Projection photoetching machine alignment sensing system based on integration of grating and lens group

Abstract

The invention discloses a projection photoetching machine alignment sensing system based on grating and lens group integration. The system comprises a light source group, a detection grating, a lens group and a detector, the light source group comprises a first light source pair and a second light source pair; both the first light source pair and the second light source pair emit light beams, and the included angle between the incident direction of the emergent light beams on the silicon wafer alignment mark and the center line of the silicon wafer alignment mark is equal to the included angle between first-order diffraction light and zero-order light after the silicon wafer alignment mark irradiated by the emergent light beams is diffracted; the horizontal plane of the detection grating and the horizontal plane of the detector form an object-image conjugate relation with the lens group; the detection grating is on the object plane of the lens group, and the detector is on the image plane of the lens group. The projection photoetching machine alignment sensing system provided by the invention is simple in structure, and can realize position detection of alignment marks of photoetching machines with sub-nanometer and deep sub-nanometer precision.

Description

Technical Field

[0001] The present invention relates to the technical field of photolithography machines, and in particular to an alignment sensing system for a projection photolithography machine based on the integration of a grating and a lens group. Background Art

[0002] In the process of using projection lithography machines to manufacture integrated circuits, the mask pattern that carries the integrated circuit layout information is transferred to the photoresist on the silicon wafer surface in an imaging manner through the projection objective lens. Integrated circuit manufacturing requires dozens or even hundreds of lithography exposure processes to accurately transfer different mask patterns layer by layer to the corresponding positions on the silicon wafer surface.

[0003] Therefore, photolithography machines require high overlay accuracy. Overlay accuracy is the core performance indicator of photolithography machines, and improving overlay accuracy is an important factor in driving the sustainable development of integrated circuit manufacturing technology. Improving the alignment accuracy of photolithography machines is the key factor in improving overlay accuracy.

[0004] The alignment of the photolithography machine is achieved by the alignment system. In order to accurately transfer each layer of pattern to the correct position on the silicon wafer surface and make its position error relative to the previous layer of pattern within the tolerance range, the position of the silicon wafer and the mask must be detected before exposure, and the alignment between the silicon wafer and the mask is performed by calculating the positional relationship between the silicon wafer and the mask.

[0005] The precise detection of the position of the silicon wafer is completed by the alignment sensor system. The precise sensing of the position of the silicon wafer is the prerequisite for the high-precision alignment of the lithography machine. Therefore, the detection accuracy of the alignment sensor system largely determines the alignment accuracy of the lithography machine, and it can also be said that it largely determines the level of overlay accuracy.

[0006] Currently, the main manufacturers of projection lithography machines used in the manufacture of advanced-node integrated circuits are ASML of the Netherlands and NIKON of Japan. The alignment accuracy of their lithography machines used in the manufacture of advanced-node integrated circuits has reached sub-nanometer and deep sub-nanometer, and the requirements for the detection accuracy of the corresponding alignment sensor system have become very high.

[0007] NIKON's FIA (Field Image Alignment) technology can clearly detect alignment marks and obtain alignment mark images with high contrast by introducing phase contrast microscopy technology, and calculate the position mean of image intensity changes to obtain alignment mark position information. The information processing of this alignment technology is relatively simple, and it can achieve high-precision alignment. However, due to the absorption of light by materials such as photoresist on the surface of the silicon wafer, the alignment accuracy is easily affected by the change in the strength of the alignment signal, and the system has many components and a relatively complex structure. ASML's SMASH and ORION technologies are based on the principle of phase grating alignment (PGA). At different wavelengths, the position of silicon wafer alignment marks is calculated through interference signals between different diffraction orders, and have high alignment accuracy and process stability. Since the system is composed of optical devices such as self-reference interferometers and optical lenses, the structure is relatively complex and the processing and adjustment are difficult.

[0008] The nanoimprint lithography tool of Japan's CANON company uses TTM (through-the-mask) moiré fringe alignment technology to achieve alignment between the mask and the silicon wafer. The characteristics of this alignment technology are: phase gratings are processed on the mask and the silicon wafer as alignment marks respectively, and the illumination light is diffracted by the silicon wafer alignment mark and the mask alignment mark in turn to obtain positive and negative first-order diffracted light. The interference between the positive and negative first-order diffracted light forms moiré fringes, and the moiré fringes are measured and calculated to obtain the position offset of the silicon wafer and the mask. The alignment accuracy can reach sub-nanometers. However, the TTM moiré fringe alignment technology is only suitable for alignment when the gap between the mask and the silicon wafer is small, and cannot be used for the alignment of projection lithography machines with a certain distance between the mask and the silicon wafer. Summary of the invention

[0009] In view of this, the present invention provides a projection lithography machine alignment sensing system based on the integration of grating and lens group, which can solve the above-mentioned technical problems.

[0010] In order to solve the above technical problems, the present invention is implemented as follows.

[0011] A projection lithography machine alignment sensing system based on the integration of grating and lens group, comprising:

[0012] Light source group, detection grating, lens group and detector;

[0013] The light source group includes a first light source group, and the first light source group includes a first light source pair and a second light source pair for respectively illuminating in the x direction and the y direction; the two light sources in each light source pair have the same parameters and types; the light sources in the first light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensor system in the xz plane; the light sources in the second light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensor system in the yz plane;

[0014] The first light source pair and the second light source pair both emit light beams, and the angle between the incident direction of the light beams on the silicon wafer alignment mark and the center line of the silicon wafer alignment mark is equal to the angle between the first-order diffracted light and the zero-order light after the light beams irradiate the silicon wafer alignment mark and cause diffraction;

[0015] The x direction and the y direction are respectively the horizontal direction and the vertical direction of the horizontal plane under the global coordinate system of the projection lithography machine, and the z direction is the direction of the xy plane determined by the x direction and the y direction;

[0016] The horizontal plane where the detection grating is located and the horizontal plane where the detector is located form an object-image conjugate relationship with respect to the lens group; the detection grating is on the object plane of the lens group, and the detector is on the image plane of the lens group; the lens group is an afocal optical system.

