JP2008224258A - Charged particle beam apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide two types of aggregates of linear protrusions which have a large contrast in secondary electron images acquired when irradiate with an electron beam and which intersect each other at right angles, and to provide a size calibration sample for scanning electron microscopes that use the same. <P>SOLUTION: A crystal face of a (100) face single crystal silicon substrate is used to form an upper surface of a linear pattern, and (111) plane are used to form sidewalls, having acute angles to the upper surface to form a linear protrusion structure in parallel with or perpendicular to a <011> axis. A cross section, in parallel with the upper surface of the protrusion structure, is formed in such a way as to have an inverted taper structure having a decreasing width starting from the upper surface to a bottom part. A large contrast of secondary electron images acquired, from the boundaries of the two types of linear protrusions which intersect each other at right angles can be set, and accurate calibration can be carried out in the two directions of vertical and lateral directions. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sample using a semiconductor, and more particularly to a sample for dimensional calibration used for a scanning electron microscope and a manufacturing method thereof.

  The scanning electron microscope can measure dimensions using a signal waveform of secondary electrons obtained by scanning an electron beam. Before measuring the dimensions, perform measurement using a member whose dimensions are known in advance and calibrate the actual dimensions with the dimensions obtained by scanning electron microscope measurement to improve the accuracy of subsequent dimension measurements. Can do. Therefore, a sample dedicated to dimensional calibration is usually prepared in the scanning electron microscope.

  In order to perform dimensional calibration of the scanning electron microscope with high accuracy, it is important to obtain a secondary electron image having a large contrast. It is known that a large amount of secondary electrons are generated at the boundary portion of the uneven step, and a dimensional calibration sample is required to have a structure having a fine uneven step having a sharp side wall. In general, a scanning electron microscope has a function of measuring dimensions in the vertical and horizontal directions on a plane, and a dimensional calibration sample capable of calibrating two axes in the vertical and horizontal directions is required.

  As a dimensional calibration sample, a dimensional calibration sample in which a silicon substrate whose upper surface is a (110) plane is processed with an alkaline etching solution and a side wall is a (111) plane is used, as in Patent Document 1. . The (111) plane has a much slower etching rate than the (110) plane, and can form a steep sidewall, and the boundary line of the linear pattern is an accurate straight line at the atomic level. This is because the same value is obtained no matter where the dimension measurement is performed. The upper surface of the (110) plane and the (111) plane of the side wall are perpendicular to each other.

  Further, in Patent Document 2, two substrates in which a linear pattern is arranged at the same pitch are manufactured, and the two directions of the vertical direction and the horizontal direction can be calibrated by adhering to the sample stage so that the respective longitudinal directions are orthogonal to each other. I am doing so.

On the other hand, as a method that does not depend on crystal orientation, a silicon substrate is formed by RIE (Reactive Ion
Etching) can also be used for dry etching. In Patent Document 3, a material different from the material to be dry-etched is disposed at the bottom, and a sidewall having an acute angle with the top surface is formed by devising an etching gas. In Patent Document 4, a pattern is formed by exposure with ultraviolet light or an electron beam.

  Non-Patent Document 1 describes that a groove having a rhombic cross section is formed by cutting a groove so as to be parallel or perpendicular to the (110) plane by dicing and performing anisotropic etching. Moreover, it is described that the rhombus surface is formed by a (111) plane.

JP 2004-251682 A JP 2003-222715 A Japanese Patent Laid-Open No. 2000-200289 JP 2000-340521 A "Silicon processing by dicing and anisotropic etching" Tokyo Metropolitan Industrial Technology Research Institute Research Report No. 3 (2000) p117

  As described above, if the single crystal silicon substrate is processed with an alkaline etching solution, the boundary line of the linear pattern can be made an accurate straight line at the atomic level, but the silicon substrate whose upper surface is the (110) plane However, when a silicon substrate having a top surface of (100) is processed, the side walls are inclined at an obtuse angle with respect to the top surface.

  Further, in the method as disclosed in Patent Document 2, since the two substrates are bonded, the orthogonal accuracy between the vertical direction and the horizontal direction is lowered.

  Furthermore, the methods as described in Patent Documents 3 and 4 have a drawback that the boundary between the side wall and the bottom surface is rounded, the roughness of the boundary line of the linear pattern is large, and the pitch dimension measurement value varies depending on the measurement location. .

