WO2016162398A1

WO2016162398A1 - Apparatus for detecting electronic faults on silicon-based semiconductor wafers

Info

Publication number: WO2016162398A1
Application number: PCT/EP2016/057578
Authority: WO
Inventors: Thomas JÄGER; Martin Kasemann
Original assignee: Albert-Ludwigs-Universität Freiburg
Priority date: 2015-04-07
Filing date: 2016-04-07
Publication date: 2016-10-13

Abstract

An apparatus (1) for detecting electronic faults at inclusions and grain boundaries on silicon-based semiconductor wafers (2) has an illumination device (8) for illuminating the semiconductor wafers (2) with an optical excitation radiation (9) that can be used to excite the semiconductor wafers (2) to emit a photoluminescent radiation (10). To detect the photoluminescent radiation (10) emitted by a measuring point (8), a measuring device (15) is provided that has at least one semiconductor sensor chip, having a sensor area that is sensitive to the photoluminescent radiation (10), and an optical system (17), which can be used to influence the spatial propagation of the photoluminescent radiation (10) emitted by a measuring point (8) such that it impinges on the entire sensor area. The semiconductor wafer (2) is positionable at the measuring point (8) by means of a positioning device (21) that has a contact area (27) for the at least one semiconductor wafer (2), and is movable relative to the measuring point (8) parallel to a plane defined by the contact area (27). The at least one semiconductor sensor chip has an evaluation device (28) connected to it that is designed to detect the recurrence of grain boundary faults on the basis of the measurement signal (29) from the at least one semiconductor sensor chip. The largest dimension that the measuring point (8) has in the plane defined by the contact area (27) is smaller than 10 mm.

Description

Apparatus for detecting electronic defects on silicon-based semiconductor wafers

The invention relates to a method and an apparatus for detecting electronic defects at dislocations and grain boundaries on silicon-based semiconductor wafers. The apparatus comprises at least one illumination device for illuminating the semiconductor wafers with an optical excitation radiation, by means of which the semiconductor wafers can be excited to emit a photoluminescence radiation, a measuring device which has at least one semiconductor sensor chip with a sensor surface sensitive to the photoluminescence radiation and an optic, by means of which the The photoluminescence radiation emitted by the measuring point can be influenced with respect to its spatial propagation in such a way that it impinges on the entire sensor surface, a positioning device having a support surface for at least one semiconductor wafer, by means of which the semiconductor wafer can be positioned at the measuring point and parallel to a plane spanned by the support surface relative to the measuring point is movable, and an evaluation device connected to the at least one semiconductor sensor chip for detecting the position and frequency of Defects as a function of the measuring signal of the at least one semiconductor sensor chip.

Such an apparatus for classifying silicon-based semiconductor wafers intended for producing solar cells is known from US 2012/0142125 A1. The device has an illumination device with a laser diode, by means of which the surface of the semiconductor wafer can be illuminated over its entire area with optical radiation of wavelength 805 nm. As a result of this radiation, the semiconductor material is excited to emit photoluminescence radiation, which is detected by means of a measuring device which has a line sensor, for example designed as a CCD, which is integrated in a silicon semiconductor chip.

At locations where there are no electronic defects in the bulk of the semiconductor material, the photoluminescent radiation is emitted from the semiconductor material at a greater intensity than at locations having electronic defects. Such defects may be caused, in particular, by contamination of the semiconductor material that enters the semiconductor material during the manufacturing process. The impurities cause a decrease in the electrical efficiency of the semiconductor wafers. If these are used for the production of solar cells, the solar cells have a correspondingly small amount of energy. on. Such defects can be identified by evaluating the distribution of the camera-detected photoluminescence radiation, for example for purposes of quality control. A disadvantage of the known device, however, is that an expensive special camera must be used, which is sensitive to the wavelength range of the photoluminescence.

It is further known that the photoluminescent radiation is typically in the wavelength range between about 850 nm and about 1700 nm and is subdividable into two wavelength ranges, a first wavelength range ranging from about 850 nm to about 1300 nm and a second wavelength range of about 1300 nm to about 1,700 nm is enough. In a region of the semiconductor which has impurities, the luminescence is smaller at least in the first wavelength range than in a region which has no impurities. In the second wavelength range, luminescence radiation is observed which is emitted by impurities and not directly by the carrier material silicon. By restricting the detection of the photoluminescence signal to this wavelength range, a distinction can be made between different types of impurities (Kittler, M., W. Seifert, T. Arguirov, I. Tarasov, and S. Ostapenko. "Room-Temperature Luminescence and Electron- Beam Induced Current (EBIC) Recombination Behavior of Crystal Defects in Multicrystalline Silicon. "Solar Energy Materials and Solar Cells 72, no. 1 (2002): 465-72.).

It is therefore an object to provide a device of the type mentioned, which is inexpensive to produce and can be detected and analyzed with the electronic defects at kristalligrafischen Versetzun- conditions and grain boundaries in the volume of the semiconductor material in a simple manner quickly and inexpensively.

This object is achieved with the features of claim 1. These stipulate that the largest dimension which the measuring point has in the plane defined by the bearing surface is smaller than 10 mm.

