Extreme ultraviolet (EUV) lithography using interlayers or multilayer stacks with various mean free paths for secondary electron generation.

Abstract

A method for patterning a substrate includes providing a substrate and depositing a multilayer stack comprising N layers on the substrate, where N is an integer greater than 1. The N layers each include N mean free paths of secondary electrons. The method includes depositing a photoresist layer on the multilayer stack, where the N mean free paths converge at the photoresist layer. Another method for patterning a substrate includes providing a substrate and depositing a layer on the substrate, where the layer includes different mean free paths of secondary electrons. The method includes depositing a photoresist layer on the layer, where the different mean free paths of the secondary electrons converge at the photoresist layer.

Description

Technical Field

[0001] [Cross - Reference to Related Applications] This application claims the benefit of U.S. Provisional Application No. 62 / 849,115, filed May 16, 2019. The entire disclosure of the above application is incorporated herein by reference.

[0002] This disclosure relates to a substrate processing system, and more particularly to EUV lithography using an intervening layer or multilayer stack having various mean free paths for secondary electron generation.

Background Art

[0003] The description of the background art herein is for the purpose of generally presenting the content of the present disclosure. The inventions of the presently named inventors are not to be regarded as prior art to the present disclosure, either explicitly or implicitly, to the extent that they are described in a manner that does not fall within the scope of the prior art at the time of filing this application and in the context of the background art section.

[0004] Advanced photolithography is typically performed using an excimer laser having a wavelength of 193 nm. To form feature sizes smaller than 193 nm, additional techniques such as multipatterning, immersion, and / or optical proximity correction are implemented to significantly enhance the resolution below 193 nm. However, it is difficult to further reduce feature sizes using this type of photolithography.

[0005] Next - generation photolithography techniques use extreme ultraviolet (EUV) wavelengths. In EUV lithography, a power source converts a plasma into light at a wavelength of 13.5 nm, which is 1 / 14 the length of 193 nm. However, because most materials absorb photons immediately at EUV wavelengths, the short EUV wavelength requires significant changes to the photolithography process. For example, EUV lithography uses multiple mirrors instead of lenses to reflect light. The EUV lithography process is also performed in a vacuum environment. A plasma source is used instead of a laser to generate photons for printing.

[0006] EUV radiation is reflected by the photoresist layer through the mask pattern. The photoresist layer absorbs EUV photons, generating secondary electrons. Specifically, EUV photons with sufficient energy ionize atoms in the photoresist layer, causing secondary electrons to be emitted.

[0007] EUV photolithography is particularly sensitive to stochastic effects. When printing features using EUV, most features are decomposed. Due to the probability variation in the number of photons that reach the print, some areas designated for printing may not actually reach the print threshold, leaving unexposed areas or defects. The defect rate is related to the dose level. However, increasing the dose level is difficult in EUV photolithography systems. Parameters such as dose amount relative to size and dose amount relative to defects may be used to characterize the performance of EUV systems. [Overview of the project]

[0008] A method for patterning a substrate includes the steps of providing the substrate and depositing a multilayer stack containing N layers on the substrate, where N is an integer greater than 1. Each of the N layers contains N mean free paths of secondary electrons. The method includes the step of depositing a photoresist layer on the multilayer stack, where the N mean free paths converge at the photoresist layer.

[0009] Another characteristic is that the mean free path of N layers differs.

[0010] In other features, the N layers are located at a distance of N from the photoresist layer, and the mean free path of the N layers increases with distance N.

[0011] In other features, the N layers are located at a distance of N from the photoresist layer, and the mean free path of the N layers increases monotonically with distance N.

[0012] In other features, the N layers are located at a distance of N from the photoresist layer, and the mean free path of the N layers increases linearly with distance N.

[0013] In other features, the N layers are located at a distance of N from the photoresist layer, each having an absorption rate of N, and the absorption rate of the N layers increases as the distance of N increases.

[0014] Another characteristic is that each layer of the N layers has the same thickness.

[0015] Another characteristic is that each layer of the N layers has a different thickness.

[0016] In another feature, this method further includes the step of arranging the N layers in order of increasing thickness, with the thinnest layer of N being placed adjacent to the photoresist layer and the thickest layer of N being placed adjacent to the substrate.

[0017] Another feature of this method is that it further includes a step of exposing the photoresist layer to extreme ultraviolet light.

