JP2780302B2 - Exposure equipment - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exposure apparatus, and more particularly, to the projection optics of a circuit pattern on a first object surface such as a mask or a reticle in the manufacture of semiconductor integrated circuits such as ICs and LSIs. BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reduced-projection type exposure apparatus having automatic end point control means suitable for performing projection exposure by focusing on a second object surface such as a wafer with high accuracy by a system.

(Related Art) In recent years, as a device for exposing and transferring a fine circuit pattern, a large number of reduction projection type exposure devices (so-called steppers) have been used in production sites of semiconductor manufacturing devices such as ICs and LSIs. In this reduction type exposure apparatus, an image of a circuit pattern drawn on a reticle (mask) is reduced by a projection optical system and projected onto a photoresist (photosensitive material) layer on a wafer.

Recently, with further miniaturization and high integration of circuit patterns for projection exposure, an exposure apparatus capable of higher-resolution and higher-precision projection exposure has been demanded.

In general, for example, when the wavelength of the exposure light is shortened or the numerical aperture of the projection optical system is increased in order to reduce the printing line width of the circuit pattern to be projected and exposed, the depth of focus is proportionally reduced in proportion to the square or the square. It is becoming. Then, for example, there arises a problem that the refractive index of the glass material constituting the projection optical system changes due to a change in ambient temperature, air pressure, or the like, and the focus position (focus plane) fluctuates.

Further, the wafer has a certain degree of thickness and variation in bending in view of the plane processing technology. Normally, with respect to the bending of the wafer, the flatness is corrected by sucking and fixing the wafer on a wafer chuck surface processed to a flatness of 1 μm or less. However, when the thickness of the wafer varies, it cannot be corrected.

Therefore, conventionally, a focus detector associated with the projection optical system and a predetermined position is provided in a part of the exposure apparatus, the focus surface of the projection optical system is fixed, and the wafer surface is positioned at that position. Had gone.

The positioning method using this focus detector detects the focus surface indirectly, and does not directly detect the focus surface. For this reason, the mechanical distance from the mounting surface of the focus detector to the actually projected circuit pattern image plane and the focus plane of the projection optical system change due to factors such as temperature fluctuations and atmospheric pressure fluctuations, and the exposure light The optical properties of the projection optical system change due to the absorption of light, and the focus surface fluctuates, so that it is very difficult to obtain a high printing resolution.

In particular, such a problem is more important in an exposure apparatus using an excimer laser that emits light having a wavelength of 248 nm, as well as an exposure apparatus using g-line as exposure light.

(Problems to be Solved by the Invention) The present invention projects a pattern on a reticle surface onto a wafer surface via a projection optical system, and performs exposure even when ambient conditions such as ambient temperature and atmospheric pressure change. An object of the present invention is to provide an exposure apparatus capable of always detecting a focal position with high accuracy, and simultaneously detecting the focal position, the amount of deviation from a wafer, and the direction of deviation, and easily obtaining a high resolution.

(Means for Solving the Problems) A feature of the present invention for achieving the above object is an exposure apparatus for projecting and exposing a pattern on a first object plane onto a second object plane via a projection optical system. A plurality of image sensors provided on surfaces different from each other with respect to a plane conjugate to the first object surface; and a plurality of image sensors provided on the second object surface via a photographic optical system. Detected by
Processing means for obtaining an optimum position of the second object plane in the high-axis direction of the projection optical system based on output signals from the plurality of imaging elements and a defocus characteristic of the projection optical system. And

(Embodiment) FIG. 1 is a schematic view of a main part of an exposure apparatus according to one embodiment of the present invention.

In the figure, reference numeral 11 denotes a light source, for example, an excimer laser, He
-Cd lasers, ultra-high pressure mercury lamps and the like. The linearly polarized light flux from the light source 11 is reflected by mirrors 10 and 9 and then enters the illumination system 8. The illumination system 8 irradiates a light beam from the mirror 9 to a reticle or mask (hereinafter, referred to as a “reticle”) as a first object via a polarizing beam splitter 7. The circuit pattern on the reticle 1 is projected and exposed by the projection optical system 3 onto the wafer 2 as a second object.

A resist as a photoreceptor is applied on the surface of the wafer 2, and is supported by a wafer chuck 4 by suction.
At this time, the polarizing beam splitter 7 efficiently reflects the linearly polarized light beam oscillating in a predetermined direction from the illumination system 8. Reference numeral 5 denotes a θ-Z-tilt stage as a correction assisting unit, which drives and controls the wafer chuck 4 in a focus direction (Z direction), which is an optical axis direction of the projection optical system 3, and in a tilt and rotation direction. Reference numeral 6 denotes an XY stage, and a wafer chuck 4
Are drive-controlled in the X and Y directions.

