JPS62140420A - Position detector of surface - Google Patents

Abstract

PURPOSE:To correct detection by using reference beams, and to enable precise detection with excellent reproducibility by irradiating a reference position on a light-receiving element with reference beams separately from reflected beams and detecting the quantity of displacement from a reference plane on the basis of the irradiation of reference beams. CONSTITUTION:A plurality of luminous flux having different wavelengths are projected, thus equalizing the interference action of detecting beams reflected by a surface to be detected and sections (the surface of resist and the surface of a semiconductor wafer 2 in the wafer 2 on which the photo-resist is applied) in the vicinity of the surface to be detected, then reducing a detection error due to the interference action of detecting beams. A detection output from a light-receiving element for detecting a position is corrected by using predetermined reference beams. A reference light source 20 generates reference beams for detecting the drift of the light source 20. Accordingly, the drift of the light- receiving element for detecting the position of detecting beams is detected and corrected by employing reference beams, thus accurately detecting the position of the surface of the wafer 2, etc. with excellent reproducibility.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a surface position detection device that detects the distance of an object surface from a reference surface. Such a surface position detection device is used, for example, in the field of semiconductor manufacturing, for use in an automatic focus control device of an exposure device called a stepper, which repeatedly exposes a reticle pattern on the surface of a semiconductor wafer by reducing projection. It is suitably used to detect the deviation of the

[Prior Art] Conventional methods for detecting the position of a wafer surface in a reduction projection exposure apparatus include a method using an air microsensor, and a method in which a beam of light is incident on the wafer surface from an oblique direction and the amount of positional deviation of the reflected light is detected. method (optical method) is known.

However, with the method using air microsensors, ■ pattern printing cannot directly measure the length, ■ response is slower than the optical method, and ■ the distance between the air microsensor nozzle and the wafer surface is 50 mm.
There was a problem in that highly accurate detection could not be achieved unless the distance was approximately 60 μm.

On the other hand, in the case of the optical method, the length of the pattern can be measured directly and the response is fast, but due to the presence of the resist coated on the wafer, the light reflected on the resist surface and the light reflected on the wafer surface are different. There is a problem in that highly accurate position detection is difficult because interference occurs and detection errors occur.

[Object of the invention] The object of the present invention is to solve the problems of the conventional type described above,
In an optical surface position detection device, by inputting multiple light beams with different wavelengths, detection light reflected from the detection surface and its vicinity (for a semiconductor wafer coated with photoresist, the resist surface and wafer surface) is detected. The surface position detection accuracy is improved based on the concept of averaging the interference effect, reducing detection errors due to the interference effect of the detection light, and correcting the detection output of the position detection light receiving element using a predetermined reference light. There is a particular thing.

[Explanation of Examples] Hereinafter, the present invention will be explained in detail using the drawings.

FIG. 1 shows the configuration of an automatic focus control device for a reduction projection exposure apparatus according to an embodiment of the present invention. In the figure, 1 is a reduction projection lens, and a wafer 2 is located below it. The wafer 2 is placed on a stage 3 that is vertically movable. The optical system of the automatic focus control device includes a plurality of light sources 4 and 5.
(In FIG. 1, for simplicity, only two light sources are depicted as a plurality of light sources). As the light source, lasers or LEDs with different wavelengths are used. The light fluxes (detection light) emitted from the light sources 4 and 5 form the same optical path through a beam splitter (or a half mirror) 6, pass through a lens 7, are reflected by a mirror 8, and are reflected at a reflection point on the wafer 2. image is formed.

At this time, the angle of incidence of the detection light on the wafer surface is set to be 80' or more, that is, the angle θ between the wafer surface and the incident light beam is set to 10° or less, and the detection light is made to be S-polarized with respect to the wafer. , the intensity of the reflected light from the resist surface becomes dominant, and the influence of the reflected light from the wafer substrate can be reduced.

The light beam reflected by the wafer 2 is reflected by the mirror 9, and then passes through the lens 10 and polarizing plate 11 (or polarizing beam splitter).
and then a beam splitter (or half mirror).
) 22, the light enters the position sensor diode 12 and forms an image.

The polarizing plate 11 (or polarizing beam splitter) allows only the S-polarized component in the light beam reflected by the wafer to reach the position sensor diode 12, thereby greatly reducing the component reflected by the wafer substrate in the detection light. It is something.

In this automatic focus control device, by maintaining an imaging relationship between the reflection point of the light beam on the wafer surface and the incident point on the light receiving element, vertical positional deviation of the wafer can be used as the incident position of the light beam on the light receiving element. This is detected and the focal position of the projection lens is automatically controlled.

Possible causes of positional deviation detection errors in optical focus position detection devices include the tilt of the wafer and the presence of a resist, which is a light-transmitting object, coated on the wafer.
The former detection error caused by the tilt of the wafer can be eliminated in principle by maintaining the imaging relationship between the reflection point on the wafer and the incident point of the light beam on the light receiving element, as described above.

