Abstract:
A solution for alleviating variable parasitic bipolar leakages in scaled semiconductor technologies is described herein. Placement variation is eliminated for edges of implants under shallow trench isolation (STI) areas by creating a barrier to shield areas from implantation more precisely than with only a standard photolithographic mask. An annealing process expands the implanted regions such their boundaries align within a predetermined distance from the edge of a trench. The distances are proportionate for each trench and each adjacent isolation region.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention generally relates to a semiconductor structure, and more specifically to a semiconductor structure having no edge placement variation of well implants relative to the isolation structure. 
     2. Background of the Invention 
     CMOS technologies continue scale smaller and smaller. As a result parasitic bipolar leakages become harder to control. In traditional process flows, well implants are defined using purely lithographics definition done independently from lithographic steps used for defining physical isolation structures. This independence creates inherent variability. 
     BRIEF SUMMARY OF THE INVENTION 
     The following describes a structure and method for alleviating parasitic bipolar leakages in scaled semiconductor technologies. The structure has no edge (or boundary) placement variation for edges of implants under shallow trench isolation (STI) areas, in other words, the distance between the edges of the STI and the corresponding edges or boundaries of implanted wells beneath a given STI are substantially equal. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a diagram showing the problem to be solved; 
         FIG. 2  is demonstrates the various types of parasitic devices which are inadvertently formed; 
         FIG. 3  is an illustration of the problem and shows advantages offered by the solution; 
         FIGS. 4A and 4B  are each a view of simulation of electrical properties using the prior art solution; 
         FIG. 5A  is a view of an embodiment at a step in a process where a second layer is deposited onto a first substrate.  FIG. 5B  is a top view of an embodiment of the invention at that step in the process, showing second layer after deposition; 
         FIG. 6A  is a view of an embodiment at another step in the process where a third layer is deposited over the second layer on the substrate.  FIG. 6B  is a top view of this embodiment of the invention and shows the third layer overlaying the second layer on the substrate; 
         FIG. 7A  illustrates a side view of a structure which has had portions of the top substrate removed using a chemical etch process or other process which provides similar results;  FIG. 7B  illustrates the result from the top view; 
         FIG. 8A  illustrates a side view of a structure having implants (e.g. n-well, p-well) and an annealing process. The edges or boundaries of the implants are located at a predetermined distances from the planned STI placement;  FIG. 8B  shows a top view of the structure; 
         FIG. 9A  illustrates a step of depositing a fourth substrate (e.g. nitride) over the second substrate and adjacent to the third substrate and performing a polishing process.  FIG. 9B  illustrates an example top view of the results of the depositing step; 
         FIG. 10A  illustrates a side view of the structure after removing the third substrate (e.g. Polysilicon).  FIG. 10B  illustrates a top view of the structure. 
         FIG. 11A  shows the structure after an etch process to remove a portion of the first and second substrates (e.g. silicon and oxide);  FIG. 11B  shows a top view of the structure; 
         FIG. 12A  shows the structure having a fifth film deposited in the shallow trench isolation (STI) areas.  FIG. 12B  shows a top view of the structure at this step in the process; 
         FIG. 13A  illustrates an example of the structure having a similar distance between a first implant (or doped) region and an STI and a second implant (or doped) region on the other side of the STI;  FIG. 13B  shows a top view of the structure shown in  FIG. 13A ; 
         FIG. 14  illustrates a flow diagram of an example process used to make the structure; and 
         FIG. 15A  illustrates an example of the structure having a similar distance and coupled between a first implant (or doped) region and an STI and a second implant (or doped) region on the other side of the STI;  FIG. 15B  shows a top view of the structure shown in  FIG. 15A ; 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates a problematic parasitic effect shown as NPN device  130  in structure  100 . NPN device  130  represents a function that occurs when the boundaries between two (or more) implanted (or doped) regions (e.g. Pwell  125 , Nwell  120 , and N+ region  115 ) are touching or very nearly touching. The parasitic effect varies depending on the distance between the adjacent doped regions. In this example, a parasitic effect is created beneath a shallow trench isolation (STI) region  105  at the Nwell  120  and Pwell  125  junction. 