Reference numeral 101 denotes first detecting means, which includes a light projecting unit 12 for emitting a light beam for detecting the height direction of the surface of the wafer 2 and a light receiving unit 13 for receiving light reflected from the surface to be measured. The height of the surface in the Z direction is detected.

At this time, as a method of detecting the height direction (Z direction), for example, a method shown in Japanese Patent Application Laid-Open No. 62-140418 is used.

That is, the reflection point of the light beam from the surface of the wafer 2 and the light receiving element (CC
D) The incident point on the upper surface of the wafer 2
Is detected as an incident device for a light beam incident on the light receiving element surface, thereby detecting the position in the height direction.

Reference numeral 14 denotes a second detecting means for detecting a focus position of an image back-projected by the projection optical system 3 near the reticle 11 of the pattern on the wafer surface. The second detecting means 14 is, for example, a second detecting means.
As shown in the figure, four such detecting means are provided symmetrically with respect to the optical axis of the projection optical system 3 and movably in a plane parallel to the reticle. However, the number may not be four. It is sufficient if there are three or more.

In FIG. 2, reference numeral 22 denotes a pattern surface on the reticle 1 surface. 15 is an imaging lens, 16 and 17 are half mirrors, 18 and 2
Numerals 0 denote imaging devices, each of which is composed of, for example, a planar CCD. 21 is an image forming lens of the pattern surface 22 of the reticle surface, respectively.
15 shows an image forming position. That is, the CCD 18 has a conjugate relationship with the pattern surface 22 via the imaging lens 15, and the CCD 19
Is located at the position of the rear focus by the imaging lens 15, and the CCD 18 is located at the position of the front focus on the contrary, and is arranged offset by a predetermined amount.

FIG. 3A is a plan view of a main part of the reticle 1. In the figure
24 is an effective screen range, and 25 is a real element circuit pattern area. Reference numerals 26, 34, 35, and 36 denote transparent areas on the reticle 1 surface, for example, areas where a pattern as shown in FIG. 3B provided on a scribe line on the wafer surface 2 is back projected and transmitted. Is equivalent to And transparent areas 26,34,35,36
Are provided corresponding to the four second detection means 14 symmetrically arranged with respect to the optical axis of the projection optical system 3, respectively.

Referring back to FIG. 2, reference numeral 41 denotes an illumination lens, reference numeral 42 denotes an optical fiber for guiding light, and reference numeral 45 denotes a half mirror. Then, illumination light having the same wavelength as that of the exposure is introduced by the optical path switching mirror 43 shown in FIG. The illumination light is set so as to illuminate only the area of the pattern 27 provided on the wafer scribe.

 Next, the operation of this embodiment will be described.

In this embodiment, the wafer 2 is loaded on the wafer chuck 4 and fixed by a transfer system (not shown). The reticle 1 and the wafer are positioned so as to have a predetermined positional relationship by an alignment system (not shown). Then wafer 2
The height of the upper surface of the wafer 2 is measured at each position in the surface of the wafer 2 by driving the XY stage 6 by the first detecting means 101, and the variation such as the bending and thickness of the wafer 2 is measured.

Next, detection is performed by the second detection means, and before that, the second detection means 14 is set to move to a position on the reticle which is designated in advance (the positions 26, 34, 35, 36 in this example). The light from the light source 11 is guided to the optical fiber 43 by the optical path switching mirror 43, passes through the illumination lens 41 and the half mirror 45, passes through the transparent areas 26, 34, 35, and 36 on the reticle 1 surface, and passes on the wafer surface 2. Lighting.

In the scribe line area on the wafer 2 surface, the focus detection pattern as shown in FIG.
27 are formed, and the illumination light illuminates a local area on the scribe line including this pattern. Then, the pattern 27 is back-projected by the projection optical system 3 to the vicinity of the pattern surface 22 of the reticle 1, and focus detection is performed by the second detection means.

Here, the image formation plane (focus plane) of the pattern of the wafer 2 back-projected by the projection optical system 3 to the vicinity of the reticle 1 plane and the second plane
The relationship with the output signals from the respective light receiving elements (CCD) 18, 19, 20 of the detection means 14 is as shown in FIGS. 4 to 6, for example.

4 shows the output signal from the CCD 20, FIG. 5 shows the output signal from the CCD 18, and FIG. 6 shows the output signal from the CCD 19. The output characteristics as shown in FIG. 7 are obtained by processing the defocus characteristic values of the projection optical system 3 which are known in design and their respective output signals by a known electric processing system. From these results, the arithmetic means 102 detects the difference between the focus position of the projection lens 3 on the wafer surface and the pattern surface 22 of the reticle 1, that is, the amount of defocus, and converts it to the amount of defocus on the wafer surface. I have.