[0017] Preferably, the light source group further comprises a second light source group having a different wavelength from the first light source group, and the second light source group comprises a third light source pair and a fourth light source pair; the two light sources in each light source pair have the same parameters and types; the two light sources in the third light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensing system in the xz plane; the two light sources in the fourth light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensing system in the yz plane;

[0018] The third light source pair and the fourth light source pair both emit light beams, and the angle between the incident direction of the emitted light beam on the silicon wafer alignment mark and the center line of the silicon wafer alignment mark is equal to the angle between the first-order diffracted light and the zero-order light after the emitted light beam irradiates the silicon wafer alignment mark and diffracts.

[0019] Preferably, the first light source group and the second light source group are visible light sources and near-infrared light sources respectively.

[0020] Preferably, the light source group further includes a plurality of light source groups having wavelengths different from those of the first light source group and the second light source group, each light source group includes two light source pairs, and the parameters and types of the two light sources in each light source pair are the same; the layout of each light source group is: the two light sources in one light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensing system in the xz plane; the two light sources in another light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensing system in the yz plane;

[0021] The two light source pairs of each light source group emit light beams, and the angle between the incident direction of the emitted light beam on the silicon wafer alignment mark and the center line of the silicon wafer alignment mark is equal to the angle between the first-order diffracted light and the zero-order light after the emitted light beam irradiates the silicon wafer alignment mark and diffracts.

[0022] Preferably, the silicon wafer alignment mark is composed of a first grating with a period of P1, a second grating with a period of P2, a third grating with a period of P1 and a fourth grating with a period of P2, and the numerical difference between P1 and P2 is less than a first preset threshold value; the first grating and the second grating are used for position deviation detection in the x direction of the silicon wafer to be aligned, and the third grating and the fourth grating are used for position deviation detection in the y direction of the silicon wafer to be aligned; the first grating and the second grating are arranged adjacent to each other in the y direction, and the directions of the engraving lines of the first grating and the second grating are both along the y direction, and the x coordinate of the center position of the first grating is the same as that of the center position of the second grating; the third grating and the fourth grating are arranged adjacent to each other in the x direction, and the directions of the engraving lines of the third grating and the fourth grating are both along the x direction, and the y coordinate of the center position of the third grating is the same as that of the center position of the fourth grating;

[0023] The detection grating is composed of a fifth grating with a period of P2, a sixth grating with a period of P1, a seventh grating with a period of P2 and an eighth grating with a period of P1; the fifth grating and the sixth grating are used for detecting the position deviation of the silicon wafer to be aligned in the x direction, and the seventh grating and the eighth grating are used for detecting the position deviation of the silicon wafer to be aligned in the y direction; the fifth grating and the sixth grating are arranged adjacent to each other in the y direction, and the engraved directions of the fifth grating and the sixth grating are both along the y direction, and the x coordinate of the center position of the fifth grating is the same as that of the center position of the sixth grating; the relative position of the first grating and the second grating on the silicon wafer alignment mark in the y direction is the same as the relative position of the fifth grating and the sixth grating on the detection grating in the y direction; the relative position of the third grating and the fourth grating on the silicon wafer alignment mark in the x direction is the same as the relative position of the seventh grating and the eighth grating on the detection grating in the x direction.

[0024] A detection method for a projection lithography machine alignment sensor system based on the integration of a grating and a lens group, based on the projection lithography machine alignment sensor system based on the integration of a grating and a lens group as described above, the method comprising:

[0025] Step S1: determining the detection direction of the silicon wafer alignment mark 3, based on the outgoing light beam of part or all of the light sources illuminated in the illumination direction; the silicon wafer alignment mark 3 is irradiated by the outgoing light beam to generate negative first-order diffraction light and positive first-order diffraction light; the negative first-order diffraction light and the positive first-order diffraction light are diffracted again after passing through the detection grating 4, and negative first-order diffraction light and positive first-order diffraction light are obtained respectively; the negative first-order diffraction light and the positive first-order diffraction light interfere on the detection surface of the detector 6 after passing through the lens group 5, and a plurality of groups of interference fringes are generated; wherein the detection direction is the x direction or the y direction;

[0026] Step S2: obtaining two groups of moiré fringes from the plurality of groups of interference fringes, and obtaining phase information of each group of moiré fringes based on a method of decomposing the fringes; the moiré fringes are interference fringes with a period greater than a set threshold;

[0027] Step S3: determining the phase deviation based on the two groups of moiré fringes, and determining the position deviation of the silicon wafer alignment mark 3 in the detection direction.

[0028] Preferably, when the detection direction is the x direction, the position deviation Δx in the x direction is:

[0029]

[0030] Wherein, P1 and P2 are the period sizes of the first grating and the second grating of the silicon wafer alignment mark 3, respectively. It is the phase deviation determined based on two sets of moiré fringes when the detection direction is the x direction.

[0031] Preferably, when the detection direction is the y direction, the position deviation Δy in the y direction is:

[0032]

[0033] Wherein, P1 and P2 are the period sizes of the first grating and the second grating of the silicon wafer alignment mark 3, respectively. It is the phase deviation determined based on two sets of moiré fringes when the detection direction is the y direction.

