JP3139023B2 - Electron beam apparatus and focus adjustment method for electron beam apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and an apparatus for detecting a wafer height for correctly exposing a wafer as an object to be exposed to an exposure optical system of an apparatus for exposing a semiconductor circuit. In particular, the present invention relates to a method and apparatus for detecting a height at which exposure can be performed correctly without affecting a subtle change in the thickness of a transparent layer such as a resist, an exposure method, and an apparatus therefor.

[0002]

2. Description of the Related Art The prior art is disclosed in
022, JP-A-63-163833 and the like are known.

[0003]

For example, in an electron beam exposure apparatus, since the depth of focus of electron beam imaging is deep, the height of the wafer is detected with an accuracy of about several μm, and the detected height data is used. The focus control of the electron beam lens is performed. However, as LSI circuits have been miniaturized, the height detection accuracy has been required to be 1 μm or less. However, in the above-mentioned prior art, no consideration has been given to obtaining a detection accuracy of 1 μm or less.

[0004] The purpose of the invention is to solve the above problems,
It is an object of the present invention to provide a height detecting method and apparatus capable of detecting a sample height with a high accuracy of 1 μm or less by minimizing a detection error with respect to a slight change in resist thickness.

Another object of the present invention is to provide an exposure method capable of detecting a height of a substrate on which a resist is applied with high precision of 1 μm or less so that a very fine pattern can be sharply exposed at a correct position. And an apparatus therefor.

[0006]

In order to achieve the above object, according to the present invention, in a focus adjusting method for an electron beam device, a substrate having an optically transparent film formed on a surface is irradiated with an electron beam. The area of the substrate irradiated with the electron beam is irradiated with light from the direction of the Brewster angle to the surface of the substrate, and the reflected light from the area irradiated with the electron beam due to the irradiation is detected by a detector, Using the information on the position of the detected reflected light on the detector, the height of the surface of the optically transparent film is detected,
Using the information on the detected height and the information on the refractive index and the thickness of the optically transparent film, height information of an area on the substrate surface where the electron beam is irradiated is obtained, and the obtained electron beam is obtained. The focus of the electron beam irradiating on the substrate surface is adjusted according to the height information of the irradiating area.

In order to achieve the above object, according to the present invention, an electron beam apparatus is provided with a table means on which a sample having an optically transparent film formed on a surface is mounted and movable, and An electron beam irradiating means for irradiating the surface of the placed sample with an electron beam, an irradiating means for irradiating a region on the surface of the sample to which the electron beam is irradiated with light from a Brewster angle direction, and Detecting means for detecting light reflected from, and height detecting means for detecting the height of the surface of the optically transparent film using information on the position of the reflected light detected by the detecting means on the detecting means, Using the height information detected by the height detecting means and the information on the refractive index and thickness of the optically transparent film, the height information of the area on the substrate surface where the electron beam is irradiated can be obtained with an accuracy of 1 μm or less. Required height information calculating means;
A focus adjusting unit configured to adjust a focus of the electron beam based on the height information obtained by the height information calculating unit when the substrate surface is irradiated with the electron beam by the electron beam irradiating unit.

[0008]

For example, light from a semiconductor laser or the like is convergently incident on the wafer surface at an incident angle of, for example, 45 °, and reflected light is formed on a position detection sensor as an image of an irradiation spot on the wafer. I was looking for height. When such a method is used, if the thickness of the resist on the wafer slightly changes depending on the location on the wafer, a large difference occurs in the height detection value. 4 to 6 show this situation.
This is a case in which light having a wavelength of 0.633 μm is incident on 45 ° incident S-polarized light (FIG. 4) and P-polarized light (FIG. 5) on a silicon wafer with a resist thickness of 0.0 to 5.0 μm. The detected value changes by 2 to 6 μm for a change in thickness of only 2 μm, and a large error occurs. In addition, multiple wavelengths (for example, 0.54, 0.58, 0.62
Even when light of (μm) is used, a large change in detection error still occurs due to a slight change in thickness as shown in FIG.