[0018] In other features, this method further includes the steps of exposing a photoresist layer to extreme ultraviolet light and removing the exposed portion of the photoresist layer. This method further includes the step of removing the multilayer portion located in the area where the photoresist layer has been removed.

[0019] In other features, this method further includes the steps of exposing a photoresist layer to extreme ultraviolet light and removing the exposed portion of the photoresist layer to form a patterned photoresist layer. This method further includes the steps of carrying out a deposition process using the patterned photoresist layer and removing the photoresist layer and multilayer stack after the deposition process.

[0020] In other features, this method further includes the steps of exposing a photoresist layer to extreme ultraviolet light and removing the exposed portion of the photoresist layer to form a patterned photoresist layer. This method further includes the steps of performing an etching process using the patterned photoresist layer and removing the photoresist layer and multilayer after the etching process.

[0021] Further features include a method for patterning a substrate, comprising the steps of providing the substrate and depositing layers on the substrate. The layers contain various mean free paths of secondary electrons. This method also includes the step of depositing a photoresist layer on the layers. The various mean free paths of secondary electrons converge at the photoresist layer.

[0022] Another characteristic is that the mean free paths of various layers increase monotonically with distance to the photoresist layer.

[0023] Another characteristic is that the mean free path of various layers increases linearly with distance to the photoresist layer.

[0024] Another characteristic is that the mean free path of each layer increases stepwise as a function of the distance to the photoresist layer.

[0025] Another feature of this method is that it further includes a step of exposing the photoresist layer to extreme ultraviolet light.

[0026] In other features, this method further includes the steps of exposing a photoresist layer to extreme ultraviolet light and removing the exposed portion of the photoresist layer. This method further includes the step of removing the portion of the layer located in the area where the photoresist layer has been removed.

[0027] In other features, this method further includes a step of exposing a substrate to extreme ultraviolet light and a step of removing the exposed portion of the photoresist layer to form a patterned photoresist layer. This method further includes a step of performing a deposition process using the patterned photoresist layer and a step of removing the layer and the photoresist layer after the deposition process is performed.

[0028] In other features, this method further includes a step of exposing a substrate to extreme ultraviolet light and a step of removing the exposed portion of the photoresist layer to form a patterned photoresist layer. This method further includes a step of performing an etching process using the patterned photoresist layer and a step of removing the layer and the photoresist layer after the etching process is performed.

[0029] Further applicable fields of the present disclosure will become apparent from the embodiments for carrying out the invention, the claims, and the drawings. The embodiments for carrying out the invention and specific examples are intended for illustrative purposes only and are not intended to limit the scope of the present disclosure.

Brief Description of the Drawings

[0030] The present disclosure will be more deeply understood from the embodiments for carrying out the invention and the accompanying drawings.

[0031] [Figure 1] Side cross-sectional view of an exemplary substrate including a multilayer stack of layers that generate secondary electrons having various mean free paths according to the present disclosure. [Figure 2] Side cross-sectional view of an exemplary substrate including a multilayer stack of layers that generate secondary electrons having various mean free paths according to the present disclosure.

[0032] [Figure 3] Flowchart of an exemplary method for patterning a substrate using EUV lithography according to the present disclosure.

[0033] [Figure 4]Side cross-sectional view of an exemplary substrate according to the present disclosure, which includes layers having various mean free paths located between a photoresist layer and a substrate.

[0034] [Figure 5A] A graph illustrating the exemplary change in mean free paths in the layer shown in Figure 4. [Figure 5B] A graph illustrating the exemplary change in mean free paths in the layer shown in Figure 4.

[0035] [Figure 6] A flowchart illustrating an exemplary method for patterning a substrate using EUV photolithography according to this disclosure.

[0036] In drawings, reference numbers may be used repeatedly to identify similar and / or identical elements. [Modes for carrying out the invention]

[0037] Because the dose levels of available EUV sources are limited, several techniques have been employed to better utilize the available dose levels from the EUV source. For example, a film layer may be deposited between the photoresist layer and the underlying substrate. This layer enhances the generation of secondary electrons and improves the dose-to-size and dose-to-defect parameters. However, since the secondary electron generating layer can only generate a finite number of secondary electrons, this method only provides a limited improvement.

[0038] Another approach uses plasma etching smoothing techniques to improve the dose for both size and defects. By improving resist roughness, stochastic defects can be reduced, allowing for the use of lower dose specifications for both size and detection. This approach also imposes a finite limit on increasing the dose. However, this approach may be difficult to tune. As lithographic patterning films become thinner, selectivity becomes a more important consideration, and etching techniques for improving roughness will become more limited.

