Patent Publication Number: US-2012044735-A1

Title: Structures with increased photo-alignment margins

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional, of U.S. application Ser. No. 11/497,036, which was filed on Jul. 31, 2006, which is scheduled to issue on Oct. 4, 2011 as U.S. Pat. No. 8,030,222, which is a divisional, of U.S. application Ser. No. 10/931,771, which was filed on Aug. 31, 2004, which issued as U.S. Pat. No. 7,151,040 on Dec. 19, 2006, the disclosure of which is incorporated herein by reference. 
     This invention relates generally to integrated circuit fabrication and, more particularly, to masking techniques. 
    
    
     BACKGROUND OF THE INVENTION 
     As a consequence of many factors, including demand for increased portability, computing power, memory capacity and energy efficiency in modern electronics, integrated circuits are continuously being reduced in size. To facilitate this size reduction, the sizes of the constituent features, such as electrical devices and interconnect line widths, that form the integrated circuits are also constantly being decreased. 
     The trend of decreasing feature size is evident, for example, in memory circuits or devices such as dynamic random access memories (DRAMs), static random access memories (SRAMs), ferroelectric (FE) memories, etc. To take one example, DRAM typically comprises millions of identical circuit elements, known as memory cells. In its most general form, a memory cell typically consists of two electrical devices: a storage capacitor and an access field effect transistor. Each memory cell is an addressable location that can store one bit (binary digit) of data. A bit can be written to a cell through the transistor and read by sensing charge on the storage electrode from the reference electrode side. By decreasing the sizes of constituent electrical devices and the conducting lines that access them, the sizes of the memory devices incorporating these features can be decreased. Additionally, storage capacities can be increased by fitting more memory cells into the memory devices. 
     The continual reduction in feature sizes places ever greater demands on techniques used to form the features. For example, photolithography is commonly used to pattern features, such as lines, on a substrate. The concept of pitch can be used to describe the size of these features. Pitch is defined as the distance between an identical point in two neighboring features. These features are typically defined by openings in, and spaced from each other by, a material, such as an insulator or conductor. As a result, pitch can be viewed as the sum of the width of a feature and of the width of the space separating that feature from a neighboring feature. The width of the line can also be referred to as the critical dimension or feature size (F) of the line. Because the width of the space adjacent that line is typically equal to the width of the line, the pitch of lines is typically two times the feature size (2F). 
     Due to factors such as optics and light or radiation wavelength, however, photolithography techniques each have a minimum pitch below which a particular photolithographic technique cannot reliably form features. Thus, the minimum pitch of a photolithographic technique can limit feature size reduction. 
     “Pitch doubling” is one method proposed for extending the capabilities of photolithographic techniques beyond their minimum pitch. Such a method is illustrated in  FIGS. 1A-1F  and described in U.S. Pat. No. 5,328,810, issued to Lowrey et al., the entire disclosure of which is incorporated herein by reference. With reference to  FIG. 1A , photolithography is first used to form a pattern of lines  10  in a photoresist layer overlying a layer  20  of an expendable material and a substrate  30 . As shown in  FIG. 1B , the pattern is then transferred by an etch step (preferably anisotropic) to the layer  20 , forming placeholders or mandrels  40 . The photoresist lines  10  can be stripped and the mandrels  40  can be isotropically etched to increase the distance between neighboring mandrels  40 , as shown in  FIG. 1C . A layer  50  of spacer material is subsequently deposited over the mandrels  40 , as shown in  FIG. 1D . Spacers  60  are then formed on the sides of the mandrels  40  by preferentially etching the spacer material from the horizontal surfaces  70  and  80  in a directional spacer etch, as shown in  FIG. 1E . The remaining mandrels  40  are then removed, leaving behind only the spacers  60 , which together act as a mask for patterning, as shown in  FIG. 1F . Thus, where a given pitch formerly included a pattern defining one feature and one space (each having a width equal to F, for a pitch equal to 2F), the same width now includes two features and two spaces defined by the spacers  60  (each of which have a width equal to ½ F). As a result, the smallest feature size possible with a photolithographic technique is effectively decreased. 
     It will be appreciated that while the pitch is actually halved in the example above, this reduction in pitch is conventionally referred to as pitch “doubling,” or, more generally, pitch “multiplication.” That is, conventionally “multiplication” of pitch by a certain factor actually involves reducing the pitch by that factor. The conventional terminology is retained herein. Note that by forming spacers upon spacers, the definable feature size can be further decreased. Thus, pitch multiplication refers to the process generally, regardless of the number of times the spacer formation process is employed. 
     Feature sizes of contacts to the pitch multiplied lines are typically larger than the lines themselves and, so, can be formed by conventional photolithographic techniques. Such contacts can include landing pads or regular line width, e.g., non-pitch multiplied, interconnects. The pitch multiplied lines, however, can have pitches below the minimum pitch for a given photolithographic technique. Consequently, the separation between the lines can be smaller than the precision of the photolithographic technique used to pattern the landing pads or regular line width interconnects. As a result, the landing pads or regular line width interconnects can inadvertently contact two or more different lines, or might not adequately contact their intended line at all. Thus, due to resolution limitations, reliably making connections to small pitch multiplied lines is beyond the capability of many photolithographic techniques. 
     Accordingly, there is a need for methods of making connections to small conducting lines, especially conducting lines formed by pitch multiplication. 
     BRIEF SUMMARY OF THE INVENTION 
     According to one aspect of the invention, a method is provided for manufacturing a memory device. The method comprises forming a plurality of spaced, removable mandrel strips. The mandrel strips are separated by a first width in an array region of the memory device and a second width in a periphery of the memory device. The second width is greater than the first width and a portion of the mandrel strips in the array region extends at an angle relative to an other portion of the mandrel strips in the periphery. The method also comprises forming a spacer on sidewalls of each mandrel strip. The spacer forms a loop around a perimeter of each mandrel strip. 
     According to another aspect of the invention, a method is provided for fabricating an integrated circuit. The method comprises patterning a plurality of pairs of mask lines. Each pair of the mask lines forms a continuous loop. The method also comprises contacting conductive lines defined by the mask lines with contact structures. Each contact structure contacts a different conductive line. 
     According to yet another aspect of the invention, a method is provided for forming an integrated circuit. The method comprises providing a substrate having an overlying mask layer and a first photodefinable layer overlying the mask layer. A first pattern is formed in the first photodefinable layer. A second pattern is formed in the mask layer based upon the first pattern. A second photodefinable layer is formed over the mask layer. A third pattern is formed in the second photodefinable layer and transferred to the mask layer. A third photodefinable layer is formed over the mask layer and a fourth pattern is formed in the third photodefinable layer. At least the second pattern and the third pattern are then simultaneously transferred to the substrate. 
