Extreme Ultraviolet Radiation Source Module

Abstract

An extreme ultraviolet radiation source module comprises a target droplet generator configured to generate a plurality of target droplets; a first laser light source configured to generate a plurality of first laser pulses, the first laser pulses heat the target droplets to generate a plurality of target clouds; a second laser light source configured to generate a plurality of second laser pulses, the second laser pulses heat the target cloud to generate a plasma emitting extreme ultraviolet radiation; a third laser light source and a fourth laser light source, respectively configured to generate a first laser beam and a second laser beam, the first laser beam and the second laser beam are guided to a path of travel of the target cloud, and the first laser beam and the second laser beam are substantially parallel; and a monitor configured to receive the first laser beam and the second laser beam reflected by the target cloud.

Description

[0001] The present invention is a divisional application of the invention application with application date of August 23, 2018, application number of 2018109667729 and invention name of extreme ultraviolet radiation source module. Technical Field

[0002] An embodiment of the present invention relates to an extreme ultraviolet radiation source module and an extreme ultraviolet lithography system and method thereof. Background Art

[0003] The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced several generations of ICs, each with smaller and more complex circuits than the previous generation. During the evolution of ICs, functional density (i.e., the number of interconnected devices per wafer area) has generally increased, while geometric size (i.e., the smallest component (or line) that can be produced using a manufacturing process) has decreased. This shrinking process generally brings benefits by improving production efficiency and reducing associated costs. However, this shrinking process also increases the complexity of IC processing and manufacturing.

[0004] For example, there is an increased demand for performing higher resolution lithography processes. One lithography technique is extreme ultraviolet lithography (EUVL). EUVL uses scanners that use light in the extreme ultraviolet (EUV) region, which has a wavelength of about 1-100 nm. Some EUV scanners offer 4X reduced projection printing, which is similar to some optical scanners, except that EUV scanners use reflective rather than refractive optics, i.e., mirrors rather than lenses. One type of EUV light source is laser-produced plasma (LPP). LPP technology generates EUV light by focusing a high-power laser beam onto a plurality of small tin droplets to form a highly ionized plasma, producing EUV radiation of about 13.5 nm. The EUV light is then collected by an LPP collector and reflected by an optical device toward a lithography target, such as a wafer. LPP collectors are damaged and degraded by the effects of particles, ions, radiation, and, most severely, tin deposition. An embodiment of the present invention aims to improve the efficiency of the LPP EUV radiation source and reduce damage to the LPP collector. Summary of the invention

[0005] An extreme ultraviolet radiation source module comprises: a target droplet generator configured to generate a plurality of target droplets; a first laser light source configured to generate a plurality of first laser pulses, the first laser pulses heat the target droplets to generate a plurality of target clouds; a second laser light source configured to generate a plurality of second laser pulses, the second laser pulses heat the target cloud to generate a plasma emitting extreme ultraviolet radiation; a third laser light source and a fourth laser light source, respectively configured to generate a first laser beam and a second laser beam, the first laser beam and the second laser beam are guided to a path of travel of the target cloud, wherein the first laser beam and the second laser beam are substantially parallel; and a monitor configured to receive the first laser beam and the second laser beam reflected by the target cloud. BRIEF DESCRIPTION OF THE DRAWINGS

[0006] The embodiments of the present invention can be better understood according to the following detailed description and in conjunction with the accompanying drawings. It should be noted that, according to standard practice in the industry, the various components shown in the drawings are not necessarily drawn to scale. In fact, the sizes of various components may be arbitrarily enlarged or reduced to make the description clear.

[0007] Figure 1 is a schematic diagram illustrating an EUV lithography system having a laser produced plasma (LPP) EUV radiation source constructed in accordance with some embodiments.

[0008] Figure 2 is a schematic diagram illustrating an EUV radiation source in an EUV lithography system constructed according to some embodiments.

[0009] Figure 3 is a schematic diagram showing a mechanism for monitoring the speed of a target cloud cluster constructed according to some embodiments.

[0010] Figure 4 is a schematic diagram showing a method for calculating the velocity of a target cloud group according to some embodiments.

[0011] Figure 5 is a flow chart representing a method for controlling an LPP EUV radiation source constructed in accordance with some embodiments.

[0012] Figure 6 is a flow chart representing a photolithography process constructed in accordance with some embodiments.

[0013] Description of reference numerals:

[0014] 10~Photolithography system;

[0015] 12~Radiation source (extreme ultraviolet radiation source module);

[0016] 14 ~ illuminator;

[0017] 16~Photomask stage;

[0018] 18~light mask;

[0019] 20~projection optical module;

[0020] 22~Semiconductor substrate (or wafer);

[0021] 24~Substrate table;

[0022] 30~target droplet generator;

[0023] 31~excitation area;

[0024] 32~target droplet;

[0025] 34~Target cloud and fog;

[0026] 36~Laser Produced Plasma Collector (LPP Collector);

[0027] 38~Extreme ultraviolet radiation (EUV radiation);

[0028] 40~first laser light source;

[0029] 42~Laser pulse (pre-pulse; first laser pulse);

[0030] 50~second laser light source;

[0031] 52~Laser pulse (main pulse; second laser pulse);

[0032] 60~first laser beam generator;

[0033] 61~Laser light source (third laser light source);

[0034] 62~Laser beam (first laser beam);

[0035] 63~Laser light source (fourth laser light source);

[0036] 64~laser beam (second laser beam);

[0037] 70~first laser beam monitor (monitor);

[0038] 72, 74 ~ reflected laser beam;

[0039] 80~second laser beam generator;

[0040] 82~Laser beam;

[0041] 84~Reflected laser beam;

[0042] 86-second laser beam monitor (monitor);

[0043] 90~controller;

[0044] 100, 200 ~ method;

[0045] 102, 104, 106, 108, 110, 112, 114, 116 ~ operation;

[0046] 202, 204, 206, 208, 209, 210, 212 ~ operation;

[0047] A, B ~ position;

[0048] d1~distance;

[0049] P~direction;

[0050] |AB|, |AC|, |BC|~distance;

[0051] ~ speed;

[0052] t1, t2, Δt~time;

[0053] α, θ~angles. DETAILED DESCRIPTION

[0054] A plurality of different embodiments or demonstrations are provided below to implement different features of embodiments of the present invention. In order to simplify the present disclosure, a plurality of specific examples of components and configurations will be described below. Of course, these examples are only exemplary and are not limited thereto. For example, in the specification, the configuration of a first feature above or on a second feature may include an embodiment in which the first and second features are formed in direct contact, and may also include an embodiment in which other features are formed between the first and second features so that the first and second features cannot be in direct contact. In addition, the present specification may repeat reference numbers and / or letters in different examples. This repetition is for the brevity and clarity of the specification and does not itself specify the relationship between the different embodiments and / or configurations discussed.

