WO2008052405A1

WO2008052405A1 - Alignment system used in lithography apparatus and diffraction orders-combining system used in alignment system

Info

Publication number: WO2008052405A1
Application number: PCT/CN2007/001494
Authority: WO
Inventors: Rongwei Xu; Tiejun Li; Zhongyun Li
Original assignee: Shanghai Micro Electronics Equipment Co., Ltd.
Priority date: 2006-11-03
Filing date: 2007-05-08
Publication date: 2008-05-08
Also published as: CN1949087B; CN1949087A

Abstract

An alignment system (5) of a lithographic apparatus of the present invention includes a optical source module (1) for providing a light source for the alignment system (5); an illumination module (2) for transmitting the light to illuminate an alignment mark WM; an imaging module (3) at least including an objective (511) for collecting a plurality of diffraction orders produced by the alignment mark WM, a diffraction orders-combining system (513) for overlapping and interfering the same orders and a multiple wavelengths demultiplexing system (515) for demultiplexing light signals of a plurality of different wavelengths; and a detection module (516) for obtaining the positional information of the alignment mark WM by detecting intensity variations of a plurality of interfered diffraction orders.

Description

AN ALIGNMENT SYSTEM USED IN LITHOGRAPHY APPARATUS AND A DIFFRACTION ORDERS-COMBING SYSTEM USED IN THE ALIGNMENT

SYSTEM

Technical Field

The present invention relates in general to lithographic apparatus used in the manufacture of semiconductor devices, and particularly to an alignment system and a diffraction orders-combining system employed in the alignment system.

Background of the invention

Lithographic apparatus can be used in the manufacture of integrated circuits and other micro devices. In a known manufacturing process using a lithographic projection apparatus, a pattern (e.g. in a reticle) is imaged onto a substrate that is at least partially covered by a layer of radiation-sensitive material (resist).

In current apparatus, employing patterning by a reticle on a reticle table, a distinction can be made between two different types of machine. In one type of lithographic projection apparatus, each target portion is irradiated by exposing the entire reticle pattern onto the target portion at once. Such an apparatus is commonly referred to as a wafer stepper. In an alternative apparatus, commonly referred to as a step-and-scan apparatus, each target portion is irradiated by progressively scanning the reticle pattern under the projection beam in a given reference direction (the "scanning" direction) while synchronously scanning the substrate stage parallel or anti-parallel to this direction.

An essential step in a lithographic process is aligning the reticle with the chip. Semiconductor, and other, devices manufactured by lithographic techniques require multiple exposures to form multiple layers in the device and it is essential that these layers have correct overlay. As ever smaller features are imaged, overlay requirements, and hence the necessary alignment accuracy becomes stricter.

An alignment system is used for aligning a reticle and a wafer before exposure. The positional information of the reticle, and the wafer, are determined by the coordinate information to meet the demand of overlay accuracy.

The TTL alignment technology detects a wafer mark positions by a laser with different wavelength from exposure wavelength through the projection optical system. Diffraction lights from the wafer mark are collected and imaged on a reticle which comprises a reticle mark. A maximum transmission light intensity gives the correct alignment position. The wafer mark may be a phase grating or an amplitude grating.

The off-axis alignment technology utilizes an off-axis alignment system that measures wafer marks on a wafer and a fiducial mark of a fiducial plate on a wafer stage to implement the wafer alignment and the wafer stage alignment. The fiducial mark of the fiducial plate on the wafer stage is aligned with a reticle mark to implement reticle alignment.

In one known alignment type is a grating alignment. Grating-type marks on a wafer are illuminated with coherent light and the diffracted light is collected to obtain information of an alignment mark. 0 orders diffracted light are filtered out with a spatial filter, leaving ±1 orders diffracted light to be overlapped and interfered, the interfering signal gives the central alignment position.

An alignment system is utilized by the ASML company. Therein disclosed is an alignment system having a double light source having a red light, a green light and a wedges array to make a plurality of diffraction orders overlap and interfere. Alignment signal of the red and green lights are split by a polarization beam splitter. Alignment signal with sinusoidal type can be obtained by detecting a light intensity of a moire fringe that is formed by an interference of an alignment mark image and a reference grating. The double light source can inhibit destructive interference and asymmetric deformation of the alignment mark. However, since the alignment system adopts two laser sources with visible wavelengths, the absorption of low K dielectric materials within a range of visible spectrum results in the attenuation of the intensity of the alignment signal to further influence the alignment accuracy.

In addition, the wedges array needs high accuracy of manufacture, assembly and adjustment. The costs of such wedges array are high. Finally, the polarization beam splitter can not split an alignment signal with more than two wavelengths.

An another off-axis alignment system having a self-referencing interferometer constructed and arranged to project two overlapping images of an alignment mark that are relatively rotated by 180 degree, the alignment system further comprising a detector system constructed and arranged detect light intensities at a plurality of different positions in a pupil plane of the self-referencing interferometer. By detecting intensity variations at the positions of a plurality of diffraction orders in a pupil plane, positioning information of the alignment mark can be derived. This information is obtained from the relative phase in the intensity variations as the mark is scanned; the different diffraction orders will vary in intensity with different spatial frequencies. For that alignment system, manufacture of the self-referencing interferometer is very difficult and the cost is also very high. In addition, because the color demultiplexing system is based on the conventional blazed grating which is designed for a center wavelength, the diffraction efficiency for other wavelengths is very low.

Summary of invention

An object of the invention is to provide an improved alignment system used in lithography apparatus and a diffraction orders-combing system used in the alignment system, which has high stability and alignment accuracy. In order to attain the object above mentioned, an alignment system of a lithographic apparatus of the present invention includes a radiation module for providing a light source for the alignment system; an illumination module for transmitting the light to illuminate an alignment mark; an imaging module at least including an objective for collecting a plurality of diffraction orders produced by the alignment mark, a diffraction orders-combining system for overlapping and interfering the same orders and a multiple wavelengths demultiplexing system for demultiplexing light signals of a plurality of different wavelengths; and a detection module for obtaining the positional information of the alignment mark by detecting intensity variations of a plurality of interfered diffraction orders.

A diffraction orders-combing system of an alignment system of a lithographic apparatus is used for making the light spots of positive diffraction orders and the light spots of corresponding negative diffraction orders overlap and interfere.