     According to another aspect of the invention, a method is provided for semiconductor fabrication. The method comprises forming a first pattern of mask lines over a substrate by pitch multiplication. Portions of the lines extend in spaced, generally parallel relation to one another between first and second spaced planes extending perpendicular to the lines and other portions of the lines extend between third and fourth spaced planes extending perpendicular to the lines. The portions of the lines are at an angle relative to the other portions of the lines. The method also comprises separately forming a second pattern in a photodefinable material by photolithography without pitch multiplication. A remaining portion of the photodefinable material after forming the second pattern overlaps a location of at least some of the mask lines. 
     According to yet another aspect of the invention, a process is provided for forming an integrated circuit. The process comprises forming a plurality of mask lines forming closed loops. A distance between neighboring mask lines at one end of the loops is less than an other distance between neighboring mask lines at an other end of the loops. The method also comprises forming a layer of a photodefinable material over the mask lines. The ends of the closed loops extend laterally beyond boundaries of the layer of the photodefinable material. 
     According to another aspect of the invention, a partially formed integrated circuit is provided. The partially formed integrated circuit comprises a plurality of patterned mask lines which form closed loops. A photodefinable material overlies the mask lines and the ends of the closed loops extend laterally beyond boundaries of the photodefinable material. A distance between neighboring mask lines at one end of the loops is less than an other distance between neighboring mask lines at an other end of the loops. 
     According to another aspect of the invention, an integrated circuit is provided. The integrated circuit comprises a regularly repeating plurality of electrical devices arranged in an array and a plurality of conductive interconnects connecting electrical devices of the array. Each interconnect has a width and portions of the interconnects extend in spaced, generally parallel relation to one another between first and second spaced planes extending perpendicular to the interconnects and other portions of the interconnects extend in spaced, generally parallel relation to one another between third and fourth spaced planes extending perpendicular to the interconnects. The portions of the interconnects are at an angle relative to the other portions of the interconnects and the other portions of the interconnects are outside the array. The integrated circuit also comprises a plurality of contact structures. Each contact structure has a minimum dimension and at least one contact structure contacts each of the interconnects between the third and the fourth spaced planes. 
     According to yet another aspect of the invention, a memory device is provided. The memory device comprises an array region comprising a plurality of memory cells arranged in rows. Each of a plurality of conductive lines connect a row of memory cells. The memory device also comprises a periphery region comprising landing pads. Each landing pad is in contact with one of the plurality of conductive lines. The conductive lines occupy both the array region and the periphery region and a spacing between neighboring conductive lines in the periphery region is greater than a spacing between neighboring conductive lines in the array region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention will be better understood from the Detailed Description of the Preferred Embodiments and from the appended drawings, which are meant to illustrate and not to limit the invention, and wherein: 
         FIGS. 1A-1F  are schematic, cross-sectional side views of mask lines, formed in accordance with a prior art pitch multiplication method; 
         FIGS. 2A-2B  are schematic, top plan views illustrating margins of error available for forming contacts to pitch multiplied lines; 
         FIGS. 3A-3B  are schematic, top plan and cross-sectional side views, respectively, of a partially formed memory device, in accordance with preferred embodiments of the invention; 
         FIGS. 4A-4B  are schematic, top plan and cross-sectional side views, respectively, of the partially formed memory device of  FIGS. 3A and 3B  after forming lines in a photo-definable layer in the periphery of the memory device, in accordance with preferred embodiments of the invention; 
         FIG. 5  is a schematic, cross-sectional side view of the partially formed memory device of  FIGS. 4A-4B  after widening spaces between photoresist lines, in accordance with preferred embodiments of the invention; 
         FIG. 6  is a schematic, cross-sectional side view of the partially formed memory device of  FIG. 5  after etching through a hard mask layer, in accordance with preferred embodiments of the invention; 
         FIG. 7  is a schematic, cross-sectional side view of the partially formed memory device of  FIG. 6  after transferring a pattern from the photoresist layer to a temporary layer, in accordance with preferred embodiments of the invention; 
         FIG. 8  is a schematic, cross-sectional side view of the partially formed memory device of  FIG. 7  after depositing a layer of a spacer material, in accordance with preferred embodiments of the invention; 
         FIG. 9  is a schematic, cross-sectional side view of the partially formed memory device of  FIG. 8  after a spacer etch, in accordance with preferred embodiments of the invention; 
         FIG. 10A  is a schematic, cross-sectional side view of the partially formed memory device of  FIG. 9  after removing a remaining portion of the temporary layer to leave a pattern of spacers, in accordance with preferred embodiments of the invention; 
         FIG. 10B  is a schematic, top plan view of the partially formed memory device of  FIG. 10A , in accordance with preferred embodiments of the invention; 
         FIG. 10C  is a schematic, top plan view of the partially formed memory device of  FIG. 10A , in accordance with other preferred embodiments of the invention; 
         FIG. 11  is a schematic, cross-sectional side view of the partially formed memory device of  FIGS. 10A-10C  after surrounding the spacers with a removable material and forming a hard mask layer and a photodefinable layer over the spacers, in accordance with preferred embodiments of the invention; 
         FIG. 12  is a schematic, cross-sectional side view of the partially formed memory device of  FIG. 11  after forming a landing pad pattern in the photodefinable layer to overlay the spacer pattern, in accordance with preferred embodiments of the invention; 
         FIG. 13  is a schematic, cross-sectional side view of the partially formed memory device of  FIG. 12  after transferring the landing pad pattern from the photodefinable layer to the same level as the spacers, in accordance with preferred embodiments of the invention; 
         FIG. 14  is a schematic, top plan view of the partially formed memory device of  FIG. 13 , in accordance with preferred embodiments of the invention; 
         FIG. 15  is a schematic, cross-sectional side view of the partially formed memory device of  FIGS. 13-14  after etching the landing pad pattern and the spacer pattern into an underlying hard mask layer, in accordance with preferred embodiments of the invention; 
         FIGS. 16A-16B  are schematic, cross-sectional side and top plan views, respectively, of the partially formed memory device of  FIG. 15  after transferring the landing pad pattern and the spacer pattern together to an additional hard mask layer, in accordance with preferred embodiments of the invention; 
         FIG. 17  is a schematic, cross-sectional side view of the partially formed memory device of  FIGS. 16A and 16B  after forming a protective layer over and around the landing pad pattern and the spacer pattern, in accordance with preferred embodiments of the invention; 
         FIG. 18  is a schematic, top plan view of the partially formed memory device of  FIG. 17  after patterning the protective layer, in accordance with preferred embodiments of the invention; 
         FIG. 19  is a schematic, top plan view of the partially formed memory device of  FIG. 18  after etching exposed portions of spacers, in accordance with preferred embodiments of the invention; 
         FIGS. 20A and 20B  are schematic, top plan and cross-sectional side views, respectively, of the partially formed memory device of  FIG. 19  after removing the protective layer, in accordance with preferred embodiments of the invention; and 
         FIGS. 21A-21B  are schematic, cross-sectional side and top plan views, respectively, of the partially formed memory device of  FIGS. 20A-20B  after transferring the landing pad and spacer pattern to the substrate, in accordance with preferred embodiments of the invention. 