The invention is based on the finding that, for the detection of electronic defects at grain boundaries and dislocations, which are located in the volume of the semiconductor material, it is sufficient to measure the photoluminescence radiation only along a narrow strip of the wafer surface whose width is approximately the structure size corresponds to the local signal variations to be detected, which is at least smaller than 1 mm. In this case, the width of the strip may be substantially smaller than the width of the surface of the semiconductor wafer. Thus, the photoluminescence radiation by means of a simple design, inexpensive to produce, non-spatially resolved semiconductor sensor chips are associated, which is associated with a measuring point which is movable along the strip relative to the semiconductor wafer.

In a preferred embodiment of the invention, the largest dimension which the measuring point has in the plane defined by the plane defined by the bearing surface is less than 500 μm and in particular less than 200 μm. As a result, even small defects can be detected precisely.

In a further preferred embodiment of the invention

- Is the largest dimension of the sensor surface at least 500 μιη and the largest dimension, which has the measuring point in the plane defined by the support surface plane, is smaller than the largest dimension of the sensor surface or

- The largest dimension of the sensor surface is less than 500 μιη and the largest dimension, which has the measuring point in the plane defined by the support surface level is at most twice as large as the largest dimension of the sensor surface.

In one development of the invention, the evaluation device has localization means by means of which a time window can be determined in which the measuring point is arranged during the relative movement between it and the semiconductor wafer and / or in the semiconductor wafer, wherein the evaluation device comprises a comparison device for comparing the measurement signal of Having sensor chips with a limit, and wherein by means of the evaluation device, the ratio between the time duration during which the measurement signal within the time window exceeds the limit and the time duration during which the measurement signal within the time window below the limit, as a measure of the frequency of grain boundary defects determined is. This allows a simple and fast evaluation of the measurement signal.

In an advantageous embodiment of the invention, the semiconductor wafer can be positioned and moved relative to the measuring point by means of the positioning device in such a way that the measuring point has a predetermined minimum distance to the edges or edges of the semiconductor wafer, wherein the localization means of the evaluation device are additionally designed for determining a time window, within which the measuring point has at least the minimum distance to the edges of the semiconductor wafer, and that the minimum distance is at least 5 mm, optionally at least 15 mm and preferably at least 30 mm. This allows an even more accurate determination of the frequency of grain size defects. In doing so, electronic defects in the peripheral areas of the semiconductor wafer, which can falsify the measurement result for the frequency of the grain boundary defects in a central area of the semiconductor wafer which is at a distance from the edge areas, are disregarded. In a preferred embodiment of the invention, the support surface is formed by at least one conveyor belt, which is guided over deflection devices. The conveyor belt enables a flat support of the semiconductor wafers. Thus, even larger, break-sensitive semiconductor wafers can be safely positioned at the measuring point. The dimension or thickness, which have the semiconductor wafer normal to its surface, is typically less than 2 mm, usually between 40 μιη and 700 μιη and preferably at about 180 μιη. Of course, other thicknesses are conceivable. A support surface is also understood to mean a surface to which the semiconductor wafer can be sucked or pressed by means of a pressure difference.

If necessary, the device may have a plurality of sensors connected to the evaluation device for detecting the photoluminescence radiation at different measuring points. By this measure, the measurement accuracy of the device can be further improved. By way of example, the device can be set up to detect luminescence radiation at at least two measuring points and to have at least two sensors. Preferably, the device may comprise at least three or five sensors. Particularly preferably, the device can have at least seven sensors. The measuring device can be equipped with an active cooling device for the sensors. This allows a further improvement of the measurement sensitivity. The cooling device is preferably integrated by the manufacturer in a specially prepared housing of the sensor so that it does not come to a condensation of the sensor. An external cooling device can assist. The material from which the sensor is designed is chosen such that a high sensitivity of detection for the photoluminescence radiation is given. The preferred material for the realization of the sensors is therefore InGaAs, which can absorb the first and second wavelength ranges. Other available materials with such properties are germanium, lead sulfide and mercury cadmium telluride. The sensor may also be made of silicon, with the restriction that then only the first wavelength range of the photoluminescence radiation can be detected.

In a preferred embodiment of the invention, the sensor is designed as a photodiode. This enables a cost-effective design of the sensor chip with a simultaneously high detection sensitivity. The photodiodes are preferably realized in or on a semiconductor chip whose material does not necessarily have to match the material of the photodiode and which is surrounded by a housing with electrical connections. The electrical connections are directly connected to the two poles of the diodes. In an advantageous embodiment, the housing is made of metal and has an additional connection for grounding the housing. housing. By grounding the housing electrical interference is shielded in the photodiode and noise suppressed. In the housing, a plurality of photodiodes may be integrated in or on a semiconductor chip, but always in such a way that the connections to the two poles of the diodes are led out of the housing individually. If there are several diodes in a housing, it is also conceivable that one of the two poles is already connected in the housing and is implemented simply guided out of the housing and the respective other poles of the photodiodes are led out of the housing one at a time.

In a preferred embodiment of the invention, the illumination of the semiconductor wafer for excitation of photo luminescence is realized via at least one illumination unit with at least one light source, which generates an illumination spot on the semiconductor wafer, which is preferably greater in all directions than the extent of the measuring point. For this purpose, a beam shaping device can be provided which influences the radiation emitted by the light source in its spatial propagation in such a way that the illumination spot is illuminated as completely as possible over the entire surface and at least in the region of the measuring point has a very homogeneous intensity. The beam shaping device can be realized as an imaging or non-imaging beam shaping device. As components for beam shaping, optical lenses with curved surfaces, scattered gratings, scattering disks, beam-shaping mirrors, Fresnel lenses or a combination of the named components can be used.

