Abstract:
Conduction between source and drain or emitter and collector regions is an important characteristic in transistor operation, particularly for lateral bipolar transistors. Accordingly, techniques that can facilitate control over this characteristic can mitigate yield loss by promoting the production of transistors that have an increased likelihood of exhibiting desired operational performance. As disclosed herein, well regions are established in a semiconductor substrate to facilitate, among other things, control over the conduction between the source and drain regions of a lateral bipolar transistor, thus mitigating yield loss and other associated fabrication deficiencies. Importantly, an additional mask is not required in establishing the well regions, thus further mitigating (increased) costs associated with promoting desired device performance.

Description:
FIELD 
     The disclosure herein relates generally to semiconductor processing, and more particularly to fashioning a lateral bipolar transistor having one or more compensated well regions. 
     BACKGROUND 
     Several trends presently exist in the semiconductor and electronics industry. Devices are continually being made smaller, faster and requiring less power. One reason for these trends is that more personal devices are being fabricated that are relatively small and portable, thereby relying on a battery as their primary supply. For example, cellular phones, personal computing devices, and personal sound systems are devices that are in great demand in the consumer market. In addition to being smaller and more portable, personal devices are also requiring increased memory and more computational power and speed. In light of these trends, there is an ever increasing demand in the industry for smaller and faster transistors used to provide the core functionality of the integrated circuits used in these devices. 
     Accordingly, in the semiconductor industry there is a continuing trend toward manufacturing integrated circuits (ICs) with higher densities. To achieve high densities, there have been and continue to be efforts toward scaling down dimensions (e.g., at submicron levels) on semiconductor wafers, that are generally produced from bulk silicon. In order to accomplish such high densities, smaller feature sizes, smaller separations between features, and more precise feature shapes are required in integrated circuits (ICs) fabricated on small rectangular portions of the wafer, commonly known as dies. This may include the width and spacing of interconnecting lines, spacing and diameter of contact holes, as well as the surface geometry of various other features (e.g., corners and edges). 
     It can be appreciated that significant resources go into scaling down device dimensions and increasing packing densities. For example, significant man hours may be required to design such scaled down devices, equipment necessary to produce such devices may be expensive and/or processes related to producing such devices may have to be very tightly controlled and/or be operated under very specific conditions, etc. Accordingly, it can be appreciated that there can be significant costs associated with exercising quality control over semiconductor fabrication, including, among other things, costs associated with discarding defective units, and thus wasting raw materials and/or man hours, as well as other resources, for example. Additionally, since the units are more tightly packed on the wafer, more units are lost when some or all of a wafer is defective and thus has to be discarded. Accordingly, techniques that mitigate yield loss (e.g., a reduction in the number of acceptable or usable units), among other things, would be desirable. 
     SUMMARY 
     The following presents a summary to provide a basic understanding of one or more aspects of the disclosure herein. This summary is not an extensive overview. It is intended neither to identify key or critical elements nor to delineate scope of the disclosure herein. Rather, its primary purpose is merely to present one or more aspects in a simplified form as a prelude to a more detailed description that is presented later. 
     Conduction between source and drain or emitter and collector regions is an important characteristic in transistor operation, particularly for lateral bipolar transistors. Accordingly, techniques that can facilitate control over this characteristic can mitigate yield loss by promoting the production of transistors that have an increased likelihood of exhibiting desired operational performance. As disclosed herein, well regions are established in a semiconductor substrate to facilitate, among other things, control over the conduction between the source and drain regions of a lateral bipolar transistor, thus mitigating yield loss and other associated fabrication deficiencies. Importantly, an additional mask is not required in establishing the well regions, thus further mitigating (increased) costs associated with promoting desired device performance. 
     To the accomplishment of the foregoing and related ends, the following description and annexed drawings set forth certain illustrative aspects. Other aspects, advantages and/or features may, however, become apparent from the following detailed description when considered in conjunction with the annexed drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a flow diagram illustrating an example methodology for fashioning a transistor as described herein. 
         FIGS. 2-10  are cross-sectional views of an example semiconductor substrate whereon a transistor is fabricated as described herein. 
     
    
    
     DETAILED DESCRIPTION 
     The description herein is made with reference to the drawings, wherein like reference numerals are generally utilized to refer to like elements throughout, and wherein the various structures are not necessarily drawn to scale. In the following description, for purposes of explanation, numerous specific details are set forth in order to facilitate understanding. It may be evident, however, to one skilled in the art, that one or more aspects described herein may be practiced with a lesser degree of these specific details. In other instances, known structures and devices are shown in block diagram form to facilitate understanding. 
