JP3417133B2 - Electronic beam drawing device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electronic beam drawing apparatus equipped with a height detecting device for optically detecting the height of a sample surface.

[0002]

2. Description of the Related Art FIG. 1 shows an outline of an electron beam drawing apparatus. An electron beam 3 is emitted from an electron source 2 in an electron optical barrel 1 (hereinafter abbreviated as a column) held in vacuum. The electron beam 3 is passed through the deflection control circuit 5 based on the drawing data from the control computer 4, and is deflected by the deflector 6 to the sample surface 9
The deflection is controlled in two directions, which are the X and Y orthogonal directions in FIG. The electron beam 3 controlled in this way is X, Y in the vacuum sample chamber 7.
Sample surface 9 fixed on a sample stage 8 movable in any direction
Biased above to draw the desired pattern. As shown in FIG. 2, the deflected electron beam 3 has an opening angle of maximum θ with respect to the electron beam central axis 21 which is usually the normal direction of the sample surface. At this time, when a height error Δh in the Z direction is generated between the sample surface set by the deflector and the surface on which the sample actually exists, the sample position reached by the electron beam, that is, the drawing position is desired. It deviates from the position by Δx = Δh · tan θ, resulting in a drawing position (magnification) error. For example, when the opening angle .theta. Is 5 mrad and .DELTA.h is 10 .mu.m, .DELTA.x is as large as 0.05 .mu.m, remarkably reducing the positional accuracy of the drawing pattern.
Further, when an error occurs in the height position of the sample surface, the drawing pattern is rotated, or the drawing pattern is blurred due to the shift of the focus position, which deteriorates the accuracy of the drawing pattern.

As described above, when performing highly accurate drawing by the electron beam drawing apparatus, height information of the sample surface 9 is necessary. Therefore, many electron beam drawing apparatuses are provided with the height detector 10 for the sample surface.

The following method is used to match the position where the electron beam 3 reaches the sample surface 9 with the desired electron beam optical characteristic by using the value detected by the height detector 10. In the usual electron beam writer, the sample stage 8
Does not move in the Z direction, a reference plane 11 having two heights (H plane and L plane) is provided on the stage as shown in FIG. 1, and the height detector 10 is based on this reference plane 11. The gain and offset of are calibrated via the height signal processing unit 12 and the control computer 4. Further, the reference plane 11 is provided with a reference mark (not shown) capable of detecting the position of the electron beam most accurately. Then, the height of the sample surface 9 in the step between the two reference surfaces 11 is detected by interpolation with the reference surface, and the electron beam 3 is scanned on the reference mark to reflect the reflected electron signal. The position of the electron beam is detected by the electron detector. Then, the electron optical characteristic parameters such as the focus of the electron beam, the deflection sensitivity, and the magnification are determined from the information on the detected height and electron beam position.

The function required for the height detector 10 is that it can detect the height of the sample surface 9 in a non-contact, high-speed, micron order. Therefore, many of the height detectors 10 optically detect.

As an example of a conventional height detecting device, Japanese Patent Publication No. 2-
The structure of the height detector described in 6216 is shown in FIG.
This detector irradiates laser light emitted from a laser light source L onto a sample surface 9 from a diagonal direction at an incident angle α through a lens L1 via prisms P1, P2 and P3, and the reflected light is detected by a lens L2. Form an image on the device D. Then, by processing the output of the detector D,
The height position of the sample surface is measured.

Further, in another example of the conventional height detecting device (Japanese Patent Publication No. 3-70164) shown in FIG. 4, light is irradiated from an oblique direction of the sample surface, and the reflected light is projected onto the detector by a lens. This is the same method as in Japanese Patent Publication No. 2-6216 described above, except that the light irradiation unit LI and the light receiving unit LD are integrally formed, and are attached to the vacuum sample chamber 7 of the charged beam drawing apparatus, so that they can be easily formed. It is configured to be removable

[0008]

The above-mentioned conventional techniques have the following problems.

1) In the height detector shown in FIG. 4, as the column diameter increases, the distance between the lens (101, 102) closest to the sample of each of the light irradiation part LI and the light receiving part LD and the sample surface 9 is increased. Since the distance becomes long and the focal length of the lens becomes long, the entire optical system becomes large, and even a small optical system fluctuation (drift) will cause fluctuations beyond the allowable range in the height detector, which will cause deterioration of performance. . Further, it becomes difficult to adjust the position of the height detection light on the sample surface. In the charged beam drawing apparatus, when the deflection range is widened while maintaining accuracy, the outer diameter of the column 1 becomes large. Therefore, this problem becomes a problem as the performance of the drawing apparatus is improved. 2) Using laser light as the light source In Fig. 3, since the laser light has a single wavelength or a narrow band of light, optical interference occurs on the sample surface having coherence such as resist and oxide film. In particular, there is a problem that the amount of reflected light is extremely reduced when the resist and the oxide film have a specific thickness, and a large height detection error occurs.