     
    
    
     DETAILED DESCRIPTION 
     Various types of misalignments have been found to occur when forming contacts to pitch doubled lines. As shown in  FIGS. 2A and 2B , if  2 F is the minimum pitch of the photolithographic technique used for patterning photoresist to form a contact and the lines  90   a  and  90   b  have been pitch-doubled, then the width of the lines and the spaces separating the lines may be, as an example, ½ F. Given this small feature size, one type of misalignment can occur due to difficulties in accurately overlaying mask features  92 , for forming contacts, on lines  90   a  and  90   b.  If the features  92  cannot be overlaid on lines  90   a  with a tolerance of less than ¼ F, they may form an electrical short with the neighboring line  90   b  or they may not contact the line  90   a  at all. Because F is at the lower limits of the resolution of the photolithographic technique, however, patterning the contacts  90  with an accuracy of ¼ F of the line  90   a  can be difficult, if not impossible. This difficulty is exacerbated because the lines  90   a  and  90   b  are themselves formed with a certain margin of error. As a result, the margin of error for forming the features  92  is undesirably small and the features  92  may cause shorts or fail to make contact at all with the line  90   a.  As used herein, it will be appreciated that a “feature” refers to any volume or opening formed in a material, e.g., in a mask layer or in the substrate, and having discrete boundaries. 
     As shown in  FIG. 2B , another type of misalignment can occur when forming individual lines out of the connected lines  90   a  and  90   b.  It will be appreciated that pitch doubling typically forms loops as a result of spacer formation around a photoresist-defined feature; as illustrated in both  FIGS. 2A and 2B , the lines  90   a  and  90   b  are connected at their ends. These lines, however, are typically used to define conductive features that connect different electrical devices and, so, should be electrically isolated. To electrically disconnect the lines  90   a  and  90   b,  a mask  94  can be used to protect the areas to be retained. The exposed portions  96   a  and  96   b  of the line are then etched away. To ensure that the portion  96   a  is etched, the mask  94 , like the features  92  in  FIG. 2B , should be placed accurately relative to the line  90   a.  It will be appreciated that the mask  94  is typically defined by photolithography and, as a result, the difficulties associated with placing the features  92  are also present when defining the edges of the mask  94 . Consequently, it is possible that the mask may not leave all of portions  96   a  or  96   b  exposed for a subsequent etch, thereby causing a short between lines  90   a  and  90   b.  Thus, it will be appreciated that for tightly spaced lines such as pitch multiplied lines, the margin of error for forming the mask  94  is undesirably small. 
     Advantageously, preferred embodiments of the invention allow for increased tolerances in forming contacts and in separating mask features that are formed, e.g., by pitch multiplication. It will be appreciated that pitch multiplied mask features are typically closed loops at some point in the masking process, e.g., two neighboring lines connected together at their ends. In preferred embodiments, the spacing between neighboring features, e.g., the lines forming a closed loop, is increased in portions of the loop where a contact to the lines will be formed. The portions with widened spacing can be located in, e.g., the periphery of a memory device, while the lines in the array region of the memory device are more narrowly spaced. Advantageously, this widening of the space between the lines allows for an increased margin of error for forming contacts to the lines. For example, the amount by which the contact can be mis-aligned before shorting a neighboring line can be increased by the amount that the spacing between the lines is increased. Advantageously, the spacing between the features can be tailored to the requirements and tolerances of a particular photolithographic technique, if desired. 
     In addition, the portions of the lines that are widened, e.g., in the periphery of a memory device, are preferably formed at an angle relative to the other portions of the lines, e.g., in the array region of a memory device. Moreover, the angle is preferably similar for both lines of a loop formed by pitch multiplication. Advantageously, this angling allows the points of contact, including landing pads and contact points for other interconnects, to be more closely packed together than if the lines continue to extend parallel to portions of the line without contact points, e.g., in the array region of a memory device. Such an arrangement also allows more close packing than if each of the lines extends in a different direction, e.g., if one of the lines of a loop extends at less than 180° and the other extends at more than a 180° angle relative to portions of the line in the array. 
     Preferably, the mask features to be overlaid with other features correspond to conductive interconnects in an integrated circuit, e.g., a memory chip. In such cases, the mask features are preferably mask lines or other features that serve to pattern a substrate. The lines are preferably formed by pitch multiplication by patterning a first photodefinable layer. The features to contact and/or modify the lines are then overlaid on the lines by patterning a second photodefinable layer overlying the lines. In cases where the lines are used to form conductive features such as interconnects, the lines that form a closed loop can be modified to electrically separate the lines and form two or more separate conductive paths. For this electrical separation, a third photodefinable layer is preferably patterned to form a protective mask over parts of the lines that are to be retained. The exposed parts of the lines are then etched away to separate the lines. This separation of the lines can performed while the lines are lines in a mask or hard mask layer or after the lines have been transferred to the substrate. 
     In other embodiments, the electrical separation of the lines can be accomplished by forming electrical devices, such as transistors, in the path of the lines. In such cases, operation of the electrical device can be used to selectively electrically isolate the lines, as desired. 
     It will be appreciated that the “substrate” containing the conductive lines can comprise any material or materials that are to be processed through an overlying mask layer and that comprises material that ultimately forms part of the integrated circuit being fabricated. Thus, a substrate can include a layer of a single material, a plurality of layers of different materials, a layer or layers having regions of different materials or structures in them, etc. These materials can include semiconductors, insulators, conductors, or combinations thereof. 
     Preferably, the substrate comprises a conductor suitable for acting as electrical interconnects between electrical devices. For example, the substrate can comprise doped polysilicon, an electrical device active area, a silicide, or a metal layer, such as a tungsten, aluminum or copper layer, or a combination thereof. Thus, the mask lines can directly correspond to the desired placement of interconnects in the substrate. In other embodiments, the substrate can be an insulator. 
     Reference will now be made to the Figures, wherein like numerals refer to like parts throughout. It will be appreciated that  FIGS. 2A-21B  are not necessarily drawn to scale. 
