Photomask features with chromeless nonprinting phase shifting window

Abstract

Aspects of the present invention provide for a novel photomask for patterning features for an integrated circuit, the photomask including a first area transmitting light in a first phase surrounded by second area, the second area transmitting light in a second phase, the second phase opposite the first phase. No blocking material separates the first area from the second area. After development of photoresist, the transition between the first and second area causes formation of a residual photoresist feature on the photoresist surface due to phase canceling of light. If the first area is small enough, it is nonprinting, ie., the opposite sides of the residual photoresist feature formed at its perimeter merge, forming a contiguous photoresist feature, and thus a corresponding patterned feature after etch.

1 . A phase shifting photomask comprising: 
 a plurality of transmitting nonprinting windows transmitting light in a first phase;    a transmitting area transmitting light in a second phase, each transmitting window substantially entirely surrounded by and in contact with the transmitting area with no blocking material intervening,    wherein the second phase is substantially opposite the first phase, and    wherein a first width of unbroken transmitting area surrounds each transmitting window on all sides, the first width sufficient for the unbroken transmitting area to print when the photomask is used to expose photoresist.    
   
   
       2 . The photomask of  claim 1  wherein the first phase is about 180 degrees and the second phase is about 0 degrees.  
   
   
       3 . The photomask of  claim 2  wherein the shortest dimension of any of the plurality of nonprinting transmitting windows parallel to the plane of the photomask is no more than about 160 nm×S.  
   
   
       4 . The photomask of  claim 3  wherein the shortest dimension of any of the plurality of nonprinting transmitting windows parallel to the plane of the photomask is no more than about 120 nm×S.  
   
   
       5 . The photomask of  claim 3  wherein at least one of the plurality of transmitting windows is rectangular.  
   
   
       6 . The photomask of  claim 5  wherein all of the transmitting windows are rectangular.  
   
   
       7 . The photomask of  claim 3  wherein the transmitting windows are uniformly spaced.  
   
   
       8 . The photomask of  claim 2  wherein the first width of unbroken transmitting area is at least 100 nm×S.  
   
   
       9 . The photomask of  claim 3  wherein the first phase is about 0 degrees and the second phase is about 180 degrees.  
   
   
       10 . The photomask of  claim 9  wherein the shortest dimension of any of the plurality of nonprinting transmitting windows in the plane of the photomask is no more than about 160 nm×S.  
   
   
       11 . The photomask of  claim 10  wherein the shortest dimension of any of the plurality of nonprinting transmitting windows in the plane of the photomask is no more than about 120 nm×S.  
   
   
       12 . The photomask of  claim 9  wherein at least one of the plurality of transmitting windows is rectangular.  
   
   
       13 . The photomask of  claim 12  wherein all of the transmitting windows are rectangular.  
   
   
       14 . The photomask of  claim 9  wherein the transmitting windows are uniformly spaced.  
   
   
       15 . The photomask of  claim 9  wherein the first width of unbroken transmitting area is at least 100 nm×S.  
   
   
       16 . A phase shifting photomask comprising: 
 a transmitting nonprinting window transmitting light in a first phase; and    a transmitting area substantially entirely surrounding and in contact with the transmitting window on all sides with no blocking material intervening,    wherein the transmitting area transmits light in a second phase, the second phase substantially opposite the first phase, and    wherein, when used to pattern photoresist, the transmitting area is printing on all sides of the transmitting window.    
   
   
       17 . The photomask of  claim 16  wherein the first phase is about zero degrees and the second phase is about 180 degrees.  
   
   
       18 . The photomask of  claim 17  wherein a shortest dimension of the first nonprinting transmitting window parallel to the plane of the photomask is no more than about 160 nm×S.  
   
   
       19 . The photomask of  claim 17  wherein a shortest dimension of the nonprinting transmitting window parallel to the plane of the photomask is no more than about 120 nm×S.  
   
   
       20 . The photomask of  claim 17  wherein a width of the transmitting area on all sides of the transmitting window is at least 100 nm×S.  
   
   
       21 . The photomask of  claim 16  wherein the first phase is about 180 degrees and the second phase is about zero degrees.  
   
   
       22 . The photomask of  claim 21  wherein the shortest dimension of the nonprinting transmitting window parallel to the plane of the photomask is no more than about 160 nm×S.  
   
   
       23 . The photomask of  claim 21  wherein the shortest dimension of the nonprinting transmitting window parallel to the plane of the photomask is no more than about 120 nm×S.  
   