3) In order to avoid the above problem 2), white light and a slit are used as a light source, and even when the image of the slit is formed on the sample surface, it is usually used when the lens is close to the sample surface. Since the circular lens is placed in a narrow space between the column and the sample, it is limited to use a small diameter circular lens. As a result, the amount of light reaching the sample surface is reduced, which becomes a factor of deteriorating the accuracy of height detection.

4) A resist having a uniform thickness is applied on a wafer or reticle, which is a sample of an ordinary electron beam drawing apparatus. This resist has a low reflectance for visible light. Therefore, when detecting the resist surface with the height detector, it is a good idea to increase the reflectance by setting the incident angle of the detection light to the sample surface to about 80 °. However, as the incident angle increases, the incident light on the sample passes near the sample surface, which makes it difficult to arrange a lens having a large aperture.

It is an object of the present invention to provide an electron beam drawing apparatus capable of improving drawing accuracy with a highly accurate and compact height detector.

[0013]

The present invention solves the above problems by the following means.

1) In the present invention, the outer shapes of the two spherical plano-convex lenses closest to the samples of the irradiation optical system and the light receiving optical system are not regular circles but have a shape having one or more planes, and one or more of the above. The plane is parallel to the optical axis or is arranged within an angle of 1 degree from the parallel. Sandwich the optical axis
The shape is cut out from two parallel planes.

2) The angle between the plane of the lens and the sample surface is made equal to the incident angle of the optical axis with respect to the sample.

3) Further, the two lenses are mounted below the sample chamber or column with at least one of the planes as a reference.

4) Conductive treatment is applied to the two spherical plano-convex lenses closest to the sample in each of the irradiation optical system and the light receiving optical system described in 1) to 3) above.

[0018]

According to the present invention, since the lens is formed so as to match the image of the light formed by the slit, the amount of incident light is increased. In particular, by disposing the spherical plano-convex lens, the amount of received light on the light receiving element is increased, and the S / N of the height detection signal is improved. As a result, the performance of the height detector is improved, and the accuracy of the electron beam drawing apparatus can be improved.

Further, under the sample chamber or column of the electron beam drawing apparatus having a complicated structure and space limitation,
A spherical convex lens having a large opening area can be efficiently and easily arranged.

Further, by applying the conductive treatment of this shape, it is possible to prevent charge-up caused by adhesion of reflected electrons, reflected ions, secondary electrons, etc. to the lens by the electron beam.

[0021]

DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the height detecting device of the present invention will be described with reference to the drawings.

FIGS. 5 and 6 illustrate an embodiment of the height detector of the present invention. FIG. 5 shows an optical path diagram of the optical system of the height detector of this embodiment. FIG. 5 (1) is a projection view from the Z direction, and FIG. 5 (2) is a side view, that is, the sample surface is X.
FIG. 6 is a perspective view from the side including the z direction when it is on the Y plane. In FIG. 5, the alternate long and short dash line indicates the optical axis, and the dotted line indicates the light beam emitted from the slit center. FIG. 6 shows a configuration in the apparatus when the height detector of the present invention shown in FIG. 5 is applied to an electron beam drawing apparatus.

First, the outline of the optical system will be described with reference to FIG. A halogen lamp is used as the light source 51, and white light emitted from the light source 51 is applied to the slit 53 by the condenser lens 52.
The light emitted from the slit passes through the objective lens 54 and forms an image on the sample surface 9 at an incident angle θ from an oblique direction. The light reflected on the sample is condensed by the condenser lens 55 and forms an image on the light receiving element 56. Now, as shown in Fig. 5 (1), the sample surface is z by Δh.
It is assumed that the change in the direction occurs by Δd on the light receiving element 56. At this time, the optical system by the condenser lens 55

When the magnification is m, Δh and Δd are

It is known that there is a relationship of [Equation 1].

(Equation 1) Δd = 2Δhsinθ × m That is, since Δh is proportional to Δd, the sample height change is a change of the light spot position on the light receiving element. Therefore, the height of the sample can be detected by converting the light spot position into an electric signal by using the light receiving element 56 as a semiconductor position detecting element (PSD) and performing appropriate signal processing in the signal processing section.

