Abstract:
In the fabrication of integrated circuits, one specific technique for making surfaces flat is chemical-mechanical planarization. However, this technique is quite time consuming and expensive, particularly as applied to the numerous intermetal dielectric layers—the insulative layers sandwiched between layers of metal wiring—in integrated circuits. Accordingly, the inventor devised several methods for making nearly planar intermetal dielectric layers without the use of chemical-mechanical planarization and methods of modifying metal layout patterns to facilitate formation of dielectric layers with more uniform thickness. These methods of modifying metal layouts and making dielectric layers can be used in sequence to yield nearly planar intermetal dielectric layers with more uniform thickness.

Description:
RELATED APPLICATIONS  
       [0001]    This application is a Divisional of U.S. application Ser. No. 09/801,265, filed Mar. 7, 2001, which claims priority to U.S. Provisional Application No. 60/187,658, filed on Mar. 7, 2000, both of which are incorporated herein by reference. 
     
    
     
       TECHNICAL FIELD  
         [0002]    The present invention concerns methods of making integrated circuits, particularly methods of making metal masks and dielectric, or insulative, films.  
         BACKGROUND OF THE INVENTION  
         [0003]    Integrated circuits, the key components in thousands of electronic and computer products, are interconnected networks of electrical components fabricated on a common foundation, or substrate. Fabricators typically build the circuits layer by layer, using techniques, such as doping, masking, and etching, to form thousands and even millions of microscopic resistors, transistors, and other electrical components on a silicon substrate, known as a wafer. The components are then wired, or interconnected, together to define a specific electric circuit, such as a computer memory.  
           [0004]    One important concern during fabrication is flatness, or planarity, of various layers of the integrated circuit. For example, planarity significantly affects the accuracy of a photo-imaging process, known as photomasking or photolithography, which entails focusing light on light-sensitive materials to define specific patterns or structures in a layer of an integrated circuit. In this process, the presence of hills and valleys in a layer forces various regions of the layer out of focus, causing photoimaged features to be smaller or larger than intended. Moreover, hills and valleys can reflect light undesirably onto other regions of a layer and add undesirable features, such as notches, to desired features. These problems can be largely avoided if the layer is sufficiently planar.  
           [0005]    One process for making surfaces flat or planar is known as chemical-mechanical planarization or polishing. Chemical-mechanical planarization typically entails applying a fluid containing abrasive particles to a surface of an integrated circuit, and polishing the surface with a rotating polishing head. The process is used frequently to planarize the insulative, or dielectric, layers that lie between layers of metal wiring in integrated circuits. These insulative layers, which typically consist of silicon dioxide, are sometimes called intermetal dielectric layers. In conventional integrated-circuit fabrication, planarization of these layers is necessary because each insulative layer tends to follow the hills and valleys of the underlying metal wiring, similar to the way a bed sheet follows the contours of whatever it covers. Thus, fabricators generally deposit an insulative layer much thicker than necessary to cover the metal wiring and then planarize the insulative layer to remove the hills and valleys.  
           [0006]    Unfortunately, conventional methods of forming these intermetal dielectric layers suffer from at least two problems. First, the process of chemical-mechanical planarization is not only relatively costly but also quite time consuming. And second, the thickness of these layers generally varies considerably from point to point because of underlying wiring. Occasionally, the thickness variation leaves metal wiring under a layer too close to metal wiring on the layer, encouraging shorting or crosstalking. Crosstalk, a phenomenon that also occurs in telephone systems, occurs when signals from one wire are undesirable transferred or communicated to another nearby wire.  
           [0007]    Accordingly, the art needs fabrication methods that reduce the need to planarize intermetal dielectric layers, that reduce thickness variation in these layers, and that improve their electrical properties generally.  
         SUMMARY OF THE INVENTION  
         [0008]    To address these and other needs, the inventor devised various methods of making dielectric layers on metal layers, which reduce the need for chemical-mechanical planarization procedure. Specifically, a first exemplary method of the invention forms a metal layer with a predetermined maximum feature spacing and then uses a TEOS-based (tetraethyl-orthosilicate-based) oxide deposition procedure to form an oxide film having nearly planar or quasi-planar characteristics. The exemplary method executes a CVD (chemical vapor deposition) TEOS oxide procedure to form an oxide layer on a metal layer having a maximum feature spacing of 0.2-0.5 microns.  
