A lithography machine

Abstract

The present invention discloses a photolithography machine, belonging to the technical field of semiconductor manufacturing equipment, comprising a light source system, a mask loading platform and a silicon wafer worktable, wherein the mask loading platform is located between the silicon wafer worktable and the light source system, and further comprising: an isolation cover, wherein the isolation cover is located on the side of the mask loading platform away from the light source system and is detachably connected to the mask loading platform; the isolation cover and the mask loading platform form a closed cavity; an exposure aperture is arranged on the side of the isolation cover facing the silicon wafer worktable. The above-mentioned photolithography machine reduces the influence of the thermal field and the airflow field between the mask plate and the silicon wafer on the photolithography accuracy.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor manufacturing equipment, and particularly relates to a lithography machine. Background Art

[0002] The lithography process is one of the most important processes in modern very large scale integrated circuit manufacturing. The design pattern of the integrated circuit on the mask is transferred to the silicon wafer through ultraviolet exposure, and the equipment that completes this image transfer process is called a lithography machine. At the same time, as the size of the silicon wafer increases and the feature size of the integrated circuit pattern decreases, it is necessary to repeat the exposure of a silicon wafer multiple times, and this process is called stepping. During the exposure process, the workpiece stage carrying the silicon wafer needs to move at high speed continuously and be accurately positioned at each exposure position. Any slight disturbance during the exposure process, such as vibration, air flow, thermal field, etc., will have a great impact on the imaging quality, thereby reducing the lithography accuracy.

[0003] Holographic diffraction lithography is different from the mainstream projection lithography in the current integrated circuit manufacturing process. It is a new lithography technology that uses holographic mask diffraction imaging. In projection lithography, a projection objective lens is required to magnify the integrated circuit pattern on the mask and image it onto the surface of the silicon wafer. In order to increase the numerical aperture of the projection objective lens as much as possible, the distance between the projection objective lens and the silicon wafer is very close, about 3 mm. The air flow disturbance during the movement of the silicon wafer is relatively small, so the impact of air flow disturbance on imaging is rarely considered. In a holographic diffraction lithography machine, because holographic diffraction imaging is used, the distance between the silicon wafer and the holographic mask is relatively far, about 10 cm, and there is no projection objective lens between the two. The relatively long distance brings a longer optical path, resulting in a larger wave aberration introduced by air disturbance. The overall structure of the holographic diffraction lithography machine is more similar to a proximity lithography machine with an exposure resolution in the micron level. However, the difference is that the holographic diffraction lithography machine has a high resolution, the distance between the mask and the silicon wafer is larger, and the wave aberration introduced by air disturbance has a greater impact on the feature size. The exposure feature size of the holographic diffraction lithography machine is smaller, and the half-pitch line width can reach about 100 nm. The local heating of the air caused by long-term exposure, on the one hand, leads to a change in the refractive index of the air. At the same time, due to the relationship between the gas flow velocity and pressure, the air flow disturbance caused by the movement of the silicon wafer workpiece stage will also change the refractive index of the air. The change in the refractive index will introduce additional wave aberration, which will greatly affect the imaging quality and thus affect the lithography accuracy. Summary of the Invention

[0004] The technical problem to be solved by the present invention is how to solve the problem of the influence of the thermal field and air flow field between the mask and the silicon wafer on the lithography accuracy in a holographic diffraction lithography machine.

[0005] The present invention provides a photolithography machine, comprising a light source system, a mask loading platform and a silicon wafer worktable, wherein the mask loading platform is located between the silicon wafer worktable and the light source system, and further comprising: an isolation cover, wherein the isolation cover is located at a side of the mask loading platform away from the light source system and is detachably connected to the mask loading platform; the isolation cover and the mask loading platform form a closed cavity; an exposure diaphragm is arranged on the side of the isolation cover facing the silicon wafer worktable.

[0006] Optionally, the isolation cover is a cylindrical structure with an opening on one side, the open side of the cylindrical structure is detachably connected to the mask plate loading platform, and a side surface of the cylindrical structure facing the silicon wafer workpiece stage is parallel to the surface of the silicon wafer workpiece stage.

[0007] Optionally, the height of the isolation cover is 4 cm to 9.5 cm; in the photolithography operation state, the distance between the surface of the isolation cover facing the silicon wafer worktable and the surface of the silicon wafer on the silicon wafer worktable is 2 mm to 5 mm.

[0008] Optionally, ventilation holes are provided on the side walls of the isolation cover.

[0009] Optionally, the number of the ventilation openings is 2 to 8.