     An example methodology  100  for fashioning a transistor having source/drain well regions is illustrated in  FIG. 1 , and an example semiconductor substrate  200  whereon such a methodology is implemented is illustrated in cross-sectional view in  FIGS. 2-10 . As will be appreciated, forming source/drain well regions as disclosed herein mitigates yield loss by promoting the production of transistors that have more desirable current flow between source and drain regions. While the method  100  is illustrated and described below as a series of acts or events, it will be appreciated that the illustrated ordering of such acts or events are not to be interpreted in a limiting sense. For example, some acts may occur in different orders and/or concurrently with other acts or events apart from those illustrated and/or described herein. In addition, not all illustrated acts may be required to implement one or more aspects or embodiments of the description herein. Further, one or more of the acts depicted herein may be carried out in one or more separate acts and/or phases. 
     At  102 , isolation regions  202  are formed in the semiconductor substrate  200 , where the substrate may have a first conductivity type ( FIG. 2 ). For example, the substrate  200  may comprise a slight doping of p type dopant atoms (e.g., Boron (B)) and/or n type dopant atoms (e.g., Phosphorous (P), Arsenic (As) and/or Antimony (Sb)). The isolation regions  202  may be formed according to any suitable isolation techniques (e.g., shallow trench isolation (STI) and/or field oxide (FOX)) and may correspondingly comprise any suitable dielectric materials (e.g., oxide and/or nitride base materials). The isolation regions  202  serve to electrically isolate or insulate semiconductor devices (or regions thereof formed in/on the substrate from one another. By way of example, STI regions are established by forming apertures in select locations of the surface of the substrate and then filling the apertures with a dielectric material, typically followed by a chemical mechanical polishing (CMP) process to make the surface of the isolation regions uniform with the surface of the substrate. With FOX, apertures are similarly initially formed at select locations around the surface of the substrate, but then an oxide based material is grown in these apertures to establish the electrically insulating material. 
     It will be appreciated that lithography is generally used to form apertures, vias and/or any other types of openings (e.g., patterning) in different layers in semiconductor processing. Lithography refers to processes for transferring one or more patterns between various media. In lithography, a light sensitive resist coating is formed over one or more layers to which a pattern is to be transferred. The resist coating is then patterned by exposing it to one or more types of radiation or light which (selectively) passes through an intervening lithography mask containing the pattern. The light causes exposed or unexposed portions of the resist coating to become more or less soluble, depending on the type of resist used. A developer is then used to remove the more soluble areas leaving the patterned resist. The patterned resist can then serve as a mask for the underlying layer or layers which can be selectively treated (e.g., etched). Masks used in semiconductor processing (e.g., for lithography) are very expensive components of the process. Accordingly, it is advantageous to be able to utilize a mask more than once to form multiple (different) patterns/features in the same process. 
     At  104 , a first well region  204  having a second conductivity type is formed in the substrate  200  ( FIG. 3 ). The first well region may be formed by an implantation process  203  where patterned (lithographic) resist material  205  blocks dopant atoms from being implanted at other than desired areas. By way of example, if the conductivity type of the substrate  200  is p type (e.g., Boron (B)), then the conductivity type of the first well region  204  would be n type (e.g., Phosphorous (P), Arsenic (As) and/or Antimony (Sb)) (and vice versa). It will be appreciated, however, that unlike the resist material  205 , the implanted dopant atoms can pass substantially unaffected through the isolation regions  202 . The first well region  204  is dimensioned such that one or more isolation regions  202  are situated therein while other isolation regions overlie the interface or sidewalls between the first well region  204  and the substrate  200 . 
     At  106 , second  206  and third  208  well regions having the first conductivity type are formed in the first well region  204  in the substrate  200  ( FIG. 4 ). As with the first well region  204 , the second  206  and third  208  well regions can be formed by an implantation process  207  where patterned (lithographic) resist material  209  blocks dopant atoms from being implanted at other than desired areas in the substrate  200 . Importantly, the second  206  and third  208  well regions are formed with a mask that is used as part of a standard CMOS fabrication process. In this manner, a new mask need not be produced and implemented to form these regions (and thus associated substantial costs are mitigated). Rather, an existing mask, or the use thereof, can merely be adjusted to facilitate the formation of the second  206  and third  208  well regions. For example, an existing mask may merely be shifted to allow radiation to (selectively) pass therethrough so that the pattern illustrated in  FIG. 4  is indelibly formed therein, thus allowing for the formation of the second  206  and third  208  well regions (e.g., via implantation  207 ). 