The alignment system of the present invention uses a spatially coherent light source with multiple wavelengths. The multiple wavelengths light source comprises four discrete wavelengths, preferably two wavelengths of the four wavelengths within near infrared or infrared band. The multiple wavelengths light sources used by the alignment system can suppress effects of destructive interference and enhance the process adaptability of the alignment system. In addition, the illumination module used near infrared and infrared source can solve absorption problem of a low-k dielectric materials within range of visible spectrum and can be used for mark detection of a polysilicon layer.

A spatial filter is placed on an exit pupil of an objective to eliminate stray light crosstalk influence from adjacent marks of the wafer or product patterns.

The diffraction orders-combing system of the alignment system of the lithographic apparatus is used for making the light spots of positive diffraction orders and the light spots of corresponding negative diffraction orders overlap and interfere. The diffraction orders-combing system has stable structure and simple working principle, which can be applied in the manufacure.

The multiple wavelengths demultiplexing system is based on a multi-blazed grating. The blazed grating includes a polyline blazed grating, a multi-section blazed grating, and a polyline-multi-section blazed grating. The blazed grating can improve the efficiency of lights with different wavelengths and enhance the intensity of the alignment signal for enhancing the alignment accuracy.

Other objects, advantages and novel features of the invention will become more apparent from the following detailed description of the present embodiment when taken in conjunction with the accompanying drawings.

Brief description of drawings

The features of this invention which are believed to be novel are set forth with particularity in the appended claims. The invention, together with its objects and the advantages thereof, may be best understood by reference to the following description taken in conjunction with the accompanying drawings, in which like reference numerals identify like elements in the figures and in which:

FIG. 1 depicts a structure of an alignment system used in lithography apparatus and a diffraction orders-combing system used in the alignment system;

FIG. 2 is a drawing of an alignment mark on a wafer of the FIG. 1;

FIG. 3 is a structure of the alignment system of the present invention;

FIG.4, FIG.5, and FIG.6 depict the diffraction orders-combining system based on a coordinate inversion interferometer 5131, for explaining the concept of its operation;

FIG.7 illustrates an another optical path implementing overlapping and interfering of a plurality of diffraction orders light spots;

FIG.8 illustrates the principle of the diffraction order-combing system based on a prism interferometer;

FIG.9 illustrates a principle of the diffraction order-combing system based on a lateral shearing interferometer;

FIG.10 is drawings of some structures of the diffraction order-combing system based on the lateral shearing interferometer 405;

FIG.11 is drawings of some structures of the diffraction order-combing system based on a diffraction grating;

FIG 12 is drawings of some structures of a multiple wavelengths demultiplexing system of FIG.3; and

FIG 13 is a drawing of a structure of a detection optical path of FIG.3.

Detailed Description of Preferred Embodiments

The lithographic apparatus includes a illumination system 1 for providing a light source, a reticle stage 3 constructed and arranged to hold a reticle 2 having IC patterns and a first positioning device RM with a periodic optical structure, a projection system 4 for projecting the pattern of the reticle 2 onto a wafer 6, and a wafer stage 7 for holding the wafer 6 having a second positioning device WM with a periodic optical structure. The wafer stage 7 is connected to a fiducial plate 8 marked by the fiducial mark FM.

The lithographic apparatus also includes an alignment system 5, a laser interferometer 11 , mirrors 10 and 16 for measuring the position of the reticle stage 3 and wafer stage 7, a server system 13, and drive systems 9 and 14. The shift of the server system 13 and the drive systems 9 and 14 are controlled by a main control system 12.

The alignment system 5 includes a diffraction orders-combining system and a multiple wavelengths demultiplexing system, and is used for aligning the reticle 2 and the wafer 6.

The illumination system 1 includes a light source, a lens system, a mirror, and a condensor (Not shown).

The light source may be a KrF excimer laser operating at a wavelength of 248 nm, a ArF excimer laser operating at a wavelength of 193 nm, a F2 excimer laser operating at a wavelength of 157 nm, a Kr2 excirner laser operating at a wavelength of 146 nm, a Ar2 excimer laser operating at a wavelength of 126 nm, or a super high pressure mercury lamp (g-line, i-line). The illumination system 1 provides an exposure beam IL to the reticle 2.

With the aid of the drive system 14, the reticle stage 3 can move in the X-Y plane perpendicular to an optical axis of the illumination system 1. In addition, the reticle stage 3 is movable in a given direction with a given speed.

The positional information of the reticle stage 3 is measured by a heterodyne laser interferometer 15 with the help of the mirror 16 on the recticle stage 3. The heterodyne laser interferometer 15 sends the positional information of the reticle stage 3 from the drive system 14 to the main control system 12. Then the main control system 12 controls the drive system 14 to drive the recticle stage 3.

The projection system 4 is located beneath the reticle stage 3, the optical axis AX of which is parallel to the Z direction. Because the projection system 4 is a refractive optical system having a double telecentric configuration and a given magnification (e.g. 1/5 or 1/4), the illumination system 1 emits the exposure beam IL to the reticle 2, the pattern of which can project to the wafer 6 coating a photoresist by the projection system 4, to form the image with a magnification of 1/5 or 1/4 on the wafer 6.

The wafer stage 7 is located beneath the projection system 4 and has a wafer bracket (Not Shown) for fixing the wafer 6. The wafer stage 7 can be driven by the drive system 9 to move in an X direction (a scanning direction) and a Y direction (perpendicular to the scanning direction) so that the different section of the wafer 6 can be exposed. The positional information of the wafer stage 7 is measured by a heterodyne laser interferometer 11 with the help of the mirror 10 on the wafer stage 7. The heterodyne laser interferometer 11 sends the positional information of the wafer stage 7 from the serve system 13 to the main control system 12. Then the main control system 12 controls the drive system 9 to drive the movement of the wafer stage 7. The wafer 6 has the alignment mark WM with the periodic structure and the wafer stage 7 has the fiducial plate 8 marked by the fiducial mark FM. The alignment system 5 can realize wafer alignment and wafer stage alignment by using the alignment mark WM and the fidicutial mark FM, respectively. The alignment system 5 sends alignment information to the main control system 12. Then the main control system 12 controls the drive system 9 that can drive the wafer stage 7 to align the reticle 2 and the wafer 6.