[0039] Another approach is to increase the sensitivity of the photoresist layer. However, this approach requires trade-offs in dose, resolution, and roughness. Increased sensitivity will inevitably lead to a decrease in either resolution or roughness, both of which are undesirable.

[0040] The methods for patterning substrates described herein offer improvements in the parameters of dose-to-size and dose-to-defect ratios for EUV photolithography. In some examples of the herein, a multilayer laminate is deposited between a photoresist layer and a substrate. Different layers of the multilayer laminate generate secondary electrons with different mean free paths. In some examples, the mean free path of a layer in the multilayer laminate increases as its distance from the photoresist layer increases.

[0041] As described above, when a uniform monolayer is used, the generated secondary electrons have a single mean free path, resulting in a finite secondary electron density that can penetrate the photoresist layer. To overcome this limitation, multilayer stacks include multiple layers with different mean free paths of secondary electrons. In some examples, the mean free paths of the layers converge in the photoresist layer. For example, layers in a multilayer stack located farther from the photoresist layer have longer mean free paths of secondary electrons than layers located closer to the photoresist layer.

[0042] Referring to Figures 1 and 2, the substrate 10 comprises a photoresist layer 20 to be patterned. The photoresist layer 20 is deposited on a multilayer stack 22. The multilayer stack 22 consists of a layer 24-1 having a first mean free path of secondary electrons and a layer having a second mean free path of secondary electrons different from the first mean free path. 24-2 The multilayer laminate 22 is deposited on top of the underlying substrate layer 32.

[0043] After the photoresist layer 20 and the multilayer stack 22 are deposited, the substrate 10 is exposed to EUV radiation reflected from the mask pattern. In some examples, one or more additional steps may be performed to remove the exposed (or unexposed) photoresist layer and / or to remove the portion of the multilayer stack located in the area where the photoresist layer has been removed. Additional processes such as deposition and / or etching can be performed using the patterned photoresist layer 20. After the additional processes are performed, the photoresist layer 20 and the multilayer stack 22 are removed.

[0044] In Figure 2, a secondary electron generation layer 24-N of N can be used (where N is an integer greater than 1). In some examples, the secondary electron generation layer 24-N of N has different mean free paths. For example, when N=3, layer 24-3 has the longest mean free path terminating at the photoresist layer 20, layer 24-2 has an intermediate mean free path terminating at the photoresist layer 20, and layer 24-1 has the shortest mean free path terminating at the photoresist layer 20.

[0045] Next, referring to Figure 3, a method 100 for patterning a substrate and a multilayer including layers with different mean free paths is shown using EUV. Method 100 includes the step in 110 of depositing a first layer of a multilayer laminate 22 having the longest mean free path of secondary electrons on a substrate 32. In 114, an N-1 additional layer is deposited on the first layer of the multilayer laminate 22. The N-1 additional layer has a different mean free path of secondary electrons than the first layer. In some examples, the sequentially deposited layers of the multilayer laminate 22 have a shorter mean free path than the previously deposited layers of the multilayer laminate 22. In 118, a photoresist layer 20 is deposited on the multilayer laminate 22. In 122, a selected portion of the photoresist layer is exposed using EUV light and further processing is performed as described above.

[0046] In some examples, the layer furthest from the photoresist layer 20 generates secondary electrons with the longest mean free path. The mean free paths of the other layers in the multilayer stack 22 are then targeted to converge to approximately the same depth at the photoresist layer 20. In the above example with N=3, the number of secondary electrons reaching the photoresist layer 20 is approximately three times greater. As a result, the required dose can be reduced to approximately one-third.

[0047] In some examples, the mean free path of secondary electrons in each layer is controlled by selecting different materials for the corresponding layers. For example, materials with different absorption properties can be used. Collection Absorbent materials tend to have short mean free paths. In some examples, multilayer laminates 22 have high absorbency on their upper layer. Collection It has layers, and the suction gradually decreases towards the bottom. Collection It has layers.

[0048] Referring now to Figure 4, the substrate 200 comprises a photoresist layer 20 to be patterned. The photoresist layer 20 is deposited on a layer 210 having different mean free paths with varying depths. In some examples, as the perpendicular distance from the photoresist layer 20 increases, the mean free paths lengthen continuously, monotonically, or stepwise.