[0055] In addition, spatially relative terms, such as "below", "below", "below", "above", "above", and the like, are used here for ease of description to describe the relationship of one element or feature relative to other elements or features as shown in the figures. The device may be oriented in other orientations (rotated 90 degrees or in other orientations), and the spatially relative descriptors used herein are interpreted accordingly. In addition, when "about", "approximately", etc. are used to describe numbers or numerical ranges, the term is intended to include numbers within the range of + / -10% of the stated number unless otherwise specified. For example, the term "about 5nm" includes a size range of 4.5nm to 5.5nm.

[0056] One embodiment of the present invention generally relates to extreme ultraviolet (EUV) lithography systems and methods. More specifically, one embodiment of the present invention relates to an apparatus and method for improving the efficiency of a laser produced plasma (LPP) EUV radiation source and mitigating contamination on an LPP collector in an LPP EUV radiation source. One challenge faced in existing EUV lithography systems is the inefficiency in generating EUV radiation, which directly affects the yield of wafers. An object of one embodiment of the present invention is to optimize the parameters of LPP EUV radiation sources in order to improve their EUV conversion efficiency. Another challenge is the degradation of the LPP collector or EUV collector. The LPP collector collects and reflects EUV radiation and contributes to the overall EUV conversion efficiency. However, it is damaged and degraded due to the effects of particle, ion, radiation and dust deposition. Therefore, another object of one embodiment of the present invention is to reduce dust deposition on the LPP collector, thereby increasing the service life.

[0057] Figure 1is a schematic diagram of a lithography system 10 constructed according to some embodiments. The lithography system 10 may also be collectively referred to as a scanner, which is operable to perform a lithography exposure process using a corresponding radiation source and exposure mode. In the present embodiment, the lithography system 10 is an extreme ultraviolet (EUV) lithography system, which is designed to expose a photoresist layer by EUV light (or EUV radiation). The photoresist layer is a material that is sensitive to EUV light. Because gas molecules absorb EUV light, the lithography system 10 is maintained in a vacuum environment to avoid EUV intensity loss. The EUV lithography system 10 uses a radiation source 12 to generate an EUV radiation 38, whose wavelength range is, for example, EUV light between about 1 nm and about 100 nm. In a specific example, the aforementioned radiation source 12 generates EUV radiation 38 having a wavelength centered at about 13.5 nm. Therefore, the radiation source 12 is also referred to as an EUV radiation source 12. In the present embodiment, the EUV radiation source 12 generates EUV radiation 38 using a dual-pulse laser-produced plasma (LPP) mechanism, which will be described in detail later.

[0058] The system 10 also employs an illuminator 14. In various embodiments, the illuminator 14 includes a plurality of reflective optical components, such as a single mirror or a mirror system having a plurality of mirrors, to direct EUV radiation 38 from the radiation source 12 to a mask stage 16, and in particular, a mask 18 mounted on the mask stage 16. The mask stage 16 is included in the lithography system 10.

[0059] In some embodiments, the aforementioned mask stage 16 includes an electrostatic chuck (electronic chuck) for fixing the mask 18. In the present disclosure, the terms mask, photomask and reticle are used interchangeably. In the present embodiment, the mask 18 is a reflective mask. An exemplary structure of the mask 18 includes a substrate having a low thermal expansion material (LTEM). In various examples, the LTEM includes SiO2 doped with TiO2, or other suitable materials with low thermal expansion. The mask 18 includes a reflective multilayer (ML) deposited on the substrate. The ML includes a plurality of film pairs, such as a molybdenum-silicon (Mo / Si) film pair (for example, a molybdenum layer is above or below a silicon layer in each film pair). Alternatively, the ML may include a molybdenum-beryllium (Mo / Be) film pair, or other suitable materials that can be configured to highly reflect EUV light. The mask 18 may also include a capping layer, such as ruthenium (Ru), disposed on the ML for protection. The mask 18 also includes an absorber layer, such as a tantalum nitride (TaBN) layer, deposited on the ML. The absorber layer is patterned to define the integrated circuit (IC) layer. Alternatively, another reflective layer may be deposited on the ML and patterned to define the IC layer, thereby forming an EUV phase shift mask.

[0060] The aforementioned lithography system 10 also includes a projection optical module (or projection optics box (POB)) 20 for imaging the pattern of the mask 18 onto a semiconductor substrate 22 fixed on a substrate stage 24 of the lithography system 10. In various embodiments, the POB 20 has reflective optical components (e.g., for EUV lithography systems). The light directed from the mask 18, and the image of the pattern defined on the mask 18, is collected by the POB 20. The illuminator 14 and the POB 20 are collectively referred to as an optical module of the lithography system 10.

[0061] In the present embodiment, the semiconductor substrate 22 is a semiconductor wafer, such as a silicon wafer or other types of wafers to be patterned. In the present embodiment, the semiconductor substrate 22 is coated with a photoresist layer that is sensitive to EUV light. The various components included above are integrated together and can be operated to perform a photolithography exposure process.

[0062] The lithography system 10 may also include other modules or modules integrated with (or coupled with) other modules. For example, the lithography system 10 may include a gas supply module that is configured to provide hydrogen gas to the radiation source 12. The hydrogen gas helps reduce contamination in the radiation source 12.

[0063] Figure 2A radiation source 12 is shown according to some embodiments. The radiation source 12 employs a dual-pulse laser produced plasma (LPP) mechanism to generate plasma and further generate EUV radiation from the plasma.

