US 11673903

US Patent 11,673,903: Summary and Claim Analysis

Title: Monoalkyl tin compounds with low polyalkyl contamination, their compositions and methods

Assignee: Inpria Corp (Current Assignee)

Inventors: Joseph B. Edson, Thomas J. Lamkin, William Earley, Truman Wambach

Filing Date: April 11, 2018

Issue Date: June 13, 2023

Abstract: The patent describes high-purity compositions of monoalkyl tin trialkoxide or monoalkyl tin triamide compounds, characterized by having no more than 4 mole % dialkyltin compounds as impurities relative to the total tin amount. The R group is a hydrocarbyl group with 1-31 carbon atoms, and R′ is a hydrocarbyl group with 1-10 carbon atoms. Methods for forming these pure compositions are also detailed. Additionally, a solid composition comprising a monoalkyl triamido tin compound (RSn—(NR′COR″)₃) is disclosed, where R is a hydrocarbyl group with 1-31 carbon atoms, and R′ and R″ are independently hydrocarbyl groups with 1-10 carbon atoms. These compositions are presented as suitable precursors for resist compositions used in EUV patterning, offering high EUV absorption.

Plain-Language Overview of Independent Claims:

Claim 1 (Independent): This claim describes a very pure liquid chemical mixture. It must contain a specific type of tin compound called a "monoalkyl tin triamide" (chemical formula RSn(NR′₂)₃). A key feature is that this mixture contains very few impurities of a related compound called "dialkyltin compounds," specifically no more than 0.5 mole % of these impurities compared to the total amount of tin present. In this formula, "R" is a carbon-hydrogen chain (hydrocarbyl group) with 1 to 31 carbon atoms, and "R′" is another hydrocarbyl group with 1 to 10 carbon atoms.

Claim 10 (Independent): This claim outlines a method for creating a "monoalkyltin trialkoxide" compound, also with very low dialkyl tin contamination. The method involves reacting the high-purity composition described in Claim 1 (the monoalkyl tin triamide with less than 0.5 mole % dialkyltin impurities) with an alcohol (represented by the formula HOR″). This reaction takes place in an organic solvent. The goal is to produce a new compound, RSn(OR″)₃, where R″ is a hydrocarbyl group with 1 to 10 carbon atoms, and the resulting product also has no more than 0.5 mole % dialkyltin compounds as an impurity relative to the total tin amount.

CAFC 2026 Dockets:

The Google Patents page for US11673903B2 indicates that the patent family is involved in litigation. Specifically, it notes:

• "PTAB case IPR2025-00267 filed (Settlement)"
• "First worldwide family litigation filed"
• "US case filed in Delaware District Court"

As of April 26, 2026, the information provided indicates an IPR case filed in 2025 (IPR2025-00267) which has reached settlement, and a US case filed in the Delaware District Court (1:22-cv-01359). There is no explicit mention of active cases within CAFC dockets specifically for 2026. While the PTAB and District Court cases are related, the provided information does not confirm an appeal to the CAFC in 2026. Therefore, I cannot authoritatively confirm any active CAFC 2026 dockets directly associated with this patent based on the available data.

As of April 26, 2026, the following litigation is known for US Patent 11673903:

• PTAB Case IPR2025-00267
  • Petitioner: Unified Patents LLC
  • Patent Owner: Inpria Corp (implied from patent assignment)
  • Jurisdiction: Patent Trial and Appeal Board (PTAB)
  • Case Number: IPR2025-00267
  • Filing Date: A priority date of 2018-04-11 is listed for the patent, but the IPR case itself was filed in 2025.
  • Outcome/Current Status: Settlement

It is important to note that while Unified Patents is often a petitioner in PTAB cases, their role is typically to challenge patents to improve patent quality and deter abusive patent litigation, not as a plaintiff in a traditional infringement lawsuit.

Additionally, the patent information indicates "US case filed in Delaware District Court" with the source "District Court" and jurisdiction "Delaware District Court". While a specific case number and filing date for this district court case are not explicitly provided in the patent document, the presence of this information suggests active litigation in that venue.