           [0009]    A second exemplary method includes voids within the oxide, or more generally insulative, film to improve its effective dielectric constant and thus improve its ability to prevent shorting and crosstalk between metal wiring. Specifically, the exemplary method uses a TEOS process at a non-conformal rate sufficient to encourage the formation of voids, and then uses the TEOS process at a conformal rate of deposition to seal the voids. More generally, however, the invention uses a non-conformal deposition procedure to encourage formation of voids and then a more conformal deposition to seal the voids.  
           [0010]    A third exemplary method increases the metal-fill density of metal patterns to facilitate formation of intermetal dielectric layers having more uniform thicknesses. The third exemplary method adds floating metal to open areas in a metal layout and then extends non-floating metal dimensions according to an iterative procedure that entails filling in notches, and corners and moving selected edges of the layout. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]    [0011]FIG. 1 is a cross-sectional view of a partial integrated-circuit assembly  10  including a substrate  12  and metal wires  14   a ,  14   b , and  14   c ;  
         [0012]    [0012]FIG. 2 is a cross-sectional view of the FIG. 1 integrated-circuit assembly after formation of a substantially planar insulative layer  16 , including a portion  16   a  with voids and a portion  16   b  without voids;  
         [0013]    [0013]FIG. 3 is a cross-sectional view of the FIG. 2 assembly after a facet etch to improve the planarity of layer  16 ;  
         [0014]    [0014]FIG. 4 is a cross-sectional view of the FIG. 3 assembly after formation of metal wires  18   a  and  18   b , and substantially planar insulative layer  20 , including a portion  20   a  with voids and a portion  20   b  without voids;  
         [0015]    [0015]FIG. 5 is a cross-sectional view of a partial integrated-circuit assembly  21  including a substrate  22  and metal wires  24   a ,  24   b , and  24   c;    
         [0016]    [0016]FIG. 6 is a cross-sectional view of the FIG. 5 assembly after formation of an oxide spacer  26  and a substantially planar insulative layer  28 , including a portion  28   a  with voids and a portion  28   b  without voids;  
         [0017]    [0017]FIG. 7 is a cross-sectional view of the FIG. 6 assembly after a facet etch to improve the planarity of layer  28 ;  
         [0018]    [0018]FIG. 8 is a cross-sectional view of the FIG. 7 assembly after formation of metal wires  30   a  and  30   b , and substantially planar insulative layer  34 , including a portion  34   a  with voids and a portion  34   b  without voids;  
         [0019]    [0019]FIG. 9 is a cross-sectional view of a partial integrated-circuit assembly  35  including a substrate  36  and metal wires  36   a ,  36   b , and  36   c;    
         [0020]    [0020]FIG. 10 is a cross-sectional view of the FIG. 9 assembly after formation of an oxide spacer  40  and a substantially planar insulative layer  42 ;  
         [0021]    [0021]FIG. 11 is a flow chart illustrating an exemplary method of modifying a metal layout to facilitate fabrication of intermetal dielectric layers with more uniform thickness;  
         [0022]    [0022]FIG. 12 is a partial top view of a metal layout showing how the exemplary method of FIG. 11 adds metal to open areas in a metal layout;  
         [0023]    [0023]FIG. 13 is a partial top view of a metal layout showing how the exemplary method of FIG. 11 fills notches in a metal layout;  
         [0024]    [0024]FIG. 14 is a partial top view of a metal layout showing how the exemplary method of FIG. 11 fills corners in a metal layout;  
         [0025]    [0025]FIG. 15 is a partial view of a metal layout showing how the exemplary method of FIG. 11 fills in between opposing edges of live metal regions in a metal layout;  
         [0026]    [0026]FIG. 16 is a partial view of a metal layout showing how the exemplary method of FIG. 11 moves edges;  
         [0027]    [0027]FIG. 17 is a block diagram of an exemplary computer system  42  for hosting and executing a software implementation of the exemplary pattern-filling method of FIG. 11; and  
         [0028]    [0028]FIG. 18 is a simplified schematic diagram of an exemplary integrated memory circuit  50  that incorporates one or more nearly planar intermetal dielectric layers and/or metal layers made in accord with exemplary methods of the invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    The following detailed description, which references and incorporates the above-identified Figures, describes and illustrates specific embodiments of the invention. These embodiments, offered not to limit but only to exemplify and teach the invention, are shown and described in sufficient detail to enable those skilled in the art to implement or practice the invention. Thus, where appropriate to avoid obscuring the invention, the description may omit certain information known to those of skill in the art.  