[0034] Beneficial effects:

[0035] (1) The projection lithography machine alignment sensor system proposed in the present invention has a simple structure and can realize the position detection of the alignment mark of the lithography machine with sub-nanometer and deep sub-nanometer precision.

[0036] (2) The light source of the present invention controls the angle between the incident direction of the light beam on the silicon wafer alignment mark and the center line of the alignment mark in an oblique manner, so that it is equal to the angle between the first-order light and the zero-order light after the light beam irradiates the alignment mark and diffracts, thereby increasing the distance between the silicon wafer alignment mark and the alignment sensor system in the projection lithography machine in the z direction. Compared with the nanoimprint technology in which the CANON alignment technology can only be used for a small gap between the mask and the silicon wafer, the projection lithography machine alignment sensor system proposed by the present invention is suitable for the detection of the alignment mark position of the projection lithography machine.

[0037] (3) The present invention sets two sets of light sources with different wavelengths, so that the two wavelengths of light can be used to illuminate the silicon wafer alignment mark, which solves the problem of illumination light attenuation caused by process factors during the silicon wafer position detection process and enhances the signal stability of the alignment process. It overcomes the influence on the silicon wafer position detection accuracy caused by the interference of illumination light when the optical depth of the grating alignment mark on the silicon wafer is equal to half of the wavelength of the incident light, and also overcomes the absorption of visible light by the photoresist on the silicon wafer surface during the photolithography exposure process of advanced nodes, which causes the illumination light to be weakened, thereby affecting the silicon wafer position detection accuracy.

[0038] (4) Compared with the ASML and NIKON alignment sensor systems, the projection lithography machine alignment sensor system proposed by the present invention has fewer optical components, a simpler optical path, and reduced difficulty in processing core optical components and debugging the optical system. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of an optical path 1 of an alignment sensing system for integrating a grating and a lens group for detecting the position of a silicon wafer in the x direction provided by the present invention;

[0040] FIG. 2(A) is a schematic diagram of grating distribution on a silicon wafer alignment mark in the present invention;

[0041] FIG2(B) is a schematic diagram of grating distribution on the detection grating in the present invention;

[0042] Figure 3 A schematic diagram of an optical path 2 of an alignment sensing system integrating a grating and a lens group for detecting the position of a silicon wafer in the x direction provided by the present invention;

[0043] Figure 4 A schematic diagram of an optical path 3 of an alignment sensing system integrating a grating and a lens group for detecting the position of a silicon wafer in the y direction provided by the present invention;

[0044] Figure 5 A schematic diagram of an optical path 4 of an alignment sensing system integrating a grating and a lens group for detecting the position of a silicon wafer in the y direction provided by the present invention;

[0045] Figure 6 It is a schematic diagram of the optical path of the dual-wavelength integrated alignment sensing system for detecting the position of a silicon wafer in the x direction of the present invention;

[0046] Figure 7 It is a schematic diagram of the optical path of the dual-wavelength integrated alignment sensing system for detecting the position of a silicon wafer in the y direction of the present invention;

[0047] Figure 8 A schematic diagram of interference fringes between the silicon wafer alignment mark and the detection grating obtained on the detection surface of the detector in a non-aligned state according to the present invention;

[0048] Fig. 9 A schematic diagram of interference fringes between the silicon wafer alignment mark and the detection grating obtained on the detection surface of the detector in the present invention in an aligned state;

[0049] Reference numerals:

[0050] 1, first light source group; 2, second light source group; 3, silicon wafer alignment mark; 4, detection grating; 5, lens group; 6, detector; 7, silicon wafer to be aligned;

[0051] 31, first grating; 32, second grating; 33, third grating; 34, fourth grating; 41, fifth grating; 42, sixth grating; 43, seventh grating; 44, eighth grating; 61, 62, 63, 64 are moiré fringes on the detector surface;

[0052] 111, 112, 113, 114 are light sources in the first light source group; 211, 212, 213, 214 are light sources in the second light source group;

[0053] 811, a first reflector; 812, a second reflector; 813, a third reflector; 814, a fourth reflector; 821, a fifth reflector; 822, a sixth reflector; 823, a seventh reflector; 824, an eighth reflector. DETAILED DESCRIPTION

[0054] The present invention is described in detail below in conjunction with the accompanying drawings and embodiments.

[0055] like Figure 1 and Figure 4 As shown, the present invention proposes a projection lithography machine alignment sensing system based on the integration of grating and lens group, the system comprising:

[0056] Light source group, detection grating 4, lens group 5 and detector 6;

[0057] The light source group includes a first light source group 1, and the first light source group 1 includes a first light source pair and a second light source pair for respectively illuminating in the x direction and the y direction; the two light sources in each light source pair have the same parameters and types; the light sources in the first light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensor system in the xz plane; the light sources in the second light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensor system in the yz plane;

[0058] The first light source pair and the second light source pair both emit light beams, and the angle between the incident direction of the light beams on the silicon wafer alignment mark 3 and the center line of the silicon wafer alignment mark 3 is equal to the angle between the first-order diffracted light and the zero-order light after the light beams irradiate the silicon wafer alignment mark 3 and diffract.

