Abstract:
A novel trench-type decoupling capacitor structure and low-cost manufacturing process to create trench decoupling capacitors (decaps). In a unique aspect, the invention necessitates the addition of only a simplified trench to a base logic design.

Description:
BACKGROUND OF THE INVENTION 
   Field of the Invention 
   The present invention relates generally to the fabrication of semiconductor circuit chips, and more particularly to a novel trench-type decoupling capacitor for a semiconductor circuit and cost-effective process for manufacturing trench-type decoupling capacitors. 
   In 90 nm and 65 nm integrated circuit chip designs, noise-related issues are of paramount concern. Logic noise can lead to degraded circuit speeds, and at the worst case, chip failure. On-chip decoupling capacitors (commonly referred to as “decaps”) are typically used to prevent noise-related circuit degradation. However, decaps that are typically offered are large planar (polygate) capacitors that are created on thin oxides. There are three problems inherent with planar decaps. First, planar capacitors end up taking a lot of a space on a chip. As designs increasingly get larger and more complex, it will be necessary to add more decaps to the design which only fuels the desire to add more decaps to the chip. Second, large decap densities can wreak havoc on polygate linewidth control (i.e., Across Chip Linewidth Variation, ACLV). The amount of polysilicon gate conductors that needs to be etched on a wafer—also referred to as “loading”—has a direct impact on how the line etches. The more gate polysilicon one is required to etch, the higher the chances of poorer linewidth control. This unpleasant result leads to transistor degradation and device performance loss. The third, and most disconcerting problem with planar decaps, is the leakage through the thin oxide themselves. Gate leakage—primarily electron tunneling—is becoming a major concern and using more planar decaps on-chip would only aggravate the power consumption conundrum. 
   One present solution to the planar decaps is to use a trench-type capacitor as a decap. Since the trench is made directly in the silicon wafer and the sidewalls of the trench are used for the capacitor dielectric, the planar area of trench decaps can be made fairly small. Second, as the trenches are processed prior to the polygate conductor module, there is no issue of trench decaps causing ACLV problems. The main detractor of using a trench capacitor approach as a decap is the process complexity and cost. Since it takes a considerable amount of time to make a trench capacitor, the cost of adding a trench capacitor to a non-eDRAM chip design makes the implementation of trench decaps in SF designs cost prohibitive. 
   If trench capacitors could be made cheaper, it could undoubtedly be used in chip designs as a decap. 
   It would be highly desirable to provide a cost-effective manufacturing technique for the production of decoupling capacitors (decaps) in semiconductor chip designs. 
   SUMMARY OF THE INVENTION 
   This invention addresses directly the cost issue of manufacturing trench-type capacitors functioning as IC decoupling capacitor devices. 
   According to the invention, there is provided a novel decoupling capacitor structure and low-cost manufacturing process to create trench decoupling capacitors (decaps). In a unique aspect, the invention necessitates the addition of only a simplified trench to a base logic design, e.g., the addition of one (1) mask to a base logic process. 
   There are two distinct embodiments of the “low-cost” trench decap processes according to the invention. The first embodiment describes a process flow whereby the doping level of the silicon substrate regions immediately adjacent to the trench (i.e. the outer electrode of the decap) is provided by logic N-type ion implant (i.e., an N-well). This process would be the least costly of the two, however, requires specific voltage conditions to be made workable. For example, this process would require either: (1) about a 3 mm space between neighboring N-wells; or, (2) an isolation P-well structure surrounding the N-well. 
   The second embodiment of the process, although slightly more expensive, describes several ways to heavily dope the silicon substrate adjacent to the trench. The presence of the high doping level provides more flexibility in terms of voltage conditions that can be applied to the decap and also allows for capacitors to be placed virtually anywhere in a design if biased properly. 
   The two processes share the common physical structure in that a “shallow” deep trench is processed within an STI structure. Here, the trench process is performed after the STI is physically patterned and filled; this process is opposite to “eDRAM” processing where the capacitors are formed prior to STI. In addition, the number of processes to fabricate the “shallow” trench decap is greatly reduced compared to the eDRAM capacitors. Indeed, it is estimated that the “shallow” trench decap would increase a base (non-eDRAM) wafer cost by only about 5–7%. 
