Assist layers for EUV lithography

{
  "publication_number": "US8968989B2",
  "country": "US",
  "kind": "B2",
  "title": "Assist layers for EUV lithography",
  "abstract": "The present invention provides novel methods of fabricating microelectronics structures, and the resulting structures formed thereby, using EUV lithographic processes. The method involves utilizing an assist layer immediately below the photoresist layer. The assist layer can either be directly applied to the substrate, or it can be applied to any intermediate layer(s) that may be applied to the substrate. The preferred assist layers are formed from spin-coatable, polymeric compositions. The inventive method allows reduced critical dimensions to be achieved with improved dose-to-size ratios, while improving adhesion and reducing or eliminating pattern collapse issues.",
  "claims": [
    "1. A method of forming a structure, said method comprising: providing a substrate, said substrate optionally including one or more intermediate layers thereon; spin coating a composition to form an assist layer on said substrate, or on said one or more intermediate layers, if present, said assist layer being a cured film comprising at least about 0.01% by weight metal, based upon the total weight of the cured film taken as 100% by weight; forming a photoresist layer on said assist layer; and subjecting at least a portion of said photoresist layer to EUV radiation.",
    "2. The method of claim 1, said metal being selected from the group consisting of Al, Mg, Na, Zn, Co, Cu, Ga, Ge, Hf, Ti, Zr, Se, Ni, V, Ar, Sc, and Si.",
    "3. The method of claim 1, said assist layer being formed from a composition comprising a metal or metal derivative selected from the group consisting of metal halides, metal carbides, metal sulfides, metal nitrides, metal oxides, and mixtures thereof.",
    "4. The method of claim 3, wherein said metal or metal derivative is selected from the group consisting of Si, SiO 2, Si 3 N 4, AlN, Al 2 O 3, ZrC, ZrO 2, Hf, HfO 2, TiN, TiO, TiO 2, Ti 2 O 3, Mg 3 N 2, MgO, W, WO, WO 2, and WO 3.",
    "5. The method of claim 1, wherein said substrate is selected from the group consisting of silicon, SiGe, SiO 2, Si 3 N 4, aluminum, Al 2 O 3, hafnium, zirconium, titanium, magnesium, tungsten, tungsten silicide, gallium arsenide, germanium, tantalum, tantalum nitride, indium, and indium phosphide.",
    "6. The method of claim 1, wherein said assist layer is formed from a composition comprising a crosslinking agent.",
    "7. The method of claim 1, wherein said subjecting said photoresist layer to EUV radiation is carried out with a dose of from about 5 mJ/cm 2 to about 100 mJ/cm 2.",
    "8. The method of claim 1, further comprising forming a pattern in said photoresist layer after said subjecting of said photoresist layer to EUV radiation.",
    "9. The method of claim 8, further comprising transferring said pattern to said assist layer; to said intermediate layers, if present; and to said substrate.",
    "10. The method of claim 9, wherein said transferring said pattern comprises etching said assist layer; intermediate layers, if present; and said substrate.",
    "11. The method of claim 9, wherein said pattern has a resolution of less than about 32 nm.",
    "12. The method of claim 8, wherein said forming a pattern in said photoresist layer comprises contacting said photoresist layer with a developer so as to remove some of said photoresist layer.",
    "13. The method of claim 1, wherein said assist layer is formed from a composition that is substantially free of photoacid generators.",
    "14. The method of claim 1, said substrate including one or more intermediate layers, one of said intermediate layers being the uppermost intermediate layer, and said uppermost intermediate layer being a carbon layer.",
    "15. A method of forming a structure, said method comprising: providing a substrate, said substrate optionally including one or more intermediate layers thereon; forming an assist layer on said substrate, or on said one or more intermediate layers, if present, said assist layer formed from a composition comprising a crosslinking agent and being a cured film comprising at least about 0.01% by weight metal, based upon the total weight of the cured film taken as 100% by weight; forming a photoresist layer on said assist layer; and subjecting at least a portion of said photoresist layer to EUV radiation."
  ],
  "description_excerpt": "1. Field of the Invention\n\nThis invention is concerned with methods of fabricating microelectronic structures using EUV (extreme ultraviolet) lithography.\n\n2. Description of the Prior Art\n\nAs the semiconductor industry continues to follow Moore's law, the demand for ever-decreasing feature sizes requires the use of thinner films to prevent pattern collapse. Thinner films will require using a hardmask to transfer the pattern to the substrate. Extreme ultraviolet (EUV) exposure is expected to be the method of choice for single exposure lithography to achieve the required critical dimension (CD) targets of the 22-nm node and beyond. Unfortunately, EUV lithography has been hindered by a number of problems, one of the most notable being a lack of powerful radiation sources. Because of the limited amount of energy available, lithography performance can suffer, and long exposure times are needed, resulting in low throughput. One solution to this problem is to improve the sensitivity of EUV resists. This sensitivity can be further defined by the amount of energy, also called dose, needed to reach a certain feature size, or more simply put, dose to size.\n\nThe main challenge in material design, particularly with resists, is to simultaneously achieve the improvement in line width roughness (LWR) and sensitivity necessary for industry targets. LWR is a measure of the variation of the width of the lines formed by photolithography. Sensitivity is the minimum dose of energy necessary to image the photoresist.",
  "cpc": [
    "G03F 7/092",
    "B82Y 30/00",
    "B82Y 40/00",
    "G03F 7/11",
    "G03F 7/2004",
    "H10P 76/204",
    "H10P 76/2041",
    "Y10S 977/755",
    "Y10T 428/24917"
  ],
  "ipc": [
    "G03F 7/09",
    "G03F 7/20",
    "G03F 7/11",
    "G03F 7/26"
  ],
  "assignees": [
    "Brewer Science Inc"
  ],
  "inventors": [
    "Tantiboro Ouattara",
    "Carlton Washburn",
    "Vandana Krishnamurthy",
    "Douglas Guerrero",
    "Aline Collin"
  ],
  "filing_date": "2012-11-20",
  "publication_date": "2015-03-03",
  "grant_date": "2015-03-03",
  "priority_date": "2011-11-21",
  "application_number": "US-201213682050-A",
  "family_id": "48427233",
  "cited_by_count": 300,
  "citations": [
    "US6140023A",
    "JP2002198283A",
    "US6740469B2",
    "US20070148602A1",
    "US20110123779A1",
    "US20090123878A1",
    "US20090297784A1",
    "US8257910B1"
  ]
}