[0010] Optionally, an air inlet fan is provided on at least one vent, and / or an air outlet fan is provided on at least one vent.

[0011] Optionally, the ventilation openings are evenly distributed along the circumference of the side wall of the isolation cover.

[0012] Optionally, the mask loading platform has an opening suitable for placing the mask, the projection of the mask on the silicon wafer workpiece stage is a first rectangle, the projection of the exposure aperture on the silicon wafer workpiece stage is a second rectangle, and the distance between the center of the first rectangle and the center of the second rectangle is 2mm to 30mm.

[0013] Optionally, the material of the exposure aperture is quartz glass or calcium fluoride glass; the material of the isolation cover is metal or ceramic with an ultraviolet light absorption rate greater than or equal to 70%; optionally, the metal is chromium or tantalum, and the ceramic is SiC or Si3N4.

[0014] Optionally, the surface flatness of the exposure aperture is 5nm to 50nm.

[0015] The above technical solution of the present invention has the following beneficial effects:

[0016] The lithography machine provided by the technical solution of the present invention includes a light source system, a mask loading platform and a silicon wafer worktable, wherein the mask loading platform is located between the silicon wafer worktable and the light source system, and further includes: an isolation cover, wherein the isolation cover is located on the side of the mask loading platform away from the light source system and is detachably connected to the mask loading platform; the isolation cover and the mask loading platform form a closed cavity; an exposure aperture is arranged on the side of the isolation cover facing the silicon wafer worktable.

[0017] When the lithography machine is in working state, the ultraviolet light emitted by the light source system passes through the mask plate on the mask plate loading platform, then passes through the exposure aperture, and exposes the surface of the silicon wafer on the silicon wafer workpiece stage. Because the mask plate of the holographic diffraction lithography machine originally needs to be separated from the silicon wafer by a long distance (about 10 cm), the long distance brings a longer optical path, so that the lithography light needs to pass through a larger airflow field after passing through the mask plate. The airflow disturbance in this part of the airflow field will lead to the introduction of larger wave aberration, which will affect the lithography accuracy. By adding an isolation cover between the mask plate loading platform and the silicon wafer worktable, the isolation cover and the mask plate loading platform form a closed cavity; most of the space between the mask plate and the silicon wafer on the silicon wafer worktable is surrounded by the isolation cover, and the airflow field in this part of the space is relatively stable due to the sealing effect of the isolation cover. When the silicon wafer worktable moves, it will not cause airflow disturbance in the airflow field in the isolation cover, but will only affect the airflow field in a very small space between the silicon wafer worktable and the surface of the isolation cover facing the silicon wafer worktable, thereby reducing the influence of the airflow field between the mask plate and the silicon wafer on the silicon wafer worktable on the air refractive index, and improving the lithography accuracy of the lithography machine.

[0018] Furthermore, after the lithography machine has been working for a long time, the air disturbance caused by the movement of the silicon wafer worktable will cause local thermal field changes, introducing additional wavefront aberrations to the imaging. The refractive index of air is closely related to temperature. During the actual exposure process, the temperature of the air is uneven and in a dynamic change, which leads to uneven and dynamic changes in the refractive index of the air in the optical path, thereby introducing wavefront measurement errors. The temperature coefficient of the gas dn / dT = -0.9*10 -6 K -1 , that is, every 1K temperature change will cause the refractive index of air to decrease by -0.9*10 -6. A simple estimate, assuming that the optical path is 1 cm, an increase of 1K in the air temperature in the optical path will result in an optical path difference of about 1nm. At longer optical paths, the more drastic the air changes, the more serious the additional optical path difference introduced. After the lithography machine provided by the present invention has completed exposing a silicon wafer, the isolation cover can be removed to discharge the heated air in the isolation cover, and then the isolation cover can be installed to expose another silicon wafer; the silicon wafer is exposed by the above method, because when each silicon wafer is exposed, the air in the isolation cover during the optical path is fresh air, which prevents the air from being heated and forming a local heat field; and the air in the isolation cover does not flow, which can ensure the stability of the air in the isolation cover, thereby reducing the impact of airflow disturbance on the refractive index of the air, and improving the lithography accuracy of the lithography machine. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 This is a schematic diagram of the structure of the lithography machine according to an embodiment of the present application;

[0021] Figure 2 This is a flow chart of the photolithography machine of the embodiment of the present application exposing a silicon wafer;

[0022] Reference numerals:

[0023] 1. Mask loading platform; 2. Mask; 3. Isolation cover; 4. Air inlet fan; 5. Air outlet fan; 6. Exposure aperture; 7. Silicon wafer workpiece platform. DETAILED DESCRIPTION

[0024] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention. In addition, the technical features involved in the different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0025] The embodiment of the present invention provides a photolithography machine, referring to Figure 1, including a light source system, a mask loading platform 1 and a silicon wafer workbench 7, wherein the mask loading platform 1 is located between the silicon wafer workbench 7 and the light source system, and also includes: an isolation cover 3, wherein the isolation cover 3 is located on the side of the mask loading platform 1 away from the light source system and is detachably connected to the mask loading platform 1; the isolation cover 3 and the mask loading platform 1 form a closed cavity; an exposure aperture 6 is arranged on the side of the isolation cover 3 facing the silicon wafer workbench 7.