When a transparent object such as a resist is irradiated with light, the reflectance with respect to the incident angle is as shown in FIG. 2 depending on the incident angle and the polarization state of the light. That is, when the incident angle becomes the Brewster angle with the P-polarized light, the reflectance on the resist surface becomes 0%, and 100% of the light passes through the surface and enters the resist film. As a result, as shown in FIG.
The light reflected on the surface of the wafer under the resist is directed upward from below and is incident on the resist surface again. However, 100% of the light passes through the resist and escapes upward without being reflected on the resist surface. This indicates that the wafer surface under the resist is always detected regardless of the thickness of the resist. This is shown in FIG.
As compared with (b), the operation and effect of the present invention become clear.
That is, if the above conditions are not satisfied, the incident light 10 reflects off the resist surface and is not only 20 'towards the detector,
The light transmitted and reflected by the wafer travels from below to the resist surface, and the resist transmitted light travels to the detector as the detection light 20 and is reflected by the resist surface and returns to the wafer again. 20, 20 ',
20 '... Cause multiple interference. As a result, a slight change in the thickness of the resist greatly changes the interference intensity. As a result, as shown in FIGS. 4 and 5, a slight change in the resist thickness causes a large difference in the detection position, making it impossible to accurately detect the height. FIG. 3A shows the trajectory of the light beam detected by the method of the present invention, and no multiple reflection occurs inside the resist. Therefore, as shown in the graph of FIG. 5, the relationship between the thickness of the resist and the difference between the detected height and the height of the resist surface is linear, and the fluctuation of the error as shown in FIGS. 4 to 6 is not observed. Therefore, if the thickness of the resist is known, the position of the resist surface can be accurately detected.

As described above, the present invention accurately detects the resist surface or the wafer surface without being affected by a slight change in the thickness of the resist.

If the incident angle of the P-polarized light is in the range of ± 2 ° with respect to the Brewster angle, the light is slightly reflected from the resist surface, but the position of the resist surface can be detected.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on the principle of the present invention shown in the drawings and embodiments.

FIG. 1 shows the principle of detecting the height of a multilayer object according to the present invention.
FIG . Light emitted from a light source 11 such as a light emitting diode or a semiconductor laser is irradiated by a lens 12 so as to be substantially converged on a resist 31 applied on a pattern layer 32 of a wafer 3 which is an object to be detected. At this time, the light 10 irradiated by the irradiation means 1 has an incident angle of the Brewster angle θb and a polarization state of P-polarized light (a straight line polarized in a direction perpendicular to the plane including the principal ray of the incident light and the normal to the resist surface). (Polarized light). In this embodiment, since the refractive index n1 of the resist is 1.65, the Brewster angle θb is 5
8.8 °. In the case of a semiconductor exposure apparatus, the surface of an object to be detected is coated with a resist, and the refractive index thereof is almost equal to the above value. If the surface of the object has a different refractive index,
What is necessary is just to change the incident angle to the corresponding Brewster angle θb. However, this change may be determined according to the required accuracy, and in most resists, the above Brewster angle θb is sufficient.

As described with reference to FIG. 2, the light applied to the resist surface is transmitted 100% and the reflection at the surface is 0% due to the incident Brewster angle θb. As a result, only the light reflected on the surface of the pattern 32 of the wafer is incident on the position detecting means 2. The position detecting means 2 includes an image forming lens 22 and a light position detecting element 21, and a light spot on a resist (strictly, a light spot on a wafer pattern) forms an image on the light position detecting element 21. The position is detected as an electric signal. That is, if the wafer moves upward, the imaging position changes downward, and the height is obtained as an electric signal. FIG. 7 shows the relationship between the accurate resist surface height and the error in the detection position with a change in the thickness of the resist applied to the surface when the surface of the wafer to be detected is A1 or Si. is there. From this figure, the detected height is substantially a value obtained by subtracting a constant value proportional to the resist thickness from the surface of the resist, and as shown in FIGS. There is no fluctuation, and more accurate detection is possible. It should be noted that the method for accurately obtaining the above-mentioned constant value will be described later in connection with the principle of the present invention.
This will be described in detail in the following section .