Furthermore, the illumination unit is designed such that its emitted light lies in a wavelength range below the photoluminescence radiation emitted by the semiconductor wafer. The reason is that as a rule part of the excitation radiation is reflected on the surface of the semiconductor wafer and the measurement signal superimposing also falls on the detection unit, where the photoluminescence radiation relevant for the measurement has to be separated from the reflected excitation radiation via an optical filter system. For this reason, usually a very narrow-band light source, such as a laser or a light-emitting diode, is used whose maximum emitted wavelength is significantly below the wavelength range of the photoluminescence radiation detected by the sensor. For additional attenuation of the excitation radiation in the wavelength range of the photoluminescence radiation detected by the sensor, a short-pass filter can be arranged in the illumination device between the light source and the measuring point, allowing light with wavelengths below a cutoff wavelength to pass and blocking it for light having wavelengths greater than the cutoff wavelength. Excitation radiation with wavelengths below 1000 nm, typically in the range of 600 nm to 950 nm and preferably in the range of 750 to 850 nm, is generated by this device.

In a preferred embodiment of the invention, the sensor is integrated into a detection unit, which has an optical filter device in addition to the sensor. The optical filter tion first serves to separate the part of the excitation radiation reflected from the sample from the photoluminescence signal emitted by the measuring point. For this purpose, the filter device preferably has a long-pass filter whose cutoff wavelength lies in the lower wavelength range of the luminescence radiation, but above the highest wavelength of the reflected excitation radiation. The long-pass filter blocks radiation with wavelengths below the cut-off wavelength and lets radiation with wavelengths above the cut-off wavelength pass through. As long-pass filter absorption filter, dielectric reflection filter and filter of semiconductor materials come into consideration. The cut-off wavelength of the long-pass filter is typically below 1100 nm and often between 900 nm and 1000 nm.

In a further preferred embodiment of the invention, the optical filter device of the detection unit serves to separate the detection of the first wavelength range of the photoluminescent radiation from the second wavelength range of the photoluminescent radiation. Since the photoluminescence radiation in the first wavelength range is much more intense than in the second wavelength range, no filtering measures must be taken to detect the signal in the first wavelength range. The signal from the first wavelength range typically completely overlaps the signal from the second wavelength range. The signal is already sufficiently well measurable with the arrangement described so far. In order to detect the radiation from the second wavelength range of the photoluminescence radiation, instead of or in addition to the long-pass filter described above, a long-pass filter is used which passes through light having wavelengths above the lower limit of the second wavelength range and blocks it for light having wavelengths below the second wavelength range. At least one would use a long-pass filter with a cut-off wavelength above 1,250 nm and preferably a long-pass filter with a cut-off wavelength above 1,400 nm. Likewise, the functionality can be realized with a band-pass filter, which transmits light with wavelengths in the second wavelength range and for light with wavelengths outside of second waveband locks. Preferably, a wavelength range of about 1,500 to about 1,600 nm is transmitted. The filters can be designed as absorption filters or as dielectric reflection filters or as filters made of semiconductor materials.

In a preferred embodiment of the invention, an optical system is additionally integrated in the detection unit. It is the task of the optics to influence the spatial distribution of the photoluminescence radiation emitted by the measuring point in such a way that the sensor is illuminated as completely as possible over the entire surface. This can be realized by an imaging optical system or a non-imaging optical system. The optics can have optical lenses with curved surfaces, scattered gratings, beam-forming mirrors or a combination of the named components. Preferably, the optic has a domed lens or Fresnel lens. In a further preferred embodiment of the invention, the measuring device has at least two semiconductor sensor chips connected to the evaluation device. The sensor chips are integrated in detection units such that one sensor chip detects the signal of the first wavelength range of the photoluminescence radiation and the other sensor chip detects the signal of the second wavelength range of the photoluminescence radiation. Both sensor chips are aligned with their detection units on the same measuring point, so that from the relative ratios of the two signals a deeper statement about the nature of the defect present at the measuring point can be made. In a further realization of the invention, the two detection units can also be aligned with two different measuring points, which lie one behind the other on an imaginary straight line lying parallel to the direction of movement of the semiconductor wafer. In this case, the signal of the front diode must be compared with the signal of the rear diode with a time delay in the evaluation unit. The time delay t results from the distance x of the detection points and the speed v of the forward movement of the wafers after t = x / v.

The device may further comprise a housing which is adapted to receive the measuring device, the illumination device and the evaluation unit. In particular, the device can be designed as an embedded system, whereby a miniaturization and cost savings over a design by individual components may be possible. The device, in particular the housing, may for example have a power supply, in particular a power connection. The device may further comprise a control unit. A control unit is generally understood to mean an electronic device which can control and / or regulate the measuring device and / or the illumination device and / or the evaluation unit. For example, one or more electronic connections between the control unit and the measuring device, the illumination device and the evaluation unit can be provided for this purpose. The control unit may, for example, comprise at least one data processing device, for example at least one computer or microcontroller. The control unit may further comprise at least one interface, for example an electronic interface and / or a man-machine interface such as an input / output device such as a display and / or a keyboard. The control unit can be constructed, for example, centrally or decentrally. Other embodiments are conceivable. The housing may have at least one standardized interface, for example a standardized network factory interface.

