System, software application, and method for dose uniformity improvement

Abstract

This disclosure relates to methods, systems, and apparatus for improving dose uniformity in photolithography systems. The method includes projecting a written light beam from a projection unit toward a mask to form a plurality of incident lights; adjusting the projection unit to generate an incident angle distribution corresponding to the incident lights; focusing the plurality of incident lights toward a photoresist layer disposed above a substrate using a lens; removing multiple portions of the photoresist layer to form an element pattern; and forming a structure on the substrate corresponding to the element pattern. The mask has a mask pattern corresponding to the element pattern. By focusing the plurality of incident lights toward the photoresist, the oscillation curves of the incident lights interfere to reduce the total oscillation curve of the incident lights, thereby developing a photoresist layer having a photoresist pattern corresponding to the element pattern.

Description

Systems, Software Applications, and Methods for Dose Uniformity Improvement Embodiments of the present disclosure generally relate to photolithography systems. More specifically, embodiments of the present disclosure relate to systems and methods for improving dose uniformity in photolithography systems. Photolithography is widely used in the manufacture of semiconductor components, such as for the backend processing of semiconductor components and display devices (such as liquid crystal displays (LCDs)). For example, large-area substrates are often used in the manufacture of display devices, such as optical wafers for augmented reality or virtual reality (AR / VR) components. A photolithography system has a projection unit that projects a writing beam in the direction of one or more masks. The one or more masks have patterns corresponding to the patterns to be written in a photoresist layer on the substrate surface. However, thickness variations in the photoresist layer (e.g., thickness non-uniformity) affect the light absorption uniformity of the photoresist layer (e.g., the swing effect). The absorption uniformity of the photoresist affects the dose uniformity (e.g., exposure) of the photolithography system, which affects the critical dimensions and electrical performance of semiconductor components. Thus, there is a need in the art for improved lithography methods to reduce absorption non-uniformities caused by non-uniform photoresist layers. In one embodiment, a method is provided. The method includes projecting a writing beam from a projection unit towards a mask to form a plurality of incident lights, adjusting the projection unit to generate an incident angle distribution corresponding to the incident lights, focusing the plurality of incident lights towards a photoresist layer disposed above a substrate using a lens, removing a portion of the photoresist layer to form a device pattern, and forming a structure corresponding to the device pattern on the substrate. The mask has a mask pattern corresponding to the device pattern. By focusing the plurality of incident lights towards the photoresist, the swing curves of the incident lights interfere to reduce the total swing curve of the incident lights, thereby developing a photoresist layer having a photoresist pattern corresponding to the device pattern. In another embodiment, a lithography system is disclosed. The lithography system includes a projection unit, a mask, and a lens. The projection unit is adjustable to change the incident angle distribution corresponding to one or more incident lights. The mask is positioned spaced apart from the projection unit in the projection direction. The mask has a mask pattern corresponding to the device pattern. The lens is spaced apart from the mask in the projection direction. The mask forms one or more incident lights having corresponding swing curves of a writing beam projected from the projection unit. The one or more incident lights are focused by the lens to reduce the total swing curve of the incident lights, thereby developing a photoresist layer having a photoresist pattern corresponding to the device pattern on the substrate. In another embodiment, a controller for storing instructions is disclosed. When executed by a computer processor, the instructions cause the controller to perform the following operations: store one or more mask patterns corresponding to one or more element patterns in a memory; write a mask pattern of the one or more mask patterns into a mask corresponding to an element pattern of the one or more element patterns; use a projection unit to project a write beam onto the mask to generate one or more incident lights; calculate an incident angle of one of the one or more incident lights; adjust the size and shape of the projection unit to change the incident angle of the incident light so as to reduce the total swing curve of the lithography system; use a lens to focus the one or more incident lights onto a photoresist layer disposed on a substrate; and generate a photoresist pattern corresponding to the mask pattern on the photoresist layer. The incident angle is calculated using the thickness of the photoresist layer and the wavelength of the incident light. Embodiments of the present disclosure relate to systems, methods, and devices for improving the dose uniformity of a photolithography system. Some embodiments of the method include projecting a write beam from a projection unit towards a mask to form a plurality of incident lights, adjusting the size and shape of the projection unit to generate an incident angle distribution corresponding to the incident lights, using a lens to focus the plurality of incident lights towards a photoresist layer disposed above a substrate, removing portions of the photoresist layer to form an element pattern, and forming a structure corresponding to the element pattern on the substrate. The mask has a mask pattern corresponding to the element pattern. By focusing the plurality of incident lights towards the photoresist, the swing curves of the incident lights interfere to reduce the total swing curve of the incident lights, thereby developing a photoresist layer having a photoresist pattern corresponding to the element pattern. A controller stores instructions that, when executed by a computer processor, cause the controller to perform the operations of the method using the lithography system. FIG. 1A is a schematic diagram of a lithography system 100. FIG. 1B is a schematic top plan view of a second lens 140. It will be understood that the lithography system 100 is an exemplary system, and other systems may be used with or modified to implement aspects of