  In addition, the technique as described in Non-Patent Document 1 requires a predetermined depth of cut, but it is impossible to cut into a sample evenly at a fine interval such as a microscale by a dicing method. . In addition, if an attempt is made to create a finely spaced structure such as a microscale, the diamond structure is connected before the terrace structure is formed.

  As a method for solving the above-mentioned problem, when a silicon substrate having a top surface of (100) is processed with an alkaline etching solution, a (111) surface having an inclination of 54.7 ° is processed from the back surface side to form a reverse taper structure. And a reverse taper structure in which the cross-sectional area of the protruding structure constituting the linear structure decreases from the top surface toward the bottom. With this structure, it is possible to increase the contrast of the secondary electron image obtained from the uneven step boundary and to form a linear shape perpendicular to the vertical and horizontal directions on the same substrate.

  According to the above configuration, it is possible to provide a set of linear protrusions having a high contrast of the secondary electron image obtained when the electron beam is irradiated.

  Other objects and other specific configurations and effects of the present invention will be described in detail below in the embodiments of the present invention.

  Hereinafter, a linear projection assembly according to an embodiment of the present invention will be described with reference to the drawings.

  FIG. 1 is a top view showing an embodiment of a scanning dimensional calibration sample according to the present invention, and FIG. 2 is an enlarged side cross-sectional view taken along line AA ′ of FIG.

  The sample for dimensional calibration is composed of a base silicon substrate 1, a silicon oxide film layer 2, and an epitaxial silicon substrate 3, and a plurality of linear projections 21 are arranged at the same pitch α. In the linear protrusion, the upper surface 11 is the (100) surface of the epitaxial silicon substrate 3, the bottom surface 12 of the linear protrusion is the (100) surface of the base silicon substrate 1, and the side wall 13a of the linear protrusion is epitaxial silicon. The (111) plane and the side wall 13b of the substrate 3 are constituted by the (111) plane of the base silicon substrate 1. The top surface 11 and the side wall 13a of the linear protrusion 21 have an angle of 54.7 °, and the cross-sectional area has an inverse taper structure that decreases from the top surface toward the bottom. On the other hand, the bottom surface 12 and the side wall 13b of the linear protrusion also have an angle of 54.7 ° in the vicinity of the bottom, but the direction is a forward taper structure opposite to the side wall 13a. The thickness a of the epitaxial silicon substrate 3 is set larger than the processing thickness b of the base silicon substrate 1.

  FIG. 3 shows an assembly 22a and 22b in which a plurality of linear protrusions 21 are arranged at the same pitch α and arranged on the same substrate. In the present invention, since the longitudinal and lateral crystal axis directions are equivalent, the longitudinal direction of the linear protrusions 21 is arranged to be orthogonal to each other as in the aggregates 22a and 22b as in this embodiment. It is possible.

  The pitch dimension α can be arbitrarily designed, but is approximately 100 nm or less from the dimension of the semiconductor element. However, since various dimensions of the measurement object are conceivable, it is possible to improve the measurement accuracy in a wide dimension range by integrating dimensional calibration samples having various pitch dimensions. In FIG. 4, linear protrusion assemblies 22a and 22b having a pitch dimension α, linear protrusion assemblies 22c and 22d having a pitch dimension β, and linear protrusion assemblies 22e and 22f having a pitch dimension γ are integrated on the same substrate. This is an example. In this embodiment, there are three types of pitch dimensions, but it is of course possible to integrate more pitch dimensions.

軸を用いて、直線形状突起物を作るが、この軸を＜０１１＞と表す。 When the upper surface is the (100) surface, the [011] axis or

A linear protrusion is made using the axis, and this axis is represented as <011>.

