RU2325619C2 - Test object for calibration of raster electron and scanning probe microscopes - Google Patents

Abstract

FIELD: physics.

SUBSTANCE: invention pertains to the field of measuring small sections, which characterise the geometrical parameters of the profile of the topographical features of the surface of a solid body. The measurements are done in the nano-meter range (1-1000 nm) using raster electron and scanning probe microscopes. The test object is in the form of a structure with a topographical surface, the features of which have a profile, with projections of their sides on the base plane, which are larger than the probes of the raster electron and scanning probe microscopes. For all features there is an acute angle between the side edge and the lower base plane, in which case the projection is in the form of a set of steps, at least two of which join at an angle not equal and not a multiple of 180°.

EFFECT: increased accuracy of measurements and broadening of functional properties of the proposed structure.

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Description

The invention relates to the field of measuring small lengths of segments characterizing the geometric parameters of the profile of the elements of the relief of a solid surface in the nanometer range (1 ÷ 1000 nm), carried out using scanning electron (SEM) and scanning probe (SPM) microscopes.

Known test objects for calibrating SEM and SPM used to measure lengths of segments characterizing the geometric parameters of the profile of the relief elements of a solid surface [1]. These test objects are standard linear measures, which are relief step structures on the surface of a solid body, consisting of five protrusions with a geometric shape of their profile that is close to rectangular. The middle element of this structure is longer than four others. The certified step of this structure serves to calibrate the increase in SEM and SPM (determining the price of dividing the scanning scales), but does not provide measurements of the sizes of microscope probes, the values of which must be known to perform the procedure of measuring the linear dimensions of a particular element of the surface topography with high accuracy.

The closest in technical essence the execution of the test object, selected as a prototype, is the design of the test object, made in the form of a periodic single-crystal silicon structure with a relief stepped surface, the elements of which have a profile with a trapezoid shape. The projection of the sides of the trapezoid onto the base significantly exceeds the probe sizes of the above microscopes, and the acute angle of inclination of these sides relative to the lower base of the trapezoid is kept constant and equal to 54.7 ° (the angle between the crystallographic planes of silicon is (100) and (111) [2]. The prototype test object is a relief surface, which is a superposition of linearly extended steps parallel to each other and rotated relative to each other at an angle of 180 ° with a known constant angle of inclination of their side faces. A prototype test object with a calibrated step of a specific pair of elements of its structure allows you to determine the unit of the scan scale and the size of the SEM and SPM probe, but only in one direction (for example, along X).

However, the prototype test object has significant drawbacks in that for high-precision measurement of small lengths of segments characterizing the profile of the relief element, it is necessary to adjust the plane of the measured structure, which should be orthogonal to the axis of the SEM and SPM probe or make an angle with it for some models of the latter. In addition, the design of the prototype test object, as noted above, does not allow to calibrate both scanning axes of the SEM and all three scanning axes of the SPM simultaneously on the same section of the relief structure. Also, the prototype object does not allow to determine the sizes of the SEM and SPM probes simultaneously in two mutually perpendicular directions.

The problem to which this invention is directed, is to achieve a technical result, which consists in increasing the accuracy and reducing the measurement time of small lengths of segments characterizing the profile of the relief element in the entire nanometer range, performed using SEM and SPM, as well as expanding the functional properties of the proposed design due to the possibility of simultaneous calibration of SEM scanning scales along two axes and SPM along three axes, determining the linearity of scanning scales and their orthogonality, determine the dimensions of the SEM and SPM probes in two mutually perpendicular directions using the same section of the relief structure of the object.

The problem is solved in a test element for calibrating scanning electron and scanning probe microscopes, made in the form of a structure with a relief surface, the elements of which have a profile with projections of the sides on the plane of the base exceeding the dimensions of the SEM and SPM probes, and a constant constant is maintained in all elements of the relief surface acute angle between the side face and the plane of the lower base, characterized in that the relief is made in the form of a set of steps, at least two of which are joined at an angle m not equal and not a multiple of 180 °.

Thus, the distinguishing features of the invention is that the relief is made in the form of a set of steps, at least two of which are joined at an angle not equal to and not a multiple of 180 °; the fact that the steps are joined at an angle of 90 °; and also the fact that four pairs of joined steps form a relief structure of a cross-shaped protrusion.

The specified set of distinctive features allows to achieve a technical result, which consists in increasing the accuracy and reducing the measurement time of small lengths of segments characterizing the profile of the relief element in the entire nanometer range, as well as in expanding the functional properties of the proposed design due to the possibility of simultaneous calibration of SEM scanning scales along two axes and for SPM in three axes, determining the linearity of the scanning scales and their orthogonality, determining the sizes of the SEM and SPM probes in two in the direction perpendicular using the same section of the relief structure.