     With the well regions formed, a gate structure or stack is formed at  108  over a channel region defined in the substrate  200  between the second  206  and third  208  well regions. To form the gate structure, a layer of gate dielectric material  210  is formed (e.g., grown) over the substrate  200  and a layer of gate electrode material  212  is formed (e.g., deposited) over the layer of gate dielectric material ( FIG. 5 ). The layer of gate dielectric material  210  generally comprises an oxide (or other dielectric) based material and/or a high-k material, for example, and is relatively thin, being formed to a thickness of between about 1 nm and about 20 nm, for example. The layer of gate electrode material  212  generally comprises a polysilicon (or other semiconductor) based material, and is formed to a thickness of between about 20 nm and about 100 nm, for example. The layer of gate electrode material  212  and the layer of gate dielectric material  210  are then patterned (using a patterned (lithographic) resist  211  and an anisotropic etch, for example) to establish a gate structure or stack  214  comprising a gate dielectric  213  and a gate electrode  215  situated over the channel region  216  ( FIG. 6 ). 
     Source/drain regions  220  having the first conductivity type are formed in the second  206  and third  208  well regions at  110  ( FIG. 7 ). In the illustrated example, these regions  220  are also formed outside of the first well region  204 . These regions  220  may be formed by an implantation process  219  where patterned (lithographic) resist material  221  and the gate structure  214  blocks dopant atoms from being implanted at other than desired areas. It can be appreciated that some of the dopants may also be implanted into the top of the gate electrode  215 , which may be desirable depending on the type of transistor being formed. Additionally, although not illustrated, it will be appreciated that prior to forming the source/drain regions  220 , offset spacers may be formed on the sides of the gate structure  214  followed by extension implants into the substrate that are blocked by the offset spacers (and other materials, such as patterned resist, for example). Similarly, sidewall spacers (also not illustrated) may be formed over the offset spacers so that the source/drain  220  regions extend into the channel region  216  even less than the extension regions. Such offset and sidewall spacers generally comprise dielectric based materials, such as oxide and/or nitride based materials, for example. 
     At  112 , source/drain regions  224  having the second conductivity type are formed in the first well region  204 , but not in the second  206  and third  208  well regions ( FIG. 8 ). These regions  224  may be formed by an implantation process  223  where patterned (lithographic) resist material  225  (and possibly the gate structure  214  if it is not covered by resist material  225  (as illustrated)) blocks dopant atoms from being implanted at other than desired areas. The patterned resist is stripped thereafter leaving the finished device  290  ( FIG. 9 ). The method  100  then ends where further back end processing can be performed, such as where one or more conductive and/or dielectric layers can be formed and treated in some manner, for example. One or more annealing operations can likewise be performed to activate dopants of source/drain regions, for example (e.g., to drive them into channel regions). The transistor “operates”, at least in part, by conducting a current in the channel region  216  between the source/drain regions  220  when certain (respective) voltages are applied to the gate electrode  215  and the source/drain regions  220 . 
     In the illustrated example, the second  206  and third  208  well regions are formed to respective depths  230 ,  232  that are substantially greater than the respective depths  234 ,  236  of the source/drain  220  regions ( FIG. 9 ). In one example, the respective depths  234 ,  236  of the source/drain regions  220  are between about ¼ and about 1/50 th  of the respective depths  230 ,  232  of the second  206  and third  208  well regions. Similarly, the respective depths  230 ,  232  of the second  206  and third  208  well regions are between about ⅔ and about 1/20 the depth  240  of the first well region  204 . Also, the respective depths  230 ,  232  of the second  206  and third  208  well regions are less than the respective widths  242 ,  244  of the second  206  and third  208  well regions, and the respective widths  250 ,  252  of the source/drain regions  220  are likewise less than the respective widths  242 ,  244  of the second  206  and third  208  well regions. The channel region  216  has a length  260  that is less than the respective widths  242 ,  244  of the second  206  and third  208  well regions. 
     In one example, the second well region  206  is formed to a depth  230  of between about 400 nm and about 700 nm; the third well region  208  is formed to a depth  232  of between about 400 nm and about 700 nm; the source/drain regions  220  are formed to depths  234 ,  236  of between about 100 nm and about 200 nm; the first well region  204  is formed to a depth  240  of between about 500 nm and about 1000 nm; the second  206  and third  208  well regions are formed by implanting a dopant of Boron at a concentration of about 1×10 13 /cm 3 ; the source/drain regions  220  are formed by implanting a dopant of Boron at a concentration of about 1×10 15 /cm 3 ; and the first well region  204  is formed by implanting a dopant of Phosphorous at a concentration of about 1×10 13 /cm 3 . As mentioned above, it will be appreciated that while implant doses and energies may be adjusted, they are nevertheless maintained such that the junction depth of the source drain regions  220  is less than that of the second  206  and third  208  well regions which is in turn less than that of the first well region  204  (to support required voltages). Also, dopant types may be adjusted (e.g., reversed) depending on the type of device(s) being fabricated. 