Next, FIG. 6 shows the configuration when the height detecting device of the present invention is applied to an electron beam drawing device. Light emitted from a 100-watt halogen lamp light source (not shown) is inserted into an irradiation unit holder 62 attached to a sample chamber 7 of an electron beam drawing apparatus by a fiber 61. The light emitted from the end face of the fiber 61 enters a condenser lens 63 having a focal length of 30 mm. The light emitted from the condenser lens enters a rectangular slit 53 having a width of 200 μm × 3 mm. At this time, the long side of the rectangular slit 53 is perpendicular to the paper surface of the drawing and parallel to the sample surface 9. The light emitted from the slit 53 is reflected by the mirror 64 and is incident on the spherical convex lens 54 having a focal length of 80 mm which is separated from the slit 53 by about 160 mm. This spherical convex lens 54 is an objective lens. The light emitted from the objective lens 54 forms an image of the slit 53 on the sample surface 9 at a distance of 160 mm at an incident angle of 80 ° and reflects it. The reflected light is a focusing lens 5 with a focal length of 80 mm 120 mm apart.
It is condensed by 5 (spherical convex lens), passes through the mirror 64 and PSD6
Image on 5. The distance between the condenser lens 55 and the PSD 65 is 240 mm, and in the optical system of the light receiving section of the present embodiment, the magnification of the light receiving optical system is doubled, so that the height change of the sample surface 9 becomes about 3.9 times and the light receiving position changes. Becomes

In this embodiment, the incident angle is as large as 80 degrees. Therefore, the distance in the Z direction between the center (that is, the optical axis) of the two lenses (the objective lens 54 and the condenser lens 55) closest to the sample surface and the sample surface 9 is about 27.8 mm in the objective lens 54,
It is 20.8 mm with the condenser lens 55. That is, when the spherical convex lens has a circular outer shape, the diameter of the lens that can be installed is not more than this distance. In addition, the reference mark 1 on stage 8
The mirrors for interferometers, which are the position reference in the 1 and xy directions, are installed higher than the wafer surface. In addition, considering the holder of the objective and the condenser lens itself, the outer diameter of the lens can only be about 15 mm to 20 mm.

Therefore, in the present invention, the objective lens 54 and the condenser lens 55 close to the sample surface 9 are not in a circular outer shape like an ordinary spherical convex lens, but are parallel to the optical axis direction 70 of the lens as shown in detail in FIG. The lens 71 has two flat surfaces. Furthermore, the lens of FIG. 7 has two planes (72, 7) equidistant from the optical axis.
The shape cut out in 3). In the height detector of the embodiment shown in FIG. 6, a lens having an outer diameter of 40 mm is cut out at a distance between parallel planes of 15 mm.

By thus forming the lens shape having two planes parallel to the optical axis direction, the area of the lens aperture is about 3.3 times as large as that in the case of using a spherical convex lens having a diameter of 15 mm. Further, in the present invention, the objective lens is provided with the aperture stop 57 for the purpose of preventing stray light and improving the contrast of the slit image on the sample surface. The aperture stop 57 has a rectangular aperture of 10 mm × 30 mm in order to stop the light emitted from the slit. Although the aperture area is reduced by providing the diaphragm, the aperture area of the rectangular diaphragm 57 is almost twice as large as that of the circular diaphragm having a diameter of 15 mm.

As described above, by using the lens shown in FIG. 7, the amount of light reflected on the sample surface 9 and incident on the PSD increases, and the amount of current photoelectrically converted into a position signal increases. The S / N at was improved twice and the detection accuracy was improved. Specifically, a height resolution of about 0.1 μm could be obtained even on a sample surface having a reflectance of about 10%. In this embodiment, one of the two planes of the cut-out lens 71 in FIG. 7 is used as a reference and is fixedly bonded to the holder 81 (FIG. 8).
The holder 81 is composed of a hexahedral aluminum plate, and the surface opposite to the surface to which the lens is bonded is 1 in the optical axis direction as shown in FIG.
It has a slope of 0 degrees. Then, a metal thin plate 82 for preventing lens drop and charge-up prevention was connected and fixed to the winding holder 81, that is, an electrical ground level, on the outer peripheral portion of the lens. Further, the surface of the holder 81 on the 10 ° inclined side was attached to the wall of the sample chamber parallel to the sample surface with screws. In this example, push-pull screws are used to facilitate adjustment in the X and Y directions. By this mounting method, the incident angle of the lens optical axis with respect to the sample surface 9 becomes a desired 80 degrees. It is obvious that the present invention can be mounted with a small number of parts and a small space, as compared with the case where the conventional spherical lens having a circular outer shape is used to provide the holder on the outer peripheral portion.

