CN105070201B - Alignment device for the Moire fringe of lithographic equipment - Google Patents

Abstract

A moiré fringe alignment device for lithography equipment, including an illumination light source, a third 1/4 wave plate, a polarizing beam splitter, a first 1/4 wave plate, a 4f lens front group, a spatial filter, and a 4f lens Group of rear group, detector, second 1/4 wave plate, and triangular prism and data processor. Using a polarizing beam splitter, the same-order diffracted beam of the alignment mark is spatially separated into two parts, namely the transformed beam and the reference beam, and the transformed beam is rotated by a certain angle or rotated 180 degrees in the pupil plane space of the imaging module for position deflection. After passing through the imaging module, the transformation beam and the reference beam are respectively imaged and form moiré fringes on the image plane. When the position of the alignment mark moves relative to the alignment device, the moiré fringes on the image plane will align with the mark The movement amount is multiplied, and the moiré fringe is processed by the detection system to obtain the movement amount of the position information of the alignment mark, so as to align the position of the silicon wafer.

Description

Alignment device for moiré fringes of lithographic equipment

technical field

The invention relates to photolithography, in particular to a moiré fringe alignment device for photolithography equipment.

Background technique

In the manufacturing process of semiconductor integrated circuits, lithography exposure equipment is an important part of the entire industry. Chips usually need to undergo multiple lithography exposures to complete. In general, except for the first exposure, other exposures need to be exposed before exposure. The pattern of the exposure layer is precisely aligned with the pattern of the previous exposure layer to ensure the overlay accuracy of the alignment.

With the advancement of technology, the resolution of lithography has been developed to 10-20 nanometer nodes. At this time, the overlay accuracy is generally required to be 2-5nm. Factors affecting overlay accuracy include silicon wafer deformation, workpiece stage and mask stage. The reset accuracy, the alignment accuracy of the mask and the silicon wafer, etc., among which the alignment accuracy of the mask and the silicon wafer is an important factor.

For the projection exposure lithography machine, the position alignment between the mask and the silicon wafer generally adopts the coaxial + off-axis method, that is, the alignment mark on the workpiece table is used as the intermediate medium, and the coaxial alignment is used, that is, the mask Align the alignment marks on the wafer with the alignment marks on the workpiece table to establish the position coordinates of the mask and the workpiece table; through off-axis alignment, that is, the alignment marks on the silicon wafer and the alignment marks on the workpiece table Alignment, establishing the position coordinates of the silicon wafer and the workpiece table, thereby determining the position coordinates of the mask and the silicon wafer, and realizing the mask-silicon wafer position alignment, as shown in FIG. 1 .

A self-referencing interference alignment system is given in the existing patent (US7564534B2, CN102402141A), as shown in Figure 2, the principle of the alignment system is to realize the 180-degree two wavefronts of the diffracted light from the alignment mark through the image rotation device Rotate overlapping interference, detect the signal intensity after interference on the pupil plane, or measure the imaging image features on the imaging plane, and determine the position information of the alignment mark through signal analysis. In this alignment device, different order diffracted beams of the alignment mark are used to measure the position of the alignment mark. For example, for the first-order diffracted beam, the alignment mark moves for one cycle, and the alignment signal generates a position shift of two cycles. , to process the alignment signal and align the position of the alignment mark, but for lithography equipment with higher alignment accuracy requirements, the alignment accuracy of this method is limited.

Contents of the invention

In order to solve the above-mentioned problem of alignment accuracy in the prior art, the present invention provides an alignment device for moire fringes of lithography equipment, the self-reference moiré fringes generated by the device can double or tens of times The movement position of the alignment mark is enlarged, so the position information of the mark can be measured more accurately, and the alignment accuracy is higher.

Technical solution of the present invention is as follows:

A device for aligning Moiré fringes of lithography equipment, characterized in that the device includes an illumination light source, and along the output beam direction of the illumination light source are a third 1/4 wave plate, a polarization beam splitter, a first 1/4 wave plate, and 4 wave plates, 4f lens front group, on the right side of the described polarization beam splitter prism are the rear group and detector of spatial filter, 4f lens group successively, on the left side of the described polarization beam splitter prism is the second 1 successively /4 wave plate and triangular prism, the rear group of described 4f lens front group and 4f lens group constitutes 4f lens group, and described detector is positioned at the rear focal plane of the rear group of described 4f lens group, described The output terminal of the detector is connected to the input terminal of the data processor.

