Abstract:
A system and method for manufacturing a semiconductor device including multi-layer bitlines. The location of the bitlines in multiple layers provides for increased spacing and increased width thereby overcoming the limitations of the pitch dictated by the semiconductor fabrication process used. The bitlines locations in multiple layers thus allows the customization of the spacing and width according to the use of a semiconductor device.

Description:
FIELD OF THE INVENTION 
     The present invention relates to the field of semiconductors. More particularly, the present invention relates to a system and method for a multi-layer global bitlines. 
     BACKGROUND OF THE INVENTION 
     Electronic systems and circuits have made a significant contribution towards the advancement of modern society and are utilized in a number of applications to achieve advantageous results. Electronic technologies such as digital computers, calculators, audio devices, video equipment, and telephone systems have facilitated increased productivity and reduced costs in analyzing and communicating data, ideas and trends in most areas of business, science, education and entertainment. Correspondingly, as technology has advanced, electronic technologies are increasingly shrinking in size. As electronic components shrink, electrical interference and other negative effects on electrical components, such as wires, have an increasingly large impact. The tiny widths and close proximity of adjacent bitlines introduces resistance and capacitance (RC) delays that can hinder chip performance. 
       FIG. 1  shows a cross section of a conventional configuration of global bitlines of a semiconductor device  100 . Each of bitlines  102 - 110  are within layer  101  and are separated by a fixed spacing  116 . Bitlines  102 - 110  further have a uniform width  114 . The width of each of the bitlines has an impact on the resistance of the bitline. 
     The characteristic of a bitline configuration is known as pitch which is the width of the bitline and the spacing between that bitline plus the adjacent bitline. The pitch is thus shown by distance  112 . Conventionally, the pitch is fixed based on the semiconductor manufacturing process, such as 90 mm. The fixing of the pitch has thus limited conventional solutions to making changes to the spacing between the bitlines or changing the width of the bitlines. 
     Unfortunately, the fixed nature of the pitch also results in a constant RC delay making changes to the width or spacing ineffective in changing the RC delay. For example, when the width is increased, thereby reducing the resistance, the reduced spacing results in an increase in capacitance. Similarly, when the spacing is increased, thereby reducing the capacitance, the reduced width results in an increased resistance. 
     The capacitance portion of the RC delay may be expressed by the equation: 
             C   =     K   ⁢           ⁢     ɛ   0     ⁢     A   D             
Where A is the area, D is the distance between bitlines, K is the dielectric constant of the material, and ∈ 0  is the permittivity of free space. The area (A) and thickness (D) are governed by the microelectronic chip size.
 
     Conventional solutions have been focused on using materials which have a low dielectric constant. Unfortunately, the use of new materials is expensive because it requires new equipment, new tools, and achieving a yield matching previous methods and materials is increasingly difficult. 
     Accordingly, what is needed is a bitline configuration which overcomes the RC delay of conventional designs to allow semiconductor devices to be made smaller. 
     SUMMARY OF THE INVENTION 
     A system and method for manufacturing a semiconductor device including multi-layer bitlines. The location of the bitlines in multiple layers provides for increased spacing and increased width thereby overcoming the limitations of the pitch dictated by the semiconductor fabrication process used. The bitlines locations in multiple layers thus allows the customization of the spacing and width according to the use of a semiconductor device. 
     The system and method of the present invention facilitate use of bitlines with reduced capacitance by utilizing more than one layer for the bitlines. The reduced capacitance and increased spacing of the bitline allows increasing the width of the bitlines thereby reducing the resistance. Further, the ability to increase the spacing and width of the bitlines allows the bitlines to be customized for (e.g., performance) the target application or use of the semiconductor device. Moreover, the bitlines may switch layers so as to maintain substantially equal capacitance thereby making the time constant of a semiconductor device uniform. Embodiments of the present invention provide the aforementioned advantageous properties without the introduction of new materials or equipment and correspondingly little to no change in cost. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a block diagram of a cross section of a conventional bitline configuration. 
         FIG. 2  is a block diagram of a cross section of an exemplary bitline arrangement in accordance with an embodiment of the present invention. 
         FIG. 3  is a block diagram of cross section of an exemplary bitline and the corresponding sectors in accordance with an embodiment of the present invention. 
         FIG. 4  is a block diagram of an exemplary switching region of an exemplary semiconductor device in accordance with an embodiment of the present invention. 
         FIG. 5  is a block diagram of a top view of an exemplary bitline configuration of an exemplary semiconductor device in accordance with an embodiment of the present invention. 
