CN117537704A - Position measurement method, position measurement system and lithographic apparatus - Google Patents

Abstract

The invention provides a position measurement method, a position measurement system and photoetching equipment, wherein the position measurement system comprises a measured object, a reading head and a light source, the reading head comprises a first light splitting unit and a reverse retroreflection element, light beams emitted by the light source are divided into a first light beam and a second light beam with different directions through the first light splitting unit, the first light beam and the second light beam form a first diffraction light beam and a second diffraction light beam after being diffracted by the measured object, the first diffraction light beam and the second diffraction light beam both comprise positive and negative diffraction light beams, and the optical path length of the positive and negative diffraction light beams corresponding to the first diffraction light beam is equal and the optical path length of the positive and negative diffraction light beams corresponding to the second diffraction light beam is equal respectively by adjusting the physical distance or the optical path distance of a diffraction point on the reverse retroreflection element and the measured object. The optical power loss of the grating type refraction element is avoided, the optical power utilization rate of the system is improved, and the stray light level is reduced.

Description

Position measurement method, position measurement system and lithographic apparatus

Technical Field

The present invention relates to the field of photolithography, and in particular, to a position measurement method, a position measurement system, and a photolithography apparatus.

Background

The nano measurement technology is the basis of the fields of nano processing, nano control, nano materials and the like. The IC industry, precision machinery, microelectromechanical systems, etc. all require high resolution, high precision displacement sensors to achieve nanometer precision positioning.

Along with the rapid development of integrated circuits in the large-scale and high-integration directions, the alignment precision requirement of the photoetching machine is higher and higher, and accordingly, the precision of acquiring the six-degree-of-freedom position information of the workpiece table and the mask table is also improved.

The optical path of the grating ruler measuring system can be very small, usually a few millimeters, and is irrelevant to the measuring range, so that the measuring precision of the grating ruler measuring system is insensitive to environmental influence, and the grating ruler measuring system has the characteristics of high measuring stability, simple structure and easiness in miniaturization, and occupies an important place in the field of nano measurement. The high-precision and high-stability picometer precision measurement task is born in a new generation of lithography systems.

The existing two-dimensional high-precision grating ruler position measuring system can measure the displacement in the horizontal direction (X/Y) and the vertical direction (Z) through phase shift signals. According to the technical scheme, the grating is used as the light beam deflection element, the light beam direction is adjusted, the reflecting elements are integrated together, the structure is compact, the shape is regular, and the stability is high. However, in the scheme, the measuring beam passes through the refraction grating twice, so that the loss of the optical power is large, stray light is more, and the power requirement of the corresponding optical source is also increased. In this scheme, the optical path difference between the positive and negative secondary beams needs to be compensated by a glass plate method.

The existing grating in-plane one-dimensional high-precision grating ruler position measurement system also adopts a grating as a light beam deflection element, so that a compact and stable structure is realized. But also the optical power loss is large.

Disclosure of Invention

The invention aims to provide a position measurement method, a position measurement system and photoetching equipment, which are used for solving the problems that the grating is adopted as a light beam deflection element in the position measurement system, the light power loss is high, the stray light is more, and the power requirement of a corresponding light source is also increased.

In order to solve the technical problems, the invention provides a position measurement system, which comprises a measured object, a reading head and a light source, wherein the reading head comprises a first light splitting unit and a reverse retro-reflecting element, a light beam emitted by the light source is divided into a first light beam and a second light beam with different directions through the first light splitting unit, the first light beam and the second light beam are diffracted by the measured object to form a first diffraction light beam and a second diffraction light beam, both the first diffraction light beam and the second diffraction light beam comprise positive and negative diffraction light beams, and the physical distance or the optical path distance between the reverse retro-reflecting element and a diffraction point on the measured object is adjusted to respectively realize that the optical paths of the positive and negative diffraction light beams corresponding to the first diffraction light beam are equal and the optical paths of the positive and negative diffraction light beams corresponding to the second diffraction light beam are equal.

Optionally, the reading head further includes a phase delay element, and the first diffracted beam and the second diffracted beam directly reach the phase delay element and the reverse retroreflective element, and directly reach the target after being reversely retroreflected by the reverse retroreflective element and then directly reach the target again after passing through the phase delay element.

Optionally, the phase delay element and the reverse retroreflective element corresponding to the positive and negative orders of the first diffracted beam and the second diffracted beam are separated from each other.

Optionally, the reading head further includes an optical path compensation element and a phase delay element, and the first diffracted beam and the second diffracted beam reach the phase delay element and the reverse retroreflective element through the optical path compensation element, reversely retroreflect through the reverse retroreflective element, and reach the measured target again through the phase delay element and the optical path compensation element.

Optionally, the optical path compensation element, the phase delay element and the reverse retroreflection element are of an integrated structure, and the thickness of the phase delay element and/or the thickness of the reverse retroreflection element and/or the distance between the reverse retroreflection element and a diffraction point on the measured object are/is adjusted, so that the optical paths of the positive and negative orders of diffraction light beams corresponding to the first diffraction light beam are equal, and the optical paths of the positive and negative orders of diffraction light beams corresponding to the second diffraction light beam are equal.

Optionally, when the incidence angles of the first beam and the second beam are the same, the physical distances from the two reflective edges of the reverse retroreflection element to the intersection point of the opposite extension lines of the +m-order diffraction beam of the first diffraction beam and the +m-order diffraction beam of the second diffraction beam are equal, and the optical path difference between the +m-order diffraction beam of the first diffraction beam and the +m-order diffraction beam of the second diffraction beam is compensated by the thickness of the phase delay element, the thickness difference between the +m-order diffraction beam of the first diffraction beam and the +m-order diffraction beam of the second diffraction beam passing through the phase delay element is:

wherein TS is the thickness of the phase delay element through which the +m-order diffraction beam of the first diffraction beam passes, TL is the thickness of the phase delay element through which the +m-order diffraction beam of the second diffraction beam passes, L is the distance between two incident lights on the measured object, alpha is the diffraction angle of the second diffraction beam and the m-order diffraction beam after the second diffraction beam and the m-order diffraction beam are diffracted by the measured object, beta is the diffraction angle of the second diffraction beam and the m-order diffraction beam after the diffraction of the measured object, and n is the refractive index of the substrate material of the phase delay element.

