JPH04254319A - Height detection method and its equipment and exposure method and its equipment - Google Patents

Abstract

PURPOSE:To realize exposure wherein the line width irregularity of a particle beam aligner is little and the distortion of an image is small, or to accurately obtain the height of an object of a multilayered structure to be detected. CONSTITUTION:A P-polarized light 10 is converged and projected on the surface of an object to be detected or an object 3 to be exposed, at an incident angle equal to the Brewster angle thetab, and the position of a reflected light 20 is detected with a position detector 21. When the thickness of resist is known, correction is performed by its value so that the accuracy is further improved. A large detection error of height is not caused by a very little thickness change of the uppermost layer (resist) 31 of a multilayered structure, and the above purpose can be surely attained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method and apparatus for detecting the height of a wafer in order to accurately expose a wafer, which is an object to be exposed, with high resolution in an exposure optical system of an apparatus for exposing semiconductor circuits. In particular, the present invention relates to a method and device for detecting a height that enables accurate exposure without being affected by subtle changes in the thickness of a transparent layer such as a resist, and an exposure method and device.

0002

[Prior art] As a prior art, Japanese Patent Application Laid-Open No. 01-170
No. 022, JP-A-63-163833, etc. are known.

0003

[Problems to be Solved by the Invention] For example, in an electron beam exposure apparatus, the depth of focus of electron beam imaging is deep, so the height of the wafer is detected with an accuracy of several μm, and the detected height data is used to detect the height of the wafer. Focusing control of the electron beam lens is performed. However, as the miniaturization of LSI circuits progresses, the height detection accuracy is now required to be 1 μm or less. However, in the above-mentioned conventional technology, no consideration was 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 detection method and an apparatus therefor, which can detect the height of a sample with high accuracy of 1 μm or less while minimizing detection errors due to slight changes in resist thickness.

Another object of the present invention is to provide an exposure method that detects the height of a substrate coated with a resist with high accuracy of 1 μm or less, and enables extremely fine patterns to be exposed sharply and at the correct position. and to provide its equipment.

[0006]

[Means for Solving the Problems] In order to achieve the above object, the present invention uses P-polarized light as the detection light, makes the light incident such that the incident angle is Brewster's angle, and the reflected light is A height detection method and device for detecting a position.

The present invention also provides an exposure method and apparatus using the above-mentioned height detection method and apparatus.

[0008]

[Operation] For example, light from a semiconductor laser or the like is convergently incident on the wafer surface at an incident angle of 45°, and the reflected light is imaged on the position detection sensor as an image of the irradiation spot on the wafer, and the position detection value is I was looking for height. When such a method is used, if the thickness of the resist on the wafer changes slightly depending on the location on the wafer, a large difference will occur in the detected height value. 4 to 6 illustrate this situation. S-polarized light with a wavelength of 0.633 μm at 45° incidence (Figure 4
), and P-polarized light (FIG. 5) with a resist thickness of 0.
This is a case where a wafer with a silicon base is irradiated with a thickness of 0 to 5.0 μm, and the detected value is 2 to 5.0 μm for a change in thickness of only 2 μm.
It will change by as much as 6 μm, resulting in a large error. Also, multiple wavelengths (e.g. 0.54, 0.58, 0.62 μm)
Even if this light is used, a small change in thickness still causes a large change in detection error as shown in FIG.

By the way, 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 polarization state of the light. That is, when the incident angle of P-polarized light becomes Brewster's angle, 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 Figure 3(a),
The light reflected from the surface of the wafer below the resist also turns upward from below and enters the resist surface again, but without being reflected by the resist surface, 100% of the light still passes through the resist and exits upward. This shows that the wafer surface under the resist is always detected regardless of the thickness of the resist. This is shown in Figure 3 (b) for cases other than the above conditions.
), the effects of the present invention become clear. That is, if the above conditions are not met, the incident light 10 will not only be reflected from the resist surface and directed toward the detector 20';
The light transmitted through the wafer and reflected by the wafer heads toward the resist surface from below, and the resist-transmitted light heads toward the detector as detection light 20, and is reflected by the resist surface and returns to the wafer again. By repeating this process, the detected light is 20, 20', 2
0'... causes multiple interference, and as a result, even a slight change in the resist thickness causes a large change in the interference intensity. As a result, as shown in FIGS. 4 and 5, a slight change in resist thickness causes a large difference in the detection position, making accurate height detection impossible. FIG. 3(a) shows the trajectory of the light beam detected by the method of the present invention, and multiple reflections within the resist do not occur. Therefore, as shown in the graph of FIG. 5, the relationship between the resist thickness and the difference in detected height with respect to the height of the resist surface is linear, and the error fluctuations as seen in FIGS. 4 to 6 are not observed. Therefore, if the thickness of the resist is known, the resist surface position can be detected accurately.