   Further embodiments for a decap structure and manufacturing process therefore include the fabrication on SOI structure, for example, the formation in a silicon substrate having a buried insulator layer, e.g., a buried oxide (BOX) layer. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The objects, features and advantages of the present invention will become apparent to one skilled in the art, in view of the following detailed description taken in combination with the attached drawings, in which: 
       FIGS. 1(   a )– 1 ( i ) illustrate process steps for fabricating the low-cost shallow trench decap structure according to a first embodiment of the invention; 
       FIGS. 2(   a )– 2 ( f ) illustrate process steps for fabricating the low-cost shallow trench decap structure according to a second embodiment of the invention; 
       FIGS. 3(   a )– 3 ( j ) illustrate process steps for fabricating the low-cost shallow trench decap structure according to a third embodiment of the invention; 
       FIGS. 4(   a )– 4 ( j ) illustrate process steps for fabricating the low-cost shallow trench decap structure according to a fourth embodiment of the invention; 
       FIGS. 5(   a )– 5 ( h ) depict an additional embodiment for forming a decap  300  of the present invention according to a base logic process consistent with and compatible with existing logic processing methods and tool set; and, 
       FIG. 5(   i ) depicts a conceptual top view schematic of a resultant formed decap trenches  300  pointing downward into the silicon to form a high capacitance structure in a small area. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   In both embodiments of the shallow trench decap structure and process of the invention, patterning of the active Si islands is first conducted. Here, the Shallow Trench Isolation (STI) dielectric, e.g., an oxide, nitride, oxynitride material or like materials of about 300 nm–400 nm thick, provides isolation for the two contacts that need to bias the inner and outer electrode of the DT decap. Preferably, the STI region comprises an oxide insulator such as low pressure TEOS (tetraethylorthosilicate), High Density Plasma (HDP) oxide or, like oxide. The STI oxide is also used as a hardmask to facilitate silicon trench etching of 2 μm–3 μm. One concern of making the trench in STI is whether the resist mask would be robust enough to withstand the (STI) oxide RIE and Si RIE processes. To circumvent this problem, a borosilicate glass (BSG) hardmask may be deposited according to like processes implemented in forming the eDRAM trench. Since the trench depth is reduced 2X–3X, and since the STI dielectric (oxide) is also used as a hardmask, the maximum BSG thickness would need to be on the order of about 100 nm–200 nm. In addition, the STI oxide should not be adversely impacted when the BSG is removed since etch selectivity of BSG to oxide is 200:1. 
   A first embodiment of the shallow trench decap structure  10  and process of the invention, is now described with respect to  FIGS. 1(   a )– 1 ( i ). This first process embodiment according to the invention includes the fabrication of the N-well electrode. As shown in  FIG. 1(   a ), the process includes utilizing a Process of Record (POR) to form an STI region  12  in a Si-containing semiconductor substrate  20 . Illustrative examples of Si-containing materials that can be employed as the Si-containing substrate  20  include, but are not limited to: Si, SiGe, SiC, SiGeC, and layered semiconductors such as Si/SiGe, a silicon-on-insulator (SOI) or a SiGe-on-insulator (SGOI). Thus, as shown in  FIG. 1(   a ), an STI region  12  is fabricated in a substrate  20  with two insulator regions  13   a ,  13   b  formed on either side of the STI  12 . In the embodiment described, the STI width may range between 0.3 μm–0.6 μm and may range in depth from about 2500 Å to 5000 Å. The two insulator regions  13   a ,  13   b  are planarized with the surface of the STI and are typically comprised of a pad Nitride (e.g., SiN) of 1000 Å to 2000 Å thick, and a thin oxide layer (e.g., 50 Å to 100 Å thick). As shown in  FIG. 1(   b ), the next step involves etching a trench within the formed STI structure  12 . Thus, as shown in  FIG. 1(   b ), a deep trench (DT) resist mask layer is first applied and patterned to form a mask  15  having a capacitor trench etch opening  16  formed over the STI region. Optionally, under the resist mask layer  15 , a thin layer of BSG (not shown) or like material layer may first be deposited to serve as a hardmask. This BSG film would be much thinner than the one used for eDRAM processing, e.g., to a thickness ranging between 1 kÅ to 6 kÅ, and can be removed with a high degree of selectivity with respect to the STI dielectric (e.g., oxide). Then, a mask open etch process is applied to form a trench  26  within the STI  12  as shown in  FIG. 1(   c ). While for illustrative purposes an etch having straight profiles is shown in  FIG. 1(   c ), it is understood that a formed trench in the STI may have a taper. 