Optionally, the phase delay element, the reverse retroreflective element, and the optical path compensation element are a unitary structure.

Optionally, the reading head further includes a refractive element, an optical path compensation element, and a phase retardation element, where the first diffracted beam and the second diffracted beam reach the phase retardation element and the reverse retroreflective element through the refractive element and the optical path compensation element, and reach the measured target again after reversely retroreflecting through the reverse retroreflective element and passing through the phase retardation element, the optical path compensation element, and the refractive element.

Optionally, the positive and negative orders of the first and second diffracted beams correspond to the refractive element, the optical path compensation element, the phase delay element, and the reverse retroreflective element, respectively.

Optionally, the refractive element is a non-grating refractive element.

Optionally, the non-grating refractive element includes one or any combination of a beam splitter, a deflecting beam splitter, and a wedge angle prism.

Optionally, the first light beam and the second light beam are both incident on the measured object in a direction non-perpendicular to the measured object.

Alternatively, the retroreflective elements are multi-faceted prism structures.

Alternatively, the prism bases of the retroreflective elements are all cut to form the edges of the reflective prisms having right angles at the bases.

Optionally, the prism base portions of the retroreflective elements are cut such that the prism base portions of the retroreflective elements remain partially planar.

Based on the same inventive concept, the present invention also provides a lithographic apparatus comprising a position measurement system as described in any one of the above.

Based on the same inventive concept, the invention also provides a position measurement method, comprising the following steps:

the light source emits a light beam, and the light beam is divided into a first light beam and a second light beam with different directions through the first light splitting unit;

the first light beam is diffracted by the measured object to form a first diffracted light beam, the second light beam is diffracted by the measured object to form a second diffracted light beam, and the first diffracted light beam and the second diffracted light beam both comprise positive and negative diffraction light beams;

and adjusting the physical distance or the optical path distance between the reverse retroreflective element and the diffraction point on the measured object to respectively realize that the optical paths of the positive and negative diffraction beams corresponding to the first diffraction beam are equal and the optical paths of the positive and negative diffraction beams corresponding to the second diffraction beam are equal.

The positive and negative orders of the first diffraction beam are diffracted by the measured object to form a first interference beam, and the first interference beam contains horizontal displacement information of the measured object; the positive and negative orders of the second diffraction beam are diffracted by the measured object again to form a second interference beam, and the second interference beam contains horizontal displacement information and vertical displacement information of the measured object; and converting the first interference light beam into a first interference signal and converting the second interference light beam into a second interference signal, and performing displacement calculation to obtain the position information of the measured object.

In the position measurement method, the position measurement system and the photoetching equipment provided by the invention, the physical distance or the optical path distance between the reverse retroreflection element and the diffraction point on the measured object is adjusted so as to respectively realize that the optical path length of the positive and negative diffraction beams corresponding to the first diffraction beam is equal to the optical path length of the positive and negative diffraction beams corresponding to the second diffraction beam. Furthermore, the reverse retroreflection element, the phase delay element and the optical path compensation element can form an integrated structure, so that the structural stability of the integrated structure is ensured.

Drawings

FIG. 1 is a schematic view showing a ZX direction structure of a position measuring system according to a first embodiment of the present invention;

FIG. 2 is a schematic view illustrating a YZ-direction structure of a position measurement system according to a first embodiment of the present invention;

FIG. 3 is a schematic diagram illustrating an XZ direction structure of a position measurement system according to a first embodiment of the present invention;

FIG. 4 is a schematic view illustrating a ZX direction structure of a position measurement system according to a second embodiment of the present invention;

FIG. 5 is a schematic view illustrating a YZ-direction structure of a position measurement system according to a second embodiment of the present invention;

FIG. 6 is a schematic diagram illustrating an XZ direction structure of a position measurement system according to a second embodiment of the present invention;

FIG. 7 is a schematic view showing a ZX direction structure of a position measuring system according to a third embodiment of the present invention;

FIG. 8 is a schematic view showing a ZX direction structure of a position measuring system according to a fourth embodiment of the present invention;

FIG. 9 is a schematic view showing a ZX direction structure of a position measuring system according to a fifth embodiment of the present invention;

FIG. 10 is a schematic view showing a ZX direction structure of a position measuring system according to a sixth embodiment of the present invention;

fig. 11 to 12 are schematic structural views of a retroreflective element according to an embodiment of the present invention;

fig. 13-14 are schematic structural views of another retroreflective element of an embodiment of the present invention;

FIG. 15 is a schematic view showing a structure of a position measuring system ZX according to a seventh embodiment of the present invention;

FIG. 16 is a schematic view of a cylindrical lens structure according to an embodiment of the present invention;

FIG. 17 is a schematic view of a dove prism structure according to an embodiment of the present invention;

FIG. 18 is a flow chart of a position measurement method of an embodiment of the present invention;

In the drawing the view of the figure,

100-read head; 110-a first light splitting unit; 111-a second light splitting unit; 120-a reverse retroreflective element; 120a—edges of the retroreflective elements; 120 b-the bottom retained portion of the retroreflective elements plane 120b; 125-cylindrical lens structure; 126-dove prism; 1251-a lens; 1252-concave mirror; 130-a phase delay element; 140-an optical path compensation element; 150-a non-grating refractive element; 160-a polarizing element; 200-a measured target; 611-beam; 612—a first light beam; 613-a second light beam; 614-a first interference beam; 615-a second interference beam; 616—sub-beams of the first interference beam; 617-sub-beams of the second interference beam; 621-incident light beam; 622-exit beam.