     It will be appreciated that while the preferred embodiments will find application in any context in which features from different mask patterns are overlaid one other, in particularly advantageous embodiments, features formed by pitch multiplication or employing spacers on soft or hard masks are “stitched” or aligned with features formed by a masking technique with a lower resolution. Preferably, pitch multiplied mask features are made to contact features formed by conventional photolithography. Thus, the pitch multiplied features preferably have a pitch below the minimum pitch of the photolithographic technique used for patterning the other features. In addition, while the preferred embodiments can be used to form any integrated circuit, they are particularly advantageously applied to form devices having arrays of electrical devices, including integrated circuits having logic or gate arrays and volatile and non-volatile memory devices such as DRAM, ROM or flash memory. Advantageously, the pitch multiplied mask features can be used to form word lines, bit lines or active areas that are part of a continuous straight linear or irregular weaving pattern. 
       FIG. 3A  shows a top view of an integrated circuit  100 , which is preferably a memory chip. A central region  102 , the “array,” is surrounded by a peripheral region  104 , the “periphery.” It will be appreciated that, in a fully formed integrated circuit  100 , the array  102  will typically be densely populated with conducting lines and electrical devices such as transistors and capacitors. In a memory device, the electrical devices form a plurality of memory cells, which are typically arranged in a regular pattern, such as rows. Desirably, pitch multiplication can be used to form features such as rows/columns of transistors, capacitors or interconnects in the array  102 , as discussed below. On the other hand, the periphery  104  typically comprises features larger than those in the array  102 . Conventional photolithography, rather than pitch multiplication, is typically used to pattern features in the periphery  104 , because the geometric complexity of logic circuits located in the periphery  104  makes using pitch multiplication difficult, whereas the regular grid typical of memory array patterns is conducive to pitch multiplication. In addition, some devices in the periphery require larger geometries due to electrical constraints, thereby making pitch multiplication less advantageous than conventional photolithography for such devices. 
     With reference to  FIG. 3B , a partially formed integrated circuit  100  is provided. A substrate  110  is provided below various layers  120 - 160 . The substrate  110  will be patterned to form various features and the layers  120 - 160  will be etched to form a mask for this patterning, as discussed below. The materials for the layers overlying the substrate  110  are preferably chosen based upon consideration of the chemistry and process condition requirements for the various pattern forming and pattern transferring steps discussed herein. Because the layers between a topmost photodefinable layer  120  and the substrate  110  function to transfer a pattern derived from the photodefinable layer  120  to the substrate  110 , the layers between the photodefinable layer  120  and the substrate  110  are preferably chosen so that they can be selectively etched relative to other exposed materials. It will be appreciated that a material is considered selectively, or preferentially, etched when the etch rate for that material is at least about 5 times greater, preferably at least about 10 times greater, more preferably at least about 20 times greater and, most preferably, at least about 40 times greater than that for surrounding materials. 
     In the illustrated embodiment, the photodefinable layer  120  overlies a first hard mask, or etch stop, layer  130 , which overlies a temporary layer  140 , which overlies a second hard mask, or etch stop, layer  150 , which overlies an additional hard mask layer  160 , which overlies the substrate  110  to be processed (e.g., etched) through a mask. Preferably, the mask through which the substrate  110  is processed is formed in the additional hard mask layer  160 . 
     It will be understood that in common methods of transferring patterns, both the mask and the underlying substrate are exposed to an etchant, which preferentially etches away the substrate material. The etchants, however, also wear away the mask materials, albeit at a slower rate. Thus, over the course of transferring a pattern, the mask can be worn away by the etchant before the pattern transfer is complete. These difficulties are exacerbated where the substrate  110  comprises multiple layers to be etched. In such cases, the additional hard mask layer  160  is desirable to prevent the mask pattern from being worn away before the pattern transfer complete. The illustrated embodiment shows the use of the additional hard mask layer  160 . 
     It will be understood, however, that because the various layers are chosen based upon the requirements of chemistry and process conditions, one or more of the layers can be omitted in some embodiments. For example, the additional hard mask layer  160  can be omitted in embodiments where the substrate  110  is relatively simple, e.g., where the substrate  110  is a single layer of material and where the depth of the etch is moderate. In such cases, the second hard mask layer  150  may be a sufficient mask for transferring a pattern to the substrate  110 . Similarly, for a particularly simple substrate  110 , the various other layers, such the second hard mask layer  150  itself, may be omitted and overlying mask layers may be sufficient for the desired pattern transfer. The illustrated sequence of layers, however, is particularly advantageous for transferring patterns to difficult to etch substrates, such as a substrate  110  comprising multiple materials or multiple layers of materials, or for forming small features. 
     In addition to selecting appropriate materials for the various layers, the thicknesses of the layers  120 - 160  are preferably chosen depending upon compatibility with the etch chemistries and process conditions described herein. For example, when transferring a pattern from an overlying layer to an underlying layer by selectively etching the underlying layer, materials from both layers are removed to some degree. Thus, the overlying layer is preferably thick enough so that it is not worn away over the course of the etch of the underlying layer. The selected thickness, of course, depends in part on the level of selectivity of the etch chemistry. 
     In the illustrated embodiment, the photodefinable layer  120  is preferably between about 100 nm and 500 nm thick and, more preferably, about 200 nm thick. The first hard mask layer  130  is preferably between about 10 nm  and 50  nm thick and, more preferably, about 25 nm thick. The temporary layer  140  is preferably between about 50 nm and 200 nm thick and, more preferably, about 100 nm thick. The second hard mask or etch stop layer  150  is preferably between about 20 nm and 70 nm thick and, more preferably, about 50 nm thick and the additional hard mask layer  160  is preferably between about 150 nm and 500 nm thick and, more preferably, about 200-300 nm thick. 
     With continued reference to  FIG. 3B , the photodefinable layer  120  is preferably formed of a photoresist, including any photoresist known in the art. For example, the photoresist can be any photoresist compatible with 157 nm, 193 nm or 248 nm wavelength systems, 193 nm wavelength immersion systems or electron beam systems. Examples of preferred photoresist materials include argon fluoride (ArF) sensitive photoresist, i.e., photoresist suitable for use with an ArF light source, and krypton fluoride (KrF) sensitive photoresist, i.e., photoresist suitable for use with a KrF light source. ArF photoresists are preferably used with photolithography systems utilizing relatively short wavelength light, e.g., 193 nm. KrF photoresists are preferably used with longer wavelength photolithography systems, such as 248 nm systems. 
     The material for the first hard mask layer  130  is preferably inorganic; exemplary materials include silicon oxide (SiO 2 ), silicon or a dielectric anti-reflective coating (DARC), such as a silicon-rich silicon oxynitride. DARCs can be particularly advantageous for forming patterns having pitches near the resolution limits of a photolithographic technique because they can enhance resolution by minimizing light reflections. It will be appreciated that unwanted light reflections can decrease the precision with which photolithography can define the edges of a pattern. Optionally, an anti-reflective coating (ARC), e.g., a bottom anti-reflective coating (BARC) (not shown) can similarly be used in addition to, or in place of, the inorganic first hard mask layer  130  to control light reflections. 
