Selective deprotection by dye diffusion

Abstract

A method for patterning a substrate by selective deprotection by dye diffusion, comprising forming a photoresist pattern on the substrate from a layer of photoresist deposited on the substrate, and depositing a first overcoat on the photoresist pattern, the first overcoat filling openings defined by the photoresist pattern and covering the photoresist pattern, the first overcoat comprising an organic film containing a dye. The method further comprises diffusing a dye from the first overcoat into the photoresist pattern over a predetermined diffusion length to provide a diffusion region in the photoresist pattern, and removing the first overcoat from the substrate. The method further comprises activating a solubility shift agent in the diffusion region of the photoresist pattern using a second actinic radiation, depositing a second overcoat on the substrate, and developing the substrate with a second developer to remove the soluble portion of the diffusion region of the photoresist pattern.

Description

[Technical field]

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS This application is related to and claims priority to U.S. Provisional Patent Application No. 62 / 308,701, filed February 10, 2022, the entire contents of which are incorporated herein by reference.

[0002] The present invention relates to microfabrication, including microfabrication of integrated circuits, and to processes involving the patterning of semiconductor substrates. [Background technology]

[0003] In material processing methodologies (such as photolithography), creating a patterned layer typically involves applying a thin layer of radiation-sensitive material, such as photoresist, to the top surface of a substrate. This radiation-sensitive material is converted into a patterned mask that can be used to etch or transfer a pattern into an underlying layer on the substrate. Patterning a radiation-sensitive material generally involves exposure of the radiation-sensitive material to a radiation source through a reticle (and associated optics), for example using a photolithography exposure system. This exposure creates a latent image pattern in the radiation-sensitive material, which can later be developed. Development refers to dissolving and removing portions of the radiation-sensitive material to obtain a relief pattern. The removed portions of material can be either irradiated or unirradiated areas of the radiation-sensitive material, depending on the type of photoresist tone and / or developer solvent used. The relief pattern can then act as a mask layer that defines the pattern.

[0004] Preparation and development of various films for patterning may include thermal treatment or baking. For example, a freshly applied film may undergo a post-apply bake (PAB) to evaporate solvents and / or increase the rigidity or etch resistance of the structure. A post-exposure bake (PEB) may also be performed to harden a given pattern to prevent further dissolution. A manufacturing tool for application and development on a substrate typically includes one or more bake modules. Some photolithography processes include coating a substrate with a thin layer of bottom anti-reflective coating (BARC), followed by coating with resist, and then exposing the substrate to a pattern of light as a process step for creating microchips. The formed relief pattern may then be used as a mask or template for additional processing, such as transferring the pattern to an underlying layer. Summary of the Invention [Problem to be solved by the invention]

[0005] Continuing miniaturization requires improved patterning resolution. One approach is spacer technology, which defines sub-resolution line features via atomic layer deposition (ALD). However, one challenge is that if opposite tone features are desired, using spacer technology can be costly because it can be complicated, involving overcoating of another material, chemical mechanical planarization (CMP) and reactive ion etching (RIE) to excavate the spacer material and leave a narrow trench.

[0006] Spacer prevention is a self-aligned technique that uses the diffusion length of the reactive species to define the critical dimension (CD) and form narrow trenches. By spatially controlling the reactive species by exposure through a mask, narrow slot contacts can be formed instead of narrow trenches. Instead of spatial control, the reactive species can be controlled uniformly across the wafer by decomposition of a thermal acid generator through a bake process. The corresponding CD can be adjusted by modifying the molecular weight of the reactive species, the molecular structure of the reactive species, and the bake temperature and bake time. Furthermore, the CD can be controlled by the composition of the material through which the reactive species diffuses. The polarity of the components in the resin can affect the diffusivity of the acid, and the activation energy of the reactive species-sensitive components of the material is an additional means to control the process. These techniques can realize narrow slot contact features with dimensions beyond the capabilities of advanced lithography. However, the process requires a "freeze" step, i.e., a process that negates the possibility of a solubility shift in the layer with the acid generator. However, the freeze process is not perfect and can reduce throughput. [Means for solving the problem]