       First Exemplary Method of Forming Nearly Planar Dielectric Films  
       [0030]    FIGS.  1 - 4  show a number of exemplary integrated-circuit assemblies, which taken collectively and sequentially, illustrate an exemplary method of making nearly planar or quasi planar dielectric films, or layers, within the scope of the present invention. As used herein, a quasi planar film is globally planar with local nonplanarities having slopes less than or equal to 45 degrees and depths less than the thickness of the next metal layer to be deposited. The local nonplanarities typically occur over the gaps between underlying metal features.  
         [0031]    The method, as shown in FIG. 1, a cross-sectional view, begins with formation of an integrated-circuit assembly or structure  10 , which can exist within any integrated circuit, for example, an integrated memory circuit. Assembly  10  includes a substrate  12 . The term “substrate,” as used herein, encompasses a semiconductor wafer as well as structures having one or more insulative, semi-insulative, conductive, or semiconductive layers and materials. Thus, for example, the term embraces silicon-on-insulator, silicon-on-sapphire, and other advanced structures.  
         [0032]    Substrate  12  includes three representative wires or conductive structures  14   a ,  14   b , and  14   c , with a maximum (or average) feature spacing  14   s . In the exemplary embodiment, wires  14   a - 14   c  are approximately 3000-6000 angstroms thick and comprise metals, such as aluminum, gold, or silver, and nonmetals, such as heavily doped polysilicon. Spacing  14   s , in the exemplary embodiment, is 0.3 microns.  
         [0033]    Wires  14   a - 14   c  can be formed using any number of methods, for example, photolithography and dry etching. To avoid increasing feature spacing during dry etching, the exemplary embodiment forms a lateral-etch-resistant layer, that is, a layer resistant to lateral etching, on a metal layer before etching. Examples of suitable layers include a TEOS, oxide-nitride layer. Alternatively, one can add extensive serif features to the metal mask layout to avoid large open areas, especially to reduce the diagonal distance between features.  
         [0034]    [0034]FIG. 2 shows that the exemplary method next entails forming an insulative layer  16  over substrate  12  and wires  14   a - 14   b . Layer  16  has a thickness  16   t  of, for example, 6000 angstroms, and includes two layers or sublayers  16   a  and  16   b . Sublayer  16   a  includes a number of voids, particularly voids  17  between wires  14   a  and  14   b , and between wires  14   b  and  14   c , to increase its dielectric constant. Sublayer  16   b  is either substantially voidless or includes a substantially fewer number of voids than sublayer  16   a . The presence of voids in sublayer  16   a  reduces lateral electrical coupling between adjacent metal features, for example, between wires  14   a  and  14   b  and between wires  14   a - 14   c  and any overlying conductive structures.  
         [0035]    The exemplary method forms layer  16  using a combination of a non-conformal and conformal oxide depositions. In particular, it uses a CVD TEOS (chemical vapor deposition tetraethyl-orthosilicate) or PECVD TEOS (plasma-enhanced CVD TEOS) oxide deposition process at a non-conformal deposition rate to form void-filled sublayer  16   a  voids and then lowers the TEOS deposition rate to, a conformal rate to form substantially voidless sublayer  16   b.    
         [0036]    [0036]FIG. 3 shows that after forming sublayer  16   b , which includes some level of nonplanarity, the exemplary method facet etches the sublayer at an angle of about 45 degrees to improve its global planarity. (That layer  16   b  has undergone further processing is highlighted by its new reference numeral  16   b ′.) The facet etch reduces or smooths any sharp trenches in regions overlying gaps between metal features, such as wires  14   a - 14   c . As used herein, the term “facet etch” refers to any etch process that etches substantially faster in the horizontal direction than in the vertical direction. Thus, for example, the term includes an angled sputter etch or reactive-ion etch.  
