Variable focus condenser system and lithographic apparatus

Abstract

This invention provides a variable-focus condenser lens system and a photolithography apparatus. The variable-focus condenser lens system includes a light source unit, a homogenizing unit, and a first pupil adjustment unit. The homogenizing unit has a first side and a second side with unequal side lengths on its end face. The light source unit emits a light beam, and the first pupil adjustment unit adjusts the incident angle of the light beam entering the homogenizing unit to ensure that the total internal reflection period length of the light beam is the same in the directions of the first side and the second side of the homogenizing unit. This solves the problems of poor pupil ellipticity and polar balance caused by inconsistent width and height dimensions of the quartz rod end face in rectangular illumination fields without increasing costs. It improves the ellipticity and polar balance of the illumination pupil without changing the shape of the illumination field or increasing overall costs.

Description

Technical Field

[0001] This invention relates to the field of photolithography equipment technology, and in particular to a variable-focus condenser lens system and photolithography equipment. Background Technology

[0002] The illumination system is a crucial component of the exposure subsystem in a lithography machine, providing the illumination source for the projection lens system. Generally, technical evaluation indicators for illumination systems include illumination field uniformity, illumination pupil ellipticity, and polar balance. Depending on the requirements of the lithography process, common illumination field shapes are rectangular or square. For illumination systems containing reflective homogenizing units such as quartz rods, the shape of the illumination field is generally determined by the dimensions of the homogenizing unit's end face perpendicular to the optical axis. For a square field of view, the end face of the homogenizing unit (quartz rod) used in the illumination system is also square, while for a rectangular field of view, the end face of the homogenizing unit (quartz rod) is rectangular. Since the quartz rod beam coupling unit is typically designed as a spatially rotationally symmetric condenser system, a parallel beam, after passing through the condenser, enters the quartz rod at a fixed incident angle, and the angle between the incident beam and the optical axis in any spatial direction is this incident angle. According to the principles of geometric optics, when the end face of the quartz rod is square, the light beam undergoes the same number of total internal reflections in the X and Y directions perpendicular to the optical axis within the quartz rod. Therefore, the energy distribution within the illumination pupil is uniform, and the pupil performance is good. However, for an illumination system with a rectangular end face of the quartz rod, due to the different geometric dimensions in the X and Y directions, when the incident angle is the same in both directions, the light will undergo different numbers of total internal reflections in different directions after passing through the quartz rod. This results in an uneven energy distribution in different directions within the pupil, leading to poor pupil performance.

[0003] Currently, there are two main approaches to homogenizing light: one is using reflective optical elements, such as quartz rods, and the other is using optical devices such as MLA (Micro Lens Array). Compared to quartz rods, MLAs can significantly improve the performance of the illumination pupil and do not suffer from the pupil energy distribution problem mentioned in the quartz rod approach. However, MLAs are very difficult to manufacture, have poor processability, and cost tens of times more than quartz rods, making them not the optimal solution. Summary of the Invention

[0004] The purpose of this invention is to provide a variable-focus condenser lens system and a photolithography device to solve the problems of poor pupil ellipticity and polar balance caused by inconsistent width and height dimensions of the quartz rod end face in rectangular illumination fields without increasing costs.

[0005] To solve the above-mentioned technical problems, the present invention provides a variable focus condenser system, including a light source unit, a light homogenizing unit, and a first pupil adjustment unit. The end face of the light homogenizing unit includes a first side and a second side with unequal side lengths. The light source unit is used to emit a light beam, and the first pupil adjustment unit is used to adjust the incident angle of the light beam entering the light homogenizing unit so that the single total internal reflection period length of the light beam in the direction of the first side and the direction of the second side of the light homogenizing unit is the same.

[0006] Optionally, it also includes a second pupil adjustment unit located behind the optical path where the light-diffusing unit is located. The second pupil adjustment unit includes a third lens group and a fourth lens group. The first pupil adjustment unit located in front of the optical path where the light-diffusing unit is located includes a first lens group and a second lens group.

[0007] Optionally, the combined optical power of the first and fourth lens groups is zero in the X direction and positive and equal in the Y direction; the combined optical power of the second and third lens groups is positive and equal in the X direction and zero in the Y direction.