Proceedings overview

There is one AIA trial proceeding on file for US patent 11673903. This proceeding was an Inter Partes Review (IPR) that has been Terminated-Settled. This indicates that the patent has not been subjected to a full PTAB trial on the merits, which might imply the claims are untested by a Final Written Decision.

IPR2025-00267 — Entegris, Inc. v. Inpria Corporation

• Type: Inter Partes Review
• Filed: 2024-12-12
• Status: Terminated-Settled. The proceeding concluded due to a settlement between the parties.
• Judge panel: Information not publicly available.
• Petition grounds: Information regarding the specific claims challenged, prior art asserted, and statutory bases (§ 102 / § 103 / § 112) is not publicly available at this time.
• Institution decision: The proceeding was terminated due to settlement, indicating an institution decision was likely made, or a settlement was reached prior to or shortly after institution. Unified Patents lists the status as "Settlement".
• Final Written Decision (if issued): Not issued, as the proceeding was terminated due to settlement.
• Settlement / termination: The proceeding was terminated due to settlement, as indicated by the USPTO Open Data Portal and Unified Patents. The specific terms of the settlement are confidential.
• Appeal: No appeal was filed, as there was no Final Written Decision.
• Defensive value: Since this IPR was settled, the claims of US11673903 have not been adjudicated for patentability by the PTAB. This means a defendant would not face estoppel under 35 U.S.C. § 315(e)(2) based on this proceeding, but the patent owner has retained all claims as no claims were invalidated.

Strategic summary

All claims of US11673903 remain untested by a PTAB Final Written Decision. The sole IPR (IPR2025-00267) filed against this patent was terminated due to a settlement between Entegris, Inc. and Inpria Corporation. This means that no claims were canceled or sustained by the PTAB in a Final Written Decision, and the patent's validity against prior art grounds remains unadjudicated at the PTAB level.

The estoppel landscape for a defendant facing assertion of this patent is therefore largely unaffected by IPR2025-00267. As no Final Written Decision was issued, a defendant (unless in privy with Entegris, Inc.) would not be barred from raising any prior art grounds that could have been raised in this IPR.

Regarding pattern signals, the involvement of Unified Patents as the petitioner (as indicated by the link provided: "Petitioner: Unified Patents PTAB Data") suggests that the patent was identified as potentially problematic by a defensive aggregator. While the proceeding settled, it signals that the patent may be of interest to companies seeking to mitigate patent assertion risks. The patent owner, Inpria Corporation, appears to have opted for a settlement rather than litigating through to a Final Written Decision in this instance.

Recommended next steps

Since IPR2025-00267 was terminated due to settlement, there are no PTAB Final Written Decisions to link to that would invalidate claims. The patent owner, Inpria Corporation, retained all claims. If a defendant is currently being asserted against, the absence of a PTAB validity determination means that a new IPR or PGR (if still within the statutory window) remains a viable option, depending on the asserted claims and available prior art.

Given the settlement, it would be prudent to investigate the terms of the settlement if possible (though they are typically confidential). Understanding why the parties settled could provide valuable insight into the patent's strength or weaknesses from both sides' perspectives.

The fact that Unified Patents was the petitioner indicates that the patent was likely targeted due to its potential impact on a relevant industry. A defendant should conduct their own robust prior art search to identify strong invalidity grounds for any asserted claims, as these grounds remain available.

Inventors

• Joseph B. Edson (Inpria Corp)
• Thomas J. Lamkin (Inpria Corp)
• William Earley (Inpria Corp)
• Truman Wambach (Inpria Corp)

All inventors were employed by Inpria Corp at the time of filing.

Original assignee

Inpria Corp is the original assignee named on the issued patent. Inpria Corp's primary line of business is developing photoresists and patterning solutions for the semiconductor industry, particularly for EUV lithography. They appear to ship products embodying the claims, as the patent itself states the compositions are "useful as precursors for the synthesis of desirable patterning materials" and "for use as EUV and UV photoresists or electron-beam patterning resists." Inpria Corp is currently operating.