         [0037]    To optimize the slopes of any vias, one can perform the facet etch before via printing. More specifically, one can facet etch after etching any necessary vias and stripping photoresist to produce vias having greater slope and smoothness.  
         [0038]    [0038]FIG. 4 shows the results of forming a second metallization level according to the procedure outlined in FIGS.  1 - 3 . In brief, this entails forming conductive structures  18   a  and  18   b  on insulative sublayer  16   b ′ and forming an insulative layer  20  on sublayer  16   b ′ and conductive structures  18   a  and  18   b . Insulative layer  20 , like insulative layer  16 , includes void-filled sublayer  20   a  and substantially void-free sublayer  20   b ′. Sublayer  20   a  includes one or more voids  19  between conductive structures  18   a  and  18   b . Sublayer  20   b ′ was facet etch to improve its planarity. Layer  20  has a thickness  20   t , of for example 3000-6000 angstroms.  
       Second Exemplary Method of Forming Nearly Planar Dielectric Films  
       [0039]    FIGS.  5 - 8  show a number of exemplary integrated-circuit assemblies, which taken collectively and sequentially, illustrate a second exemplary method of making nearly planar or quasi planar dielectric layers within the scope of the present invention. The second method is particularly applicable to maximum metal feature spacing greater than about 0.3 microns or oxide thickness less than 6000 angstroms to allow for shallow via formation, that is, via depths less than about 4000 angstroms.  
         [0040]    More particularly, FIG. 5 shows that the method begins with formation of an integrated-circuit assembly or structure  21 , which, like assembly  10  in FIG. 1, can exist within any integrated circuit. Assembly  10  includes a substrate  22  which supports three representative wires or conductive structures  24   a ,  24   b , and  24   c , with a desired feature spacing  24   s . In the exemplary embodiment, spacing  24   s  is greater than 0.3 microns. Some embodiments set a minimum spacing of 0.17 microns. However, the present invention is not limited to any particular spacing.  
         [0041]    [0041]FIG. 6 shows that the exemplary method next entails forming an insulative spacer  26  and an insulative layer  28 . Insulative spacers  26 , which consists of silicon dioxide for example, lies over portions of substrate  22  adjacent wires  24   a - 24   c  to reduce the effective separation of wires  24   a - 24   c . The exemplary method uses a TEOS oxide deposition and subsequent etching to form spacers  26 . Insulative layer  28  has a thickness  28   t  of, for example, 4000 angstroms, and includes two sublayers  28   a  and  28   b , analogous to sublayers  16   a  and  16   b  in the first embodiment. Specifically, sublayer  28   a  includes a number of voids  27  between the wires to increase its dielectric constant, and sublayer  28   b  is either substantially voidless or includes a substantially fewer number of voids than sublayer  28   a . A two-stage TEOS oxide deposition process, similar to that used in the first embodiment, is used to form layer  28 .  
         [0042]    [0042]FIG. 7 shows that after forming sublayer  28   b , which includes some level of nonplanarity, the exemplary method facet etches the sublayer at an angle of about 45 degrees to improve its global planarity.  
         [0043]    [0043]FIG. 8 shows the results of forming a second metallization level according to the procedure outlined in FIGS.  5 - 7 . This entails forming conductive structures  30   a  and  30   b  on insulative sublayer  28   b ′ and forming an insulative spacer  32  and an insulative layer  34 , which, like insulative layer  28 , includes void-filled sublayer  34   a  and substantially void-free sublayer  34   b ′. Sublayer  34   a  includes voids  31  between conductive structures  30   a  and  30   b , and sublayer  34   b ′ is facet etched to improve its planarity.  
       Third Exemplary Method of Forming Nearly Planar Dielectric Films  
       [0044]    [0044]FIGS. 9 and 10 show a number of exemplary integrated-circuit assemblies, which taken collectively and sequentially, illustrate a third exemplary method of making nearly planar or quasi planar dielectric layers within the scope of the present invention. In contrast to the first and second embodiment, the third exemplary embodiment is intended for forming insulative films on metal layers with maximum feature spacing up to about 0.5 microns.  
