Patent Number: 
Section: description

First of all, the expression of crystal lattice plane indices (Miller indices) will be briefly explained. A germanium crystal and a silicon crystal, which are used in embodiments of the invention, each has a crystal structure of cubic lattice, so that there are six lattice planes equivalent to (100) plane. These equivalent planes are represented by {100} in general. Similarly, there are six directions equivalent to [100] direction, these equivalent directions being represented by  less than 100 greater than . This specification uses such general expressions. FIG. 1 is a plan view of the first embodiment of the invention and FIG. 2 is its perspective view. Referring to FIG. 2, a channel-cut monochromator 10 is made of a germanium single crystal block. The block is a parallelepiped of 35 mm long, 20 mm wide and 25 mm high and has five kinds of reflecting surface pairs formed by processing grooves on the block. Each groove is 20 mm deep and therefore each reflecting surface is 20 mm high. The channel-cut monochromator has a bottom surface which can be a reference plane. The block has been cut so as to be a parallelepiped having a crystallographic axis shown in FIG. 2. That is, a longitudinal edge 52 is parallel to  less than 100 greater than  direction, a lateral edge 54 is parallel to  less than 110 greater than  direction and a vertical edge 56 is parallel to  less than 110 greater than  direction. The grooves can be machined by a diamond wheel machine, a diamond-tool NC milling machine or a supersonic processing machine. Referring to FIG. 1, the first reflecting surface pair 11 is composed of two reflecting surfaces 12 and 14 parallel to each other for diffracting X-rays by Ge{220} or Ge{440} plane. That is, the reflecting surfaces 12 and 14 are so processed as to be parallel to {220} and {440} planes of germanium single crystal. The {220} and {440} planes are parallel to each other and are different in interplaner spacing (d-value) only. The reflecting surfaces 12 and 14 are parallel to a longitudinal side 90 of the single crystal block. The second reflecting surface pair 16 is composed of two reflecting surfaces 18 and 20 parallel to each other for diffracting X-rays by Ge {400} plane. That is, the reflecting surfaces 18 and 20 are so processed as to be parallel to {400} plane of germanium single crystal. The reflecting surfaces 18 and 20 are perpendicular to the longitudinal side 90. The third reflecting surface pair 22 is composed of two reflecting surfaces 24 and 26 parallel to each other for diffracting X-rays by Ge {422} plane. That is, the reflecting surfaces 24 and 26 are so processed as to be parallel to {422} plane of germanium single crystal. The reflecting surfaces 24 and 26 are inclined by 54.7 degrees to the longitudinal side 90. The fourth reflecting surface pair 28 is composed of two reflecting surfaces 30 and 32 parallel to each other for diffracting X-rays by Ge {511} plane. That is, the reflecting surfaces 30 and 32 are so processed as to be parallel to {511} plane of germanium single crystal. The reflecting surfaces 30 and 32 are inclined by 74.4 degrees to the longitudinal side 90. The fifth reflecting surface pair 34 is composed of two reflecting surfaces 36 and 38 parallel to each other for diffracting X-rays by Ge {111} plane. Although the reflecting surface 36 is parallel to {111} plane of germanium single crystal, the other reflecting surface 38 is not parallel to {111} plane of germanium single crystal. That is, the reflecting surface 38 is an asymmetrical reflecting surface for condensing a beam width. The reflecting surface 36 is inclined by 35.3 degrees to the longitudinal side 90. There is a direct path between the two reflecting surfaces 12 and 14 of the first reflecting surface pair 11. An X-ray beam 42 can pass through the direct path in no contact with any reflecting surfaces. Surfaces other than the reflecting surfaces mentioned above, for example, side surfaces 86 and 88 shown in FIG. 3, have been suitably cut off so as not to intercept various incident X-ray beams and output X-ray beams. In FIG. 1, the channel-cut monochromator 10 can be rotated around an axis of rotation 40 which extends perpendicularly to the drawing sheet. The five kinds of reflecting surface pairs are designed based on an imaginary circle 46 whose center coincides with the axis of rotation 40. That is, each