The device can be integrated into a production line and / or a process line, in particular for production monitoring. In the production line and / or process line, the Semiconductor wafer by means of the positioning device in the transport direction to the measuring device to be movable.

The measuring device can have a plurality of detection units with sensor chips. For example, the measuring device may have four to ten detection units. The measuring device may have at least one outer detection unit, which is aligned with at least one detection point, also referred to as a measuring point, on edge regions of the semiconductor wafer. In principle, a detection unit which is set up to detect photoluminescence radiation from edge regions of the semiconductor can be understood as an "external detection unit." The outer detection unit can be set up to detect photo-luminescence radiation from edge regions of the semiconductor wafer which are arranged parallel to the transport direction. By way of example, the measuring device may have at least two external detection units, which are each aligned with one or several detection sites in the edge regions of the semiconductor wafer, For example, the measuring device may comprise a plurality of external detection units, which in each case point to one or several detection points in the edge regions of the semiconductor wafer The measuring device may comprise at least one inner detection unit which is set up to emit photoluminescence radiation from a region of the semiconductor wafer detect which of the border areas is limited. The region can be arranged within the surface of the semiconductor wafer surrounded by the edge regions. The inner detection unit may be arranged between the outer detection units. The region may be arranged within a central region of the semiconductor wafer, in which the distance of the region from the edges of the semiconductor wafer corresponds at least to the width of the edge regions. For example, the measuring device can have three inner detection units, which are arranged between two outer detection units. Furthermore, a plurality of measuring devices can be provided along the production line and / or process line in the transport direction of the semiconductor.

In a further embodiment, the device may comprise at least one image sensor. For example, the sensor can be designed as an image sensor, for example as a pixelated sensor, in particular as a CCD camera. By way of example, the device may have one or more image sensors which are set up to detect photoluminescence radiation in the edge regions of the semiconductor wafer. For example, the device can have one or more image sensors which are set up to detect photoluminescence radiation in the central region of the semiconductor wafer. For example, the device may have at least one image sensor which is set up to detect both photoluminescence radiation in the edge regions and in the central region. A number of pixels of the image sensor for detecting photoluminescence radiation in the peripheral areas may be smaller than a number of pixels of the image sensor for detecting photoluminescence radiation in the central area. examples For example, the number of pixels of the image sensor for detecting photoluminescence radiation in the edge regions may be smaller by a factor of 10 than the number of pixels of the image sensor for detecting photoluminescence radiation in the central region. Other numbers and ratios of pixels are conceivable.

In a further aspect, a use of the device according to the invention for detecting electronic defects at dislocations and grain boundaries on silicon-based semiconductor wafers in a multi-lane device is proposed. A "multi-lane device" can be understood as meaning a device which has a plurality of tracks, for example production and / or test tracks, and is set up for multi-track use. Lane production line and / or a multi-lane tester, for example, a multi-lane wafer tester Due to their high production costs, known detection units for semi-conductor production testing are disadvantageous and multi-lane use (multi-lane use). However, in known detection units only about 3600 wafers per hour, which corresponds to the throughput of the process line, can be tested on one track, The production of a device according to the invention can be simple and cost-efficient, so that multi-lane use For example, throughput in a wafer production inspection device may be such mentioned wafer sorter, are increased and a throughput of several production lines can be realized. The throughput of such a multi-lane production line may be proportional to the number of tracks. For example, a multi-lane production line may comprise five, parallel lanes. The term "parallel" can be understood to mean spatially and / or temporally parallel.Furthermore, the device can be integrated into existing process plants, in particular with shared use of the available automation, so that 100% control is possible in a cost-efficient manner For example, immediately before and / or immediately after and / or in a first process step of a production line for producing a solar cell from wafers, so that early detection of defects and sorting out is possible The first process step is typically a wet-chemical treatment of rough-cut silicon - Wafers.

For example, an integration of the device in a process line before and / or after a wet chemical process plant. Typically, the first process step in manufacturing solar cells may include etching wafers in a sequence of chemical baths to remove surface defects and to apply one or more textures. This can be realized, for example, in the process line by a so-called "inline texture." Chemical processes can be slow in this case, for example, the feed rate can be less than one wafer per second. zessschritt in several, for example, five, tracks parallel with slow feed done. A wet chemistry process plant may include a loading unit located at a beginning of the wet chemistry process plant. The loading unit can be set up to position wafers on at least one transport device of the wet chemical processing unit, for example a conveyor belt. The wet scrubbing system transport device may be configured to convey the wafers into a reaction chamber with plastic rollers. For example, the device according to the invention can be arranged in the transport direction of the wafer in front of a wet chemical processing plant and / or in front of a reaction chamber of a wet chemical process plant. In this embodiment, a first sorting unit, which is set up to sort out wafers before passing through a wet chemistry, may be arranged upstream of the wet-chemical processing installation. The first sorting unit can be set up to detect a signal of the sensor chips and / or of the evaluation device of the device and to take it into account when sorting the wafers. For example, the device can be set up to determine a spatial and temporal variation of the intensity of the photoluminescence radiation and to generate at least one classification signal dependent thereon. The first sorting unit may be arranged to take into account the classification signal, for example by including the classification signal in automation sorting algorithms. For example, it is also possible to prevent defective wafers, for example wafers with a low efficiency potential, from undergoing wet chemistry. Furthermore, the probability of a mechanical breakage of the wafer can be reduced. Thus, a saving of the following process costs can be achieved.