As described above, the present invention accurately detects the resist surface or wafer surface without being affected by subtle changes in resist thickness.

Note that if the incident angle of the P-polarized light is in the range of ±2° with respect to Brewster's angle, it will be slightly reflected from the resist surface, but the resist surface position can be detected.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below based on embodiments shown in the drawings.

FIG. 1 shows an embodiment of the multilayer object height detection device of the present invention. Light emitted from a light source 11 such as a light emitting diode or a semiconductor laser is transmitted through a lens 12 to a resist 3 coated on a pattern layer 32 of a wafer 3, which is an object to be detected.
The light is irradiated so that it almost converges to 1. At this time, the incident angle of the light 10 irradiated by this irradiation means 1 is Brewster's angle θ
b, and the polarization state is P-polarized light (linearly polarized light that is polarized in the direction perpendicular to the plane containing the principal ray of the incident light and the normal to the resist surface).
Make it so that In this example, the refractive index n1 of the resist is
is 1.65, so the Brewster angle θb is 58.
It becomes 8°. In the case of a semiconductor exposure apparatus, the surface of the object to be detected is coated with a resist, and the refractive index of the resist is almost equal to the above value. If the refractive index of the surface of the object to be detected differs, the incident angle may be changed to a Brewster angle θb corresponding to the difference. However, this change may be determined depending on the required accuracy, and the above-mentioned Brewster angle θb is sufficient for most resists.

As explained above with reference to FIG. 2, the light irradiated onto the resist surface is 100% transmitted due to the incidence at the Brewster angle θb, and 0% of the light is reflected at the surface. As a result, only the light reflected from the surface of the pattern 32 on the wafer enters the position detection means 2. The position detection means 2 consists of an imaging lens 22 and an optical position detection element 21, and detects a light spot on the resist (strictly speaking, a light spot on the wafer pattern).
is imaged on the optical position detection element 21, and the imaged position is detected as an electrical signal. That is, if the wafer moves upward, the imaging position changes downward, so the height can be determined as an electrical signal. In Figure 7, the surface of the wafer, which is the object to be detected, is A.
In the case of No. 1 and Si, the relationship between the accurate resist surface height and the detected position error is shown as the thickness of the resist applied to the surface changes. From this figure, the detected height is approximately the value obtained by subtracting a constant value proportional to the resist thickness from the resist surface, and as shown in FIGS. 4 to 6,
The detection value does not fluctuate greatly due to a slight change in resist thickness, and more accurate detection becomes possible. Note that a method for accurately determining the above-mentioned constant value will be explained in detail in Examples described later.

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 onto the wafer 3. An electron beam resist is coated on the wafer 3, and various LSI circuit patterns are exposed on this surface with an electron beam. 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 to move to the next exposure area. At that time, the circuit pattern exposed on the wafer 3 is CP
Based on the graphic data from U8', a blanker 52 controls ON/OFF of the electron beam to form a graphic of a desired shape. In addition, the blanking aperture 53 is used to turn the electron beam 41 ON/O during blanking of the electron beam (the position indicated by the broken line).
Used as a shutter for FF.

In the electron beam exposure apparatus, when a circuit pattern of 0.5 μm or less is directly exposed onto the wafer 3 with an electron beam,
It is necessary to correct warping of the entire wafer or height variations due to local unevenness due to the heat treatment process. This amount of warpage can reach as much as 200 μm. For these reasons, the height detection means are provided between the lens system 6' and the wafer 3 in FIG. That is, from the irradiation means 1 shown in FIG.
P-polarized light is irradiated at the Brewster angle θ toward the center of the exposure area on the wafer 3, which is directly under the electron beam, and the reflected light is detected by the position detection means 2. The height of the resist surface is detected as shown below. 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 above height displacement.