[0049] After depositing photoresist layers 20 and 210 onto the underlying substrate layer 32, the substrate 200 is exposed to EUV radiation reflected from the mask pattern. In some examples, one or more additional steps may be performed to remove exposed (or unexposed) photoresist and / or to remove layer 210 located in areas where photoresist layer 20 has been removed. Additional processes such as deposition and / or etching can be performed using the patterned photoresist layer 20. After the additional processes are performed, photoresist layers 20 and 210 are removed.

[0050] Referring now to Figures 5A and 5B, there are many ways to change the mean free path in layer 210. For example, the mean free path can increase with distance (linearly, monotonically, stepwise, etc.). In Figure 5A, the mean free path increases linearly with distance. In Figure 5B, the mean free path increases stepwise as a function of distance to the photoresist layer.

[0051] Next, referring to Figure 6, a method 300 for patterning a substrate using EUV photolithography, a photoresist layer 20, and a layer 210 having various mean free paths of secondary electrons is shown. In this method 300, a layer having various mean free paths of secondary electrons is placed on top of the underlying substrate layer 32. 210 The process includes a step of depositing a photoresist. In step 314, the photoresist layer 20 is deposited on layer 210. In step 318, a selected portion of the photoresist layer 20 is exposed using EUV light and further processing is performed as described above.

[0052] In other examples, local dose increases can also be modified by adjusting the mean free path across all layers.

[0053] Absorption of EUV photons into the lower layer of the stacked material results in the generation of photoelectrons (also known as primary electrons). Primary electrons with sufficient energy ionize atoms and release secondary electrons.

[0054] In a uniform layer, the inelastic mean free path (IMFP) of secondary electrons is a function of electron energy, resulting in a finite density of secondary electrons that can penetrate the photoresist. Multilayer films can be developed within the critical range of electron energy when the film exhibits a longer IMFP for secondary electrons generated further away from the photoresist, thereby increasing the energy deposited on the photoresist by secondary electrons.

[0055] Layers further away from the photoresist generate secondary electrons with longer mean free paths (within the critical range of electron energy capable of inducing the desired chemical reaction in the photoresist). Layers closer to the photoresist generate secondary electrons with shorter mean free paths (within the critical range of electron energy capable of inducing the desired chemical reaction in the photoresist).

[0056] In the example above, the number of generated secondary electrons reaching the photoresist is expected to increase as a result of the multilayer arrangement. One potential property for changing the mean free path is to change the film density. Since higher density is expected to result in a shorter mean free path, a potential stack consists of a high-density film at the top of the multilayer stack, with the density gradually decreasing towards the bottom. The multilayer films are not limited to separate materials and may be a single material with a gradient. The thickness of the photoresist at which a significant change in the effective dose is achieved can be changed by adjusting the IMFP of all layers. Examples of materials are shown in the table below. [Table 1]

[0057] In a multilayer structure, the thickness of each layer may be the same or different. In some examples, the total thickness of the multilayer structure may be within a predetermined thickness (e.g., 10 nm). When the thicknesses of the layers in the multilayer structure differ, the layers are arranged in a monotonically increasing order from the top to the bottom of the stack. The thinnest layer is located at the top of the stack directly beneath the photoresist, and the thickest layer is located at the bottom of the stack directly above the substrate.

[0058] For example, a multilayer structure may include 2 to 4 layers, with a total thickness of 5 nm. For example, a multilayer structure may include 2 layers, each having a thickness of 2.5 nm. For example, a multilayer structure may include 4 layers, each having a thickness of 1.25 nm. For example, a multilayer structure may include 2 layers: one layer with a thickness of 2 nm placed directly beneath a photoresist layer, and another layer with a thickness of 3 nm placed directly beneath the 2 nm layer and directly above the substrate.

[0059] In another example, the multilayer structure may consist of 2 to 4 layers, with a total thickness of 10 nm. For example, the multilayer structure may consist of 2 layers, each having a thickness of 5 nm. For example, the multilayer structure may consist of 4 layers, each having a thickness of 2.5 nm. For example, the multilayer structure may consist of one layer with a thickness of 4 nm placed directly beneath the photoresist layer, 4 It may include two layers: one nm layer and another 6 nm thick layer located directly beneath the substrate. For example, a multilayer stack may include three layers: a first layer 2 nm thick located directly beneath the photoresist layer, a second layer 3 nm thick located directly beneath the first layer, and a third layer 5 nm thick located directly beneath the 3 nm layer and directly above the substrate. Various other examples are possible.

