RU34744U1 - Device for determining the presence of elastic deformations in single-crystal plates - Google Patents

Description

Device for determining the presence of elastic deformations in single-crystal plates

The proposed utility model relates to x-ray means for detecting the presence of elastic deformations in single-crystal wafers and is intended, in particular, for use in monitoring the production of substrates for microcircuits in microelectronics.

A device is known for detecting the presence of elastic deformations in a single crystal, using which a method based on the interaction with a single crystal of monochromatic infrared radiation is implemented (see: Y. Kawano et. AL, Infra Red System GaAs / AlGaAs., J.Appl. Phys. 2001 , 89, p. 4037 1). In places of violation of the periodicity and orientation of the crystal lattice, interference maxima of infrared radiation are detected by semiconductor sensors. In single-crystal materials with metal interatomic bonds (germanium, silicon, arsenic, etc.), the transfer of thermal vibrations along them leads to a smearing of these maxima and an increase in the background until they merge. This makes it impossible to use this device in the production of single crystal wafers of a wide range.

A device is also known by which an x-ray method is implemented to detect the presence of elastic deformations in single-crystal plates (see: O. Brimmer. Zeitschrift fur Naturforschungen, 15A, s. 875, 1960 2). This method is based on identifying

 23/20 deviations in the mutual orientation of crystallographic planes.

The surface of the single crystal plate is irradiated with a widely diverging x-ray beam. Diffracted radiation is recorded on a flat film. The recorded interference diffraction pattern is compared with the pattern obtained from a reference single crystal plate, and the presence or absence of elastic deformations in a controlled single crystal plate is judged by the degree of discrepancy. The angular divergence of the irradiating beam is set in such a way as to ensure the fulfillment of the diffraction conditions for two to three families of crystallographic planes. The device known from 2, contains means for positioning a monocrystalline controlled plate and an x-ray source with a means of forming a beam of this radiation. The formed beam is oriented with the possibility of exposure to x-ray radiation on a monocrystalline controlled plate placed in a means for its positioning. The device also contains means for recording the interference pattern of diffraction, which is a film.

For the most commonly used materials of single-crystal plates, the angular divergence of the irradiating beam can reach 30–40 °. The use of a beam with such a large divergence entails a large irradiated surface area of a single-crystal plate participating in diffraction, and, as a result, leads to the formation of an averaged interference pattern caused by diffraction at different geometric points of the surface. Therefore, an unambiguous interpretation of the interference diffraction pattern recorded on the film is difficult. As a consequence, the probability of erroneous control results is high. In addition, when using photographic film as a means for recording the interference pattern to simultaneously satisfy the requirements for resolution 37NII7 /

2

Longer exposure times, up to several hours, are necessary for stitching and contrast. This is a fundamental obstacle to continuous monitoring in line production, forcing it to be limited to spot inspection of a small number of plates.

The device known from 2 is closest to the proposed utility model.

The proposed utility model provides a technical result consisting in increasing the reliability of control and ensuring its expressness, which creates the possibility of continuous control of single-crystal plates at different stages of the production process. Below, when disclosing the device proposed as a utility model and describing examples of its specific implementation, other types of technical result achieved will be named.

The device proposed as a utility model, as well as the one closest to it, known from 2, comprises means for positioning a monocrystalline controlled plate and an x-ray source with a means for generating a beam of this radiation. The formed beam is oriented with the possibility of exposure to x-ray radiation on a monocrystalline controlled plate placed in a means for its positioning. The device also contains means for recording the interference pattern of diffraction.

To achieve the above types of technical result in the proposed device as a useful model, in contrast to the specified closest to it, the means of forming a beam of x-ray radiation to act on a controlled single crystal plate is made in the form of a converging beam of a focusing x-ray lens. The lens is mounted with the possibility of arranging its output focus inside the monocrystalline wafer being controlled or from the opposite side with respect to the one onto which said beam falls. The focusing x-ray lens, in addition, is installed with the possibility of simultaneous diffraction for several crystallographic planes. Moreover, the means for recording the interference pattern of diffraction contains one or more position-sensitive x-ray detectors installed with the possibility of receiving diffracted radiation in the entire range of angles containing interference maxima corresponding to reflections from the crystallographic planes of the material of the monocrystalline wafer in the form of a PCC, where n is equal to H , K or L and is different for different crystallographic planes.

The use of a converging x-ray beam, the rays of which intersect at a point located inside the monocrystalline wafer being monitored or from the opposite side to the one onto which the specified beam falls, and the presence of a focusing x-ray lens forming such a beam in the proposed device is necessary to ensure local exposure . This makes it possible to exclude the formation of an averaged interference diffraction pattern and to scan the surface of a single-crystal plate in order to obtain the distribution of elastic strains.

