Digital holographic lithography method based on light source phase coding and binary mask collaborative optimization
A digital holographic lithography method that combines light source phase encoding with binarized mask optimization solves the problems of resolution improvement and high mask manufacturing difficulty in extreme ultraviolet projection lithography, achieving high-resolution and low-cost lithography results.
Patent Information
- Application Number
- CN202511956090.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-23
- Publication Date
- 2026-02-27
AI Technical Summary
Existing extreme ultraviolet projection lithography technology faces challenges such as difficulty in improving resolution, high system complexity, and high cost. In particular, the traditional mask structure is difficult and costly to manufacture, making it difficult to meet the requirements of holographic lithography for mask design flexibility and rapid iteration.
A digital holographic lithography method employing co-optimization of light source phase encoding and binarized mask is proposed. By simplifying the light source modulation degree of freedom and mask structure, and combining light source phase encoding and binarized mask, a joint optimization model is constructed to achieve a high-resolution, low-cost lithography process.
It significantly reduces the difficulty and cost of mask manufacturing, improves the engineering feasibility and mass production adaptability of the system, enhances imaging resolution and stability, and reduces sensitivity to mask manufacturing errors.
Smart Images
Figure CN121578604A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of photolithography, and in particular to a digital holographic photolithography method, specifically a novel photolithography technique based on the collaborative optimization of light source phase encoding and binarized mask. Background Technology
[0002] Photolithography is a core component of integrated circuit manufacturing, and its precision directly determines the feature size and process node of the chip. Over the past four decades, continuous iterations of photolithography have propelled the long-term continuation of Moore's Law, with the ever-shrinking wavelength of light sources enabling the rapid evolution of critical device dimensions to the nanometer scale. However, since the commercialization of extreme ultraviolet (EUV) lithography (13.5 nm exposure wavelength), resolution improvements have slowed significantly, and Moore's Law is approaching its physical limits. Existing EUV projection lithography architectures face severe engineering and economic challenges: EUV light sources have extremely low energy efficiency, and the light energy utilization rate of molybdenum / silicon multilayer reflective systems is limited; simultaneously, the pursuit of higher resolution through increased numerical aperture leads to complex object aberrations, extremely high manufacturing precision requirements, and a sharp increase in system integration difficulty and cost. For example, the 0.55 numerical aperture EUV lithography machine produced by ASML costs over 200 million euros per unit. Overall, the traditional development model that relies on "wavelength reduction + numerical aperture improvement" can no longer sustain the evolution of future advanced processes. The existing extreme ultraviolet projection lithography architecture has reached saturation in terms of resolution and sensitivity, exhibiting the marginal reduction characteristics of "high investment and low gain".
[0003] To meet the higher demands of next-generation high-end chips on lithography resolution, throughput, and energy efficiency, global lithography technology is accelerating its transformation towards an innovative architecture centered on the combination of holographic optics and computational lithography. Thanks to breakthroughs in extreme ultraviolet (EUV) high-coherence light source technologies (such as EUV high-harmonic femtosecond lasers and free-electron lasers), the synergistic optimization of coherent illumination wavefront modulation and digital holographic imaging has become the core path for the development of next-generation EUV lithography. This architecture, through light field modulation, wavefront coding, and digital inversion imaging, aims to overcome the inherent limitations of traditional projection lithography in terms of light source utilization, system complexity, and resolution. Internationally, related technologies have made rapid progress; for example, research at JILA Laboratories and IMEC / ASML in the United States, as well as the cuLitho platform launched by NVIDIA / Synopsys, have all confirmed the feasibility of this technical route. Domestically, although some progress has been made in key components and electromagnetic field modeling of projection lithography architectures, systematic research on EUV digital holographic lithography technology is still in its early stages, lacking a complete technical roadmap and application experience.