       FIG. 2  represents the growing complexity of the problem as more devices are manufactured within smaller areas on a wafer (e.g. scaling semiconductor technologies to become smaller and smaller). Structure  200  shows two parasitic devices (npn and pnp) created between an N+ region  225 , Pwell  205  and Nwell  210 ; and P+ region  230 , Nwell  210  and Pwell  205  respectively. 
       FIG. 3  shows a prior art solution to the parasitics problem as structure  300 . Structure  300  is a hyper-abrupt junction varactor having p+-n junctions  315 , cathode contact  335 , anode contact  330 , an N cathode implant region  320 , Nwells  325   a  and  325   b , n+ regions  310   a  and  310   b , and STIs  305   a - d . This figure demonstrates the size of the structure required to avoid generation of the variable parasitic devices. 
     In conventional processing, STI is defined prior to well implants. In some cases, the implants penetrate the side walls of one or more of STIs  305 .  FIG. 3A  shows ‘n+ii’, ‘P&amp;Nii’, and ‘n+ii’ ion implants, which extend into the STI walls  305  for each device. The small geometries result in narrow anode widths as shown in  FIG. 3A . Degradation of an ideality factor is significant for small geometry diodes such as P-n diodes bounded by STIs having implant penetration. An ideality factor is a constant adjustment factor used to correct for discrepancies between an ideal PN junction equation and a measured device. 
       FIG. 4A  shows a simulated degradation of the ideality factor as a function of width. Simulated device  1  shown in  FIG. 3  has a width of 1 um resulting in an ideality factor of 1.16 or greater. Device  2  has a width of 0.5 um and a corresponding ideality factor of between 1.13 and 1.15. Likewise, device  3  has a width of 0.25 um and an ideality factor of less than 1.13. The decreasing widths directly correlate with decreasing ideality factors. 
       FIG. 4B  shows a simulation plot for a percent capacitance degradation after 25 hours of stress (reverse bias mode) at 4.5V and 140° C. As the varactor width (in um) increases the percent capacitance change approaches 0% after 25 hours of stress. The reliability degradation of the varactor capacitance is directly proportional to the degradation of the ideality factor. 
       FIG. 5A  shows a side view of a structure  500  having a substrate  510  (for example a layer of silicon such as one used for a wafer), and a film  505  is deposited over substrate  510  (for example a layer of oxide);  FIG. 5B  shows a top view of structure  500 , which shows film  505  deposited over substrate  510 . 
       FIG. 6A  shows a side view of a structure  600  having a third film  610  (for example a Polysilicon layer) deposited over substrate  510 ;  FIG. 6B  shows the top view of structure  600  having the top layer of film  610 . 
       FIG. 7A  shows a structure  700  after patterning. The process may include, for example a photolithography step and a subsequent etching step. The process generates structure  700  which shows a patterned film  610 ;  FIG. 7B  illustrates an example of a top view of structure  700  having the patterned film  610  and the exposed film  505  beneath. 
       FIG. 8A  shows a side view of a structure  800  having been through processing that includes, for example, a well implant step (e.g. ion implant or doping step) and an annealing step. Wells  810   a  and  810   b  are formed in substrate  510  through, for example, the use of a photomask (not shown) followed by ion implantation, thermal activation, and annealing, and may be, for example, n-wells ( 810   a ) or p-wells ( 810   b ). Substrate  510 , directly beneath film  610  (and corresponding photomasks) is shielded from the implants. The implanting step is followed by an annealing process. In this example implant areas  810  expand during the annealing process such that their edges (or boundaries) are located a predetermined distance from the edges of film  610 ;  FIG. 8B  shows a top view of structure  800 , which shows films  610  and  505 . Implants  810  are beneath film  505  and their boundaries are shown as dotted lines  810   a  and  810   b . The boundaries reside at predetermined distances from the edges of film  610  shown by way of illustration as W 1 , W 2 , W 3 , and W 4 . 