         FIG. 6  is a block diagram of a top view of another exemplary bitline configuration in accordance with an embodiment of the present invention. 
         FIG. 7  is a flowchart of a method for manufacturing a semiconductor device in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Reference will now be made in detail to the preferred embodiments of the invention, a semiconductor isolation material deposition system and method, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. Furthermore, in the following detailed description of the present invention, numerous specific details are set forth in order to provide a thorough understanding of the present invention. However, it will be obvious to one ordinarily skilled in the art that the present invention may be practiced without these specific details. In other instances, well known methods, procedures, components, and circuits have not been described in detail as not to unnecessarily obscure aspects of the current invention. 
     Some portions of the detailed descriptions which follow are presented in terms of procedures, logic blocks, processing, and other symbolic representations of operations on data bits within a computer memory. These descriptions and representations are the means generally used by those skilled in data processing arts to effectively convey the substance of their work to others skilled in the art. A procedure, logic block, process, etc., is here, and generally, conceived to be a self-consistent sequence of steps or instructions leading to a desired result. The steps include physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical, magnetic, optical, or quantum signals capable of being stored, transferred, combined, compared, and otherwise manipulated in a computer system. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like. 
     It should be borne in mind, however, that all of these and similar terms are associated with the appropriate physical quantities and are merely convenient labels applied to these quantities. Unless specifically stated otherwise as apparent from the following discussions, it is appreciated that throughout the present application, discussions utilizing terms such as “processing”, “computing”, “calculating”, “determining”, “displaying” or the like, refer to the action and processes of a computer system, or similar processing device (e.g., an electrical, optical, or quantum, computing device), that manipulates and transforms data represented as physical (e.g., electronic) quantities. The terms refer to actions and processes of the processing devices that manipulate or transform physical quantities within a computer system&#39;s component (e.g., registers, memories, other such information storage, transmission or display devices, etc.) into other data similarly represented as physical quantities within other components. 
       FIG. 2  is a block diagram of a cross section of an exemplary bitline arrangement in accordance with an embodiment of the present invention. Semiconductor device  200  includes bitlines  202 - 210 , terminal metal layer  226 , and layers  220 - 224 . Terminal metal layer  226  facilitates the communicative coupling of semiconductor device  200  to another device (e.g., processor, memory device, peripheral, audio/video device, etc.). For example, a pad coupled to terminal metal layer  226  may allow semiconductor device  200  (e.g., a memory device) to communicate with a processor or other electronic device. In one exemplary embodiment, terminal metal layer  226  includes an alloy of Aluminum and Copper. Semiconductor device  200  may be manufactured with a 45 mm and beyond (e.g., smaller) semiconductor manufacturing process. 
     In one embodiment, layers  220  and  222  are below terminal metal layer  226 . Layer  220  includes bitlines  202 ,  206 , and  210 . Layer  222  includes bitlines  204  and  208 . In one embodiment, bitlines  202 - 210  are global bitlines. Bitlines  202 - 210  may be made with variety of materials including, but not limited to, copper or tungsten. It is appreciated that portions of bitlines  202 - 210  may be within layer  220  and  222 . 
     It is appreciated that one or more layers may be between layers  222  and  224 . Further, it is appreciated that there may be local layer interconnects in layers between layers  222  and  224 . In one embodiment, layer  220  may be a metal last (ML) layer and layer  222  may be a metal three (M3) layer. It is also appreciated that semiconductor device can have a variety of layers (e.g., 9 layers, 20 layers, etc.) 
     In one embodiment, bitlines  202 - 210  facilitate access to data in date storage elements  230 ,  232 , and other data storage elements. It is appreciated that semiconductor device  200  may have other types of elements or devices in layer  224 . 
     The horizontal component of the pitch of an embodiment of the present invention may be substantially similar to the pitch of the semiconductor fabrication process. For example, the horizontal pitch  218  may be fixed based on the semiconductor fabrication process and spacing  216  is accordingly sized based on the semiconductor fabrication process. Further, embodiments of the present invention in the horizontal plane may have two bitlines in two times the pitch (e.g.,  212 ) defined by the semiconductor fabrication process. It is appreciated that embodiments of the present invention are not limited or restricted to the pitch of the semiconductor fabrication process. 
     Embodiments of the present invention thus increase the horizontal spacing between adjacent bitlines (e.g., bitlines  202  and  206 ) in the same layer (e.g., layer  220 ). The capacitance of adjacent bitlines may be expressed by the equation: 
             C   =     K   ⁢           ⁢     ɛ   0     ⁢     A   D             
Where A is the area, D is the distance between bitlines, K is the dielectric constant of the material, and ∈ 0  is the permittivity of free space.