Furthermore, the wet-chemical processing plant may have a discharge unit with a second sorting unit, which may be set up to classify and sort wafers on the basis of predetermined criteria. The terms "first" and "second" sorting unit are used as pure names and in particular provide no information about an order and / or whether, for example, even more sorting units are available. For example, the device according to the invention can be arranged in the transport direction of the wafer behind a reaction chamber of a wet chemical processing plant. The second sorting unit can be set up to detect a signal of the sensor chips and / or of the evaluation device of the device according to the invention or of the combined device and to take this into account when sorting the wafers. For example, the device according to the invention can be set up to determine a spatial and temporal variation of the intensity of the photoluminescence radiation and to generate at least one classification signal dependent thereon. The second sorting unit may be arranged to take into account the classification signal, for example by including the classification signal in automation sorting algorithms. In particular, the device according to the invention can be retrofitted into an existing wet-chemical processing plant and an existing sorting unit of the wet-chemical processing plant can be used. In another aspect, a method is proposed for detecting electronic defects at dislocations and grain boundaries on silicon-based semiconductor wafers. In the method, a device according to one of the preceding embodiments is used. With regard to definitions and embodiments of the method, reference may be made to the above-described definitions and embodiments of the device.

The method comprises the following method steps:

Moving the semiconductor wafers parallel to a plane spanned by a bearing surface relative to a measuring point;

- Positioning the semiconductor wafer at the measuring point;

- Illuminating the semiconductor wafer with an optical excitation radiation, by means of which the semiconductor wafer for the emission of a photoluminescence radiation can be excited;

Detecting the photoluminescence radiation emitted by the measuring point with a measuring device which has at least one semiconductor sensor chip with a sensor surface which is sensitive to the photo luminescence radiation and an optical system by means of which the photoluminescence radiation emitted by a measuring point influences the spatial propagation thereof. is flowed that it impinges on the entire sensor surface, and generating at least one measurement signal of the semiconductor sensor chip;

Detecting a frequency of a position and / or a frequency of the defects in dependence on the measurement signal.

The process steps can be carried out in the order given. However, another order is conceivable. Furthermore, the method and in particular the method steps can be carried out repeatedly.

In the method, it can be detected whether the measuring point is completely arranged within a central region and a time window is determined within which the measuring point is arranged within the central region of the semiconductor wafer. A central region can be understood as meaning a region of the semiconductor wafer in which a distance of the region from the edges of the semiconductor wafer corresponds at least to the width of the edge regions. The method may further comprise a comparing step of comparing the measurement signal to a predetermined threshold, wherein a ratio between a time period during which the measurement signal within the time window exceeds the threshold and a period during which the measurement signal within the time window is the threshold is determined as a measure of the frequency of grain boundary defects.

Embodiments of the invention are explained in more detail with reference to the drawing. It shows 1 is a side view of a first embodiment of a device for detecting grain boundary defects on semiconductor wafers,

2 is a plan view of the device shown in Fig. 1,

3 shows a schematic representation of a lighting device for emitting an excitation radiation onto a surface of a semiconductor wafer,

4A is a schematic representation of a first measuring device for detecting

photoluminescence,

4B is a schematic representation of a second measuring device for detecting

photoluminescence,

Fig. 5 is a plan view of a portion of a arranged on a conveyor belt

Semiconductor wafers,

6 shows a side view of a second exemplary embodiment of the device for detecting grain boundary defects on semiconductor wafers,

Fig. 7 is a graphical representation of a measurement signal of a photodiode, wherein on the

Abscissa the time t and on the ordinate the signal strength is plotted

Fig. 8 shows an embodiment of a measuring device according to the invention, and

9 shows an embodiment of a measuring device according to the invention in a multi-lane device.

A device designated as a whole by 1 in FIG. 1 serves to detect grain boundary defects on silicon-based semiconductor wafers 2 from which solar cells are to be produced. The semiconductor wafers 2 have a planar surface with first, second, third and fourth edge regions 3, 4, 5, 6, each extending along an edge of the semiconductor wafer 2 adjacent thereto. The width which the edge regions 3, 4, 5, 6 have at right angles to the direction of extension of the wafer edges and parallel to the wafer plane is 15 mm in the exemplary embodiment shown in the drawing.

As can be seen in FIG. 2, the first edge region 3 and the second edge region 4 run parallel to one another. The third edge region 5 is transverse to the first and the second edge region 3, 4 and extends parallel to the fourth edge region 6. In the embodiment shown in FIG. 2, the semiconductor wafers 2 have a square shape. But there are also other embodiments conceivable. Thus, the semiconductor wafer 2 can also be designed rectangular or diamond-shaped. The dimension or thickness which the wafers have normal to their surface is preferably about 180 μm. Of course, other thicknesses are conceivable.