reflecting surface pair is so designed that an X-ray beam incident on the reflecting surface pair or its extension line is tangent to the imaginary circle 46 whose radius is 2.5 mm. In this embodiment, an X-ray beam is reflected two times (i.e., one time at each reflecting surface of the pair) at all of the five kinds of reflecting surface pairs and then goes out from the monochromator. Each reflection surface of the five kinds of reflection surface pairs is perpendicular to the reference plane. The axis of rotation 40 of the monochromator is also perpendicular to the reference plane. FIG. 3 is a plan view showing a manner in which X-rays coming from in seven kinds of directions are reflected by or pass through the channel-cut monochromator shown in FIG. 1. The X-ray beam indicated by xe2x80x9cdirectxe2x80x9d is to pass through the monochromator 10 in no contact with any reflecting surface. The X-ray beam indicated by xe2x80x9c220xe2x80x9d is to be reflected by {220} plane of germanium crystal. Similarly, the X-ray beams indicated by 440, 400, 422, 511 and 111 are to be reflected by {440}, {400}, {422}, {511} and {111} planes of germanium crystal. It is noted that a direction perpendicular to the drawing sheet coincides with  less than 110 greater than  direction of the germanium crystal. Although FIG. 3 shows various directions of incident X-ray beams with the channel-cut monochromator 10 being stationary, the incident X-ray beam is generally always in the same direction in the actual high-resolution X-ray diffractometer, so that the channel-cut monochromator 10 is rotated to alter the direction of the incident X-ray beam to the monochromator. There will be described hereinafter, with referring to drawings, the seven states of monochromator rotation for seven directions of the incident X-ray beams. FIG. 4 shows a state in which an X-ray beam 42 passes through the direct path. The channel-cut monochromator 10 is so rotated and adjusted around the axis of rotation 40 that the reflecting surfaces 12 and 14 become parallel to the X-ray beam 42. The X-ray beam 42 passes through the channel-cut monochromator 10 so as to be tangent to the imaginary circle 46, so that the X-ray beam 42 is in no contact with any reflecting surface. The distance between the reflecting surface 12 and the X-ray beam 42 is 1 mm. This direct beam is usable for X-ray diffraction measurement of a polycrystalline thin film. FIG. 5 shows a state in which an X-ray beam is diffracted by {220} plane of germanium crystal. The channel-cut monochromator 10 is so rotated around the axis of rotation 40 that the first reflecting surface 12 of the first reflecting surface pair is inclined by 22.65 degrees to the X-ray beam 42. Stating in detail, the channel-cut monochromator 10 is rotated clockwise by 22.65 degrees from the state shown in FIG. 4. The X-ray incident angle value to the first reflecting surface 12 is determined by the wavelength of the used characteristic X-ray (CuKxcex11 in the embodiment), the d-value of {220} plane of germanium crystal and the Bragg""s law. The X-ray beam 42 is incident so as to be tangent to the imaginary circle 46. The X-ray beam 42 is incident on the first reflecting surface 12 and diffracted by {220} plane of germanium crystal and then is incident on the second reflecting surface 14 and similarly diffracted by {220} plane to go out as an output X-ray beam 48. The X-ray beam 48 becomes parallel to the incident X-ray beam 42 but is shifted translationally by a distance L. Therefore, if an X-ray beam was incident on the desired region of a sample in the state shown in FIG. 4, it is necessary to shift the sample translationally by the distance L for irradiating the same desired region when the optical system is altered to the state shown in FIG. 5. Of course, the X-ray source requires no movement. An X-ray beam from this {220} reflection has comparatively a high intensity and is suitable for reflection coefficient measurement (near the total reflection region with glancing incident angles). The {220} reflection is also suitable for the four-crystal monochromator, as shown in FIG. 11 explained below, for obtaining the rocking curve. FIG. 6 shows a state in which an X-ray beam is diffracted by {440} plane of germanium crystal. A reflecting surface pair to be used is the first reflecting surface pair (reflecting surfaces 12 and 14) which is the same pair as for {220} reflection