[0064] Reference Figure 2 The radiation source (or EUV source or extreme ultraviolet (EUV) radiation source module) 12 includes a target droplet generator 30, a first laser light source 40, a second laser light source 50, a LPP collector 36, a first laser beam generator 60, a first laser beam monitor 70, a second laser beam generator 80, a second laser beam monitor 86 and a controller 90. The components of the radiation source 12 will be further described below.

[0065] The target droplet generator 30 is configured to generate a plurality of target droplets 32. In one embodiment, the target droplets 32 are tin (Sn) droplets, i.e., droplets having tin or a tin-containing material, such as a eutectic alloy containing tin, such as lithium (Li) and xenon (Xe). In one embodiment, each of the plurality of target droplets 32 has a diameter of about 30 micrometers (μm). In one embodiment, the target droplets 32 are generated at a rate of about 50 kilohertz (kHz) and introduced into an excitation region 31 in the radiation source 12 at a speed of about 70 meters / second (m / s).

[0066] The aforementioned first laser light source 40 is configured to generate a plurality of laser pulses 42. The second laser light source 50 is configured to generate a plurality of laser pulses 52. In the present embodiment, the laser pulse 42 has a smaller intensity and a smaller spot size than the laser pulse 52. Therefore, the laser pulse 42 is also called a pre-pulse, and the laser pulse 52 is called a main pulse. The pre-pulse 42 is used to heat (or preheat) the target droplets 32 to generate a plurality of low-density target clouds 34, which are subsequently heated (or reheated) by the corresponding main pulse 52, thereby increasing the emission of EUV radiation 38. In the present embodiment, when the target cloud 34 generated by the pre-pulse 42 is heated by the main pulse 52, the main pulse 52 is referred to as the "corresponding" pre-pulse 42. The EUV radiation 38 is further reflected by the collector 36 and the EUV radiation 38 is focused for use in a lithography exposure process, such as Figure 3 In one embodiment, a droplet catcher (not shown) is installed opposite to the target droplet generator 30. The aforementioned droplet catcher is used to capture excess target droplets 32. For example, the two laser pulses 42 and 52 may intentionally miss some target droplets 32.

[0067] The collector 36 is designed with appropriate coating materials and shapes to serve as a reflector for collecting, reflecting and focusing EUV. In some embodiments, the collector 36 is designed to have an elliptical geometry. In some embodiments, the coating material of the collector 36 is similar to the reflective multilayer of the EUV mask 18. In some examples, the coating material of the collector 36 includes ML (e.g., a plurality of Mo / Si film pairs) and may further include a capping layer (e.g., Ru) coated on the ML to substantially reflect EUV radiation 38. In some embodiments, the collector 36 may also include a grating structure designed to effectively scatter laser beams and laser pulses directed toward the collector. For example, a silicon nitride layer is coated on the collector 36 and patterned to have a grating pattern. In the EUV lithography system 10( Figure 1 ) is the useful life of the collector 36. During the EUV production process, the reflective surface of the collector 36 is bombarded by various particles, ions, and radiation. Over time, the reflectivity of the collector 36 decreases due to particle accumulation, ion damage, oxidation, blistering, etc. Among them, particle (e.g., tin debris) deposition is a major factor. The method and apparatus of the present disclosure are to help reduce tin debris on the surface of the collector 36.

[0068] In various embodiments, the aforementioned pre-pulse 42 has a spot size of about 100 μm or less, and the main pulse 52 has a spot size of about 200 μm-300 μm, for example 225 μm. The laser pulses 42 and 52 are generated to have a certain driving power to achieve wafer mass production, for example, a throughput of 125 wafers per hour. In one embodiment, the pre-pulse 42 is equipped with a driving power of about 2 kilowatts (kW), and the main pulse 52 is equipped with a driving power of about 19 kW. In various embodiments, the total driving power of the laser pulses 42 and 52 is at least 20 kW, for example 27 kW. In one embodiment, the first laser light source 40 is a carbon dioxide (CO2) laser light source. In another embodiment, the first laser light source 40 is a neodymium-dopedyttrium aluminum garnet (neodymium-dopedyttrium aluminum garnet, Nd:YAG) laser light source. In one embodiment, the second laser light source 50 is a CO2 laser light source.

[0069] The pre-pulse 42 and the main pulse 52 are directed into the excitation region 31 through windows (or lenses) 44 and 54, respectively. The aforementioned windows 44 and 54 are made of suitable materials that are substantially transparent to the respective laser pulses. The pre-pulse 42 and the main pulse 52 are directed toward the target droplet 32 ​​and the target cloud 34 at appropriate angles to obtain the best EUV conversion efficiency. For example, the pre-pulse 42 can be directed toward the target droplet 32 ​​at an angle (e.g., 5 degrees) that deviates from the normal by a few degrees to interact with it. The main pulse 52 is also properly aligned with the target cloud 34 to obtain the maximum EUV conversion efficiency.

[0070] The generation of the aforementioned pre-pulse 42 and the main pulse 52 is synchronized with the generation of the target droplet 32. In one embodiment, the above synchronization is achieved by using a second laser beam generator 80 and a laser beam monitor 86. The second laser beam generator 80 is configured to generate a laser beam 82, which is directed to the path of travel of the target droplet 32. When the target droplet 32 ​​moves along the path, the laser beam 82 is reflected by the target droplet 32, and the monitor 86 receives the reflected laser beam 84, and the monitor 86 notifies the controller 90 of the existence of the target droplet 32. Thereafter, the controller 90 notifies the laser light source 40 to initiate a trigger for generating the pre-pulse 42. In one embodiment, the laser beam monitor 86 can directly notify the laser light source 40 without involving the controller 90.

[0071] When the target droplet 32 ​​moves through the excitation region 31 (eg Figure 3 As shown, where the target droplets 32 move in the X direction), the pre-pulse 42 heats the target droplets 32 (in the Z direction) and converts them into a low-density target cloud 34. Figure 3 In the embodiment, the X direction and the Z direction are perpendicular. In an alternative embodiment, the X direction and the Z direction may be non-perpendicular, for example, with an inner angle of 85 degrees. The delay between the pre-pulse 42 and the main pulse 52 is controlled by the controller 90 to allow the target cloud 34 to form and expand. The method and apparatus using the present embodiment can adjust the delay so that when the main pulse 52 heats the target cloud 34, the target cloud 34 expands to an optimal size and geometry. If the target cloud 34 is too small (at the target size), the main pulse 52 may not be able to fully convert them into EUV irradiated plasma, thereby reducing EUV conversion efficiency. If the target cloud 34 is too large, the main pulse 52 may miss some parts and become a contaminant on the LPP collector 36. In addition, the energy level of the pre-pulse 42 (which determines the speed of the target cloud along the Z direction) is also appropriately controlled by the controller 90 so that the target cloud 34 reaches the appropriate area of ​​the main pulse 52. If the target cloud 34 is only partially heated by the main pulse 52 , not only will the EUV conversion efficiency be reduced, but excessive tin debris will also be deposited on the collector 36 .

