JPS62192609A - Depth measuring method for fine irregularity - Google Patents

Abstract

PURPOSE:To take an accurate measurement without being restricted by a visual field by controlling the values of currents supplied to an X-axial and a Y-axial deflecting coils provided on the electron beam passage between an electron gun and a sample independently by an electron beam control part. CONSTITUTION:The image of the sample 3 which has a longitudinal section including a finely irregular part as a surface is magnified by a scanning type electron microscope to measure the depth of the irregularity. At this time, the electron beam control part 4 supplies currents having optional values to the X-axial and Y-axial deflecting coils 8 and 8a, and 9 and 9a arranged opposite each other through X-axial deflecting devices 10 and 11. Thus, the scan amplitude of an electron beam 2 which illuminates the surface of the sample 3 is controlled independently in the X-axial and Y-axial directions. Consequently, the magnification of the image displayed on the screen of a CRT 5 with the secondary electron beam 6 is made larger in the depth direction of the irregularity than in the plane direction. Thus, the irregularity shape is grasped accurately and then the depth is measured; and this kind of measurement is facilitated and the accuracy of information for an analysis of an extremely small area is improved.

Description

[Detailed description of the invention] [Technical field to which the invention pertains]

The present invention relates to a method for measuring the depth of minute irregularities formed on a substrate.

[Prior art and its problems]

For example, thin films with discontinuous steps from the underlying layer, such as wiring or protective films deposited on the surface of semiconductor devices, are difficult to maintain due to the width of wiring, etc., as seen in recent semiconductor devices with increased integration density. When measuring the thickness of such a thin film, which is small and has narrow groove dimensions between the lines, often on the order of - or less, trace the surface of the i with a needle-like contact and measure the step part of the film. Amplify and record the amplitude of the contact, including the
When using the well-known stylus method, which calculates the film thickness from this amplitude, the diameter of the tip of the contact is usually several -
Because of this, it has become difficult to correctly trace the groove portions that form the steps of the thin film with such minute dimensions as described above. Furthermore, it is impossible to reduce the diameter of the tip of the contact so as to suit this purpose. Therefore, a direct observation method involves enlarging a cross-sectional sample of a thin film, including the underlying substrate, cut vertically using an optical microscope or scanning electron microscope, and measuring the film thickness from the enlarged longitudinal cross-sectional shape of the thin film. It is more accurate and effective for measuring thin film thicknesses. For example, if the boundary between the substrate and the film can be clearly observed, such as an aluminum film wired as a wire on the silicon substrate of a semiconductor device, the method for . What is necessary is to enlarge it in the film thickness direction to a size that is easy to measure. However, when measuring the thickness of an epitaxial film used in a semiconductor device, for example, by growing a GaAs epitaxial Full film on a GaAs crystal plate and opening a window in a part of the film, a vertical section sample is prepared and observed under magnification. However, since the substrate and film are made of the same material, the boundary between them does not appear clearly, and this relationship is shown in the schematic cross-sectional view of FIG. When you want to measure the film thickness A of the epitaxial film 13 formed on the GaAs crystal plate 12 in FIG. 2, even if you enlarge the cross-sectional sample, the boundary between the crystal plate 12 and the epitaxial film 13 in FIG. is not clear. Therefore, in this case, the window brightness that serves as the reference line for the measurement of the membrane [A] is at the bottom B.
must be brought into the field of view of a microscope, but with ordinary optical microscopes and scanning electron I! When enlarging an observation sample with a Ji microscope, in the case of a cross-sectional sample whose film thickness is to be measured because it is uniformly enlarged two-dimensionally, if it is enlarged sufficiently large to make it easy to measure the film thickness, Along with this, the film surface direction is also enlarged by the same magnification. For example, in Figure 2, if A is 0.01 pm and the outer diameter of part B is 1 μ-, it will be magnified 400,000 times to make A 4 cranes. When enlarged, part B is 4
0C1l, it does not enter the field of view of an optical microscope or a scanning electron microscope, and the reference line in the direction of the film surface cannot be correctly captured. That is, in such a case, a problem arises in that it is impossible to observe a microscope image with an enlarged cross section due to field of view limitations. Of course, the stylus method cannot be applied as mentioned above. For convenience of explanation, the method and problem of determining the thickness of the epidural membrane have been described above, but in short, in order to measure the depth of minute irregularities, the shape of the cross section is enlarged using a scanning electron microscope and directly measured. It is best to observe it, but when doing so, it is necessary to make sure that the uneven shape is included in the same field of view. It should be noted that minute irregularities are not only formed on the surface, but also apply to cases where they are formed inside the object, such as at the boundaries of joints, for example. The present invention has been made in view of the above-mentioned points, and its purpose is to improve the size of the field of view when measuring the depth of minute irregularities formed on a substrate using a longitudinal section sample. It is an object of the present invention to provide a method that allows easy and accurate measurement by obtaining a microscopic image that is enlarged in the depth direction than in the surface direction without being restricted by the above.