shown in FIG. 5. Since {440} plane and {220} plane are parallel to each other, the same reflection surface pair can be used, noting that the d-values are different so that the incident angle of the X-ray beam 42 to the reflecting surface 12 should be altered. That is, the channel-cut monochromator 10 is so rotated around the axis of rotation 40 that the first reflecting surface 12 is inclined by 50.38 degrees to the X-ray beam 42. Stating in detail, the channel-cut monochromator 10 is rotated clockwise by 50.38 degrees from the state shown in FIG. 4. The X-ray beam 42 is incident so as to be tangent to the imaginary circle 46. The X-ray beam 42 is incident on the first reflecting surface 12 and diffracted by {440} plane of germanium crystal and then is incident on the second reflecting surface 14 and similarly diffracted by {440} plane to go out as an output X-ray beam 48. The X-ray beam 48 becomes parallel to the incident X-ray beam 42 but is shifted translationally by a distance which is different from that in FIG. 5. An X-ray beam from this {440} reflection has a lower intensity than that from {220} reflection but a high resolution and is suitable for the four-crystal monochromator, as shown in FIG. 11 explained below, for obtaining rocking curves. FIG. 7 shows a state in which an X-ray beam is diffracted by {400} plane of germanium crystal. The channel-cut monochromator 10 is so rotated around the axis of rotation 40 that the first reflecting surface 18 of the second reflecting surface pair is inclined by 33.0 degrees to the X-ray beam 42. Stating in detail, the channel-cut monochromator 10 is rotated counterclockwise by 57.0 degrees from the state shown in FIG. 4. The X-ray beam 42 is incident so that its extension line 50 is tangent to the imaginary circle 46. The X-ray beam 42 is incident on the first reflecting surface 18 and diffracted by {400} plane of germanium crystal and then is incident on the second reflecting surface 20 and similarly diffracted by {400} plane to go out as an output X-ray beam 48. An X-ray beam from this {400} reflection is suitable for obtaining rocking curves with the quasi parallel arrangement. That is, when the rocking curve of GaAs {400} plane (or an epitaxial layer growing thereon) is measured, an X-ray beam diffracted by {400} plane of germanium crystal can be used to make the quasi parallel arrangement of the double crystal method. The d-value of {400} plane of germanium crystal is close to the d-value of GaAs {400} plane to be measured. FIG. 8 shows a state in which an X-ray beam is diffracted by {422} plane of germanium crystal. The channel-cut monochromator 10 is so rotated around the axis of rotation 40 that the first reflecting surface 24 of the third reflecting surface pair is inclined by 41.84 degrees to the X-ray beam 42. Stating in detail, the channel-cut monochromator 10 is rotated counterclockwise by 83.46 degrees from the state shown in FIG. 4. The X-ray beam 42 is incident so that its extension line is tangent to the imaginary circle 46. The X-ray beam 42 is incident on the first reflecting surface 24 and diffracted by {422} plane of germanium crystal and then is incident on the second reflecting surface 26 and similarly diffracted by {422} plane to go out as an output X-ray beam 48. An X-ray beam from this {422} reflection is suitable for obtaining rocking curves with the quasi parallel arrangement. That is, when the rocking curve of an asymmetrical {422} plane of GaAs (or an epitaxial layer growing thereon) is measured, an X-ray beam diffracted by {422} plane of germanium crystal can be used to make the quasi parallel arrangement of the double crystal method. FIG. 9 shows a state in which an X-ray beam is diffracted by {511} plane of germanium crystal. The channel-cut monochromator 10 is so rotated around the axis of rotation 40 that the first reflecting surface 30 of the fourth reflecting surface pair is inclined by 45.03 degrees to the X-ray beam 42. Stating in detail, the channel-cut monochromator 10 is rotated counterclockwise by 29.37 degrees from the state shown in FIG. 4. The X-ray beam 42 is incident so that its extension line 50 is tangent to the imaginary circle 46. The X-ray beam 42 is incident on the first reflecting surface 30 and diffracted by {511} plane of germanium crystal and then is incident on the second reflecting surface 32 and similarly diffracted by {511} plane to go out as