[0072] In the present embodiment, the first laser beam generator 60 and the laser beam monitor 70 are configured to monitor the speed of the target cloud 34 in the Z direction. The controller 90 uses the monitored speed to adjust the energy level of the pre-pulse 42, the energy level of the main pulse 52, the delay between the pre-pulse 42 and the corresponding main pulse 52, other parameters of the laser light sources 40 and 50, or a combination thereof. By optimizing one or more of the above parameters, the EUV conversion efficiency of the EUV source 12 and the life of the collector 36 can be improved.

[0073] See also Figure 3 In the present embodiment, the first laser beam generator 60 includes a laser light source 61 (third laser light source) configured to generate a laser beam 62 (first laser beam) and a laser light source 63 (fourth laser light source) configured to generate a laser beam 64 (second laser beam). When approaching a straight line, the laser beams 62 and 64 are parallel to each other and have a distance d1, and this distance d1 is measured on the same plane where the two laser beams 62 and 64 are located along a direction perpendicular to the two laser beams 62 and 64. When considering the spot size and scattering effect of the laser beams 62 and 64, the above approximate value can be obtained along the central axis of each laser beam. The first and second laser beams 62 and 64 may have the same or different wavelengths. In addition, the first and second laser beams 62 and 64 may be in the visible light band or the invisible light band, such as infrared or near-infrared. In some embodiments, in reference to Figure 3 For analysis of the following discussion, laser beams 62 and 64 are substantially parallel to each other, ie, they are considered parallel.

[0074] Figure 3 The target droplet 32 ​​enters and passes through the excitation region 31 ( Figure 2 ) at different times and positions. When the target droplet 32 ​​is released from the target droplet generator 30, the target droplet 32 ​​moves at an initial speed. Move. Speed is along Figure 1 In one embodiment, the speed The magnitude of is about 70 m / s, which can be measured and determined. After the target droplet 32 ​​is hit by the pre-pulse 42, its velocity changes in both direction and magnitude. The new velocity of the target droplet 32 It’s speed The speed caused by the pre-pulse 42 Speed Along the Z direction. In this embodiment, the Z direction is perpendicular to the X direction.

[0075] Laser beams 62 and 64 are directed to the path of the target cloud 34. When laser beam 62 strikes the target cloud 34 (at position A and time t1), laser beam 62 is reflected as laser beam 72 (reflected first laser beam). When laser beam 64 strikes the target cloud 34 (at position B and time t2), the laser beam is reflected as laser beam 74 (reflected second laser beam). In the present embodiment, the energy levels of laser beams 62 and 64 are configured to be low enough so that they do not cause any change in the speed of the target cloud 34, and high enough so that the reflected laser beams 72 and 74 can be detected by laser beam monitor 70. Laser beam monitor 70 receives reflected laser beams 72 and 74, and calculates the time Δt=t2-t1 that the target cloud 34 travels from position A to position B. In one embodiment, monitor 70 calculates time Δt using the time of actually receiving reflected laser beams 72 and 74 as an approximation. This approximation is sufficiently accurate because, given the velocities of laser beams 72 and 74, the different paths traveled by reflected laser beams 72 and 74 are negligible in the calculation.

[0076] Then, the controller 90 uses the time Δt and other parameters such as the distance d1, the angle between the laser beams 62 and 64 and the X direction, and the speed. Other information about the size of the This will be later Figure 4 Further explanation.

[0077] Controller 90 use speed The size (i.e., the speed of the target cloud 34 along the Z direction) ) to adjust various parameters in the EUV source 12. For example, the controller 90 may use it to adjust the delay between the pre-pulse 42 and the corresponding main pulse 52. In one embodiment, an initial delay between the pre-pulse 42 and the corresponding main pulse 52 may be set based on an empirical value (e.g., obtained from the past). Then, using the calculated speed To adjust the delay in time so as to generate (or trigger) the main pulse 52 at the appropriate time to maximize the EUV conversion efficiency. For another example, the controller 90 may use the calculated speed To adjust the energy level of the pre-pulse 42 in order to optimize the speed To further illustrate, the optimal or near-optimal speed of the target cloud 34 along the Z direction may be determined experimentally and set in the controller 90 as a predetermined speed or predetermined speed range. If the calculated speed is greater than the predetermined speed, the controller 90 will notify the laser light source 40 to reduce the energy level in the pre-pulse 42, which will then reduce the speed of the target cloud 34 along the Z direction. If the speed is less than the predetermined speed, the controller 90 will notify the laser light source 40 to increase the energy level in the pre-pulse 42, which will then increase the speed of the target cloud 34 along the Z direction. This will increase the speed of the target cloud 34 is maintained within a predetermined range to maximize EUV conversion efficiency and reduce contamination on the LPP collector 36 .

[0078] The aforementioned monitor 70 is configured to distinguish between laser beams 72 and 74 reflected by different target clouds 34. This avoids detection aliasing, where laser beams reflected by different target clouds 34 are used to calculate the time Δt. In an embodiment, the two laser beams 72 and 74 have different wavelengths. Alternatively, the two laser beams 72 and 74 have the same wavelength. The monitor 70 can use the wavelength (or wavelengths) of the laser beams 72 and 74 and other information to avoid detection aliasing. For example, the target droplet generator 30 can be configured to generate target droplets 32 at intervals much greater than the estimated time Δt. The monitor 70 can then use such information to appropriately remove aliasing, for example, by removing the calculated time Δt that is out of range.

[0079] Figure 4 shows the speed used to calculate an example In this embodiment, the speed In the X direction, the speed In the Z direction perpendicular to the X direction, the speed Then along a direction P that forms an angle α with the X direction.