         [0045]    [0045]FIG. 9 shows that the method begins with formation of an integrated-circuit assembly or structure  35 , which like assembly  10  in FIG. 1 and assembly  21  in FIG. 5, can exist within any integrated circuit. Assembly  35  includes a substrate  36  which supports three representative wires or conductive structures  38   a ,  38   b , and  38   c , with a desired feature spacing  38   s  of about 0.5 microns.  
         [0046]    [0046]FIG. 10 shows the results of forming an oxide spacers  40  and an insulative layer  42 . The exemplary embodiment forms one or more oxide spacers  40  which is about 1000 angstroms wide, and thus reduces the effective spacing between conductors  38   a - 38   c  by 2000 angstroms. Forming insulative layer  42  entails executing a flow-fill procedure, such as TRIKON-200 by Trikon Technologies, Inc. To obtain global and local planarity, one can reduce the maximum feature space by using oxide/TEOS spacer as taught in the second exemplary method, or by enlarging the metal feature, or by adding floating metal between the metal features.  
       Exemplary Method of Promoting Uniform Thickness of Intermetal Dielectric Layers  
       [0047]    To facilitate the formation of more uniformly thick inter-metal dielectric layers, such as those described above, the inventor developed specific methods of (and related computer software) for increasing the pattern density of metal layouts. The methods and associated software take a given metal layout and modify, or fill, open areas of the layout to increase pattern density and thus promote uniform thickness or reduce thickness variation across dielectric layers formed on metal layers based on the layouts. These methods and software can thus be used, for example, to facilitate formation of the conductive structures shown in FIGS. 1, 5, and  9 .  
         [0048]    The exemplary method generally entails iteratively measuring a given layout, adding floating metal to fill large open areas in the layout, and extending or filling out existing metal areas to meet maximum feature spacing, or gap, criteria. FIG. 11 shows a flow chart of the exemplary method, which is suitable for implementation as a computer-executable program.  
         [0049]    Specifically, the flow chart includes a number of process or decision blocks  110 ,  120 ,  130 , and  140 . The exemplary method begins at process block  110  which entails measuring a given layout. This entails determining open (unmetallized or nonconductive) areas large enough to be filled with floating metal and identifying live metal areas that require additional metal to obtain desired spacing. Floating metal is metal that is not coupled to a signal path or component, whereas live metal is metal that is coupled to a signal path or component.  
         [0050]    After executing block  110 , the exemplary method proceeds to block  120  which entails adding floating metal to any large areas identified in block  110 . To illustrate, FIG. 12 shows a hypothetical layout having a live metal region  200  with open area  210 . In general, if dimension A is greater than the sum of dimension S 1 , dimension S 2 , and L (the maximum feature spacing criteria), the exemplary method adds floating metal, such as floating metal region  220 .  
         [0051]    After adding floating metal, the exemplary method adds live metal as indicated in block  120  of FIG. 11. FIG. 12 is again instructive of the exemplary method. If dimension B is less than the sum of dimension S 1 , dimension S 2 , and L, the exemplary method adds metal as indicated by added active metal region  230 . process block  104  which entails filling in notches in the layout.  
         [0052]    More particularly, the exemplary method follows an iterative process for adding live (or non-floating) metal, as indicated by blocks  130   a - 130   g.    
         [0053]    Block  130   a  entails filling notches in the current live metal. FIG. 13 shows a live metal region  300  of a hypothetical metal layout having a notch  310 . Included within notch  310  are a series of iteratively added live metal regions  320 - 325 . The amount of metal added at each iteration can be selected using a minimum surface area criteria or computed dynamically each iteration. The exemplary embodiment repeatedly adds metal to the notch until it is filled, before advancing to block  310   b . However, other embodiments can advance to block  310   b  before the notch is filled, relying on subsequent trips or iterations through the first loop in the flowchart to complete filling of the notch.  