FIG. 9 shows an embodiment of the present invention, which is a reduction projection exposure apparatus using ultraviolet light among particle beam exposure apparatuses. The ultraviolet light (i-line or excimer laser light) emitted from the exposure illumination system 4 illuminates the reticle 5, and the light transmitted through the reticle enters the reduction lens 6. The circuit pattern 51 drawn on the reticle is imaged onto the wafer 3 by a reduction lens. The minimum line width of the circuit pattern 51 is 0.5 μm
(on wafer equivalent) or less, the depth of focus is ±1.0μ
m or less. Therefore, considering that the thickness of the resist applied to the wafer surface is approximately 1 μm, it is necessary to accurately capture the resist surface or the lower surface of the resist, that is, the wafer pattern surface. However, in the reduction exposure apparatus, the wafer 3 is exposed by driving the wafer stage 7 and exposing the wafer 3 in a step-and-repeat manner, so that the height of the wafer changes after the stage is moved, so that the resist surface is precisely aligned with the above resist surface each time the stage is moved. Or it is necessary to accurately detect the back side. Therefore, in this embodiment, from between the reduction lens and the wafer, the method explained in the embodiment of FIG.
The irradiation means 1' irradiates P-polarized light at the Brewster's angle toward the approximate center of the exposure area, and the position detection means 2' detects the reflected light.As explained in FIG. Detect the position of.

What is detected by the method shown in FIG. 9 is the back side of the resist, that is, the position between the pattern surface and the resist surface.
When detecting the surface, since the thickness T of the applied resist is known in advance, by inputting that value to the detection circuit 82 from the input terminal or input terminal 81, the height of the resist surface can be determined. H is determined from the detected height value H' and the input resist thickness value T based on the following formula.

[0019]

[Math 1]

[0020] Since n=1.65 in a normal resist, the Brewster angle θ is θ=58.7 from tan￣1n.
8°, and H=0.367T+H'. The control circuit 83 determines the difference ΔH between the height H of the resist surface determined in this manner and the target height H0 known in advance, and controls the wafer stage 7 to realize highly accurate exposure.

[0021]

[Effects of the Invention] The present invention makes it possible to accurately detect the height of a transparent resist surface without being affected by the thickness of the resist, and enables charged particle exposure with small pattern drawing distortion and small line width variations. The realization of optical exposure has made it possible to form fine patterns with high precision.

[Brief explanation of the drawing]

FIG. 1 is a detection principle diagram of a multilayer object height detection device according to the present invention.

FIG. 2 is a diagram showing the relationship between the angle of incidence on a transparent object and the reflectance.

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

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

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

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

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

FIG. 8 is a diagram showing an embodiment of an electron beam exposure apparatus according to the present invention.

FIG. 9 is a diagram showing an embodiment of a reduction exposure apparatus according to the present invention.

[Explanation of symbols]

1. irradiation means, 2. position detection means, 3. Detected object, 4. exposure lighting system, 4'. electron source, 5. reticle, 6. reduction lens, 6’. electron beam lens, 7,71. wafer stage, 72. dynamic focus correction coil, 8,8'. control circuit, 10. irradiation light, 20. detection light.

Claims (9)

[Claims] Claim 1: Directs the light obtained from the light source onto the surface of the object to be measured.
A height detection method characterized by irradiating polarized light with an incident angle approximately at Brewster's angle, forming an image of reflected light from the surface, and detecting its position. 2. The height detection method according to claim 1, wherein the height detection result is corrected using information regarding the refractive index and thickness of the object to be measured. 3. The height detection method according to claim 1, wherein the object to be measured is formed of a multilayer object. 4. An irradiation means for irradiating light emitted from a light source onto an object to be measured in a P-polarized state at an incident angle of approximately Brewster's angle; 1. A height detection device comprising a detection means for detecting an image. 5. The apparatus according to claim 4, further comprising an input means for inputting information regarding the refractive index and thickness of the multilayer object, and a correction means for correcting the height detection result using the information. height detection device. 6. Irradiating the surface of the object to be exposed with light obtained from a light source as P-polarized light with an incident angle approximately at Brewster's angle;
An exposure method comprising: forming an image of reflected light from the surface, detecting the position thereof, controlling the detected position of the surface of the object to be exposed, and exposing the surface with a desired pattern. 7. The exposure method according to claim 6, wherein the desired pattern is exposed to charged particles or light. 8. An irradiation means for irradiating the surface of an object to be exposed with light emitted from a light source in a P-polarized state at an incident angle of approximately Brewster's angle; A height detection device including a detection means for detecting an image, a control device for controlling the position of the object to be exposed based on height information detected by the height detection device, and a control device for controlling the position of the exposed object based on height information detected by the height detection device; An exposure apparatus that exposes a controlled object to a desired pattern. 9. The exposure apparatus according to claim 8, wherein said exposure apparatus is constituted by a particle beam exposure apparatus.