Pitch-based subresolution assist feature design

A method of manufacturing an integrated circuit (IC) comprising the steps of:

• providing system parameters of a lithographic projection system having an annular illumination source, said system parameters including a projection numerical aperture NA, and a wavelength λ, an inner radius σinner and an outer radius σouter of said annular illumination source;
• providing a write delta ΔW of a mask writer tool;
• Providing an IC design layout including a plurality of first critical features arranged in a pattern having a critical pitch PCrit, wherein the critical pitch is greater than or equal to a minimum pitch PMin of the design layout and less than a maximum pitch PMax of the design layout at which optical interaction is significant;
• determining the outer radius σouter according to the equation
• 35 σ outer = λ 2 ⁢ NAP Min ;
• determining a critical radius σCrit corresponding to the critical pitch PCrit according to the equation
• 36 σ Crit = λ 2 ⁢ NAP Crit ;
• determining the inner radius σinner by solving the equation
• 37 ∫ σ inner σ outer ⁢ ⅆ σ ⁡ ( σ Crit - σ ) ⁢ σ ⁢ ⁢ cos - 1 ⁡ [ ( σ Crit - 1 4 ⁢ σ Crit ) ⁢ σ + 1 4 ⁢ σ Crit ⁢ σ ] = 0 ;
• determing a transition pitch PTrans having a value that is the smaller of
• 38 λ 2 ⁢ NA ⁢ ⁢ σ inner
• and (2PCrit−ΔW), wherein said transition pitch is the greatest pitch for which subresolution assist features (SRAFs) are not required;
• identifying a plurality of second critical features within the design layout having a design pitch PD that is greater than or equal to the transition pitch plus the write delta (PTrans+ΔW);
• disposing one or more SRAFs within said IC design layout between each of said second critical features, wherein one SRAF is disposed between each of the second critical features if the design pitch PD has a value (PTrans+ΔW)≦PD≦(3PCrit−ΔW), or a number of SRAFs N greater than or equal to two are disposed between each of the second critical features where N satisfies the relation (N+1)PCrit≦PD≦[(N+2)PCrit−ΔW] if the design pitch PD has a value greater than or equal to 3PCrit and less than or equal to said maximum pitch PMax, to form a modified IC design layout including a final combined pattern of SRAFs and said second critical features having a combined pitch PCombined, wherein said combined pitch substantially corresponds to said critical pitch;
• and
• designing a mask layout of a mask in accordance with said modified IC design layout, said mask for use with a lithographic projection system having said system parameters, and said mask to be formed using a mask writer tool having said write delta.

A computer program product comprising:

• a computer usable medium having computer readable program code means embodied therein for causing a computer to determine a configuration of subresolution assist features (SRAFs) in a mask manufacturing an integrated circuit (IC) design layout, the computer readable program code means in said computer program product comprising:
• computer readable program code means for causing a computer to store parameters of a lithographic projection system, said parameters including a projection numerical aperture NA and a wavelength λ of an annular illumination source, the annular illumination source having radial dimensions ranging from an inner radius σinner to an outer radius σouter;
• computer readable program code means for causing a computer to store a critical pitch PCrit of a first pattern of critical features, a minimum pitch PMin and a maximum pitch PMax of patterns in an IC design layout, wherein said critical pitch PCrit is greater than or equal to a minimum pitch PMin of the IC design layout and less than a maximum pitch PMax of the IC design layout;
• computer readable program code means for causing a computer to determine said outer radius σouter and said inner radius σinner of the annular illumination source wherein so that a critical radius σCrit has a value σinner≦σCrit≦σouter, wherein σCrit provides an optimal image for patterns having said critical pitch PCrit;
• computer readable program code means for causing a computer to store a transition pitch PTrans larger than said critical pitch PCrit;
• computer readable program code means for causing a computer to identify a second pattern of second critical features within the IC design layout having a design pitch PD that is larger than said transition pitch PTrans;
• computer readable program code means for causing a computer to dispose one or more SRAFs between each of said second critical features to form a modified IC design layout including a final combined pattern of SRAFs and said second critical features, said final combined pattern having a combined pitch PCombined, wherein said combined pitch PCombined substantially corresponds to PCrit;
• and
• computer readable program code means for causing a computer to design a mask, layout for manufacturing a mask for use with said lithographic projection system including said annular illumination source having said inner radius σinner and said outer radius σouter, wherein said mask layout corresponds to said modified IC design layout including said final combined pattern of said one or more SRAFs and said second critical features.

A computer program product comprising:

• a computer usable medium having computer readable program code means embodied therein for causing a computer to determine a configuration of subresolution assist features (SRAFs) in a mask manufacturing an integrated circuit (IC) design layout, the computer readable program code means in said computer program product comprising:
• computer readable program code means for causing a computer to store parameters of a lithographic projection system, said parameters including a projection numerical aperture NA and a wavelength λ of an annular illumination source, the annular illumination source having radial dimensions ranging from an inner radius σinner to an outer radius σouter;
• computer readable program code means for causing a computer to store a write delta ΔW of a mask writer tool;
• computer readable program code means for causing a computer to store an IC design layout including a plurality of first critical features arranged in a pattern having a critical pitch PCrit, wherein the critical pitch PCrit is greater than or equal to a minimum pitch PMin of the IC design layout and less than a maximum pitch PMax of the IC design layout;
• computer readable program code means for causing a computer to determine the outer radius σouter according to the equation
• 45 σ outer = λ 2 ⁢ NAP Min ;
• computer readable program code means for causing a computer to determine a critical radius σCrit corresponding to the critical pitch PCrit according to the equation
• 46 σ Crit = λ 2 ⁢ NAP Crit ;
• computer readable program code means for causing a computer to determine the inner radius σinner by solving the equation
• 47 ∫ σ inner σ outer ⁢ ⁢ ⅆ σ ⁡ ( σ Crit - σ ) ⁢ σcos - 1 ⁡ [ ( σ Crit - 1 4 ⁢ σ Crit ) ⁢ σ + 1 4 ⁢ σ Crit ⁢ σ ] = 0 ;
• computer readable program code means for causing a computer to determine a transition pitch PTrans having a value that is the smaller of
• 48 λ 2 ⁢ N ⁢ ⁢ A ⁢ ⁢ σ inner
• and (2PCrit−ΔW);
• computer readable program code means for causing a computer to identify a plurality of second critical features within the design layout having a design pitch PD that is larger than the sum of the transition pitch and the write resolution (PTrans+ΔW);
• computer readable program code means for causing a computer to dispose one SRAF between each of said plurality of second critical features if said design pitch PD has a value (PTrans+ΔW)≦PD≦(3PCrit−ΔW), or causing a computer to dispose 2 or more SRAFs between each of the second critical features, where the number of SRAFs N satisfies the relation (N+1)PCrit≦PD≦[(N+2)PCrit−ΔW], if the design pitch PD has a value greater than or equal to 3PCrit and less than or equal to the maximum pitch PMax.