[0008] Optionally, the first and fourth mirror groups are mirror-symmetric about the homogenizing unit, and the second and third mirror groups are mirror-symmetric about the homogenizing unit.

[0009] Optionally, the first mirror group, the second mirror group, the third mirror group, and the fourth mirror group each include at least one movable mechanism, which is used to adjust the incident angle of the light beam entering the homogenizing unit.

[0010] Optionally, the first lens group, the second lens group, the third lens group, and the fourth lens group each include at least one lens.

[0011] Optionally, the first and second mirror groups are decoupled, the third and fourth mirror groups are decoupled, the first and fourth mirror groups are coupled, and the second and third mirror groups are coupled.

[0012] Optionally, a movable mechanism is provided at the incident end face of the light homogenizing unit, the movable mechanism being used to adjust the incident angle of the light beam entering the light homogenizing unit.

[0013] Optionally, the beam undergoes the same number of total internal reflections in the direction of the first side and the direction of the second side within the homogenizing unit.

[0014] Optionally, the light-diffusing unit includes a quartz rod.

[0015] Optionally, the end face of the quartz rod is rectangular.

[0016] Based on the same inventive concept, the present invention also provides a photolithography apparatus, including any of the aforementioned variable-focus condenser lens systems.

[0017] In the variable-focus condenser lens system and photolithography equipment provided by the present invention, the variable-focus condenser lens system includes a light source unit, a light homogenizing unit, and a first pupil adjustment unit. By adjusting the incident angle of the light beam entering the light homogenizing unit, the single total internal reflection period length of the light beam in the direction of the first side and the direction of the second side in the light homogenizing unit is the same. Without changing the shape of the illumination field of view or increasing the overall cost, the ellipticity and polar balance of the illumination pupil are improved.

[0018] Furthermore, the first pupil adjustment unit located in front of the optical path of the homogenizing unit includes a first lens group and a second lens group, and the second pupil adjustment unit located behind the optical path of the homogenizing unit includes a third lens group and a fourth lens group. Each of the first, second, third, and fourth lens groups includes at least one movable mechanism, or a movable mechanism is provided at the incident end face of the homogenizing unit. The movable structures adjust the first, second, third, and fourth lens groups, or the homogenizing unit, to adjust the incident angle of the light beam entering the homogenizing unit, so that the single total internal reflection period length of the light beam in the direction of the first side and the direction of the second side within the homogenizing unit is the same. Furthermore, the homogenizing unit includes a quartz rod with a rectangular end face. Thus, in the case of a rectangular illumination field of view, without increasing cost, the problems of pupil ellipticity and poor polar balance caused by inconsistent width and height dimensions of the quartz rod end face are solved. Attached Figure Description

[0019] Figure 1 This is a schematic cross-sectional view of the optical structure of a variable-focus condenser lens system according to an embodiment of the present invention in the XZ direction;

[0020] Figure 2 This is a schematic cross-sectional view of the optical structure of a variable-focus condenser lens system according to an embodiment of the present invention in the YZ direction;

[0021] Figure 3 This is a schematic cross-sectional view of the optical structure of a variable-focus condenser lens system according to another embodiment of the present invention in the XZ direction;

[0022] Figure 4 This is a schematic cross-sectional view of the optical structure of a variable-focus condenser lens system according to another embodiment of the present invention in the YZ direction;

[0023] Figure 5 This is a schematic diagram of the beam path of a variable-focus condenser system according to an embodiment of the present invention;

[0024] In the picture,

[0025] 11a - First lens group; 11b - Second lens group; 11c - Third lens group; 11d - Fourth lens group; 12a - First movable lens; 12b - Second movable lens; 12c - Third movable lens; 12d - Fourth movable lens; 12e - Fifth movable lens; 13 - Light homogenizing unit. Detailed Implementation