FIG. 2 is a drawing of the alignment mark WM on the wafer 6 of the FIG. 1. The alignment mark WM on the wafer 6 is two-dimensional phase grating that is formed by four groups grating Pa, Pb, Pc, and Pd, and a centre cross line. Gratings Pa and Pc are symmetrically distributed on the two sides of the centre cross line in x direction. Gratings Pb and Pd are symmetrically distributed on the two sides of the centre cross line in y direction. The grating Pb and the grating Pc have the same first period Pl, i.e. Pb=Pc=Pl . The grating Pa and the grating Pd have the second grating period P2, i.e. Pb=Pc=P2.

A capture range of the alignment system 5 can be expanded by choosing different grating periods of the alignment mark. Capture range = ±P1P2/[2(P2-P1)]. A line/ space ratio of the basic gating period of the four groups gratings is 1 : 1. In general, the basic grating period of the grating can be segmented to enhance the intensity of a high orders diffracted light. In addition, the alignment mark WM on the wafer 6 with smaller size is suitable for a narrower scribe lane (e.g. 40μm.^χ40μm).

FIG. 3 is a structure of the alignment system 5 of the present invention. The alignment system 5 includes an optical source module 1, an illumination module 2, an image module 3 and a detection module 4. The alignment system 5 has a feature that the positional information of the alignment mark is available by detecting intensity variation of the interfering fringes formed by positive and negative diffraction spots with the same orders in a pupil plane. The alignment system 5 has high signal-noise ratio and good adaptability and sensitivity. An alignment accuracy of the alignment system 5 achieves to 7-9nm, which completely satisfy alignment requirement of Lithographic apparatus with CD of lOOnm or less.

The alignment system 5 uses a spatially coherent light source with multiple wavelengths. The multiple wavelengths light source includes four discrete wavelengths (e.g. 532nm, 633nm, 785nm, 850nm), preferably two wavelengths of the four wavelengths within near infrared or infrared band. Multiple wavelengths light sources λl, λ2, λ3, and λ4 are transmitted by a polarization-preserving optical fiber 501 to a fiber Coupler 502. These light sources are coupled by the fiber coupler 502 and are transmitted to a polarization-preserving optical fiber 504 via a multiplexer 503. Finally, the polarization-preserving optical fiber 504 outputs these light sources to the illumination module 2.

The multiple wavelengths light sources used by the alignment system 5 can suppress effects of destructive interference and enhance the process adaptability of the alignment system 5. In addition, the illumination module 1 used near infrared and infrared source can solve absorption problem of a low-k dielectric materials within range of visible spectrum and can be used for mark detection of a polysilicon layer.

The illumination module 1 also includes a laser module (Not Shown) that provides a laser source with high brightness. In order to enhance the signal noise ratio, the laser module uses a phase modulation to modulate the laser source. The alignment signal is demodulated by the electrical signal processing module. The laser source may be a semiconductor laser or a fiber laser.

The multiple wavelengths beam is followed through a polarizer 505, an illumination aperture stop 507, a lens 508 and a mirror 509a located on the flat plate 509 to form a reflected light into an imaging optical path. An aperture stop 507, an objective 511 and elements arranged between an aperture stop 507 and an objective 511 form a Kohler illumination system. The lens 506 is condenser.

The imaging optical path includes the objective 511 with large numerical aperture and long working-distance, a achromatic quarter wave plate 510, a spatial filter 512, the diffraction orders-combining system 513, a analyzer 514 and the multiple wavelengths demultiplexing system 515.

The light source emits a spatially coherent beam of radiation which illuminates the mark WM which reflects and scatters the radiation. These reflected and scattered radiations are collimated by objective 511. As the key element in the imaging optical path, the objective 511 may have a high NA, e.g. NA=O.8, for collecting the diffraction orders reflected from the marks WM. When NA is equal to 0.8, objective 511 allows detecting the marks with a small pitch of 1.1 μm with an illumination radiation having a wave length of 850nm.

When the pitch of the marks is of the same order of magnitude as the wavelength used, the diffraction Efficiency of the grating is related to the polarization of the light source. Therefore, the achromatic quarter wave plate 501 is placed adjacent to the objective 511 to convert the linear polarization light into right or left circularly polarized light.

The circularly polarized light contains two orthogonally polarized components so there is always one component that will efficiently diffract the light.

A spatial filter 512 is placed on an exit pupil of the objective 511 to eliminate stray light crosstalk influence from the adjacent marks of the wafer or product patterns.

A plurality of diffraction orders can be made to overlap and interfere by the diffraction orders-combining system 513. The multiple wavelengths light source illuminates the alignment mark WM with two-dimensional structure that produce the different diffraction orders in X direction or in Y direction.

On the basis of the dispersion element, the multiple wavelengths demultiplexing system 515 includes a prism (e.g. Cornu prism or Littrow prism), a blazed grating and an echelon grating. The multiple wavelengths demultiplexing system 515 may be a beam splitter system, the types of which includes an interference filter, a color separation grating, a diffraction optics element and so on. It is desired to choose a transmission type blazed grating that includes a polyline blazed grating, a multi-section blazed grating, and a polyline-multi-section blazed grating.

A detection optical path 516 includes a first optical path for coarse alignment and a second optical path for fine alignment. The plurality of diffraction orders overlap and interfere to image on a reference mark plate in pupil plane. The central positional information of the alignment mark is available by measuring intensity variation or phase variation of a plurality of diffraction orders reflected and transmitted at the reference mark.

The diffraction orders-combining system 513 of the present invention includes a diffraction orders-combining system based on a coordinate inversion interferometer 5131, a diffraction orders-combining system based on a prism interferometer 5132, a diffraction orders-combining system based on a lateral shearing interferometer 5133, and a diffraction orders-combining system based on a diffraction grating 5134.

FIG.4, FIG.5, and FIG.6 depict the diffraction orders -combining system based on a coordinate inversion interferometer 5131, for explaining the concept of its operation.

The diffraction orders-combining system based on the coordinate inversion interferometer 5131 can produces two overlapping and relatively rotated images of the alignment mark so that the positive and the corresponding negative diffraction orders overlap and interfere.

The coordinate inversion interferometer of the present invention has different interference theory, a new mathematical expression of the optical path difference, a new expression of an interference wave surface, all of which are different from the self-referencing interferometer described in the existing technology.

The self-referencing interferometer descried in the existing technology is constructed and arranged to project two overlapping images of an alignment mark that are relatively rotated by 180 degrees. The incident wavefront is described by W(p,θ). Two incident wavefronts are rotated by ±90 degree respectively and interfere to produce an interference pattern. The interfering wavefronts are expressed as W(p,θ-π/2) and W(p,θ+π/2) respectively. The optical path difference is denoted by OPD, OPD= W(p,θ-π/2)-W(p,θ+π/2).