     The temporary layer  140  is preferably formed of amorphous carbon, which offers very high etch selectivity relative to the preferred hard mask materials. More preferably, the amorphous carbon is a form of amorphous carbon that is highly transparent to light and which offers further improvements for mask alignment. 
     As with the first hard mask layer  130 , the second hard mask layer  150  is preferably an inorganic material, with examples including a dielectric anti-reflective coating (DARC) (e.g., a silicon oxynitride), a silicon oxide (SiO 2 ) or silicon. In addition, a bottom anti-reflective coating (BARC) (not shown) can also optionally be used to control light reflections. While the first and the second hard mask layers  130  and  150  can be formed of different materials, these layers are preferably formed of the same material for ease of processing and to minimize the number of different deposition tools and etch chemistries utilized, as described below. Like the temporary layer  140 , the additional hard mask layer  160  is preferably formed of amorphous carbon. 
     It will be appreciated that the various layers discussed herein can be formed by various methods known to those of skill in the art. For example, various vapor deposition processes, such as chemical vapor deposition, can be used to form the hard mask layers. Spin-on-coating processes can be used to form the photodefinable layers. In addition, amorphous carbon layers can be formed by chemical vapor deposition using a hydrocarbon compound, or mixtures of such compounds, as carbon precursors. Exemplary precursors include propylene, propyne, propane, butane, butylene, butadiene and acetelyne. A suitable method for forming amorphous carbon layers is described in U.S. Pat. No. 6,573,030 B1, issued to Fairbairn et al. on Jun. 3, 2003, the entire disclosure of which is incorporated herein by reference. 
     In a first phase of the method in accordance with the preferred embodiments and with reference to  FIGS. 4-10 , pitch multiplication in the array region of the partially formed integrated circuit  100  is performed. 
     With reference to  FIGS. 4A and 4B , a pattern comprising spaces or trenches  122  defined by photodefinable material  124  is formed in the photodefinable layer  120 .  FIG. 4A  shows a schematic top view of a part of the pattern in the partially formed memory device  100  and  FIG. 4B  shows a schematic side view, as viewed through the vertical plane  4 B of  FIG. 4A . The photodefinable layer  120  can be patterned by, e.g., photolithography, in which the layer  120  is exposed to radiation through a reticle and then developed. After being developed, the remaining photodefinable material, photoresist in the illustrated embodiment, comprises lines  124 , which define spaces  122 . 
     With continued reference to  FIG. 4A , while they can be any size, the widths F A1  and F A2  of the photoresist lines  124  and the spaces  122  in the array  102  are preferably both approximately equal, for simplicity of processing and to allow a high density of lines in the array. In addition, the widths F A1  and F A2  are preferably at or near the limits of the photolithographic technique used to pattern the photodefinable layer  120 . Thus, the sum of F A1  and F A2  may be at the minimum pitch of the photolithographic technique. 
     Also, while they can be any size, to simplify processing, the widths F P1  and F P2  in the periphery  104  are preferably also preferably both approximately equal. F P1  and F P2 , however, are preferably about 1.5 time greater and, more preferably about 1.5 to about 3 times greater than each of F A1  and F A2 , to allow for an increased margin of error in aligning mask patterns derived from the photoresist lines  124  and the spaces  122  with other features. It will be appreciated that the actual widths of F P1  and F P2  can be varied, depending upon the resolution and overlay accuracy of the methods later used to define the features that will contact the lines  124 . 
     Preferably, part of the lines  124  in the periphery  104  are formed at an angle  126  relative to portions of the lines  124  located in the array  102 . Preferably, the angle  126  is less than about 90°, preferably greater than about 30°, more preferably between about 30-90° and is about 90° in the illustrated embodiment. In addition, the angle  126  is most preferably the same and bends in the same direction for all lines  124 . 
     As shown in  FIG. 5 , the lines  124  can optionally be narrowed by etching, to form spaces  122   a  and  124   a.  The photoresist lines  124  are preferably etched using an isotropic etch, such as a sulfinur oxide plasma, e.g., a plasma comprising SO 2 , O 2 , N 2  and Ar. The extent of the etch is preferably selected so that the width of the spaces  122   a  and the lines  124   a  correspond to the desired spacing of the spacers to be formed, as will be appreciated from the discussion below with respect to  FIGS. 8-10 . Advantageously, because lines  124   a  are typically narrower in the array  102  ( FIG. 3A ), this etch allows the formation of lines  124   a  in the array  102  that are narrower than would be possible using the photolithographic technique originally used to pattern the photodefinable layer  120 . In addition, the etch can smooth the edges of the lines  124   a,  thereby improving the uniformity of those lines  124   a.  In other embodiments, this narrowing of the lines  124  can be performed after transferring the pattern in the photodefinable layer  120  to the first hard mask layer  130  and/or the temporary layer  140 . 
     The pattern of the (modified) photodefinable layer  120  is preferably transferred to a layer  140  of material that can withstand the process conditions for spacer material deposition and etch, discussed below. In other embodiments, where the deposition and etch of spacer material is compatible with the photodefinable layer  120 , the spacer material can be deposited directly on the photodefinable layer  120 . 
     In the illustrated embodiment, in addition to having higher heat resistance than photoresist, the material forming the temporary layer  140  is preferably selected such that it can be selectively removed relative to the material for the spacers  175  ( FIG. 10 ) and the underlying layer  150 . As noted above, the layer  140  is preferably formed of amorphous carbon. Because the preferred chemistries for etching photoresist also typically etch significant amounts of amorphous carbon and because chemistries are available for etching amorphous carbon with excellent selectivity relative to a variety of materials, a hard mask layer  130 , selected from such materials, preferably separates the layers  120  and  140 . As noted above, suitable materials for the hard mask layer  130  include inorganic materials, such as DARCs, silicon oxides or nitrides, and silicon. 
     The pattern in the photodefinable layer  120  is preferably transferred to the hard mask layer  130 , as shown in  FIG. 6 . This transfer is preferably accomplished using an anisotropic etch, such as an etch using a fluorocarbon plasma, although a wet (isotropic) etch may also be suitable if the hard mask layer  130  is suitably thin. Preferred fluorocarbon plasma etch chemistries include CFH 3 CF 2 H 2  and CF 3 H. 