[0059] The x direction and the y direction are respectively the horizontal direction and the vertical direction of the horizontal plane under the global coordinate system of the projection lithography machine, and the z direction is the direction of the xy plane determined by the x direction and the y direction;

[0060] The horizontal plane where the detection grating 4 is located and the horizontal plane where the detector 6 is located form an object-image conjugate relationship with respect to the lens group 5; the detection grating 4 is on the object plane of the lens group 5, and the detector 6 is on the image plane of the lens group 5; the lens group 5 is an afocal optical system.

[0061] In the present invention, the first light source pair includes light source 111 and light source 112, and the second light source pair includes light source 113 and light source 114. Light source 111 and light source 112 have the same parameters and types, and are symmetrically distributed on both sides of the central optical axis of the alignment sensing system in the xz plane, and are used for illumination of the position detection of the silicon wafer alignment mark 3 in the x direction. Light source 113 and light source 114 have the same parameters and types, and are symmetrically distributed on both sides of the central optical axis of the alignment sensing system in the yz plane, and are used for light source illumination of the position detection of the silicon wafer alignment mark 3 in the y direction.

[0062] Light source 111 and light source 112 emit light beams, and the angle between the incident direction of the light beams on the silicon wafer alignment mark 3 and the center line of the silicon wafer alignment mark 3 is equal to the angle between the first-order diffracted light and the zero-order light after the light beams diffract when irradiating the silicon wafer alignment mark 3; light source 113 and light source 114 emit light beams, and the angle between the incident direction of the light beams on the silicon wafer alignment mark 3 and the center line of the silicon wafer alignment mark 3 is equal to the angle between the first-order diffracted light and the zero-order light after the light beams diffract when irradiating the silicon wafer alignment mark 3.

[0063] like Figure 2(A)-Figure 2(B) As shown, the silicon wafer alignment mark 3 is composed of a first grating 31 with a period P1, a second grating 32 with a period P2, a third grating 33 with a period P1 and a fourth grating 34 with a period P2, and the numerical difference between P1 and P2 is less than a first preset threshold value; the first grating 31 and the second grating 32 are used for position deviation detection of the silicon wafer 7 to be aligned in the x direction, and the third grating 33 and the fourth grating 34 are used for position deviation detection of the silicon wafer 7 to be aligned in the y direction; the first grating 31 and the second grating 32 are arranged adjacent to each other in the y direction, and the scribed lines of the first grating 31 and the second grating 32 are both along the y direction, and the center position of the first grating 31 and the center position of the second grating 32 have the same x coordinate; the third grating 33 and the fourth grating 34 are arranged adjacent to each other in the x direction, and the scribed lines of the third grating 33 and the fourth grating 34 are both along the x direction, and the center position of the third grating 33 and the center position of the fourth grating 34 have the same y coordinate.

[0064] The detection grating 4 is composed of a fifth grating 41 with a period of P2, a sixth grating 42 with a period of P1, a seventh grating 43 with a period of P2, and an eighth grating 44 with a period of P1; the fifth grating 41 and the sixth grating 42 are used to detect the position deviation of the silicon wafer 7 to be aligned in the x direction, and the seventh grating 43 and the eighth grating 44 are used to detect the position deviation of the silicon wafer 7 to be aligned in the y direction; the fifth grating 41 and the sixth grating 42 are arranged adjacent to each other in the y direction, and the fifth grating 41 and the sixth grating 42 are arranged adjacent to each other in the y direction. The directions of the engraved lines are all along the y direction, and the center position of the fifth grating 41 and the center position of the sixth grating 42 have the same x coordinate; the relative position of the first grating 31 and the second grating 32 on the silicon wafer alignment mark 3 in the y direction is the same as the relative position of the fifth grating 41 and the sixth grating 42 on the detection grating in the y direction; the relative position of the third grating 33 and the fourth grating 34 on the silicon wafer alignment mark in the x direction is the same as the relative position of the seventh grating 43 and the eighth grating 44 on the detection grating in the x direction.

[0065] In the present invention, when detecting the x-direction position of the silicon wafer alignment mark 3, the silicon wafer alignment mark 3 on the silicon wafer 7 to be aligned is illuminated by the light source 111 and the light source 112. The angle between the incident direction of the light beam on the silicon wafer alignment mark 3 and the center line of the silicon wafer alignment mark 3 is equal to the angle between the first-order light and the zero-order light after the light beam irradiates the silicon wafer alignment mark 3 and diffracts. The positive first-order diffraction light generated after the light source 111 irradiates the silicon wafer alignment mark 3 and the negative first-order diffraction light generated after the light source 112 irradiates the silicon wafer alignment mark 3 pass through the detection grating 4 when propagating upward. The positive and negative first-order lights generated by the further diffraction of the detection grating 4 are converged on the detection surface of the detector 6 after passing through the lens group 5, wherein there are two groups of interference fringes with a period greater than a set threshold value, and the phase difference between the two groups of interference fringes with amplified periods is used. The position deviation Δx between the silicon wafer alignment mark 3 and the detection grating 4 in the x direction can be calculated.

[0066] The present invention is an alignment sensing system with a simple structure and capable of achieving sub-nanometer and deep sub-nanometer precision. The present invention can achieve the alignment precision of the photolithography machines of ASML, NIKON and CANON. Compared with the alignment sensing systems of ASML and NIKON, the present invention has a simple structure. Compared with the nano-imprinting technology in which the gap between the mask and the silicon wafer is small, which can only be used for the alignment technology of CANON, the alignment sensing system proposed by the present invention is suitable for the alignment mark position detection of the projection photolithography machine.

[0067] In the present invention, the light source, detection grating 4, lens group 5 and detector 6 constituting the alignment sensor system of the projection lithography machine are integrated to form an integrated alignment sensor system of the projection lithography machine.