In order to detect the grain boundary defects, the device 1 has a lighting device 7, by means of which the semiconductor wafers 2 can be illuminated at a measuring point 8 with an optical excitation radiation 9. The wavelength of the excitation radiation 9 is selected such that the semiconductor wafers 2 can be excited by the excitation radiation 9 for emission of a photoluminescence radiation 10 with a wavelength deviating from the wavelength of the excitation radiation 9. The intensity of the photo luminescence radiation 10 is dependent on the intensity of the excitation radiation 9 and the presence of grain boundary defects in the semiconductor material. In a semiconductor material that has no grain boundary defects, such as impurities, the intensity of the photo luminescence radiation 10 is greater than that of a corresponding semiconductor material has the defects. The illumination device 7 has as light source 11 a light emitting diode whose radiation preferably comprises a wavelength of 790 nm. Instead of the light-emitting diode, a laser diode or another suitable light source can also be provided.

As can be seen in FIG. 3, between the light source 11 and the measuring point 8 to be illuminated with it a beam-shaping device 12 is arranged, which may, for example, have a lens. The beam shaping device 12 can be designed as imaging or non-imaging optics. Before and / or behind the beam shaping device 12, optical filters 13, 14 may be provided in the beam path of the illumination device 7, which are impermeable to the wavelength of the photo luminescence 10.

The device 1 also has a measuring device 15, which has a semiconductor sensor chip based on InGaAs, in which a single photodiode 16 is integrated, which has a sensor surface sensitive to the photoluminescence radiation 10. However, the semiconductor chip can also have another semiconductor substrate, such as silicon. The photodiode 16 is preferably sensitive in a wavelength range from 850 nm to 1600 nm and in particular between 950 nm and 1600 nm. By means of the measuring device 15 is photo luminescence 10 detectable, which is emitted from the measuring point 8.

In Fig. 4A it can be seen that the measuring device 15 has an optical system 17 with a lens by means of which the light emitted by a measuring point 8 photo luminescence 10 can be influenced with respect to their spatial spread such that it impinges on the entire sensor surface. Instead of the lens, however, another imaging or non-imaging optics may be provided, which directs the photoluminescence radiation 10 impinging on them from the direction of the measuring point 8 to the sensor surface of the photodiode 16. In the beam path in front of and / or behind the optics 17 optical filter elements 18, 19 may be arranged, which are transparent to the photo luminescence radiation 10 and radiation with the wavelength of the photo luminescence radiation 10 different wavelength lock.

In the embodiment shown in Fig. 4B, the measuring device 15 for detecting photo luminescence radiation 10, which is emitted from the measuring point 12, two measuring units 15A, 15B, of which a first measuring unit 15A in a first wavelength range and a second measuring unit 15B in a second wavelength range is sensitive. The first wavelength range extends from 850 nm to 1,300 nm and the second wavelength range from 1,300 nm to 1,700 nm. Each measuring unit 15A, 15B has in each case a photodiode 16A, 16B and an optical system 17A, 17B associated therewith, which are shown as imaging or not imaging optics can be configured. The optics 17A, 17B is configured in such a way that the photo luminescence radiation 10 emitted by the measuring point 8 strikes the entire sensor surface of the optics 17A, 17B in each case. In the beam path in front of and / or behind the optics 17A, 17B of each measuring unit 15A, 15B optical filter elements 18A, 19A and 18B, 19B are respectively arranged. The filter elements 18A, 19A are transparent to the first wavelength range and the filter elements 18B, 19B for the second wavelength range. Wavelengths outside the wavelength range associated with the respective measuring unit 15A, 15B are blocked by the filter arrangements formed by the filter elements 18A, 19A and 18B, 19B, respectively.

In Fig. 5, the measuring point 8 and the surface 20, which illuminates the first illumination device 7, each indicated schematically by a circular area. The diameter of the illuminated surface 20 is greater than the diameter of the measuring point 8. The difference a between the radius of the measuring point 8 and the radius of the illuminated surface 20 is greater than the diffusion length and is preferably about a few microns.

In the embodiment shown in FIG. 1, the illumination device 7 and the measuring device 15 are arranged on the same side of the semiconductor wafer 2. As can be seen in FIG. 6, however, it is also possible for the illumination device 7 and the measuring device 15 to be arranged on mutually opposite sides of the semiconductor wafer 2. The device 1 further has a positioning device 21, by means of which the semiconductor wafers 2 can be positioned at the measuring point 8 and are movable relative to the measuring point 8 in a transport direction 22 oriented parallel to the wafer plane. The positioning device 21 has two parallel spaced, about deflection devices 23, 24 circulating conveyor belts 25, 26 which are spaced apart in the direction of two mutually parallel axes about which they rotate. The upper sides of the upper runs of the conveyor belts 25, 26 form a contact surface 27 arranged in a plane, on which the semiconductor wafers 2 can be positioned in order to move them in the transport direction 22 relative to the illumination device 7 and the measuring device 15. The conveyor belts 25, 26 are drivable by means of a positioning drive, not shown in detail in the drawing. The positioning drive, for example, have a position-controlled servo motor, which is in drive connection with the conveyor belts 25, 26 via rollers and / or gears. Of course, other embodiments of the positioning are conceivable that allow a feed 35 of the semiconductor wafer 2 in the transport direction 22 with preferably constant speed. With the aid of the positioning device 21, the semiconductor wafers can be positioned relative to the measuring point 8 in such a way that the measuring point is completely within a central region bounded by the edge regions 3, 4, 5, 6 in the plan view of the plane in which the bearing surface 27 is arranged Semiconductor wafer 2 is arranged. In this case, the measuring point 8 is completely within a circle which is arranged in the plane of the support surface 27 and has a diameter d which is less than 100 μιη and preferably less than 50 μιη.

