth of the microwave; a – empiric factor, which was determined from comparison with passivated wafers from the same bricks) L – diffusion length D – diffusion coefficient S – surface recombination velocity for as cut surface (S = 2.0e+5) For further information please read: [1] J. Schmidt, Thesis, Universität Hannover, 1998 Fig. 1: Example of an oxide passivated Cz-Si wafer with a gradient in the oxide thickness Related Solutions and Industries: Epitaxial Layers & Thin Films , Photovoltaic , Research and Development Matching Products MDP series MDPlinescan Versatile OEM Unit for Lifetime Measurements on Silicon Samples, from Bricks to Processed Wafers Learn more MDP series MDPspot Quick and Simple Lifetime Measurement Made Easy Learn more MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more MDP series MDPpro Advanced Lifetime Measurement System for Quality Control and Material R&D on Semiconductors Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Photoconductivity measurements of implanted samples Implantation of B and P are used for many applications in the microelectronic industry, but so far there was no method available to check the homogeneity of these implantations without contacting the samples and (Alttext zu lang) In this case not the lifetime, but the photoconductivity or signal height is the most sensitive parameter for detecting inhomogeneity in implantations. It depends strongly on the resistivity and the lifetime itself. In the MDPmap and MDPingot equipment it is possible to integrate up to 4 lasers with different wavelength. Furthermore it is possible to measure with different pulse length from a very short pulse of only 100 ns, where no carrier diffusion takes place to a pulse length of several ms, where the carriers diffuse into the sample depth. Hence by varying the laser wavelength and the pulse length, it is possible to measure with different penetration. In this case a 660 nm laser with a pulse length of 100 ns was chosen; hence a penetration depth of approximately 4 µs was achieved. Figure 1 shows the implanted P doses in the measured Cz-Si sample and figure 2 demonstrates how the different doses can be distinguished by photoconductivity measurements. Fig. 1: implanted P dosis with a depth of only 2 µm Fig. 2: measured photoconductivity of the sample with different implanted P doses Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more MDP series MDPpro 850+ Advanced Solution for Quality Control of Monocrystalline Silicon Ingots, Bricks, and Wafers Learn more MDP series MDPpro Advanced Lifetime Measurement System for Quality Control and Material R&D on Semiconductors Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Lifetime determination of epitaxial silicon thin-film layers In the PV as well as the microelectronic industry there are a lot of applications, were thin epitaxial layers are used. Because of that it is necessary to control the quality of the epitaxial layers with contact less and (Alttext zu lang) With MDP it is possible to measure the lifetime of minority carriers and the photoconductivity in epitaxial layers as fast and exactly as possible with a high resolution. The measurement of epitaxial layers and the determination of their quality is a huge challenge for lifetime measuring methods, since the signal intensity is very small and the results are very difficult to interpret due to the many recombination sites (fig. 1). In the MDPmap and MDPingot equipment it is possible to integrate up to 4 lasers with different wavelength and hence different penetration depth. Furthermore it is possible to measure with different pulse length from a very short pulse of only 100 ns, where no carrier diffusion takes place to a pulse length of several ms, where the carriers diffuse into the sample depth. Hence by varying the laser wavelength and the pulse length, it is possible to measure with different penetration depth and deduce from the lifetime results, which recombination site is the most dominant one. Figure 2 shows an example where a sample series with different substrate qualities and epitaxial layer thicknesses were measured, demonstrating the dependence of the measured lifetime from the substrate, interface quality and surface quality. For more information about the determination of lifetime of epitaxial layers read: [1] D. Walter, P. Rosenits, F. Kopp, B. Berger, K. Dornich, W. Warta: “Determining the epitaxial carrier lifetime by microwave-detected photoconductance measurements”, Proc. Of