DE19840197A1 - Method to identify and characterize crystal defects in monocrystalline semiconductor material; involves testing sample of monocrystalline semiconductor material using micro-Raman spectroscopy - Google Patents

Abstract

The invention relates to a method and a device for the rapid, non-destructive detection and characterization of crystal defects in monocrystalline semiconductor material, characterized in that a sample body made of monocrystalline semiconductor material is examined using mu-Raman spectroscopy.

Description

The invention relates to a method for non-destructive, online-compatible and fast quality control of monocrystalline semiconductor material and for process control in silicon wafer production, especially after mechanical Machining steps and thermal treatments of the Silicon wafer.

In order for further processing into components or integrated circuits must be suitable monocrystalline semiconductor material, such as Silicon material, meet certain requirements. So must Material with crystal defects, such as Dislocations, reliably identified, characterized and be sorted out.

There are already growth-related crystal defects the growth of monocrystalline semiconductor material. However, crystal defects can only occur during the subsequent one Manufacture and processing of semiconductor wafers or Components are generated. In this case one speaks of process-induced crystal defects. Crystal defects can both on the sample surface, for example microcracks, as also inside the sample, for example slides and Dislocations occur.

When manufacturing silicon wafers are used for control the mechanical processing steps within the Production sequences at regular intervals geometric disc parameters, such as the diameter, the Thickness, the edge profile shape and the surface quality of the outer interfaces.

Due to the mechanical processing steps within of the individual manufacturing sequences occur on the surface and in areas near the surface of the silicon wafers too Defects in the homogeneous silicon lattice, so-called subsurface  Damage (SSD). To control these defects are in wafers from the processing line at regular intervals removed and examined.

In early processing stages in which the wafers are not yet polished, the surface structure can only be examined using destructive measuring methods, for example with defect sets. This is anisotropic etching. One component of the etching solution, for example HNO ₃ , oxidizes the semiconductor material, a second, for example HF, dissolves the oxide and another, for example CH ₃ COOH, controls the etching rate as a kind of diluent. The etching in the area of a crystal defect is different in comparison to the crystalline perfect environment. This difference is then examined, for example with an optical reflected light microscope.

All defect etching processes change the sample material both chemically and morphologically. The silicon wafers become unusable for further processing and must be used as Loss to be written off.

Another method for examining such Surfaces, according to the state of the art, the Transmission electron microscopy finished semiconductor wafer an electrical Circuit applied and this later in several Work steps examined. These examinations are mostly undertaken by later buyers of the finished product and allow conclusions to be drawn about the quality of the semiconductor wafers usually only after a long time, so that corrective measures cannot take effect immediately.

EP-A 0735378 describes a method for surface detection by determining the electrical parameters using the Measuring principle of photothermal heterodyne spectroscopy (PTH)  in connection with photoluminescence heterodyne spectroscopy (PLH).

A disadvantage of PTH / PLH spectroscopy is that a Characterization of the crystal defects is not possible. Another disadvantage of these methods is that they are not direct Information is obtained. It is always an analogy to one Model substance necessary. On the one hand, a high level at PTH Response signal is required and on the other hand the PLH is very The areas of application are sensitive to impurities very limited. Both methods are about it and very slow procedures.

In other methods, according to the prior art, for Control of the surface quality of monocrystalline These become semiconductor material only after further Processing steps, at a later time from the Machining line ejected when the outer interface has such a low roughness that the use of scattered light systems is possible. With this method is the recording of the errors occurring in the Surface structure of the silicon wafers and their assignment to occurring process fluctuations only with difficulty or partly at all not possible.

The methods and devices for detection and Characterization of crystal defects on the surface of monocrystalline semiconductor materials according to the prior art Technology does not work non-destructively or only with high to operate technical effort. All procedures always lead too high failure rates in production because of this Processes all have an enormous time lag in production bring with it only small fragments of the silicon wafers can be examined and the silicon wafer for further Production become unusable.