[Key points of the invention]

The present invention uses a scanning electron microscope to irradiate the surface of a cross-sectional sample with an electron beam in a vacuum container, scan an electron probe over the sample surface, and detect secondary electrons emitted from the sample surface.
A secondary electron image is transferred to a CRT (CathodeRay Tub).
e) The current flowing through the X-axis deflection coil and Y-axis deflection coil, which are installed in the electron beam path between the electron gun that generates and accelerates the electron beam and the sample, and which are arranged opposite each other as a pair. By independently controlling the size using the electron beam control unit, even if the magnification in the depth direction (X-axis) of the secondary electron image displayed on the C27 plane is increased, the magnification in the plane direction (Y-axis) The magnification of the image is set so that it can be kept within the observable range.

[Embodiments of the invention]

The present invention will be explained below based on examples. FIG. 1 is a system diagram of an apparatus schematically showing essential parts for explaining a scanning electronic RA microscope used in the present invention. In Fig. 1, an electron beam 2 emitted from an electron gun 1 and accelerated
irradiates the surface of the longitudinal section sample 3 as a finely focused electron probe. While secondary electrons are generated from the sample surface two-dimensionally scanned by an electron probe through interaction with the material constituting the sample 3, the beam of the CRT 5 is generated by the electron beam controller 4 in synchronization with the scanning of the sample surface. If the secondary electrons 6 generated from the sample surface are detected and amplified by the detector 7, and the brightness of the CRT is modulated according to the intensity, the sample image by the detected secondary electrons can be created on the C27 surface. You can get on top. In this process, the scanning electron microscope has X-axis deflection coils 8, 8a and Y-axis deflection coils 9.98, which are arranged as a pair facing each other in the path of the irradiated electrons vA2 between the electron gun 1 and the sample 3. The scanning amplitude of the electron probe on the sample surface is determined by the coil currents from the X-axis electron deflection device 10 and the Y-axis electron deflection device 11, which are arranged perpendicular to each other and connected to the electron beam control unit 4. . The ratio of the scanning amplitude of the beam of the CRT 5 to the scanning amplitude of the electron probe on the sample surface becomes the magnification of the microscope. Therefore, by decreasing the scanning amplitude on the sample surface, the microscope magnification can be increased, and by increasing the scanning amplitude, the microscope magnification can be decreased. In a normal scanning electron microscope, the relationship between the scanning amplitude in the X direction and the scanning amplitude in the Y direction is fixed at 1:l, so the microscopic image is magnified to the same magnification in both the vertical and horizontal directions. In contrast,
The present invention differs from the conventional art in that the X-axis side coils 8, 8a and the Y-axis side coils 9,9a each have an
The electron beam control unit 4, which is capable of passing a current of arbitrary magnitude from the O and YIII electron deflection device 11, controls the current flowing to the X-axis side coil 8.8a and the Y-axis side coils 9, 9a independently of each other. The point is that it is controlled. That is, as a result, microscopic images having independently set vertical magnification and horizontal magnification are displayed on the CRT surface. Therefore, when observing a cross-sectional sample to measure the depth of minute irregularities using a scanning electron microscope, it is necessary to increase the magnification in the depth direction and decrease the magnification in the plane direction as described above. According to the present invention, the required concavo-convex shaped portion can be made to appear within the mirror field of view, and according to the present invention, the depth direction can be approximately 1n11, and the width of the bottom of the concave portion can be formed over a wide range from several nanometers to several tens of nanometers. It becomes possible to actually measure the Since the magnification ratios in both the vertical and horizontal directions can be independently set arbitrarily, it is preferable to set them so as to facilitate measurement according to the actual condition of the sample to be measured. In addition, in FIG. 1, the electron gun 1. Vertical section sample 3° detector 7
．． X-axis side coils 8, 8a, and Y-axis side coils 9.
98 are all arranged in a vacuum container,
In FIG. 1, illustration of the vacuum container is omitted. Further, the irradiation electron beam 2 and the secondary electrons 6 are represented by dotted lines, and their traveling directions are shown by arrows.