The illumination light source is a multi-wavelength light source, and its output light beam is linearly polarized light.

The detector is a CCD.

The spatial filter is a variable filter.

A device for aligning Moiré fringes of lithography equipment, characterized in that the device includes an illumination light source, and along the output beam direction of the illumination light source are a third 1/4 wave plate, a polarization beam splitter, a first 1/4 wave plate, and 4 wave plates, 4f lens front group, the first half wave plate, the first birefringent crystal, the second half wave plate, the polarizing beam splitting prism in the upper part of the right side of the polarizing beam splitting prism The lower part on the right side is the second birefringent crystal, followed by the spatial filter, the rear group of the 4f lens group and the detector, and on the left side of the polarization beam splitter is the second 1/4 wave plate , field lens and reflecting mirror, the rear group of described 4f lens group and 4f lens group constitutes 4f lens group, and described detector is positioned at the rear focal plane of described 4f lens group rear group, and described detection The output terminal of the device is connected to the input terminal of the data processor.

The illumination light source is a multi-wavelength light source, and its output light beam is linearly polarized.

The detector is a CCD.

The spatial filter is a variable filter.

The field mirrors and reflection mirrors can be replaced by rectangular prisms.

The alignment device spatially separates the diffracted beam of the alignment mark into a transformed beam and a reference beam through a polarization beam splitter, rotates the transformed beam through a certain angle in space through a triangular prism, and then simultaneously interferes and forms the transformed beam and the reference beam through a lens. There is a certain angle between the interference fringes formed by the two groups of diffracted beams on the imaging surface, thus forming moiré fringes on the image surface. Movement magnification, measuring the movement of the moiré fringes can determine the position information of the alignment mark. Since the moiré fringes formed by the diffracted light beam can multiply or magnify the positional movement of the alignment mark by several tens of times, the position information of the alignment mark can be measured more accurately.

Or the alignment device can also spatially separate the diffracted light beam of the alignment mark into a transformed light beam and a reference light beam through a polarization beam splitter, the transformed light beam is spatially displaced through a birefringent crystal, and then the reference light beam and the displaced light beam are separated through a lens. The converted light beams interfere with imaging at the same time. Since the interference fringes formed by the two groups of diffracted beams on the imaging plane have different periods, self-referencing moiré fringes are formed on the image plane. The moiré fringes move with the movement of the alignment marks and The positional movement of the alignment mark is amplified to determine the position information of the alignment mark by measuring the movement of the moiré fringe. The moiré fringe formed by the diffracted beam can multiply or dozens of times the positional movement of the alignment mark magnification, so that the position information of the alignment mark can be measured more accurately.

The above-mentioned alignment device adopts two or more groups of illumination light beams with different wavelengths to improve the process adaptability of the alignment device and improve the contrast of the moiré fringes. At the same time, according to the requirements of the process, different diffraction-order sub-beams for the alignment marks are used to improve the alignment accuracy and process adaptability.

For details, refer to the description in the examples.

Technical effect of the present invention is as follows:

The invention utilizes the self-referencing Moiré fringe to amplify the moving position of the alignment mark by several times or dozens of times, so that the position information of the mark can be measured more accurately. The structure and alignment method can obtain higher alignment accuracy than that in the reference patent.

Description of drawings

Figure 1 is a schematic diagram of mask silicon wafer alignment process

Figure 2 is a schematic diagram of the existing patent alignment principle

Figure 3 is a schematic structural view of Embodiment 1 of the alignment device of the present invention

Fig. 4 is a schematic structural diagram of a triangular prism in Embodiment 1 of the alignment device of the present invention

Fig. 5 is a schematic diagram of the position of the diffracted beam on the spectral plane of Embodiment 1 of the alignment device of the present invention

Fig. 6 is a schematic diagram of moiré fringes produced by embodiment 1 of the alignment device of the present invention

Figure 7 is a schematic structural view of Embodiment 2 of the alignment device of the present invention

Fig. 8 is a schematic diagram of the optical path structure of the birefringent crystal in Embodiment 2 of the alignment device of the present invention

Fig. 9 is a schematic diagram of the positions of diffracted beams on the spectral plane of embodiment 2 of the alignment device of the present invention

Figure 10 is a schematic diagram of moiré fringes produced by embodiment 2 of the alignment device of the present invention

detailed description

The present invention will be further described below in conjunction with the examples and drawings, but the examples should not limit the protection scope of the present invention.