Detailed Description

The invention will be described in further detail with reference to the drawings and the specific embodiments thereof in order to make the objects, advantages and features of the invention more apparent. It should be noted that the drawings are in a very simplified form and are not drawn to scale, merely for convenience and clarity in aiding in the description of embodiments of the invention. Furthermore, the structures shown in the drawings are often part of actual structures. In particular, the drawings are shown with different emphasis instead being placed upon illustrating the various embodiments. It should be further understood that the terms "first," "second," "third," and the like in this specification are used merely for distinguishing between various components, elements, steps, etc. in the specification and not for indicating a logical or sequential relationship between the various components, elements, steps, etc., unless otherwise indicated.

Specifically, please refer to fig. 1, which is a schematic diagram illustrating a ZX direction structure of a position measurement system according to a first embodiment. In this embodiment, the X direction is a first horizontal direction, the Y direction is a second horizontal direction, and the Z direction is a vertical direction, where the X direction, the Y direction, and the Z direction are perpendicular to each other. As shown in fig. 1, the present embodiment provides a position measurement system including a measured object 200, a reading head 100, and a light source (not shown in the figure).

The reading head 100 includes a first light splitting unit 110 and a reverse retroreflecting element 120, the light source emits a light beam 611 to be split into a first light beam 612 and a second light beam 613 with different directions by the first light splitting unit 110, at least one of the first light beam 612 and the second light beam 613 is not perpendicularly incident on the measured object 200, for example, the first light beam 612 is perpendicularly incident on the measured object 200 and the second light beam 613 is not perpendicularly incident on the measured object 200 in the embodiments of fig. 7, 9 and 10; for example, in the embodiments of fig. 1-6 and 8, both first beam 612 and second beam 613 are non-normally incident to object under test 200. The first light-splitting unit 110 is configured to achieve a beam-splitting effect, that is, splitting the light beam 611 into a first light beam 612 and a second light beam 613, where the first light-splitting unit 110 is, for example, a beam splitter, a polarization beam splitter, or a beam splitter grating.

The object under test 200 diffracts the first beam 612 and the second beam 613. The object 200 to be measured is a two-dimensional minute periodic repeating structure. In this embodiment, the object 200 is, for example, a reflection type grating. The first beam 612 reaches the measured target 200 to form a first diffracted beam, the first diffracted beam includes a ±m-order diffracted beam, the second beam 613 reaches the measured target 200 to form a second diffracted beam, the second diffracted beam includes a ±m-order diffracted beam, and a physical distance or an optical path distance between the retro-reflective element 120 and a diffraction point on the measured target 200 is adjusted to respectively achieve that an optical path length of a positive and negative order diffracted beam corresponding to the first diffracted beam is equal to an optical path length of a positive and negative order diffracted beam corresponding to the second diffracted beam.

In the embodiment of FIGS. 1-3, the readhead 100 further includes a refractive element, an optical path compensation element 140, and a phase retardation element 130, and the first and second diffracted beams reach the phase retardation element 130 and the retro-reflective element 120 via the refractive element and the optical path compensation element 140, and reach the measured target 200 again after being retro-reflected via the retro-reflective element 120 and then via the phase retardation element 130, the optical path compensation element 140, and the refractive element. In the present embodiment, the positive and negative orders of the first and second diffracted beams correspond to the separate refractive element, optical path compensation element 140, phase delay element 130, and retro-reflective element 120, respectively. The refractive element is a non-grating refractive element 150. The non-grating-type refractive element 150 is used to achieve a beam deflection effect, that is, the non-grating-type refractive element 150 is used to achieve deflection of the + -m-order diffraction beam of the first diffraction beam and the + -m-order diffraction beam of the second diffraction beam. The non-grating refractive element 150 is, for example, one or any combination of a beam splitter, a deflecting beam splitter, and a wedge prism. After the non-grating refractive element 150 is used, the orientation of the retro-reflective element 120 needs to be adjusted according to the refractive angle of the non-grating refractive element 150, so that the light beams entering and exiting the retro-reflective element 120 are parallel, offset by a certain distance, and have opposite transmission directions.

In the embodiment of fig. 1 to 3, specifically, the ±m-order diffracted beam of the first diffracted beam passes through the non-grating refractive element 150, the optical path compensating element 140 and the phase delaying element 130 to reach the reverse retroreflecting element 120, and after reversely retroreflecting by the reverse retroreflecting element 120, the first diffracted beam passes through the phase delaying element 130, the optical path compensating element 140 and the non-grating refractive element 150 again to reach the measured object 200, and the optical path distance between the reverse retroreflecting element 120 and the diffraction point on the measured object 200 is adjusted by adopting the non-grating refractive element 150 and the optical path compensating element 140, so as to achieve that the optical paths of the positive and negative orders diffracted beams of the first diffracted beam are equal. The + -m-order diffraction beam of the second diffraction beam passes through the non-grating refraction element 150, the optical path compensation element 140 and the phase delay element 130 to reach the reverse retroreflection element 120, and passes through the phase delay element 130, the optical path compensation element 140 and the non-grating refraction element 150 in turn after reversely retroreflecting by the reverse retroreflection element 120 to reach the measured object 200 again, and the optical path distance between the reverse retroreflection element 120 and the diffraction point on the measured object 200 is adjusted by adopting the non-grating refraction element 150 and the optical path compensation element 140 so as to realize the equal optical paths of the positive and negative order diffraction beams of the second diffraction beam.