an output X-ray beam 48. An X-ray beam from this {511} reflection is suitable for obtaining rocking curves with the quasi parallel arrangement. That is, when the rocking curve of an asymmetrical {511} plane of GaAs (or an epitaxial layer growing thereon) is measured, an X-ray beam diffracted by {511} plane of germanium crystal can be used to make the quasi parallel arrangement of the double crystal method. FIG. 10a shows a state in which an X-ray beam is diffracted by {111} plane of germanium crystal. The channel-cut monochromator 10 is so rotated around the axis of rotation 40 that the first reflecting surface 36 of the fifth reflecting surface pair is inclined by 13.64 degrees to the X-ray beam 42. Stating in detail, the channel-cut monochromator 10 is rotated clockwise by 158.34 degrees from the state shown in FIG. 4. The X-ray beam 42 is incident so that its extension line is tangent to the imaginary circle 46. The X-ray beam 42 is incident on the first reflecting surface 36 and diffracted by {111} plane of germanium crystal and then is incident on the second reflecting surface 38 which is not parallel to the first reflecting surface 36 as described in detail below. FIG. 10b is an enlarged plan view of the vicinity of the fifth reflecting surface pair. Although the first reflecting surface 36 is parallel to {111} plane 58 of the germanium crystal, the second reflecting surface 38 is inclined counterclockwise by xcex1=10.7 degrees to {111} plane 58. When an X-ray beam is diffracted by {111} plane 58 of the germanium crystal at the second reflecting surface 38, the X-ray beam width is condensed to one eighth. That is, the beam width W2 of the output X-ray beam 48 becomes one eighth of the beam width W1 of the incident X-ray beam 42. For example, when the beam width of the incident X-ray beam 42 is 0.8 mm, the beam width of the output X-ray beam 48 becomes 0.1 mm. The condensed X-ray beam 48 from this asymmetrical {111} reflection has comparatively a high intensity and is suitable for reflection coefficient measurement. The fifth reflecting surface pair may have two asymmetrical reflecting surfaces. FIG. 18 is an enlarged plan view showing such a modification. The first reflecting surface 60 is inclined clockwise by 7.2 degrees to {111} plane 58 of the germanium crystal while the second reflecting surface 62 is inclined counterclockwise by 7.2 degrees to {111} plane 58 of the germanium crystal. An incident X-ray beam 42 is diffracted by {111} plane 58 at the first reflecting surface 60 to have a beam width condensed to {fraction (1/3.16)} (a square root of one tenth). It is further diffracted by {111} plane 58 also at the second reflecting surface 62 to have a beam width further condensed to {fraction (1/3.16)} (a square root of one tenth). As a result, the beam width W2 of the output X-ray beam 48 becomes one tenth of the beam width W1 of the incident X-ray beam 42. The channel-cut monochromator according to the invention may include two or more kinds of reflecting surface pairs each having one or two asymmetrical reflecting surface. Besides, not only the condensing-type asymmetrical reflecting surface but also the expanding-type asymmetrical reflecting surface may be used. The channel-cut monochromator shown in FIG. 1 may be combined with itself to form the four-crystal monochromator. FIG. 11 is a plan view showing such an application. Two channel-cut monochromators 10a and 10b are arranged so as to be mirror symmetrical. Each channel-cut monochromator is so adjusted in posture that X-rays are diffracted by {220} plane of germanium crystal. An incident X-ray beam 42 is reflected by the first reflecting surface pair of the first channel-cut monochromator 10a and further reflected by the first reflecting surface pair of the second channel-cut monochromator 10b to go out as an output X-ray beam 48. The output X-ray beam 48 is on the same straight line as the incident X-ray beam 42. It is noted that the right-side channel-cut monochromator 10b may be an ordinary channel-cut monochromator having only one reflecting surface pair for {220} reflection. In stead of {220} reflection, {440} reflection of the germanium crystal may be combined with itself similarly to form the four-crystal monochromator. Although the channel-cut monochromator 10 is made of germanium single crystal in the embodiment described above, it may be made of silicon single crystal. X-ray beams