[0026] In this embodiment, when the lithography machine is in operation, ultraviolet light emitted by the light source system passes through the mask plate 2 located on the mask plate loading platform 1, and then passes through the exposure aperture 6 to expose the surface of the silicon wafer located on the silicon wafer workpiece stage 7. Because the mask plate 2 of the holographic diffraction lithography machine originally needs to be separated from the silicon wafer by a long distance (about 10 cm), the long distance brings a longer optical path, so that the lithography light needs to pass through a larger airflow field after passing through the mask plate 2. The airflow disturbance in this part of the airflow field will lead to the introduction of larger wave aberration, which will affect the lithography accuracy. By adding an isolation cover 3 between the mask plate loading platform 1 and the silicon wafer worktable 7, the isolation cover 3 and the mask plate loading platform 1 form a closed cavity; most of the space between the mask plate and the silicon wafer on the silicon wafer worktable 7 is surrounded by the isolation cover, and the airflow field in this part of the space is relatively stable due to the sealing effect of the isolation cover 3. When the silicon wafer worktable moves, it will not cause airflow disturbance in the airflow field in the isolation cover 3, but will only affect the airflow field in a very small space between the silicon wafer worktable 7 and the surface of the isolation cover 3 facing the silicon wafer worktable 7, thereby reducing the influence of the airflow field between the mask plate 2 and the silicon wafer on the silicon wafer worktable 7 on the air refractive index, thereby improving the lithography accuracy of the lithography machine.

[0027] Furthermore, after the lithography machine has been working for a long time, the air disturbance caused by the movement of the silicon wafer worktable will cause local thermal field changes, introducing additional wavefront aberrations to the imaging. The refractive index of air is closely related to temperature. During the actual exposure process, the temperature of the air is uneven and in a dynamic change, which leads to uneven and dynamic changes in the refractive index of the air in the optical path, thereby introducing wavefront measurement errors. The temperature coefficient of the gas dn / dT = -0.9*10 -6 K -1 , that is, every 1K temperature change will cause the refractive index of air to decrease by -0.9*10 -6 A simple estimate is that if the optical path is 1 cm, a 1K increase in the air temperature in the optical path will result in an optical path difference of about 1 nm. When the optical path is longer, the more drastic the air change, the more serious the additional optical path difference will be. Figure 2, after the exposure of a silicon wafer by the lithography machine, the isolation cover can be disassembled to discharge the heated air inside the isolation cover, and then the isolation cover can be reinstalled to expose another silicon wafer; by exposing the silicon wafer through the above method, since the optical path passes through fresh air inside the isolation cover during the exposure of each silicon wafer, the air is prevented from being heated to form a local thermal field; moreover, the air inside the isolation cover does not flow, which can ensure the stability of the air inside the isolation cover, thereby reducing the influence of air flow disturbance on the refractive index of the air and improving the lithography accuracy of the lithography machine.

[0028] In this embodiment, the isolation cover 3 is a cylindrical structure with an opening on one side. The side of the cylindrical structure with the opening is detachably connected to the mask plate loading table 1, and the surface of the cylindrical structure facing the silicon wafer worktable 7 is parallel to the surface of the silicon wafer worktable 7. Specifically, the way that the side of the cylindrical structure with the opening is detachably connected to the mask plate loading table can be snap connection or threaded connection, as long as it is convenient for disassembly and assembly. There is no specific limitation on the material of the isolation cover, as long as it is a metal or ceramic with an ultraviolet light absorption rate greater than or equal to 70%. The metal is, for example, chromium or tantalum; the non-oxide ceramic is, for example, SiC or Si3N4. The absorption spectra of the above materials cover the deep ultraviolet band and can capture ultraviolet photons from 5 eV to 40 eV, thereby reducing the influence of stray light caused by the reflection of the isolation cover wall on the exposure. If the material of the isolation cover is a metal or ceramic with an ultraviolet light absorption rate greater than or equal to 90%, there will be less stray light caused by the reflection of the isolation cover wall, which is more beneficial to improving the lithography accuracy of the lithography machine.