     The pattern is then transferred to the temporary layer  140 , as shown in  FIG. 7 , preferably using a sulfur-containing plasma, e.g., a plasma containing SO 2 , O 2  and Ar. Advantageously, the sulfur-containing plasma can etch carbon of the preferred temporary layer  140  at a rate greater than about 20 times and, more preferably, greater than about 40 times the rate that the hard mask layer  130  is etched. A suitable sulfur-containing plasma is described in U.S. patent application Ser. No. 10/931,772 to Abatchev et al., filed Aug. 31, 2004, entitled Critical Dimension Control, the entire disclosure of which is incorporate herein by reference. It will be appreciated that the sulfur-containing plasma can simultaneously etch the temporary layer  140  and also remove the photodefinable layer  120 . The resulting lines  124   a  constitute the placeholders or mandrels upon which a pattern of spacers  175  ( FIG. 10 ) will be formed. 
     As shown in  FIG. 8 , a layer  170  of spacer material is preferably next deposited conformally over the hard mask layer  130 . The spacer material can be any material capable of use as a mask to transfer a pattern to the underlying additional hard mask layer  160 . The spacer material preferably: 1) can be deposited with good step coverage, 2) can be deposited at a low temperature compatible with the temporary layer  140 ; 3) can be selectively etched relative to the directly underlying layer, e.g., the hardmask layer  150 ; and 4) allows the temporary layer  140  and the underlying second hardmask layer  150  to be etched without itself being worn away. Preferred materials include silicon nitrides and silicon oxides. 
     As shown in  FIG. 9 , the spacer layer  170  is then subjected to an anisotropic etch to remove spacer material from horizontal surfaces  180  of the partially formed integrated circuit  100 . Such an etch, also known as a spacer etch, can be performed using a fluorocarbon plasma, which can also advantageously etch the hard mask layer  130 . 
     Next, the amorphous carbon of the preferred temporary layer  140  can be selectively removed, using, e.g., a sulfur-containing plasma.  FIGS. 10A ,  10 B and  10 C show a pattern of spacers  175  left after the amorphous carbon etch.  FIG. 10B  schematically shows a top view of the spacers  175  and  FIG. 10A  shows a side view, taken along the vertical plane  10 A. 
       FIG. 10C  illustrates an embodiment in which the spacer lines  175  have an angled segment  177  to smooth the transition between the different angled portions of the spacers  175  for ease of optical proximity correction (OPC). It has been found that sharp corners can be difficult to form at the small dimensions typical of pitch multiplied lines. For example, the tips of these corners can be prone to breaking off, either at the level of the layers  120 - 160  or of the substrate  110 . This breaking off on the level of the layers  120 - 160  can cause openings within a particular line, or shorts between neighboring lines to be patterned in the substrate  110 , or pieces in the substrate  110  breaking off may themselves cause the shorts. Thus, to decrease the sharpness of the corners and to minimize this breaking off, the photodefinable layer  120  is preferably patterned to allow formation of transitional segments  177  at an intermediate angle between the angle  126  formed by the segments  178 , between first and second planes  14  and  16 , respectively, and the segments  179 , between third and fourth planes,  10 A and  12 , respectively. For example, the transitional segments  177  can be formed at an angle of 45° in cases where the periphery segments  178  and the array segments  179  are at a 90° angle relative to teach other. It will be appreciated that more than one transitional segment  177  can be formed between the segments  178  and  179  to further ease the transition between the segments  178  and  179 . 
     Thus, as shown in  FIGS. 10A-10C , pitch multiplication in the array of the partially formed integrated circuit  100  has been accomplished and a pattern of spacers  175  has been formed based upon a pattern originally formed in the photodefinable layer  120 . In the illustrated embodiment, the pitch of the spacers is half, and the density double, that of the photoresist lines  124  ( FIG. 4 ) originally formed by photolithography. It will be appreciated that the spacers  175  generally follow the outline of the pattern or lines  124  formed in the photodefinable layer  120 , thereby forming a closed loop. 
     Next, in a second phase of methods according to the preferred embodiments, a second pattern is stitched or overlapped with the pattern of spacers  175 . In the illustrated embodiment, the second pattern is overlaid on the spacers  175  to pattern features that will contact the features defined by the spacers  175 . To form this second pattern, the spacers  175  are preferably first protected by forming a planarizing protective layer  200  over and around the spacers  175 , as shown in  FIG. 11 . In addition, another photodefinable layer  220  is preferably formed to allow the second pattern to be formed. The protective layer  200  is preferably at least as tall as the spacers  175  so that the photodefinable layer  220  can be formed completely overlying the spacers  175 . 0   
     The protective layer  200  is preferably formed of a material that is readily removed selectively relative to the spacers  175 . For example, the protective layer  200  can be formed of a photoresist, and may be the same or a different photoresist from that used to form the photodefinable layer  120  ( FIGS. 3-6 ), which can be the same or a different material from than used to form the photodefinable layer  220 . In other embodiments, the protective layer  200  is formed of amorphous carbon, which can be etched with excellent selectivity relative to the spacers  175 . In the illustrated embodiments, the protective layer  200  is formed of an anti-reflective coating, preferably a spin-on organic BARC, and the photodefinable layer  220  is formed of a photoresist. Optionally, a hard mask or etch stop layer (not shown) can be formed between the layers  200  and  220 . 
     A pattern corresponding to contacts to features to be defined by the spacers  175  is next formed in the photodefinable layer  220 . It will be appreciated that the photodefinable layer  220  can be patterned using any photolithographic technique, including the same photolithographic technique used to pattern the photodefinable layer  120 . 
     Thus, with reference to  FIG. 12 , a pattern of mask features  222  is formed in the photodefinable layer  220 . It will be appreciated that the mask features  222  can be used to pattern features of different sizes than the spacers  175 , including landing pads, local interconnects, periphery circuitry etc. As illustrated, the mask features  222  preferably overlap the pattern of spacers  175  to ultimately form landing pads using the mask features  222 . 
     The pattern of features  222  is then transferred to the same level as the spacers  175 . The protective layer  200  is preferably preferentially etched using an anisotropic etch, such as an etch with a sulfur-containing, preferably a SO 2 — containing, plasma, as shown in  FIG. 13 . The spacers  175  and the feature  202 , together forming a pattern  230 , are left remaining after the protective layer etch.  FIG. 14  shows a schematic top view of the resulting partially formed memory device  100 .  FIG. 13  shows a side view of the memory device  100 , taken along the vertical plane  13  of  FIG. 14 . 