   Further, as shown in  FIG. 1(   d ), a DT Si Reactive Ion Etch (RIE) technique is applied to further extend the depth of the trench  26  below the STI bottom in the Si substrate  20  to a target depth of, for example, 1 μm–3 μm according to the invention. After the trench  26  is etched, as shown in  FIG. 1(   e ), a node SiN dielectric process may then be used, as in eDRAM techniques, to fill the trench with the capacitor dielectric, i.e., node fill, which may comprise SiN or other oxide material layer. Thus, as shown in  FIG. 1(   e ), the DT resist and optional BSG hardmask layers are first stripped, and a node process implemented to deposit the decap dielectric material layer  32  such as a nitride material (e.g., SiN), oxynitride, or oxide material (e.g., HfO 2 , AlO 2 ) that conforms to the bottom and sidewalls of the decap trench  26 . In the embodiment described herein, a SiN node dielectric is deposited to a thickness of approximately 40 Å or greater. It is understood that the decap dielectric layer thickness may vary depending upon the capacitance value, dielectric film material, trench depth, trench area, and other design considerations. For example, the depth of the trench may be reduced at a reduced cost, by depositing a high-epsilon (K) dielectric. For example, HfO 2  has 5× the dielectric constant of the POR oxynitride that is used in eDRAM designs. If it is desired to have equivalent capacitance, the DT etch may be simply reduced to ⅕ the depth thereby making a 0.4 μm–0.5 μm deep trench), for example. 
   Then, as shown in  FIG. 1(   f ), a highly doped N+ polysilicon is deposited in the trench  26  and then recessed in the trench to form the decap structure inner electrode  35 . Particularly, the deposited N+ polysilicon material  35  is deposited within the trench  26  and then a chemical mechanical polish (CMP) step is applied to remove the formed node SiN laying over the STI and Pad SiN regions adjacent the trench. The N+ polysilicon fill (polyfill)  35  is then recessed within the trench so that a surface thereof is at the Si active region surface  33 . The recessing of the N+ polysilicon within the decap trench  26  is performed using a reactive ion etch process, for example, with the Pad SiN utilized as a polish stop. Finally, after recessing the polyfill, as depicted in  FIG. 1(   g ), the POR Pad film (Pad SiN) is stripped, for example by an (HF-based) nitride deglaze step followed by a hot phosphoric acid step to etch off the pad SiN. A pad oxide may remain if a pad stack was provided. 
   In the embodiment shown in  FIG. 1(   g ), the DT decap implements a logic NW doping for the outer electrode  45 . Thus, an N-well implant is provided by: forming a resist mask layer on the wafer, and, exposing and opening up the area in which the N-well implant is to be received. An ion implantation technique well known in the art is used to provide the N-well dopant species, e.g., phosphorus, P, to a targeted depth below the STI level, using energies of up to 1 MeV. Since the projected range (Rp) of the logic N-well (NW) is usually 1 mm or less, at least half the trench sidewall would be butting against P-type silicon. However, this scenario is actually good for obtaining high capacitance if the trench fill is positively biased (e.g., the N-well  45  would be held at ground) as an N-type inversion layer would be created in the P-type silicon. Since the N-doping level of the outer electrode is “light” (e.g., doping on the order of 1×10 17 –1×10 18 /cm 3 ), and if the biasing of the outer plate is at ground, a large depletion region would be created in the NW field. This would require an NW—NW space of about 3 μm or, providing an isolation P-well around decaps as would be fabricated using known techniques. 