Furthermore, changes of the Silicon surface and the near-surface layers  (Subsurface Damage SSD) insufficient in terms of occurred phase transformations in the silicon lattice characterized. This SSD results from mechanical Processing steps.

These phase transformations of the silicon lattice are shown in Dependence of the induced structural change in subsequent heat treatments, such as at Coatings (epitaxy, rear of the pane with poly-Si and / or LTO oxide layer) or heat processes such as tempering, RTP (rapid-thermal-processing) or RTA (rapid-thermal-annealing), activated and thereby reduce the yield of this Manufacturing steps.

All of these methods contradict the thoughts and Requirements of an economic and modern Quality philosophy.

There was therefore the task of one method and one Device for non-destructive, online-compatible and rapid quality control in silicon wafer production, especially after mechanical processing steps and thermal treatments of the silicon wafers are available too put.

It has now been found that by using µ-Raman spectroscopy as a supporting measurement method for targeted production of silicon with defined Material properties, in turn, from the crystal structure and whose perfection depends on a process is provided that the disadvantages described owns.

The invention relates to a method and Device for the detection and characterization of Crystal defects in monocrystalline semiconductor material, characterized in that a specimen  monocrystalline semiconductor material with µ-Raman spectroscopy is examined.

Μ-Raman spectroscopy is a structural analysis method which has been used to generate laser light sources of Raman scattered radiation has found widespread use.

Since the Raman effect is scattering on the crystal lattice is about crystal perfection and the Crystal orientation dependent. You can therefore use this Process not only amorphous and crystalline areas differ, but also the order within the Determine crystal. It is also possible to get tensions in Measure material because of the frequency of the lattice vibrations is directly dependent on the stress conditions in the material.

Strategies are available through the use of µ-Raman spectroscopy available which is faster, non-destructive and therefore an integrable in the semiconductor production line Enable quality control and process control. For the first time it was possible to edit Phase changes occurring in silicon using a for to describe the production control acceptable method. It is used when assessing existing ones Machining process when evaluating new Machining processes and their integration in one Process sequence and can be an integral part of an almost feedback control loop operated.

The application of µ-Raman spectroscopy relates to both Crystals and their bulk properties, such as Point defect clusters, voids and oxygen excretions, as also on silicon wafers and those running there Phase transformations in mechanical and chemical Processing steps and heat treatments. This Solid state reactions, for example phase transformations and precipitations, are caused by changes in pressure and in the temperature triggered and are also time-dependent.  

The µ-Raman spectroscopy can according to the invention for example to optimize process sequences, for example with a view to eliminating costly manufacturing steps such as etching become. Novel process steps, for example in the mechanical processing, can be with the Evaluate µ-Raman spectroscopy and its integration into a Optimize process chain. A big advantage of application of the µ-Raman spectroscopy according to the invention in that the high measuring speed Fault detection on the monocrystalline semiconductor wafers in the The meaning of a "fast feedback module" is an online-compatible one Process control allows. This is the result of the measurements computer controlled with a corresponding reference continuously compared and in the production process for Control of processing tools used. Farther can also be used on the state of conservation of the Tools, such as grinding wheels or Einkorn diamond tools, conclusions can be drawn.

Many individual steps in the process chains during production and processing of monocrystalline semiconductor materials, for example silicon wafers can be optimized in this way.

The method according to the invention can be used with silicon Seed crystals, silicon single crystals and silicon Wafers on all orientations of the crystal lattice (after Miller) can be used, preferably on Si single crystals and Si wafers with the technically significant Crystal orientations <100 <, <111 <and <110 <.

Through the use of µ-Raman spectroscopy according to the invention you have a method that is non-destructive works, and secondly, no special ones Environmental conditions such as ultra high vacuum requirement. In contrast to those discussed in the prior art Methods for surface detection are here in situ for the first time Measurements possible. By the advantage that this method is high  it can also work with local resolution (<1 µm) for short-range Detect grid changes. To create one corresponding x-ray reflexes are, for example, approximately 50 Atomic layers are necessary, while for a Raman spectrum only one Fraction of that is necessary.