[0068] like Figure 6 , Figure 7As shown, further, the light source group also includes a second light source group 2 with a wavelength different from that of the first light source group 1, and the second light source group 2 includes a third light source pair and a fourth light source pair; the two light sources in each light source pair have the same parameters and types; the two light sources in the third light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensing system in the xz plane; the two light sources in the fourth light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensing system in the yz plane;

[0069] The third light source pair and the fourth light source pair both emit light beams, and the angle between the incident direction of the emitted light beam on the silicon wafer alignment mark 3 and the center line of the silicon wafer alignment mark 3 is equal to the angle between the first-order diffracted light and the zero-order light after the silicon wafer alignment mark 3 irradiated by the emitted light beam is diffracted.

[0070] Furthermore, the first light source group 1 and the second light source group 2 are visible light sources and near-infrared light sources respectively.

[0071] In the present invention, the light source group also includes a second light source group 2 having a different wavelength from the first light source group 1, and the second light source group 2 includes a light source 211, a light source 212, a light source 213, and a light source 214; the parameters and types of the light source 211 and the light source 212 are the same, and the parameters and types of the light source 213 and the light source 214 are the same.

[0072] Furthermore, the light source group also includes several light source groups whose wavelengths are different from those of the first light source group 1 and the second light source group 2, each light source group includes two light source pairs, and the parameters and types of the two light sources in each light source pair are the same; the layout of each light source group is: the two light sources in one light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensing system in the xz plane; the two light sources in another light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensing system in the yz plane.

[0073] Before the silicon wafer is exposed to photolithography, it is necessary to perform processes such as chemical mechanical polishing. This process will change the grating alignment mark morphology on the silicon wafer, such as changing the groove depth of the grating, that is, the optical depth. When the optical depth of the grating is half of the wavelength of the incident light, the first-order light intensity of the grating diffraction is zero, so alignment cannot be performed. At the same time, in the photolithography exposure process of advanced nodes, the photoresist on the surface of the silicon wafer has an absorption effect on visible light, which leads to the weakening of the illumination light. In order to solve the problems in the alignment process caused by these process factors, the present invention can use multiple wavelengths (greater than or equal to 2 wavelengths) light source to detect the position of the silicon wafer. Therefore, the present invention configures the light source into multiple groups so that multiple groups of light sources can provide greater than or equal to 2 wavelengths. The reason for selecting a near-infrared light source is that the near-infrared light will not be absorbed in the photoresist, and the intensity of the signal light source can be guaranteed.

[0074] Furthermore, the projection lithography machine alignment sensing system includes a reflector corresponding to the light source one by one, and the reflector is used to adjust the incident direction of the light beam emitted by the light source on the silicon wafer alignment mark 3, so that the angle between the incident direction of the light beam on the silicon wafer alignment mark 3 and the center normal of the silicon wafer alignment mark 3 is equal to the angle between the first-order diffraction light and the zero-order light after the light beam is diffracted when irradiating the alignment mark 3.

[0075] like Figure 6-Figure 7 As shown, the first reflector 811, the second reflector 812, the third reflector 813, the fourth reflector 814, the fifth reflector 821, the sixth reflector 822, the seventh reflector 823, and the eighth reflector 824 correspond to the light sources one by one, respectively, so as to adjust the incident direction of the light beam emitted by the light source on the silicon wafer alignment mark 3.

[0076] The present invention also provides a method for detecting the position of silicon wafer alignment marks based on a projection lithography machine alignment sensor system integrated with a grating and a lens group. Based on the projection lithography machine alignment sensor system integrated with a grating and a lens group as described above, the method comprises:

[0077] Step S1: determining the detection direction of the silicon wafer alignment mark 3, based on the outgoing light beam of part or all of the light sources illuminated in the illumination direction; the silicon wafer alignment mark 3 is irradiated by the outgoing light beam to generate negative first-order diffraction light and positive first-order diffraction light; the negative first-order diffraction light and the positive first-order diffraction light are diffracted again after passing through the detection grating 4, and negative first-order diffraction light and positive first-order diffraction light are obtained respectively; the negative first-order diffraction light and the positive first-order diffraction light interfere on the detection surface of the detector 6 after passing through the lens group 5, and a plurality of groups of interference fringes are generated; wherein the detection direction is the x direction or the y direction;

[0078] Step S2: obtaining two groups of moiré fringes from the plurality of groups of interference fringes, and obtaining phase information of each group of moiré fringes based on a method of decomposing the fringes; the moiré fringes are interference fringes with a period greater than a set threshold;

[0079] Step S3: determining the phase deviation based on the two groups of moiré fringes, and determining the position deviation of the silicon wafer alignment mark 3 in the detection direction.

[0080] When the detection direction is the x direction, the position deviation Δx in the x direction is:

[0081]

[0082] in, It is the phase deviation determined based on two sets of moiré fringes when the detection direction is the x direction.

[0083] When the detection direction is the y direction, the position deviation Δy in the y direction is:

[0084]

[0085] in, It is the phase deviation determined based on two sets of moiré fringes when the detection direction is the y direction.

[0086] In the present invention, a detector with a small pixel size, a lens group with a high magnification, and a grating with a small difference between the period P1 and the period P2 (that is, the first set threshold is small) are used, which can effectively increase the period of the moiré fringes on the detector surface, thereby increasing the detection sensitivity of the silicon wafer alignment mark position and improving the detection accuracy of the silicon wafer alignment mark position.

[0087] The effectiveness of the calculation of the position deviation of the present invention is explained by reasoning that the detection direction is the x direction.