As can be seen in FIGS. 1 and 6, the apparatus 1 has an evaluation device 28 connected to the photodiode 16, which serves to detect the frequency of the grain boundary defects as a function of the measurement signal 29 of the photodiodes 16. The evaluation device 28 has locating means not shown in detail in the drawing, by means of which it can be detected whether the measuring point 8 is arranged completely within the central region, ie the distance between the measuring point 8 and the edges of the semiconductor wafer 2 is at least the width of the edge regions 3, 4, 5 , 6 corresponds. The localization means are designed to determine a time window within which the measuring point 8 is arranged within the central region of the semiconductor wafer 2.

In addition, the evaluation device has a comparison device by means of which the measurement signal 29 of the photodiodes 16 is comparable to a predetermined limit value 30. By means of the evaluation device 28, the ratio between the time duration during which the measurement signal 29 exceeds the limit value 30 within the time window and the time duration during which the measurement signal 29 falls below the limit value 30 within the time window can be determined as a measure of the frequency of the grain boundary defects. 8 shows an exemplary embodiment of a measuring device 15. The measuring device 15 may have at least two outer detection units 36, 37 which are each aligned with one or several measuring points 8 on edge regions 3, 4 of the semiconductor wafer 2. The measuring device 15 can have a plurality of inner detection units 38, which are arranged between the outer detection units 36, 37. For example, the measuring device 15 may have three inner detection units 38, which are arranged between two outer detection units 36, 37. For example, the measuring device 15 can also have four, five, six, seven or up to ten internal detection units 38. In principle, embodiments with more than ten internal detection units 38 are also conceivable. The sensors 42, 43 of the outer detection units 36, 37 and the sensors 39 of the inner detection units 38 can be designed as photodiodes and / or as image sensors. The sensors 42, 43 may be configured identically to the sensors 39 of the inner detection units 38 or may be configured differently from the sensors 39 of the inner detection units 38.

9 shows an exemplary embodiment of a measuring device 15 in a multi-lane device 41, for example a multi-lane production line. The manufacture of a device 1 can be simple and cost-efficient, so that multi-lane use is possible. The multi-lane device 41 may include a plurality of tracks 40. For example, a multi-lane device 41 may comprise five parallel tracks 40 on which the semiconductor wafers 2 are moved in the transport direction 22. Over each track 40, a measuring device 15 may be arranged. The respective measuring device 15 may have at least two outer detection units 36, 37, which are respectively aligned with one or several measuring points 8 on edge regions 3, 4 of the semiconductor 2, and three inner detection units 38, which see between two outer detection units 36, 37 are.

List of Reference Devices

Semiconductor wafer

first edge area

second border area

third edge area

fourth edge area

lighting device

measuring point

excitation radiation

Photo luminescence radiation

light source

Beamformer

Optical filter

measuring device

A measuring unit

B measurement unit

photodiode

A photodiode

B photodiode

optics

A look

B optics

optical filter element

A optical filter element

B optical filter element

optical filter element

A optical filter element

B optical filter element

area

positioning

transport direction

deflecting

conveyor belt

Aufiagefläche Evaluation device measuring signal

limit

feed

outer detection unit outer detection unit inner detection unit sensor

track

Multi-lane device sensor

sensor

Claims

claims

Device (1) for detecting electronic defects at dislocations and grain boundaries on semiconductor wafers (2) based on silicon, with at least one illumination device (8) for illuminating the semiconductor wafers (2) with an optical excitation radiation (9), by means of which the semiconductor wafers ( 2) for emitting a photoluminescent radiation (10) are excitable, with a measuring device (15) having at least one semiconductor sensor chip with a luminescence for the photo (10) sensitive sensor surface and an optic (17), by means of the from a measuring point (8) from sent photo luminescence (10) with respect to their spatial spread is influenced such that it impinges on the entire sensor surface, with a support surface (27) for at least one semiconductor wafer (2) having positioning means (21), by means of which the semiconductor wafer (2) positionable at the measuring point (8) and parallel to one of the bearing surface (27) plane spanned relative to the measuring point (8) is movable, and with an at least one semiconductor sensor chip associated evaluation device (28) for detecting the frequency of the position and / or the frequency of defects in dependence on the measuring signal (29) of the at least one semiconductor sensor chip, characterized in that the largest dimension, which has the measuring point (8) in the of the bearing surface of (27) plane spanned, smaller than 10 mm.

Device (1) according to claim 1, characterized in that the largest dimension, which has the measuring point (8) in the plane defined by the bearing surface (27), is less than 500 μιη and in particular less than 200 μιη.