     With reference to  FIG. 14 , it will be appreciated that the distance separating individual features  202  is preferably determined by the resolution of the photolithographic technique used to define the features  202 . Thus, the features  202  are preferably sized and located for reliable formation during integrated circuit fabrication. For example, the features  202  can have a minimum dimension of about 0.30 μm or less and the minimum distance between the features  202  and the spacers  175 , e.g., preferably about 0.20 μm or less, or, more preferably, about 0.10 μm or less, can be smaller than the minimum separation between two features  202 , e.g., preferably about 0.40 μm or less, or, more preferably, about 0.25 μm or less. This is because the separation between individual features  202  is determined by the native photolithographic resolution, while the separation between features  202  and spacers  175  is determined by the overlap capability of the photo tools, which typically allows higher tolerances than the native photolithography resolution. As a result, patterns can typically be overlaid each other with greater accuracy than individual features can be photolithographically defined in any individual mask layer. Thus, because of the different tolerances for placing the features  202  relative to teach other and relative to the spacers  175 , the features  202  can be overlaid on and placed closer to the spacers  175  than they can be formed next to each other. 
     With reference to  FIGS. 15 and 16 , the pattern  230  is preferably transferred down to the additional hard mask layer  160 . Preferably, the additional hard mask layer  160  comprises a material having good etch selectivity to the substrate  110 , and vice versa, to allow for an effective transfer and later mask removal. To transfer to the pattern  230 , the hard mask layer  150  overlying the additional hard mask layer  160  is first etched ( FIG. 15 ). The hard mask layer  150  is preferably anisotropically etched, preferably using a fluorocarbon plasma. Alternatively, an isotropic etch may be used if the hard mask layer  150  is relatively thin. The additional hard mask layer  160  is then anisotropically etched, preferably using a SO 2 — containing plasma, which can simultaneously remove the mask features  202  formed from the protective material  200 .  FIG. 16A  shows a schematic side view of the resulting partially formed memory device  100 .  FIG. 16B  shows a schematic top plan view of the partially formed memory device  100 , with  FIG. 16A  being the side view taken along the vertical plane  16 A. 
     Next, in a third phase of methods according to the preferred embodiments, loops formed by the spacers  175  are etched. This etch preferably forms two separate lines of spacers  175  corresponding to two separate conductive paths in the substrate  110 . It will be appreciated that more than two lines can be formed, if desired, by etching the spacers  175  at more than two locations. 
     To form the separate lines, a protective mask is formed over parts of the lines to be retained and the exposed, unprotected parts of the line are then etched. The protective mask is then removed to leave a plurality of electrically separated lines. 
     With reference to  FIG. 17 , a protective material forming a second protective layer  300  is preferably deposited around and over the spacers  175  and the parts of the layers  150  and  160  forming the pattern  230 . The protective material is preferably a photodefinable material such as photoresist. Optionally, an anti-reflective coating (not shown) can be provided under the layer  300 , e.g., directly above the substrate  110 , to improve photolithography results. The photoresist and the anti-reflective coating can be deposited using various methods known in the art, including spin-on-coating processes. With reference to  FIG. 18 , a protective mask  310  is subsequently patterned in the second protective layer  300 , e.g., by photolithography, to protect desired parts of the underlying pattern  230  from a subsequent etch. To separate the spacers  175  of one loop into two separate lines, portions of the loops are exposed for etching in at least two separate locations. To simplify processing, the exposed portions of the loops are preferably the ends of the loops formed by the spacers  175 , as illustrated. 
     In other embodiments, it will be appreciated that the protective layer  300  can be formed of any material that can be selectively removed, e.g., relative to the spacers  175 , the layers  150 - 160  and the substrate  110 . In those cases, the protective mask  310  can be formed in another material, e.g., photoresist, overlying the layer  300 . 
     Advantageously, where the ends of the spacers  175  extend in a straight line, the length and simple geometry of the straight lines can minimize the precision required for forming the protective mask  310 ; that is, the protective mask need only be formed so that it leaves the ends of the spacers  175  exposed. Thus, by centering the mask a comfortable distance from the ends of the spacers  175 , a misaligned mask may cause slightly more or less of the spacers  175  to be exposed, but can still accomplish the objective of leaving the ends exposed. Consequently, the margin of error for aligning the protective mask  310  is larger than if the mask  310  where required to form a geometrically complex shape that required specific parts of the shape to be aligned with specific parts of the spacers  175 . Moreover, the spacers  175  can be formed longer to further increase the margin of error for aligning the protective mask  310 . 
     With reference to  FIG. 19 , the exposed portions of the spacers  175  are etched away. Where the spacers  175  comprise silicon oxide or nitride, preferred etch chemistries include a fluorocarbon etch or in the case of spacers  175  formed of an oxide, such as silicon oxide, the extruded loops can be etched using a wet chemistry, e.g., a buffered oxide etch. After being etched, the spacers  175  no longer form a loop with a neighboring spacer  175 , as shown in  FIG. 20A . The etched spacers  175  thus form a modified pattern  230   a.    FIG. 20B  shows a side view of the resulting structure, taken along the vertical plane  20 A of  FIG. 20A . 
     With reference to  FIGS. 20A and 20B , the protective material is preferably selectively removed. Where the material is photoresist or BARC, preferred etch chemistries include anisotropic etches, such as with a SO 2 — containing plasma. In other embodiments, the partially formed integrated circuit  100  can be subjected to an ash process to remove the protective material. It will be appreciated that the spacers  175  are not attacked during this removal step and that the layer  160  is protected by the second hard mask layer  150 . 
     With reference to  FIGS. 21A and 21B , the modified pattern  230   a  is transferred to the substrate  110  using the spacers  175  and the layers  150  and  160  as a mask. Given the disparate materials typically used for the additional hard mask layer  160  and the substrate  110  (e.g., amorphous carbon and silicon or silicon compounds, respectively), the pattern transfer can be readily accomplished using conventional etches appropriate for the material or materials of the substrate  110 . Advantageously, any etch chemistry appropriate for the substrate material(s) is can be used. For example, where the substrate comprises an insulator, such as silicon oxide, a fluorocarbon etch comprising CF 4  or C 2 F 6  can be used to etch the substrate. Where the substrate comprises polysilicon, a HBr/Cl 2  etch can be used. In addition, the skilled artisan can readily determine suitable etch chemistries for other substrate materials, such as conductors, including aluminum, transition metals, and transition metal nitrides. For example, an aluminum substrate can be etched using a fluorocarbon etch. 
     Where the substrate  110  comprises layers of different materials, a succession of different chemistries, preferably dry-etch chemistries, can be used to successively etch through the different layers. It will be appreciated that, depending upon the chemistry or chemistries used, the spacers  175  and the hard mask layer  150  may be etched, as shown in  FIG. 21A . Amorphous carbon of the additional hard mask layer  160 , however, advantageously offers excellent resistance to conventional etch chemistries, especially those used for etching silicon-containing materials. Accordingly, the additional hard mask layer  160  can effectively be used as a mask for etching through a plurality of substrate layers, or for forming high aspect ratio trenches. The additional hard mask layer  160  can later be removed for further processing of the substrate  110 . 