 
     The increased spacing of embodiments of the present invention increases the distance between the bitlines (D) and thus the increased spacing results in a decrease in the capacitance. In one embodiment, the capacitance between adjacent bitlines is reduced by 50%. It is appreciated that the closeness of the layers (e.g., layers  220  &amp;  222 ) can effect the capacitive load associated with each of the bitlines. 
     Correspondingly, the increased spacing allows for the width of bitlines  202 - 210  to be increased without substantially changing the capacitance on bitlines  202 - 210 . The resistance of a bitline may be expressed by the equation: 
             R   =     ρ   ⁢           ⁢     l   A             
Where A is the cross sectional area, l is the length, and ρ is the resistivity of the material.
 
     The increased spacing thus allows an increase in cross sectional area (A) or width which results in a decrease in resistance of the bitline. In one embodiment, the width on below layer (e.g., M3) can be used to compensate for the capacitance introduced by a terminal metal layer (e.g., terminal metal layer  226 ). 
     Embodiments of the present invention thus allow the resistance and capacitance to be customized for the target application or use of semiconductor device  200 . For example, where the semiconductor device is a memory device (e.g., flash memory) the resistance (or width) and capacitance (or spacing) can be customized for read, erase, or program operations. 
     In one embodiment, semiconductor device  200  is a memory device (e.g., flash memory and the like). A memory device in accordance with an embodiment of the present invention may include a first data storage element (e.g., data storage element  230 ) and a second data storage element (e.g., data storage element  232 ) in a first layer (e.g., layer  224 ). The memory device further includes a first global bitline (e.g., bitline  202 ) for accessing the first data storage element (e.g., data storage element  230 ) and a second global bitline (e.g., bitline  204 ) for accessing the second data storage element (e.g., data storage element  232 ). The first global bitline is within a second layer and the second global bitline is within a third layer. The memory device may also include a fourth layer which includes a terminal metal (e.g., terminal metal layer  226 ). 
     In one embodiment, a portion the first global bitline may further be within the third layer and a portion of the second global bitline may be within the second layer. The first global bitline and the second global bitline may span one or more sectors within a single layer. The width of the first and the second global bitline may be customized for a target application of the memory device (e.g., cell phone, smart phone, computer, personal digital assistant, gaming console, audio/video device and the like). 
       FIG. 3  is a block diagram of a cross section of an exemplary bitline and the corresponding sectors in accordance with an embodiment of the present invention.  FIG. 3  illustrates a bitline spanning and switching layers over one or more sectors (e.g., sectors  0 - 4 ). Bitline  300  includes portions  302  in an upper or first layer, via  303 , portions in lower or second layer  304 . In one embodiment, bitline  300  is a global bitline which is alternatively connected or changes layers with each sector. The switching of layers may occur in a sector select area (e.g., sector select areas  320 - 326 ) with a via or layer interconnect (e.g., via  303 ). It is appreciated that the global bitlines may be in one or more layers and the layers may not be adjacent. 
     Referring to the previous example, a global bitline may start in an metal three (M3) layer in Sector  0 , switch to metal last (ML) layer and continues in ML in Sector  1 , switch to M3 in sector  2 , switch to ML in sector  3 , and switch to M3 in sector  4 . In one embodiment, the switching occurs after each sector in the corresponding sector select area across the complete bank. 
       FIG. 4  is a block diagram of an exemplary switching region of an exemplary semiconductor device in accordance with an embodiment of the present invention. As described herein, the bitlines may have a relatively increased width on each layer so the resistance is reduced. 
     In order to facilitate avoiding contact in areas of bitline layer changes, the bitlines are thinned down or reduced in width at points where there is a change in layers (e.g, with via  406 ). Portions of the bitlines  404  in a lower layer (e.g., M3) are reduced in width as layer changes to the portions of bitlines  402  in an upper layer (e.g., ML). In one embodiment, the bitlines have a reduced width in a sector select area. It is appreciated that embodiments may still include a horizontal spacing between bitlines on different layers (e.g., spacing  216  of  FIG. 2 ). 