The use of the proposed device of reflections from crystallographic planes of the pKK type, where n can correspond to H, K or L, is necessary to simultaneously hit these planes in the reflecting position and to ensure that the common plane of their normals coincides with the diffraction plane. This, in turn, makes it possible to control changes in diffraction angles for families of crystallographic planes that are sequentially tilted to a larger angle

Щ) (with increasing index n) relative to the surface of a single-crystal plate. In the presence of elastic strains in a single crystal plate, the influence of the slope of the diffraction planes relative to the surface on the change in the diffraction angle has a known dependence, which allows one to quantify the value of elastic strains. The use of position-sensitive x-ray detectors in the proposed device for recording the interference pattern of diffraction provides high accuracy and express analysis, the ability to pair with high-speed computing tools for the automated processing of information contained in the output signals of the detectors, and display its results. The proposed device and its use are illustrated by drawings, which show: in FIG. 1 is a diagram of a diffraction pattern formation; in FIG. 2 - simultaneous reflections by several crystallographic planes; in FIG. 3 - differences in the angular positions of the normals to the planes and the angular positions of interference reflexes for different reflecting planes; in FIG. 4 - geometric relationships for calculating the angular positions of the normal to the reflecting plane with pKK indices; in FIG. 5 and FIG. 6 - mutual arrangement of the nodes of the proposed device for two cases of the location of the point of intersection of the rays of a converging x-ray beam using one extended position-sensitive detector; Msi /

in FIG. 7 a and b - the mutual placement of the main nodes of the proposed device when using multiple position-sensitive detectors;

in FIG. 8 and FIG. 9 - respectively, the simultaneous diffraction from planes 111, 511 and planes 111, 311 at different values of the convergence of the beam acting on the single crystal plate.

When using the proposed device (see Fig. 1), a monocrystalline wafer 1 is exposed to a converging x-ray beam 3 and the interference diffraction pattern is recorded by a position-sensitive detector (or several position-sensitive detectors). Position-sensitive detectors are placed so that their windows are in plane 5, perpendicular to the surface of the single crystal plate 1. In addition, position-sensitive detectors should be placed so that the expected positions of interference maxima 7 for the material of the controlled plates are within their windows, taking into account their possible changes in the presence of elastic deformations. The number of position-sensitive detectors used depends on the window size of the specific position-sensitive detectors available to the researcher. If there is one position-sensitive detector with an extended window, for example, curved along an arc of a circle to which a large angle corresponds, then one such detector may be sufficient. It is necessary that a single or several detectors provide reception of diffracted radiation in the angular range, including all interference maxima for the selected system of crystallographic planes.

IW of a single-crystal plate 1) with traces of intersection of the diffraction cones 6 with the detection plane 5. Using one or more position-sensitive detectors, the relative positions of these maxima are determined and the presence of elastic deformations in a monocrystalline wafer is judged by it. The impact on the monocrystalline controlled plate is carried out by a converging X-ray beam 3 generated by an X-ray focusing lens (Kumakhov lens, see, for example, US Pat. No. 5,192,869, publ. 09.03.93 3). The point of intersection of the rays of this beam (the output focus of the x-ray lens) should be located inside the monocrystalline plate 1 being monitored or on the opposite side with respect to the one onto which the indicated converging x-ray beam 3 falls (for the horizontal position of the plate 1 and beam 3 incident on it on top, as in Fig. 1, inside or under the plate 1). A convergent x-ray beam 3 can also be obtained using curved single crystals, multilayer nanocoatings, but most efficiently using multicapillary optics based on the principle of total external reflection of x-rays (Kumakhov focusing x-ray lens 3). The presence of crystallographic planes in any single crystal plate with the last two homonymous indices of the form pX, where n can take the values of H, K or L (which do not coincide for different planes), leads to the following. When one of these planes is brought into a position parallel to the surface of the monocrystalline plate under study (so that the diffraction plane orthogonal to this surface coincides with the crystallographic plane of the PCC perpendicular to the PCC planes), simultaneous diffraction from those PCC planes that have 3 X-rays in the converging cone find a beam with an angle of incidence on them that satisfies the diffraction equation 2dsin0 pA, where d is the interplanar

the distance for the reflecting family of planes, A, is the wavelength of the incident X-ray radiation, n is the order of reflection, 0 is the diffraction angle. In FIG. 2, the OCC plane coinciding with the diffraction plane is indicated by the number 4 and is the diagonal plane of the cube. The planes 111, 311, 511 are chosen as an example. The planes 111 and 511 in the production of single-crystal silicon wafers, depending on the tasks, are basic, that is, brought to a position parallel to the surface of the single-crystal plate. Most often, single-crystal silicon wafers are produced with a base plane 111, therefore, in FIG. 2 and further, it is this case that is considered, although all the arguments remain valid for the case with the base plane 511.