FIG. 8 shows an electron beam exposure apparatus according to the present invention. The electron beam 41 emitted from the electron beam source 4 ′ passes through a lens system 6 ′ having a reduction and focusing lens and is imaged on the wafer 3. An electron beam resist is applied on the wafer 3, and various LSI circuit patterns are exposed to the electron beam on this surface. When the exposure of one area is completed, the wafer stage 71 on which the wafer 3 is fixed is driven by step and repeat, and moves to the next exposure area. At this time, the circuit pattern exposed on the wafer 3 is CP
Based on the graphic data from U8 ', a graphic of a desired shape is formed by ON / OFF control of the electron beam by the blanker 52. When the electron beam is blanked (position indicated by a broken line), the blanking aperture 53 turns on / off the electron beam 41.
Used as an FF shutter.

In an electron beam exposure apparatus, when a circuit pattern of 0.5 μm or less is directly exposed on the wafer 3 by an electron beam,
It is necessary to correct the height variation due to the warpage of the entire wafer or the local unevenness due to the heat treatment process. The amount of warpage may reach 200 μm. For these reasons, the height detecting means is the lens system 6 'of FIG.
It is provided between. That is, the irradiation means 1 shown in FIG. 8 irradiates P-polarized light at a Brewster angle θ toward the center of the exposure area on the wafer 3 which coincides with the position immediately below the electron beam. Is detected, and the height of the resist surface portion is detected as described in FIG. The height position information obtained at this time is fed back to the dynamic focus correction coil 72 through the detection circuit 8, and a pattern is formed while correcting the focus of the electron beam in accordance with the height displacement.

FIG. 9 is a diagram for explaining the principle of the present invention .
This is an example in which the principle of the present invention is applied to a reduction projection exposure apparatus using ultraviolet light among particle beam exposure apparatuses. Ultraviolet rays (i-ray or excimer laser light) emitted from the exposure illumination system 4 illuminate the reticle 5, and light transmitted through the reticle is reduced by a reduction lens 6.
Incident on. The circuit pattern 51 drawn on the reticle is imaged on the wafer 3 by the reduction lens. When the minimum line width of the circuit pattern 51 becomes 0.5 μm or less (converted on the wafer), the depth of focus becomes ± 1.0 μm or less. Therefore, the thickness of the resist applied on the wafer surface is about 1 μm.
In consideration of the above, it is necessary to accurately capture the surface of the resist or the lower surface of the resist, that is, the surface of the wafer pattern. However, in the reduction exposure apparatus, since the wafer 3 is driven by the wafer stage 7 and exposed in a step-and-repeat manner, the height of the wafer after the movement of the stage fluctuates. Alternatively, it is necessary to accurately detect the back surface.
For this reason, in the present embodiment, FIG.
According to the method described in the embodiment, the irradiation means 1 'irradiates P-polarized light at a Brewster angle toward substantially the center of the exposure area, and the position detection means 2' detects reflected light.
As described with reference to FIG. 3, the position on the substantially back surface of the resist is detected.

What is detected by the method of FIG. 9 is the back surface of the resist, that is, the position between the pattern surface and the resist surface.
When detecting the surface, the thickness T of the applied resist is known in advance, and if the value is input to the detection circuit 82 from the input terminal or the input terminal 81, the height of the resist surface can be detected. H is obtained from the detected height value H ′ and the input resist thickness value T based on the following equation.

[0019]

(Equation 1)

[0020] So, under normal resist is n = 1.65, is the Brewster angle θ than tan ~ ¹ n θ = 58.78
°, and H = 0.367T + H '. The difference ΔH between the height H of the resist surface thus obtained and the previously known target height H ₀ is obtained by the control circuit 83, and the wafer stage 7 is controlled to realize highly accurate exposure.

[0021]

According to the present invention, the height of the transparent resist surface can be accurately detected without being affected by the thickness of the resist, and the charged particle exposure with a small pattern drawing distortion can be performed.
There By realizing the formation of high-precision fine pattern becomes possible.

[Brief description of the drawings]

FIG. 1 illustrates the principle of detecting the height of a multilayer object according to the present invention.
1 is a schematic front view of a height detecting device according to an embodiment .

FIG. 2 is a diagram showing a relationship between an incident angle on a transmission object and a reflectance.

FIG. 3 is a diagram showing ± layer thicknesses and detected values of height detection of a multilayer object.

FIG. 4 is a diagram showing a relationship between a resist thickness and a detection error when detection is performed at an incident angle of 45 ° with P-polarized light.