[0029] In one embodiment, refer to Figure 1 , the height H of the isolation cover 3 is the distance between the surface of the isolation cover 3 facing the mask plate loading table 1 and the surface of the isolation cover 3 facing the silicon wafer worktable 7. Specifically, the height H of the isolation cover 3 is 4 cm to 9.5 cm; for example: the height of the isolation cover is 4 cm, 5 cm, 6 cm, 7 cm, 8 cm, 9 cm or 9.5 cm, and other values within the above range. If the height of the isolation cover is less than 4 cm, the distance between the surface of the isolation cover 3 facing the silicon wafer worktable 7 and the silicon wafer worktable is too large, and when the lithography machine exposes, the air flow disturbance caused by the movement of the silicon wafer worktable 7 increases, affecting the refractive index of light in the air; if the height of the isolation cover is greater than 9.5 cm, the distance between the surface of the isolation cover 3 facing the silicon wafer worktable 7 and the silicon wafer worktable 7 is too small, which causes difficulties in the disassembly and assembly of the isolation cover 3 and also increases the cost.

[0030] In one embodiment, during the lithography operation state, the distance between the surface of the isolation cover 3 facing the side of the silicon wafer worktable 7 and the surface of the silicon wafer located on the silicon wafer worktable 7 is 2 mm to 5 mm, such as 2 mm, 3 mm, 4 mm or 5 mm, and other values within the above range. If the distance between the surface of the isolation cover 3 facing the side of the silicon wafer worktable 7 and the surface of the silicon wafer located on the silicon wafer worktable 7 is less than 2 mm, the distance between the surface of the isolation cover 3 facing the silicon wafer worktable 7 and the silicon wafer worktable 7 is too small, making it difficult to disassemble and assemble the isolation cover 3; if the distance between the surface of the isolation cover 3 facing the side of the silicon wafer worktable 7 and the surface of the silicon wafer located on the silicon wafer worktable 7 is greater than 5 mm, the distance between the surface of the isolation cover 3 facing the silicon wafer worktable 7 and the silicon wafer worktable 7 is too large, and when the lithography machine exposes, the airflow disturbance caused by the movement of the silicon wafer worktable 7 increases, affecting the refractive index of light in the air.

[0031] In this embodiment, ventilation openings are provided on the side wall of the isolation cover 3. Specifically, the ventilation openings have a closed state and an open state. When the ventilation openings are in the closed state, the isolation cover 3 and the mask plate loading table 1 form a closed cavity. When the ventilation openings are in the open state, the air inside the isolation cover 3 circulates and exchanges with the outside air through the ventilation openings. After the lithography machine finishes exposing one silicon wafer, there is no need to disassemble the isolation cover 3. As long as the ventilation openings are opened, the heated air inside the isolation cover 3 is circulated and exchanged with the outside air, and then the ventilation openings are closed, and the exposure of another silicon wafer can be carried out.

[0032] Furthermore, the number of the ventilation openings is 2 to 8, such as 2, 3, 4, 5, 6, 7 or 8. If the number of the ventilation openings is 1, the efficiency of circulating and exchanging the heated air inside the isolation cover 3 with the outside air by opening the ventilation opening is too low; if the number of the ventilation openings is greater than 8, the number of the ventilation openings to be opened or closed is too large, and the operation time of opening or closing the ventilation openings is too long, affecting the operation efficiency; at the same time, it is easier to have the situation that the enclosure is not tight, resulting in the disturbance of the airflow field inside the isolation cover 3.

[0033] In one embodiment, an intake fan is provided on at least one ventilation opening. Since the fan can provide additional power to the air and increase the rate of air circulation, the efficiency of circulating and exchanging the heated air inside the isolation cover with the outside air can be improved.

[0034] In another embodiment, an exhaust fan is provided on at least one ventilation opening. The principle is the same as above and will not be elaborated.

[0035] In yet another embodiment, referring to Figure 1 , an intake fan 4 is provided on at least one ventilation opening, and an exhaust fan 5 is provided on at least one ventilation opening. The principle is the same as above and will not be elaborated.

[0036] In this embodiment, the ventilation openings are evenly distributed circumferentially along the side wall of the isolation cover 3. Such an arrangement is beneficial for the heated air inside the isolation cover 3 to circulate and exchange with the outside air more fully and evenly.