[0007] According to one embodiment of the present invention, a method of patterning a substrate includes forming a photoresist pattern on the substrate from a layer of photoresist deposited on the substrate, the layer of photoresist including a solubility-shifting agent, the photoresist pattern being formed by activating the solubility-shifting agent using a first pattern of actinic radiation and removing soluble portions of the layer of photoresist by developing the substrate using a first developer; depositing a first overcoat on the photoresist pattern, the first overcoat filling openings defined by the photoresist pattern and covering the photoresist pattern, the first overcoat including an organic film including a dye; causing the dye to diffuse from the first overcoat into the photoresist pattern by a predetermined diffusion length, thereby providing a diffusion region in the photoresist pattern; and removing the first overcoat from the substrate. The method further includes activating a solubility shift agent in the diffusion region of the photoresist pattern using a second actinic radiation, where the solubility shift agent is activated sufficiently to meet a threshold sensitivity in the diffusion region without meeting a threshold sensitivity of the photoresist pattern, depositing a second overcoat on the substrate, and removing the soluble portion of the diffusion region of the photoresist pattern by developing the substrate with a second developer, where the second overcoat is insoluble in the second developer. According to one embodiment, the removal of the soluble portion of the diffusion region of the photoresist pattern forms a spacer prevention feature between the remaining photoresist pattern and the second overcoat. The method may further include transferring the spacer prevention feature to an underlying layer by an etching process.

[0008] According to one embodiment of the present invention, a method of patterning a substrate includes forming a photoresist pattern on the substrate from a layer of photoresist deposited on the substrate, the layer of photoresist including a solubility shift agent, the photoresist pattern being formed by activating the solubility shift agent using a first pattern of actinic radiation and removing soluble portions of the layer of photoresist by developing the substrate using a first developer; depositing a first overcoat on the photoresist pattern, the first overcoat filling openings defined by the photoresist pattern and covering the photoresist pattern, the first overcoat including an organic film including a dye; diffusing the dye from the first overcoat into the photoresist pattern by a predetermined diffusion length, thereby providing a first diffusion region in the photoresist pattern; and removing the first overcoat from the substrate. The method further includes depositing a second overcoat on the substrate, activating a solubility shift agent in the first diffusion region of the photoresist pattern using a second actinic radiation, diffusing the solubility shift agent into the second overcoat to result in a second diffusion region in the second overcoat, where the solubility shift agent is sufficiently activated to meet a sensitivity threshold in the second diffusion region without meeting a sensitivity threshold of the second overcoat, and developing the substrate with a second developer to remove a soluble portion of the second diffusion region of the second overcoat, where the second overcoat and the first diffusion region of the photoresist pattern are insoluble in the second developer. According to one embodiment, the removal of the soluble portion of the second diffusion region of the second overcoat forms a spacer prevention feature between the remaining first diffusion region of the photoresist pattern and the second overcoat. The method may further include transferring the spacer prevention feature to an underlying layer by an etching process. According to another embodiment, removal of the soluble portion of the second diffusion region forms an air gap feature in the second overcoat.

[0009] It should be understood that the order of description of the various steps described herein has been presented for clarity of description. In general, the steps may be performed in any suitable order. Moreover, although each of the various features, techniques, configurations, etc. described herein may be described in separate parts of this disclosure, it is understood that each concept may be practiced independently of one another or in combination with one another. Thus, the present invention may be embodied and viewed in many different ways.

[0010] It should be noted that this Summary section does not specify all embodiments and / or incrementally novel aspects of the invention described in this disclosure or claims. Instead, this Summary provides only a preliminary discussion of different embodiments and corresponding points of novelty over the prior art. For further details and / or possible aspects of the invention and embodiments, the reader is referred to the Detailed Description section and corresponding figures of the present disclosure, which are discussed further below. [Brief description of the drawings]