Formed by an X-ray focusing lens 11 (only its output end 2 is shown in Fig. 2), a converging x-ray beam 3 with an angle of convergence irradiates a very small surface area — irradiation zone 8 of a single crystal plate 1. According to the above basic diffraction equation of the total number of x-rays in a convergent beam 3, each plane (111, 311, 511) “chooses for itself a suitable X-ray beam incident on it at a certain angle to meet the diffraction condition. If the angle at the convergence of beam 3 is sufficient to contain such rays for all the indicated planes, each of them gives reflection 6 at the angle of diffraction to this crystallographic plane. Having drawn circle 9 in plane 4 with a center in the irradiation zone 8 of the single-crystal plate 1, it is possible to install a position-sensitive detector (s) in equally spaced regions of the irradiation zone 7 to simultaneously fix the entire interference diffraction pattern in plane 4.

8

If the angle between the crystallographic planes KKK and 1 ZhK is designated a (see Fig. 3), then for a cubic lattice in the general case, the angle between the planes with indices hi ki li and h2 k2 b can be found by the formula:

cos "h .. + U.

/ 72 72 j2 / 72 72 j2.

, + /, V / Z2 + A: 2 + / 2

This is the angle between the NI and M2 normals to the NCC and NCC planes (Fig. 3), but it is not at all equal to the angular distance between interference maxima during diffraction from the NAC and NCC planes, which also depends on the interplanar distance d, which is different for the NCC and NCC planes . However, the converging beam 3, formed by the X-ray lens 11, falling into zone 8 on the surface of the single crystal wafer 1 with the KKK base plane and having a beam inside it, which hits the system of NKK planes at the diffraction angle to these planes, will deviate by a completely different angle than from the system planes KKK conditionally deployed at an angle a and reduced to the NCC position.

In the general case, it is necessary to start from the trigonometric relations illustrated in FIG. 4.

This drawing shows a single cube, the orientation of which in an ideal single crystal relative to the surface depends on the coordinate system. We denote the angle of inclination of the normal to the reflecting planes not parallel to the surface, by a, that is, a is the angle between the normals ANi and AX to the planes under study. The diffraction plane in this case is the ANiX plane. If, as a result of elastic deformations of the crystal lattice of a single-crystal plate, the ANiX plane tilts relative to the normal ANi by an angle p, that is, it moves to the AN2T position, and, accordingly, the direction AX becomes iMb L, it becomes the direction AT, then the angle for the angle y between the new normal AT

the investigated plane and the normal ANi, you can get the following formula: COS 7

10

1

tg / + 1

using this formula to change the angle of inclination of the normal for each angle of inclination of the diffraction plane, you can find the angle of inclination T (3 diffraction planes, at which it is necessary to obtain the desired direction of the projection of the normal onto the surface of the single crystal, that is, to solve the inverse problem: determine the angle P from the angle y, knowing the angle a. In other words, it is possible not only to measure the elastic deformation of the crystal lattice of the investigated single-crystal plate with a smaller number of exposures by setting a position-sensitive sensor in advance detector at the calculated angle, but also determine the deformations in the directions for the anisotropic problem.

A number of experts interpret elastic deformations in a single crystal as the presence of stresses in it. In view of this interpretation, the present invention is also suitable for determining the presence of such stresses.

The proposed device for determining the presence of elastic deformations in single crystal plates (Fig. 5) contains an x-ray tube 12, an x-ray lens 11 with an output end 2 for forming a converging x-ray beam 3, a two-coordinate positioning system 14 of the studied single-crystal plate 1 and a position-sensitive detector 13 or a set of positional sensitive detectors placed on one arc opposite the expected positions of interference diffraction maxima from the studied crystallographic eskih planes. Forming Tool

an X-ray beam for influencing a monocrystalline plate under control - an X-ray lens 11 - is configured to form a converging knot 3. The intersection point of the rays of this beam (output focus of the lens And) is located inside (below the surface) of the monocrystalline plate 1 (Fig. 5) or under this plate. If this point goes deep below the surface or when it leaves the opposite side of the monocrystalline wafer in relation to the one onto which beam 3 falls (Fig. 6), the size of the irradiation zone 8 on the wafer surface 1 increases. In this case, the data on elastic deformations the crystal lattices are averaged over a controlled area, the interference maximums of diffraction become wider, maintaining the coordinate of the center of gravity of the maximum only at large diffraction angles. In FIG. Figure 6 shows how the asymmetry of the CCC reflection increases markedly with respect to the CCC reflections, and, especially, the LKK reflection. A significant further increase in the irradiation zone leads to the same errors in the control of elastic deformations in the crystal lattice of a single-crystal plate, which are characteristic of the known medium 2, which is closest to the proposed one.