The invention is illustrated by the drawings.

Figure 1 shows a schematic representation of a test object for calibrating SEM and SPM according to the invention. The proposed test object includes a substrate 1 with a embossed surface, which is two steps with a common upper 2 and lower 3 bases and side inclined faces 4 and 5, intersecting at an angle of 6 (shown as a crossing at an angle of 90 °). In both steps, a well-known and constant angle 9 is maintained between the side faces of steps 4 and 5 and the plane of the base 3. Since the upper and lower bases of both steps are common, the heights 7 and 11 of both steps are the same. Accordingly, the projections of the sides of the profile of the relief 8 and 12 on the plane of the base 3 are also the same. The side faces of the steps intersect in a straight line 10.

Figure 2 shows an embodiment of a test object according to the invention, in which four pairs of steps (13-14; 15-16; 17-18; 19-20) are joined, forming a relief structure of a cross-shaped protrusion.

SEM calibration using the test object according to the invention is performed as follows. The test object is mounted on a table for microscope samples and then its surface is scanned with a SEM probe at the required electron energy of the probe. SEM should work in the mode of collection by its detector of secondary slow electrons. On the SEM monitor screen, a part of the relief image is set near the intersection of the side faces of steps 4 and 5 (see Fig. 1). Then this image is transferred using an interface device to a personal computer, in which the processing of video signal curves is performed. These curves determine the length of the segments in image pixels characterizing the projections of the side walls of steps 8 and 12 according to the method described in [3]. The passport of the test object shows the certified values of these projections in nanometers. Dividing the passport values of the corresponding projections by their measured lengths in pixels, we obtain the price of dividing the scan scales in two mutually perpendicular directions. In this case, the obtained data does not depend on operator errors when focusing the probe on the sample. Having obtained these results, the values of the sizes of the electron probe in these two directions are determined from the video signal curves according to the method from [3]. Such SEM calibration allows to increase accuracy and reduce measurement time.

Calibration of the SPM using the test object according to the invention is as follows. The test object is installed on the SPM table for samples and scan the area of the relief near the intersection of the side faces 4 and 5 (see figure 1). The certified values of the dimensions of the relief elements (for example, the projections of the lateral sides 4 and 5 and the step height) given in the passport of the test object make it possible to calibrate the division price of all three scan scales using the measured video signal curves, check their mutual orthogonality and the passport size data element of the relief structure in the form of a cross-shaped protrusion to determine the size of the SPM probe according to the method described in [3]. Such simultaneous calibration of the SPM along its three scanning axes increases accuracy and reduces the measurement time of small lengths.

A test object for calibrating SEM and SPM with mutually perpendicular mating steps can be manufactured using standard microelectronics processes using photolithography and anisotropic etching of a single-crystal silicon wafer, the working surface of which is oriented along the crystallographic plane (100).

The test object according to the invention can find wide application for calibration of SEM and SPM used as measuring instruments for short lengths of relief elements of products manufactured by micro- and nanotechnologies.

Literature

1. M.T. Postek, A.E. Viladar, J.S. Villarrubia. Is a production level scanning microscope linewidth standard possible? // Procedings SPIE, vol. 3898, pp. 42-56, (2000).

2. Ch.P. Volk, E.S. Gornev, Yu.A. Novikov, Yu.V. Ozerin, Yu.I. Plotnikov, A. M. Prokhorov, A. V. Rakov. Test object for calibration of scanning electron microscopes // Patent for invention No. 2207503, priority dated March 29, 2001, registered June 27, 2003.

3. Ch.P. Volk, E.S. Gornev, Yu.A. Novikov, Yu.V. Ozerin, Yu.I. Plotnikov, A. M. Prokhorov, A. V. Rakov. A linear measure of the micron, submicron, and nanometer ranges for measuring the sizes of VLSI elements using scanning electron and atomic force microscopes // Microelectronics, 2002, v.31, No. 4, p.243-262.

Claims (3)

1. A test object for calibrating scanning electron and scanning probe microscopes, made in the form of a structure with a relief surface, the elements of which have a profile with projections of the sides on the plane of the lower base, exceeding the sizes of the SEM and SPM probes, and in all elements of the relief surface a constant sharp the angle between the side face and the plane of the lower base, characterized in that the relief is made in the form of a set of steps, at least two of which are joined at an angle not equal and not multiple 180 °. 2. The test object according to claim 1, characterized in that the joined steps are located at an angle of 90 ° to each other. 3. The test object according to any one of claims 1 and 2, characterized in that four pairs of joined steps form a relief structure of a cross-shaped protrusion.

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