the 25th EU PVSEC , submitted (2010) [2] K. Dornich, T. Hahn, J.R. Niklas: “Non-destructive electrical characterization and topography of silicon wafers and epitaxial layers”, Mater. Res. Soc. Symp. Proc. Vol. 864 , 549-554 (2005) Fig. 1: recombination site, which contribute to the measured lifetime Fig. 2: measured lifetime of samples with different substrate qualities and epitaxial layer thicknesses Related Solutions and Industries: Epitaxial Layers & Thin Films Matching Products MDP series MDPpro 850+ Advanced Solution for Quality Control of Monocrystalline Silicon Ingots, Bricks, and Wafers Learn more MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more MDP series MDPpro Advanced Lifetime Measurement System for Quality Control and Material R&D on Semiconductors Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Minority carrier lifetime The minority carrier lifetime is one of the most important and significant material parameters. It i Minority carrier lifetime The minority carrier lifetime is one of the most important and significant material parameters. It is extremely sensitive to smallest amounts of impurities or intrinsic defects and hence an ideal parameter for inline characterization of material quality and process control. It is of essential importance for the performance of many semiconductor devices. The minority carrier lifetime is defined as the average time it takes an excess minority carrier to recombine. It is strongly dependent on the magnitude and type of recombination processes in the semiconductor. The main different types of recombination are: SRH recombination ⇒ via defects Auger recombination ⇒ via a three particle process intrinsic or radiative recombination ⇒ via band to band \(\cfrac{1}{\tau_{bulk}} =\cfrac{1}{\tau_{SRH}} + \cfrac{1}{\tau_{Auger}} + \cfrac{1}{\tau_{rad}}\) For silicon SRH is often the dominant recombination mechanism. The minority carrier lifetime in the bulk depends accordingly on the number of defects present and on their recombination properties. In silicon the lifetime can be as high as 1ms, where as in a direct semiconductor as GaAs, where the intrinsic recombination is dominant, the lifetime is only in the range of ns...µs. Besides the defect properties the minority carrier lifetime is dependent on the injection level (excess carrier concentration) and the doping concentration. Figure 1 and 2 display this dependencies for all different lifetimes. Fig. 2: injection dependence of all important recombination rates Fig. 3: doping dependence of all important recombination rates The measured effective lifetime is composed of the bulk lifetime and surface lifetime, which depends on the surface properties of a sample. Hence the surface has to be passivated, if you want to measure the bulk properties of your sample. If you want to investigate the surface passivation quality a FZ-Si wafer is recommendable, because the bulk recombination can be neglected. \(\cfrac{1}{\tau_{eff}} = \cfrac{1}{\tau_{bulk}} + \cfrac{1}{\tau_{surface}}\) Besides that the measured effective lifetime is dependent on the measuring method. For more details read: [1] S. Rein, Lifetime Spectroscopy - A Method of Defect Characterization in Silicon for Photovoltaic Applications, Vol. 85 (Springer, Berlin Heidelberg, 2005) [2] D. K. Schroder, Semiconductor Material and Device Characterization, 2 ed. (John Wiley & Sons, New York, 1998) Matching Products MDP series MDpicts pro High-Resolution, Temperature-Dependent Lifetime Measurement System for Precise Material Characterization Learn more MDP series MDPpro 850+ Advanced Solution for Quality Control of Monocrystalline Silicon Ingots, Bricks, and Wafers Learn more MDP series MDPlinescan Versatile OEM Unit for Lifetime Measurements on Silicon Samples, from Bricks to Processed Wafers Learn more MDP series MDpicts Temperature-Dependent Lifetime Measurement System for Advanced Material Analysis Learn more RES series RESmap High-Precision Resistivity Mapping System for Accurate Material Analysis Learn more MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more MDP series MDPspot Quick and Simple Lifetime Measurement Made Easy Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Photoconductivity When light of sufficient energy is absorbed by a semiconductor, the number of free electrons and holes changes and raises the electrical conductivity of the semiconductor. Photoconductivity When light of sufficient energy is absorbed by a semiconductor, the number