[0004] However, existing technologies in extreme ultraviolet holographic lithography still face the following key challenges: First, while coherent light sources provide rich phase information encoding capabilities, there is a lack of advanced collaborative optimization strategies that balance forward physical models and inverse iterative optimization in effectively transforming this highly controllable capability into the final high-resolution pattern. Second, traditional complex three-dimensional multilayer mask structures are difficult and expensive to manufacture, making them unsuitable for the flexibility and rapid iteration requirements of holographic lithography in mask design. Therefore, there is an urgent need in this field for an innovative technical solution that combines advanced light source phase modulation with a binary mask structure that is easy to manufacture and significantly reduces costs through light source-mask collaborative optimization. This would effectively solve the problems of high manufacturing costs and complex mask engineering while ensuring lithographic accuracy. Summary of the Invention
[0005] This invention aims to overcome the shortcomings of existing extreme ultraviolet projection lithography technology by proposing a digital holographic lithography method based on the collaborative optimization of light source phase encoding and binary mask. By introducing the degree of freedom of light source modulation and simplifying the mask structure, it is hoped to achieve high-resolution and low-cost extreme ultraviolet digital holographic lithography, thereby overcoming the physical limit of traditional projection lithography in terms of resolution improvement, and solving the problems of high manufacturing difficulty and high cost of existing complex three-dimensional multilayer mask structures.
[0006] To solve the above-mentioned technical problems, the present invention adopts the following solution: The digital holographic lithography method of the present invention, based on the collaborative optimization of light source phase encoding and binarized mask, is characterized by the following steps: Step 101: Analyze the incident light field Apply light source phase encoding It is then co-encoded with the binary amplitude mask M to form the light field after the mask is transmitted. ; Step 102: Using the angular spectrum propagation model to... The light propagates to the wafer plane and is obtained from the wafer surface light field. ; Step 103, Construction intensity With target graphics The joint optimization function J is obtained, and the joint optimization function J is solved by an iterative optimization method. During the iteration process, the light source phase code is jointly updated. The phase parameters and amplitude parameters of the binary amplitude mask M are used to obtain the optimal light source phase encoding and the optimal binary amplitude mask; Step 104: Based on the optimal light source phase encoding and the optimal binary amplitude mask, perform digital holographic lithography exposure and development on the wafer surface to form a high-resolution angular interference nodal line pattern on the wafer surface.
[0007] The method described in this invention is also characterized in that, in step 101, the light field after mask transmission is obtained using equation (2). : (2) In equation (2), It is the transmission operator of the binary amplitude mask M. The parameter representing the binary amplitude mask M, express The light field after propagating over a distance d.
[0008] Furthermore, in step 102, the light field on the wafer surface is obtained using equation (3). : (3) In equation (3), and These are the Fourier transform and its inverse transform, respectively. is the angular spectral transfer function, used to describe the propagation process of the light field from the exit plane of the binary amplitude mask M to the wafer plane.
[0009] Furthermore, in step 103, the joint optimization function J is constructed using equation (5): (5) In equation (5), Represents the square of the modulus. This represents the square of the L2 norm.
[0010] Furthermore, the phase encoding of the light source is constructed using equation (1). Orbital angular momentum spiral phase function: (1) In equation (1), The topological charge representing the orbital angular momentum. Represents the polar coordinates in the horizontal plane. The imaginary unit; The binary amplitude mask M has a periodic structure in the polar direction, and the angular period of the binary amplitude mask M is related to the topological charge. They are inversely proportional.
[0011] The present invention provides an electronic device, including a memory and a processor, characterized in that the memory is used to store a program supporting the processor in performing the method described therein, and the processor is configured to execute the program stored in the memory.
[0012] The present invention discloses a computer-readable storage medium storing a computer program, characterized in that the computer program is executed by a processor to perform the steps of the method described thereon.
[0013] Compared with existing technologies, the beneficial effects of this invention are reflected in: 1. This invention introduces phase encoding at the light source end and performs collaborative optimization design with the binary amplitude mask, transferring the complex optical field modulation function originally undertaken by the mask to the programmable and controllable light source phase encoding. This simplifies the mask structure from the traditional multi-layer, high aspect ratio, deep subwavelength three-dimensional structure to a planar binary amplitude mask, thereby significantly reducing the mask's processing difficulty, manufacturing cost, and process complexity, and improving the system's engineering feasibility and mass production adaptability.
[0014] 2. This invention achieves the coordinated design of light source phase modulation and mask diffraction characteristics by constructing a joint optimization model of light source phase encoding parameters and mask binarization structure parameters, enabling high-frequency information to participate in the imaging process in a coherent manner. This effectively avoids the problem of high-frequency components being hard-filtered out during the propagation stage, thereby improving the lithography system's ability to transmit and reconstruct high spatial frequency information.