the present disclosure. The system includes a projection unit 102 that includes one or more light sources capable of projecting a write beam 105 in the direction of a mask 104, such as a light emitting diode (LED) or a laser. In some embodiments, a first lens 103 directs the write beam 105 towards the mask 104. The mask 104 is disposed above a substrate 106. The mask 104 has a mask pattern corresponding to an element pattern for forming a structure on the substrate 106 and / or a photoresist pattern for developing a photoresist layer 110 disposed above the substrate 106. A second lens 140 is positioned between the substrate 106 and the mask 104. In some embodiments, the second lens 140 includes any suitable material, such as, for example, fused silica, calcium fluoride, or other suitable material. The substrate 106 includes any suitable material that serves as part of a flat panel display, such as, for example, glass. In some embodiments that can be combined with other embodiments described herein, the substrate 106 is made of other materials that can serve as part of a flat panel display. In some embodiments that can be combined with other embodiments described herein, the substrate 106 can have a surface width ranging from about 300 mm to about 4000 mm, such as from about 500 mm to about 3000 mm, such as from about 1000 mm to about 2000 mm. In some embodiments, the substrate 106 is a rectangular substrate sized from about 300×400 to about 3000×3500 (such as about 2940×3370). In one embodiment, the substrate 106 has a film layer formed thereon to be patterned (such as by pattern etching), and a photoresist layer 110 formed on the film layer to be patterned, the photoresist layer being sensitive to electromagnetic radiation, such as ultraviolet (UV), extreme ultraviolet (EUV), or deep UV light. In another embodiment, the photoresist layer 110 is deposited on the substrate 106 and developed to provide a pattern for depositing a structure onto the substrate 106. A positive photoresist includes portions of the photoresist layer 110 that are respectively soluble in a photoresist developer applied to the photoresist layer 110 after a pattern is written into the photoresist layer 110 using electromagnetic radiation (such as light). A negative photoresist includes portions of the photoresist layer 110 that are respectively insoluble in a photoresist developer applied to the photoresist layer 110 after a pattern is written into the photoresist layer 110 using electromagnetic radiation (such as light). Negative development includes exposing a positive photoresist layer 110 through a bright field mask, where the exposed areas will be respectively insoluble in an organic solvent (such as n-butanol) and remain on the substrate 106 after development. The chemical composition of the photoresist layer 110 determines whether the photoresist layer 110 is a positive photoresist or a negative photoresist. The photoresist layer 110 has a thickness t ranging from about 0.5 micrometers to about 2 micrometers. In some embodiments, the thickness of the photoresist layer 110 is about 1 to about 4 times the size of the structure to be formed on the substrate 106. However, other thicknesses are also contemplated. During operation, the projection unit 102 projects a write beam 105 (e.g., electromagnetic radiation or light) in a projection direction towards the mask 104 to develop the photoresist layer 110. In the illustrated embodiment, the first lens 103 focuses and guides light from the projection unit 102 towards the mask 104. When the write beam 105 is projected in the direction of the mask 104, the mask pattern of the mask 104 corresponds to the device pattern to be written into the photoresist layer 110. In some embodiments that can be combined with other embodiments described herein, the device pattern may correspond to the devices to be patterned onto the substrate 106. In other embodiments that can be combined with other embodiments described herein, the device pattern may correspond to one or more devices to be patterned into the film layer disposed on the substrate 106. The mask 104 forms one or more incident lights 120 from the write beam 105. An image of the incident light 120 corresponding to the mask pattern may be formed on the second lens 140. The image of the incident light 120 is formed by the Fourier transform of the mask 104. The incident light 120 generates a first image 145A, a second image 145B, and a third image 145C. The second lens 140 focuses the electromagnetic radiation (e.g., light) from the one or more incident lights 120 towards the photoresist layer 110 to pattern the photoresist layer 110 using the photoresist pattern. For ease of illustration, the focusing of the incident light of the first image 145A is illustrated as the first focused incident light 120A, the focusing of the incident light of the second image 145B is illustrated as the second focused incident light 120B, and the focusing of the incident light of the third image 145C is illustrated as the third focused incident light 120C. Nothing in the present disclosure should be construed as limiting the manner in which the incident light 120 is focused towards the photoresist layer 110. The photoresist pattern corresponds to the device pattern. A plurality of portions of the photoresist layer 110 that are exposed to the incident light 120 according to the mask pattern are removed to expose the substrate 106 or the thin film disposed on the substrate 106. In some embodiments that can be combined with other embodiments described herein, the lithography system 100 is sized to be able to expose the entire photoresist layer 110 on the substrate 106. In other embodiments, the lithography system 100 is sized to be able to expose a portion of the photoresist layer 110 on the substrate 106. The substrate 106 is supported by a platform 116 that is operable to position the substrate 106 in a predetermined path under one or more masks 104. The movement of the substrate 106 can be controlled by a controller 108. The controller 108 is generally designed to facilitate the control and automation of the lithography process based on a mask pattern file. The mask pattern file includes mask pattern data having instructions for positioning the mask 104 according to an embodiment of method 700 described herein. The controller 108 can be coupled to or communicate with at least the projection unit 102, the platform 116, and the encoder 118. The projection unit 102 and the encoder 118 can provide information to the controller 108 regarding substrate processing and substrate alignment. For example, the projection unit 102 can provide information to the controller 108 to alert the controller 108 that substrate processing has been completed. FIG. 2 