If the incident wavefront W(p,θ) is in the right-hand coordinate system, the interference wavefronts that produced by rotating the incident wavefront over ±90 degree respectively are in the right-hand coordinate system.

The principle of the coordinate inversion interferometer is that the incident wavefront is reverted relative to the X coordinate and to the Y coordinate respectively, which are then made to interfere. The two interfering wavefronts are different from the incident wavefront in expression of the optical path difference.

The coordinate inversion interferometer is non-sensitive to a symmetrical aberration and is sensitive to non symmetrical aberration. The sensitivity of the coordinate inversion interferometer to the non symmetrical aberration is increased by one time than the sensitivity of a common interferometer. The incident wavefront is described by W(x,y). Two interfering wavefronts produced by the coordinate inversion are W(-x,y) and W(x,-y). The optical path difference is donoted by OPD, OPD=W(-x,y)-W(x,-y). If the incident wavefront W(x,y) is in the right handed coordinate system, interference wavefronts W(-x,y) and W(x,-y) are also in the left handed coordinate system.

An image of an incident wavefront is an "R" type image 1, which is reverted to an image 2 by x coordinate inversion. The "R" type image 1 is inverted to the image 3 by y coordinate inversion. The image 4 is obtained by rotating the image 1 over 180 degree. The image 2 and the image 3 can not be obtained by rotating the image 1, which can only be obtained by x coordinate inversion and by y coordinate inversion respectively. It is assumed that the incident wavefront is "R" type image 1 shown in FIG 4(a). The interference wavefronts based on the self-referencing interferometer are the image 1 and the image 4, and the interference wavefronts based on the coordinate inversion interferometer are image 2 obtained by X coordinate inversion and the image 3 obtained by Y coordinate inversion.

The diffraction orders-combining system 5131 consists of three main parts: a polarizing beam splitter 101 to split an incident wavefront and recombine two interfering wavefronts, a prism system 102 which produces two interfering wavefronts from an incident wavefront by X coordinate inversion and by Y coordinate inversion respectively, and a achromatic wave plate 103 (quarter or half wave plate). For stability reasons, the polarizing beam splitter 101, the prism system 102 and the achromatic wave plate 103 are glued to form a compact unit that is the diffraction orders-combining system 5131.

The incident light of the diffraction orders-combining system 5131 is linear polarized light.

The polarized orientation of a polarization beam surface 101a is oriented at 45 degree relative to the polarization beam surface 101a. The incident light is split by the polarization beam surface 101a and enters the prism system 102. Both prisms in the prism system 102 reflect two lights that overlap by x coordinate inversion and y coordinate inversion. The two overlapping lights are orthogonally plane polarized.

The polarized orientation of an analyzer 514 shown in FIG3 is oriented at 45 degree relative to the two overlapping lights.

When the incident wavefront is in the right handed coordinate system 104 (o-xyz), the two emergent wavefronts are in the left handed coordinate system 105 ( O₁-X^₁Z₁ ) and a left handed coordinate system 106(O₂-X₂V₂Z₂) respectively. The reflection times of the two overlapping lights are an odd numbers. The prism system 102 includes at least a roof prism that is used for inverting the y coordinate of the one light and inverting the x coordinate of the another light. If the z coordinate is an axis direction, the two overlapping lights change the polarization direction after the two overlapping light through the quarter wave plate or the half-wave plate respectively.

In FIG.4, if an image of an incident wavefront 107a is an "R" type image in the right handed coordinate system, which is reverted to an image 107b by x coordinate inversion and inverted to an image 107c by y coordinated inversion. The images 107b and 107c are in the left handed coordinate system. Therefore, the images 107b and 107c overlap and interfere, all of which can not obtained by rotating the image 107a.

FIG. 5 depicts structures of the diffraction orders-combining system based on a coordinate inversion interferometer 5131.

FIG. 5(a) and FIG. 5(b) depict a detailed structure of the coordinate inversion interferometer.

FIG. 5(c) depicts an entire structure of the interferometer.

In FIG 5(a), a right-angle edge of a right-angle prism 109 is perpendicular to a right-angle edge of a right-angle prism 111. The incident wavefront in the right handed coordinate system is splitted by a splitter surface 108a of a beam splitter 108, reflected by the right-angel prism 109, inverted by the y coordinate system and then reflected by a cubic prism 110 to form an emergent beam 1. A transmitted beam is reflected by the right-angle prism 111, reverted by x coordinate system and then reflected by a reflection surface 112a of a cubic prism 112 to form an emergent beam 2. The emergent beam 1 is reflected by a cubic prism 113 and a splitter 114 to form an outgoing beam.

The emergent beam 2 is reflected by a right-angle reflector prism 115 and a splitter surface 114a of the splitter 114 to obtain an another outgoing beam. The two outgoing beam are overlap and interfere, all of which are in the left handed coordinate system.

The splitters 108 and 114 may be polarizing beam splitters. Thus, a polarization beam surface 114a and 108a and an achromatic half- wave plate (Not Shown) are used for interchanging polarization states of two interfering beams. Polarization directions of the two interfering beam are perpendicular to each other. Then, the two interfering beam are combined by an analyzer 514 to overlap and interfere. In addition, The right-angle prisms 109 and 11 with Brewster incidence angles can implement the coordinate inversion, vertical polarization and interference.

For stability reasons, all of the optical elements are glued to form on a compact unit. The coordinate inversion interferometer is a Mach-Zehnder interferometer with equal optical path, which can produces two overlapping and coordinates inverted images of the alignment mark so that the positive and the corresponding negative diffraction orders overlap and interfere.

The coordinate inversion interferometer described in the present invention includes various structure types, such as a Michelson type, a Jamin type, a Sagnac type, a plane type, and various combined optical elements (such as a prism including a penta prism, a half penta prism, a right-angle prism, a Porro prism and a Rhomboid prism), a len, a plane, a wedge, a grating and so on.

FIG.6 is a view useful in explaining the coordinate inversion of a plurality of diffraction orders for overlapping and interfering based on the diffraction orders-combining system 5131.

FIG. 6 takes a monochromatic light as an example. In FIG.6, Solid circles represent the light spots of positive diffraction orders and hollow circles represent the light spots of negative diffraction orders.