Device (1) according to claim 1 or 2, characterized

the largest dimension of the sensor surface is at least 500 μm and the largest dimension which the measuring point (8) has in the plane defined by the support surface (27) is smaller than the largest dimension of the sensor surface or

that the largest dimension of the sensor surface is less than 500 μιη and that the largest dimension, which has the measuring point (8) in the plane defined by the support surface (27) level, at most twice as large as the largest dimension of the sensor surface.

Device (1) according to one of claims 1 to 3, characterized in that the measuring device (15) between the measuring point (8) and the sensor surface an optical film tereinrichtung having a long-pass filter whose cut-off wavelength is below 1100 nm and in particular between 900 nm and 1000 nm.

Device (1) according to one of claims 1 to 4, characterized in that the illumination device (8) comprises a light source and / or at least one filter element, which are designed such that the excitation radiation (9) to a wavelength range below 1000 nm, in particular is limited to a wavelength range below 950 nm, optionally to a wavelength range below 850 nm, in particular to a wavelength range between 600 nm and 950 nm and preferably to a wavelength range between 750 nm and 850 nm or lies in such a wavelength range.

Device (1) according to one of claims 1 to 5, characterized in that the sensor chip as a photodiode (16, 16A, 16B) is formed, which is preferably realized with InGaAs, germanium or mercury-cadmium telluride.

Device (1) according to one of claims 1 to 6, characterized in that the device (1) has a plurality of the evaluation device (28) connected semiconductor sensor chips for detecting the photo luminescence (10) at different measuring points (8).

Device (1) according to one of claims 1 to 7, characterized in that the measuring device (15) at least two measuring units (15A, 15B) for detecting the photoluminescent radiation (9), of which at least a first measuring unit (15A) in a first Wavelength range and at least one second measuring unit (15B) is sensitive in a second wavelength range, and that the first wavelength range is preferably between 850 nm to 1300 nm and the second wavelength range preferably between 1300 nm to 1700 nm.

Device (1) according to one of claims 1 to 8, characterized in that the bearing surface (27) by at least one conveyor belt (25, 26) is formed.

Device (1) according to one of claims 1 to 9, characterized in that the evaluation device (28) has localization means by which a time window can be determined, in which the measuring point (8) during the relative movement between it and the semiconductor wafer (2) and / or in the semiconductor wafer (2), that the evaluation device (28) has a comparison device for comparing the measurement signal (29) of the sensor chip with a limit value (30), and that by means of the evaluation device (28) the ratio between the time duration while the measuring signal (29) within the time window exceeds the limit value (30) and the time duration during which the measuring signal (29) within the time window below the limit value (30) can be determined as a measure of the frequency of the grain boundary defects.

Device (1) according to one of claims 1 to 10, characterized in that the semiconductor wafer (2) by means of the positioning device (21) relative to the measuring point (8) positionable and movable, that the measuring point (8) at least a predetermined minimum distance to the parallel to the direction of movement oriented edges or edges of the semiconductor wafer (2), and that the minimum distance is at least 10 mm, optionally at least 20 mm and preferably at least 30 mm.

Device (1) according to one of claims 1 to 11, wherein the measuring device (15) has at least one outer detection unit (36, 37), which on at least one measuring point (8) in the edge regions (3, 4) of the semiconductor wafer (2). is aligned.

Device (1) according to one of claims 1 to 12, wherein the measuring device (15) has at least one inner detection unit (38) which is set up to detect photo-luminescence radiation (10) from a region of the semiconductor wafer (2) is limited by the edge regions (3, 4).

Device (1) according to one of claims 1 to 13, wherein the device (1) comprises at least one image sensor.

Use of a device (1) according to any one of claims 1 to 14 for detecting electronic defects at dislocations and grain boundaries on silicon-based semiconductor wafers (2) in a multi-lane device (41).

A method of detecting electronic defects at dislocations and grain boundaries on silicon-based semiconductor wafers (2), wherein a device (1) according to any one of the preceding claims is used, the method comprising the steps of:

Moving the semiconductor wafer (2) parallel to a plane defined by a support surface (27) relative to a measuring point (8);

Positioning the semiconductor wafer (2) at the measuring point (8);

Illuminating the semiconductor wafer (2) with an optical excitation radiation (9) by means of which the semiconductor wafers (2) can be excited to emit a photoluminescence radiation (10);

Detecting the from the measuring point (8) emitted photo luminescence (10) with a measuring device (15), the at least one semiconductor sensor chip with a for the photo luminescence radiation (10) sensitive sensor surface and an optics (17), by means of which of a measuring point (8) emitted photoluminescence (10) is influenced with respect to their spatial spread such that it impinges on the entire sensor surface, and generating at least one Measuring signal (29) of the semiconductor sensor chip;

Detecting a frequency of a position and / or a frequency of the defects in dependence on the measurement signal (29).

Method according to the preceding claim, wherein in the method it is detected whether the measuring point (8) is arranged completely within a central region and a time window is determined within which the measuring point (8) is arranged within the central region of the semiconductor wafer (2).

Method according to the preceding claim, wherein the method further comprises a comparing step in which the measuring signal (29) is compared with a predetermined limit value (30), wherein a ratio between a time period during which the measuring signal (29) within the time window the limit value (30), and a time period during which the measurement signal (29) within the time window below the limit (30) is determined as a measure of the frequency of the grain boundary defects.