FIG. 3 is a schematic structural diagram of Embodiment 1 of the moiré fringe alignment device of the present invention. It can be seen from the figure that Embodiment 1 of the moiré fringe alignment device used in lithography equipment according to the present invention includes an illumination light source 101, along which the output beam direction of the illumination light source is followed by a third 1/4 wave plate 110 and a polarization beam splitter prism 103 , the first 1/4 wave plate 104, 4f lens front group 105, the rear group 112 of spatial filter 111, 4f lens group and detector 113 are successively on the right side of described polarization beam splitter prism 103, in described The left side of polarization beam splitter prism 103 is followed by second 1/4 wave plate 108 and triangular prism 109, the rear group 112 of described 4f lens front group 105 and 4f lens group forms 4f lens group, and described detector 113 is positioned at The rear focal plane of the rear group of the 4f lens group, the output terminal of the detector 113 is connected to the input terminal of a data processor (not shown in the figure).

The illuminating light source 101 provides the illuminating light beam 102 of parallel linear polarization state, and this illuminating light beam 102 is the first 1/4 wave plate 104 that the crystal axis angle is 11.25 degrees through the polarization beam splitting prism 103, and the front group 105 of 4f lens is irradiated to the silicon chip 107 On the alignment mark 106, the alignment mark 106 is a grating structure, and the light beam is diffracted on the alignment mark 106, for example, the diffraction order is 1-7, and the diffracted light beam passes through the front group 105 of the 4f lens group and passes through the crystal axis angle again After the first 1/4 wave plate 104 of 11.25 degrees becomes circularly polarized light and enters the polarization beam splitter prism 103, the polarization beam splitter prism 103 performs semi-reflection and semi-transmission, that is, the beam component (reference beam) of the parallel polarization state passes through the polarization beam splitter Prism 103, the light beam component (converted light beam) of vertically polarized state is reflected by polarization splitting prism 103, and reflected light is converted into circularly polarized state after the second 1/4 wave plate 108 of 22.5 degrees through crystal axis direction, enters triangular prism 109, After passing through the triangular prism 109, the positive order diffracted beam and the negative order diffracted beam of the alignment mark are exchanged in the Y direction. (detailed optical path structure diagram refers to the description in Fig. 6 and Fig. 7), after the diffracted light beam through the triangular prism 109 passes through the second 1/4 wave plate 108 whose crystal axis direction is 22.5 degrees again, the polarization state of the light beam is changed to parallel, and After completely passing through the polarization splitter prism 103 and passing through the spatial filter 111 , the two diffracted light beams in parallel polarization states are imaged on the detector 113 after passing through the rear group 112 of the 4f lens group. The other half of the diffracted beam (reference beam, parallel polarization state component) of the alignment mark 106 passes through the polarizing beam splitter prism 103, and enters the third 1/4 wave plate 110 whose crystal axis direction is 22.5 degrees, and the crystal axis direction is 22.5 degrees The surface of the third 1/4 wave plate 110 is coated with a reflective film. After reflection, after passing through the third 1/4 wave plate 110 whose crystal axis direction is 22.5 degrees again, the polarization state changes to vertical, and is reflected by the polarization beam splitter prism 103. Finally, after passing through the spatial filter 111 and the rear group 112 of the 4f lens group, the image is imaged on the detector 113, and the direction of the interference fringes formed by the reference beam and the transformed beam on the image plane has a certain included angle, thereby forming Moiré image.

In Fig. 3, the other diffraction orders of the alignment mark 106 have the same optical path structure principle as the first-order diffraction order, and the optical path structure principle in the YZ plane is the same as that in the XY plane, so as to achieve multi-level alignment in two directions Align the mark position.

Fig. 4 is the schematic diagram of the structure of the triangular reflective prism 109 used in the optical path structure of the alignment device of embodiment 1, respectively the top view (left) and the side view (right) of this triangular prism 109, the vertex angle of this triangular reflective prism 109 is a right angle, 4 pieces The sides have a certain angle of inclination, that is, surface 1 and surface 2 have the same angle with respect to the bottom edge of the XY plane, such as 89 degrees, and surface 3 and surface 4 have the same angle with respect to the bottom edge of the YZ plane, such as 89 degrees. Light in Fig. 1, this triangular reflective prism 109 plays in the Y direction of XY plane, and the incident+1R diffracted beam is reflected to the position of-1R diffracted beam, and the incident-1R diffracted beam is reflected to the position of+1R diffracted beam. In the YZ plane, the outgoing -1R diffracted beam is shifted in the Z direction relative to the +1R incident beam, and the same outgoing +1R diffracted beam is shifted in the Z direction relative to the -1R incident beam, that is, the two outgoing rays have the same but displacement in the opposite direction.