[0026] The variable-focus condenser lens system and photolithography equipment proposed in this invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. The advantages and features of this invention will become clearer from the following description. It should be noted that the drawings are all in a very simplified form and use non-precise proportions, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0027] For details, please refer to Figure 1 This is a schematic cross-sectional view of the optical structure of a variable-focus condenser lens system according to an embodiment of the present invention in the XZ direction. Figure 1 As shown, this embodiment provides a variable-focus condenser lens system, including a light source unit (not shown in the figure), a light homogenizing unit 13, and a first pupil adjustment unit. The end face of the light homogenizing unit 13 includes a first side and a second side with unequal side lengths. The light source unit emits a light beam, which enters the first pupil adjustment unit, the light homogenizing unit 13, and the second pupil adjustment unit in sequence. The incident angle of the light beam entering the light homogenizing unit 13 is adjusted so that the single total internal reflection period length of the light beam in the direction of the first side and the direction of the second side within the light homogenizing unit 13 is the same.

[0028] Specifically, the first pupil adjustment unit located in front of the optical path where the homogenizing unit 13 is located includes a first lens group 11a and a second lens group 11b, and a second pupil adjustment unit located behind the optical path where the homogenizing unit 13 is located, the second pupil adjustment unit including a third lens group 11c and a fourth lens group 11d. The first lens group 11a, the second lens group 11b, the third lens group 11c, and the fourth lens group 11d are arranged sequentially along the light propagation direction, such that the combined focal power of each lens group has different values ​​in the X and Y directions in a plane perpendicular to the optical axis. The first lens group 11a has zero optical power in the X direction and optical power in the Y direction. The lenses in this group can be cylindrical lenses with optical power in the Y direction. The second lens group 11b has optical power in the X direction and zero optical power in the Y direction. The lenses in this group can also be cylindrical lenses with optical power in the X direction. Cylindrical lenses are used to separate the incident angles of the light beam in the directions of the first and second sides of the end face of the homogenizing unit 13, ensuring that the light beam undergoes the same number of reflections on the end face of the homogenizing unit 13, thus guaranteeing the uniformity of the light beam. The first lens group 11a, the second lens group 11b, the third lens group 11c, and the fourth lens group 11d, arranged sequentially along the incident direction of the light beam on the optical axis of the variable-focus condenser system, are combined lens groups that include at least one lens; each lens group may also include multiple lenses. The combined optical power of the lens group is characterized as follows: the combined optical power values ​​of the lens group alternate in the X and Y directions along the incident direction of the beam. Specifically, when the lens group consists of the first lens group 11a and the fourth lens group 11d, the combined optical power is positive in the Y direction and zero in the X direction; when the lens group consists of the second lens group 11b and the third lens group 11c, the combined optical power is positive in the X direction and zero in the Y direction. The homogenizing unit 13 is located between the second lens group 11b and the third lens group 11c, and is equidistant from both.

[0029] The first lens group 11a and the fourth lens group 11d are mirror-symmetric structures about the homogenizing unit 13, and the second lens group 11b and the third lens group 11c are also mirror-symmetric structures about the homogenizing unit 13. The combined optical power of the first lens group 11a and the fourth lens group 11d is zero in the X direction and positive and equal in the Y direction; the combined optical power of the second lens group 11b and the third lens group 11c is positive and equal in the X direction and zero in the Y direction. In this embodiment, the light-diffusing unit 13 is, for example, a quartz rod. That is, the third lens group 11c is a lens group symmetrical to the second lens group 11b about the quartz rod, with optical power in the X direction and zero optical power in the Y direction. The lenses in this lens group can be cylindrical lenses with optical power in the X direction. The fourth lens group 11d is a lens group mirror-symmetrical to the first lens group 11a about the quartz rod, with zero optical power in the X direction and optical power in the Y direction. The lenses in this lens group can be cylindrical lenses with optical power in the Y direction. A symmetrical rear cylindrical lens group is provided at the exit end of the light-diffusing unit 13 to restore the pupil. The first lens group 11a, the second lens group 11b, the third lens group 11c, and the fourth lens group 11d, along with the quartz rod, have a generally symmetrical structure, the purpose of which is to keep the shape of the input pupil of the condenser lens system unchanged.