On the other hand, the presence of the latter resist causes interference between the light reflected from the resist surface and the light reflected from the wafer surface, which appears as a shift in the center of gravity of the intensity of the light beam focused on the photodetector. . This means that the detected position differs depending on the thickness of the resist or the wavelength of the light used as the detection light.

Therefore, in order to enable more accurate position detection,
It is absolutely necessary to eliminate the interference effect of the resist on this detection light.

Next, the reduction of detection errors due to the interference effect of the resist with respect to the detection light will be explained using FIGS. 2 and 3.

FIG. 2 shows that a light beam 13 having a constant beam diameter and a uniform intensity within the beam diameter is incident on a wafer 2 coated with a resist 14 in an imaged state, and the surface of the resist 14 and the wafer 2 are 2 is a schematic diagram showing a state in which a light beam 15 exhibiting different intensity distributions within the beam diameter is formed by reflection on the surface of the light beam 2. FIG.

Further, FIG. 3 is a graph showing the intensity distribution in a state where the light beam 15 reflected and formed by the surfaces of the resist 14 and the wafer 2 is imaged on the light receiving element by the optical system.

In FIG. 2, a light beam 13 having a constant beam diameter and exhibiting a uniform intensity distribution within the beam diameter is incident on a wafer 2 coated with a resist 14 from an oblique direction. At this time, the light beam 13 undergoes multiple reflections between the component reflected by the surface of the resist 14 and the component transmitted through the resist 14 between the surface of the wafer 2 and the surface of the resist 14, and then exits outside the resist 14 again. It is divided into components that go. Resist 14 like this
The components reflected on the surface of the wafer 2 and the components reflected on the surface of the wafer 2 are combined to form a light beam 15 having different intensity distributions within the beam diameter, as shown in FIG. This light beam 15 passes through the mirror 9, lens 10, polarizing plate 11 and beam splitter 22 shown in FIG.
imaged on top.

In FIG. 3, the graph (■) shows the light intensity distribution on the light receiving element when a certain wavelength λ1 is used as detection light. Also,
Graphs ■ and ■ are for different wavelengths λ2. The light intensity distribution on the light receiving element is shown when λ3 is used as detection light. Roughly speaking, graph (2) shows the light intensity distribution on the light receiving element when a plurality of wavelengths λ1 to λn are used as detection light.

The intensity distribution of the detected light on the light receiving element when a monochromatic (or quasi-monochromatic) light source is used as the detection light is shown in the graphs ■ and ■.
, ■, a complicated intensity distribution is exhibited due to interference between the component reflected from the surface of the resist 14 and the component reflected from the surface of the wafer 2. Further, the distribution state of this intensity differs depending on the wavelength of the detection light and the thickness of the resist 14. Also,
Center of gravity of the intensity distribution of light detected by the light receiving element 16.17.
18 is output as a position signal, but if the wavelength of the detection light or the thickness of the resist 14 changes, the interference state changes, and the positions of the centers of gravity 16, 17, and 18 also change, resulting in detection errors.

By the way, this is what the inventors found after various studies, but when multiple monochromatic (or quasi-monochromatic) light sources are used as detection light, the intensity distribution of the detection light on the light receiving element is As shown in the graph ■, by using a multi-wavelength light source, the interference effect due to the presence of the resist is averaged out, and the center of gravity 19 of the intensity distribution of the detected light also shows a stable value regardless of the resist film thickness. . Therefore, by optically detecting the wafer surface position using such a multi-wavelength light source, it is possible to eliminate position detection errors caused by the presence of resist.

In addition, as shown in Figure 1, in addition to using multiple light sources with different wavelengths, the angle θ that the incident light makes with the wafer should be 10" or less, and the detection light should be S (two lights) with respect to the wafer. By using this, reflected light on the wafer surface is reduced, and the effects of the present invention can be further enhanced.

Furthermore, when a position sensor detector is used as a light-receiving element, a time change (drift) of a reference point in the position sensor detector is a factor that causes a detection error in a position signal. The reference light source 20 is for generating reference light for detecting this drift 1-.

Next, the drift correction of the position sensor detector 12 in the apparatus shown in FIG. 1 will be explained.

In the apparatus shown in the figure, the optical axis of the optical system and the reference point of the position sensor detector 12 are set such that the position signal of the position sensor detector 12 obtained from the reference light source 20 and the plurality of light sources 4.5 is zero. shall be adjusted when assembling and adjusting.

When actually aligning the wafer 2 with the focal plane of the projection lens 1, the reference light source 20 is first turned on to emit light before detecting the detection light for the wafer 2. Then, the light beam emitted from the reference light source 20 passes through the lens 21 and has its direction changed by the beam splitter 22, and then forms an image on the reference point of the position sensor detector 12. By detecting the position signal, it is possible to measure a change Δ over time in an electric signal (hereinafter referred to as a reference point signal) indicating the reference point of the position sensor detector 12.