         [0054]    Block  130   b  entails filling in corners in the current live metal, meaning the live metal after filling notches. FIG. 14 illustrates a live metal region  400  having a corner  410  and added L-shaped live metal regions  420 - 423  and a rectangular live metal region  424 . (Other embodiments add other shapes of live metal regions.) The amount of metal added at each iteration can be selected using a minimum surface area or single-dimensional criteria or computed dynamically each iteration. The exemplary embodiment repeatedly adds metal to the corner until it is filled, before advancing to block  130   c . However, other embodiments can advance to block  310   b  before the notch is filled, relying on subsequent trips through the inner loop to complete filling of the notch.  
         [0055]    Block  130   c  entails filling in between opposing edges of adjacent live metal regions to achieve a desired spacing, such as a maximum desired spacing L. FIG. 15 shows live metal regions  510  and  520 , which have respective opposing edges  510   a  and  520   a . The exemplary method entails adding live metal regions, such as live metal regions  521 - 523 , one edge such as edge  520   a  to achieved the maximum desired spacing L. However, other embodiments add live metal to both of the opposing edges to achieve the desired spacing. Still other embodiments look at the lengths of the opposing edges and use one or both of the lengths to determine one or more dimensions of the added live metal regions.  
         [0056]    After filling in between opposing edges of existing live metal regions, the exemplary method advances to decision block  130   d  in FIG. 11. This block entails determining whether more live metal can be added. More precisely, this entails measuring the layout as modified by the live metal already added and determining whether there are any adjacent regions that violate the desired maximum spacing criteria. (Note that some exemplary embodiments include more than one maximum spacing criteria to account for areas where capacitive effects or crosstalk issues are of greater importance than others.) If the determination indicates that more metal can be added execution proceeds back to block  130   a  to fill in remaining notches, and so forth. If the determination indicates that no more live metal can be added to satisfy the maximum spacing criteria, execution to proceeds to block  130   e  in FIG. 11.  
         [0057]    Block  130   e  entails moving (or redefining) one or more edges (or portions of edges) of live metal regions in the modified layout specification. To illustrate, FIG. 16 shows live metal regions  610  and  620 , which have respective edges  610   a  and  620   a . It also shows the addition of live metal region  630  to edge  620   a , which effectively extends the edge. Similarly, edge  620   a  has been extended with the iterative addition of live metal regions  631  and  632 . The additions can be made iteratively using a dynamic or static step size, or all it once by computing the size of an optimal addition to each edge. Exemplary execution then proceeds to decision block  130   f.    
         [0058]    In decision block  130   f , the exemplary method decides again whether more metal can be added to the layout. If more metal can be added, the exemplary method repeats execution of process blocks  104 - 122 . However, if no metal can be added, the method proceeds to process block  140  to output the modified layout for use in a fabrication process.  
         [0059]    Although not show explicitly in the exemplary flow chart in FIG. 11, the exemplary method performs data compaction to minimize or reduce the amount of layout data carried forward from iteration to iteration. Data compaction reduces the number of cells which define the circuit associated with the metal layout and the computing power necessary to create the metal layout.  
         [0060]    The exemplary compaction scheme flattens all array placement into single instance placements. For example, a single array placement of a cell incorporating a 3×4 matrix flattens to 12 instances of a single cell. It also flattens specific cells, such as array core cells, vias, or contacts, based on layout or user settings. Additionally, it flattens cells which contain less than a predetermined number of shapes regardless of any other effects. For example, one can flatten cells having less than 10, 20, or 40 shapes. Lastly, the exemplary compaction scheme attempts to merge shapes to minimize overlapping shapes and redundant data.  
         [0061]    The appropriate or optimum degree of flattening depends largely on the processing power and memory capabilities of the computer executing the exemplary method. Faster computers with more core memory and swap space can handle larger number of shapes per cell and thus have less need for flattening than slower computers with less core memory and swap space. In the extreme, a complete circuit layout can be flattened into one cell.  
         [0062]    If a given layout design is not a single flat list of shapes but includes two or more cells placed into each other as instances, additional precaution should be taken to reduce the risk of introducing unintended shorts into the layout during the pattern-fill process. In the exemplary embodiment, this entails managing the hierarchy of cells.  
         [0063]    The exemplary embodiment implements a hierarchy management process which recognizes that each cell has an associated fill area that will not change throughout the metal-fill process. The exemplary management process entails executing the following steps from the bottom up until all cell dependencies are resolved. For each instance in each cell, the process creates a temporary unique copy of the cell associated with a given instance. After this, the process copies metal from other cells into the cell being examined if it falls into the fill area. The process then copies metal from other cell into the cell if the metal falls into a ring around the fill area. Next, the process identifies, extracts, and marks conflict areas.  