[0037] In one embodiment, the mask plate loading table 1 has an opening adapted to place the mask plate 2. The projection of the mask plate 2 on the silicon wafer workpiece table 7 is a first rectangle, and the projection of the exposure aperture 6 on the silicon wafer workpiece table 7 is a second rectangle. The distance between the centers of the first rectangle and the second rectangle is 2 mm to 30 mm, such as 2 mm, 5 mm, 20 mm, 25 mm or 30 mm, and other values within the above range. A suitable distance between the mask plate 2 and the exposure aperture 6 is beneficial for separating the exposure pattern and the twin image and improving the utilization rate of the illumination energy. If the distance between the centers of the first rectangle and the second rectangle is less than 2 mm, the exposure pattern and the twin image cannot be separated; if the distance between the centers of the first rectangle and the second rectangle is greater than 30 mm, only higher diffraction-order ultraviolet light can be utilized, resulting in a reduction in energy utilization rate.

[0038] In one embodiment, the size of the second rectangle is 28 mm * 35 mm, slightly larger than the exposure field of view. The exposure field of view refers to the exposure range formed on the silicon wafer when the lithography machine performs one exposure on the silicon wafer.

[0039] In this embodiment, the material of the exposure aperture 6 is quartz glass or calcium fluoride glass. Quartz glass is made by melting various pure natural quartz (such as quartz crystals, quartz sand, etc.). The optical properties of transparent quartz glass are very excellent, and it has good transmittance in the continuous wavelength range from ultraviolet to infrared radiation. When calcium fluoride exists in a glass state, it is calcium fluoride glass, which has a high transmittance between ultraviolet and mid-infrared (250 nm to 7 μm), up to 95% at most. Both quartz glass and calcium fluoride glass allow ultraviolet light to pass through, and they are the best materials for making exposure apertures.

[0040] In one embodiment, the surface flatness of the exposure aperture 6 is 5 nm to 50 nm, such as 5 nm, 10 nm, 20 nm, 30 nm, 40 nm or 50 nm, and other values within the above range. If the surface flatness of the exposure aperture is less than 5 nm, the precision required for making the exposure aperture increases, and the cost is too high; if the surface flatness of the exposure aperture is greater than 50 nm, the surface flatness of the exposure aperture decreases, affecting the path of light refracted through the exposure aperture, and thus affecting the lithography precision.

[0041] Obviously, the above embodiments are merely examples given for clear illustration and are not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or modifications derived therefrom still fall within the protection scope of the present invention.

Claims

1. A lithography machine for holographic diffraction lithography, comprising a light source system, a mask loading stage, and a wafer stage. The mask loading stage is located between the wafer stage and the light source system, and is characterized in that, It further includes: An isolation cover, which is located on the side of the mask plate loading table away from the light source system and is detachably connected to the mask plate loading table; the isolation cover and the mask plate loading table form a closed cavity, and the height of the isolation cover is 4 cm to 9.5 cm; in the lithography operation state, the distance between the surface of the isolation cover facing the wafer stage and the surface of the wafer on the wafer stage is 2 mm to 5 mm; an exposure aperture is provided on the side of the isolation cover facing the wafer stage.

2. The lithography machine according to claim 1, wherein The isolation cover is a cylindrical structure with one side open, and the side with the opening of the cylindrical structure is detachably connected to the mask plate loading table, and the surface of the cylindrical structure facing the wafer stage is parallel to the surface of the wafer stage.

3. The lithography machine according to claim 1, wherein Ventilation openings are provided on the side wall of the isolation cover.

4. The lithography machine according to claim 3, wherein The number of the ventilation openings is 2 to 8.

5. The lithography machine according to claim 4, wherein An intake fan is provided on at least one ventilation opening, and / or an exhaust fan is provided on at least one ventilation opening.

6. The lithography machine according to claim 3, wherein The ventilation openings are evenly distributed along the circumferential direction of the side wall of the isolation cover.

7. The lithography machine according to any one of claims 1 to 6, wherein the mask plate loading table has an opening adapted to place a mask plate, and wherein The projection of the mask plate on the wafer stage is a first rectangle, the projection of the exposure aperture on the wafer stage is a second rectangle, and the distance between the centers of the first rectangle and the second rectangle is 2 mm to 30 mm.

8. The lithography machine according to claim 7, characterized in that, The material of the exposure aperture is quartz glass or calcium fluoride glass; the material of the isolation cover is a metal or ceramic with an ultraviolet light absorption rate of greater than or equal to 70%; the metal is chromium or tantalum, and the ceramic is SiC or Si3N4.

9. The lithography machine according to claim 8, characterized in that, The surface flatness of the exposure aperture is 5 nm to 50 nm.

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