5 is a schematic diagram of the position of the diffracted beam in the spectrum plane of Embodiment 1, that is, the relative position of the converted beam and the reference beam in the spectrum plane. The converted beam has a position offset relative to the reference beam in the YZ plane, and the size of the position offset is given by The inclination angles of the four faces of the triangular reflective prism 108 are determined.

6 is a schematic diagram of imaging of the diffracted beam in the rear focal plane of the 4f lens group in Embodiment 1, and the converted beam and the reference beam form Moiré fringes on the focal plane of the rear group of the 4f lens. The period d of the moire fringes is determined by the angle θ between the two sets of interference fringes. For example, if the period of the two sets of interference fringes is p, then the period of the moiré fringes is D=p/sinθ. Combined with the optical path analysis in Figure 1, when the alignment mark (grating) moves position a, the imaging of the transformation beam and the reference beam move in opposite directions by position a respectively, and the movement amount of the Moiré fringe is 2a/sinθ.

FIG. 7 is a schematic structural diagram of Embodiment 2 of the moiré fringe alignment device of the present invention.

The illumination light source 101 provides an illumination light beam 102 in a parallel linear polarization state, and the illumination light beam 102 passes through the third 1/4 wave plate 110, the polarization beam splitter prism 103 and the third 1/4 wave plate 104 whose crystal axis angle is 11.25 degrees, before the 4f lens The group 105 is irradiated onto the alignment mark 106 of the silicon wafer 107, the alignment mark 106 is a grating structure, and the light beam is diffracted on the alignment mark 106, for example, the diffraction order is 1-7, and the diffracted light beam passes through the 4f lens group before The group 105 and the first 1/4 wave plate 104 with a crystal axis angle of 11.25 degrees become circularly polarized light and enter the polarization beam splitter 103, and the polarization beam splitter 103 performs semi-reflection and semi-transmission, that is, the beam component of the parallel polarization state (reference beam) passes through polarization beam splitter 103, and the beam component (converted beam) of vertically polarized state is reflected by polarization beam splitter 103, and the reflected light is converted into a circle after being passed through the second 1/4 wave plate 108 whose crystal axis direction is 22.5 degrees Polarization state, after passing through the field lens 201 and the reflector 202, align the positive order diffracted beam and the negative order diffracted beam in the Y direction, and then pass through the second 1/4 wave plate 108 with a crystal axis direction of 22.5 degrees Afterwards, the polarization state of the light beam changes to be parallel and completely passes through the polarization beam splitter prism 103. After the positive order diffracted light such as +1R passes through the first half-wave plate 203 whose crystal axis direction is 45 degrees, the polarization state becomes vertical and passes through the double After the refraction crystal 204, the light beam is displaced in the Y direction, and the polarization state changes to parallel after passing through the second half-wave plate 205 with a crystal axis direction of 45 degrees, and the direction of the negative-order diffracted beam such as -1R does not change after passing through the birefringent crystal 206 After the positive and negative order diffracted beams pass through the spatial filter 111 , the diffracted beams in two parallel polarization states are imaged on the detector 113 after passing through the rear group 112 of the 4f lens group. The other half of the diffracted beam (reference beam, parallel polarization state component) of the alignment mark passes through the polarization beam splitter prism 103, and then enters the third 1/4 wave plate 110 whose crystal axis direction is 22.5 degrees, and the crystal axis direction is 22.5 degrees. The surface of the third 1/4 wave plate 110 is coated with a reflective film. After reflection, after passing through the third 1/4 wave plate 110 whose crystal axis direction is 22.5 degrees again, the polarization state changes to vertical, and after being reflected by the polarization beam splitter prism 103 After negative order diffracted light such as -1T passes through the first half-wave plate 203 whose crystal axis direction is 45 degrees, the polarization state becomes parallel. After the second half-wave plate 205 at 45 degrees, the polarization state is changed to be vertical, and the positive-order diffracted beam, such as +1T, is displaced in the Y direction after passing through the birefringent crystal 206. After the positive- and negative-order diffracted beam passes through the spatial filter 111, the two After the diffracted light beam of the vertical polarization state passes through the rear group 112 of the 4f lens group, it is imaged on the detector 113 after passing through the spatial filter 111 and the rear group 112 of the 4f lens group, and is imaged on the detector 113, the reference beam and the converted light beam There is a certain included angle in the direction of the interference fringes formed on the image plane, so that a Moiré fringe image is formed on the image plane.