In FIG.6 (a), 116 is a drawing for showing the distribution of the plurality of diffraction spots on an input plane (i.e. plane xy) of the coordinate inversion interferometer. In FIG.6 (b), 117 is a drawing for showing the distribution of the plurality of diffraction spots by x coordinate inversion on an output plane (i.e. plane X^₁). Comparing with the drawing of 116, the positive diffraction spots and the corresponding negative diffraction spots in an X₁ axis are interchanged with each other, and the diffraction spots in an y_t axis are unchanged in the drawing of 117.

In FIG.6 (c), 118 is a drawing for showing the distribution of the plurality of diffraction orders light spots by y coordinate inversion on an output plane (i.e. plane x₂y₂). Comparing with the drawing of 116, the positive orders diffraction light spots and the negative orders diffraction light spots in an y₂ axis are interchanged with each other and the diffraction light spots in an X₂ axis are unchanged in the drawing of 118.

In FIG.6 (d), 119 is a drawing for explaining the output plane (i.e. plane xjyO and the output plane (i.e. plane x₂y₂) are overlapped to make the plurality of diffraction orders overlap and interfere.

FIG.7 illustrates another optical path implementing overlapping and interfering of a plurality of diffraction orders light spots. A diffraction orders-combining system in the FIG.7 may be a prism interferometer 5132, a lateral shearing interferometer 5133, or a diffraction grating 5134. This diffraction orders-combing system has some difference with the diffraction orders-combing system based on the coordinate inversion interferometer 5131. Firstly, the diffraction orders-combining system in the FIG.7 has a different principle and a method to implement the overlapping and interfering of the plurality of diffraction orders light spots. Secondly, because the diffraction orders-combining system in the FIG.7 doesnot include the roof prism, the optical axis of the incident beam only need be adjusted and overlapped with the optical axis of the diffraction orders-combining system in a single plane. Two diffraction order-combining systems are used for making positive orders and the negative orders light spots overlap and interfere, respectively.

FIG.8 illustrates the principle of the diffraction order-combing system based on a prism interferometer 5132. The principle is that +1 - +n orders and -1 - -n orders diffraction lights of the alignment mark overlap and then made to interfere by reflection and refraction in different optical paths.

FIG. 8(a) is a drawing of a structure of the diffraction order-combing system. The diffraction order-combing system includes two right angle prisms 301 and 302, which are glued with each other. A gluing covering is denoted by 303, the positive diffraction orders by black arrows, and the negative diffraction orders by hollow arrows. The positive diffraction orders illuminate the right-angle prism 301 and then are reflected by a reflection surface 301a and the gluing covering 303 to form an outgoing light from the reflection surface 301a. The negative diffraction orders illuminate the right-angle prism 302 and then are reflected by a reflection surface 302a and the gluing covering 303 to form an outgoing light from the reflection surface 301a. Two outgoing lights overlap so that the positive and the corresponding negative diffraction orders overlap and interfere.

FIG 8(b) describes a structure of a prism group. The prism group consists of four 60 degree right-angle prisms 304, 305, 306 and 307 that are glued together.

FIG.8(d) illustrates a structure of the diffraction order-combing system based on the prism interferometer 5132. The diffraction order-combing system 5132 includes right-angle prisms 311 and 312, an achromatic quarter wave plate 313 and a plate 310 for compensating an optical path difference induced by the achromatic quarter wave plate 313. The right-angle prisms 311 and 312 are glued together to form a gluing covering 312a that is a polarization beam surface. The positive diffraction orders enter the right-angle prism 312 after splitting by the polarization beam surface 312a, and then are transmitted twice by the achromatic quarter wave plate 313. Two transmitted lights from the achromatic quarter wave plate 313 are orthogonally plane polarized, which enter an analyzer 514 to overlap the positive diffraction orders and the negative diffraction orders. FIG.8(d) illustrates another structure of the diffraction order-combing system based on the prism interferometer 5132. This diffraction order-combing system 5132 consists of two same Dove prisms 314 and 315 that are glued together. A gluing covering 316 is a beam splitter surface. The positive diffraction orders are launched into the Dove prism 314, and go out .from the beam splitter surface 316. The beam splitter surface 316 is used for reflecting a part of light from the prism 314 to form an outgoing light that is a inverted image of the incident light, and transmitting an another parts of light from the prism 314 to from an outgoing light that is an erect image of the incident light. Thus, the erect image of the positive diffraction orders and the inverted image of the negative diffraction orders overlap and interfere, and the inverted image of the positive diffraction orders and the erect image of the negative diffraction orders overlap and interfere.

FIG.9 illustrates a principle of the diffraction order-combing system based on a lateral shearing interferometer 5133. The diffraction order-combing system 5133 utilizes the lateral shearing interferometer so that the positive and the corresponding negative diffraction orders overlap and interfere.

The negative diffraction orders are inverted by an image rotation prism 403 (e.g. Dove prism), and then come into the lateral shearing interferometer 405. The positive diffraction orders come into the lateral shearing interferometer 405 after the light pass through an OPD (Optical Path Difference) compensator 402. In the lateral-shear interferometer 405, the plurality of diffraction orders 404 are interfered with a shifted version of themselves 404a in an overlapping domain so that the positive and the corresponding negative diffraction orders overlap and interfere by adjusting a shearing amount appropriately.

Fig 10 is drawings of some structures of the diffraction order-combing system based on the lateral shearing interferometer 405.

FIG 10(a) illustrates a single parallel-plate shearing interferometer 405. An incident beam is reflected by a front surface 407a of a plate 407 and reflected by a rear surface 407b of the plate 407 to generate two shearing beams. The shearing amount is determined by an incident angle and a thickness of the plate 407. Because the single parallel -plate shearing interferometer 405 is an interferometer with unequal optical path, the optical path can be compensated by adjusting the thickness of the OPD compensator 402.

FIG 10 (b) is a drawing of a Michelson interferometer structure of the lateral shearing interferometer 405 with equal optical path.

The lateral shearing interferometer 405 is the Michelson interferometer with equal optical path. The interferometer 405 includes a splitter 408 for splitting an incident wavefront and recombining two interfering wavefronts, and two right-angle prisms 409 and 410 for folding wavefront from the splitter 408. The right-angle prisms 410 shifts along the surface 408a to induce a proper shear amount. The splitter 408 and the two right-angle prisms 409 and 410 are glued together for stability.