Next, the manufacturing process of this invention is demonstrated using FIG.
(A) A silicon oxide film layer 2 and an epitaxial silicon substrate 3 are formed on a base silicon substrate 1. This structure is the same as that of a general SOI (Silicon on Insulator) wafer. Thereafter, a thermal oxide film layer 4 is formed by thermal oxidation.
(B) A photoresist 5 is formed on the thermal oxide film layer 4, a linear pattern is drawn by EB (Electoron Beam), and development is performed. Sensitivity and development with ultraviolet rays may be performed using a reduced projection exposure apparatus, but it is difficult to obtain resolution when the pitch dimension is 100 nm or less.
(C) A part of the thermal oxide film layer 4 is removed by dry etching, and then the photoresist 5 is entirely removed.
(D) The epitaxial silicon substrate 3 is etched by immersion in an alkaline etching solution such as an aqueous potassium hydroxide solution. At this time, the side wall 13c of the linear protrusion 21 is formed in a tapered shape having an inclination of 54.7 ° with respect to the upper surface 11.
(E) A part of the silicon oxide film layer 2 is removed and immersed in hydrofluoric acid. At this time, an acute angle protrusion 17 appears on the epitaxial silicon substrate 3. At this time, although the thermal oxide film layer 4 is also melted, the thermal oxide film layer 4 is thicker than the silicon oxide film layer 2 and therefore remains even if a part of the silicon oxide film layer 2 is removed.
(F) The substrate is again immersed in an alkaline etching solution such as an aqueous potassium hydroxide solution, and the epitaxial silicon substrate 3 and the base silicon substrate 1 are etched. At this time, since the etching speed of the acute angle protrusion 17 with respect to the aqueous potassium hydroxide solution is very high, the acute angle protrusion 17 has an acute angle with respect to the upper surface 11 of the linear protrusion 21 when the base silicon substrate 1 is slightly processed. A side wall 13a is formed.
(G) Finally, the thermal oxide film layer 4 is removed. The thermal oxide film layer 4 is an insulating film and is removed because a phenomenon occurs in which charge is accumulated when the electron beam is irradiated and charge-up occurs, making it difficult to obtain a secondary electron image. If this can be ignored, this step may be omitted.

  Incidentally, in FIG. 5B, EB (Electoron Beam) is used to form a linear pattern, but in this method, it is necessary to draw all the linear patterns every time a sample for dimensional calibration is manufactured. It becomes expensive. As a means for solving this problem, a method may be considered in which a metal mold in which a linear pattern is formed in advance is manufactured, and the pattern is transferred by pressing against a resin formed on the epitaxial silicon substrate. Such a method is called a nanoimprint technique, and is attracting attention as an inexpensive fine structure transfer technique.

Then, the manufacturing process of this invention to which nanoimprint technology is applied is demonstrated using FIG.
(A) A photoresist 5 is formed on the single crystal silicon substrate 6, a linear pattern is drawn by EB (Electoron Beam), and development is performed. Sensitivity and development with ultraviolet rays may be performed using a reduced projection exposure apparatus, but it is difficult to obtain resolution when the pitch dimension is 100 nm or less.
(B) Dry etching is performed by RIE (Reactive Ion Etching). A boundary 20 between the side wall 18 and the bottom surface 19 formed by RIE processing has a rounded shape. After the RIE process is completed, the photoresist 5 is completely removed.
(C) A concave metal mold 7 made of, for example, nickel is manufactured by electroforming.
(D) Further, the convex metal mold 8 is manufactured from the concave metal mold 7.
(E) As in FIG. 5B, the convex metal mold 8 is pressed against the photoresist 5 formed on the thermal oxide film layer 4. In this case, since it is not necessary to expose the resin, other resin may be used instead of the photoresist. When the convex metal mold 8 is pressed, it is heated to a temperature at which the photoresist 5 is softened. If necessary, the convex metal mold 8 is also heated. Also, when pressing, the surrounding atmosphere is evacuated so that bubbles do not remain at the interface.
(F) Hold the convex metal mold 8 fully pressed for several seconds to several minutes, and pull up the convex metal mold 8 after cooling. The linear pattern formed on the convex metal mold 8 is transferred. For example, a release agent such as silicone oil is applied to the upper surface of the convex metal mold 8 so that the convex metal mold 8 can be pulled up smoothly. A slight photoresist residual film 9 remains on the thermal oxide film layer 4.
(G) The photoresist residual film 9 is removed by, for example, dry etching. In this state, the state shown in FIG.

  Thereafter, the same steps as in FIGS. 5C to 5G may be performed.

  In this method, once a linear pattern is formed by EB (Electoron Beam) to produce a metal mold, a fine linear pattern can be efficiently formed by repeating the steps of FIGS. 6 (e) to 6 (g). Can be manufactured.