In Figure 7, the other diffraction orders of the alignment mark are the same as the optical path structure principle of the 1st order diffraction order, and the optical path structure principle in the YZ plane is the same as that of the XY plane, so as to achieve multi-level alignment marks in two directions position alignment.

As shown in Figure 8, it is a schematic diagram of the optical path structure of the birefringent crystal used in the optical path structure of Embodiment 2. The converted light beam -1R is in a parallel polarization state, and the birefringent crystal with a fixed crystal axis direction is o light, and the reference beam +1T is In the vertical polarization state, the birefringent crystal with a fixed crystal axis direction is e-ray. The positional offset Δ of the two beams of light passing through the birefringent crystal is related to the wavelength of the beam, the direction of the crystal axis and the thickness of the birefringent crystal. The light path structures of the transformation beam +1R and the reference beam -1T are the same as those described above.

The diffracted beam on another plane in Fig. 8, that is, the YZ plane, has the same optical principle as described above.

Fig. 9 is a schematic diagram of the position of the diffracted beam in the spectrum plane of Embodiment 2, that is, the converted beam has a 180-degree rotation relative to the reference beam on the YZ plane, and there is a position translation, and the position translation is related to the wavelength of the beam, the direction of the crystal axis and the birefringent crystal. Determined by thickness and refractive index.

Figure 9 shows the relative positions of the transformed beam and the reference beam in the spectral plane of the first-order diffracted beam, and the principles of other diffraction orders are the same.

Fig. 10 is a schematic diagram of Moiré fringes formed by diffracted light beams on the mirror surface of the imaging object in Example 2. Reference beams +1T and -1T form interference fringes with a period of P1, and transformed light beams +1R and -1R form interference fringes with a period of P2 , because the polarization states of the two groups of light beams are perpendicular to each other, the two groups of interference fringes do not interfere with each other, but the light intensity is superimposed, thus forming Moiré fringes on the image plane. The period P of Moiré fringes is related to the periods P1 and P2 of two sets of interference fringes. For example, the period of two sets of interference fringes is the least common multiple of P=P1 and P2. For example, P1=8.8um, P2=8um, then P=88um , Moiré fringe moving amount D=mark moving amount d*2*P, that is, the moiré fringe doubles the moving amount of the mark, thereby improving the alignment accuracy of the alignment mark. Wherein the interference fringe period P1 (P2)=4f The focal length X of the rear group of the lens group is aligned with the wavelength of the light source, and the distance of the diffracted beam on the spectrum plane.

The Moiré fringes of other diffraction orders of the alignment mark in Fig. 10 are the same as that of the first order.

(Supplementary alignment method in conjunction with attached drawings).

Claims (5)

1. A kind of 1. alignment device of Moire fringe for lithographic equipment, it is characterised in that the device includes lighting source (101), It is the 3rd quarter wave plate (110), polarization splitting prism (103), the 1st successively along lighting source (101) the output beam direction Group (105) before wave plate (104), 4f lens, the top half on the right side of described polarization splitting prism (103) is first successively Half-wave plate (203), the first birefringece crystal (204), the second half-wave plate (205), on the right side of described polarization splitting prism (103) The latter half be the second birefringece crystal (206), be followed successively by spatial filter (111), rear group (112) of 4f lens groups thereafter It is the second quarter wave plate (108), field lens (201) successively in the left side of described polarization splitting prism (103) with detector (113) With speculum (202), rear group (112) of described 4f lens preceding group (105) and 4f lens groups form 4f lens groups, described spy Survey the back focal plane that device (113) is located at rear group (112) of described 4f lens groups, the output termination of described detector (113) The input of data processor.
2. 2. the alignment device of Moire fringe as claimed in claim 1, it is characterised in that described lighting source (101) is more ripples Long light source, its output beam are linear polarization.
3. 3. the alignment device of Moire fringe as claimed in claim 1, it is characterised in that described detector (113) is CCD.
4. 4. the alignment device of Moire fringe as claimed in claim 1, it is characterised in that the spatial filter (111) is variable Wave filter.
5. 5. the alignment device of Moire fringe as claimed in claim 1, it is characterised in that described field lens (201) and speculum (202) replaced with right-angle prism.