[0080]

[0081] From time t1 to time t2, the target cloud 34 travels a distance |AC| in the X direction and a distance |BC| in the Z direction, resulting in a total distance |AB| in the P direction (neglecting gravity and other forces including the laser beam 62 applied to the target cloud 34). In addition, the laser beams 62 and 64 are parallel and have a distance d1 between them, and form an angle θ with the X direction. From the following equations (2) and (3):

[0082]

[0083] It can be deduced that:

[0084]

[0085] From equation (4), we can deduce:

[0086]

[0087] From equations (1) and (5), we can deduce:

[0088]

[0089] When the parameters v1, d1 and θ are known, the speed v3 can be calculated according to equation (6) by measuring the time Δt (for example, by the laser beam monitor 70). In one embodiment, the speed v1 can be determined or preset by the laser light source 40. For example, in one embodiment, the speed v1 can be set to approximately 70 m / s. The distance d1 and the angle θ can be determined by configuring the laser light sources 61 and 63. In one embodiment, the angle θ is set to 0 degrees, where the laser beam 62 / 64 travels in the X direction. In another embodiment, the angle θ is set to 180 degrees, where the laser beam 62 / 64 travels in the opposite direction of the X direction. In any of the above embodiments, equation (6) can be simplified to:

[0090]

[0091] In systems where the X and Z directions are not perpendicular, pre-pulse 42 also provides a velocity component in the X direction to target cloud 34. In such systems, equation (7) can still be used, and equation (6) may need to be adjusted to account for the contribution of pre-pulse 42 in the X direction. In some embodiments, laser beams 62 and 64 are substantially parallel to each other, i.e., their non-parallel angle in excitation region 31 is negligible for the above analysis.

[0092] Through the aforementioned disclosed system including the first laser beam generator 60 , the laser beam monitor 70 and the controller 90 , the EUV source 12 is able to control various parameters in the laser light sources 40 and 50 to optimize EUV conversion efficiency and minimize contamination on the LPP collector 36 .

[0093] Figure 5 A method 100 for generating EUV radiation according to the present embodiment is shown. Additional operations may be provided before, during, and after the method 100, and some of the operations described may be replaced, deleted, or moved for other embodiments of the method. The method 100 is an example, and the embodiments of the present invention are not limited thereto except as expressly set forth in the claims. The method 100 is described below in conjunction with the EUV source 12, as shown in FIGS. 2 and 3.

[0094] In operation 102, the method 100 described above uses, for example, a target droplet generator 30 ( Figure 2 ) to generate a plurality of target droplets. The target droplets may include a material containing tin and are introduced into the excitation region at a predetermined speed (eg, about 70 m / s) and along a first direction.

[0095] In operation 104, the method 100 heats the target droplets by a plurality of first laser pulses to generate a plurality of target clouds. For example, the first laser pulses may be generated by the first laser light source 40 ( Figure 2 ).

[0096] In operation 106, the method 100 heats the target cloud by a plurality of second laser pulses to generate EUV irradiated plasma. For example, the second laser pulses may be generated by the second laser light source 50 ( Figure 2 ).

[0097] In operation 108, the method 100 directs the first and second laser beams toward the target cloud. For example, the first and second laser beams may be generated by the first laser beam generator 60 (FIGS. 2 and 3). In this embodiment, the first and second laser beams are parallel or substantially parallel to each other and are directed along a second direction. In one embodiment, the first and second directions are parallel (i.e., they form an angle of 0° or 180°). In another embodiment, the first and second directions form an angle greater than 0° and less than 180°.

[0098] In operation 110, the method 100 receives the first and second laser beams after they are reflected by the target cloud. For example, the reflected first and second laser beams may be received by the laser beam monitor 70 (FIGS. 2 and 3).

[0099] In operation 112, the method 100 calculates a delay between the reflected first laser beam and the reflected second laser beam. For example, the delay may be calculated by the laser beam monitor 70 or the controller 90 (FIGS. 2 and 3).

[0100] In operation 114, the method 100 calculates the velocity of the target cloud along the direction in which the first laser pulse travels. For example, the method 100 may calculate the velocity of the target cloud using a set of data including the velocity of the target droplet along the first direction, the distance between the first and second laser beams, the angle between the first and second directions, and the delay between the reflected first and second laser beams. For example, the method 100 may calculate the velocity of the target cloud using equation (6) or (7).

[0101] In operation 116, the aforementioned method 100 adjusts one or more parameters of the first and second laser light sources based on the calculated speed of the target cloud. For example, when the calculated speed of the target cloud is greater than (less than) a predetermined expected speed, the method 100 may reduce (increase) the energy level in the first laser pulse. For another example, the method 100 may adjust the delay between the first laser pulse and the corresponding second laser pulse based on the calculated speed of the target cloud.

[0102] Figure 6 2 is a flow chart of a method 200 of an EUV lithography process implemented by the EUV lithography system 10 constructed according to some embodiments. Additional operations may be provided before, during, and after the method 200, and some of the operations described may be replaced, deleted, or moved for other embodiments of the method. The method 200 is an example, and it is not intended to limit the present disclosure beyond what is expressly recited in the claims.

[0103] The aforementioned method 200 includes operation 202, which loads an EUV mask such as the mask 18 to the lithography system 10, which is operable to perform an EUV lithography exposure process. The mask 18 contains an IC pattern to be transferred to a semiconductor substrate (e.g., wafer 22). Operation 202 may also include various steps, such as fixing the mask 18 on the mask stage 16 and aligning it.

[0104] The method 200 described above includes an operation 204 of loading a wafer 22 into a lithography system 10. The wafer 22 is coated with a photoresist layer. In the present embodiment, the photoresist layer is sensitive to EUV radiation from a radiation source 12 of the lithography system 10.