  FIG. 7 schematically shows the intensity of secondary electrons obtained by irradiating an electron beam from above on a sample for dimensional calibration according to the present invention. When the opening 14 between the linear protrusions is observed from the upper surface side, the boundary 15 between the bottom surface 12 and the side wall 13b of the linear protrusion is not visible, and the secondary electron image obtained from the upper boundary 16 of the linear protrusion is not visible. The contrast can be increased, and the signal waveform with the pitch dimension α can be accurately captured.

  On the other hand, FIG. 8 schematically shows the intensity of secondary electrons obtained by applying an electron beam from above to a silicon substrate obtained by dry etching a linear structure as shown in FIG. Is. When the structure of the embodiment of the present invention is not used, the boundary 20 between the RIE processing side wall 18 and the RIE processing bottom surface 19 has a rounded shape, and is obtained from each linear protrusion boundary when irradiated with an electron beam. The contrast of the secondary electron image is reduced. In this case, the signal waveform having the pitch dimension α cannot be accurately captured, and it is difficult to perform accurate dimension calibration.

  As described above, by using the structure of the present invention, the contrast of the secondary electron image obtained from each linear projection boundary when the electron beam is irradiated can be increased, and dimensional calibration can be performed with high accuracy. Is possible.

(Advantages of structure)
The dimensional calibration sample of the present invention is also excellent in structure. When the opening 14 between the linear protrusions is observed from the upper surface side, the boundary 15 between the bottom surface 12 and the side wall 13b of the linear protrusion 21 becomes invisible. In addition, the 16 inverted taper structure prevents the secondary electrons from the bottom surface 12 from proceeding. Thereby, the upper boundary 16 of the linear protrusion can be observed with a large contrast. Furthermore, by making the vicinity of the bottom of the linear protrusion a forward tapered structure, it is possible to reduce the concentrated stress even when an excessive force is applied to the linear protrusion and realize a robust structure. Further, when measuring the size of the linear protrusion from the upper surface side with a scanning electron microscope, secondary electrons emitted from the bottom surface 12 become noise, but the noise decreases because the bottom surface is lowered by the thickness b. There is also an effect that is further reduced.

  As shown in FIG. 9, the dimensional calibration sample 31 manufactured in this way is bonded to, for example, a stainless steel sample stage 32 with, for example, an epoxy-based adhesive 33, and finally attached to the corner of the stage 34.

FIG. 10 is a diagram in which a stage 34 on which a dimensional calibration sample 31 is mounted is incorporated in an electron microscope apparatus. In the electron microscope apparatus 35, an electron beam 37 emitted from an electron source 36 enters a measurement object 41 through a focusing lens 38, an objective lens 39, an aberration correction lens 40, and the like, and secondary electrons emitted therefrom. Is detected by the secondary electron detector 42. If dimension calibration is required, the stage 34 may be moved to observe the dimension calibration sample 31 installed at the corner of the stage 34. In an electron microscope used for dimensional inspection of a silicon wafer, the measurement object 41 is a silicon wafer having a substantially constant thickness so that the surface of the dimensional calibration sample 31 and the surface of the measurement object 41 are on the same plane. By designing and making the focal position of the electron beam the same, dimensional calibration can be reflected more accurately. In addition, it is possible to automatically perform dimensional calibration by systematizing the movement of the stage 34 and the image processing of the secondary electron image.

It is a top view which shows embodiment of this invention. It is side surface sectional drawing which shows embodiment of this invention. It is a top view which shows the example of arrangement | positioning of embodiment of this invention. It is a top view which shows the example of integration of embodiment of this invention. It is a figure explaining the manufacturing process of this invention. It is a figure explaining the 2nd manufacturing process of this invention. It is the figure which showed typically the intensity | strength of the secondary electron obtained by applying an electron beam to embodiment of this invention. It is a schematic diagram of the secondary electron intensity for comparing and explaining the effect of the embodiment of the present invention. It is the figure which incorporated the sample for electron microscope adjustment manufactured by the embodiment of the present invention in the stage of an electron microscope. It is the figure which incorporated the sample for electron microscope adjustment manufactured by the embodiment of the present invention in the electron microscope device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Base silicon substrate 2 Silicon oxide film layer 3 Epitaxial silicon substrate 4 Thermal oxide film layer 5 Photoresist 6 Single crystal silicon substrate 7 Concave metal type 8 Convex metal type 9 Photoresist residual film 11 Linear protrusion upper surface 12 Bottom surface 13a, 13b, 13c Side wall 14 Opening part 15 between linear protrusions Bottom-side wall boundary 16 Straight-shaped protrusion upper boundary 17 Acute protrusion 18 RIE processed side wall 19 RIE processed bottom surface 20 Boundary 21 Linear-shaped protrusions 22a, 22b, 22c, 22d , 22e, 22f Linear projection assembly 31 Dimensional calibration sample 32 Sample stage 33 Adhesive 34 Stage 35 Electron microscope device 36 Electron source 37 Electron beam 38 Focusing lens 39 Objective lens 40 Aberration correction lens 41 Measurement object 42 2 Secondary electron detector a Epitaxial silicon substrate thickness b Base silicon Plate working thickness alpha, beta, pitch γ-linear shape projections