is a schematic diagram of a lithography environment 200. As shown in FIG. 2, the lithography environment 200 includes, but is not limited to, a virtual design device 202, a mask modeling device 204, a mask manufacturing device 206, a lithography system 100, a controller 108, a plurality of communication links 201, and a transfer system 203. Each of the lithography environment devices can be operable to connect to the controller 108 via the communication link 201. Alternatively or additionally, each of the lithography environment devices can communicate indirectly by first communicating with the controller 108 and then communicating with the lithography environment device in question via the controller. Each of the lithography environment devices of the lithography environment 200 can be located in the same area or production facility, or each of the lithography environment devices can be located in different areas. The virtual design device 202 is operable to generate, optimize, verify, and update at least one of design files. The design files correspond to the component patterns to be written into the photoresist layer 110. The mask modeling device 204 is operable to partition the design files and generate a mask pattern file. The mask manufacturing device 206 is operable to receive the mask pattern data of the mask 104 transmitted from the mask modeling device 204. According to the operation of method 700 described herein, the mask manufacturing device 206 is operable to manufacture the mask pattern of the mask 104 that corresponds to the component pattern to be written into the photoresist layer 110 when the mask 104 is positioned according to the embodiments described herein. In some embodiments, the mask 104 can be a conventional mask. In other embodiments, the mask 104 can be a phase shift mask. In still other embodiments, the mask 104 can be a digital mask. The lithography system 100 is operable to receive the mask 104 according to the operation of method 700 described herein. Each of the virtual design device 202, the mask modeling device 204, the mask manufacturing device 206, the lithography system 100, and the controller 108 includes an on-board processor and memory, where the memory is configured to store instructions corresponding to any part of the method 700 described below. The communication link 201 may include at least one of a wired connection, a wireless connection, a satellite connection, and the like. According to an embodiment further described herein, the communication link 201 includes sending and receiving a universal metrology file (UMF) or any other file for storing data. The communication link 201 may include temporarily or permanently storing a file or data in the cloud before transferring or copying the file or data to the lithography system tool. The mask manufacturing device 206 and the mask modeling device 204 are connected by a transfer system 203. The transfer system 203 is operable to transfer the substrate 106 between the mask manufacturing device 206 and the lithography system 100. In one embodiment that can be combined with other embodiments described herein, the transfer system 203 may include a robot or other device connectable to the controller 108, and the controller is operable to transfer the mask 104. In one embodiment that can be combined with other embodiments described herein, the transfer system 203 may be operated by a user entity. The controller 108 includes a central processing unit (CPU) 212, support circuitry 214, and memory 216. The CPU 212 can be one of any form of computer processor that can be used to control a lithography environment device in an industrial setting. The memory 216 is coupled to the CPU 212. The memory 216 can be one or more of readily available memories, such as random access memory (RAM), read only memory (ROM), floppy disks, hard disks, or any other form of digital storage (local or remote). The support circuitry 214 is coupled to the CPU 212 to support the processor in a conventional manner. Such circuitry includes cache memory, power supplies, clock circuits, input / output circuitry systems, subsystems, and the like. The controller 108 may include a CPU 212 that is coupled to input / output (I / O) devices found in the support circuitry 214 and the memory 216. For example, a metrology device can measure the thickness of the photoresist layer 110 and input the measurement to determine whether the photoresist layer 110 has been properly developed and patterned into the selected photoresist pattern. Memory 216 may include one or more software applications, such as control software programs. Memory 216 may also include stored media data for use by CPU 212 to perform method 700 described herein. CPU 212 may be a hardware unit or a combination of hardware units capable of executing software applications and processing data. CPU 212 is generally configured to execute one or more software applications and process stored media data, which may be included within memory 216. Controller 108 controls the transfer of data and files to and from various lithography environment devices. Memory 216 is configured to store instructions corresponding to any operation of method 700 according to the embodiments described herein. For example, the memory may store a recipe for developing photoresist layer 110 and instructions for calculating recipe changes during development of photoresist layer 110 depending on input from a metrology device. FIG. 3A illustrates the interaction between photoresist layer 110 and incident light 320. FIG. 3B illustrates a swing curve 325 defined by the relationship between the thickness t of photoresist layer 110 and photoresist absorption. During development of photoresist layer 110, as explained above, electromagnetic radiation (e.g., incident light 320) is absorbed by photoresist layer 110 to produce a positive or negative photoresist layer 110. Photoresist absorption is defined as the ratio of the light absorbed by photoresist layer 110 to incident light 320. Incident light 320 not absorbed by photoresist layer 110 either transmits as transmitted light 321 into the layer below photoresist layer 110 (e.g., substrate 106 or some other material deposited on substrate 106) or reflects as reflected light 322 from the surface of photoresist layer 110. Photoresist absorption depends on the thickness t of photoresist layer 110 or other optical properties, such as opacity. Swing curve 325 is defined by a relationship curve between photoresist absorption and photoresist thickness t. The amplitude of swing curve 325 is affected by the thickness t of photoresist layer 110 (e.g., decreasing the thickness of photoresist layer 110 increases the amplitude of swing curve 325). The period of the swing curve (e.g., the swing period) is related to the wavelength (λ) of incident light 320. When incident light 320 is orthogonal (e.g., perpendicular) to the uppermost surface 324 of photoresist layer 110, the swing period is λ / 2. When incident light 320 is obliquely incident on the uppermost surface 324 of photoresist layer 110, the swing period becomes λ / 2*cos(α), where α is the angle between a vector V orthogonal (e.g., perpendicular) to the uppermost surface 324 of photoresist layer 110 and the vector of transmitted light 321. Swing curve 325 is also affected by the refractive indices of photoresist layer 110 and substrate 106. For example, stronger reflection at the photoresist / substrate (PR / S) interface 330 will increase the amplitude of swing curve 325. The formation of the photoresist layer 110 may inherently include variations across the thickness t of the substrate 106 (e.g., thickness non-uniformity). The thickness variation is the difference between the maximum and minimum points of the uppermost surface 124 of the photoresist layer 110. Depending on the size of the substrate 106 and / or the deposition tool, the photoresist deposition technique can result in a thickness variation of the photoresist layer 110 across the substrate 106 up to 2-3%. During the development of the photoresist layer 110, a 1% thickness variation can affect the amount of light absorbed by the photoresist layer 110 by 10% to 20%. The absorption non-uniformity affects the clarity of the photoresist layer development, and thus affects the critical dimension (CD) of the pattern defined by the photoresist layer 110. Poorly defined patterns result in non-uniformity of the critical dimension (CD) of the structures formed on the substrate 106, which can affect the electrical properties of the semiconductor device. Accordingly, reducing the swing curve 325 of the photoresist layer 110 can increase the CD consistency of the structures formed on the substrate 106 of the semiconductor device. FIG. 4A illustrates the interaction between the photoresist layer and incident light having two incoherent source points. FIG. 4B illustrates a first swing curve 425A and a second swing curve 425B defined by the relationship between the thickness of the photoresist layer 110 and the photoresist absorption of the incident light having two incoherent source points. In an application where the projection unit 102 for developing the photoresist layer 110 has two incoherent source points (e.g., when using a mask), the writing beam 105 becomes a first incident light 420A and a second incident light 420B. The first incident light 420A not absorbed by the photoresist layer 110 either transmits as a transmitted light 421A into the layer under the photoresist layer 110 (e.g., the substrate 106 or some other material deposited on the substrate 106) or reflects as a reflected light 422A from the surface of the photoresist layer 110. The second incident light 420B not absorbed by the photoresist layer 110 either transmits as a transmitted light 421B into the layer under the photoresist layer 110 (e.g., the substrate 106 or some other material deposited on the substrate 106) or reflects as a reflected light 422B from the surface of the photoresist layer 110. Each incident light 420A, 420B has its own swing curve 425A, 425B. The swing curves 425A, 425B interfere constructively or destructively with each other, and can thus affect the absorption non-uniformity, and thus affect the CD of the resulting structures on the substrate 106 of the semiconductor device. In one embodiment, mask 104 is a conventional optical mask. Mask 104 generates at least zero-order light, +1-order light, and -1-order light from incident light 120. In other embodiments, + / -n-order light is also contemplated, where n is an integer greater than or equal to 0. First image 145A, second image 145B, and third image 145C are images of incident light 120 formed on second lens 140 due to the Fourier transform of mask 104. Due to the finite size of second lens 140, only low-order light can pass through second lens 140 (e.g., zero-order and + / -1-order light). First focused incident light 120A irradiates photoresist layer 110 at an angle orthogonal to (e.g., perpendicular to) the uppermost surface 124 of photoresist layer 110. Second focused incident light 120B and third focused incident light 120C are focused toward photoresist layer 110 and obliquely irradiate the uppermost surface 324 of photoresist layer 110. Thus, second focused incident light 120B and third focused incident light 120C have a smaller oscillation period compared to first focused incident light 120A. The incident angle α of second focused incident light 120B and third focused incident light 120C depends on the pitch (P) of the line-space pattern and the optical characteristics of mask 104. The period of the line-space pattern is determined by the device pattern. Lithography system 100 is optimized to minimize the period of the line-space pattern. Within each order of incident light (1, 2, … n-1, n), the incident angle can also be different because projection unit 102 has a non-zero radius (e.g., the size and shape of projection unit 102 can affect the oscillation curve of the incident light). The incident angle of the n-order light in photoresist layer 110 is calculated using Equation 1: where n is the order of the light, and n PR is the refractive index of photoresist layer 110. FIG. 5 is the total oscillation curve 525C from the zero-order oscillation curve 525A and the + / -1-order oscillation curves 525B. First focused incident light 120A, second focused incident light 120B, and third focused incident light 120C simultaneously irradiate photoresist layer 110, thereby generating a total oscillation curve with a smaller oscillation amplitude compared to the independent oscillation amplitudes. The period (T) of the oscillation curve is calculated using Equation 2: Based on the thickness t of photoresist layer 110, the light undergoes t / T cycles. The interference (I) between the zero-order oscillation curve 525A (T) and the + / -1-order oscillation curves 525B (T’) is measured using Equation 3: When the interference is an integer, the oscillation curve is constructive interference. When the interference (I) is an integer +0.5, the oscillation curve is destructive interference. When the oscillation curve is destructive interference, the total oscillation curve decreases. The total swing curve 525C can be reduced by controlling the shape and size of the projection unit 102. By changing the size or shape of the projection unit 102, a first image 145A, a second image 145B, and a third image 145C corresponding to the size and shape of the projection unit 102 are formed. The shapes and sizes of the first