FIG.10 (c) is a drawing of another Michelson interferometer structure of the lateral shearing interferometer 405 with equal optical path. The interferometer 405 consists of two tetragonal prisms 411 and 412 that are glued together to form a gluing covering 413. An incident light is split by the gluing covering 413 to form two splitting lights. The two splitting lights are reflected by the prisms 411 and 412 respectively. Then, two reflected lights are combined by the gluing covering 413. The relative shift of the two tetragonal prisms on the gluing covering 413 induces a certain shearing amount. For stability reasons, the prisms 411 and 412 are glued together after adjusting to an appropriate shearing amount.

FIG.10 (d) is a drawing of a cycle interferometer structure of the lateral shearing interferometer 405 with equal optical path. The interferometer 405 consists of two half penta prisms 414 and 415 that are glued together to form a gluing covering 416. An incident light is split by the gluing covering 416 to form two splitting lights. The two splitting lights are reflected by the prisms 414 and 415 respectively. Then, two reflected lights are combined by the gluing covering 413. The relative shift of the two half penta prisms on the gluing covering 416 produces a certain shearing amount.

For stability reasons, the prisms 414 and 415 are glued together after adjusting to an appropriate shearing amount.

FIG.11 illustrates the principle of the diffraction order-combing system based on a diffraction grating 5134. The principle is that +1 - +n orders and -1 - -n orders diffraction lights of the alignment mark are diffracted by the same grating to implement the overlapping and interfering of the plurality of diffraction orders light spots. Different color beams must be separated before the system 5134.

FIG. 11 (a) is a drawing of a structure of the diffraction order-combing system 5134. The diffraction order-combing system 5134 includes a mirror 602 and a grating 603, which are perpendicular with each other. A plurality of diffraction orders light spots 601 with single wavelength enter into the mirror

602 with an incident angle ( π/2-α ) , reflected by the mirror 602 and then incident on the grating 603. The negative diffraction orders are incident on the grating

603 with an incident angle α directly. The positive diffraction orders and the negative diffraction orders have the same incident angle α relative to a normal direction of the grating 603.

Based on the diffraction formula of the grating: dsinα=λ (d is the period of the grating 603, α is the +1 order diffraction angle of the grating 603), the positive and negative diffraction orders from the grating 603 in direction perpendicular to the surface of the grating 603 overlap and interfere. Compare the distribution of the overlapping diffraction orders light spots with the distribution of the incident diffraction orders light spots, lateral dimension is magnified K times (K=H/h=l/cosα>l). Therefore, the system 5134 not only can overlap and interfere the negative and the positive diffraction light spots, but also can expand beam to facilitate the detection of multi-detection. Because the negative and the positive diffraction orders lights have different optical paths, the overlapping lights there between induce proper optical path difference. The optical path difference is varied with the diffraction orders and the space of the light spots. In order to compensate the optical path difference, plane-plates with different thickness or a diffraction optics element are located in the optical path of the negative diffraction orders.

The mirror 602 and the grating 603 are glued together onto a glass substrate for stability. The grating 603 may be a reflected type, a diffracted type, an amplitude type, or a phase type.

FIG. 11 ( b ) depicts another structure of the diffraction orders-combining system based on the diffraction grating 5134. The system 5134 is used for overlapping and interfering the diffraction spots in x direction and in y direction. The system 5134 includes a phase grating 605 for diffracting the diffraction spots in x direction, a phase grating 606 for diffracting the diffraction spots in y direction, and a mirror 607 for reflecting the spots in x direction to a surface of the phase grating 605 and reflecting the spots in y direction to a surface of the phase grating 606. Perpendicular to the surface of the phase grating 605 and the surface of the phase grating 606, the positive and negative diffraction spots that have same order overlap and interfere.

Phase gratings 605 and 606 may have same periods or different periods. The incident angle α_x of the diffraction light in x direction may be equal to or different from the incident angle α_y of the diffraction light in y direction.

FIG.11 (c) is a view of an optical path of the diffraction orders-combining system based on the diffraction grating 5134 The diffraction spot 608 has -1 - -n orders diffraction light that is rotated 180 degrees by a image rotation prism 610 (e.g. Dove prism), and is refracted by a lower half part of a double wedge prism 612, to enter into the phase grating 613 with an incident angle α¹. The positive diffraction orders pass into an OPD compensator 609 and then are refracted by an upper half part of the double wedge prism 612. The refraction lights enters to the phase grating 613 with an incident angle α'. α' is ±1 orders diffraction angle of the phase grating 613.

FIG.12 depicts a structure of the multiple wavelengths demultiplexing system 515 of FIG. 3.

An illuminator is constructed to illuminate an alignment mark with light of multiple wavelengths to produce a plurality of overlapping diffraction orders having different wavelengths. The multiple wavelengths demultiplexing system 515 is used for demultiplexing light of different wavelengths. The multiple wavelengths demultiplexing system 515 include prisms (such as Cornu prism and Littrow prism), blazing gratings, echelon gratings, interference filters, and diffraction optics elements (e.g. CSG-colour separation grating).

The multiple wavelengths demultiplexing system 515 is based on a multi-blazed grating. Conventional blazed gratings are optimized for a specific wavelength by varying the blaze angle of the grating. The efficiency is high for the specified wavelength, but on the other hand the efficiency is lower for other wavelengths.

Thus, the multi-blazed grating can avoid problems produced by the Conventional blazed grating. The multi-blazed grating has two types that are a polyline type and a multi-section type. The polyline type includes two planes with different blazed angle instead of one blazed angle of a common blazed grating. The two planes with different blazed angle operate at the same time so that the grating has two blazed wavelengths that have two maximum values on a power-wavelength curve drawing. The power-wavelength curve can cover a larger wavelength range with high diffraction efficiency.

The polyline type is suitable for an infrared grating with a small groove density and a broad groove surface.

The principle of the multi-section type is that the surface of the blazed grating comprise of a plurality of sections determined by the demultiplexed wavelength numbers. These sections have the same groove density and different blazed angles. It is not difficult to scribe the surface of the blazed grating with multi-sections, so a high groove density can be implemented.

FIG 12 (a) depicts a structure of the multiple wavelengths demultiplexing system 515 for demultiplexing the different wavelength by using a transmitted type multi-blazed grating 701.