In the embodiment of FIGS. 4-7, the readhead 100 further includes a phase delay element 130, and the first and second diffracted beams directly reach the phase delay element 130 and the reverse retro-reflective element 120, and are reversely retro-reflected by the reverse retro-reflective element 120, then directly reach the target 200 again after passing through the phase delay element 130. In the present embodiment, the positive and negative orders of the first and second diffracted beams correspond to the discrete phase retarder 130 and the inverse retroreflector 120, respectively. Specifically, the ±m-order diffracted light beams of the first diffracted light beam directly reach the reverse retroreflective element 120 through the phase delay element 130, are reversely retroreflected by the reverse retroreflective element 120, and then directly reach the target 200 to be measured again through the phase delay element 130 in sequence. The + -m-order diffraction beam of the second diffraction beam directly reaches the reverse retroreflection element 120 through the phase delay element 130, reversely retroreflects through the reverse retroreflection element 120, and then directly reaches the measured object 200 again through the phase delay element 130 in sequence. In this embodiment, the refraction element is not adopted, the ±m-order diffraction beams of the first diffraction beam and the second diffraction beam do not refract in the optical path, and the ±m-order diffraction beams of the first diffraction beam and the second diffraction beam are only reversely retroreflected by the reversely retroreflecting element 120, and since the positive and negative order diffraction beams of the first diffraction beam and the second diffraction beam correspond to the discrete phase delay element 130 and the reversely retroreflecting element 120, respectively, that is, the first diffraction beam+m-order diffraction beam, the first diffraction beam-m-order diffraction beam, the second diffraction beam+m-order diffraction beam and the second diffraction beam-m-order diffraction beam correspond to the respective phase delay element 130 and the reversely retroreflecting element 120, respectively, the physical distances between the reversely retroreflecting element 120 and the diffraction point on the measured object 200 can be adjusted, so that in this embodiment, the optical path lengths of the first diffraction beam ±m-order diffraction beam and the optical path length of the ±m-order diffraction beam of the second diffraction beam are respectively equal.

In the embodiment of fig. 8 to 10, the readhead further includes an optical path compensating element 140 and a phase delaying element 130, and the first diffracted beam and the second diffracted beam reach the phase delaying element 130 and the reverse retro-reflective element 120 through the optical path compensating element 140, and reach the measured object 200 again after being retro-reflected through the reverse retro-reflective element 120, through the phase delaying element 120 and the optical path compensating element 140. In the present embodiment, the optical path compensation element 140, the phase delay element 130, and the reverse retroreflective element 120 are an integrated structure. The retroreflective elements 120 are, for example, multi-surface prismatic structures for simultaneously achieving retroreflection of more than one light beam. The reverse retroreflection element 120 can offset a distance for each of the light beams at different angles of incidence for more than one light beam, and reverse retroreflection of the light beam. The phase retardation element 130 is used to change the polarization state of the light beam, for example, one of a quarter wave plate, an eighth wave plate, a glass plate, and any combination thereof. The optical path compensation element 140 is used for compensating the deviation of the optical path length of the positive and negative orders of the diffracted light beams, and the optical path compensation element 140 is, for example, a glass plate, and can also be used for realizing the optical path difference compensation effect by mutually matching the thickness of the phase delay element 130, the thickness of the reverse retroreflective element 120 and the distance between the reverse retroreflective element and the diffraction point. The retroreflective elements 120 may be multi-angle rectangular prism combinations that may be formed by adhesive bonding, preferably multi-reflecting surface prism structures that may be cut in one piece. The top ends of the reverse retroreflective elements 120 may be a plurality of surfaces that differ in angle, or height; preferably, the surfaces may be the same. When the top ends of the reverse retroreflection elements 120 are the same surface, the substrates of the phase delay elements 130 or the optical path compensation elements 140 need to be inclined at a certain angle to compensate for the deviation of the included angle between the reverse retroreflection elements 120 and the incident light beam in order to realize the reverse retroreflection of the light beam. The reverse retroreflection element 120, the phase delay element 130 and the optical path compensation element 140 in the integrated structure can be bonded by glue or optical glue, so that a relatively stable optical assembly structure is formed, and the structural stability is improved. Optical path compensation may be achieved by adding an additional glass plate, and preferably by increasing the thickness of the corresponding phase delay element.

The second diffracted beam of the first diffracted beam is formed by passing through the measured object 200, and the second diffracted beam of the first diffracted beam includes the + -m th order second diffracted beam, and the + -m th order second diffracted beam of the first diffracted beam forms the first interference beam 614, and the first interference beam 614 contains horizontal displacement information. The second diffracted beam of the second diffracted beam is formed by passing through the measured object 200, and includes the + -m order second diffracted beam, and the + -m order second diffracted beam of the second diffracted beam forms the second interference beam 615, and the second interference beam 615 contains horizontal and vertical displacement information. The first beam 612, the + -m-order diffracted beam of the first diffracted beam, and the optical path of the + -m-order second diffracted beam of the first diffracted beam constitute a first measurement channel, i.e., a horizontal measurement channel. The + -m-order diffraction beams of the first diffraction beam in the horizontal measuring channel are symmetrically distributed with respect to a plane perpendicular to the horizontal displacement, i.e. the + -m-order diffraction beams of the first diffraction beam are symmetrically distributed with respect to the YZ plane. The second measuring channel, i.e. the vertical measuring channel, is formed by the second light beam, the + -m-order diffracted light beam of the second diffracted light beam and the optical path of the + -m-order second diffracted light beam of the second diffracted light beam. The + -m-order diffraction beams of the second diffraction beam in the vertical measuring channel are asymmetrically distributed relative to a plane perpendicular to the horizontal displacement, namely the + -m-order diffraction beams of the second diffraction beam are asymmetrically distributed relative to the YZ plane; the first interference signal formed by the diffraction beam of the first diffraction beam and the second interference signal formed by the diffraction beam of the second diffraction beam have strong environment interference resistance.

The optical path compensation element 140 is used to compensate for the coherence length deviation of the positive and negative order diffracted beams of the oblique incident beam. In the present embodiment, the optical path compensation element 140 is at least used for performing optical path compensation on the-m-order diffracted beam of the second diffracted beam, so that the optical path lengths of the-m-order diffracted beam of the second diffracted beam and the +m-order diffracted beam of the second diffracted beam are the same. The optical path compensation element 140 is, for example, a glass plate or the like. The optical path compensation element 140 may cooperate with each other by the thickness of the phase delay element 130, the thickness of the reverse retroreflective element 120, and the position of the reverse retroreflective element from the diffraction point to achieve an optical path difference compensation effect.