[0105] The aforementioned method 200 includes an operation 206 of configuring the EUV radiation source 12. Operation 206 includes configuring the target droplet generator 30, configuring the first laser light source 40, configuring the second laser light source 50, configuring the first laser beam generator 60, configuring the laser light monitor 70, and configuring the controller 90. The target droplet generator 30 is configured to generate target droplets 32 having appropriate materials, appropriate sizes, appropriate speeds, and appropriate moving speeds and directions. The first laser light source 40 is configured to generate pre-pulses 42. The second laser light source 50 is configured to generate a main pulse 52 at a predetermined time after the corresponding pre-pulse 42. The first laser beam generator 60 is configured to generate two lasers 62 and 64, which are parallel or substantially parallel to each other. The laser beam monitor 70 is configured to receive the laser beams 62 and 64 after they are reflected by the target cloud, and calculate the delay between the reflected laser beams 72 and 74. The controller 90 is configured to calculate the speed of the target cloud, and the speed is calculated using the delay between the reflected laser beams 72 and 74 and other information. Controller 90 may be configured with a predetermined range of expected velocities of the target cloud.

[0106] The foregoing method 200 includes an operation 208 by performing a lithography exposure process on a wafer 22 in a lithography system 10. In operation 208, the target droplet generator 30 and the laser light sources 40 and 50 are started and operated according to operation 208. The pre-pulse 42 heats the target droplet 32 ​​to generate a target cloud 34. The main pulse 52 heats the target cloud 34, and the target cloud 34 generates a plasma that emits EUV radiation. During operation 208, the EUV radiation generated by the radiation source 12 is irradiated on the mask 18 (through the illuminator 14) and further projected on the photoresist layer coated on the wafer 22 (through the POB 20), thereby forming a latent image on the photoresist layer. In some embodiments, the lithography exposure process is implemented in a scanning mode.

[0107] The aforementioned method 200 includes an operation 209, which controls the EUV radiation source 12 to optimize the EUV conversion efficiency by monitoring the speed of the target cloud. During operation 209, the first and second laser beams 62 and 64 are directed toward the target cloud 34. The laser beam monitor 70 receives the reflected first and second laser beams 72 and 74 and calculates the delay between the reflected laser beams 72 and 74. The controller 90 calculates the speed of the target cloud using the delay between the reflected laser beams 72 and 74 and other information. The first laser light source 40 can adjust the energy level of the pre-pulse 42 based on the calculated speed of the target cloud. The second laser light source 50 can adjust the delay between the main pulse 52 and the corresponding pre-pulse 42 based on the calculated speed of the target cloud. Operation 209 ensures that the target cloud 34 has an optimal shape and size when heated by the main pulse 52, thereby improving the EUV conversion efficiency and reducing the amount of debris on the LPP collector 36. In this embodiment, operations 208 and 209 are performed simultaneously.

[0108] The aforementioned method 200 may include other operations to complete the photolithography process. For example, the method 200 may include an operation 210 of developing the exposed photoresist layer to form a plurality of defined openings thereon. Specifically, after the photolithography exposure process in operation 208, the wafer 22 is transferred from the photolithography system 10 to a developing unit to perform a developing process on the photoresist layer. The method 200 may also include other operations, such as various baking steps. For example, the method 200 may include a post-exposure baking (PEB) step between operations 208 and 210.

[0109] The method 200 may further include other operations, such as operation 212, to perform a manufacturing process on the wafer through the opening of the photoresist pattern. In one example, the manufacturing process includes an etching process using the photoresist pattern as an etching mask on the wafer 22. In another example, the manufacturing process includes an ion implantation process using the photoresist pattern as an implantation mask on the wafer 22.

[0110] Although not intended to be limiting, one or more embodiments of the present disclosure provide many benefits for the manufacture of semiconductor devices. For example, embodiments of the present disclosure provide devices and methods for increasing EUV conversion efficiency while reducing contamination on LPP collectors. Embodiments of the present disclosure may be implemented or integrated into existing EUV lithography systems.

[0111] In an exemplary aspect, the present disclosure relates to an ultraviolet (EUV) radiation source module. The EUV radiation source module includes a target droplet generator configured to generate a plurality of target droplets; a first laser light source configured to generate a plurality of first laser pulses that heat the target droplets to generate a plurality of target clouds; a second laser light source configured to generate a plurality of second laser pulses that heat the target cloud to generate a plasma emitting EUV radiation; a third and a fourth laser light source, respectively, for generating a first and a second laser beam, which are directed to a path of travel of the target cloud, wherein the first and second laser beams are substantially parallel; and a monitor configured to receive the first and second laser beams reflected by the target cloud.

[0112] In one embodiment, the EUV radiation source module further includes a controller configured to adjust at least one parameter of the first and second laser light sources based on a set of data including a distance between the first and second laser beams and a delay between the first and second laser beams when the monitor receives the second laser beam. In another embodiment, the aforementioned data also includes an angle between the travel direction of the first and second laser beams and another travel direction of the target droplet. In another embodiment, the aforementioned data also includes the speed of the target droplet. In another embodiment, the angle is configured to be 0 degrees or 180 degrees. In some embodiments, at least one parameter includes an energy level of the first laser pulse. In some embodiments, the aforementioned at least one parameter includes a delay between one of the first laser pulses and a corresponding one of the second laser pulses, the second laser pulse heating a target cloud generated by one of the first laser pulses.

[0113] In one embodiment, the EUV radiation source module further comprises a collector configured to collect and reflect EUV radiation. In one embodiment, the EUV radiation source module further comprises a fifth laser light source configured to generate a third laser beam, the third laser beam being directed onto the path of the target droplet; and another monitor configured to receive the third laser beam reflected by the target droplet.

[0114] In another exemplary aspect, the present disclosure relates to an ultraviolet (EUV) lithography system. The EUV lithography system includes a radiation source. The radiation source includes a target droplet generator configured to generate a plurality of target droplets; a first laser light source configured to generate a plurality of first laser pulses that heat the target droplets to generate a plurality of target clouds; a second laser light source configured to generate a plurality of second laser pulses that heat the target cloud to generate a plasma emitting EUV radiation; a third and a fourth laser light source, respectively, for generating a first and a second laser beam, which are directed to a path of travel of the target cloud, wherein the first and the second laser beams are parallel; a monitor configured to receive the first and the second laser beams reflected by the target cloud; a collector for collecting and reflecting EUV radiation. The EUV lithography system also includes a mask stage configured to hold an EUV mask; a wafer stage for holding a semiconductor wafer; and one or more optical modules configured to direct EUV radiation from a radiation source to image an integrated circuit (IC) pattern defined on the EUV mask onto the semiconductor wafer.