The structure of the transmitted type grating 701 is based on the structure of the polyline type and the structure of the multi-section type. The grating 701 includes two multi-section type gratings 701a with a grating period d_\ and 701b with a grating period d₂. The grating 701a is a polyline type infrared grating with blazed angles P₁1 and β₁₂. for blazing two infrared wavelengths λ₁ and λ₂( e.g. 785 nm- 850 nm ). The grating 701b is a common grating with a blazed angle β₂. The blazed angle β₂ is optimized by a central wavelength (λ₃+λ₄)/2 (e.g. 582.5nm) produced by a wavelength λ₃ (e.g. 532 nm) and a wavelength λ₄ (e.g. 633nm). The depressed diffractive efficiency for the wavelength λ₃ and λ₄ is acceptable.

In addition, the grating 701 also consists of threes multi-section blazed gratings 701a and 701b and 701 with grating periods d_1? d₂ and d₃ respectively. The grating 701a is a polyline type with blazed angle P₁₁ and β₁₂ for blazing two infrared wavelengths

and λ₂. The gratings 701b and 701c are common blazed grating with blazed anglesβ₂ and β₃ optimized by the wavelengths λ₃ and λ₄ respectively.

FIG 12(b) depicts another structure of the multiple wavelengths demultiplexing system 515 based on a interference filter. Lights with respective wavelengths

, λ₂, λ₃ and λ₄ illustrate to a first splitter 702 and then enter to a long wave-pass filter 704. The filter 704 filters the lights with wavelengths λ₃ and λ₄. The lights with wavelengths X₁ and λ₂ are splitted by a second splitter 705 to form a reflection light tr and a transmitted light tt. The reflection light tr is reflected by a right-angle prism 707, and filtered by a short wave-pass filter 708 to form an outgoing light λ₂. The transmitted light tt enters into the short wave-pass filter 708 to form an outgoing light λi. A reflection light r reflected by the first splitter 702 enters to a short wave-pass filter 703 that filters the lights with wavelength λ₃ and λ₄. The lights with wavelengths λι and λ₂ are splitted by a third splitter 709 to form a reflection light rr and a transmitted light rt. The reflection light rr is filtered by a short wave-pass filter 710 to form a outgoing light λ₄. The transmitted light rt is reflected by a right-angle prism 711, filtered by a long wave-pass filter 712 to form an outgoing light λ₃.

FIG 12(c) depicts another structure of the multiple wavelengths demultiplexing system 515 based on the interference filter and the multi blazed grating. Lights with respective wavelengths X₁ , λ₂, λ₃ and λ₄ illustrate to a first splitter 713 and then enter to a long wave-pass filter 716. The filter 716 filters the lights with wavelengths λ₃ and λ₄. The lights with wavelengths λ_\ and λ₂ enter to a first blazed grating 717 and then exit from the first blazed grating 717 with different exit angles respectively. A reflection light r splitted by the first splitter 713 is reflected by a right-angle prism 714 to form a reflection light rr. Then, the reflection light rr is filtered by a short wave-pass filter 715 that filters the lights with wavelengths X₁ and λ₂. The lights with wavelengths λ₃ and λ₄ enter to a second blazed grating 718 and then exit from the second blazed grating 718 with different exit angles respectively.

The first and second blazed gratings 717 and 718 may be polyline type multi blazed grating 719a having a grating period d_t and blazed angles P₁₁ and β₁₂, or a multi-section blazed grating 719b having a grating periods d₂₁ and d₂₂ and corresponding blazed angles β₂₁ and β₂₂, or a common blazed grating 719c having a grating periods d₃ and corresponding blazed angles β₃.

FIG 13 is a drawing of a structure of the detection module 516. In FIG 13, a detection optical path 800 of a light having wavelength X₁ is as follow. The detection module comprises two optical patlis.The incident light is split by the splitter 801 to form a first optical path (i.e. reflection light) for coarse alignment and a second optical path (i.e. transmission light) for fine alignment. The reflection light transmitting a scribe plate 809, is focused by a focus lens 810 to enter into a fiber 811. By the fiber 811, the images of an alignment mark and the scribe are imaged on a CCD camera 813 via a projection lens 812.

An optical system composed of Lens 802 and 804 are used for imaging an exit pupil of the diffraction orders-combining system 513 onto a reference plate 806 having a grating type reference mark. A spatial filter 803 is located at the middle image location of the optical system for eliminating stray light and cross-talk effects from the adjacent marks or product structures. In addition, a spatial light modulator 805 is set on an exit pupil plane of the diffraction orders-combining system 513 to select a plurality of specific diffraction orders that overlap and interfere. The spatial light modulator 805 may be a programmable LCD panel. A fibers array 807 and a detector 808 (or detectors array) detect the transmitted intensity from the reference plate 806. According to the relative phase information in the intensity variations as an alignment mark is scanned, the positions of the alignment mark can be obtained.

In another detection optical path 516 (Not shown), the reference plate 806 can be removed. By detecting intensity variations at the positions of a plurality of diffraction orders in a pupil plane, positioning information of an alignment mark can be derived. Those information is obtained from the relative phase in the intensity variations as an alignment mark is scanned; the different diffraction orders will vary in intensity with different spatial frequencies.

The apparatus of the present invention is applied not only into the integrated circuit manufacture, but also into the other manufactures that includes a micro electromechanical system manufacture, a micro-opto-electro-mechanical system manufacture, an integrated micro-optical system manufacture, a LCD panel manufacture, and a film head manufacture and so on. The term "wafer" of the present invention should be broadly interpreted as referring to the terms "substrate". The terms "light" and "beam" includes all types of Electromagnetic Radiation, such as KrF excimer laser with a wavelength of 248nm, a ArF excimer laser with a wavelength of 193nm, a F2 excimer laser with a wavelength of 157nm, a Kr2 excimer laser with a wavelength of 146nm, a Ar2 excimer laser with a wavelength of 126nm, a super high pressure mercury lamp (g-line, i-line), a ultraviolet light source having a wavelength range from 5 to 20nm, a ion beam or a electron beam and so on.

Claims

What is claimed is:

1. An alignment system of a lithographic apparatus, comprising: a radiation module for providing a light source for the alignment system; an illumination module for transmitting the light to illuminate an alignment mark with periodic optical structure; an imaging module at least including an objective for collecting a plurality of diffraction orders produced by the alignment mark, a diffraction orders-combining system for overlapping and interfering the same orders and a multiple wavelengths demultiplexing system for demultiplexing light signals of a plurality of different wavelengths; and a detection module for obtaining the positional information of the alignment mark by detecting intensity variations of a plurality of interfered diffraction orders.