Next, a position signal S of the detection light relative to the wafer 2 is detected. At this time, the time interval for measuring the temporal change Δ of the reference point signal and the position signal S is so small that no temporal change of the reference point signal of the position sensor detector 12 occurs. Since this position signal S includes the temporal change Δ of the reference point signal of the position sensor detector 12, by subtracting the position signal Δ when the reference light source 20 is emitted, highly accurate position detection is possible. Become.

That is, if the focal position detection device is controlled using the position signal (S-Δ), highly accurate positioning that does not include the influence of changes in the reference point of the position sensor detector 120 over time becomes possible.

In addition, by providing the stopper 23 at a position shifted toward the light receiving element by the focal length of the lens system 10 from the principal point of the detection side lens system 10 on the light receiving element side, the resist surface on the patterned wafer can be It is assumed that the higher-order diffracted light components of the reflected light that are reflected more are cut. As a result, even when performing position detection on a wafer with a pattern, the optical center of gravity of the detection light does not change due to higher-order diffracted light components. In other words, highly accurate position detection is possible even for wafers with patterns.

Note that the above-mentioned averaging of the interference effect can also be achieved by mixing the above-mentioned lights of multiple wavelengths, irradiating the same onto the wafer at the same time, and detecting the reflected light. The detection may be performed by individually detecting the signals by irradiating them, etc., and then calculating and processing the obtained plurality of detection signals. In particular, according to the latter method, it is possible to process even the deviation of the irradiation optical path for every eight lights due to adjustment errors and the like. This can be done, for example, by measuring the light-receiving position every 8 lights using a reference wafer to which no resist is applied in advance, and then correcting the deviation of these light-receiving positions by arithmetic processing when actually measuring the wafer surface position.

[Effects of the Invention] As explained above, according to the present invention, multiple lights of different wavelengths are used, so when there are multiple reflective surfaces for the detection light beam, such as a wafer surface coated with resist, The detection error due to the interference of the detected light is reduced, and the drift of the light receiving element for detecting the position of this detected light is reduced.
Since the reference light is used for detection and correction, the surface position of a wafer or the like can be detected accurately and with good reproducibility.

Further, the apparatus of the present invention is particularly effective for focusing a reduction projection lens of a reduction projection exposure apparatus that requires highly accurate focus detection. In this case, since highly accurate focus detection is possible, a pattern with high resolution can be formed, and a circuit with a higher degree of integration can be created.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing an automatic focus control device according to an embodiment of the present invention. FIG. 2 shows the resist surface and the image formed when a light beam is incident at a low angle on a wafer coated with resist. Figure 3, a cross-sectional view showing the state of reflection of a light beam on the wafer surface, shows the intensity distribution of the detected light when the light beam reflected on the wafer coated with resist enters the light receiving element and forms an image. This is a graph showing. 1... Reduction projection lens, 2... Wafer, 3... Stage, 4,5.20... Laser (or LED),
6... Beam splitter (or half mirror), 7
, 10.21... Lens system, 8.9... Mirror, 1
1゜22...Polarizing plate (or polarizing beam splitter)
, 12... Position sensor diode (or split sensor diode or C0D), 13... Luminous flux (incident luminous flux), 14... Resist, 15... Luminous flux (
reflected light flux), 16.17.18.19... center of gravity of intensity distribution, 23... stopper.

Claims (1)

[Claims] 1. A means having a plurality of light emitting means having different wavelengths and projecting light of each of these wavelengths onto a surface to be measured from an oblique direction; and a means for receiving reflected light from the surface to be measured; A light receiving element that outputs an analog electrical signal according to the light receiving position; a light source that irradiates a reference light to a reference position on the light receiving element separately from the reflected light; and an output of the light receiving element when the reflected light is received. and an electric signal processing means for detecting the amount of deviation of the surface to be measured from the reference surface based on the output when the reference light is received. 2. The surface position detection device according to claim 1, wherein the light projecting means includes a first optical system that forms substantially the same optical path for the light emitted from each of the light emitting means. 3. The surface position detection device according to claim 1 or 2, wherein the incident light on the surface to be measured is S-polarized light, and the angle between the incident light and the surface to be measured is 10 degrees or less. 4. The surface position detection device according to claim 1, 2 or 3, wherein the light projecting means simultaneously projects light of each of the wavelengths. 5. The surface position detection device according to claim 1, 2 or 3, wherein the light projecting means projects the light of each of the wavelengths in a time-division manner. 6. The surface position detection device according to any one of claims 1 to 5, further comprising a second optical system that makes the surface to be measured and the light receiving surface of the light receiving element substantially conjugate. 7. The surface position detection device according to any one of claims 1 to 6, wherein the surface to be measured is a sensitive material surface of a substrate coated with a sensitive material or a substrate surface.