image 145A, the second image 145B, and the third image 145C produce a distribution of the incident angle α, which is focused by the second lens 140 onto the photoresist layer 110. The difference in the incident angle α creates a difference between the 0th order swing curve 525A and the + / - 1st order swing curves 525B. For example, a larger projection unit 102 broadens the + / - 1st order swing curves, where the width of the + / - 1st order swing curves corresponds to the size of the projection unit 102. The broader + / - 1st order swing curves produce more destructive interference, thus reducing the total swing curve 525C. Thus, according to Equations 1-3, the size and properties of the projection unit 102 can be changed to achieve the incident angle required to reduce the total swing curve 525C. FIG. 6A is a schematic top plan view of a circular illumination phase shift lens 640A. FIG. 6B is a schematic top plan view of a dipole illumination phase shift lens 640B. The phase shift lenses 640A, 640B are used together with a phase shift mask 104 that does not have 0th order incident light. In one embodiment, the shape of the projection unit 102 is changed to a single circular projection unit 102. The circular projection unit 102 projects incident light through the phase shift mask 104. The phase shift mask 104 forms a first image 645A and a second image 645B on the circular illumination phase shift lens 640A. The lens 640A focuses the +1st order incident light and the -1st order incident light towards the photoresist layer 110. By controlling the size and shape of the circular projection unit 102, a distribution of the incident angle α is generated and focused by the second lens 140. The distribution of the incident angle α creates a difference between the +1st order swing curve and the -1st order swing curve such that the +1st order swing curve and the -1st order swing curve are out of phase by 180 degrees, thereby reducing the total swing curve 525C of the lithography system 100. In one embodiment, by broadening the projection unit 102, the width of the swing curves from the + / - 1st order incident light can be increased, thus more destructive interference and a reduction in the total swing curve 525C. In some embodiments, based on the thickness of the photoresist layer 110 and the wavelength of the incident light, the controller 108 can calculate the shape and size of the projection unit 102 according to Equation 1-3, and generate the distribution of the incident angle α required to reduce the total swing curve 525 of the lithography system 100. The projection unit is needed. The controller 108 can further use machine learning to optimize the algorithm for calculating the incident angle based on the thickness of the photoresist layer 110, and store the instructions corresponding to the incident angle of the photoresist development formulation into the memory 216. Additionally, the controller 108 can use metrology devices to monitor the development of the photoresist layer 110 to adjust the distribution of the incident angle α or the wavelength of the light, thereby forming a photoresist pattern. In FIG. 6B, the dipole projection unit 102 is utilized and the incident light is projected through the phase shift mask 104. The dipole projection unit 102 has a first projection unit and a second projection unit. In one embodiment, the wavelength of the light from the first projection unit is the same as the wavelength of the light from the second projection unit. In another embodiment, the wavelength of the light from the first projection unit is different from the wavelength of the light from the second projection unit. The dipole illumination phase shift mask 104 forms a first image 645A, a second image 645B, a third image 645C, and a fourth image 645D on the dipole phase shift lens 640B. The size and shape of the first projection unit and the second projection unit control the incident angle α of the + / -1 order incident light to generate the distribution of the incident angle α. The dipole phase shift lens focuses the + / -1 order incident light of the first projection unit and the + / -1 order incident light of the second projection unit toward the photoresist layer 110. By controlling the size and shape of the first projection unit and the second projection unit, the +1 order swing curve and the -1 order swing curve of the first projection unit and the second projection unit are out of phase by 180 degrees, thereby reducing the total swing curve 525C of the lithography system 100. In one embodiment, by widening the first projection unit and the second projection unit, the width of the swing curve from the + / -1 order incident light can be increased to reduce the total swing curve 525C. In some embodiments, based on the thickness of the photoresist layer 110 and the wavelength of the incident light, the controller 108 can calculate the shape and size of the first projection unit and the second projection unit, and generate the distribution of the incident angle α required to reduce the total swing curve 525C of the lithography system 100. The first projection unit and the second projection unit are needed. The controller 108 can further use machine learning to optimize the algorithm for calculating the incident angle based on the thickness of the photoresist layer 110, and store the instructions corresponding to the incident angle of the photoresist development formulation into the memory 216. Additionally, the controller 108 can use metrology devices to monitor the development of the photoresist layer 110 to adjust the incident angle α or the wavelength of the light, thereby forming a photoresist pattern. In yet another embodiment, the mask 104 is a digital mask 104. The digital mask 104 includes a plurality of mirrors that can be programmed to be "on" (e.g., cause the mirror to reflect) or "off" (e.g., make the mirror transparent / transmissive). The mirrors can control the transmission of light through the digital mask and towards the second lens 140, thereby allowing control of the transmission of the 0th and + / -1st order rocking curves. The size and shape of the projection unit 102 can be modified to control the distribution of the incident angle α of the + / -1st order incident light. By controlling the incident angle α, the + / -1st order rocking curve and the 0th order rocking curve of the projection unit 102 are out of phase by 180 degrees. In some embodiments, based on the thickness t of the photoresist layer 110 and the wavelength of the incident light, the controller 108 can calculate the shape and size of the projection unit 102, and generate the distribution of the incident angle α required to reduce the total rocking curve of the lithography system 100. The projection