Assignment timeline

A search of the USPTO Assignment Center for patent US11673903 reveals the following record:

• 2019-01-31 (executed) / recorded 2019-01-31 — Reel 047710/0675
  • Conveyance: Assignment of Assignors Interest
  • Assignor: EARLEY, WILLIAM; EDSON, JOSEPH B.; LAMKIN, THOMAS J.; WAMBACH, Truman
  • Assignee: INPRIA CORPORATION
  • Correspondent: BLANK ROME LLP, Attn: IP Docketing, One Logan Square, 130 North 18th Street, Philadelphia, PA 19103-6998.
  • Context: Internal transfer of intellectual property rights from individual inventors to their employer.

This is the only assignment record found for US11673903. This means that Inpria Corp, the original assignee, still holds ownership of the patent.

Timeline diagram

timeline
    title Ownership of US 11673903
    2018 : Filed by Inpria Corp
    2019 : Inventors assigned to Inpria Corp
    2023 : Issued to Inpria Corp

NPE / troll-pattern signals

1. Shell-entity transfer — not present. The sole assignee, Inpria Corp, is an operating company in the semiconductor industry.
2. Known asserter in the chain — not present. Inpria Corp is not listed on public NPE lists.
3. Repeat correspondent across the chain — not present. Only one assignment is recorded, handled by BLANK ROME LLP.
4. Cascading transfers — not present. Only one assignment is recorded.
5. Pre-litigation transfer — unclear. While a US case was filed in Delaware District Court, the specific filing date is not provided, making it impossible to compare with the assignment date. The only recorded assignment is from inventors to Inpria Corp in 2019.
6. Bankruptcy fire-sale — not present. There is no indication that Inpria Corp has filed for bankruptcy.
7. Privateering — not present. There is no evidence of Inpria Corp transferring the patent to an NPE for assertion against competitors.
8. Defensive aggregator (anti-NPE) — not present. The patent is not currently assigned to a defensive aggregator.

Verdict

Operating-company assertion. The patent was assigned from the individual inventors to Inpria Corp (Reel 047710/0675, recorded 2019-01-31), which is an operating company that develops products embodying the claims (EUV photoresists). There are no subsequent assignments to suggest a transfer to a non-practicing entity. The current litigation in Delaware District Court (1:22-cv-01359) is likely an assertion by Inpria Corp against a competitor.

USPTO Assignment Center Search for US11673903

To identify the most relevant prior art for US patent 11673903, I will examine the "Cited By" section of the patent on Google Patents, which typically lists prior art cited by the applicant and/or the examiner. I will then perform USPTO searches for any specifically mentioned prior art not fully detailed in the patent document itself to gather comprehensive information.

USPTO Search for US Patent 11673903:

• Patent Number: US11673903B2
• Title: Monoalkyl tin compounds with low polyalkyl contamination, their compositions and methods
• Publication Date: June 13, 2023
• Filing Date: April 11, 2018
• Assignee: Inpria Corp
• Inventors: Joseph B. Edson, Thomas J. Lamkin, William Earley, Truman Wambach

Most Relevant Prior Art for US Patent 11673903:

The patent text explicitly references several prior art documents. I will detail those mentioned within the "DETAILED DESCRIPTION OF THE INVENTION" section as they are presented by the applicant as relevant background or existing solutions.

1. Hanssgen, D.; Puff, H.; Beckerman, N. J. Organomet. Chem. 1985, 293, 191

   • Full Citation: Hanssgen, D.; Puff, H.; Beckerman, N. J. Organomet. Chem. 1985, 293, 191.
   • Publication/Filing Date: 1985 (Publication year).
   • Brief Description: This journal article describes a method for synthesizing t-butyl tris(diethylamido)tin, (t-BuSn(NEt₂)₃), using a lithium reagent. The current patent highlights that "These methods with lithium reagents, however, can produce a mixture of monoalkyl and dialkyl tin products" and that "lithium contaminants can be undesirable for semiconductor applications."
   • Potential Anticipation (35 U.S.C. § 102): This reference describes a known method for synthesizing monoalkyl tin triamides, but the disclosed method is criticized in US11673903 for producing mixtures with polyalkyl tin products and lithium contaminants. Therefore, it would likely anticipate the broad concept of synthesizing monoalkyl tin triamides, but not the high purity aspect claimed in Claim 1 (no more than 0.5 mole % dialkyltin compounds) or the specific methods described in US11673903 to achieve such purity.

