JPH01209304A - Device for detecting position - Google Patents

Abstract

PURPOSE:To homogenize a distribution of outgoing beams and improve positioning accuracy by a method wherein a plural number of light fluxes are provided and a light flux having a cross section according to the shape of a physical optical element is formed by overlapping a portion of the light fluxes. CONSTITUTION:Light beams emitted from light sources 1, 1a are made parallel by projector lenses 2, 2', respectively, and enters an exposure region including an alignment mark 41M via a beam splitter 92. the alignment mark 41M has a function of a convex lens which focuses the beam to a point Q on a transmission-type zone plate. A wafer alignment mark 41W has a function as a convex mirror which focuses the beams focused to the point Q and forms an image on a detecting plane 90 of a photodetector 38. Difference in position is calculated by the photodetector 38 and a wafer stage 102 is transferred according to this calculated value so as to align a mask 101 and a wafer 102.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a highly accurate alignment device, and particularly to a device for relative alignment between a mask or a reticle and a wafer in a semiconductor exposure apparatus.

[Conventional technology]

In recent years, semiconductors have become highly integrated, and IMBi
Mass production of 4 Mbit DRAM began in 2013, and the trend is toward higher integration.

With this increase in integration density, the minimum line width on the wafer surface has become less than 1 μm, and the alignment (alignment, alignment) accuracy between the mask and wafer required for semiconductor exposure equipment is less than 0.2 μm. It becomes.

Conventionally, alignment marks have been provided on masks and wafers, and alignment has been performed based on their positional information.

There are alignment methods that perform evaluation by detecting pattern deviations on masks and wafers through image processing, or by detecting the focal point position of an irradiation beam using a zone plate as a mark. Among them, the method of fabricating zone plates on the mask and wafer respectively and detecting the positional deviation of the incident beam is attracting attention because it is not easily affected by mark defects (USP 4,037,969, Japanese Patent Application Laid-Open No. 157033-1982). ).

The configuration is shown in FIG. 1O.

The parallel beam emitted from the light source 72 is focused by a condensing lens 76, passes through a condensing point 78, and is irradiated onto the alignment mark on the mask 68 and the alignment mark on the wafer 60. These alignment marks are composed of reflective zone plates, each of which creates a focal point on a plane perpendicular to the optical axis including 78.

This displacement of the focal point on the plane is guided onto a detector 82 using lenses 76 and 80 and detected. At this time, FIG. 11 shows a detailed explanation of the imaging relationship of light from the mask mark and the wafer mark.

A portion of the light beam diverged from the condensing point 78 is diffracted by the mask mark on the mask 68 to form a condensing point that focuses the mask position in the vicinity of the condensing point 78 .

A part of the light passes through the mask 68 as zero-order transmitted light and is irradiated onto the alignment mark on the wafer 60 without changing the wavefront. The light diffracted from the wafer mark passes through the mask 68 again.
The light is transmitted as zero-order transmitted light and is focused near 78 to form a focusing point that focuses on the wafer position. That is, wafer 6
In forming the focal point of 0 light, the mask only functions as a transparent light.

The focal point position of the wafer mark thus formed moves by Δσ', which is approximately the same as Δσ, along a plane including 78 and perpendicular to the optical axis in accordance with the deviation Δσ of the wafer with respect to the mask. This Δσ′ is detected by a photoelectric detector 82.
The amount of lateral deviation between the mask and wafer is detected by
The control circuit 84 that receives the output signal of the detector 82 drives the fine movement mechanism 64 based on this signal, thereby adjusting the mask 6.
8 and the wafer 60 are aligned.

[Problem to be solved by the invention] As mentioned above, when detecting the position between the mask and the wafer using a physical optical element such as a Fresnel zone plate, monochromatic light (or quasi-monochromatic light) is used as the light source. Since a laser beam is usually used, the illuminance distribution on the alignment mark is generally close to a Gaussian distribution. In particular, in the case of a semiconductor laser, as shown in FIG. 5, the divergence angle of the luminous flux is different in the direction parallel to and perpendicular to the active stratification layer, and the divergence angle in the perpendicular direction is generally large. FIG. 5 shows how a light source image of the semiconductor laser 1 is formed by providing a condensing lens 2, and the illuminance distribution near the pupil plane of the condensing lens 2 is generally a far-field pattern, and the illuminance distribution near the light source image is shown in FIG. is called a near-field pattern, and when the astigmatism of the semiconductor laser is sufficiently small, the wavefront at the position of the light source image (this is called the beam waist position) becomes a plane wave, and the e-2 of the spot at that time becomes a plane wave.
The radius of intensity is called the beam waist radius.