[0030] In one embodiment, such as Figure 1 and Figure 2 As shown, the first lens group 11a, the second lens group 11b, the third lens group 11c, and the fourth lens group 11d each include at least one movable mechanism. The movable mechanism is used to adjust the incident angle of the light beam entering the homogenizing unit 13, finely adjusting the incident angle in real time to improve pupil performance. In this embodiment, the movable mechanism is, for example, a movable lens. That is, the first lens group 11a is provided with at least a first movable lens 12a, the second lens group 11b is provided with at least a second movable lens 12b, the third lens group 11c is provided with at least a third movable lens 12c, and the fourth lens group 11d is provided with at least a fourth movable lens 12d. Each lens group may also have multiple movable lenses.

[0031] In another embodiment, such as Figure 3 and Figure 4 As shown, a movable mechanism is provided at the incident end face of the beam homogenizing unit 13. This movable mechanism, for example, is a fifth movable lens 12e, which is used to adjust the incident angle of the light beam entering the beam homogenizing unit 13. By changing the position of the fifth movable lens 12e to the incident end face of the quartz rod, the tilt of the quartz rod can be adjusted by finely adjusting the offset of the movable mechanism in the X and Y directions, thereby changing the angle of the light beam incident on the quartz rod and achieving an optimal matching combination of the incident angles in the X and Y directions.

[0032] The movable mechanism is used to make real-time fine adjustments based on the actual processing and assembly of optical lenses, quartz rods and other related lighting optical units, so as to reduce the optical processing technology requirements of optical components such as condenser lenses and quartz rods, improve the processability, reduce the difficulty of optical assembly and reduce the overall manufacturing cost.

[0033] Please refer to Figure 1 The input beam is typically parallel or quasi-parallel, with a diameter of D and a circular pupil. After passing through the first mirror group 11a and the second mirror group 11b, the input beam is separated into beams in the X and Y directions. The incident angle of the X-direction beam onto the quartz rod is θx, resulting in an elliptical pupil. After homogenization by the quartz rod, the divergence angle of the outgoing beam is also θx, and the pupil shape remains elliptical. Then, through the mirror-symmetric third mirror group 11c and fourth mirror group 11d, the pupil is reshaped back into a circle, maintaining consistency with the input. The length of the first side of the quartz rod in the X direction is w, which is the longer side.

[0034] Figure 2 This is a schematic cross-sectional view of the optical structure of a variable-focus condenser lens system according to an embodiment of the present invention in the YZ direction; as shown. Figure 2 As shown, the input beam is generally parallel or quasi-parallel, with a diameter of D and a circular pupil. After passing through the first mirror group 11a and the second mirror group 11b, the collimated input beam is separated into beams in the X and Y directions. The incident angle of the Y-direction beam onto the quartz rod is θy, resulting in an elliptical pupil. After homogenization by the quartz rod, the divergence angle of the outgoing beam is also θy, and the pupil shape remains elliptical. Then, through the mirror-symmetric actions of the third mirror group 11c and the fourth mirror group 11d, the pupil is transformed back into a circle, consistent with the input. The length of the second side of the quartz rod in the Y direction is h, which is the shorter side. The Y-direction dimension h of the quartz rod is smaller than the X-direction dimension w, and the corresponding incident angle θy is also smaller than θx. According to the principle of uniform light distribution of quartz rods and related geometric optics knowledge, there must exist an optimal set of matching incident angles θx and θy such that the number of total internal reflections of the light beam in the X and Y directions within the quartz rod is the same. At this time, the pupil energy distribution is optimally balanced and the pupil performance is the best.

[0035] Figure 5 This is a schematic diagram of the beam path of a variable-focus condenser lens system according to an embodiment of the present invention; as shown... Figure 5 As shown, the beam of light, after being focused by the condenser (first mirror group 11a and second mirror group 11b), is converged from parallel light to an incident angle of θ before entering the quartz rod. Through simple geometric optics derivation, the following formula can be obtained:

[0036]

[0037] Where L is the length of the quartz rod, Φ is the end face dimension, n is the refractive index of the material, θ is the incident angle, and R is the length of the single total internal reflection period of the beam within the quartz rod. We can then conclude that:

[0038] N = L / R (2)

[0039] Where N is the total number of reflections of the light beam within the quartz rod.