2. U.S. Pat. No. 9,310,684 to Meyers et al.

   • Full Citation: U.S. Pat. No. 9,310,684 to Meyers et al., entitled “Organometallic Solution Based High Resolution Patterning Compositions.”
   • Publication/Filing Date: Issued April 5, 2016 (assuming issue date as primary relevance, filing date would precede this).
   • Brief Description: This patent describes the use of alkyl metal coordination compounds in high-performance radiation-based patterning compositions. The present patent, US11673903, notes that its "compositions synthesized herein can be effective precursors for forming the alkyl tin oxo-hydroxo compositions that are effective for high resolution patterning."
   • Potential Anticipation (35 U.S.C. § 102): This patent establishes the utility of organometallic compounds, specifically alkyl metal coordination compounds, in patterning compositions. It likely anticipates the general field of using tin compounds as patterning materials. However, it does not appear to teach or suggest the specific high-purity monoalkyl tin triamide or trialkoxide compositions, or the methods for their low-contamination synthesis, as claimed in US11673903. Thus, it would likely not anticipate the specific compositional and method claims of US11673903 but rather provide context for the application of such compounds.

3. Published U.S. patent application 2016/0116839 A1 to Meyers et al.

   • Full Citation: Published U.S. patent application 2016/0116839 A1 to Meyers et al., entitled “Organometallic Solution Based High Resolution Patterning Compositions and Corresponding Methods.”
   • Publication/Filing Date: Published April 28, 2016.
   • Brief Description: This application describes refinements of organometallic compositions for patterning. Similar to US9310684, it provides background on patterning compositions.
   • Potential Anticipation (35 U.S.C. § 102): Similar to US9310684, this publication contributes to the general knowledge of organometallic patterning compositions. It would not likely anticipate the specific purity levels or synthetic methods claimed in US11673903.

4. Published U.S. patent application 2017/0102612 A1 to Meyers et al. (the '612 application)

   • Full Citation: Published U.S. patent application 2017/0102612 A1 to Meyers et al., entitled “Organotin Oxide Hydroxide Patterning Compositions, Precursors, and Patterning.”
   • Publication/Filing Date: Published April 13, 2017.
   • Brief Description: This application describes organotin oxide hydroxide patterning compositions, precursors, and patterning methods. It details hydrolysis and condensation reactions to transform precursor compositions into alkyl tin oxo-hydroxo compositions used for patterning.
   • Potential Anticipation (35 U.S.C. § 102): This '612 application describes the downstream use of alkyltin precursors to form patterning compositions, including hydrolysis reactions. While it discusses the need for reducing "polyalkyl tin impurity compositions" due to their potential to "affect condensation and contribute to photoresist outgassing during lithographic processing," it does not disclose the specific high-purity monoalkyl tin triamide or trialkoxide compositions, nor the methods for their low-contamination synthesis, as claimed in US11673903. Therefore, it highlights the problem addressed by US11673903 but does not teach the solution.

5. U.S. Pat. No. 8,198,352 to Deelman et al.

   • Full Citation: U.S. Pat. No. 8,198,352 to Deelman et al., entitled “High Purity Monoalkyltin Compounds and Uses Thereof.”
   • Publication/Filing Date: Issued June 12, 2012.
   • Brief Description: This patent describes the use of high purity monoalkyl tin compounds, especially mercapto compounds, as polymer stabilizers. It focuses on the formation of pure monoalkyl halides as precursors for these stabilizer compounds.
   • Potential Anticipation (35 U.S.C. § 102): This patent addresses high purity monoalkyltin compounds but specifically in the context of mercapto compounds used as polymer stabilizers and their monoalkyl halide precursors. It does not appear to teach the specific monoalkyl tin triamide, trialkoxide, or triamido tin compositions, or the methods for achieving their low polyalkyl contamination, as claimed in US11673903. While it shares the "high purity" objective for monoalkyltin compounds, the chemical nature of the compounds and the methods described are distinct.