An essential factor of the application according to the invention is that it is a very fast measuring method, the moreover with other measuring methods, such as from DE-A 198 27 202 known, can be coupled. In one Operated in "scanning mode", even larger ones can Sample areas quickly characterized and the homogeneity of Material and process are determined. This can be done either for the entire spectrum or better just for individual characteristic bands or wavenumber ranges occur.

Of the phase changes in silicon caused by Machining processes are still several polymorphs by Silicon has been described. From high pressure experiments with Diamond cells are known to be hydrostatic in silicon Pressing 10 to 13 Gpa in from the diamond structure (Si-I) a metallic phase (Si-II, β-Sn structure) changes. With With increasing pressure, further metallic phases form. At Pressure relief finds a conversion back to different semiconducting phases, preferably in the rhombohedral Si-XII phase and in the cubic Si-II phase, instead, which under Normal conditions remain metastable (R. J. Needs et al., Phys. Rev. B 51, 9652 [1995]; J. Crain et al. Rep. Prog. Phys. 58, 705 [1995]).

Through conductivity measurements during indentation hardness tests it was found that the metallic Si-II also during can form mechanical contacts, so far assumed that an amorphous phase remains after relief (D. R. Clarke et al. Phys. Rev. Lett. 60, 2156 [1988]; I. V. Gridneva et al. Phys. Stat. Solodi (a) 14, 177 [1972]).  

It was measured using hardness impressions in µ-Raman spectroscopy Silicon observed that in addition to amorphous silicon in the Impression areas also known from high-pressure experiments Si-III and Si-XII phases can arise (A. Kailer et al. J. Appl. Phys., 81, 3057 [1997] and Y.G. Gogotsi et al. Mater. Res. Innovations, 1, 3 [1997]).

The results of the experiments described above delivered are considered significant for the processing of Silicon to look at, as in the manufacture of monocrystalline semiconductor wafers, for example Silicon wafers, processing methods used Phase changes of the silicon lattice on the surface and the underlying layers.

These phase transformations of the grid affect one the processing step itself and the other the entire processing chain for the production of silicon wafers. For example, in the case of ductile material removal the metallization of the silicon lattice the volume due to cracks less damaged. On the one hand, the effectiveness is one mechanical steps subsequent chemical removal step from the Si phase appearing on the surface of the wafer the depth of the damage to be removed depends on the other significant by means of etching.

The invention is described below with the aid of illustrations in schematic representation explained in more detail. The one in these Raman spectra shown in the figures are used according to the invention for Evaluation of the Si surfaces.

Figures 1a to 1c show Raman spectra of several monocrystalline silicon samples after they were separated from a silicon single crystal rod using an internal hole saw (ID). In Fig. 1a, in addition to the crystalline Si phase at 521 cm ^-1 , caused by mechanical processing steps, a second band at 465 cm ^-1 , superimposed on this band, can be assigned to an amorphous Si phase.

In a further sample, in Fig. 1b, in addition to a hardly shifted Si-I band at 519 cm ^{-1, there is} an additional band shifted to smaller wavenumbers, which is assigned to a hexagonal Si-IV band.

Fig. 1c shows a Si sample after separation by means of an internal hole saw from a silicon single crystal rod within a fracture surface, which has a band at 519 cm ^-1 , which is assigned to the Si-I phase. In summary, it can be seen that during the separation using an internal hole saw, strongly changing proportions of amorphous and crystalline phases occur. The Si-I band is in some cases very widespread, coupled with a shift to smaller wavenumbers, which can be attributed to a phase transition to the hexagonal diamond structure, the Si-IV phase. Other areas of the samples that have microscopic fracture surfaces are characterized by pure Si spectra with an SI-I phase.

Fig. 2 shows a Raman spectrum of a monocrystalline silicon sample after it has been separated from a silicon single crystal rod by means of a wire saw (Multi-Wire-Saw, MWS) in contrast to the examples above. The Raman spectra recorded by these MWS samples vary less than those of the samples sawed off with an internal hole saw. All spectra are characterized by the crystalline Si-I phase, with only small amounts of amorphous phase being observed. The voltage-induced band shifts observed in some of these spectra indicate pressure fluctuations in processing.