reflected by {400}, {422} and {511} planes of the silicon crystal are usable, as in the case of germanium, for measurement of GaAs samples with the quasi parallel arrangement of the double crystal method. Next, the second embodiment of the invention will be explained by referring to FIG. 12 showing a plan view of the second embodiment and FIG. 13 showing its perspective illustration. In FIG. 12, A hybrid-type channel-cut monochromator 67 is composed of a channel-cut monochromator 64 made of silicon single crystal and a channel-cut monochromator 66 made of germanium single crystal united (bonded) to each other to form an integral unit. The two channel-cut monochromators 64 and 66 have the same shape and are united so as to be centrosymmetrical around the axis of rotation 40. The hybrid-type channel-cut monochromator 67 is expected to measure silicon or GaAs, which is typical semiconductor crystal, and to obtain rocking curves with the parallel arrangement or the quasi parallel arrangement of the double crystal method. The rocking curve of silicon single crystal (or an epitaxial layer growing thereon) can be measured with the silicon channel-cut monochromator 64 in the parallel arrangement of the double crystal method, while the rocking curve of GaAs single crystal (or an epitaxial layer growing thereon) can be measured with the germanium channel-cut monochromator 66 in the quasi parallel arrangement of the double crystal method. There will be explained first a shape of the silicon channel-cut monochromator 64. The first reflecting surface pair 68 is composed of two reflecting surfaces 70 and 72 parallel to each other for diffracting X-rays by {400} plane of silicon crystal. The second reflecting surface pair 74 is composed of two reflecting surfaces 76 and 78 parallel to each other for diffracting X-rays by {422} plane of silicon crystal. The third reflecting surface pair 80 is composed of two reflecting surfaces 82 and 84 parallel to each other for diffracting X-rays by {511} plane of silicon crystal. The three kinds of reflecting surface pairs are designed based on an imaginary circle 46. That is, each reflecting surface pair is so designed that an X-ray beam incident on the reflecting surface pair or its extension line is tangent to the imaginary circle 46, this structure being the same as the first embodiment shown in FIG. 1. The germanium channel-cut monochromator 66 also includes the three kinds of reflecting surface pairs. It is noted that the hybrid-type channel-cut monochromator 67 has no direct path. FIG. 14 is a plan view showing a manner in which X-rays coming from in six kinds of directions are reflected by the hybrid-type channel-cut monochromator 67 shown in FIG. 1. The X-ray beam indicated by xe2x80x9cSi 400xe2x80x9d is to be reflected by {400} plane of silicon crystal. Similarly, the X-ray beams indicated by Si 422 and Si 511 are to be reflected by {422} and {511} planes of silicon crystal. Besides, the X-ray beams indicated by Ge 400, Ge 422 and Ge 511 are to be reflected by {400}, {422} and {511} planes of germanium crystal. It is noted that a direction perpendicular to the drawing sheet coincides with  less than 110 greater than  direction of silicon crystal and germanium crystal. Although FIG. 14 shows various directions of incident X-ray beams with the channel-cut monochromator 67 being stationary, the incident X-ray beams are generally always in the same direction in the actual high-resolution X-ray diffractometer, so that the channel-cut monochromator 67 is rotated to alter the direction of the incident X-ray beam to the monochromator 67. There will be described hereinafter the six states of monochromator rotation for six directions of the incident X-ray beams. FIG. 15 shows a state in which an X-ray beam is diffracted by {511} plane of silicon crystal. FIG. 16 shows a state in which an X-ray beam is diffracted by {400} plane of silicon crystal. FIG. 17 shows a state in which an X-ray beam is diffracted by {422} plane of silicon crystal. In each state, the channel-cut monochromator 67 is so rotated by the predetermined angle around the axis of rotation 40 that each reflecting surface is inclined by the predetermined angle (an incident angle satisfying the Bragg""s law) to the incident X-ray beam. Similarly, using germanium crystal, the channel-cut monochromator 67 is rotated to diffract X-rays by Ge {511} Ge {400} and Ge {422} planes.