The inverse retroreflective element 120 is used for deflecting the light beam by a certain distance, inversely retroreflecting the light beam, realizing that the incident light beam is parallel to the outgoing light beam, the direction is inverse, and offset by a certain distance, namely, the inverse retroreflective element 120 is used for inversely retroreflecting the + -m-order diffraction light beam of the first diffraction light beam and the + -m-order diffraction light beam of the second diffraction light beam. The retroreflective element 120 is, for example, one or any combination of a right angle prism and a mirror group, a retroreflective prism assembly, or the like. In the position measurement system provided in this embodiment, the rotation stroke of the secondary diffraction of the retro-reflective element 120 and the measured object 200 has little influence on measurement, the Z-direction stroke does not influence the light spot overlap ratio, the redundancy is high, and smaller light spot layout distribution can be realized.

Fig. 11 to 12 are schematic structural views of a retroreflective element according to an embodiment of the present invention; fig. 11 is a schematic structural view of a retroreflective element viewed from one direction, and fig. 12 is a schematic structural view of a retroreflective element viewed from another direction, and as shown in fig. 11 and 12, the retroreflective element 120 is a multi-reflecting surface prism structure. The prism bases of the retroreflective elements 120 are all cut to form the edges 120a of the retroreflective elements having a right angle phi at the base. Fig. 13-14 are schematic structural views of another retroreflective element of an embodiment of the present invention; fig. 13 is a schematic structural view of another retroreflective element viewed from one direction, and fig. 14 is a schematic structural view of another retroreflective element viewed from another direction, and as shown in fig. 13 and 14, the retroreflective element 120 is a multi-reflecting surface prism structure. The prism bottom portions of the retroreflective elements 120 are cut such that the bottoms of the retroreflective elements remain partially planar 120b.

FIG. 15 is a schematic view showing a structure of a position measuring system ZX according to a seventh embodiment of the present invention; in this embodiment, the phase delay element 130 and the reverse retroreflecting element 120 are an integrated structure, and the thickness of the phase delay element 130 and/or the thickness of the reverse retroreflecting element 120 and/or the distance between the reverse retroreflecting element 120 and the diffraction point on the measured object 200 are adjusted so as to achieve that the optical paths of the positive and negative order diffraction beams corresponding to the first diffraction beam are equal and the optical paths of the positive and negative order diffraction beams corresponding to the second diffraction beam are equal. When the incidence angles of the first light beam and the second light beam are the same, the optical path length of the first light beam plus the optical path length of the m-order diffraction light beam of the second light beam and the optical path length of the m-order diffraction light beam of the second light beam are equal as the first light beam and the second light beam are completely symmetrical relative to the YZ plane; and the positive and negative m-order diffraction beam optical paths of the second beam are equal, and after equivalent substitution, the n-m-order diffraction beam optical path of the second beam is equal to the first beam and the m-order diffraction beam optical path of the first beam. The physical distances from the two reflective edges of the reverse retroreflection element to the intersection point of the opposite extension lines of the +m-order diffraction beam of the first diffraction beam and the +m-order diffraction beam of the second diffraction beam are equal, the optical path difference between the +m-order diffraction beam of the first diffraction beam and the +m-order diffraction beam of the second diffraction beam is compensated by the thickness of the phase delay element 130, and then the thickness difference between the +m-order diffraction beam of the first diffraction beam and the +m-order diffraction beam of the second diffraction beam passing through the phase delay element 130 is:

Wherein TS is the thickness of the phase delay element through which the +m-order diffraction beam of the first diffraction beam passes, TL is the thickness of the phase delay element through which the +m-order diffraction beam of the second diffraction beam passes, L is the distance between two incident lights on the measured object, alpha is the diffraction angle of the second diffraction beam and the m-order diffraction beam after the second diffraction beam and the m-order diffraction beam are diffracted by the measured object, beta is the diffraction angle of the second diffraction beam and the m-order diffraction beam after the diffraction of the measured object, and n is the refractive index of the substrate material of the phase delay element. The above calculation method is equally applicable to the thickness difference of the phase retarder 130 of the-m-order diffracted beam of the first diffracted beam and the-m-order diffracted beam of the second diffracted beam. The above calculation method belongs to a preferred embodiment, and can be calculated directly from the actual path length in the case where the physical distances of the opposite extension lines of the +m-order diffraction beam of the first diffraction beam and the +m-order diffraction beam of the second diffraction beam are not equal.

FIG. 16 is a schematic view of a cylindrical lens structure according to an embodiment of the present invention; FIG. 17 is a schematic view of a dove prism structure according to an embodiment of the present invention; in yet another embodiment of the present invention, the retroreflective elements 120 may also be beam steering by other alternative structures, for example, the retroreflective elements 120 include a cylindrical lens structure 125 and a dove prism 126. The cylindrical lens structure 125 is composed of a lens 1251 and a concave mirror 1252, the spherical center of the concave mirror 1252 is disposed on the principal point (thin lens center) of the lens 1251, and the focal point of the lens 1251 is disposed on the reflecting surface of the concave mirror 1252; the incident beam 621 is converged by the lens 1251 onto the concave mirror 1252, reflected by the concave mirror 1252, and after passing through the lens 1251, the outgoing beam 622 is still parallel to the original incident beam 621, but in opposite directions and offset by a certain distance. The incident beam 621 enters the dove prism 126, and the outgoing beam 622 after being reflected by the dove prism 126 is still parallel to the original incident beam 621, but is opposite in direction and offset by a certain distance.

The readhead 100 may further comprise a second splitting unit 111 for splitting the first interference beam 614 into sub-beams 616 of three first interference beams having different directions, each of which, after passing through polarizers disposed with polarization directions at 60 degrees apart, forms three optical signals having phases at 120 degrees apart, by which phase detection is achieved. And, the second beam splitter 111 splits the second interference beam 615 into sub-beams 617 of the first interference beam having three different directions, each of which forms three optical signals having 120 degrees of phase difference by passing through polarizers disposed at angles of 60 degrees of polarization direction difference, and phase detection is achieved by the three optical signals.

As shown in fig. 3, the position measurement system may further comprise a polarizing element 160 for polarization selection of the output light, i.e. the polarizing element 160 is used for collecting the first interference beam 614 and the second interference beam 615.