Figures 3a to 3c show Raman spectra of several monocrystalline silicon samples after they have been ground on their surface. While amorphous and hexagonal phase components could be detected in sawn samples, metastable high-pressure phases are also added to ground Si surfaces, which indicates the formation of metallic silicon during the grinding process. In Fig. 3a a ground sample (Mesh 320) is shown, in which one can see that in addition to the band of an amorphous phase component at 475 cm ^-1 there is also a weak band at 354 cm ^-1 , that of the crystalline, metastable Si-XII Phase is to be assigned. With finer grinding processes (Mesh 600), several bands of the metastable Si-III phase at 434 cm ^-1 , 484 cm ^-1 and 167 cm ^-1 and the Si-XII phase at 397 cm ^-1 were shown in Fig. 3b and 352 cm ^-1 . Fig. 3c shows the spectrum of a sample that was processed with the finest grinding wheel grit (Mesh 4000). In this case, a small proportion of the metastable high pressure phase Si-XII at 353 cm ^-1 can only be seen in the case of a multiple stretched spectrum, in addition to the band of the Si-I phase at 521 cm ^-1 . A portion of the amorphous phase can no longer be observed.

The claimed device for performing the inventive method according to the independent Device claim includes a µ-Raman spectrometer, a Holding and transport device and a receiving device and can also with an optical measurement and Detection system, for example a reflected light microscope be equipped.

By the inventive method and the device for Carrying out the process eliminates the production Editing and subjective assessment of specific processed semiconductor material, such as Silicon test disks, as well as the disposal of toxic Process media such as chromic acids. That claimed Process can be applied to any monocrystalline Apply semiconductor material and can therefore at any Job in a production line for silicon wafers to get integrated. The automated recording, storage and evaluation of the measured values by a process computer enables one taking place in the production line Assessment of the material after each one Processing step.  

FIG. 4 shows a device in a combination of the individual devices that is possible for carrying out the method according to the invention.

Monocrystalline semiconductor material ( 2 ) is automatically transferred, for example by a holding and transport device ( 1 ), to a position suitable for the examination. With a scanning device ( 6 ), the sample ( 2 ) to be examined is specifically moved during the measurement. A µ-Raman spectrometer ( 3 ) and a reflected light microscope ( 4 ) are arranged over the sample to be examined. The individual measuring methods are then applied in succession or simultaneously to the sample ( 2 ) to be examined. After the measured values of the sample have been obtained, a decision is made, for example by means of a computer-assisted analysis of the comparison with a database, as to whether the material is further processed or discarded. The measured values are stored in a process computer ( 5 ). In the last step, the sample ( 2 ) is removed from the measuring device ( 1 ) again by the holding and transport device.

Claims (7)

1. A method for the rapid, non-destructive detection and characterization of crystal defects in monocrystalline semiconductor material, characterized in that a sample body made of monocrystalline semiconductor material is investigated with µ-Raman spectroscopy. 2. The method according to claim 1, characterized in that Phase changes caused by processing steps, can be detected. 3. The method according to claim 1 or 2, characterized in that the result of the inspection for quality control and for process control in the production of monocrystalline Silicon wafers is used. 4. The method according to claim 1 to 3, characterized in that a computer-aided analysis of the measured values and the Comparison of the data obtained in this way with the data of one Fault database captured by a process computer, stored and is evaluated. 5. The method according to claim 1 to 4, characterized in that the specimen after every single processing step in a production line for the production of Silicon single crystals and silicon wafers are examined can. 6. The method according to claim 1 to 5, characterized in that the method with other methods of detection and Characterization of crystal defects can be combined. 7. Device for quick, non-destructive detection and Characterization of crystal defects in monocrystalline Semiconductor material comprising a µ-Raman spectrometer, a Holding and transport device and a process computer.