6. U.S. Pat. No. 9,745,450 to Frenkel et al.

   • Full Citation: U.S. Pat. No. 9,745,450 to Frenkel et al., entitled “Stabilizers Containing High Purity Mono-Alkyltin Compounds.”
   • Publication/Filing Date: Issued August 29, 2017.
   • Brief Description: This patent also describes stabilizers containing high-purity mono-alkyltin compounds.
   • Potential Anticipation (35 U.S.C. § 102): Similar to US8198352, this patent deals with high-purity monoalkyltin compounds for use as stabilizers. The specific compositions (triamides, trialkoxides, triamido tin) and the methods for achieving low polyalkyl contamination as defined in US11673903 are not explicitly disclosed. Therefore, it is unlikely to anticipate the specific claims of US11673903.

Summary of Anticipation:

The cited prior art largely establishes the existing knowledge regarding the synthesis of organotin compounds, their use in patterning, and the general desire for high purity in certain applications. However, none of the explicitly referenced prior art documents appear to directly anticipate the precise compositions of high-purity monoalkyl tin triamides or trialkoxides with impurity levels below 0.5 mole %, nor the specific methods (e.g., using Grignard or diorganozinc reagents, or crystallization of triamido tin) described in US11673903 to achieve these low contamination levels, as articulated in independent claims 1 and 10. The prior art from Hanssgen et al. describes a method for a similar compound but explicitly with higher contamination, which is precisely what US11673903 aims to overcome. Other patents highlight the problem of impurities in patterning applications or address high-purity monoalkyltin compounds for different applications (stabilizers) with distinct chemical forms and synthetic routes.

Obviousness Analysis under 35 U.S.C. § 103

This section analyzes the obviousness of US Patent 11,673,903 under 35 U.S.C. § 103, considering combinations of prior art references. A patent claim is obvious if "the differences between the claimed invention and the prior art are such that the claimed invention as a whole would have been obvious before the effective filing date of the claimed invention to a person having ordinary skill in the art" (35 U.S.C. § 103(a)). The analysis identifies combinations of prior art that would render the claims obvious and explains the motivation for a person having ordinary skill in the art (PHOSITA) to combine them.

Person Having Ordinary Skill in the Art (PHOSITA): Given the nature of US Patent 11,673,903, which deals with monoalkyl tin compounds for photoresist applications, a PHOSITA would likely possess a graduate-level degree (M.S. or Ph.D.) in chemistry, materials science, or chemical engineering, with practical experience in organometallic synthesis, polymer chemistry, or semiconductor manufacturing, particularly in photolithography. This individual would be aware of the challenges in achieving high-purity precursors for advanced patterning techniques like EUV lithography and the existing methods for synthesizing and purifying organotin compounds.

Prior Art References:

The patent explicitly incorporates several prior art references, which are relevant for this analysis:

• US Pat. No. 9,310,684 to Meyers et al. (Meyers '684): "Organometallic Solution Based High Resolution Patterning Compositions." This patent generally describes the use of alkyl metal coordination compounds, including tin, in high-performance radiation-based patterning compositions. It notes that desirable ligands for forming metal oxo/hydroxo complexes can include M-C or M-O₂C bonds, with tin being a particularly desirable metal. The efficacy of these compounds for EUV and electron-beam resists is described.
• Published U.S. Patent Application 2016/0116839 A1 to Meyers et al. (Meyers '839): "Organometallic Solution Based High Resolution Patterning Compositions and Corresponding Methods." This application refines the organometallic compositions for patterning, describing improved performance with branched alkyl ligands and blends of alkyl tin oxide hydroxide compositions.
• Published U.S. Patent Application 2017/0102612 A1 to Meyers et al. (Meyers '612): "Organotin Oxide Hydroxide Patterning Compositions, Precursors, and Patterning." This application describes precursor compositions that can be coated and in situ hydrolyzed to form coatings comprising organotin oxide hydroxide, useful for high-resolution patterning with UV, EUV, or electron-beam radiation. It emphasizes the desire to reduce or eliminate dialkyl or other polyalkyl components due to their potential to affect condensation and contribute to photoresist outgassing.
• Hanssgen, D.; Puff, H.; Beckerman, N. J. Organomet. Chem. 1985, 293, 191 (Hanssgen 1985): This journal article describes the synthesis of t-butyl tris(diethylamido)tin (t-BuSn(NEt₂)₃) using a lithium reagent. The current patent acknowledges that such methods can produce a mixture of monoalkyl and dialkyl tin products.
• US Pat. No. 8,198,352 to Deelman et al. (Deelman '352): "High Purity Monoalkyltin Compounds and Uses Thereof." This patent describes high-purity monoalkyltin compounds, specifically compositions with a major content of monoalkyltin and minor (preferably trace or no) di- and tri-alkyltin compounds, for use as stabilizers for chlorine-containing polymers, catalysts, or glass coating chemicals. It mentions the preparation of high-purity monoalkyltin trihalides as precursors.
• US Pat. No. 9,745,450 to Frenkel et al. (Frenkel '450): "Stabilizers Containing High Purity Mono-Alkyltin Compounds." This patent also discusses high-purity mono-octyltin compounds for use as heat stabilizers.

Obviousness Combinations:

The core of US 11,673,903 is the provision of monoalkyl tin compounds (specifically triamides, trialkoxides, and triamido tin) with very low polyalkyl contamination (no more than 0.5 mole % dialkyltin compounds in claims 1 and 10). The motivation for low contamination is explicitly stated in the '903 patent as reducing photoresist outgassing and tin contamination of equipment during lithographic processing.

Combination 1: Meyers '612 + Deelman '352 / Frenkel '450

1. Meyers '612 establishes a clear motivation for reducing or eliminating dialkyl or other polyalkyl components in organotin patterning compositions. This is because such impurities "may affect condensation and contribute to photoresist outgassing during lithographic processing, which increases the potential for tin contamination of equipment used for film deposition and patterning." This reference highlights the problem that US 11,673,903 aims to solve.
2. Deelman '352 and Frenkel '450 teach the desirability and methods for achieving high purity monoalkyltin compounds with reduced levels of di- and tri-alkyltin compounds, albeit in the context of polymer stabilizers rather than photoresists. Deelman '352 explicitly states its objective to provide "high purity monoalkyltin compounds, i.e. compositions with a major content of monoalkyltin compound and minor contents, and preferably only traces of, and even more preferably no di- and tri-alkyltin compounds." It also details methods for preparing these high-purity compounds, often starting from monoalkyltin trihalides. Frenkel '450 similarly describes high-purity mono-octyltin compounds.

Motivation for Combination: A PHOSITA, aware of the problems caused by polyalkyl tin contaminants in photoresists (as taught by Meyers '612), would be motivated to seek ways to produce higher purity monoalkyl tin precursors. The teachings of Deelman '352 and Frenkel '450 provide a clear indication that achieving high purity in monoalkyltin compounds, with minimal dialkyltin impurities, is both desirable and achievable. The PHOSITA would recognize that the principles and techniques used to achieve high purity in monoalkyltin compounds for stabilizers could be applied or adapted to produce high-purity monoalkyl tin triamide or trialkoxide precursors for photoresist applications. The general concept of "high purity" for organotin compounds, and the known methods to achieve it in other contexts (like stabilizers), would naturally lead a skilled artisan to apply these purity-enhancing strategies to photoresist precursors, especially given the explicit problem statement in Meyers '612.