The interference maxima corresponding to the reflections from the crystallographic planes of the material of the monocrystalline controlled, having the form of a PCC, where n can take the values of H, K or L (different for different crystallographic planes selected), can be detected by two position-sensitive detectors (Fig. 1a and one with large angle of simultaneous registration. On the other hand from the x-ray tube

12 with a lens 11, if installed at large angles of reflection (Fig. 76), another position-sensitive detector 13 can be placed. Layout schemes of position-sensitive detectors

monocrystalline wafer 1 on the supporting arc 15 may be different depending on the objectives of the study. All angles of mutual disorientation of the crystallographic planes of the pKK type are always counted from the base plane of the KKK single crystal wafer or any of the pKK, depending on the manufacture of the wafers. The error in bringing the crystallographic plane to the base plane is established on an X-ray diffractometer-comparator and is entered in the passport of a series of semi-finished single-crystal plates at the first stage of their production. The process of determining the presence of elastic deformations in single-crystal plates using the proposed device can be automated. To do this, when using the device, the outputs of one or more position-sensitive detectors included in its composition are connected to the means for processing their output signals and displaying the information resulting from the processing. This tool is made with the possibility of determining the relative position of the indicated interference maxima and comparing it with the reference for the specified system of crystallographic planes of the material of the monocrystalline controlled plate. Using an example of single-crystal silicon wafers with a base plane of 111, we tested and demonstrated the possibility of obtaining a diffraction pattern and determining the relative orientation of the crystallographic planes 111, 311, 511 by shifting the centers of gravity of their interference maxima even when using X-ray lenses with low angular convergence for X-ray tubes with an anode of cobalt. Pa fig. 8 shows simultaneous diffraction from planes 111 and 511 at angular convergence at 4 °, and in FIG. 9 - simultaneous diffraction from the planes 111 and 311 at an angular convergence of 3 ° for x-ray tubes with an anode of vanadium. When using X-ray 12

lenses with angular convergence at ° for a silicon single-crystal wafer, the conditions of simultaneous diffraction for the planes 111,311,511 can be fulfilled.

The same conditions for simultaneous diffraction from the planes 111.311 and 511 for silicon single-crystal wafers can also be satisfied when using an x-ray lens with an angular convergence of less than 5 °. For this, it is necessary to use an X-ray tube with a mixed Co-V anode. Then the two Ka wavelengths present in the primary X-ray beam — the Co and V series — will not only allow us to obtain a simultaneous interference diffraction pattern from the indicated planes, but also to obtain it at two different wavelengths. This is especially important, since the presence of simultaneous reflection from the crystallographic planes 111 in cobalt and vanadium radiation gives the most accurate natural standard for angular measurements of all other quantities. The interference maxima do not overlap, and the planes 111 and 511 reflect in the Co radiation, and in the V radiation

Ka - planes 111 and 311.

in experiments using a 10 W x-ray tube and x-ray lenses having the above-mentioned convergence angles of the formed beam, the centers of gravity of interference maxima were determined with an error of 12 arc seconds at exposure times of up to 20 seconds,

Sources of information

1.Y. Kawano et. Al., Infra Red System GaAs / AlGaAs., J. Appl. Phys. 2001, 89, p. 4037.

2.O. Brummer. Zeitschrift ftir Naturforschungen, ISA, s. 875.1960.

Claims (1)

A device for determining the presence of elastic deformations in single crystal wafers, comprising a means for positioning a monocrystalline wafer and a source of x-ray radiation with means for generating a beam of this radiation oriented with the possibility of influencing the monocrystalline wafer placed in the means for positioning it, as well as means for detecting interference diffraction pattern, characterized in that the means of forming a beam of x-ray The radiation for influencing the monocrystalline wafer under control is made in the form of a focusing x-ray lens forming a converging beam, mounted with the possibility of positioning its output focus inside the monocrystalline wafer or on the opposite side with respect to the one onto which the specified beam, and with the possibility of simultaneous diffraction for several crystallographic planes, and the means for recording the interference pattern of diffraction contains one or several position-sensitive X-ray detectors installed with the possibility of receiving diffracted radiation in the entire range of angles containing interference maxima corresponding to reflections from the crystallographic planes of the material of the monocrystalline plate under control, having the form nKK, where n is H, K or L and is not the same for different crystallographic planes.