JPH04220937A - Resolution evaluating specimen and its manufacture - Google Patents

Abstract

PURPOSE:To heighten the evaluation accuracy for the resolution of a scanning electron microscope by laminating a first films consisting of a first material and a second films consisting of the second material alternately one over another, and providing a plurality of cut surfaces in the thickness direction of the resultant laminate. CONSTITUTION:A resolution evaluating specimen 1 is prepared by laminating the first films 3 consisting of the first material and the second films 4 consisting of the second material alternately on a semiconductor base board 2, and therein cut surfaces A, B extending in the directions perpendicularly intersecting each other are furnished in the thickness direction of the films 3, 4. According to this arrangement where the cut surface of specimen 1 is composed of two surfaces A, B, the correction of astigmatism of a scan type electron microscope can be made quickly and certainly, and also contamination attached to the objective stop of the microscope be found in early stage. Because a vivid observation image is obtained, the evaluation accuracy for the resolution of microscope can be enhanced.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a resolution evaluation technique, and more particularly to a technique that is effective when applied to the evaluation of resolution in optical instruments such as scanning electron microscopes.

0002

[Background Art] In the manufacturing process of semiconductor integrated circuits, as devices become smaller, there is a need for higher precision in process evaluation techniques such as observation of integrated circuit patterns and dimensional measurements. There is a need for further improvement in resolution.

One of the methods for evaluating the resolution of a scanning electron microscope is a technique described in Japanese Patent Application Laid-Open No. 1-254836. The resolution evaluation method described in the above-mentioned document involves depositing several thin films of a predetermined thickness on a semiconductor wafer, such as a SiO2 film and a polycrystalline silicon film, alternately, and then cutting the wafer in the thickness direction. , after polishing this cut surface,
A resolution evaluation sample is prepared by selectively etching one of the thin films (for example, a SiO2 film) with an aqueous hydrofluoric acid solution. Next, the cut surface of this sample is observed with a scanning electron microscope, and the resolution of the scanning electron microscope is evaluated and determined based on whether a predetermined thin film can be confirmed.

0004

[Problems to be Solved by the Invention] However, since the resolution evaluation method described above observes only one cross section of the sample, it takes a long time to correct the astigmatism of the microscope, and it is difficult to obtain the best image. There was a problem that it was difficult to Furthermore, when observing only one direction of a sample for a long period of time, there is a problem in that the image gradually becomes unclear due to contamination (foreign matter) adhering to the objective aperture of the microscope.

An object of the present invention is to provide a technique that can improve the accuracy of evaluating resolution in a scanning electron microscope.

The above and other objects and novel features of the present invention will become apparent from the description of the present specification and the accompanying drawings.

[0007]

[Means for Solving the Problems] The resolution evaluation sample of the present invention is a laminated film formed by alternately depositing a first thin film made of a first material and a second thin film made of a second material. Two cutting surfaces are provided in the thickness direction, extending in directions perpendicular to each other.

[0008]

[Operation] According to the above-described means, by providing observation surfaces in two directions of the sample, the astigmatism of the microscope can be corrected in a short time and reliably. Also, this allows
Contamination adhering to the objective aperture of a microscope can be detected at an early stage.

[0009]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a plan view of a main part of a resolution evaluation sample which is an embodiment of the present invention, and FIG. 2 is a sectional view of a main part of this resolution evaluation sample.

As shown in FIGS. 1 and 2, a resolution evaluation sample 1 includes a first thin film 3 made of an SiO2 film and a second thin film made of a polycrystalline silicon film on a semiconductor substrate 2 made of silicon, for example. 4 are deposited alternately.

In the above resolution evaluation sample 1, the thin films 3 and 4
Cut planes A and B extending in directions orthogonal to each other are provided in the thickness direction of the plate. In addition, each cut surface A,
A step is provided between the two types of thin films 3 and 4 exposed to B.

The resolution evaluation sample 1 is manufactured, for example, as follows. First, as shown in FIG. 3, the surface of the semiconductor substrate 1 is thermally oxidized to form a first thin film 3 made of SiO2 film. Then, the thicknesses of the thin film 3 at multiple locations are measured using, for example, an ellipsometer, and the average value thereof is recorded as the thickness (t) of the thin film 3. The thickness (t) of the thin film 3 is set to be approximately the same as the resolution of the scanning electron microscope to be evaluated.

Next, as shown in FIG. 4, a second thin film 4 made of polycrystalline silicon is deposited on the thin film 3 using, for example, chemical vapor deposition (CVD). Subsequently, the surface of the thin film 4 is thermally oxidized to form a first thin film 3 made of SiO2 film. At this time, as described above, the average value of the thicknesses of the thin film 3 at a plurality of locations is recorded as the thickness (t) of the thin film 3. In this way, repeat the above series of operations several times,
As shown in FIG. 5, a multilayer film is formed by alternately depositing several layers of a first thin film 3 and a second thin film 4, each of which has a known film thickness (t).

Next, by patterning the laminated film by etching using a photoresist as a mask,
As shown in FIG. 6, two cut planes A and B extending in directions orthogonal to each other are formed in the thickness direction of the laminated film. In addition, in FIG. 6, the front (cross section) is the cut plane A.

Next, one thin film 3 (SiO2 film) of the thin films 3 and 4 exposed on the cut surfaces A and B, respectively.
The resolution evaluation sample 1 shown in FIG. 1 and FIG. can get.