   Referring now to  FIGS. 1(   h ) and  1 ( i ), the formed outer electrode (N-well)  45  and inner electrode (polyfill)  35  of the DT decap need to be connected to the metal layers to be subsequently formed. As shown in  FIG. 1(   h ), using regular CMOS device processing, N+ source or drain regions  47   a ,  47   b , e.g., for NFETs, may be formed using ion implantation (I/I) techniques in the active Si (Rx) layer  20 . First, a resist layer is deposited, patterned, exposed and etched to form contact openings above the N+ source or drain contact regions  47   a ,  47   b , and above the inner decap electrode  35 . Then, an anneal process is performed to form the silicide contact using any metal that is capable of reacting with silicon to form a metal silicide. Examples of such metals include, but are not limited to: Ti, Ta, W, Co, Ni, Pt, Pd and alloys thereof. Particularly, a metal such as cobalt or nickel is deposited to the exposed silicon, and then an anneal process is performed to form the metal silicide regions, e.g., cobalt silicide or nickel silicide regions  46 . A thin layer of nitride e.g., 500 Å thick, is then deposited above the exposed N+ source or drain regions and silicide regions. A deposition of a BPSG layer  52  is then conducted, patterned with a resist, and etched to open up contact areas  36  within the BPSG layer. The nitride layer above the silicide is etched, stopping on the silicide, so that only the silicide is exposed for the contact areas  36 .  FIG. 1(   i ) illustrates the resulting structure formed after the process of depositing contacts  55  to the inner decap electrode (to bias the polyfill inner electrode  35 ) as well as on the N+S/D diffusions adjacent to the trench decap (to bias the outer electrode  45 ). Particularly, using well known techniques, a contact material, typically a metal such as Tungsten, is deposited in the etched contact areas  36  in the BPSG layer above the formed silicide contacts to form the wire level contacts  55  (“plugs”). As the diffusions and top of the trench is silicided, the connection to the decap has a very low resistance since there is no buried strap feature used in this process (unlike eDRAM where the connection to the trench capacitor is through a N+ polysilicon buried strap). Interlevel and intralevel dielectrics and metal layers M 1 , M 2 , formed of Tungsten, Aluminum or Copper are then wired to the plugs  55  using conventional MOL and BEOL processing to contact respectively, the inner electrode  35  and outer electrodes  45  respectively of the decap  10 . 
   In accordance with the first embodiment described herein with respect to  FIGS. 1(   a )– 1 ( i ), the only additional costs beyond the POR cost is cost of the additional mask needed to form the decap trench and the cost of performing the associated process steps of opening the DT mask open etch, the DT RIE step, the node process and the N+ polyfill deposition, CMP and recess steps. 
   Because the N-well formed is lightly doped, under certain bias conditions, a depletion region may form that affects the performance of the device. For example, if the N-well (forming the outer decap electrode) is at ground and the inner decap electrode (trench) is at a positive voltage, a depletion region forms that may affect another device, e.g., PFET area nearby, because of the depletion formed in the N-well. Rather than enforcing a ground rule, which would increase the device area, the solution in accordance with the second embodiment is now described. In this second embodiment, the sidewalls of the trench decaps are doped which provides more flexibility in placing decaps within a circuit. In this scenario, it is envisioned that the N-well can be biased at Vdd and the trench is at ground voltage. In this configuration, then N-wells can be merged together and one can place p-FETs in these Vdd-biased N-wells. Thus, a substantial reduction in decap area would result as compared to the structure described in accordance with the first embodiment. 
   Thus, after the trench has been lithographically defined and etched as shown in process steps described herein with respect to  FIGS. 1(   a )– 1 ( d ) are performed, as shown in  FIG. 2(   a )(i)– 2 ( a )(iii), there are several ways that a thin, heavily-doped N-type diffusion layer may be provided in the “shallow” trench decaps. One method of doping the sidewalls of the trench is to perform an angled implant of dopant, e.g., P or As. For example, as shown in  FIG. 2(   a )(i), dopant ions  60  may be implanted in the trench sidewalls  27  at an angle of incidence of, for example, 5 degrees or less angle from normal incidence, depending on the depth of the trench. A second method, as shown in  FIG. 2(   a )(ii), utilizes a gas-phase doping process whereby the open DT trench  26  is exposed to high concentration P or As gases  61 . A third method, as shown in  FIG. 2(   a )(iii) is to simply fill the trenches with a doped gas  62 , e.g., ASG (arsenic silicate glass) or PSG (phosphorus silicate glass) material layers, and perform an anneal, i.e., conduct a short high temperature outdiffusion step to outdiffuse the dopant from the silicate glass into the Si substrate. In each of the methods described, the highly doped N-type trench diffusion layer  65  (outdiffused plate) shown in  FIGS. 2(   a )(i)– 2 ( a )(iii) are formed to a thickness of approximately 500 Å of less. Since the active Si diffusion islands are protected with pad SiN, one could avoid many of the processes that are part of the buried plate process presently used in eDRAM. These steps include: (1) a resist fill of the trench, (2) a chemical downstream etch (CDE) of the resist to 1 μm below the Si surface, (3) an oxide etch to remove the doped oxide from the upper region of the DT, (4) a wet clean of the resist, and, (5) an oxide capping layer. Chosen methods for providing the outdiffused plate, according to the second embodiment, is the implant or gas phase doping procedure as these methods are the least costly. Continuing, as shown in steps depicted in  FIGS. 2(   b ) through  2 ( f ), the N-well (decap outer electrode) is formed by ion implantation, and more particularly, the same exact process steps as described herein with respect to corresponding  FIGS. 1(   e ) to  FIG. 1(   h ) are performed to result in a trench decap structure  10 , except for the presence of the outdiffused plate  65 . The presence of the high dopant outdiffuse plate  65  prevents depletion into the substrate, i.e., thus reducing the device footprint. 