[0011] [Figure 1A] 1 illustrates a substrate processing method for forming spacer prevention trenches according to one embodiment. [Figure 1B] 1 illustrates a substrate processing method for forming spacer prevention trenches according to one embodiment. [Figure 1C] 1 illustrates a substrate processing method for forming spacer prevention trenches according to one embodiment. [Figure 1D] 1 illustrates a substrate processing method for forming spacer prevention trenches according to one embodiment. [Figure 1E] 1 illustrates a substrate processing method for forming spacer prevention trenches according to one embodiment. [Figure 1F] 1 illustrates a substrate processing method for forming spacer prevention trenches according to one embodiment. [Figure 1G] 1 illustrates a substrate processing method for forming spacer prevention trenches according to one embodiment. [Figure 1H]1 illustrates a substrate processing method for forming spacer prevention trenches according to one embodiment. [Figure 1I] 1 illustrates a substrate processing method for forming spacer prevention trenches according to one embodiment. [Figure 2A] 4 illustrates a substrate processing method for forming spacer prevention trenches according to another embodiment. [Figure 2B] 4 illustrates a substrate processing method for forming spacer prevention trenches according to another embodiment. [Figure 2C] 4 illustrates a substrate processing method for forming spacer prevention trenches according to another embodiment. [Figure 2D] 4 illustrates a substrate processing method for forming spacer prevention trenches according to another embodiment. [Figure 2E] 4 illustrates a substrate processing method for forming spacer prevention trenches according to another embodiment. [Figure 3A] 1 illustrates a substrate processing method for forming air gaps in a membrane according to another embodiment. [Figure 3B] 1 illustrates a substrate processing method for forming air gaps in a membrane according to another embodiment. [Figure 3C] 1 illustrates a substrate processing method for forming air gaps in a membrane according to another embodiment. [Figure 3D] 1 illustrates a substrate processing method for forming air gaps in a membrane according to another embodiment. [Figure 3E] 1 illustrates a substrate processing method for forming air gaps in a membrane according to another embodiment. [Figure 3F] 1 illustrates a substrate processing method for forming air gaps in a membrane according to another embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The technology disclosed herein employs a track-based solution to precisely control the depth of reaction within an organic film by using diffusible dye molecules. This process spatially alters the transparency of the film via diffusion of dye from the outer film, thereby controlling with nanometer precision the depth at which photochemical reactions occur in the film or patterned features upon exposure to light.

[0013] According to one embodiment, a process for forming spacer prevention trenches in a patterned photoresist is described in detail. First, photoresist is patterned via photolithography on a substrate, including creating a photoresist pattern 100 including a series of nanoscale features 115 on an underlayer 110 and a base layer 105, as shown in a side cross-sectional view, FIG. 1A. The photoresist pattern 100 is formed from a layer of photoresist deposited on the substrate, the layer of photoresist including a solubility shifting agent, and the photoresist pattern 100 is formed by activating the solubility shifting agent using a pattern of first actinic radiation, and removing the soluble portion of the layer of photoresist by developing the substrate using a first developer. The layer of photoresist may be composed of, but is not limited to, an acid-deprotectable resin, a photoacid generator (PAG), and a quencher. These components are designed to meet the transparency requirements dictated by the wavelength of the incident photons to ensure uniform absorption throughout the depth of the photoresist.

[0014] Next, an organic film called the first overcoat 120 is deposited over the photoresist pattern 100, as shown in FIG. 1B. The first overcoat 120 can be deposited by spin-on deposition. The first overcoat 120 fills the openings defined by the photoresist pattern 100 and covers the photoresist pattern 100. Spin-on deposition typically results in an overburden area or thickness of material on the top surface of the substrate feature. The formulation of the first overcoat 120 is cast in a solvent or blend of solvents to prevent dissolution of the underlying photoresist pattern 100 or intermixing of the two films. The first overcoat 120 can be composed of, but is not limited to, a resin and a dye. The composition and concentration of the dye components are designed to meet the requirements of photon absorption, diffusivity and reactivity. The dye selected has a high absorption cross-section and non-bleaching properties at the specified wavelength. The dye may contain an acid amplifier that decomposes in the presence of acid to produce more acid by an acid catalyzed mechanism. Examples of acid amplifiers include compounds that produce fluorinated sulfonic acids upon decomposition.

[0015] Next, the dye molecules are diffused from the first overcoat 120 into the photoresist pattern 100 through a bake process, as shown in Figure 1C. The elevated temperature brings the dye molecules from the first overcoat 120 into the photoresist pattern 100 to a depth defined by the bake temperature, bake time, dye concentration and dye diffusivity. The predetermined diffusion length into the photoresist pattern results in a diffusion region 125 in the nanoscale feature 115 of the photoresist pattern 100.

[0016] Next, as shown in Figure ID, the substrate is washed with a solvent system selected to remove the first overcoat 120 selective to the photoresist pattern 100. The solvent system can be aqueous or organic and is defined by the composition of the first overcoat resin.