[0015] 3. This invention introduces a light source phase encoding with orbital angular momentum characteristics and combines it with a binary amplitude mask with angular period matching to form a high-contrast angular interference nodal line structure on the wafer surface. This effectively enhances the interference modulation capability of the angular spatial frequency components, thereby significantly improving the angular imaging resolution of the system and achieving a resolution capability that surpasses that of traditional illumination and mask combinations.
[0016] 4. By concentrating key high-frequency modulation information on the phase encoding side of the light source, rather than relying on the fine subwavelength structure of the mask, this invention significantly reduces the system's sensitivity to mask critical size deviations, processing errors, and illumination condition fluctuations, thereby improving the stability and process tolerance of the digital holographic lithography process. Attached Figure Description
[0017] Figure 1 A schematic flowchart of the digital holographic lithography method of the present invention; Figure 2 This invention provides a schematic diagram of the propagation model of the light field from the light source to the mask and then to the wafer, including... , and Location relationship diagram; Figure 3 Example diagram of the binary amplitude mask M obtained by the optimization of this invention; Figure 4 The high-resolution angular interference nodal lines formed on the wafer surface of this invention (i.e. ) and target graphics The comparison chart. Detailed Implementation
[0018] In this embodiment, a digital holographic lithography method based on the collaborative optimization of light source phase encoding and binarized mask is described, such as... Figure 1 As shown, it includes the following steps: Step 1: Construct an extreme ultraviolet (EUV) digital holographic lithography system and generate the incident light field. A highly coherent EUV source with a working wavelength of 13.5 nm is used as the incident light source. The EUV source is either a high-harmonic femtosecond laser or a free-electron laser, used to generate the incident light field. This provides coherent light conditions for subsequent holographic propagation and interference.
[0019] Step 2: Apply source phase encoding to the incident light field The orbital angular momentum spiral phase is applied to the incident light field. Above, a phase-encoded light field is formed, wherein the light source phase is encoded. Represented as Equation (1); (1) In equation (1), The topological charge number, representing orbital angular momentum. Represents the angular coordinates in the polar coordinate system. The imaginary unit is used. Topological load number. It participates in joint optimization as an adjustable discrete parameter to control the angular phase distribution characteristics of the optical field.
[0020] Step 3: Set up a binary amplitude mask and form a cooperatively encoded optical field.
[0021] After the light field, after phase encoding of the light source, propagates to the mask plane, a binary amplitude mask M(x,y) is introduced, whose transmission amplitude A M ∈{0, 1}. The structural parameters of the binary amplitude mask include the ring width, radius, and spatial arrangement, and are used as one of the joint optimization variables. The angular period Λ of the binary amplitude mask M is related to the orbital angular momentum topological charge. Satisfy the preset matching relationship This ensures that the angular frequency components generated by mask diffraction and the orbital angular momentum phase gradient are coherently superimposed in the angular direction, thereby enhancing the angular interference modulation effect. The phase-encoded optical field and the binary amplitude mask work together to form the mask transmission optical field. Its mathematical expression is equation (2): (2) In equation (2), It is a mask transmission operator. The distance from the light source to the mask. The geometric parameters representing the mask M, express The light field after propagating a distance d. The spatial relationship of the propagation model is as follows: Figure 2 As shown, an example of a mask structure is as follows: Figure 3 As shown.
[0022] Step 4: Calculate the light field on the wafer surface based on the angular spectrum propagation model.
[0023] Step 4.1: Modeling the forward propagation of the light field.
[0024] Transmitting light field through the mask As input, the propagation is transmitted to the wafer plane via the angular spectrum propagation model. The complex amplitude optical field on the wafer surface was obtained. Its propagation model is expressed as equation (3): (3) In equation (3), and These are the Fourier transform and its inverse transform, respectively. is the angular spectral transfer function, used to describe the propagation process of the light field from the exit plane of the binary amplitude mask M to the wafer plane.
[0025] Step 4.2: Construct the angular spectrum transfer function The expression used to describe the free-space propagation characteristics from the mask plane to the wafer plane is given by equation (4): (4) In equation (4), For transmission distance, Extreme ultraviolet light wavelength, and It is a spatial frequency component.
[0026] Step 5: Construct a joint optimization function and perform iterative optimization to solve it.