         [0064]    This exemplary pattern-filling method and other simpler or more complex methods embodying one or more filling techniques of the exemplary embodiment can be used in combination with the methods of making nearly planar intermetal dielectric layers described using FIGS.  1 - 10 . More precisely, one can use a pattern-filling method according to the invention to define a layout for a particular metal layer, form a metal layer based on the layout, and then form a nearly planar intermetal dielectric layer according to the invention on the metal layer. The combination of these methods promises to yield not only a nearly planar dielectric layer that reduces or avoids the need for chemical-mechanical planarization, but also a dielectric layer with less thickness deviation because of the adjusted pattern fill density of the underlying metal layer.  
       Exemplary Computer System Incorporating Pattern-Filling Method  
       [0065]    [0065]FIG. 17 shows an exemplary computer system or workstation  42  for hosting and executing a software implementation of the exemplary pattern-filling method. The most pertinent features of system  42  include a processor  44 , a local memory  45  and a data-storage device  46 . Additionally, system  42  includes display devices  47  and user-interface devices  48 . Some embodiments use distributed processors or parallel processors, and other embodiments use one or more of the following data-storage devices: a read-only memory (ROM), a random-access-memory (RAM), an electrically-erasable and programmable-read-only memory (EEPROM), an optical disk, or a floppy disk. Exemplary display devices include a color monitor, and exemplary user-interface devices include a keyboard, mouse, joystick, or microphone. Thus, the invention is not limited to any genus or species of computerized platforms.  
         [0066]    Data-storage device  46  includes layout-development software  46   a , pattern-filling software  46   b , an exemplary input metal layout  46   c , and an exemplary output metal layout  46   d . (Software  46   a  and  46   b  can be installed on system  42  separately or in combination through a network-download or through a computer-readable medium, such as an optical or magnetic disc, or through other software transfer methods.) Exemplary storage devices include hard disk drives, optical disk drives, or floppy disk drives. In the exemplary embodiment, software  46   b  is an add-on tool to layout-development software  46   a  and layout  46   c  was developed using software  46   a . However, in other embodiments, software  46   b  operates as a separate application program and layout  46   c  was developed by non-resident layout-development software. General examples of suitable layout-development software are available from Cadence and Mentor Graphics. Thus, the invention is not limited to any particular genus or species of layout-development software.  
       Exemplary Integrated Memory Circuit  
       [0067]    [0067]FIG. 18 shows an exemplary integrated memory circuit  50  that incorporates one or more nearly planar intermetal dielectric layers and/or metal layers within the scope of the present invention. One more memory circuits resembling circuit  50  can be used in a variety of computer or computerized systems, such as system  42  of FIG. 17.  
         [0068]    Memory circuit  50 , which operates according to well-known and understood principles, is generally coupled to a processor (not shown) to form a computer system. More particularly, circuit  50  includes a memory array  52 , which comprises a number of memory cells  53   a ,  53   b ,  53   c , and  53   d ; a column address decoder  54 , and a row address decoder  55 ; bit lines  56   a  and  56   b ; word lines  57   a  and  57   b ; and voltage-sense-amplifier circuit  58  coupled in conventional fashion to bit lines  56   a  and  56   b . (For clarity, FIG. 18 omits many conventional elements of a memory circuit.)  
       CONCLUSION  
       [0069]    In furtherance of the art, the inventor has presented several methods for making nearly planar intermetal dielectric layers without the use of chemical-mechanical planarization. Additionally, the inventor has presented a method of modifying metal layouts to facilitate formation of dielectric films with more uniform thickness. These methods of modifying metal layouts and making dielectric layers can be used in sequence to yield nearly planar intermetal dielectric layers with more uniform thickness.  
         [0070]    The embodiments described above are intended only to illustrate and teach one or more ways of practicing or implementing the present invention, not to restrict its breadth or scope. The actual scope of the invention, which embraces all ways of practicing or implementing the invention, is defined only by the following claims and their equivalents.