       FIG. 5  is a block diagram of top view an exemplary bitline configuration of an exemplary semiconductor device in accordance with an embodiment of the present invention. Bitline  502  start on a lower layer (as shown by the stripes) (e.g., M3) in sector  0  and switches to an upper layer (e.g., ML) in sector  1 . Bitline  504  starts in an upper layer (e.g., ML) in sector  0  and switches to a lower layer (e.g., M3) in sector  1 . Bitlines  502  and  504  alternate switching layers as each sector is entered. Any variations in capacitance of each layer are dealt with by having substantially equal portions of each bitlines within each layer (e.g., an equal number of portions in a first or lower layer and a second or upper layer). This allows the capacitance across each bitline line to be substantially equal and thus the time constant across the semiconductor device (e.g., memory device) to be consistent or uniform. For example, for bitlines alternating layers with each sector with a M3 layer having a higher capacitance than a ML layer, having substantially equal portions of each bitline in the ML and M3 layers results in substantially similar capacitance across each bitline 
       FIG. 6  is a block diagram of a top view of another exemplary bitline configuration in accordance with an embodiment of the present invention. Semiconductor device  600  includes exemplary bitline  601 , sector select areas  616  and  618 , and areas of one or more sectors  604 ,  606 , and  608 . In one embodiment, bitline  601  spans one or more sectors within a single layer. Bitline  601  includes portions  614  and  610  within a first layer (e.g., M3) and a portion  612  within a second layer (e.g., ML). In one embodiment, semiconductor  600  has a total number of sectors  602  with bitline  601  spanning the sectors. 
     For example, for a 512 Mb device where semiconductor  600  has 16 sectors, bitline portion  614  spans the 4 sectors of area  608  and 4 sectors of area  610  in a M3 layer. Bitline portion  612  spans the 8 sectors of area  604  in a ML layer. It is appreciated that substantially equal portions of bitline  601  are within each layer (e.g., layers M3 and ML) and bitlines could change layers in any pattern (e.g., every 2, 3, or 5 sectors) such that equal portions are within each layer. 
       FIG. 7  is a flowchart of a method for manufacturing a semiconductor device in accordance with an embodiment of the present invention. With reference to  FIG. 7 , flowchart  700  illustrates example blocks used by various embodiments of the present technology. It is appreciated that the blocks of flowchart  700  may be performed in an order different than presented, and that not all of the blocks in flowchart  700  may be performed. Exemplary method  700  may be used to manufacture a portion of a memory device (e.g., semiconductor device  200 ). It is appreciated that flowchart  700  may be carried out by a semiconductor manufacturing device or fabrication device. 
     At block  710 , a first layer is formed including a plurality of data storage elements. As described herein, the data storage elements may be memory cells of memory device. 
     At block  720 , a second layer is formed including a first global bitline (e.g., bitline  202 ). The first global bitline may be for accessing a first portion of the plurality of data storage elements (e.g., data storage element  202 ). 
     At block  730 , a third layer is formed including a second global bitline. The second global bitline (e.g., bitline  204 ) may be for accessing a second portion of the plurality of data storage elements (e.g, data storage element  232 ). As described herein, the third layer may further include a portion of the first global bitline and the second layer may further include a portion of the second global bitline. Further, substantially equal portions of the first global bitline and the second global bitline may be within the second layer and the third layer respectively. Portions of each global bitline switching layers (e.g., in sector select areas) may have a reduced width. 
     In one embodiment, the first and second global bitlines may span one or more sectors within a single layer. Further, where the first global bitline and the second global bitline are horizontally adjacent, the width of the first global bitline may be increased (e.g., to reduce resistance) without substantially changing the capacitance of the first global bitline and the second global bitline. 
     At block  740 , a terminal metal layer for communicatively coupling the semiconductor device to another device (e.g., processor, memory device, peripheral, audio/video device, etc.). 
     Thus, a system and method of the present invention facilitates use of bitlines with reduced capacitance by utilizing more than one layer for the bitlines. The reduced capacitance and increased spacing of the bitline allows increasing the width of the bitlines thereby reducing the resistance. Further, the ability to increase the spacing and width of the bitlines allows the bitlines to be customized for (e.g., performance) the target application or use of the semiconductor device. Moreover, the bitlines may switch layers so as to maintain substantially equal capacitance thereby making the time constant of a semiconductor device uniform. Embodiments of the present invention provide the aforementioned advantageous properties without the introduction of new materials or equipment and correspondingly little to no change in cost. 
     The foregoing descriptions of specific embodiments of the present invention have been presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the invention to the precise forms disclosed, and obviously many modifications and variations are possible in light of the above teaching. The embodiments were chosen and described in order to best explain the principles of the invention and its practical application, to thereby enable others skilled in the art to best utilize the invention and various embodiments with various modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the Claims appended hereto and their equivalents.