[0088] like Figure 1 As shown, after the light beam a emitted by the light source 111 irradiates the first grating 31 with a period of P1, a negative first-order diffraction light a1 is generated. -1 It propagates upward and passes through the third grating 41 with a period of P2 on the detection grating 4. After the light beam b emitted by the light source 112 irradiates the first grating 31 with a period of P1, a positive first-order diffraction light b1 is generated. +1 It propagates upward through the third grating 41 with a period of P2 on the detection grating 4.

[0089] Diffracted light a1 -1 The complex amplitude of is:

[0090]

[0091] Where A0 is the amplitude of beam a, is the initial phase of beam a, x w is the x-direction position of the first grating 31 with a period of P1 on the silicon wafer alignment mark 3.

[0092] Diffracted light b1 +1 The complex amplitude of is:

[0093]

[0094] like Figure 3 As shown, light beams a and b illuminate the second grating 32 with a period of P2 and then diffract to generate diffracted light a2 -1 With b2 +1 , the complex amplitudes are:

[0095]

[0096] Diffraction light a1 generated by silicon wafer alignment mark 3 -1 , b1 +1 , a2 -1 , b2+1 Diffraction occurs on the detection grating 4 .

[0097] in:

[0098] The diffracted light a1 generated by the first grating 31 with a period P1 -1 and b1 +1 Diffraction occurs on the third grating 41 with a period of P2, and the diffracted light a1 -1 After diffracted by the third grating 41 with a period of P2, positive first-order light a1 is generated -1,+1 And the negative first-order light a1 -1,-1 , diffracted light b1 +1 After being diffracted by the third grating 41 with a period of P2, the positive first-order light b1 is generated. +1,+1 And the negative first-order light b1 +1,-1 . By diffracted light a1 -1,+1 With b1 +1,-1 Interference can form moiré fringes.

[0099] a1 -1,+1 With b1 +1,-1 The complex amplitudes are:

[0100]

[0101] Among them, A1 is the diffracted light a1 -1 and b1 +1 The amplitude of the positive and negative first-order diffracted light after diffraction by the detection grating 4, x p To detect the x-direction position of the grating 4.

[0102] The diffracted light a2 generated by the second grating 32 with a period of P2 -1 and b2 +1 Diffraction occurs at grating 42, and the diffracted light a2 -1 After being diffracted by the fourth grating 42 with a period of P1, positive first-order light a2 is generated. -1,+1 And negative first-order light a2 -1,-1 , diffracted light b2 +1 After being diffracted by the fourth grating 42 with a period of P1, the positive first-order light b2 is generated. +1,+1 And the negative first-order light b2 +1,-1 . By diffracted light a2 -1,+1 With b2 +1,-1 Interference can form moiré fringes.

[0103] Diffracted light a2 -1,+1 With b2 +1,-1 The complex amplitudes are:

[0104]

[0105] Diffracted light a1-1,+1 , a1 -1,-1 , b1 +1,-1 , b1 +1,+1 , a2 -1,+1 , a2 -1,-1 , b2 +1,-1 , b2 +1,+1 After passing through the lens group 5, interference occurs on the detector 6. Among them, the diffracted light a1 -1,+1 With diffracted light b1 +1,-1 Interference forms moiré fringes, diffracted light a2 -1,+1 With diffracted light b2 +1,-1 Interference forms moiré fringes, such as Figure 8 shown.

[0106] In theory, a1 -1,+1 , a1 -1,-1 , b1 +1,-1 , b1 +1,+1 These four beams will interfere with each other on detector 6. -1,+1 With b1 +1,-1 In addition to the moiré fringes formed by interference, the period of other interference fringes is much smaller than the detector pixel size, and the background interference light formed can be removed by post-processing information, for example, by Fourier transform and filtering it in the frequency domain. -1,+1 , a2 -1,-1 , b2 +1,-1 , b2 +1,+1 They will also interfere with each other, and the influence of the background interference light can also be removed.

[0107] Diffracted light a1 -1,+1 With b1 +1,-1 Interference occurs, and the light intensity distribution of the interference fringes 61 is:

[0108]

[0109] Diffracted light a2 -1,+1 With b2 +1,-1 Interference occurs, and the light intensity distribution of the interference fringes 62 is:

[0110]

[0111] When there is a position deviation Δx between the detection grating 4 and the silicon wafer alignment mark 3 in the x direction, p =x w +Δx, the light intensity distributions of interference fringes 61 and 62 are respectively:

[0112]

[0113] When Δx is not zero, the interference fringes 61 and 62 on the detector 6 are not aligned, as shown in FIG. Figure 8 When the position deviation Δx is zero, the interference fringes 61 and 62 are aligned. Fig. 9 shown.

[0114] When Δx is not zero, there is a phase difference between the two groups of fringes. Phase Difference The relationship with the position deviation Δx can be expressed as:

[0115]

[0116] Therefore, the position deviation Δx in the x direction between the silicon wafer alignment mark 3 and the detection grating 4 that the alignment sensing system needs to detect is:

[0117]

[0118] when When it is greater than 2π, it exceeds the detection range, so the detection range x of the alignment sensor system range for:

[0119]

[0120] The above Δx is the position deviation in the x direction between the detection grating 4 and the silicon wafer alignment mark 3. After the light source 111 and the light source 112 irradiate the first grating 31 with a period of P1 and the second grating 32 with a period of P2 on the silicon wafer alignment mark 3, the generated diffracted light is diffracted by the third grating 41 with a period of P2 and the fourth grating 42 with a period of P1 on the detection grating, and the lens group 5 converges the diffracted light on the detector 6, and the moiré fringes on the detector 6 are processed to obtain the position deviation Δx, thereby determining the position of the silicon wafer alignment mark 3 in the x direction.