In particular embodiments, the light source and polarizing element 160 of the position measurement system may be transmitted via optical fibers. The light-in optical fiber, the light-out optical fiber and the reading head 100 can be integrated into an optical fiber micro-structure, so that the structure size is reduced, the measurement convenience of the system is improved, and the application range is enlarged.

Further, the position measurement system may further include an optical signal processing section (not shown in the figure) for converting the first interference beam and the second interference beam into a first interference signal and a second interference signal and performing displacement resolution based on the first interference signal and the second interference signal.

The embodiment also provides a lithographic apparatus comprising the position measuring device. The measured object 200 is a two-dimensional tiny periodic repeating structure, and the measured object 200 is, for example, a reflective grating. The position measuring device is, for example, a two-dimensional high-precision grating scale system device.

The embodiment also provides a lithographic apparatus comprising a position measurement system as claimed in any one of the preceding claims.

FIG. 18 is a flow chart of a position measurement method of an embodiment of the present invention; as shown in fig. 18, the present embodiment further provides a position measurement method, including:

step S10, a light source emits a light beam, and the light beam is divided into a first light beam and a second light beam with different directions through a first light splitting unit;

step S20, the first light beam is diffracted by the measured object to form a first diffracted light beam, the second light beam is diffracted by the measured object to form a second diffracted light beam, and the first diffracted light beam and the second diffracted light beam both comprise positive and negative orders of diffracted light beams;

and step S30, adjusting the physical distance or the optical path distance between the reverse retroreflection element and the diffraction point on the measured object to respectively realize that the optical paths of the positive and negative diffraction beams corresponding to the first diffraction beam are equal and the optical paths of the positive and negative diffraction beams corresponding to the second diffraction beam are equal.

In step S10, the light beam 611 emitted by the light source may be transmitted through the optical fiber, where the light beam 611 is divided into a first light beam 612 and a second light beam 613 with different directions by the first light beam splitting unit 110, at least one of the first light beam 612 and the second light beam 613 is not perpendicularly incident on the measured object 200, for example, in the embodiments of fig. 7, 9 and 10, the first light beam 612 is perpendicularly incident on the measured object 200, and the second light beam 613 is not perpendicularly incident on the measured object 200; for example, in the embodiments of fig. 1-6 and 8, both first beam 612 and second beam 613 are non-normally incident to object under test 200.

In step S20, the first beam 612 is diffracted by the measured object 200 to form a first diffracted beam, and in the embodiments of fig. 7, 9 and 10, the ±m-order diffracted beams of the first diffracted beam are symmetrically distributed with respect to a plane perpendicular to the horizontal displacement, that is, the ±m-order diffracted beams of the first diffracted beam are symmetrically distributed with respect to the YZ plane. In the embodiments of fig. 1-6 and 8 the + -m-order diffracted beams of the first diffracted beam are asymmetrically distributed with respect to a plane perpendicular to the horizontal displacement, i.e. the + -m-order diffracted beams of the first diffracted beam are asymmetrically distributed with respect to the YZ plane.

In this embodiment, when the first light beam 612 perpendicularly enters the measured object, the diffraction formula is:

P*sinθ1＝mλ；

wherein P is the grid distance of the measured object, lambda is the wavelength, m is the diffraction order, + -m= + -1, 2,3 …, and θ1 is the diffraction angle of the first light beam.

It can be seen that the +m diffraction beam is generated along the X direction, and after passing through the phase delay element 130, it is offset by a certain distance by the reverse retroreflection element 120. After the reverse retroreflected light beam passes through the phase delay element 130 again, it is incident on the measured object 200 at an angle θ. And, the-m-order diffracted beam of the first beam 612 is secondarily diffracted by the measured object 200 after passing through the phase delay element 130 and the reverse retroreflecting element 120 as well. The + -m-order second-order diffracted beam of the first beam 612 forms a first interference beam 614 in the outgoing optical path, the first interference beam 614 includes a first interference signal Φch1, and after passing through the second beam splitting unit 111 and the polarizing element 160, the first interference signal is detected to obtain information about the horizontal X-displacement of the measured target 200 relative to the reading head 100. The physical distance between the retro-reflective element 120 and the diffraction point on the measured object 200 is adjusted to achieve the equality of the optical path lengths of the + -m-order diffraction beams of the first diffraction beam and the equality of the optical path lengths of the + -m-order diffraction beams of the second diffraction beam, respectively.

In the embodiment of fig. 1-3, the +m diffraction beam is generated along the X direction, and is offset by a certain distance by the reverse retroreflection element 120 after passing through the non-grating refractive element 150, the optical path compensation element 140, and the phase delay element 130. The reverse retroreflected light beam is again incident on the measured object 200 at an angle θ after passing through the phase delay element 130, the optical path compensation element 140, and the non-grating refractive element 150. And, the-m-order diffracted beam of the first beam 612 is secondarily diffracted by the measured object 200 after passing through the non-grating refractive element 150, the optical path compensation element 140, the phase delay element 130, and the reverse retroreflective element 120 as well. The + -m-order second-order diffracted beam of the first beam 612 forms a first interference beam 614 in the outgoing optical path, the first interference beam 614 includes a first interference signal Φch1, and after passing through the second beam splitting unit 111 and the polarizing element 160, the first interference signal is detected to obtain information about the horizontal X-displacement of the measured target 200 relative to the reading head 100. The optical path distance between the reverse retroreflection element 120 and the diffraction point on the measured object 200 is adjusted to achieve the equality of the optical path length of the diffraction beam of the first diffraction order + -m and the optical path length of the diffraction beam of the second diffraction order + -m, respectively.