   
       24 . The photomask of  claim 21  wherein a width of the transmitting area on all sides of the transmitting window is at least 100 nm×S.  
   
   
       25 . A phase shifting photomask comprising: 
 a plurality of spatially separate transmitting nonprinting windows transmitting light in a first phase; and    a transmitting area transmitting light in a second phase, the second phase substantially opposite the first, the transmitting area entirely surrounding and in contact with each of the transmitting windows of the first plurality;    wherein each transmitting window is separated from its nearest neighbor in the plurality by an unbroken length of transmitting area having at least a first dimension, and    wherein the smallest dimension of each window is no more than about 160 percent of the first dimension.    
   
   
       26 . The photomask of  claim 25  wherein the first phase is about zero degrees and the second phase is about 180 degrees.  
   
   
       27 . The photomask of  claim 26  wherein the first dimension is at least about 100 nm×S.  
   
   
       28 . The photomask of  claim 27  wherein the smallest dimension of each window is less than about 160 nm×S.  
   
   
       29 . The photomask of  claim 26  wherein the plurality of transmitting nonprinting windows are arranged in a grid pattern.  
   
   
       30 . The photomask of  claim 25  wherein the first phase is about 180 degrees and the second phase is about zero degrees.  
   
   
       31 . The photomask of  claim 30  wherein the first dimension is at least about 100 nm×S.  
   
   
       32 . The photomask of  claim 31  wherein the smallest dimension of each window is less than about 160 nm×S.  
   
   
       33 . The photomask of  claim 30  wherein the plurality of transmitting nonprinting windows are arranged in a grid pattern.  
   
   
       34 . A phase shifting photomask comprising: 
 a transmitting nonprinting window having a first shifting degree;    a second transmitting area having a second shifting degree, the second transmitting area entirely surrounding and in contact with the first transmitting window, wherein the second transmitting area is printing on all sides of the transmitting window; and    wherein the second shifting degree is substantially opposite the first shifting degree.    
   
   
       35 . The photomask of  claim 34  wherein the first shifting degree is about zero degrees and the second shifting degree is about 180 degrees.  
   
   
       36 . The photomask of  claim 35  wherein the shortest dimension of the second transmitting area in the plane of the photomask is no more than about 160 nm×S.  
   
   
       37 . The photomask of  claim 36  wherein the shortest dimension of the second transmitting area in the plane of the photomask is no more than about 120 nm×S.  
   
   
       38 . The photomask of  claim 22  wherein the second transmitting area has a rectangular shape.  
   
   
       39 . The photomask of  claim 34  wherein the first shifting degree is about 180 degrees and the second shifting degree is about zero degrees.  
   
   
       40 . The photomask of  claim 39  wherein the shortest dimension of the second transmitting area in the plane of the photomask is no more than about 160 nm×S.  
   
   
       41 . The photomask of  claim 40  wherein the shortest dimension of the second transmitting area in the plane of the photomask is no more than about 120 nm×S.  
   
   
       42 . The photomask of  claim 39  wherein the second transmitting area has a rectangular shape.  
   
   
       43 . A method for forming a patterned feature on a wafer surface, the method comprising: 
 transmitting light through a phase shifting photomask onto photoresist covering the wafer surface;    forming an isolated first residual photoresist feature between a first wafer area exposed to light in a first phase and a second wafer area exposed to light in a second phase, wherein the first phase is substantially opposite the second phase, and    wherein the second wafer area entirely surrounds the first wafer area in the plane of the wafer; and    forming the patterned feature from the photoresist feature.    
   
   
       44 . The method of  claim 43  wherein the first phase is about zero degrees and the second phase is about 180 degrees.  
   
   
       45 . The method of  claim 44  wherein: 
 the step of forming an isolated photoresist feature comprises developing photoresist, and    the step of forming the patterned feature comprises etching, and    the first residual photoresist feature defines a closed shape having a perimeter, and,    after the developing step and before the etching step, no portion of the wafer surface is exposed within the perimeter.    
   
   
       46 . The method of  claim 45  wherein the shortest dimension of the photoresist feature measured in the plane of the wafer surface is no greater than about 150 nm.  
   
   
       47 . The method of  claim 44  further comprising forming a plurality of residual photoresist features, 
 wherein each photoresist feature of the plurality is exposed to light in the first phase, and    each photoresist feature of the plurality is entirely surrounded by the second wafer area.    
   