[0115] In one embodiment, the EUV lithography system further comprises a controller configured to calculate a first velocity of the target cloud along the direction of travel of the first laser light pulse. In another embodiment, the controller is further configured to calculate the first velocity based on a set of data, the data set comprising a distance between the first and second laser beams and a delay between the first and second laser beams when received by the monitor. In another embodiment, the set of data further comprises an angle between the directions of travel of the first and second laser beams and another direction of travel of the target droplet. In another embodiment, the controller is further configured to adjust the energy level of the first laser pulse based at least on the first velocity. In yet another embodiment, the controller is configured to adjust a delay between one of the first laser pulses and a corresponding one of the second laser pulses, the second laser pulse heating a target cloud generated by one of the first laser pulses.

[0116] In another exemplary aspect, the present disclosure relates to a method for extreme ultraviolet (EUV) lithography. The method includes generating a target droplet; heating the target droplet by using a first laser pulse generated by a first laser light source to generate a target cloud; directing first and second laser beams to a path of the target cloud, wherein the first and second laser beams are parallel; receiving the first and second laser beams reflected by the target cloud; and heating the target cloud by a second laser pulse generated by a second laser light source to generate EUV radiation plasma.

[0117] In one embodiment, the method further comprises calculating a delay between the time when the first laser beam is reflected by the target cloud and the time when the second laser beam is reflected by the target cloud. In another embodiment, the method further comprises calculating a first speed of the target cloud along the direction of travel of the first laser pulse. In another embodiment, the method further comprises adjusting an energy level of the first laser light source. In yet another embodiment, the method further comprises adjusting a trigger delay between the first laser light source and the second laser light source.

[0118] The foregoing text summarizes the features of many embodiments, so that those skilled in the art can better understand the embodiments of the present invention from various aspects. Those skilled in the art should understand and can easily design or modify other processes and structures based on the embodiments of the present invention, and thereby achieve the same purpose and / or achieve the same advantages as the embodiments introduced herein. Those skilled in the art should also understand that these equivalent structures do not depart from the inventive concept and scope of the embodiments of the present invention. Various changes, substitutions or modifications may be made to the embodiments of the present invention without departing from the inventive concept and scope of the embodiments of the present invention.

Claims

1. An extreme ultraviolet radiation source module, comprising: A target droplet generator is configured to generate a plurality of target droplets to an excitation region, wherein a travel path of the target droplets is along a first direction; a first laser light source configured to generate a plurality of first laser pulses to the excitation region, wherein the first laser pulses heat the target droplets at a first point in the excitation region to generate a plurality of target clouds, wherein a travel path of the target clouds is along a second direction different from the first direction; a second laser light source configured to generate a plurality of second laser pulses to the excitation region, the second laser pulses heating the target clouds at a second point in the excitation region to generate a plasma emitting extreme ultraviolet radiation; a third laser light source and a fourth laser light source, respectively configured to generate a first laser beam and a second laser beam, the first laser beam and the second laser beam being directed to the travel path of the target clouds between the first point and the second point in the excitation region, wherein the first laser beam and the second laser beam are parallel; and A monitor is configured to receive the first laser beam and a second laser beam reflected by the target clouds to monitor a speed of the target clouds in a third direction along which the first laser pulses travel, the third direction being different from the first direction and the second direction.

2. The extreme ultraviolet radiation source module of claim 1, further comprising: A controller is configured to adjust at least one parameter of the first laser light source and the second laser light source based on a set of data, the set of data including a distance between the first laser beam and the second laser beam and a delay between the first laser beam and the second laser beam when received by the monitor.

3. The extreme ultraviolet radiation source module of claim 2, wherein the set of data further comprises an angle between a direction of travel of the first and second laser beams and the first direction of travel of the target droplets. 4 . The extreme ultraviolet radiation source module of claim 3 , wherein the set of data further comprises a velocity of the target droplets along the first direction.

5. The extreme ultraviolet radiation source module of claim 3, wherein the angle is configured to be 0 degrees or 180 degrees.

6. The extreme ultraviolet radiation source module of claim 2, wherein: The at least one parameter includes an energy level of the first laser pulses.

7. The EUV radiation source module of claim 2, wherein the at least one parameter comprises a delay between one of the first laser pulses and a corresponding one of the second laser pulses, the one of the second laser pulses heating a target cloud generated by the one of the first laser pulses.

8. The extreme ultraviolet radiation source module of claim 1, further comprising: a fifth laser light source configured to generate a third laser beam directed onto the travel path of the target droplets before the excitation region; as well as Another monitor is configured to receive the third laser beam reflected by the target droplets to monitor a speed of the target droplets along the first direction.

9. An extreme ultraviolet lithography system, comprising: A radiation source, wherein the radiation source comprises: A target droplet generator configured to generate a plurality of target droplets to an excitation region, wherein a travel path of the target droplets is along a first direction; a first laser light source configured to generate a plurality of first laser pulses to the excitation region, wherein the first laser pulses heat the target droplets at a first point in the excitation region to generate a plurality of target clouds, wherein a travel path of the target clouds is along a second direction different from the first direction; a second laser light source configured to generate a plurality of second laser pulses to the excitation region, the second laser pulses heating the target clouds at a second point in the excitation region to generate plasma emitting EUV radiation; a third laser light source and a fourth laser light source, configured to generate a first laser beam and a second laser beam, respectively, the first laser beam and the second laser beam being directed to the travel path of the target clouds between the first point and the second point in the excitation region, wherein the first laser beam and the second laser beam are parallel; a monitor configured to receive the first laser beam and the second laser beam reflected by the target clouds to monitor a first speed of the target clouds in a third direction along which the first laser pulses travel, the third direction being different from the first direction and the second direction; and a collector configured to collect and reflect the EUV radiation; a mask stage configured to hold an extreme ultraviolet mask; a wafer stage configured to hold a semiconductor wafer; and One or more optical modules are configured to direct the EUV radiation from the radiation source to image an integrated circuit pattern defined on the EUV reticle onto the semiconductor wafer.

10. The EUV lithography system of claim 9, further comprising: A controller is configured to calculate the first speeds of the target clouds along the third direction in which the first laser pulses travel.