In the embodiments of fig. 8-10, the +m diffraction order beam is generated along the X direction, and after passing through the optical path compensation element 140 and the phase delay element 130, it is offset by a certain distance by the reverse retroreflection element 120 to be reversely retroreflected. After passing through the phase delay element 130 and the optical path compensation element 140 again, the reverse retroreflected light beam enters the measured object 200 at an angle θ. And, the-m-order diffracted beam of the first beam 612 is secondarily diffracted by the measured object 200 after passing through the optical path compensation element 140, the phase delay element 130, and the reverse retroreflecting element 120 as well. The + -m-order second-order diffracted beam of the first beam 612 forms a first interference beam 614 in the outgoing optical path, the first interference beam 614 includes a first interference signal Φch1, and after passing through the second beam splitting unit 111 and the polarizing element 160, the first interference signal is detected to obtain information about the horizontal X-displacement of the measured target 200 relative to the reading head 100. The optical path distance between the reverse retroreflection element 120 and the diffraction point on the measured object 200 is adjusted to achieve the equality of the optical path length of the diffraction beam of the first diffraction order + -m and the optical path length of the diffraction beam of the second diffraction order + -m, respectively.

The second beam 613 forms a second diffracted beam by the first diffraction of the measured object 200, and the diffraction beam of the second diffracted beam of + -m orders is asymmetrically distributed with respect to a plane perpendicular to the horizontal displacement, that is, the diffraction beam of the second beam of + -m orders is asymmetrically distributed with respect to the YZ plane, and m is the diffraction order.

The second beam 613 is non-normally incident to the measured object 200 at an angle γ according to the diffraction formula:

P*(sinγ+sinθ2)＝mλ，

wherein P is the grid distance of the measured object, lambda is the wavelength, m is the diffraction order, + -m= + -1, 2,3 …, and θ2 is the diffraction angle of the second light beam.

It can be seen that the +m-order diffracted beam is generated along the X direction, and the diffraction angle θ2=β, after passing through the phase delay element 130, is offset by a certain distance by the reverse retroreflection element 120. After passing through the retroreflective element 120 again, the retroreflective light beam enters the object 200 to be measured at an angle β, and the second diffracted light beam of the second light beam 613 exits through the second spectroscopic unit 111. And, a-m-order diffracted beam is generated in the X direction, and the diffraction angle θ2=α, after passing through the phase delay element 130, is offset by a certain distance by the reverse retroreflection element 120. After the reverse retroreflected light beam passes through the phase delay element 130 again, it enters the measured object 200 at an angle α, and the second diffracted light beam of the second light beam 613 exits through the second beam splitting unit 111. The + -m-order secondary diffraction beam of the second beam 613 exits along the same optical path and direction, and when the + -m-order secondary diffraction beam of the second beam 613 exits along the same optical path and direction, a second interference beam 615 is formed, the second interference beam 615 includes a second interference signal phich2, and after passing through the second beam splitting unit 111 and the polarizing element 160, the second interference signal is detected to obtain displacement information of the measured object 200 in the horizontal X-direction and the vertical Z-direction relative to the reading head 100.

In the exemplary embodiments of fig. 7, 9 and 10, the first beam, the ±m-order diffracted beam of the first diffracted beam and the optical path of the ±m-order second diffracted beam of the first diffracted beam form a first measuring channel, i.e. a horizontal measuring channel. The + -m-order diffraction beams of the first diffraction beam in the horizontal measuring channel are symmetrically distributed with respect to a plane perpendicular to the horizontal displacement, i.e. the + -m-order diffraction beams of the first diffraction beam are symmetrically distributed with respect to the YZ plane. In the embodiments of fig. 1-6 and 8, the first light beam, the + -m-order diffracted light beam of the first diffracted light beam and the + -m-order second diffracted light beam of the first diffracted light beam form a first measurement channel, i.e. a horizontal measurement channel. The + -m-order diffraction beams of the first diffraction beam in the horizontal measuring channel are asymmetrically distributed with respect to a plane perpendicular to the horizontal displacement, i.e. the + -m-order diffraction beams of the first diffraction beam are asymmetrically distributed with respect to the YZ plane.

The second measuring channel, i.e. the vertical measuring channel, is formed by the second light beam, the + -m-order diffracted light beam of the second diffracted light beam and the optical path of the + -m-order second diffracted light beam of the second diffracted light beam. The + -m-order diffraction beams of the second diffraction beam in the vertical measuring channel are asymmetrically distributed with respect to a plane perpendicular to the horizontal displacement, i.e. the + -m-order diffraction beams of the second diffraction beam are asymmetrically distributed with respect to the YZ plane.

In step S30, the first interference beam and the second interference beam are converted into a first interference signal and a second interference signal and displacement calculation is performed. The displacement calculation comprises horizontal displacement and vertical displacement, wherein the horizontal displacement is independently measured, and the vertical displacement is obtained through calculation decoupling.

Assuming that when m=1, the displacement amount Δx of the measured object 200 with respect to the reading head in the X direction and the displacement amount Δz in the Z direction are calculated as:

wherein, phi Ch1 is the phase variation of the second diffraction beam outputting the first diffraction beam, phi Ch2 is the phase variation of the second diffraction beam outputting the second diffraction beam, P is the grid distance of the measured object, lambda is the wavelength, alpha is the-1 diffraction angle of the second diffraction beam, and beta is the +1 diffraction angle of the second diffraction beam.

In summary, in the position measurement method, the position measurement system and the lithography apparatus provided by the invention, by adjusting the physical distance or the optical path distance between the reverse retroreflection element and the diffraction point on the measured object, so as to respectively realize that the optical path length of the positive and negative order diffraction beams corresponding to the first diffraction beam is equal to that of the positive and negative order diffraction beams corresponding to the second diffraction beam. Furthermore, the reverse retroreflection element, the phase delay element and the optical path compensation element can form an integrated structure, so that the structural stability of the integrated structure is ensured.

In this specification, each embodiment is described in a progressive manner, and each embodiment focuses on the difference from other embodiments, so that the same similar parts of each embodiment are referred to each other.

It should also be appreciated that while the present invention has been disclosed in the context of a preferred embodiment, the above embodiments are not intended to limit the invention. Many possible variations and modifications of the disclosed technology can be made by anyone skilled in the art without departing from the scope of the technology, or the technology can be modified to be equivalent. Therefore, any simple modification, equivalent variation and modification of the above embodiments according to the technical substance of the present invention still fall within the scope of the technical solution of the present invention.