       FIG. 9A  shows structure  900  after several processing steps, for example, a nitride deposition step, and a planarization step such as by chemical mechanical planarization (CMP). Structures  910  (e.g. a nitride) is deposited over film  505  then a step such as a planarization step for example, is used to polish structures  910  to be nearly even with the top of film  610 ;  FIG. 9B  shows a top view of structure  900  having structures  910  and film  610  visible. 
       FIG. 10A  shows structure  1000  after film  610  has been removed. The patterned film  610  may be removed using a stripping process, for example;  FIG. 10B  shows a top view of structure  1000  having structures  910  and film  505 . 
       FIG. 11A  shows a side view of structure  1100  where film  505  and substrate  510  have undergone a stripping and/or etching process (for example a reactive ion etching (RIE) process known to those of ordinary skill in the semiconductor manufacturing field) to generate trenches  1110   a  and  1110   b  (or depressions, channels, etc.). Optionally, additional processing may be implemented at this stage, for example additional ion implant processes;  FIG. 11B  shows a top view of structure  1100  with exposed substrate  510 , implant areas  810 , and structures  910 . 
       FIG. 12A  shows a side view of a structure  1200  having a material  1210   a  and  1210   b , such as an isolation material (e.g. oxide) for example, deposited over structure  1200  to fill-in trenches  1110   a  and  1110   b  respectively, thereby creating a shallow trench isolation area. A subsequent polishing step (e.g. a CMP) step is used after deposition.  FIG. 12B  shows a top view of structure  1200  having structures  910  and the isolation materials  1210  in trenches  1110  visible from the top. One edge of trench  1110   b  is shown as edge or boundary  1220 , a second boundary of trench  1110   b  is shown as boundary  1230 . A first and second boundary of trench  1110   a  is shown as boundaries  1240  and  1250  respectively. 
       FIG. 13B  shows a top view of structure  1300  which includes a substrate  510  having the material  1210   a  and  b  (e.g. oxide to create an STI) and at least a first region (e.g. a doped or ion implanted region  810   a ); the trench  1110   a  having the first edge or first boundary  1220  (e.g. the side wall or bottom of the trench  1110   b  or material  1210   b ); the first region  810   a  having a boundary  1320  (e.g. the edge or boundary of the doped region  810   a  where it connects to an adjacent substance such as oxide material of  1210   b ); the first region (e.g. the doped region  810   a ) being coupled to (e.g. touching) at least a first portion of the trench  1110   b  (e.g. the bottom and/or side of the trench  1110   b  or material  1210   b ) such that a portion of the boundary  1320  of the first region  810   a  is at a predetermined distance W 1  from the first edge  1220  of trench  1110   b  (e.g. with respect to the side of the trench and doped regions as shown as W 1  between elements  810   a  and  1210 ). 
       FIGS. 13A and 13B  also show the structure  1300 , having a second region  810   b  (e.g. another doped region); the second region  810   b  having a second boundary  1330  (e.g. edge) coupled to at least a second portion  1230  of the material  1210   b  (e.g. a sidewall and/or bottom of trench  1110   b ) such that a second portion of the second boundary  1330  (e.g. a portion of the boundary around second region  801   b ) is at a second predetermined distance (W 2 ) from a second edge boundary  1230  of trench  1110   b . The predetermined distance, W 1 , and the second predetermined distance W 2 , are substantially similar (e.g. W 1  is about equal to W 2 ). 
     Likewise,  FIGS. 13A and 13B  show: the second trench  1110   a  having a material  1210   a , a boundary  1240  of trench  1110   a , and a doped region  810   b  having a boundary  1340  and adjacent to material  1210   a . The distance between boundaries  1240  and  1340  is shown as W 3 . Region  810   a  further has a second boundary  1350  adjacent to a second boundary  1350  of material  1210   a . The distance between boundary  1250  and boundary  1350  is shown as W 4 . Where W 3  and W 4  are substantially equal. 
     The predetermined distance from the first edge (W 1 ) and the second predetermined distance (W 2 ), may be within, for example, about 10 nm, 10 nm should not be construed as a limitation however. Likewise, the predetermined distance (W 3 ) is equivalent to within 10 nm of the distance (W 4 ). 