[0017] After removing the first overcoat 120, the substrate undergoes a second lithographic exposure step shown in FIG. 1E. The exposure step uses a second actinic radiation 130 to activate the solubility shifting agent in the diffusion regions 125 of the photoresist pattern 100, where the solubility shifting agent is activated sufficiently to meet the sensitivity threshold in the diffusion regions 125 without meeting the sensitivity threshold of the photoresist pattern 100. In the exposure step, the majority of the photons are absorbed in the areas of the patterned features that are diffused with the dye. The exposure dose is specified to achieve a critical number of PAG decomposition reactions required for solubility shift in the dye-infused areas. The presence of the dye reduces the number of PAG-photon interactions in the body of the pattern.

[0018] Then, after exposure, the activation step further includes baking the substrate at high temperature to promote deprotection of the resin via reaction with the photogenerated acid. The differential PAG decomposition from the dye-infused areas to the main part of the pattern allows for selective deprotection of the dye-infused areas. The resulting diffusion region 135 is shown in FIG. 1F.

[0019] Next, an organic film called second overcoat 140 is deposited over the photoresist pattern 100, as shown in FIG. 1G, where the second overcoat 140 fills the openings defined by the photoresist pattern 100 and covers the photoresist pattern 100. The formulation of the second overcoat 140 is cast in a solvent or blend of solvents to prevent dissolution of the underlying photoresist or intermixing of the two films. The second overcoat 140 is composed of a resin designed to have a low but non-zero dissolution rate in an aqueous developer such as tetramethylammonium hydroxide to controllably remove the film from the top of the photoresist pattern 100.

[0020] The substrate is then developed with a second developer to remove the soluble portions of the diffusion regions 135 of the photoresist pattern 100, where the second overcoat 140 is essentially insoluble in the second developer. For example, the second developer may include an aqueous medium that disrupts the second overcoat 140 and dissolves the portions of the photoresist that have exceeded a critical level of deprotection. As shown in FIG. 1H, a spacer prevention trench 145 is formed having a critical dimension defined by the dye diffusion length.

[0021] The spacer prevention features can then be etched transferred into the underlying layer 110, as shown in Figure 1I. For example, the underlying layer 110 can include a hard mask.

[0022] 2A-2E illustrate a substrate processing method for forming spacer prevention trenches according to another embodiment. Photoresist pattern 100 of FIG. 1D is reproduced as photoresist pattern 200 in FIG. 2A.

[0023] Next, as shown in FIG. 2B, a second overcoat 140, which is an organic film, is deposited over the photoresist pattern 200, filling the openings defined by the photoresist pattern 200 and covering the photoresist pattern 200. The formulation of the second overcoat 140 is cast in a solvent or blend of solvents to prevent dissolution of the underlying photoresist or intermixing of the two films. The second overcoat 140 is composed of a resin designed to have a low but non-zero dissolution rate in an aqueous developer such as tetramethylammonium hydroxide to controllably remove the film from the top of the photoresist pattern 200.

[0024] After deposition of the second overcoat 140, the substrate undergoes a second lithographic exposure step shown in Figure 2C. The exposure step exposes the substrate to second actinic radiation 170 that activates the solubility shifting agent in the diffusion regions 125 of the photoresist pattern 200. The second actinic radiation 170 can include short wavelength radiation having a wavelength between about 13.5 nm and about 365 nm, for example 266 nm.

[0025] Then, after exposure, the activation step further includes baking the substrate at high temperature as shown in Figure 2D to promote deprotection of the resin via reaction with the photogenerated acid that diffuses the solubility shifting agent into the second overcoat, resulting in a second diffusion region 150 in the second overcoat 140. The solubility shifting agent is activated sufficiently to meet the sensitivity threshold in the second diffusion region 150 without meeting the sensitivity threshold of the second overcoat 140.

[0026] The substrate is then developed with a second developer to remove the soluble portions of the second diffusion regions 150 of the second overcoat 140, and the second overcoat 140 and the diffusion regions 125 of the photoresist pattern 200 are insoluble in the second developer. The removal of the soluble portions of the second diffusion regions 150 of the second overcoat 140 forms spacer prevention features 155 between the remaining diffusion regions 125 of the photoresist pattern 200 and the second overcoat 140, as shown in FIG. 2E. The method may then include transferring the spacer prevention features to the underlying layer 110 by an etching process.