2. An alignment system according to claim 1, wherein the light source is a light source with multiple wavelengths that includes four discrete wavelengths with preferably two wavelengths in near infrared or infrared band.

3. An alignment system according to claim 1 , wherein the light source may be a semiconductor laser or a fiber laser.

4. An alignment system according to claim 1 or claim 2 or claim 3, wherein the light incident on a wafer is a circular polarization light.

5. An alignment system according to claim 1, wherein the alignment mark is dual-dimension phase grating structure formed by four groups gratings that is symmetrically distributed on the two sides of the centre cross in x direction and in y direction, the two gratings for the same direction alignment have different periods.

6. An alignment system according to claim 1, wherein the objective has large numerical aperture and long working-distance.

7. An alignment system according to claims 1 to 6, wherein a spatial filter is located on an exit pupil plane of the objective.

8. An alignment system according to claim 1, wherein the diffraction orders-combing system is used for making the light spots of positive diffraction orders and the corresponding light spots of negative diffraction orders overlap and interfere, respectively.

9. An alignment system according to claim 1, wherein the diffraction orders-combing system is based on a coordinate inversion interferometer which has a principle that a plurality of diffraction orders is reverted relative to a X coordinate and to a Y coordinate respectively, which are then made to overlap and interfere.

10. An alignment system according to claim 9, wherein the coordinate inversion interferometer comprises a polarization beam splitter, a prism system and an achromatic quarter wave plate.

11. An alignment system according to claim 10, wherein the polarization beam splitter, the prism system and the achromatic quarter wave plate are glued with each other for stability.

12. An alignment system according to claim 9, wherein the coordinate inversion interferometer is Mach-Zehnder type structure comprising two right-angle prisms.

13. An alignment system according to claim 9, wherein the coordinate inversion interferometer comprises various structure types having a Michelson type, a Jamin type, a Sagnac type, a plane type, and various combined optical elements that comprises a prism, a lens, a plane-plate, a wedge, and a grating.

14. An alignment system according to claim 1, wherein the alignment system further comprises two diffraction orders-combining systems which implement the overlapping and interfering of the light spots of positive diffraction orders and the corresponding negative diffraction orders and the detecting of alignment signals in two perpendicular directions respectively.

15. An alignment system according to claims 1 or claim 8 or claim 14, wherein the diffraction orders-combining system is based on a prism interferometer, which is used for overlapping and interfering the light spots of positive diffraction orders and the light spots of negative diffraction orders by reflection and refraction with different optical paths within the prism interferometer.

16. An alignment system according to claim 15, wherein the prism interferometer is constructed by four right-angle prisms glued with each other.

17. An alignment system according to claim 15, wherein the prism interferometer is constructed by two right-angle prisms glued with each other.

18. An alignment system according to claim 15, wherein the prism interferometer is constructed by two Dove prisms.

19. An alignment system according to claim 1 or claim 8 or claim 14, wherein the diffraction order-combing system is based on a lateral shearing interferometer which utilizes the lateral shearing interference of at least two lights so that the light spots of positive and corresponding negative diffraction orders overlap and interfere.

20. An alignment system according to claim 19, wherein the coordinate inversion interferometer comprises various structure types having a Michelson type, a Mach-Zehnder type, a Cycle type, a Jamin type, a Sagnac type, a plane type, a prism type and a grating type.

21. An alignment system according to claim 1 or claim 8 or claim 14, wherein the diffraction orders-combining system is based on a diffraction grating, which implement the overlapping and interfering of the light spots of positive diffraction orders and corresponding negative diffraction orders by means of the same grating.

22. An alignment system according to claim 1, wherein the multiple wavelengths demultiplexing system is based on a dispersion element, or an interference filter, or a diffraction optics element.

23. An alignment system according to claim 22, wherein the types of the dispersion element includes a prism, a blazed grating, and an echelon grating.

24. An alignment system according to claim 23, wherein the blazed grating is multi-blazed grating having a polyline type and a multi-section type and a polyline-section combined type.

25. An alignment system according to claim 1, wherein the detection module comprises two optical paths that the first optical path for coarse alignment and the second optical path for fine alignment.

26. An alignment system according to claim 25, wherein the first optical path comprises an optical system for imaging an alignment mark and a scribe on a CCD camera.

27. An alignment system according to claim 25, wherein the second optical path comprises an optical system for imaging the exit pupil of a diffraction order-combing system onto a reference plate having a reference mark.

28. An alignment system according to claim 27, wherein a spatial filter is located at the middle image plane of the optical system.

29. An alignment system according to claim 27, wherein a spatial light modulator is located on an exit pupil plane of the diffraction orders-combining system.

30. An alignment system according to claim 27, by measuring the intensity transmitted from the reference plate, the positions of the alignment mark are derived from the relative phase information in the intensity variations as an alignment mark is scanned.

31. An alignment system according to claim 25, the light intensities further may be measured directly at the positions of a plurality of interfered diffraction orders in a pupil plane, positioning information of an alignment mark is derived from the relative phase information.

32. A diffraction orders-combing system of an alignment system of a lithographic apparatus, wherein the diffraction orders-combing system is used for making the light spots of positive diffraction orders and the light spots of corresponding negative diffraction orders overlap and interfere.

33. A diffraction orders-combing system according to claim 32, wherein the diffraction orders-combing system is based on a coordinate inversion interferometer which has a principle that a plurality of diffraction orders is reverted relative to a X coordinate and to a Y coordinate respectively, which are then made to overlap and interfere.

34. A diffraction orders-combing system according to claim 32, wherein the diffraction orders-combining system is based on a prism interferometer, which is used for overlapping and interfering the light spots of positive diffraction orders and the light spots of corresponding negative diffraction orders by reflection and refraction with different optical paths in the same prism interferometer.

35. A diffraction orders-combing system according to claim 32, wherein the diffraction order-combing system is based on a lateral shearing interferometer which utilizes the lateral shearing interference of at least two lights so that the light spots of positive and corresponding negative diffraction orders overlap and interfere.

36. A diffraction orders-combing system according to claim 32, wherein the diffraction orders-combining system is based on a diffraction grating, which implement the overlapping and interfering of the light spots of positive diffraction orders and corresponding negative diffraction orders by means of the same grating.