[0027] Step 5.1: Using the light intensity of the wafer surface With target graphics The error between them is the optimization objective. Using equation (5), a joint optimization function J is constructed: (5) In equation (5), Represents the square of the modulus. The square of the L2 norm is used to represent the joint optimization variables, which include the orbital topology charge. And the geometric parameters of the binary amplitude mask M.
[0028] Step 5.2: The joint optimization function J is minimized using an iterative optimization strategy. The iterative process includes forward propagation to calculate the optical field and error function values on the wafer surface, and backward propagation to update the orbital angular momentum topological charge. The mask structure parameters are determined, and during the iteration process, both the mask binarization constraint and the topological load integer constraint are applied until the joint optimization function J converges.
[0029] Step 6: Perform extreme ultraviolet exposure and development based on the optimization results.
[0030] The optimal orbital angular momentum topological charge obtained by iterative optimization and the optimal binary amplitude mask M * Digital holographic lithography exposure and development are performed on the wafer to form a high-resolution angular interference nodal line structure on the wafer surface.
[0031] Step 7: Finally, through measurement and comparison, it is verified that the present invention can improve the angular resolution of the wafer surface by ≥1.6 times. For example... Figure 4 As shown, 401 represents the high-resolution angular interference nodal line pattern formed on the wafer surface using the digital holographic lithography method based on the collaborative optimization of light source phase encoding and binarized mask according to the present invention; 402 represents the corresponding target pattern. Through comparison... Figure 4 As can be seen from parts 401 and 402, the angular interference nodal lines obtained by the method of the present invention are highly consistent with the target image in terms of the number of nodal lines, angular spacing and edge sharpness, indicating that the present invention can effectively improve angular resolution under single exposure conditions.
[0032] In this embodiment, an electronic device includes a memory and a processor. The memory stores a program that supports the processor in executing the above-described method, and the processor is configured to execute the program stored in the memory.
[0033] In this embodiment, a computer-readable storage medium stores a computer program, which is executed by a processor to perform the steps of the above method.
Claims
1. A method of digital holographic lithography based on phase encoding of light source in cooperation with binary mask optimization, characterized in that, The method comprises the following steps: Step 101, encode the incident light field Applying light source phase encoding and in cooperation with the binary amplitude mask M, form the light field transmitted by the mask ; Step 102, propagating the angular spectrum to the wafer plane by an angular spectrum propagation model, and obtaining a wafer surface light field ; Step 103, Construction intensity With target graphics The joint optimization function J is obtained, and the joint optimization function J is solved by an iterative optimization method. During the iteration process, the light source phase code is jointly updated. The phase parameters and amplitude parameters of the binary amplitude mask M are used to obtain the optimal light source phase encoding and the optimal binary amplitude mask; Step 104, performing digital holographic lithography exposure and development processing on the wafer surface based on the optimal light source phase encoding and the optimal binary amplitude mask, so as to form a high-resolution angular interference node line pattern on the wafer surface.
2. The method of claim 1, wherein, The step 101 is to obtain the light field transmitted by the mask using formula (2) : (2) in formula (2), is the transmission operator of the binary amplitude mask M, denotes the parameters of the binary amplitude mask M, denotes the light field after propagation over a distance d.
3. The method of claim 1, wherein, The step 102 is to obtain the light field on the wafer surface by using formula (3) : (3) In formula (3), and are the Fourier transform and its inverse, respectively, is the angular spectrum transfer function, which describes the propagation of the optical field from the exit plane of the binary amplitude mask M to the wafer plane.
4. The method of claim 1, wherein, In step 103, a joint optimization function J is constructed by using formula (5): (5) In formula (5), denotes the square of the modulus, denotes the square of the two-norm.
5. The method of claim 1, wherein, constructing the phase encoding of the light source with formula (1) orbit angular momentum helical phase function: (1) In formula (1), denotes the topological charge of the orbital angular momentum, denotes the polar angular coordinate in the transverse plane, is the imaginary unit; The binary amplitude mask M has a periodic structure in the polar angular direction, and the angular period of the binary amplitude mask M is inversely proportional to the topological charge of the vortex beam.
6. An electronic device comprising a memory and a processor, characterized in that The memory is used for storing a program supporting the processor to execute the method in any one of claims 1-5, and the processor is configured to execute the program stored in the memory.
7. A computer-readable storage medium having stored thereon a computer program, characterized in that The computer program, when executed by the processor, performs the steps of the method in any one of claims 1-5.