Claims (18)

1. The position measurement system is characterized by comprising a measured object, a reading head and a light source, wherein the reading head comprises a first light splitting unit and a reverse retroreflection element, light beams emitted by the light source are divided into first light beams and second light beams with different directions through the first light splitting unit, the first light beams and the second light beams form first diffraction light beams and second diffraction light beams after being diffracted by the measured object, the first diffraction light beams and the second diffraction light beams all comprise positive and negative diffraction light beams, and the physical distance or the optical path distance between the reverse retroreflection element and a diffraction point on the measured object is adjusted to respectively achieve that the optical paths of the positive and negative diffraction light beams corresponding to the first diffraction light beams are equal and the optical paths of the positive and negative diffraction light beams corresponding to the second diffraction light beams are equal.

2. The position measurement system of claim 1, wherein the readhead further comprises a phase delay element, the first and second diffracted beams directly reaching the phase delay element and the reverse retro-reflective element, and after reverse retro-reflection by the reverse retro-reflective element, directly reaching the target under test again after reverse retro-reflection by the phase delay element.

3. The position measurement system of claim 2, wherein the phase delay element and the reverse retro-reflective element corresponding to the positive and negative orders of the first and second diffracted beams are separated from each other.

4. A position measurement system as set forth in claim 1 wherein the readhead further comprises an optical path compensation element and a phase delay element, the first and second diffracted beams reaching the phase delay element and the reverse retro-reflective element via the optical path compensation element and reaching the target under test again after being retro-reflected via the reverse retro-reflective element via the phase delay element and the optical path compensation element.

5. The position measurement system of claim 4, wherein the phase delay element and the counter-retroreflective element are of unitary construction, and wherein the thickness of the phase delay element and/or the thickness of the counter-retroreflective element and/or the distance of the counter-retroreflective element from a diffraction point on the object under test is adjusted to achieve equal optical lengths of the positive and negative orders of diffracted light beams corresponding to the first diffracted light beam and equal optical lengths of the positive and negative orders of diffracted light beams corresponding to the second diffracted light beam.

6. The position measurement system of claim 5, wherein when the incidence angles of the first beam and the second beam are the same, the physical distances from the two reflective edges of the retro-reflective element to the intersection of the +m-order diffracted beam of the first diffracted beam and the +m-order diffracted beam of the second diffracted beam are equal, and the optical path difference between the +m-order diffracted beam of the first diffracted beam and the +m-order diffracted beam of the second diffracted beam is compensated by the thickness of the phase delay element, the thickness difference between the +m-order diffracted beam of the first diffracted beam and the +m-order diffracted beam of the second diffracted beam passing through the phase delay element is:

wherein TS is the thickness of the phase delay element through which the +m-order diffraction beam of the first diffraction beam passes, TL is the thickness of the phase delay element through which the +m-order diffraction beam of the second diffraction beam passes, L is the distance between two incident lights on the measured object, alpha is the diffraction angle of the second diffraction beam and the m-order diffraction beam after the second diffraction beam and the m-order diffraction beam are diffracted by the measured object, beta is the diffraction angle of the second diffraction beam and the m-order diffraction beam after the diffraction of the measured object, and n is the refractive index of the substrate material of the phase delay element.

7. The position measurement system of claim 4, wherein the phase delay element, the reverse retro-reflective element and the optical path compensation element are a unitary structure.

8. The position measurement system of claim 1, wherein the readhead further comprises a refractive element, an optical path compensation element, and a phase retardation element, the first and second diffracted beams reaching the phase retardation element and the reverse retro-reflective element via the refractive element and the optical path compensation element, and reaching the target after being retro-reflected via the reverse retro-reflective element and reaching the target again via the phase retardation element, the optical path compensation element, and the refractive element.

9. The position measurement system of claim 8, wherein the positive and negative orders of the first and second diffracted beams correspond to the refractive element, the optical path compensation element, the phase delay element, and the retro-reflective element, respectively, that are separate.

10. The position measurement system of claim 8, wherein the refractive element is a non-grating refractive element.

11. The position measurement system of claim 10, wherein the non-grating refractive element comprises one or any combination of a beam splitter, a deflecting beam splitter, and a wedge prism.

12. The position measurement system of claim 1, wherein the first beam and the second beam each impinge on the object under test in a direction that is non-perpendicular to the object under test.

13. The position measurement system of claim 1, wherein the retroreflective elements are multi-faceted prism structures.

14. The position measurement system of claim 13, wherein the prism bases of the retroreflective elements are all cut to form the edges of the reflective prisms having right angles in the bases.

15. The position measurement system of claim 13, wherein the prism base portion of the retroreflective elements is cut such that the prism base of the retroreflective elements remains partially planar.

16. A lithographic apparatus comprising a position measurement system as claimed in any one of claims 1 to 15.

17. A method of position measurement, comprising:

the light source emits a light beam, and the light beam is divided into a first light beam and a second light beam with different directions through the first light splitting unit;

the first light beam is diffracted by the measured object to form a first diffracted light beam, the second light beam is diffracted by the measured object to form a second diffracted light beam, and the first diffracted light beam and the second diffracted light beam both comprise positive and negative diffraction light beams;

And adjusting the physical distance or the optical path distance between the reverse retroreflective element and the diffraction point on the measured object to respectively realize that the optical paths of the positive and negative diffraction beams corresponding to the first diffraction beam are equal and the optical paths of the positive and negative diffraction beams corresponding to the second diffraction beam are equal.

18. The position measurement method of claim 17, wherein the positive and negative orders of the first diffracted beam are diffracted by the measured object to form a first interference beam, the first interference beam containing horizontal displacement information of the measured object; the positive and negative orders of the second diffraction beam are diffracted by the measured object again to form a second interference beam, and the second interference beam contains horizontal displacement information and vertical displacement information of the measured object; and converting the first interference light beam into a first interference signal and converting the second interference light beam into a second interference signal, and performing displacement calculation to obtain the position information of the measured object.