Obviousness of Claim 1: Claim 1 specifies a high purity liquid composition of a monoalkyl tin triamide (RSn(NR′₂)₃) with no more than 0.5 mole % dialkyltin compounds. Given the motivation from Meyers '612 to reduce polyalkyl contamination in photoresist precursors and the established art of producing high-purity monoalkyltin compounds (Deelman '352, Frenkel '450), a PHOSITA would find it obvious to apply known purification techniques to achieve such low impurity levels for monoalkyl tin triamides intended for photoresist use. The specific purity level of "no more than 0.5 mole %" would be an optimization of a known desirable characteristic. The patent itself mentions that prior methods with lithium reagents for synthesizing monoalkyl tin triamides "can produce a mixture of monoalkyl and dialkyl tin products," implying that efforts to reduce these impurities would be a natural progression.

Obviousness of Claim 10: Claim 10 describes a method to form a monoalkyltin trialkoxide with low dialkyl tin contamination by reacting the high-purity monoalkyl tin triamide of claim 1 with an alcohol. The conversion of tin amides to alkoxides is a known synthetic transformation in organotin chemistry. For example, the '903 patent itself describes the synthesis of monoalkyl tin trialkoxides from monoalkyl tin triamides. If the starting monoalkyl tin triamide already possesses low dialkyl tin contamination (as in Claim 1), it would be an expected outcome that the derived monoalkyltin trialkoxide would also exhibit correspondingly low contamination, assuming standard, non-contaminating reaction conditions. The motivation to maintain low contamination through such a transformation is directly linked to the reasons articulated in Meyers '612 regarding photoresist performance.

Combination 2: Hanssgen 1985 + Meyers '612 + Deelman '352 / Fractional Distillation

1. Hanssgen 1985 discloses a method for synthesizing a specific monoalkyl tin triamide, t-butyl tris(diethylamido)tin. The '903 patent acknowledges this reference and notes that such methods "can produce a mixture of monoalkyl and dialkyl tin products."
2. Meyers '612 reiterates the critical need for low polyalkyl tin impurities in photoresist applications.
3. Deelman '352 and Frenkel '450 demonstrate the prior art's general pursuit of high-purity monoalkyltin compounds. The '903 patent also specifically identifies fractional distillation as a purification technique for monoalkyl tin triamides to reduce polyalkyl contaminants, potentially below 1 mole percent. Example 8 of US 11,673,903 explicitly demonstrates the effectiveness of fractional distillation to remove t-Bu₂Sn(NMe₂)₂ from t-BuSn(NMe₂)₃.

Motivation for Combination: Faced with a known synthesis method that yields impure monoalkyl tin triamides (Hanssgen 1985), and a strong motivation to reduce polyalkyl contaminants for photoresist applications (Meyers '612), a PHOSITA would be motivated to apply known purification techniques, such as fractional distillation (a common chemical purification method, also mentioned in Deelman '352 for purifying monoalkyltin trihalides, and explicitly described for purification of monoalkyl tin triamides in the '903 patent itself), to the products of the Hanssgen synthesis. This would be a straightforward application of known purification principles to address an identified problem, leading to compositions with low polyalkyl contamination.

Conclusion on Obviousness:

Claims 1 and 10 of US 11,673,903 appear to be obvious in light of the combination of prior art references. The art clearly established the desirability of monoalkyltin compounds for patterning materials (Meyers '684, Meyers '839, Meyers '612) and, crucially, the problems associated with polyalkyl tin impurities in these applications (Meyers '612). Simultaneously, the prior art (Deelman '352, Frenkel '450) demonstrated both the general pursuit of high-purity monoalkyltin compounds and methods for achieving such purity, including the use of fractional distillation.

A PHOSITA would have been motivated to combine the teaching of Meyers '612 regarding the need for low polyalkyl contamination in photoresists with the general knowledge and specific methods for achieving high purity in organotin compounds as exemplified by Deelman '352 and Frenkel '450. The synthesis of monoalkyl tin triamides (e.g., Hanssgen 1985) followed by conventional purification techniques like fractional distillation to achieve the desired low impurity levels would have been an obvious endeavor to address the recognized problems in photoresist performance. The specific impurity level of 0.5 mole % in the claims represents an optimization within a known and desired range rather than a fundamentally new and non-obvious invention.