11. The EUV lithography system of claim 10, wherein the controller is further configured to calculate the first speed based on a set of data comprising a distance between the first laser beam and the second laser beam and a delay between the first laser beam and the second laser beam when received by the monitor. 12 . The EUV lithography system as claimed in claim 11 , wherein the set of data further comprises an angle between a direction of travel of the first laser beam and the second laser beam and the first direction in which the target droplets travel.

13. The EUV lithography system of claim 10, wherein the controller is further configured to adjust an energy level of the first laser pulse based at least on the first speed.

14. The EUV lithography system of claim 10, wherein the controller is further configured to adjust a delay between one of the first laser pulses and a corresponding one of the second laser pulses, wherein the corresponding one of the second laser pulses heats a target cloud generated by the one of the first laser pulses.

15. A method of extreme ultraviolet lithography, comprising: Generating a target droplet to an excitation region, wherein a moving path of the target droplet is along a first direction; Heating the target droplet at a first point in the excitation region by using a first laser pulse generated by a first laser light source to generate a target cloud, wherein a travel path of the target cloud is along a second direction different from the first direction; heating the target cloud at a second point in the excitation region by a second laser pulse generated by a second laser light source to generate EUV radiation plasma; directing a first laser beam and a second laser beam onto a path of travel of the target cloud between the first point and the second point in the excitation region, wherein the first laser beam and the second laser beam are parallel; and The first laser beam and the second laser beam reflected by the target cloud are received to monitor a first velocity of the target cloud along a third direction of the first laser pulse, the third direction being different from the first direction and the second direction.

16. The method of extreme ultraviolet lithography according to claim 15, further comprising: Calculating a delay between the first laser beam being reflected by the target cloud and the second laser beam being reflected by the target cloud; as well as The first velocity of the target cloud group along the third direction of the first laser pulse is calculated.

17. The method of extreme ultraviolet lithography according to claim 16, further comprising: An energy level of the first laser light source is adjusted.

18. The method of extreme ultraviolet lithography according to claim 16, further comprising: A trigger delay between the first laser light source and the second laser light source is adjusted.

19. A method of extreme ultraviolet lithography, comprising: Generating a target droplet to an excitation region, wherein a moving path of the target droplet is along a first direction; Heating the target droplet in the excitation region by a first laser pulse to generate a target cloud, wherein a moving path of the target cloud is along a second direction different from the first direction; Directing a first laser beam and a second laser beam onto the travel path of the target cloud in the excitation region; as well as The first laser beam and the second laser beam reflected by the target cloud are received to monitor a velocity of the target cloud along a third direction of the first laser pulse, the third direction being different from the first direction and the second direction.

20. The method of extreme ultraviolet lithography as claimed in claim 19, further comprising: A delay between the first laser beam being reflected by the target cloud and the second laser beam being reflected by the target cloud is calculated.

21. The method of extreme ultraviolet lithography of claim 20, wherein the delay is approximated using another delay between when the first laser beam reflected by the target cloud is received and when the second laser beam reflected by the target cloud is received.

22. The method of extreme ultraviolet lithography according to claim 20, further comprising: An energy level of the first laser pulse is adjusted based on at least information derived from the delay.

23. The method of extreme ultraviolet lithography as claimed in claim 19, further comprising: The target cloud is heated in the excitation region using a second laser pulse having a higher drive power than the first laser pulse.

24. The method of extreme ultraviolet lithography as claimed in claim 23, further comprising: Calculating a first delay between the first laser beam reflected by the target cloud and the second laser beam reflected by the target cloud; as well as A second delay between when the first laser pulse heats the target droplet and when the second laser pulse heats the target cloud is adjusted based on information derived from at least the first delay.

25. An extreme ultraviolet radiation source comprising: A target droplet generator configured to generate a plurality of target droplets to an excitation region, wherein a travel path of the target droplets is along a first direction; A first laser light source is configured to generate a plurality of first laser pulses to the excitation region, wherein the first laser pulses heat the target droplets in the excitation region to generate a plurality of target clouds, wherein a travel path of the target clouds is along a second direction different from the first direction; a second laser light source and a third laser light source, configured to respectively generate a first laser beam and a second laser beam directed onto the travel path of the target clouds in the excitation region; and A monitor is configured to receive the first laser beam and the second laser beam reflected by the target clouds to monitor a speed of the target clouds along a third direction of the first laser pulses, the third direction being different from the first direction and the second direction.

26. The extreme ultraviolet radiation source of claim 25, further comprising: A controller is configured to adjust at least one parameter of the first laser light source based on information including a delay between when the monitor receives the first laser beam and when the monitor receives the second laser beam.

27. The extreme ultraviolet radiation source of claim 26, wherein the information further comprises a speed at which the target droplets travel, a distance between the first laser beam and the second laser beam, or an angle between a direction of travel of the first laser beam and the second laser beam and the first direction in which the target droplets travel.

28. The extreme ultraviolet radiation source of claim 25, further comprising: A fourth laser light source is configured to generate a plurality of second laser pulses, which heat the target clouds in the excitation region to generate plasma emitting extreme ultraviolet radiation.

29. A method of extreme ultraviolet lithography, comprising: Generating a target droplet to an excitation region, wherein a moving path of the target droplet is along a first direction; Using a first laser light source to generate a first laser pulse; Heating the target droplet at a first point in the excitation region by the first laser pulse to generate a target cloud, wherein a travel path of the target cloud is along a second direction different from the first direction; Using a second laser light source to generate a second laser pulse; heating the target cloud at a second point in the excitation region using the second laser pulse; Derived a velocity of the target cloud in the excitation region along a third direction of travel of the first laser pulse, wherein the third direction is different from the first direction and the second direction; and Information including the velocity is used to adjust at least one parameter of the first laser source and an energy level of the second laser source so that when the second laser pulse heats the target cloud at the second point in the excitation region, the target cloud expands to an optimal size and geometry.

30. The method of extreme ultraviolet lithography of claim 29, wherein the derivation of the velocity of the target cloud comprises: generating a first laser beam and a second laser beam parallel to each other; directing the first laser beam and the second laser beam to the target cloud in the excitation region; and The first laser beam and the second laser beam reflected by the target cloud are received.

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