The material of the lens is a glass material for BK7 lens and has no conductivity. Reflected electrons and secondary electrons from the sample surface directly strike the objective lens 54 and the condenser lens 55, which are closest to the sample surface 9 shown in FIG. Therefore, a conductive film is coated on the lens surface, conduction is established from a metal thin plate for preventing fall, and this is set to the ground potential of the electron beam drawing apparatus. As a result, the phenomenon of deteriorating the characteristics of the electron optical system due to charge-up hardly occurred.

[0032]

As described above, according to the present invention, in the height detector of the sample surface, the amount of light received on the light receiving element is increased to improve the S / N of the height detection signal. Furthermore, a spherical convex lens having a large aperture area can be efficiently and easily arranged under the sample chamber or column of the charged particle beam drawing apparatus having a complicated structure and limited space.

As a result, it is possible to provide a compact electron beam drawing apparatus equipped with a highly accurate height detector.

[0034]

[Brief description of drawings]

FIG. 1 is a diagram showing an outline of an electronic beam drawing apparatus.

FIG. 2 is a diagram for explaining a relationship between an electronic beam opening angle and a height error.

FIG. 3 is a view showing an example (No. 1) of a conventional sample surface height detector for an electron beam drawing apparatus.

FIG. 4 is a diagram showing an example (No. 2) of a conventional sample surface height detector for an electron beam drawing apparatus.

FIG. 5 is a diagram showing an outline of an optical system of a height detector of the present invention.

FIG. 6 is a diagram illustrating an example of a height detector for an electronic beam drawing apparatus according to the present invention.

FIG. 7 is a diagram illustrating the outer shape of a spherical convex lens for a height detector of the present invention.

FIG. 8 is a diagram illustrating a method of attaching a spherical convex lens.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electro-optical system lens barrel (column), 2 ... Electron source, 3 ... Electron beam, 6 ... Deflector, 7 ... Sample chamber, 8 ... Sample stage,
9 ... Sample surface, 10 ... Height detector, 12 ... Height signal processing unit, 21 ... Electron beam central axis, 51 ... Halogen lamp,
52 ... Condenser lens, 53 ... Slit, 54 ... Objective lens, 55 ... Condensing lens, 56 ... Light receiving element, 57 ... Aperture, 61 ... Fiber, 64 ... Mirror, 65 ... PSD, 7
1 ... Spherical convex lens, 72, 73 ... Cut plane, 81
... Lens holder, 82 ... Metal thin plate

Continuation of front page (51) Int.Cl. ⁷ identification code FI H01L 21/027 H01L 21/30 541Z (56) Reference JP-A-7-134964 (JP, A) JP-A-4-203947 (JP, A ) JP-A 61-34936 (JP, A) JP-A 58-119642 (JP, A) JP-A 60-53021 (JP, A) JP-A 60-95845 (JP, A) JP-A 61- 140803 (JP, A) JP 52-103965 (JP, A) JP 6-67608 (JP, A) JP 6-67006 (JP, A) JP 5-290796 (JP, A) JP-A-5-231863 (JP, A) Actual development Sho-60-107813 (JP, U) Special table HEI 8-501635 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01J 37/305 G03F 7/20 504 G03F 7/20 521 G21K 5/04 H01J 37/21 H01L 21/027

Claims (3)

(57) [Claims] 1. A white light source , an irradiation side optical system that forms an image of light emitted from the white light source on a sample having a light-coherent sample surface, and collects and receives reflected light from the sample. a light receiving side optical system for focusing on the element surface, and a light receiving element for knowing the change in the light receiving position, electron beams equipped with a detector for detecting a change in the imaging position on the light receiving surface - beam drawing An apparatus for writing an electron beam, comprising a sample height detecting device having a spherical plano-convex lens provided in each of a light irradiation optical system and a light receiving optical system. 2. A white light source, interference light friendly light emitted from the light source
An optical system on the irradiation side that forms an image with a lens in a diagonal direction on a sample that has an interfering sample surface, or a slit and the image of the slit irradiated with light emitted from the light source are imaged on the sample with a spherical plano-convex lens from an oblique direction. an irradiation-side optical system for the front
In order to detect the change in the light receiving position of the light receiving element and the light receiving side optical system that collects the reflected light from the sample with a spherical plano-convex lens and forms an image on the light receiving element surface height detecting device comprising a electron beam to detect the detection portion of the selected sample includes the - in beam drawing apparatus, the sample height detection device, the optical system of each sample of the light irradiation side and the light receiving side closest to the spherical plano-convex lens is constituted by a lens having at least one or more planes, electron beam wherein the one or more planes, characterized in that it is arranged substantially parallel to the lens optical axis - beam drawing apparatus. 3. The electron beam drawing apparatus according to claim 1, further comprising a conductive film formed on the lens surface.