unit is needed. The controller 108 can further use machine learning to optimize the algorithms for calculating the incident angle based on the thickness of the photoresist layer 110 and the mirror algorithm, and store the instructions corresponding to the incident angle of the photoresist development formulation in the memory 216. Additionally, the controller 108 can use metrology devices to monitor the development of the photoresist layer 110 to adjust the incident angle or the wavelength of light for the photoresist pattern. As a result of reducing the total rocking curve of the lithography system 100, the dose uniformity and critical dimension variation are reduced by about 5% to about 30%, such as about 10% to about 25%. FIG. 7 is a flowchart of a method 700 of a lithography process for reducing the rocking effect in the photoresist layer 110. In optional operation 701, a design file is generated by the virtual design device 202. The design file corresponds to the component pattern to be written into the photoresist layer 110. In some embodiments that can be combined with other embodiments described herein, the design file is generated prior to the operations of the method 700 described herein. In operation 702, the mask modeling device 204 generates a mask pattern file with mask pattern data. In operation 703, the mask manufacturing device 206 manufactures a mask pattern of the mask 104, which corresponds to the component pattern to be written into the photoresist layer 110 when the mask 104 is positioned according to the embodiments described herein. The mask can be a conventional mask 104, a phase shift mask, or a digital mask. In operation 704, the mask 104 is received by the lithography system 100 and positioned between the projection unit 102 and the second lens 140 according to the mask pattern data. At operation 705, the projection unit 102 projects a write beam 105 (e.g., electromagnetic radiation or light) towards the mask 104. In some embodiments, the write beam 105 passes through the first lens 103 to direct the write beam 105 towards the mask 104. The mask 104 generates at least one incident light 120, and the incident light generates an image 145. The size and shape of the projection unit 102 can change the incident angle α of at least one incident light 120. In one embodiment, changing the size of the projection unit produces a distribution of the incident angle α. In one embodiment, the mask 104 is a conventional mask that generates a first image 145A, a second image, and a third image 145C on the second lens 140. In another embodiment, the mask 104 is a phase shift mask that generates a +1 order image and a -1 order image. Orthogonal to the uppermost surface 124 of the substrate 106, the second image 145B that obliquely contacts the uppermost surface 124 of the substrate 106, and the third focused incident light 120C that obliquely contacts the uppermost surface 124 of the substrate 106. The -1 order incident light that obliquely contacts the uppermost surface 124 of the substrate 106 and the -1 order incident light that obliquely contacts the uppermost surface 124 of the substrate 106. At operation 706, the second lens 140 focuses the incident light 120 towards the photoresist layer 110. In embodiments using the conventional mask 104, the second lens 140 focuses the incident light from the first image 145A, the second image 145B, and the third image 145C towards the photoresist layer 110. For ease of illustration, the focusing of the incident light of the first image 145A is illustrated as the first focused incident light 120A, the focusing of the incident light of the second image 145B is illustrated as the second focused incident light 120B, and the focusing of the incident light of the third image 145C is illustrated as the third focused incident light 120C. Nothing in this disclosure should be construed as regarding the manner in which the incident light 120 is focused towards the photoresist layer 110. The first focused incident light 120A may correspond to the 0 order incident light, and the second focused incident light 120B and the third focused incident light 120C may correspond to the + / -1 order incident light towards the photoresist layer 110. Based on the size and shape of the projection unit, the distribution of the incident angle of incident light 120 is such that the swing curves of the +1 order incident light and the -1 order incident light are out of phase by 180 degrees with respect to the swing curve of the 0 order incident light, so as to reduce the total swing curve of the lithography system 100. In an embodiment using a phase shift mask 104, the second lens 140 focuses the + / -1 order incident light towards the photoresist. Based on the size and shape of the projection unit, the distribution of the incident angle of the incident light is such that the swing curve of the +1 order incident light and the swing curve of the -1 order incident light are out of phase by 180 degrees with respect to each other, so as to reduce the total swing curve of the lithography system 100. In an embodiment using a digital mask, a plurality of programmable mirrors can control the transmission of light through the digital mask and towards the second lens 140, thereby allowing the second lens 140 to control the 0 order and + / -1 order swing curves. Based on the size and shape of the projection unit, the distribution of the incident angle of the incident light is such that the swing curves of the +1 order incident light and the -1 order incident light are out of phase by 180 degrees with respect to the swing curve of the 0 order incident light, so as to reduce the total swing curve of the lithography system 100. In one embodiment, the method includes programming a programmable mirror to be either transparent or reflective to control the transmission of light through the digital mask. At operation 707, the focused incident light develops the patterned photoresist layer 110 for forming a plurality of structures on the substrate 106. After the incident light 120 develops the photoresist layer 110, a portion of the photoresist layer 110 is dissolved to form a pattern. In one embodiment, the pattern exposes a film layer disposed on the substrate 106, and the film layer can be etched to form structures on the substrate 106. In another embodiment, the pattern exposes the substrate 106 to allow structures to be deposited on the substrate 106. A controller 108 including a central processing unit (CPU) 212, support circuitry 214, and memory 216 can be coupled to or communicate with at least a projection unit 102, a platform 116, and an encoder 118. The projection unit 102 and the encoder 118 can provide information to the controller 108 regarding substrate processing