     Thus, with reference to  FIG. 21B , the pattern of lines  400  and landing pads  410  can be formed in the integrated circuit  100 . Where the substrate  110  is a conductor (e.g., doped semiconductor or metallic materials), the lines  400  can be interconnect lines, e.g., for connecting memory cells in the array of a memory device to the landing pads  410 . In addition, while landing pads  410  are illustrated, the preferred embodiments allow any structure to be contacted to the lines  400 . For example, larger width interconnects (not shown) can be patterned and directly contacted to the lines  400 . Note that the etched surfaces exhibit exceptionally low edge roughness. 
     It will be appreciated that formation of contacts according to the preferred embodiments offers numerous advantages. For example, the widened lines facilitate connection of interconnects with larger structures, including, e.g., landing pads and larger line width interconnects, by improving alignment tolerances. The increased distance between neighboring lines increases margins for gap fill and/or reduces capacitive coupling between unrelated lines. Moreover, the angling of the lines allow for closer packing of features such as landing pads. 
     Also, the surfaces of trenches and lines in substrates formed according to the preferred embodiments exhibit exceptionally low edge roughness. For example, for lines having a line width of about 50 nm, the edge roughness can be less than about 5 nm rms, and more preferably between about 1 nm and about 2 nm rms. 
     In addition, because multiple patterns, with different size features, can be consolidated on a single final mask layer before being transferred to a substrate, overlapping patterns can easily be transferred to the substrate. Thus, pitch-doubled features and features formed by conventional photolithography can easily be formed connected to each other. Moreover, noted above, exceptionally small features can be formed, while at the same time achieving exceptional and unexpectedly low line edge roughness. While not limited by theory, it is believed that such low line edge roughness is the result of consolidating mask patterns from multiple layers onto a single layer, such as the layer  160 . Forming the spacers  175  and performing multiple anisotropic etches to transfer the pattern from the level of the temporary layer  140  to the additional hard mask layer  160  and then to the substrate  110  and forming and removing the second protective layer  300  are believed to beneficially smooth the surfaces of the mask features in the layer  160 . 
     Moreover, the preferred amorphous carbon etch chemistries disclosed herein allow the use of thin hard mask layers, such as the layers  130  and  150 , relative to the depth that underlying amorphous carbon layers, such as the layers  140  and  160 , are etched. This advantageously reduces demands on the etch selectivity of materials used for the layers (e.g., photoresist layers) overlying the hard mask layers and also reduces demands on the chemistries used to etch the hard mask layers while at the same time ensuring that the additional hard mask layers form thick enough masks to withstand subsequent substrate etches. 
     It will also be appreciated that, in any of the steps described herein, transferring a pattern from a first level to a second level involves forming features in the second level that generally correspond to features on the first level. For example, the path of lines in the second level will generally follow the path of lines on the first level and the location of other features on the second level will correspond to the location of similar features on the first level. The precise shapes and sizes of features can vary from the first level to the second level, however. For example, depending upon etch chemistries and conditions, the sizes of and relative spacings between the features forming the transferred pattern can be enlarged or diminished relative to the pattern on the first level, while still resembling the same initial “pattern.” Thus, the transferred pattern is still considered to be the same pattern as the initial pattern. In contrast, forming spacers around mask features can change the pattern. 
     It will also be appreciated that various modifications of the illustrated embodiments are possible. For example, in preferred embodiments, an objective of etching, or cutting, the loops of the spacers  175  is to form two or more separate conductors. However, the cutting step, including, e.g., protecting, masking and etching, can be performed after any number of steps in preferred process flows. For example, the spacer loops can be transferred to the substrate and the substrate is itself protected with a mask and the loops cut in the substrate itself. In other embodiments, the loops can be cut after various process steps, such as after formation of the spacers (e.g.,  FIG. 10A ), after patterning of landing pads or other features (e.g. after any of steps illustrated in  FIGS. 12-13 ), or after consolidating the spacer pattern and the pattern of the landing pads or other features onto a single level (e.g. after any of steps illustrated in  FIGS. 14-20 ). 
     In a particularly advantageous embodiment, the loops can be cut before transferring the pattern  230  to the layer  160  ( FIGS. 13-16B ). With reference to  FIG. 13 , the pattern  230  is preferably transferred to the hard mask layer  150 . Next, the material forming the features  202  can be removed. It will be appreciated that, to prevent etching the additional mask layer  160 , the hard mask layer  150  can be supplemented with one or more additional layers of material. For example, an amorphous silicon layer and a silicon oxide layer can be used to separate the additional hard mask layer  160  and the spacers  175  and the material of the features  202 . The protective layer  300  can then be deposited directly on the the spacers  175 , the etched hard mask layer  150  and the un-etched additional hard mask layer  160 . The protective mask  310  can then be formed, the loops cut, and the protective mask  310  can subsequently be removed. After removal of the mask  310 , the modified (cut) pattern  230  can be transferred to the additional hard mask layer  160 . Advantageously, by cutting the loops before forming deep trenches in the additional hard mask layer  160 , the protective layer  300  is not deposited into deep trenches, thereby increasing the ease and completeness with which the mask  310  can later be removed. 
     In addition, the pitch of the spacers  175  can be more than doubled. For example, further pitch multiplication can be accomplished by forming additional spacers around the spacers  175 , then removing the spacers  175 , then forming spacers around the spacers that were formerly around the spacers the  175 , and so on. An exemplary method for further pitch multiplication is discussed in U.S. Pat. No. 5,328,810 to Lowrey et al. Thus, the spacers  175  and the conductive lines formed from those spacers can have any desired pitch, including but not limited to about 200 nm or less and about 100 nm or less. 
     Moreover, more than two patterns, e.g., corresponding to landing pads and interconnects, can be consolidated on a mask layer before transferring the consolidated pattern to the substrate. In such cases, additional hard mask layers can be deposited between the layers  140  and  160 . For example, patterns corresponding to landing pads and interconnects can be transferred to a supplemental mask layer (not shown) overlying the hard mask layer  150  and then the sequence of steps illustrated in FIGS.  11 - 14  can be performed to form the new pattern in an overlying photodefinable layer and to transfer the patterns to the substrate  110 . The supplemental mask layer preferably comprises a material that can be selectively etched relative to the hard mask layer  150  and a protective layer (not shown) that surrounds the landing pads and interconnect patterns after being transferred to the supplemental mask layer. While illustrated with straight lines, it will be appreciated that the lines formed by the spacers  175  can follow any path, including an irregular weaving pattern. 
     Also, while “processing” through the various mask layers preferably involve etching an underlying layer, processing through the mask layers can involve subjecting layers underlying the mask layers to any semiconductor fabrication process. 
     In addition, the principles and advantages discussed herein are applicable to a variety of contexts in which two or more adjacent mask patterns are to be mated within overlapping regions. 
     Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.