[0121] like Figure 4 and Figure 5 As shown, for detecting the position deviation Δy between the grating 4 and the silicon wafer alignment mark 3 in the y direction, the detection principle is the same as that in the x direction and will not be repeated here.

[0122] The present invention provides a specific embodiment of a detection method for a projection lithography machine alignment sensor system based on the integration of a grating and a lens group, based on the projection lithography machine alignment sensor system based on the integration of a grating and a lens group as described above.

[0123] Take the x-direction position detection of silicon wafer as an example.

[0124] The helium-neon laser LGK7665-18 of Lubang Company is used as the light source 111 and the light source 112, and the light beam with a wavelength of 632.8nm is emitted to illuminate the silicon wafer alignment mark 3.

[0125] The silicon wafer alignment mark 3 is composed of a grating 31 with a period of 2 μm and a grating 32 with a period of 2.05 μm. The detection grating 4 is composed of a grating 41 with a period of 2.05 μm and a grating 42 with a period of 2 μm.

[0126] Light beams a and b illuminate the silicon wafer alignment mark 3, with an incident angle of 18°.

[0127] Detector 6 uses Hikvision MV-CU200-20GM (NPOE), with a pixel size of 1.4μm×1.4μm and a resolution of 5120×3840.

[0128] The light intensity I1 of the moiré fringe 61 and the light intensity I2 of the moiré fringe 62 formed at the detector 6 are expressed as follows:

[0129]

[0130] When there is a position deviation Δx between the detection grating 4 and the silicon wafer alignment mark 3 in the x direction, p =x w +Δx, the intensities of the two sets of moiré fringes with amplified periods are:

[0131]

[0132] When there is a deviation Δx between the silicon wafer alignment mark 3 and the detection grating 4 in the x direction, the two groups of interference fringes 61 and fringes 62 on the detector 6 will also be offset. Figure 8 , there is a phase difference between the two groups of fringes Displacement deviation Δx and phase difference The relationship is:

[0133]

[0134] The position deviation Δx between the silicon wafer alignment mark 3 to be detected and the detection grating 4 is:

[0135]

[0136] The lens group 5 is an afocal system that can magnify the beam aperture. When the magnification is 20 and the pixel size of the detector 6 is 1.4 μm, the minimum detectable phase shift is 7π / 2050, and the minimum detectable position offset of the silicon wafer alignment mark 3 is 0.86 nm. When the magnification of the lens group 5 is further increased, the pixel size of the detector 6 is further reduced, and the difference between the grating periods P1 and P2 on the silicon wafer alignment mark 3 is smaller, the minimum detectable position offset of the silicon wafer alignment mark 3 can be further reduced.

[0137] When dual-wavelength light is used for wafer position detection, another light source, Lubang laser LBL-785-50mW, emits near-infrared light with a wavelength of 785nm. After adjustment by the reflector, the incident direction on the wafer alignment mark is at an angle of 23° to the normal of the surface where the wafer alignment mark is located. After diffraction by the wafer alignment mark 3, the positive and negative first-order diffracted light is passed through the integrated alignment sensor system, forming moiré fringes on the detector surface, and the position information of the wafer alignment mark 3 can be obtained based on the moiré fringes.

[0138] The above specific embodiments only describe the design principle of the present invention. The shapes and names of the components in the description may be different and are not limited. Therefore, those skilled in the art in the field of the present invention may modify or replace the technical solutions recorded in the above embodiments; and these modifications and replacements do not deviate from the creative purpose and technical solutions of the present invention and should all fall within the protection scope of the present invention.

Claims

1. A projection lithography machine alignment sensing system based on the integration of grating and lens group, characterized in that: The system includes: A light source group, a detection grating (4), a lens group (5) and a detector (6); The light source group comprises a first light source group (1), the first light source group (1) comprises a first light source pair and a second light source pair for respectively performing illumination in the x direction and the y direction; the two light sources in each light source pair have the same parameters and types; the light sources in the first light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensor system in the xz plane; the light sources in the second light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensor system in the yz plane; The first light source pair and the second light source pair both emit light beams, and the angle between the incident direction of the emitted light beams on the silicon wafer alignment mark (3) and the center line of the silicon wafer alignment mark (3) is equal to the angle between the first-order diffracted light and the zero-order light after the silicon wafer alignment mark (3) irradiated by the emitted light beam is diffracted; The x direction and the y direction are respectively the horizontal direction and the vertical direction of the horizontal plane under the global coordinate system of the projection lithography machine, and the z direction is the direction of the xy plane determined by the x direction and the y direction; The horizontal plane where the detection grating (4) is located and the horizontal plane where the detector (6) is located form an object-image conjugate relationship with respect to the lens group (5); the detection grating (4) is on the object plane of the lens group (5), and the detector (6) is on the image plane of the lens group (5); the lens group (5) is an afocal optical system.

2. The system according to claim 1, characterized in that The light source group also includes a second light source group (2) having a different wavelength from the first light source group (1), and the second light source group (2) includes a third light source pair and a fourth light source pair; the two light sources in each light source pair have the same parameters and types; the two light sources in the third light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensor system in the xz plane; the two light sources in the fourth light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensor system in the yz plane; The third light source pair and the fourth light source pair both emit light beams, and the angle between the incident direction of the emitted light beams on the silicon wafer alignment mark (3) and the center line of the silicon wafer alignment mark (3) is equal to the angle between the first-order diffracted light and the zero-order light after the emitted light beams irradiate the silicon wafer alignment mark (3) and are diffracted.