【Effect of the invention】

For example, when quantitatively determining the depth of an object with minute irregularities, such as a surface or a joint, a scanning method is used using a sample whose surface is a longitudinal section of the object, including the irregularities. Electronic S! It is preferable to perform magnified observation and length measurement using a JIm mirror, but in the conventional method, the image magnified with a microscope is
Since it will be enlarged to the same size in both the axial direction and the Y-axis direction,
If the depth direction of the uneven part is magnified sufficiently to make it easy to measure the length, the planar direction is also enlarged more than necessary and it becomes impossible to capture the same field of view, making it impossible to accurately capture the uneven shape.In contrast, in the present invention, the embodiment As mentioned above, by controlling the magnitude of the current flowing through the X-axis deflection coil and Y-axis deflection coil of a scanning electron microscope, the scanning amplitude of the electron probe on the sample surface can be adjusted in the X-axis direction and the Y-axis direction. Since the microscopic image is displayed on the CRT screen by setting each direction independently, even if the magnification is sufficiently large to facilitate length measurement in the depth direction of the unevenness, the image in the plane direction will not be visible from the field of view. Since the magnification ratio in the plane direction can be reduced to the extent that deviation does not occur, it is possible to measure the depth after accurately grasping the uneven shape. This type of measurement is easy to perform, and it is also possible to This improves the accuracy of information obtained when performing analysis.

[Brief explanation of drawings]

FIG. 1 is a system diagram of essential parts of a scanning electron microscope, and FIG. 2 is a schematic cross-sectional view of a semiconductor element. 1: Electron gun, 2: Irradiation electron beam, 3: Longitudinal section sample, 4: Electron beam control section, 5: CRT, 6: Secondary electron, 7: Detector, 8.8as X-axis deflection coil, 9, 9a: Y-axis deflection coil, 10: X-axis electron deflection device, 11: Y-axis electron deflection device.

Claims (1)

[Claims] 1) Using a sample whose surface is a vertical cross section of an object having minute irregularities, the irregular shape is enlarged using a scanning electron microscope, and the depth of the irregularities is measured using electron beam control. A current of an arbitrary magnitude is passed through an X-axis electron deflection device and a Y-axis electron deflection device, respectively, to the X-axis deflection coil and the Y-axis deflection coil, which are arranged facing each other as a pair, to generate electrons that irradiate the sample surface. By independently controlling the scanning amplitude of the line in the X-axis direction and the Y-axis direction, the magnification ratio of the secondary electron image displayed on the CRT surface is made larger in the depth direction than in the plane direction of the unevenness. A method for measuring the depth of minute irregularities.