[0040] For a quartz rod with a rectangular end face, to make the number of reflections in the X and Y directions equal, the R values ​​in both directions must be the same. The length of the first side of the quartz rod in the X direction is w, which is the long side Φx, and the length of the second side in the Y direction is h, which is the short side Φy. Since the dimensions of the long and short sides at the end face are not the same, i.e., Φx is not equal to Φy, there exists a set of solutions θx and θy such that Rx = Ry, thus ensuring that the pupil energy is distributed uniformly in both directions. In other words, the number of total internal reflections N of the light beam in the first and second side directions within the homogenizing unit 13 is the same.

[0041] By adjusting the incident angles θx and θy, Rx = Ry can be achieved. There are two methods to adjust the incident angles θx and θy. The first method is... Figure 1 and Figure 2 The adjustment of the first movable lens 12a, the second movable lens 12b, the third movable lens 12c, and the fourth movable lens 12d adjusts the first lens group 11a, the second lens group 11b, the third lens group 11c, and the fourth lens group 11d, thereby adjusting the incident angles θx and θy. The second method is... Figure 3 and Figure 4 The fifth movable lens 12e is adjusted, and the offset of the fifth movable lens 12e in the X and Y directions is finely adjusted to adjust the tilt of the light homogenizing unit 13, so as to change the angle of the beam incident on the light homogenizing unit 13, and change the incident angle θx and incident angle θy to obtain Rx=Ry.

[0042] The movable mechanism used in this embodiment can employ an open-loop or closed-loop automatic control system to achieve real-time adjustment of the pupil performance. It is worth noting that the first lens group 11a and the second lens group 11b are decoupled, and the third lens group 11c and the fourth lens group 11d are decoupled. The first lens group 11a and the fourth lens group 11d are coupled, while the second lens group 11b and the third lens group 11c are coupled. That is, the adjustment amount of the movable mechanism of the first lens group 11a is equal in magnitude but opposite in direction to the adjustment amount of the fourth lens group 11d, and the adjustment amount of the movable mechanism of the second lens group 11b is equal in magnitude but opposite in direction to the adjustment amount of the third lens group 11c.

[0043] The variable-focus condenser system provided in this embodiment is mainly suitable for the ultraviolet to deep ultraviolet spectral range, especially for i-line (i-line photoresist), KrF, and ArF lithography illumination systems. It can be widely used in 193nm to 365nm node technologies, and particularly in 248nm node technologies.

[0044] The variable-focus condenser lens system provided in this embodiment can balance the pupil energy distribution in different directions within the illumination subsystem of a lithography machine exposure system with a rectangular illumination field of view, without changing the shape of the illumination field of view or increasing the overall cost. This significantly improves the performance of the illumination pupil, including pupil ellipticity and polar balance. Specifically, it can solve the inherent problem of substandard pupil performance in the P8 / P8S illumination system, while improving the optical fabrication capabilities of the condenser lens, quartz rod, and diffractive optical element (DOE), and reducing costs.

[0045] This embodiment also provides a lithography apparatus, including any of the variable-focus condenser lens systems described above. This embodiment provides an illumination subsystem solution using a quartz rod as the system homogenization unit, applicable to step lithography machines, which features excellent performance, simple structure, and low manufacturing cost.

[0046] In summary, the variable-focus condenser lens system and lithography equipment provided by this invention include a light source unit, a homogenizing unit, and a first pupil adjustment unit. By adjusting the incident angle of the light beam entering the homogenizing unit, the single total internal reflection period length of the light beam in the direction of the first side and the direction of the second side within the homogenizing unit is the same. This improves the ellipticity and polar balance of the illumination pupil without changing the shape of the illumination field of view or increasing the overall cost. Furthermore, the first pupil adjustment unit located in front of the optical path of the homogenizing unit includes a first lens group and a second lens group, and the second pupil adjustment unit located behind the optical path of the homogenizing unit includes a third lens group and a fourth lens group. Each of the first, second, third, and fourth lens groups includes at least one movable mechanism, or a movable mechanism is provided at the incident end face of the homogenizing unit. The movable structures adjust the first, second, third, and fourth lens groups, or the homogenizing unit, to adjust the incident angle of the light beam entering the homogenizing unit, so that the single total internal reflection period length of the light beam in the direction of the first side and the direction of the second side within the homogenizing unit is the same. Furthermore, the homogenizing unit includes a quartz rod with a rectangular end face. Thus, in the case of a rectangular illumination field of view, without increasing cost, the problems of pupil ellipticity and poor polar balance caused by inconsistent width and height dimensions of the quartz rod end face are solved.