3. The system according to claim 2, characterized in that The first light source group (1) and the second light source group (2) are respectively visible light sources and near-infrared light sources.

4. The system according to claim 1, characterized in that The light source group also includes a plurality of light source groups having wavelengths different from those of the first light source group (1) and the second light source group (2), each light source group includes two light source pairs, and the parameters and types of the two light sources in each light source pair are the same; the layout of each light source group is such that the two light sources in one light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensor system in the xz plane; and the two light sources in another light source pair are symmetrically distributed on both sides of the central optical axis of the alignment sensor system in the yz plane; The two light source pairs of each light source group both emit light beams, and the angle between the incident direction of the emitted light beams on the silicon wafer alignment mark (3) and the center line of the silicon wafer alignment mark (3) is equal to the angle between the first-order diffracted light and the zero-order light after the emitted light beam irradiates the silicon wafer alignment mark (3) and diffracts.

5. The system according to any one of claims 1 to 4, characterized in that: The silicon wafer alignment mark (3) is composed of a first grating (31) with a period of P1, a second grating (32) with a period of P2, a third grating (33) with a period of P1, and a fourth grating (34) with a period of P2, wherein the numerical difference between P1 and P2 is less than a first preset threshold value; the first grating (31) and the second grating (32) are used for detecting the position deviation of the silicon wafer (7) to be aligned in the x direction, and the third grating (33) and the fourth grating (34) are used for detecting the position deviation of the silicon wafer (7) to be aligned in the y direction; the first grating (3 1) is arranged adjacent to the second grating (32) in the y direction, and the directions of the engraving lines of the first grating (31) and the second grating (32) are both along the y direction, and the x coordinate of the center position of the first grating (31) and the center position of the second grating (32) are the same; the third grating (33) and the fourth grating (34) are arranged adjacent to each other in the x direction, and the directions of the engraving lines of the third grating (33) and the fourth grating (34) are both along the x direction, and the y coordinate of the center position of the third grating (33) and the center position of the fourth grating (34) are the same; The detection grating (4) is composed of a fifth grating (41) with a period of P2, a sixth grating (42) with a period of P1, a seventh grating (43) with a period of P2, and an eighth grating (44) with a period of P1; the fifth grating (41) and the sixth grating (42) are used for detecting the position deviation of the silicon wafer (7) to be aligned in the x direction, and the seventh grating (43) and the eighth grating (44) are used for detecting the position deviation of the silicon wafer (7) to be aligned in the y direction; the fifth grating (41) and the sixth grating (42) are arranged adjacent to each other in the y direction, and the engraved lines of the fifth grating (41) and the sixth grating (42) are both along the y direction, and the x coordinates of the center position of the fifth grating (41) and the center position of the sixth grating (42) are opposite to each other. The seventh grating (43) and the eighth grating (44) are arranged adjacent to each other in the x direction, and the engraved lines of the seventh grating (43) and the eighth grating (44) are both along the x direction, and the y coordinates of the center position of the seventh grating (43) and the center position of the eighth grating (44) are the same; the relative position of the first grating (31) and the second grating (32) on the silicon wafer alignment mark (3) in the y direction is the same as the relative position of the fifth grating (41) and the sixth grating (42) on the detection grating in the y direction; the relative position of the third grating (33) and the fourth grating (34) on the silicon wafer alignment mark in the x direction is the same as the relative position of the seventh grating (43) and the eighth grating (44) on the detection grating in the x direction.

6. A detection method for a projection lithography machine alignment sensor system based on the integration of a grating and a lens group, based on the projection lithography machine alignment sensor system based on the integration of a grating and a lens group as claimed in any one of claims 1 to 5, characterized in that: The method comprises: Step S1: determining the detection direction of the silicon wafer alignment mark (3), based on the outgoing light beam of part or all of the light source illuminated in the illumination direction; the silicon wafer alignment mark (3) is irradiated by the outgoing light beam to generate negative first-order diffraction light and positive first-order diffraction light; the negative first-order diffraction light and the positive first-order diffraction light are diffracted again after passing through the detection grating (4), and negative first-order diffraction light and positive first-order diffraction light are obtained respectively; the negative first-order diffraction light and the positive first-order diffraction light are interfered on the detection surface of the detector (6) after passing through the lens group (5), and a plurality of groups of interference fringes are generated; wherein the detection direction is the x direction or the y direction; Step S2: obtaining two groups of moiré fringes from the plurality of groups of interference fringes, and obtaining phase information of each group of moiré fringes based on a method of decomposing the fringes; the moiré fringes are interference fringes with a period greater than a set threshold; Step S3: determining the phase deviation based on the two groups of moiré fringes, and determining the position deviation of the silicon wafer alignment mark (3) in the detection direction.

7. The method as claimed in claim 6, characterized in that When the detection direction is the x direction, the position deviation Δx in the x direction is: Wherein, P1 and P2 are the periods of the first grating (41) and the second grating (42) of the silicon wafer alignment mark (3), respectively. It is the phase deviation determined based on two sets of moiré fringes when the detection direction is the x direction.

8. The method as claimed in claim 6, characterized in that When the detection direction is the y direction, the position deviation Δy in the y direction is: Wherein, P1 and P2 are the periods of the first grating (41) and the second grating (42) of the silicon wafer alignment mark (3), respectively. It is the phase deviation determined based on two sets of moiré fringes when the detection direction is the y direction.

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