On the other hand, alignment marks in semiconductor exposure equipment are preferably placed on the scribe line in order to reduce the occupied area.
In that case, it is customary to keep the scribe line width within the range of 20 to 100 μm (with a length of 500 μm or less). At this time, the method generally used is to condense the light using the condenser lens 2 shown above and create a beam waist on the alignment mark.

However, the illuminance distribution at this time becomes a Gaussian distribution as described above, and has the following problems.

That is, as shown in FIG. 6, if the beam and the mark deviate from the normal positional relationship and the illuminance distribution on the alignment mark changes greatly, a phenomenon occurs in which the center of gravity of the diffraction focus of the condensed light beam shifts. For example, in the example shown in FIG. 10, the center of gravity of the spot on the sensor surface formed by the grating lens on the mask and the grating lens on the wafer moves, which causes a decrease in alignment accuracy. This also becomes a factor in other physical optical elements, such as variations in the center of gravity of the diffracted light beam. To solve this problem, it is possible to position the irradiation light with respect to the mark with high precision, or to enlarge the diameter of the irradiation spot on the mark and use the light from the center. However, the former requires a complicated mechanism for measuring the length of the light emitting and receiving optical systems, and the latter reduces the signal light reaching the sensor surface and applies partial force illumination light without marks.
This has the disadvantage of increasing the scattered noise component therefrom, resulting in a decrease in S/N.

In view of the drawbacks of the conventional examples described above, the present invention has been developed to detect the position of an object by detecting the deflected light beam by a physical optical element such as a Fresnel zone plate on the object, even if there is a change in the positional relationship between the beam and the mark. Detection accuracy deteriorates (< and S
An object of the present invention is to provide a position detection device that does not easily cause a decrease in /N.

[Means to solve the problem]

In order to solve the above-mentioned problems, the present invention provides a plurality of light beams and partially overlaps each light beam to form a light beam having a cross-sectional shape according to the shape of the physical optical element, thereby irradiating the alignment mark. The distribution is made substantially uniform without reducing the energy of the light, and even if there is some variation between the mark and the beam, the output luminous flux does not vary.

In other words, the alignment mark is irradiated with a combined light beam of multiple light beams set at predetermined intervals, and the irradiation energy distribution becomes closer to uniformity within the alignment mark compared to the case of irradiating a single beam of light. At the same time, they are arranged so that the energy outside the alignment mark is thick (lower).
It is possible to provide an alignment device that does not cause deterioration in alignment accuracy even if the setting accuracy of the alignment mark on the pickup casing including the light receiving system is poor. This conceptual diagram is shown in FIG.

〔Example〕

FIGS. 1(a), (b), and (C) are views of a mask aligner equipped with a position detection device of the first embodiment that best illustrates the features of the present invention. FIG. The configuration diagram of the position detection device of the embodiment, FIG. 1(b) is a diagram of the same principle, FIG.
C) In this embodiment, the position detection mark is supported by the aligner body 95 via a mask chuck 96. A master wafer alignment head 94 is arranged above the main body 95.

In order to align the mask 101 and the wafer 102, alignment marks 41M and 41W are set on the mask 1, respectively.
01 and is printed on the wafer 102.

1 and 1' are semiconductor lasers that are monochromatic light sources, 2 and 2'
is a condensing lens for condensing the light beam of the semiconductor laser, 3
is a half mirror for combining two beams of light.

Light source 1. The light beams emitted from the light beams 1' are each turned into parallel lights by the projection lenses 2 and 2', and are incident on the exposure area 43 including the alignment mark 41M, which passes through the beam splitter 92. The alignment mark 41M is a transmissive zone plate that functions as a convex lens to focus light on the point Q. The wafer alignment mark 41W is a reflective zone plate and functions as a convex mirror that images the light focused on the point Q onto the detection surface 90 of the photoelectric detector 38.

