JPH0217929B2 - - Google Patents

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.
It is suitably used for an automatic focus control device of an exposure apparatus called a stepper which repeatedly performs reduction projection exposure of a reticle pattern onto the surface of a semiconductor wafer to detect a shift between the wafer surface and the reticle pattern imaging plane.

[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. (optical method) is known.

However, with the air microsensor method, the length of the pattern printed area cannot be directly measured, the response is slower than the optical method, and the distance between the air microsensor nozzle and the wafer surface must be kept close to 50 to 60 μm. High precision detection is not possible.

There was such a problem.

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

In addition, in the case of the optical method, the reflected light from the wafer is received by a position detection light receiving element, and the output from this light receiving element is detected according to the receiving position of the reflected light.
The position of the wafer is detected based on this output, but there is a problem in that the output from the light receiving element fluctuates due to changes in temperature, humidity, etc., resulting in detection errors.

[Objective of the Invention] In view of the above-mentioned problems with the conventional type, an object of the present invention is to detect the surface to be detected and its vicinity (photograph) by inputting a plurality of light beams with different wavelengths in an optical surface position detection device. In the case of a semiconductor wafer coated with resist, the interference effect of the detection light reflected from the resist surface and the wafer surface is averaged, reducing detection errors due to the interference effect of the detection light, and the predetermined reference light (standard light) is The objective is to improve surface position detection accuracy based on the concept of correcting the detection output of the position detection light receiving element using the sensor.

[Summary of the Invention] In order to achieve the above object, the surface position detection device of the present invention is a device for detecting the surface position of a wafer 2 coated with resist, in which the wafer is irradiated with a plurality of lights having different wavelengths. light projecting means 4, 5, 6, 7, 8, photoelectric conversion means 12, and a standard for outputting a reference signal from the photoelectric conversion means by irradiating reference light onto a predetermined position on the light receiving surface of the photoelectric conversion means; Light irradiation means 20, 21, 22 and the reflected light generated by the wafer due to light irradiation by the light projecting means are focused on the light receiving surface of the photoelectric conversion means, and the reflected light is transmitted from the photoelectric conversion means to the predetermined position. and a condensing optical system 9, 10, 11, 22, 23 that outputs a position signal according to the condensing position of the wafer. The present invention is characterized in that a light projecting means and the condensing optical system are arranged, and the surface position of the wafer is detected based on the reference signal and the position signal from the photoelectric conversion means.

[Description of Examples] Examples of the present invention will be described below with reference to 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 has a plurality of light sources 4 and 5 (for simplicity, only two light sources are depicted as a plurality of light sources in FIG. 1). As a light source, lasers or LEDs with different wavelengths are used. The light flux (detection light) emitted from these light sources 4 and 5 is sent to a beam splitter (or a half mirror may be used)
6 to form the same optical path, and after passing through a lens 7, it is reflected by a mirror 8 and an image is formed on a reflection point on the wafer 2. Here, the plurality of light sources 4 and 5, the beam splitter 6, the lens 7, and the mirror 8 constitute a light projecting means for irradiating the wafer 2 with a plurality of lights having different wavelengths.

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

The light beam reflected by the wafer 2 is reflected by the mirror 9, passes through the lens 10 and the polarizing plate 11 (or polarizing beam splitter), and further passes through the beam splitter (or half mirror) 22, and then passes through the position sensor diode 12 ( The light enters the photoelectric conversion means) and forms an image. Here, mirror 9 and lens 10
The polarizing plate 11, the beam splitter 22, and the stopper 23 constitute a condensing optical system that condenses reflected light generated by the wafer 2 onto the position sensor diode 12.

Polarizing plate 11 (or polarizing beam splitter)
This is to allow only the S-polarized component in the light beam reflected by the wafer to reach the position sensor diode 12, thereby further reducing the component reflected by the wafer substrate in the detection light.

As shown in the figure, this automatic focus control device includes light projecting means 4, 5, 6, 7, 8, condensing optical systems 9, 10, 11, 22, 23, and a position sensor diode 12, and By maintaining an imaging relationship between the reflection point of the light beam on the surface and the incident point on the photodetector, vertical positional deviation of the wafer can be detected as the incident position of the light beam on the photodetector, and the focal position of the projection lens can be adjusted. I am trying to do automatic control.

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, but the detection error caused by the former tilt of the wafer is , as described above, can be eliminated in principle by maintaining an imaging relationship between the reflection point on the wafer and the incident point of the light beam on the light receiving element.

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 a wafer 2 coated with a resist 14.
A light beam 13 having a constant beam diameter and uniform intensity within the beam diameter is incident on the beam in an imaged state,
2 is a schematic diagram showing a state in which a light beam 15 showing different intensity distributions within the beam diameter is formed by reflection on the surface of the resist 14 and the surface of the wafer 2. FIG. Further, FIG. 3 is a graph showing the intensity distribution of the light beam 15 reflected and formed by the resist 14 and the surfaces of the wafer 2, when the light beam 15 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 repeats multiple reflections between the surface of the resist 14 and the surface of the wafer 2 after passing through the resist 14 and the surface of the resist 14, and then exits 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. 1, and forms an image on the light receiving element 12.