       FIG. 14  shows a flow diagram of a method  1400  of making structure  1300 . Step  1410 : deposit a material film  505  such as a thin oxide for example, over a substrate  510  such as a silicon wafer. 
     Step  1415 : deposit a second film  610 , such as Polysilicon, adjacent to film  505 ; 
     Step  1420 : perform photolithography using a reticle and photoresist, which will shield substrate  510  from unwanted implantation and guide self-alignment of the wells  810  to the STIs  1210 ; 
     Step  1425 : perform an etch process to remove film  610  where any implants  810  are desired; 
     Step  1430 : implant in the exposed film  505  to generate implant areas or wells  810 ; 
     Step  1435 : anneal the subsequent structure to evenly expand areas  810  under film  610 ; 
     Step  1440 : deposit a structure  910  (e.g. nitride) over film  505 ; 
     Step  1445 : perform a CMP process to even the thickness of structure  910  with film  610 ; 
     Step  1450 : remove film  610  (e.g. Polysilicon) using a stripping process; 
     Step  1455 : perform an RIE step on the exposed substrate  510  and film  505  (e.g. oxide and silicon); 
     Step  1460 : optionally, perform additional implants into exposed substrate  510 ; 
     Step  1465 : deposit a film such as an oxide to generate isolation regions (STIs)  1210 ; 
     Step  1470 : perform a CMP process to remove overfill of trenches; 
     Step  1475 : remove structures  910  (e.g. nitride); and 
     Step  1480 : perform the process of record (POR). For example, forming FETs and wires to create a functional IC. 
       FIGS. 15A and 15B  show a side and top view of structure  1500 , respectively. Structure  1500  includes a substrate  510  having the material  1210   a  and  b  (e.g. oxide to create an STI) and at least a first region (e.g. a doped or ion implanted region  810   a ); the trench  1110   b  having the first edge or first boundary  1220  (e.g. the side wall or bottom of the trench  1110   b  or material  1210   b ); the first region  810   a  having a boundary  1530  (e.g. the edge or boundary of the doped region  810   a  where it connects to an adjacent substance such as oxide material of  1210   b ); the first region (e.g. the doped region  810   a ) being coupled to (e.g. touching) at least a first portion of the trench  1110   b  (e.g. the bottom and/or side of the trench  1110   b  or material  1210   b ) such that a portion of the boundary  1530  of the first region  810   a  is at a predetermined distance W 8  from the first edge  1220  of trench  1110   b  (e.g. with respect to the side of the trench and doped regions as shown as W 8  between elements  810   a  and  1210 ). 
       FIGS. 15A and 15B  also show the structure  1500 , having a second region  810   b  (e.g. another doped region); the second region  810   b  having the same boundary  1530  (e.g. edge) as doped region  810   a  and coupled to at least a second portion  1230  of the material  1210   b  (e.g. a sidewall and/or bottom of trench  1110   b ) such that a second portion of the boundary  1530  (e.g. a portion of the boundary around second region  801   b ) is at a second predetermined distance (W 7 ) from a second edge boundary  1230  of trench  1110   b . The predetermined distance, W 7 , and the second predetermined distance W 8 , are substantially similar and coupled (e.g. W 7  is about equal to W 8 ). 
     Likewise,  FIGS. 15A and 15B  show the second trench  1110   a  having a material  1210   a , a boundary  1240  of trench  1110   a , and a doped region  810   b  having a boundary  1550  and adjacent to material  1210   a . The distance between boundaries  1240  and  1550  is shown as W 6 . Region  810   a  further has boundary  1550  adjacent and coupled to a boundary  1250  of material  1210   a . The distance between boundary  1250  and boundary  1550  is shown as W 5 . Where W 5  and W 6  are substantially equal. 
     It should be apparent to one of ordinary skill in the art that the foregoing description and drawings are meant to provide an illustrative example of developing regions that are self-aligned with edges such as edges of shallow trenches and changes to the structure and process may be modified without departing from the spirit and scope of the invention.