FIG. 5 is a diagram illustrating a relationship between a resist thickness and a detection error when detection is performed with S-polarized light at an incident angle of 45 °.

FIG. 6 is a diagram illustrating a relationship between a resist thickness and a detection error when detection is performed at an incident angle of 45 ° with P + S polarized light.

FIG. 7 is a diagram illustrating a resist thickness and a detection error when detection is performed with P-polarized light at an incident angle of 59 ° close to the Brewster angle (58.78 °).

FIG. 8 is a schematic front view of an electron beam exposure apparatus according to the present invention.

FIG. 9 is a schematic front view of a reduction exposure apparatus illustrating the principle of the present invention.
FIG .

[Explanation of symbols]

 1. Irradiation means; 2. position detecting means; 3. the detected object; Exposure illumination system, 4 '. 4. an electron beam source; Reticle; Reduction lens, 6 '. Electron beam lens, 7,71. 72. wafer stage, Dynamic focus correction coil, 8, 8 '. 9. control circuit; Irradiation light, 20. Detection light.

────────────────────────────────────────────────── ─── Continued on the front page (72) Norio Kaneko, Inventor 882, Ma, Kata-shi, Ibaraki, Naka Plant, Hitachi, Ltd. (56) References JP-A-60-7922 (JP, A) JP-A-1 -107139 (JP, A) JP-A-59-188931 (JP, A) JP-A-60-136311 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/027

Claims (8)

(57) [Claims] An electron beam is irradiated on a substrate having an optically transparent film formed on a surface thereof , and light is irradiated to a region of the substrate irradiated with the electron beam with respect to the surface of the substrate at a Brewster angle. One
Irradiated from direction, the irradiation with detected by the detector light reflected from the area that is irradiated with the electron beam, the optically transparent with information on the position on the detector of the detected reflected light Detecting the height of the surface of the film, irradiating the electron beam on the substrate surface using the information of the detected height and the information of the refractive index and thickness of the optically transparent film. Determining the height information of the region where the electron beam is irradiated, and adjusting the focus of the electron beam irradiating on the substrate surface according to the obtained height information of the region irradiating the electron beam. Focusing method for line device 2. The method according to claim 1, wherein the irradiation light is P-polarized light.
Brewster irradiates polarized light to the area irradiated with the electron beam.
The height information of an area irradiated with the electron beam is obtained with an accuracy of 1 μm or less by irradiating from an angle direction and detecting reflected light from the substrate surface due to the irradiation. 2. The focus adjusting method for an electron beam device according to claim 1. 3. The focus adjusting method for an electron beam apparatus according to claim 1, wherein said optically transparent film is a resist. 4. The electron beam apparatus according to claim 1乃<br/> optimum 3, characterized in that the reflected light from the area that is irradiated with the electron beam, and detecting the imaging Focus adjustment method. Wherein said electron beam apparatus, the focus adjusting method of the electron beam apparatus according to any one of claims 1 to 3, characterized in that an electron beam exposure apparatus. 6. A table means on which a sample having an optically transparent film formed on the surface is mounted and movable, and an electron beam irradiating means for irradiating an electron beam on the surface of the sample mounted on the table means. , Bed in a region of irradiating the electron beam on the surface of the sample
Irradiating means for irradiating a light from Ryusuta angular direction, detecting means for detecting light reflected from the sample is irradiated by said irradiation means, said reflected light of said detected by the detecting means
Height detecting means for detecting the height of the surface of the optically transparent film using information on the position on the detecting means, and information of the height detected by the height detecting means and the optically transparent Height information calculating means for obtaining height information of an area of the substrate surface to be irradiated with the electron beam with an accuracy of 1 μm or less using information of a refractive index and a thickness of a film; An electron beam apparatus comprising: a focus adjusting unit that adjusts a focus of the electron beam based on the height information obtained by the height information calculating unit when the surface is irradiated with the electron beam. 7. The irradiating means emits an electron beam on the substrate.
7. The electron beam apparatus according to claim 6, wherein a region to be irradiated is irradiated with P-polarized light from a Brewster angle direction . Wherein said electron beam apparatus, an electron beam apparatus according to claim 6 or 7, characterized in that an electron beam exposure apparatus.