In FIG. 3, the graph shows the light intensity distribution on the light receiving element when a certain wavelength λ ₁ is used as detection light. Further, the graphs and graphs show the light intensity distribution on the light receiving element when different wavelengths λ ₂ and λ ₃ are used as detection light. Furthermore, the graph shows the light intensity distribution on the light receiving element when a plurality of wavelengths λ ₁ to λn are used as detection light.

When a monochromatic (or quasi-monochromatic) light source is used as the detection light, the intensity distribution of the detection light on the light receiving element is as shown in the graph . shows a complex intensity distribution due to interference of reflected components.
Further, the distribution state of this intensity differs depending on the wavelength of the detection light and the thickness of the resist 14. In addition, the center of gravity 16,1 of the intensity distribution of the detected light is determined by the light receiving element.
7 and 18 are output as position signals, but if the wavelength of the detection light or the thickness of the resist 14 changes, the interference state changes, and the center of gravity 16, 17, 18
The position of will also change, which will appear as a detection error.

By the way, this is what the inventors of the present invention have determined after various studies.
As shown in the graph, when multiple monochromatic (or semi-monochromatic) light sources are used as detection light, the intensity distribution of the detection light on the photodetector is as follows: As a result, 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 exhibits a stable value regardless of the thickness of the resist. 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.

Additionally, as shown in Figure 1, multiple light sources with different wavelengths should be used, the angle θ between the incident light and the wafer should be 10 degrees or less, and S-polarized light with respect to the wafer should be used as the detection light. As a result, 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. Reference light source 20
is for generating a reference light (reference light) for detecting this drift.

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

In the device shown in the figure, the optical axis of the optical system and the reference point of the position sensor diode 12 are set such that the position signal of the position sensor diode 12 obtained from the reference light source 20 and the plurality of light sources 4 and 5 is zero. Adjustment shall be made when assembling and adjusting this device.

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 reference light emitted from the reference light source 20 passes through the lens 21 and is redirected by the beam splitter 22, and then passes through the position sensor diode 1.
The image is formed on the second reference point. By detecting the position signal, the position sensor diode 12
It is possible to measure the temporal change Δ of an electrical signal indicating a reference point (hereinafter referred to as a reference point signal). Here, the reference light source 20, lens 21, and beam splitter 22 constitute a reference light irradiation means for outputting a reference point signal from the position sensor diode 12.

Next, a position signal S of the detection light relative to the wafer 2 is detected. At this time, the time interval at which the time-dependent change Δ of the reference point signal and the position signal S are measured is so small that the reference point signal of the position sensor diode 12 does not change over time. Since this position signal S includes the radial change Δ of the reference point signal of the position sensor diode 12,
By subtracting the position signal Δ when the reference light source 20 emits light, highly accurate position detection becomes possible. In other words, if the focal position detection device is controlled using the position signal (S-Δ),
Highly accurate positioning is possible without being affected by changes in the reference point of the position sensor diode 12 over time.

At this time, by providing a stopper 23 at a position shifted toward the light receiving element by the focal length of the lens system 10 from the principal point on the light receiving element side of the lens system 10 on the detection side, the resist surface on the patterned wafer can be It is assumed that high-order diffracted light components of the reflected light are cut out. 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 plural wavelengths of light and irradiating the same onto the wafer at the same time, and detecting the reflected light. The detection may be carried out by individually detecting the light beams by irradiating the light beams in divided portions, etc., and then performing arithmetic processing on the plurality of detection signals obtained. In particular, according to the latter method, it is possible to process even deviations in the irradiation optical path of each light due to adjustment errors and the like. This can be done by, for example, measuring the light receiving position for each light using a reference wafer to which no resist is applied in advance, and 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 caused by the interference of the detected light is reduced, and the drift of the light receiving element used to detect the position of the detected light is detected and corrected using the reference light, making it possible to accurately and reproducibly determine the surface position. The surface position of a wafer, etc. can be detected well.

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, and 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 the light beam on the wafer surface, shows the distribution of the intensity 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, 11, 22 ... Polarizing plate (or polarizing beam splitter), 12 ... Position sensor diode (or split sensor diode or CCD), 13 ... Luminous flux (incident luminous flux), 14...
...Resist, 15... Luminous flux (Reflected luminous flux, 16, 1
7, 18, 19... center of gravity of intensity distribution, 23... stopper.

Claims (1)

[Claims] 1. In an apparatus for detecting the surface position of a wafer coated with resist, a light projecting means for irradiating the wafer with a plurality of lights having different wavelengths, a photoelectric conversion means, and a predetermined position on the light receiving surface of the photoelectric conversion means. a reference light irradiation means for irradiating a reference light onto the wafer and outputting a reference signal from the photoelectric conversion means; a condensing optical system for outputting a position signal from the photoelectric conversion means according to a condensing position of the reflected light with respect to the predetermined position; The surface position detection is characterized in that the light projecting means and the light condensing optical system are arranged so as to change, and the surface position of the wafer is detected based on the reference signal from the photoelectric conversion means and the position signal. Device.