[0047] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to mutually. In addition, different parts between embodiments can also be combined with each other, and this invention does not limit this.

[0048] Furthermore, it should be understood that although the present invention has been disclosed above with reference to preferred embodiments, these embodiments are not intended to limit the present invention. For any person skilled in the art, many possible variations and modifications can be made to the technical solutions of the present invention based on the disclosed technical content, or equivalent embodiments can be modified accordingly, without departing from the scope of the present invention. Therefore, any simple modifications, equivalent changes, and modifications made to the above embodiments based on the technical essence of the present invention, without departing from the content of the present invention, shall still fall within the scope of protection of the present invention.

Claims

1. A variable-focus condenser lens system, characterized in that, The device includes a light source unit, a light homogenizing unit, and a first pupil adjustment unit. The end face of the light homogenizing unit includes a first side and a second side with unequal side lengths. The light source unit is used to emit a light beam, and the first pupil adjustment unit is used to adjust the incident angle of the light beam entering the light homogenizing unit so that the single total internal reflection period length of the light beam in the direction of the first side and the direction of the second side of the light homogenizing unit is the same.

2. The variable-focus condenser lens system as described in claim 1, characterized in that, It also includes a second pupil adjustment unit located behind the optical path where the light-diffusing unit is located. The second pupil adjustment unit includes a third lens group and a fourth lens group. The first pupil adjustment unit located in front of the optical path where the light-diffusing unit is located includes a first lens group and a second lens group.

3. The variable-focus condenser lens system as described in claim 2, characterized in that, The combined optical power of the first and fourth lens groups is zero in the X direction and positive and equal in the Y direction; the combined optical power of the second and third lens groups is positive and equal in the X direction and zero in the Y direction.

4. The variable-focus condenser lens system as described in claim 2, characterized in that, The first and fourth mirror groups are mirror-symmetric about the homogenizing unit, and the second and third mirror groups are mirror-symmetric about the homogenizing unit.

5. The variable-focus condenser lens system as described in claim 2, characterized in that, The first mirror group, the second mirror group, the third mirror group, and the fourth mirror group each include at least one movable mechanism, which is used to adjust the incident angle of the light beam entering the homogenizing unit.

6. The variable-focus condenser lens system as described in claim 2, characterized in that, The first lens group, the second lens group, the third lens group, and the fourth lens group each include at least one lens.

7. The variable-focus condenser lens system as described in claim 2, characterized in that, The first and second mirror groups are decoupled, and the third and fourth mirror groups are decoupled. The first and fourth mirror groups are coupled, and the second and third mirror groups are coupled. The coupling relationship is such that the adjustment amount of the movable mechanism of the first mirror group is equal in magnitude but opposite in direction to the adjustment amount of the fourth mirror group, and the adjustment amount of the movable mechanism of the second mirror group is equal in magnitude but opposite in direction to the adjustment amount of the third mirror group.

8. The variable-focus condenser lens system as described in claim 1, characterized in that, A movable mechanism is provided at the incident end face of the light homogenizing unit, which is used to adjust the incident angle of the light beam entering the light homogenizing unit.

9. The variable-focus condenser lens system as described in claim 1, characterized in that, The beam undergoes the same number of total internal reflections in the direction of the first side and the direction of the second side within the homogenizing unit.

10. The variable-focus condenser lens system as claimed in claim 1, characterized in that, The light-diffusing unit includes a quartz rod.

11. The variable-focus condenser lens system as described in claim 10, characterized in that, The end face of the quartz rod is rectangular.

12. A photolithography apparatus, characterized in that, Includes the variable-focus condenser lens system according to any one of claims 1-11.

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