[0027] 3A-3F show a substrate processing method for forming air gaps in a membrane according to another embodiment. Photoresist pattern 100 of FIG. 1D is reproduced as photoresist pattern 300 in FIG. 3A.

[0028] Next, as shown in FIG. 3B, an organic film called second overcoat 140 is deposited over the photoresist pattern 300, filling the openings defined by the photoresist pattern 300 and covering the photoresist pattern 300. The formulation of the second overcoat 140 is cast in a solvent or blend of solvents to prevent dissolution of the underlying photoresist or intermixing of the two films. The second overcoat 140 is composed of a resin designed to have a low but non-zero dissolution rate in an aqueous developer such as tetramethylammonium hydroxide to controllably remove the film from the top of the photoresist pattern 100.

[0029] After deposition of the second overcoat 140, the substrate undergoes a second lithographic exposure step shown in FIG. 3C. The exposure step exposes the substrate to second actinic radiation 175 that activates the solubility shifting agent in the diffusion regions 125 of the photoresist pattern 300, particularly in the top horizontal regions of the diffusion regions 125 of the photoresist layer. The second actinic radiation 175 can include long wavelength radiation. The second actinic radiation 175 can include long wavelength radiation having a wavelength between about 300 nm and about 400 nm.

[0030] Then, after exposure, the activation step further includes baking the substrate at high temperature as shown in Figure 3D to promote deprotection of the resin via reaction with the photogenerated acid that diffuses the solubility shifting agent into the second overcoat 140, resulting in a second diffusion region 160 in the second overcoat 140. The solubility shifting agent is sufficiently activated to meet the sensitivity threshold in the second diffusion region 160 without meeting the sensitivity threshold of the second overcoat 140.

[0031] The substrate is then developed with a second developer, removing the soluble portions of the second diffusion regions 160 of the second overcoat 140, and the second overcoat 140 and the diffusion regions 125 of the photoresist pattern 300 are insoluble in the second developer. The removal of the soluble portions of the second diffusion regions 160 of the second overcoat 140 forms an air gap feature 165 between the remaining diffusion regions 125 of the photoresist pattern 300 and the second overcoat 140. This is shown in FIG. 3E.

[0032] According to another embodiment, the substrate of Figure 3D is developed with a second developer that results in removal of the second diffusion regions 160 of the second overcoat 140, the diffusion regions 125 of the photoresist pattern 300, and of soluble portions of the photoresist pattern 300, the second overcoat 140 being insoluble in the second developer. As shown generally in Figure 3F, removal of the soluble portions forms air gap features 180 in the second overcoat 140.

[0033] To aid in understanding various embodiments, various techniques have been described as multiple separate operations. The order of description should not be construed to imply that these operations are necessarily order dependent. In fact, these operations need not be performed in the order presented. The described operations may be performed in a different order than in the described embodiments. In additional embodiments, various additional operations may be performed and / or described operations may be omitted.

[0034] As used herein, "substrate" or "target substrate" generally refers to an object to be processed according to the present invention. A substrate may include any material portion or structure of a device, particularly a semiconductor or other electronic device, for example a base substrate structure such as a semiconductor wafer, a reticle, or a layer provided on or overlying a base substrate structure such as a thin film. Thus, substrate is not limited to any particular base structure, underlying layer, or overlying layer, whether patterned or not, but is intended to include such layers or base structures, and any combination of layers and / or base structures. While the description may refer to a particular type of substrate, it is for illustrative purposes only.

[0035] Those skilled in the art will also appreciate that many variations are possible in the operation of the techniques described above while still achieving the same objectives of the invention. Such variations are intended to be included within the scope of the present disclosure. Thus, the above description of embodiments of the invention is not intended to be limiting. Rather, any limitations of embodiments of the invention are set forth in the following claims.