Under this arrangement, the wafer 2 is at Δ with respect to the mask 1.
When there is a lateral shift by σ, the positional shift Δδ of the center of gravity of the luminous flux on the detection surface 90 is expressed as follows.

It will be done.

It becomes 99 times. At this time, Δδ is proportional to Δσ, as is clear from the equation, and if the resolution of the sensor is 0.1 μm, the detected positional deviation amount Δσ
has a position resolution of 0.001 μm.

In this manner, the amount of positional deviation Δσ9 is determined by the photoelectric detector 38, and based on this amount, the wafer stage 102a is moved by the amount of positional deviation Δσ in a direction that corrects the deviation using a wafer stage driving means (not shown). This makes it possible to accurately align the mask and wafer.

By combining the two light beams, the light beam irradiated onto the mask 101 is directed in the longitudinal direction (X direction) of the light intensity mark of the portion irradiated onto the mark, as shown in FIG. 1(b).
becomes almost uniform. Therefore, even if the incident position of the light beam is slightly shifted in the vertical direction of the drawing, the symmetry of the light intensity of the portion of the light beam irradiated onto the mark will not change in practical terms. Therefore, as shown in FIG. 7, the fluctuation of the diffracted light due to the above-mentioned beam deviation hardly occurs. Further, the area for illuminating the periphery of the mark is sufficiently smaller than that in the case where the spot diameter of the irradiation light beam is enlarged and the mark is irradiated in a central portion where there is little variation in diffracted light. Therefore, the amount of disturbance light including scattered light from the surrounding area is small. Note that marks 41M and 41W have a lens action only in the X direction as a deflection action, and in the X direction, the traveling direction of the light flux is It has the effect of deflecting at a certain angle.

FIGS. 2 and 3 show other embodiments 2 and 3, which are examples in which a polarizing beam splitter 7 and a half-wave plate 8 are used. These are intended to improve the drawback of the first embodiment that energy is lost in the 71-fumirror 3. That is, in general, the polarization plane of a semiconductor laser is the short axis direction of the far field pattern, and the characteristics of a polarizing beam splitter that transmits P polarized light and reflects S polarized light are used to make the active layer of the semiconductor laser. By selecting the direction and the position of the half-wave plate as shown in FIG. 2 or 3, the long side and short axis side of the far field can be set without energy loss. In addition, in the optical path after combining the two beams, the beam whose principal ray is 6 on the reflection side is S-polarized light, and 6' on the transmission side is S-polarized light.
Since the luminous flux whose principal ray is P-polarized light, a quarter-wave plate 9 is installed to make both circularly polarized light. This is a particularly preferable means when it is desired to avoid a phenomenon in which the diffraction efficiency differs depending on the grating direction and the direction of the polarization plane when the lattice spacing of the physical optical element serving as the alignment mark includes one close to the wavelength. If the grating interval is sufficiently longer than the wavelength, it is not necessary to set the quarter-wave plate 9. Furthermore,
As another embodiment, as shown in FIG. 4, a partially reflecting mirror 10 having a transmitting part except for the totally reflecting part 10a and a composite lens 11 may be combined. In addition, in FIGS. 1 to 4, it is preferable that the chief rays of each light beam be substantially parallel in order to prevent the image size on the sensor surface from becoming thick.The method of overlapping the light beams will be explained in detail.

The emission angle of a semiconductor laser is - half intensity.

The side parallel to the active stratification layer is shown as θ//, and the side perpendicular to the active stratification layer is shown as θ, and for convenience, the distance between the light source and the main plane on the light source side of the condensing lens is assumed to be g. In a so-called collimated state where a geometrical optical light source image is formed at infinity, g becomes the focal length f of the condenser lens. On the other hand, if the light intensity distribution of a semiconductor laser, etc. is I(x, y), and the radius determined by the e-2 intensity mentioned above is ω8 and ω, then, according to the general rule, The radius of half intensity is gt
an [θy//2] and gtan (θ on/2)
Therefore, if we consider that the X-axis and y-axis match the θ7/ direction and the θ upward direction, respectively, g tanθ///2ω// = g tan & h
/ It is thought to be 2ω.