Claims (13)

In the sample for dimensional calibration in which a plurality of protruding structures are arranged in a predetermined direction with a predetermined interval,
A sample for calibrating a dimension, characterized in that the width of the cross section parallel to the upper surface of each protruding structure becomes narrower from the upper surface toward the lower side in the arrangement direction. In the sample for dimensional calibration in which a plurality of protruding structures are arranged in a predetermined direction with a predetermined interval,
Each protrusion structure has a cross section parallel to the upper surface of the protrusion structure, and an upper layer in which the width along the arrangement direction becomes narrower from the upper surface downward,
A sample for dimensional calibration characterized by comprising a lower layer that exists below the upper layer and becomes wider as it goes downward.   3. The sample for dimensional calibration according to claim 1, wherein a shape of a cross section parallel to the upper surface of each protruding structure is a rectangle. In the sample for dimensional calibration according to claim 1 or 2,
A dimensional calibration sample, wherein at least two dimensional calibration samples in which the arrangement direction of the protruding structure of the dimensional calibration sample is perpendicular to each other are formed on a single crystal silicon substrate. 3. The sample for dimensional calibration according to claim 1 or 2, wherein the upper surface of the protruding structure is constituted by a (100) plane of silicon crystal, and the arrangement direction of the protruding structure is the [011] axis or

Dimensional calibration sample characterized by being an axis.   5. The dimension calibration sample according to claim 4, wherein the interval between the protruding structures in each dimension calibration sample is different. In the sample for dimensional calibration according to claim 2,
The sample for dimensional calibration, wherein a width of the cross-sectional shape of the lower layer of the protruding structure is smaller than a width of the cross-sectional shape of the upper layer.   In a sample for dimensional calibration in which a plurality of protrusion structures are arranged at a predetermined interval, each protrusion structure is composed of an upper layer and a lower layer silicon substrate, and an upper layer silicon substrate is formed on the upper part of the convex portion of the lower layer silicon substrate. And the upper silicon substrate has a cross section parallel to the upper surface, and the width along the arrangement direction becomes narrower from the upper surface to the lower side.   9. The sample for dimensional calibration according to claim 8, wherein a cross-sectional area parallel to the upper surface of the silicon substrate under each protrusion structure is smaller than that of the upper surface.   Etching a part of the upper silicon substrate of the substrate having the upper and lower silicon substrates via the oxide layer, and removing a part of the oxide layer from the part where the upper silicon is removed by the etching, Further, a method for preparing a dimensional calibration sample, wherein a part of the upper layer and the lower layer silicon is removed from the portion where the oxide layer is removed. A charged particle source;
A stage on which the sample is mounted;
An objective lens for focusing the charged particle beam emitted from the charged particle source on the sample;
In a charged particle beam apparatus having
A charged particle beam apparatus comprising the dimensional calibration sample according to claim 1. The charged particle beam device according to claim 11, wherein
A charged particle beam apparatus characterized in that the surface of the sample when the sample is mounted on the stage and the height of the upper surface of the sample for dimensional calibration are the same. A charged particle source;
A stage on which the sample is mounted;
An objective lens for focusing the charged particle beam emitted from the charged particle source on the sample;
A charged particle detector for detecting charged particles emitted from the sample;
In a charged particle beam apparatus having
10. A charged particle beam apparatus according to claim 1, wherein a length obtained from a detection signal intensity formed based on a signal of the charged particle detector is determined based on a sample having a dimension of any one of claims 1 to 9.

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