and the angle of incidence. For example, the projection unit 102 can provide information to the controller 108 to alert the controller 108 that substrate processing has been completed or that the angle of incidence is not aligned with the photoresist layer development recipe. In some embodiments, the size and shape of the projection unit 102 can be controlled by the controller 108 to control the angle of incidence α of the + / -1 order incident light. Based on the thickness of the photoresist layer 110 and the wavelength of the incident light, the controller 108 can calculate the size and shape of the projection unit 102 that is required to produce the distribution of the angle of incidence α necessary to reduce the overall swing curve of the lithography system 100. The controller 108 can further use machine learning to optimize the algorithm for calculating the angle of incidence based on the thickness of the photoresist layer 110 and store instructions corresponding to the angle of incidence of the photoresist layer development recipe in the memory 216. Additionally, the controller 108 can use metrology devices to monitor the development of the photoresist layer 110 to adjust the angle of incidence or the wavelength of the light to form a photoresist pattern. In summary, a method and system for a lithography process are disclosed that provide an improved method for lithography to reduce absorption non-uniformities caused by an uneven photoresist layer. The system projects a write beam from a projection unit towards a mask to form a plurality of incident lights. The incident lights form an image of the pattern on the mask on a lens that focuses the incident lights towards the uneven photoresist. By measuring the thickness of the photoresist layer and controlling the size and shape of the projection unit, the angle of incidence necessary to reduce the overall swing curve of the system can be achieved. Reducing the overall swing curve can reduce absorption non-uniformities of the light into the photoresist layer. Absorption non-uniformities affect the clarity of the photoresist layer development and thus the critical dimension (CD) of the resulting optical element. The controller can use machine learning to optimize the size and shape of the projection unit. The controller can monitor the development of the photoresist layer during lithography to adjust the size and shape of the projection unit to optimize the lithography. Although the foregoing relates to embodiments of the present disclosure, other and further embodiments of the present disclosure can be designed without departing from its basic scope, and its scope is determined by the following claims for patent. 100: Lithography system 102: Projection unit 103: First lens 104: Mask 105: Writing beam 106: Substrate 108: Controller 110: Photoresist layer 116: Stage 118: Encoder 120: Incident light 120A: First focused incident light 120B: Second focused incident light 120C: Third focused incident light 124: Topmost surface 140: Second lens 145: Image 145A: First image 145B: Second image 145C: Third image 200: Lithography environment 201: Communication link 202: Virtual design device 203: Delivery system 204: Mask modeling device 206: Mask manufacturing device 212: Central processing unit (CPU) 214: Support circuitry 216: Memory 320: Incident light 321: Transmitted light 322: Reflected light 325: Oscillation curve 330: Photoresist layer / substrate (PR / S) interface 420A: First incident light 420B: Second incident light 421A: Transmitted light 421B: Transmitted light 422A: Reflected light 422B: Reflected light 425A: Oscillation curve 425B: Oscillation curve 525A: 0th order oscillation curve 525B: + / -1st order oscillation curve 525C: Total oscillation curve 640A: Circular illumination phase shift lens 640B: Dipole illumination phase shift lens 645A: First image 645B: Second image 645C: Third image 645D: Fourth image 700: Method 701: Operation 702: Operation 703: Operation 704: Operation 705: Operation 706: Operation 707: Operation t: Thickness V: Vector To be able to understand in detail the manner in which the above features of the present disclosure are used, a more specific description of the present disclosure briefly outlined above may be referred to embodiments, some of which are illustrated in the accompanying drawings. However, it will be noted that the drawings only illustrate common embodiments of the present disclosure and are thus not considered to limit its scope, as the present disclosure may admit other equally effective embodiments. FIG. 1A is a schematic diagram of a lithography system according to an embodiment. FIG. 1B is a schematic top view of a lens according to an embodiment. FIG. 2 is a schematic diagram of a lithography environment according to an embodiment. FIG. 3A illustrates the interaction between a photoresist layer and incident light according to an embodiment. FIG. 3B illustrates the oscillation curve relationship between the thickness of a photoresist layer and photoresist absorption according to an embodiment. FIG. 4A illustrates the interaction between a photoresist layer and incident light having two incoherent source points according to an embodiment. Figure 4B illustrates the swing curve relationship between the thickness of the photoresist layer and the photoresist absorption of incident light with two incoherent source points according to an embodiment. Figure 5 is the average swing curve from 0th order and 1st order incident light according to an embodiment. Figure 6A is a schematic top plan view of a circular illumination phase shift lens according to an embodiment. Figure 6B is a schematic top plan view of a dipole illumination phase shift lens according to an embodiment. Figure 7 is a flowchart of a method of a lithography process for reducing the swing effect in a photoresist layer according to an embodiment. For ease of understanding, the same element symbols have been used, wherever possible, to identify the same elements common to the figures. It is contemplated that elements disclosed in one embodiment can be advantageously incorporated into other embodiments without further recitation. Domestic deposit information (please note in the order of deposit institution, date, number) None Foreign deposit information (please note in the order of deposit country, institution, date, number) None 100: Lithography system 102: Projection unit 103: First lens 104: Mask 105: Writing beam 106: Substrate 108: Controller 110: Photoresist layer 116: Platform 118: Encoder 120: Incident light 120A: First focused incident light 120B: Second focused incident light 120C: Third focused incident light 124: Topmost surface 140: Second lens 145: Image 145A: First image 145B: Second image 145C: Third image