Thus ω/7. After finding ωyo, for example, optical technology]
contact vol1.22. No.7 ('84), P53~
The intensity distribution when an arbitrary lens system is combined can be considered using mathematical formulas based on the characteristics of a laser beam as analyzed in P.65.

In the configurations shown in FIGS. 1 to 4, the alignment mark indicates the beam waist radius of the irradiation beam in the alignment direction (X direction), here the alignment direction. , the amount that is the sum of the positioning mark size in the beam alignment direction, the extra width that is made wider to allow room for the projection system to irradiate the beam, and the uncertainty width (generally about 5 to 20 μm on each side) ( That is, assuming that the irradiation width (irradiation width) is 2a1 and the principal ray interval between the two beams is 2t, it is preferable to set the distance t as follows. This is shown in Figure 8.

With a signal of , and the unevenness of illuminance is also reduced.

Practically speaking Conditions of about 100% are preferable.

When the distribution is numerically evaluated, it becomes clear that when the lower limit value is below, the beam spacing becomes relatively narrow and the illuminance around the mark decreases.On the other hand, when the upper limit value is exceeded, the beam spacing becomes relatively narrow. This results in a situation in which the illuminance is broadly reduced in the central area, and it deviates from the appropriate range. A specific example of a numerical value is beam waist size ω. If the illumination area radius a is set to 170 and 1 μm, the beam interval 2t will be 210 μm, and the position 0, which is the peak value in Figure 7, will be
The ratio of point illumination or ■:◎ is 1:0.89, with little unevenness (energy irradiated within 2a is 66% of the total, achieving high efficiency).

The above example uses two light sources, but as shown in FIG. 8, three light sources may be used depending on the mark size and the characteristics of the semiconductor laser. In addition, in FIGS. 2 and 3, an optical system (usually referred to as a beam expander) having an angular magnification that reduces the beam in an afocal system is provided in the system after beam combination, or vice versa. can be selected depending on design needs.

It is clear that the present invention can also be applied to other position detection devices that detect light beams polarized by physical optical elements, such as the devices mentioned in the conventional example.

〔Effect of the invention〕

As explained above, according to the present invention, when detecting the polarized light beam using a physical optical element and detecting the position of an object,
Even if a beam shift occurs, it is now possible to alleviate the deterioration in accuracy.

[Brief explanation of the drawing]

FIGS. 1(a), (b), and (c) are a block diagram, a principle diagram, and a detailed view of the mark part of the position detection device according to the first embodiment of the present invention, and FIGS. 2(a) and (b) are 3(a) and 3(b) are diagrams of the beam combining section of the position detecting device according to the third embodiment of the present invention, and FIG. 5 is a diagram illustrating the light emission pattern of a semiconductor laser. FIG. 6 is a diagram illustrating conventional problems. FIG. 7 is a diagram illustrating the problems of the conventional method. A diagram explaining the concept of the effect, FIG. 8 is a diagram of an example of the light intensity distribution of the luminous flux synthesized by the present invention, FIG. 9 is a diagram of the principle of the position detection device according to the fifth embodiment of the present invention, and FIG. The figure is a block diagram of a conventional position detection device, and FIG. 11 is a diagram of the same detection principle. In the figure, 1.1', 1'... Semiconductor laser 2.2', 2''... Condensing lens (or collimator lens) 3.3'...・・・・・・・・・
・Half Mira・5,5' ・・・・・・・・・・・・
Mark center line 6. 6', 6'...Principal ray of projected light beam 7...Polarizing beam splitter 8... ...Half-wave plate 9... Quarter-wave plate lO.
...... Partial reflecting mirror 11...
・・・・・・・・・・・・It is a composite lens.

Claims (1)

[Claims] (1) A means for irradiating a light beam onto a physical optical element provided on an object to be aligned, and detecting the light beam irradiated by the irradiation means and deflected by the physical optical element to determine the position of the object. and means for detecting;
The irradiation means partially overlaps the plurality of light beams to form a light beam having a cross-sectional shape according to the shape of the physical optical element,
A position detection device characterized by irradiating the luminous flux.