     It will be appreciated that more than just one gate structure  214  and corresponding source/drain regions can be established without having to add to the method  100  illustrated in  FIG. 1  (or use an additional mask). For example, a dual sided arrangement  300  that can be formed in a similar manner by patterning for more source/drain regions, well regions and gate structures is illustrated in  FIG. 10 . In the illustrated example, there is a fourth well region  262  having the first electrical conductivity type in the first well region  204 , for example. Regardless of the arrangement, it can be seen (in  FIGS. 9 and 10 ) that a first face  264  of the second well region  206  faces a first face  266  of the third well region  208  across the channel region  216 , at least some of an isolation region  202  is located over a second face  270  of the second well region  206  opposite the first face  264  of the second well region  206  or at least some of an isolation region  202  is located over a second face  272  of the third well region  208  opposite the first face  266  of the third well region  208 , the gate structure  214  resides over the first face  264  of the second well region  206  and the first face  266  of the third well region  208 , and at least some of an isolation region  202  is located over an interface  280  between the first well region  204  and the substrate  200 . 
     A transistor fashioned as described herein can be referred to as a “lateral” bipolar transistor due the lateral arrangement between the second well region  206  (having the first conductivity type), the channel region  216  of the first well region  204  (having the second conductivity type) and the third well region  208  (having the first conductivity type). The (increased) depths of the second  206  and third  208  well regions (relative to the source/drain regions  220  and/or the channel region  216 ) correspond to a larger cross sectional emitter/collector area (per total device area), which promotes an increased current density (which is desirable). That is, the amount of current that can be conducted (e.g., in the channel region  216 ) is increased without increasing the size of the device. This also improves (e.g., increases) the current gain of the resulting device, or the ratio of the collector current to the base current. 
     As illustrated herein, the second  206  and third  208  well regions (as well as any other additional well regions, such as fourth well region  262 ) are formed concurrently. That is, because a single (existing) mask is used in patterning an associated (lithographic) resist ( 209  in  FIG. 4 ), and because the same implantation or implantations ( 207  in  FIG. 4 ) are used to establish the well regions  206 ,  208 ,  262 , etc., there is little to no variation among these regions (e.g., between the respective depths  230 ,  232  of the second  206  and third  208  well regions and/or between the respective widths  242 ,  244  of the second  206  and third  208  well regions). For example, any mask misalignment will affect the wells the same (e.g., they will all be similarly shifted). Because these regions play such an important role in the operation of the device, this lack of variation promotes uniform and consistent performance in the operation of the device, as well as among multiple devices produced across a wafer or die. 
     It will be appreciated that the substrate may comprise any type of semiconductor body (e.g., silicon, SiGe, SOI) such as a semiconductor wafer and/or one or more dies on a wafer, as well as any other type of semiconductor and/or epitaxial layers associated therewith. Also, while reference is made throughout this document to exemplary structures in discussing aspects of methodologies described herein (e.g., those structures presented in  FIGS. 2-10  while discussing the methodology set forth in  FIG. 1 ), those methodologies are not to be limited by the corresponding structures presented. Rather, the methodologies (and structures) are to be considered independent of one another and able to stand alone and be practiced without regard to any of the particular aspects depicted in the drawings. Additionally, unless indicated to the contrary, layers described herein, can be formed in any suitable manner, such as with spin-on, sputtering, growth and/or deposition techniques, etc. 
     Also, equivalent alterations and/or modifications may occur to those skilled in the art based upon a reading and/or understanding of the specification and annexed drawings. The disclosure herein includes all such modifications and alterations and is generally not intended to be limited thereby. In addition, while a particular feature or aspect may have been disclosed with respect to only one of several implementations, such feature or aspect may be combined with one or more other features and/or aspects of other implementations as may be desired. Furthermore, to the extent that the terms “includes”, “having”, “has”, “with”, and/or variants thereof are used herein, such terms are intended to be inclusive in meaning—like “comprising.” Also, “exemplary” is merely meant to mean an example, rather than the best. It is also to be appreciated that features, layers and/or elements depicted herein are illustrated with particular dimensions and/or orientations relative to one another for purposes of simplicity and ease of understanding, and that the actual dimensions and/or orientations may differ substantially from that illustrated.