[0060] For several exemplary single-layer configurations, the thickness of the single layer with various mean free paths may be less than or equal to a predetermined thickness (e.g., 10 nm). Furthermore, in any configuration, the thickness of the photoresist layer may be, for example, 20 nm to 40 nm. The method of this disclosure reduces the EUV dose by approximately 10%, resulting in significant cost savings.

[0061] The foregoing is essentially descriptive and is by no means intended to limit the Disclosure, its application, or use. The broad teachings of this Disclosure can be implemented in various forms. Thus, although this Disclosure includes certain examples, the true scope of this Disclosure should not be so limited, as other modifications become apparent when examining the drawings, specification, and the claims below. It should be understood that one or more steps within a Method may be performed in a different order (or simultaneously) without altering the principles of this Disclosure. Furthermore, although each embodiment is said to have certain features, any one or more of those features described in relation to the embodiments of this Disclosure may be implemented in other embodiments and / or in combination with features of other embodiments (even if such combination is not specified). In other words, the embodiments described are not mutually exclusive, and rearrangements of one or more embodiments remain within the scope of this Disclosure.

[0062] Spatial and functional relationships between elements (e.g., between modules, between circuit elements, between semiconductor layers, etc.) are described using a variety of terms, including “connected,” “engaged,” “joined,” “adjacent,” “nearby,” “above,” “upward,” “downward,” and “positioned.” When a relationship between a first element and a second element is described in the above disclosure, unless it is explicitly stated to be “direct,” the relationship may be a direct relationship in which no other intervening elements exist between the first and second elements, or it may be an indirect relationship in which one or more intervening elements exist (spatially or functionally) between the first and second elements. The expression “at least one of A, B, and C” as used herein should be interpreted as meaning the logic using the non-exclusive logic OR (A OR B OR C), and not as “at least one of A, at least one of B, and at least one of C.”

Claims

1. A method for patterning a circuit board, A step of depositing a first layer on a substrate, wherein the first layer comprises silicon (Si) or silicon oxynitride (SiON) and has a first thickness of 3 nm (nanometers) or 6 nm, and the first layer includes a first mean free path of secondary electrons. A step of depositing a second layer on the first layer, wherein the second layer comprises tin (Sn) or tin oxide (SnO₂) and comprises a second thickness, the second thickness being 2 nm or 4 nm when the first thickness is 3 nm or 6 nm, and the second layer comprises a second mean free path of secondary electrons that is smaller than the mean free path of the first layer. A step of depositing a photoresist layer on the second layer, wherein the photoresist layer comprises a chemically amplified organic photoresist material, and the first mean free path and the second mean free path converge in the photoresist layer. Methods that include...

2. The method according to claim 1, A method in which the first mean free path of the first layer and the second mean free path of the second layer are different.

3. The method according to claim 1, A method wherein the first layer and the second layer are located at a first distance and a second distance, respectively, from the photoresist layer, and the first mean free path of the first layer and the second mean free path of the second layer increase in proportion to the first distance and the second distance.

4. The method according to claim 1, The first layer and the second layer are located at a first and second distance, respectively, from the photoresist layer, and the first mean free path of the first layer and the second mean free path of the second layer increase monotonically with respect to the first and second distances, respectively.

5. The method according to claim 1, A method wherein the first layer and the second layer are located at a first distance and a second distance, respectively, from the photoresist layer, and the first mean free path of the first layer and the second mean free path of the second layer increase linearly with respect to the first and second distances.

6. The method according to claim 1, A method wherein the first layer and the second layer are located at a first distance and a second distance, respectively, from the photoresist layer, and have a first absorptivity and a second absorptivity, wherein the first absorptivity of the first layer and the second absorptivity of the second layer increase as the first distance and the second distance decrease, respectively.

7. The method according to claim 1, further, A method comprising the step of exposing the photoresist layer to extreme ultraviolet light.

8. The method according to claim 1, further, The process of exposing the photoresist layer to extreme ultraviolet light, A step of removing the exposed portion of the photoresist layer, A step of removing the portions of the first layer and the second layer located in the area where the photoresist layer has been removed, Methods that include...

9. The method according to claim 1, further, The process of exposing the photoresist layer to extreme ultraviolet light, The process involves removing the exposed portion of the photoresist layer to form a patterned photoresist layer, A step of performing an etching process using the patterned photoresist layer, After performing the etching process, the process involves removing the photoresist layer, the first layer, and the second layer. Methods that include...

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