Claims

1. 1. A method of patterning a substrate, comprising the steps of: forming a photoresist pattern on the substrate from a layer of photoresist deposited on the substrate, the layer of photoresist including a solubility shift agent, the photoresist pattern being formed by activating the solubility shift agent using a first pattern of actinic radiation and removing soluble portions of the layer of photoresist by developing the substrate using a first developer; depositing a first overcoat on the photoresist pattern, the first overcoat filling openings defined by the photoresist pattern and covering the photoresist pattern, the first overcoat comprising an organic film containing a dye; Diffusing the dye from the first overcoat into the photoresist pattern over a predetermined diffusion length to obtain a diffusion region in the photoresist pattern; removing the first overcoat from the substrate; activating the solubility shift agent in the diffusion region of the photoresist pattern using a second actinic radiation, wherein the solubility shift agent does not meet a sensitivity threshold of the photoresist pattern and is sufficiently activated to meet a sensitivity threshold in the diffusion region; depositing a second overcoat over the substrate; developing the substrate with a second developer to remove soluble portions of the diffusion regions of the photoresist pattern, the second overcoat being insoluble in the second developer; A method comprising:

2. 2. The method of claim 1, wherein removal of the soluble portions of the diffusion regions of the photoresist pattern forms spacer prevention features between a remaining photoresist pattern and the second overcoat.

3. The method of claim 2 further comprising transferring the spacer prevention features to an underlying layer by an etching process.

4. The method of claim 1 , wherein diffusing the dye from the first overcoat comprises baking the substrate.

5. 10. The method of claim 1, wherein the second actinic radiation has a wavelength between about 13.5 nm and about 365 nm.

6. The method of claim 1 , wherein the dye comprises an acid amplifier.

7. The method of claim 1 , wherein the first overcoat and the second overcoat are deposited on the substrate by spin-on deposition.

8. 10. The method of claim 1, wherein the photoresist comprises an acid-deprotectable resin, a photoacid generator (PAG), and a quencher.

9. The method of claim 1, wherein the dye reduces the number of PAG-photon interactions in the photoresist pattern.

10. 1. A method of patterning a substrate, comprising the steps of: forming a photoresist pattern on the substrate from a layer of photoresist deposited on the substrate, the layer of photoresist including a solubility shift agent, the photoresist pattern being formed by activating the solubility shift agent using a first pattern of actinic radiation and removing soluble portions of the layer of photoresist by developing the substrate using a first developer; depositing a first overcoat on the photoresist pattern, the first overcoat filling openings defined by the photoresist pattern and covering the photoresist pattern, the first overcoat comprising an organic film containing a dye; diffusing the dye from the first overcoat into the photoresist pattern over a predetermined diffusion length to obtain a first diffusion region in the photoresist pattern; removing the first overcoat from the substrate; depositing a second overcoat over the substrate; activating the solubility shift agent in the first diffusion region of the photoresist pattern using a second actinic radiation to diffuse the solubility shift agent into the second overcoat, thereby resulting in a second diffusion region in the second overcoat, the solubility shift agent not meeting a sensitivity threshold of the second overcoat, and being sufficiently activated to meet a sensitivity threshold in the second diffusion region; developing the substrate with a second developer to remove soluble portions of the second diffusion region of the second overcoat, the second overcoat and the first diffusion region of the photoresist pattern being insoluble in the second developer; A method comprising:

11. 11. The method of claim 10, wherein removal of the soluble portion of the second diffusion region of the second overcoat forms a spacer prevention feature between the remaining first diffusion region of the photoresist pattern and the second overcoat.

12. The method of claim 10 further comprising transferring the spacer prevention features to an underlying layer by an etching process.

13. The method of claim 10 , wherein diffusing the dye from the first overcoat comprises baking the substrate.

14. 11. The method of claim 10, wherein the second actinic radiation has a wavelength between about 300 nm and about 400 nm.

15. The method of claim 10 , wherein the dye comprises an acid amplifier.

16. The method of claim 10 , wherein removal of the soluble portion of the second diffusion region forms an air gap feature in the second overcoat.

17. 11. The method of claim 10, further removing the first diffusion region of the photoresist pattern and the photoresist pattern by developing the substrate with the second developer.

18. The method of claim 10 , wherein the first overcoat and the second overcoat are deposited on the substrate by spin-on deposition.

19. 11. The method of claim 10, wherein the photoresist comprises an acid-deprotectable resin, a photoacid generator (PAG), and a quencher.

20. The method of claim 10, wherein the dye reduces the number of PAG-photon interactions in the photoresist pattern.

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