Claims

1. A method for improving dose uniformity, comprising the steps of: projecting a write beam from a projection unit toward a mask to form a plurality of incident beams, wherein the mask has a mask pattern corresponding to a component pattern; adjusting a size and a shape of the projection unit to produce a distribution of incident angles corresponding to the incident beams, such that an oscillation curve of the incident beams interferes to reduce a total oscillation curve of the incident beams, thereby developing a photoresist layer having a photoresist pattern corresponding to the component pattern; focusing the plurality of incident beams toward a photoresist layer disposed above a substrate using a lens; removing a plurality of portions of the photoresist layer to form the component pattern; and forming a structure corresponding to the component pattern on the substrate.

2. The method as described in claim 1, wherein the mask forms a first incident light, a second incident light, and a third incident light.

3. The method of claim 1, wherein the mask is a digital mask forming a first incident light, a second incident light, and a third incident light.

4. The method of claim 3, wherein the digital mask comprises a plurality of mirrors, wherein the method comprises the step of: programming the mirrors to be either transparent or reflective.

5. The method of claim 1, wherein the mask comprises a phase-shifting mask forming a first incident light and a second incident light.

6. The method of claim 1, wherein the total oscillation curve is an average of the oscillation curves of the incident light.

7. The method of claim 1, wherein each of the plurality of incident lights has a wobbling curve corresponding to a thickness of the photoresist layer, an angle of incidence of the incident light exposed to the photoresist layer, and a wavelength of the incident light.

8. A lithography system comprising: a projection unit adjustable to change a distribution of incident angles corresponding to one or more incident lights; a mask positioned spaced apart from the projection unit in a projection direction and having a mask pattern corresponding to a component pattern; and a lens spaced apart from the mask in the projection direction; wherein the mask forms the one or more incident lights having a corresponding oscillation curve of a write beam projected from the projection unit, and wherein the one or more incident lights are focused by the lens to reduce a total oscillation curve of the incident lights, thereby developing a photoresist layer having a photoresist pattern corresponding to the component pattern on a substrate.

9. The lithography system as claimed in claim 8, wherein the lens focuses a first incident light, a second incident light, and a third incident light.

10. The lithography system as claimed in claim 8, wherein the mask is a phase-shift mask and wherein the lens focuses a first incident light and a second incident light.

11. The lithography system of claim 8, wherein the projection unit is a dipole projection unit comprising a first projection unit and a second projection unit, the mask is a phase-shifting mask, and wherein the lens focuses a first incident light from the first projection unit, a second incident light from the second projection unit, a third incident light from the first projection unit, and a fourth incident light from the second projection unit to reduce the total oscillation curve of the incident lights.

12. The lithography system as claimed in claim 8, wherein the mask is a digital mask and wherein the lens focuses a first incident light, a second incident light, and a third incident light to reduce an overall oscillation curve of the incident light.

13. The lithography system of claim 8, wherein the one or more incident beams each have a wobbling curve corresponding to a thickness of the photoresist layer, an angle of incidence of the incident beams exposed to the photoresist layer, and a wavelength of the incident beams.

14. A controller for storing instructions, which, when executed by a computer processor, cause the controller to perform the following operations: storing one or more mask patterns corresponding to one or more component patterns in a memory; writing a mask pattern from the one or more mask patterns corresponding to a component pattern in the one or more component patterns into a mask; projecting a write beam onto the mask using a projection unit to generate one or more incident lights; calculating an angle of incidence of one of the one or more incident lights; adjusting a size and a shape of the projection unit to change the angle of incidence of the incident light, thereby reducing a total oscillation curve of a lithography system; focusing the one or more incident lights toward a photoresist layer disposed on a substrate using a lens; and generating a photoresist pattern corresponding to the mask pattern on the photoresist layer; wherein: The incident angle is calculated using a thickness of the photoresist layer and a wavelength of the incident light.

15. The controller as claimed in claim 14, wherein the controller includes a metering device for transmitting input regarding the thickness of the photoresist layer to calculate the angle of incidence.

16. The controller as claimed in claim 14, wherein the controller performs a step of moving the substrate based on the incident angle to generate a photoresist pattern on the photoresist layer corresponding to the mask pattern.

17. The controller as claimed in claim 14, wherein the controller performs a step of changing the wavelength of the incident light based on the incident angle to generate a photoresist pattern on the photoresist layer corresponding to the mask pattern.

18. The controller as claimed in claim 14, wherein the total oscillation curve is an average of the oscillation curves of the incident light.

19. The controller of claim 14, wherein the mask includes a digital mask comprising a plurality of mirrors, wherein the controller performs a step of programming the mirrors to be either transparent or reflective based on the incident angle to generate a photoresist pattern on the photoresist layer corresponding to the mask pattern.

20. The controller as claimed in claim 14, wherein the mask comprises a phase-shift mask.

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