Such detection is performed for each position on the surface of the wafer 2 by the respective second detection means 14. From this result, in this example, the defocus amounts (as viewed from the reticle) at four points around one screen on the wafer could be detected. Further, similar detection is performed by driving the XY stage 6 over the entire surface of the wafer. Calculation means 102 based on the detection result by the second detection means and the detection result by the first detection means
The wafer 2 is controlled by the θ-Z-tilt stage 5 based on the signal from the controller 2 so that the wafer 2 is positioned at the optimum position in the Z direction by the projection optical system of the reticle 1, for example, for each shot.

For example, the wafer 2 is driven and controlled by the θ-Z-tilt stage 5 for each shot so as to correct the inclination and the focus of the wafer surface, thereby performing exposure.

As described above, in the present embodiment, the first detecting means detects the wafer bending and thickness variation, and the second detecting means detects the absolute value and the inclination of the focus shift, and calculates the optimum focus position based on the both to perform correction driving. Exposure is performed.

FIG. 8 is a schematic view of a main part of another embodiment of the second detecting means according to the present invention.

In the figure, a single light receiving element (CCD) 18 is driven and controlled in a focusing direction by a driving mechanism 28 using a piezoelectric element 29 such as a piezo element, so that the projection optical system 3 focuses the wafer surface. Has been detected. In this case, the driving amount is detected and controlled by known means.
As another example, the light-receiving element may be fixed and the θ-Z stage may be moved up and down. The handling of the signal output from the light receiving element 18 at each position is the same as the detection method shown in FIG.

In the above-described embodiment, θ-Z-ti
Although the wafer 2 is driven up and down using the lt stage and positioned on the focus plane, the wafer 2 can be substantially positioned on the focus plane without using the θ-Z-tilt stage. Any means may be used.

For example, in FIG. 1, a part of the mirror 9 is a semi-transmissive surface, a part of the illumination light beam is guided to the wavelength monitor 30, and a light source
The focus wavelength may be corrected by measuring the oscillation wavelength from 11, calculating the wavelength correction amount required for focus correction by the arithmetic processing system 31, and correcting the wavelength by the wavelength correction unit 32.

For example, since the relationship between the wavelength of the projection optical system and the focus position at the wavelength λ (248 nm) is as shown in FIG. 9, the focus position may be controlled by changing the oscillation wavelength based on this relationship. At this time, in order to prevent light leakage during the wavelength correction operation, a shutter 33 may be provided, and the shutter may be opened and closed.

In addition, when the wafer has no or little bending or thickness variation, it can be performed without the first detecting means.

The focus detection pattern may have a shape different from that of the embodiment, or may be an actual element pattern if exposure fog is allowed or non-exposure wavelength light is used as illumination light.

(Effects of the Invention) According to the present invention, when a pattern on a reticle surface is projected onto a wafer surface via a projection optical system, and exposure is performed, the pattern is always high even when environmental conditions such as ambient temperature and atmospheric pressure change. The focus position can be detected with high accuracy, and the focus position, the amount of deviation from the wafer, and the direction of the deviation can be simultaneously detected, so that an exposure apparatus that can easily obtain high resolution can be achieved.

[Brief description of the drawings]

FIG. 1 is a schematic view of a main part of an embodiment of the present invention, and FIGS.
(A) and (B) are explanatory views of a part of FIG.
FIG. 6 is an explanatory diagram of an output signal relating to a focus surface obtained from the detecting means according to the present invention, and FIG. 7 is an explanatory diagram showing a relationship between a defocus amount from the focus surface and an output signal obtained from the detecting means in the present invention. FIG. 8 is a schematic view of a main part of another embodiment of a part of the present invention, and FIG. 9 is an explanatory diagram showing a relationship between a wavelength of an illumination light beam and a focus position by a projection optical system in the present invention. In the figure, 1 is a reticle, 2 is a wafer, 3 is a projection optical system, 4 is a wafer chuck, 5 is a correction driving means (θ-Z-tilt stage), 6 is an XY stage, 7, 9, and 10 are mirrors, and 11 is a mirror. light source,
101 is a first detecting means, 14 is a second detecting means, 102 is a calculating means, 18, 19, 20 are CCDs, 28 is a driving mechanism, 29 is a piezoelectric element, 26,
Numerals 34, 35 and 36 are transparent areas, and 25 is a real element circuit pattern area.

Continuation of front page (58) Field surveyed (Int.Cl. ⁶ , DB name) H01L 21/027

Claims (1)

(57) [Claims] 1. An exposure apparatus for projecting and exposing a pattern on a first object plane onto a second object plane via a projection optical system, wherein the exposure apparatus is provided on a plane different from a plane conjugate with the first object plane. A plurality of image sensors, a pattern for focus position detection on the second object plane, which is detected by the plurality of image sensors via the projection optical system, and an output signal from the plurality of image sensors and the projection optical system Processing means for obtaining an optimum position of the second object plane in the optical axis direction of the projection optical system based on the defocus characteristic of the exposure apparatus.