of free electrons and holes changes and raises the electrical conductivity of the semiconductor. This increase is called photoconductivity and is dependent of the excess electron and hole concentrations and their mobility via the following equation. [1] \(\Delta\sigma = e \cdot(\mu_{n}\Delta n + \mu_{p} \Delta p)\) [2] \(\Delta\sigma = e \cdot G\) opt \(\cdot \tau \cdot(\mu_{n} + \mu_{p})\) G opt is the optical generation rate, which depends on the incident light intensity, the light spot on the sample and the wavelength. [3] \(G\) opt \(= \alpha \cdot \phi \cdot(1 - R)e^{\alpha x}\) Equation 2 implies that the photoconductivity is proportional to the product of lifetime t and the mobility µ. Therefore, it is also proportional to the square of the diffusion length L, which is defined as: [4] \(L = \sqrt{D \cdot \tau} = \sqrt{\frac{e}{kT} \cdot \mu{\tau}}\) Matching Products MDP series MDpicts pro High-Resolution, Temperature-Dependent Lifetime Measurement System for Precise Material Characterization Learn more MDP series MDPpro 850+ Advanced Solution for Quality Control of Monocrystalline Silicon Ingots, Bricks, and Wafers Learn more MDP series MDPlinescan Versatile OEM Unit for Lifetime Measurements on Silicon Samples, from Bricks to Processed Wafers Learn more MDP series MDpicts Temperature-Dependent Lifetime Measurement System for Advanced Material Analysis Learn more RES series RESmap High-Precision Resistivity Mapping System for Accurate Material Analysis Learn more MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more MDP series MDPspot Quick and Simple Lifetime Measurement Made Easy Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com

Resistivity measurement and mapping Resistivity mapping and measurement The electrical resistivity directly depends on the density of the semiconductor and is therefore a useful parameter to monitor doping profiles and homogeneity. The lifetime and diffusion length depend on the doping density as well. Since doping shifts the fermi level, it increases the rate of SRH recombination in most cases. In addition, since Auger recombination is more likely in heavily doped material, the recombination process itself is enhanced as the doping increases. In our systems the resistivity is measured via the non-contact eddy current method. Eddy current is caused when a sample is exposed to a changing magnetic field due to variations of the field with time, for example if an AC current flows in a coil in close proximity to the sample. This causes a current within the bulk of the sample and the circulating eddies of current create induced magnetic fields that oppose the change of the original magnetic field. The greater the electrical conductivity of the sample , the greater are the currents that are developed and the greater the opposing field will be. In other words the electrical loss in the material is measured, which is directly related to the resistivity of the sample. Note that the measurement depends also on the distance from the coil to the sample and therefore on geometrical features of the sample. Resistance measurements on wafers and bricks The resistivity is one of the most important electrical parameters of a material. It is a key parameter for the performance of semiconductor devices as e.g. solar cells and depends on the doping density of the material. Hence, it is necessary to measure the resistivity with a high accuracy and a high resolution, in order to detect inhomogeneity in the doping density. Read more Matching Products MDP series MDpicts pro High-Resolution, Temperature-Dependent Lifetime Measurement System for Precise Material Characterization Learn more MDP series MDPpro 850+ Advanced Solution for Quality Control of Monocrystalline Silicon Ingots, Bricks, and Wafers Learn more MDP series MDPlinescan Versatile OEM Unit for Lifetime Measurements on Silicon Samples, from Bricks to Processed Wafers Learn more MDP series MDpicts Temperature-Dependent Lifetime Measurement System for Advanced Material Analysis Learn more RES series RESmap High-Precision Resistivity Mapping System for Accurate Material Analysis Learn more MDP series MDPmap Precision Lifetime Charachterization with Exceptional Sensitivity Learn more MDP series MDPspot Quick and Simple Lifetime Measurement Made Easy Learn more Get in touch Do not hesitate to contact us – we are available to assist you with any inquiries or requests. Use our inquiry tool or reach out via email: sales @ freiberginstruments.com