   
       48 . The method of  claim 47  wherein each of the plurality of photoresist features defines a closed shape having a perimeter, and, after the developing step and before the etching step, no portion of the wafer surface is exposed within the perimeter.  
   
   
       49 . The method of  claim 48  wherein the plurality of photoresist features is uniformly spaced.  
   
   
       50 . The method of  claim 48  wherein the plurality of photoresist features is randomly spaced.  
   
   
       51 . The method of  claim 48  wherein a patterned feature is formed on the wafer surface from each of the plurality of photoresist features, and wherein the patterned features are portions of memory cells forming a first memory level in a memory array, the first memory level formed at a first height above a substrate.  
   
   
       52 . The method of  claim 51  wherein the memory array is a monolithic three dimensional memory array, the array further comprising at least a second memory level formed at a second height above the substrate, the second height different from the first height.  
   
   
       53 . The method of  claim 43  wherein the first phase is about 180 degrees and the second phase is about zero degrees.  
   
   
       54 . The method of  claim 53  wherein: 
 the step of forming an isolated photoresist feature comprises developing photoresist, and    the step of forming the patterned feature comprises etching, and    the first residual photoresist feature defines a closed shape having a perimeter, and,    after the developing step and before the etching step, no portion of the wafer surface is exposed within the perimeter.    
   
   
       55 . The method of  claim 54  wherein the shortest dimension of the photoresist feature measured in the plane of the wafer surface is no greater than about 150 nm.  
   
   
       56 . The method of  claim 55  further comprising forming a plurality of residual photoresist features, 
 wherein each photoresist feature of the plurality is exposed to light in the first phase, and    each photoresist feature of the plurality is entirely surrounded by the second wafer area.    
   
   
       57 . The method of  claim 56  wherein each of the plurality of photoresist features defines a closed shape having a perimeter, and, after the developing step and before the etching step, no portion of the wafer surface is exposed within the perimeter.  
   
   
       58 . The method of  claim 57  wherein the plurality of photoresist features is uniformly spaced.  
   
   
       59 . The method of  claim 57  wherein the plurality of photoresist features is randomly spaced.  
   
   
       60 . The method of  claim 57  wherein a patterned feature is formed on the wafer surface from each of the plurality of photoresist features, and wherein the patterned features are portions of memory cells forming a first memory level in a memory array, the first memory level formed at a first height above a substrate.  
   
   
       61 . The method of  claim 60  wherein the memory array is a monolithic three dimensional memory array, the array further comprising at least a second memory level formed at a second height above the substrate, the second height different from the first height.  
   
   
       62 . A method for forming photoresist features on a wafer surface using a photomask, the method comprising: 
 transmitting light through a first mask area onto a first wafer area, the first mask area having a first shifting degree;    transmitting light through a second mask area onto a second wafer area, the second mask area having a second shifting degree,    wherein the second mask area entirely surrounds and is on all sides in contact with the first mask area, and the first shifting degree is substantially opposite the second shifting degree; and    developing photoresist, wherein, after the developing step, a closed residual photoresist feature remains between the first wafer area and the second wafer area, and wherein the closed residual photoresist feature is isolated and not merged with any adjacent photoresist feature.    
   
   
       63 . The method of  claim 62  wherein the first shifting degree is about zero degrees and the second shifting degree is about 180 degrees.  
   
   
       64 . The method of  claim 63  wherein, after the developing step, no wafer surface is exposed within the first wafer area.  
   
   
       65 . The method of  claim 62  wherein the first shifting degree is about 180 degrees and the second shifting degree is about zero degrees.  
   
   
       66 . The method of  claim 65  wherein, after the developing step, no wafer surface is exposed within the first wafer area.  
   
   
       67 . A monolithic three dimensional memory array comprising: 
 a plurality of patterned features, the plurality of patterned features patterned using a photomask comprising:    a plurality of spatially separate first transmitting windows, wherein the transmitting windows transmit light in a first phase; and    a transmitting area of the photomask, each transmitting window substantially surrounded by and in contact with the transmitting area,    wherein the transmitting area transmits light in a second phase, the second phase substantially opposite the first phase.    
   
   
       68 . The monolithic three dimensional memory array of  claim 67 , wherein the patterned features comprise substantially coplanar pillars.  
   
   
       69 . The monolithic three dimensional memory array of  claim 68  wherein the pillars have a diameter no more than about 150 nm.