After that, cut surface A of the resolution evaluation sample 1
, B with a scanning electron microscope to be evaluated, and in the obtained observation image, the thickness (t) of the thin film 3
The resolution of the scanning electron microscope is evaluated and determined based on whether or not it can be confirmed.

Here, cut surface A of the resolution evaluation sample 1
, B. For example, in a scanning electron microscope that obtains an observation image using secondary electrons generated when a sample is scanned with an electron beam, atomic number effects and Combined with edge effects, the cut surfaces A and B can be clearly observed with good contrast.

In this way, the resolution evaluation sample 1 of this example
According to this, the following actions and effects can be obtained.

(1). By configuring the cut plane of resolution evaluation sample 1 into two cut planes A and B that are perpendicular to each other,
Compared to conventional resolution evaluation samples that have a cut plane in only one direction, the astigmatism of the microscope can be corrected more quickly and reliably.

(2). By providing observation surfaces in two directions of the resolution evaluation sample 1, contamination adhering to the objective aperture of the microscope can be detected at an early stage.

(3). According to (1) and (2) above, a clear observation image can be obtained, so that the accuracy of evaluating the resolution in a scanning electron microscope can be improved.

FIG. 7 is a sectional view of a main part of a resolution evaluation sample 1 which is another embodiment of the present invention. This resolution evaluation sample 1
are the film thicknesses of the first thin films 3, 3, 3 (t1, t2, t
3) is made gradually thicker, that is, it changes in stages. Thereby, without creating a large number of resolution evaluation samples 1, it is possible to quickly evaluate the resolution of scanning electron microscopes with various performances using one resolution evaluation sample 1.

[0023] Above, the invention made by the present inventor has been specifically explained based on examples, but the present invention is not limited to the above-mentioned examples, and can be modified in various ways without departing from the gist thereof. Needless to say.

For example, the flatness of the observation surface can be improved by forming a cut surface by etching and then polishing the cut surface using fine alumina particles or the like.

[0025]Due to charging of the resolution evaluation sample, the image may become unclear or observation may become impossible during observation. In such cases, impurities of a predetermined conductivity type may be introduced into the polycrystalline silicon film that is the second thin film, or
By depositing a conductive film such as an Al film or a W (tungsten) film on the top layer of the sample, the above problems can be avoided and resolution evaluation can be performed smoothly and quickly.

[0026] The materials constituting the first and second thin films are:
It is not limited to the combination of SiO2 film and polycrystalline silicon film, but may be a combination of any other materials.

The method for forming the first and second thin films is not limited to the thermal oxidation method or the CVD method, but may be any method other than the sputtering method as long as the film thickness can be well controlled.

In the above explanation, a resolution evaluation sample for a scanning electron microscope has been explained, but the present invention is not limited to this, and can be widely applied to observation devices using general charged particle beams, and furthermore, to resolution evaluation samples for optical instruments. can.

[0029]

[Effects of the Invention] Among the inventions disclosed in this application, the effects obtained by the typical inventions will be briefly explained as follows.
It is as follows.

[0030] In the present invention, two cut surfaces are provided in mutually orthogonal directions in a laminated film formed by alternately depositing a first thin film made of a first material and a second thin film made of a second material. According to the resolution evaluation sample, it is possible to improve the accuracy of resolution evaluation in a scanning electron microscope.

[Brief explanation of the drawing]

FIG. 1 is a plan view of a main part of a resolution evaluation sample that is an embodiment of the present invention.

FIG. 2 is a sectional view of a main part of this resolution evaluation sample.

FIG. 3 is a sectional view of a main part of a semiconductor substrate showing a method of manufacturing this resolution evaluation sample.

FIG. 4 is a sectional view of a main part of a semiconductor substrate showing a method of manufacturing this resolution evaluation sample.

FIG. 5 is a sectional view of a main part of a semiconductor substrate showing a method of manufacturing this resolution evaluation sample.

FIG. 6 is a sectional view of a main part of a semiconductor substrate showing a method of manufacturing this resolution evaluation sample.

FIG. 7 is a cross-sectional view of a main part of a resolution evaluation sample according to another embodiment of the present invention.

[Explanation of symbols]

1 Resolution evaluation sample 2 Semiconductor substrate 3 Thin film 4 Thin film A Cut surface B Cut surface

Claims (5)

[Claims] Claim 1: Two cuts extending in directions orthogonal to each other in a laminated film formed by alternately depositing a first thin film made of a first material and a second thin film made of a second material. A resolution evaluation sample characterized by having a surface. 2. The resolution evaluation sample according to claim 1, wherein the thickness of either the first or second thin film is changed stepwise. 3. The resolution evaluation sample according to claim 1, wherein a step is provided between the first and second thin films along the cut surface. 4. A laminated film is formed by alternately depositing a first thin film made of a first material and a second thin film made of a second material while measuring the thickness of at least one of the films. and a step of patterning the laminated film by etching using a photoresist as a mask to form two cut surfaces extending in directions orthogonal to each other in the laminated film. The method for producing a resolution evaluation sample according to claim 1 or 2. 5. Forming a laminated film by alternately depositing a first thin film made of a first material and a second thin film made of a second material while measuring the thickness of at least one of the films. a step of patterning the laminated film by etching using a photoresist as a mask to form two cut surfaces extending in directions orthogonal to each other in the laminated film; A step of providing a step between the first and second thin films by selectively etching one of the exposed first and second thin films. A method for producing a resolution evaluation sample according to item 3.