   In accordance with the second embodiment described herein with respect to  FIGS. 2(   a )– 2 ( f ), the only additional costs beyond the POR cost is cost of the additional mask needed to form the decap trench and the cost of performing the associated process steps of opening the DT mask open etch, the DT RIE step, the node process and the N+ polyfill deposition, CMP and recess steps and, the outdiffusion process steps which range depending upon the process step implemented. 
   The approaches described herein, provide a very simple increase in decoupling capacitance available for logic based processing and provides a simple well isolation for improved n+/p+ space with no extract process cost. This synergy coupled with the low added process cost and growing need for on chip decoupling capacitance makes this approach very attractive for 9SF and 10SF applications and beyond. 
   The low-cost decoupling capacitor according to further embodiments of the invention is now described herein with respect to  FIGS. 3 and 4 . In the third embodiment, the trench decaps are made at a lower cost, exhibit higher frequency response while lowering the overall leakage of a decap design and lowering the area set aside for decaps and, are integrated into an silicon-on-insulator (SOI) designs. There are two distinct “low-cost” trench decap structures and process variations described: a first variation described herein with respect to  FIGS. 3(   a )– 3 ( j ) depicts a process flow where the trench decap design is quickly and seamlessly integrated into an existing SOI technology process. The process calls for an additional two (2) masks: a DT mask and a block-level N-well mask such that the outer plate of the trench decap can be contacted through existing substrate contacts for SOI (e.g., doped poly contacts). In the second variation process described herein with respect to  FIGS. 4(   a )– 4 ( j ), a different trench decap process and structure is described whereby metal contacts, such as Tungsten (W), or other metal materials are used to contact the outer plate of the trench decap. This second unique structure may provide a faster capacitive decoupling response since the Tungsten (W) resistance is significantly lower than doped substrate contact polysilicon. This second process also calls for the same aforementioned masks, the DT mask and the block-level N-well mask. The two processes share the common physical structure in that a decap trench of, approximately 2 μm–3 μm deep, is processed. As the decap trench is to be formed to a depth of about 2 μm–3 μm deep, the number of processes to fabricate the trench decap is greatly reduced compared to conventional eDRAM capacitors. 
   In the decap structure according to the third embodiment, described herein with respect to  FIGS. 3(   a )– 3 ( j ), the trench process is performed after the STI regions are physically patterned and filled. That is, this process is polar opposite to “eDRAM” processing where the capacitors are formed prior to STI. 
   The process flow described with respect to  FIG. 3(   a ) illustrates the resulting structure of the STI process of record and particularly the formed STI regions  71   a – 71   c  extending through to a BOX (buried oxide layer) layer  70 . The STI regions are first patterned and formed by etching through: a Pad nitride or nitride stack  74 , the thin active silicon layer  72  and through the thin BOX layer  70 . Etching of the BOX layer  70  is an optional step, and the STI may be formed to the top of the BOX layer, i.e., etched through to the bottom of the silicon layer  72 . The width of the STI region may be about 0.3 Im to 0.6 Im, however, the depth may range up to 500 Å to 1000 Å, but may range up to a depth up to 2500 Å. Then, the STI is filled with an oxide, e.g., LP-TEOS, and HDP oxide, as described herein. After the POR STI module, the DT lithography, mask open, and Si RIE process is conducted. That is, as described herein with respect to  FIGS. 1 and 2  herein, a resist mask  78  and/or an optional hardmask (e.g., BSG) is applied, and patterned to expose the STI region  71   b  and, a deep trench etch is performed through the STI opening in the mask  78  to a depth of 2 μm to 3 μm as shown in  FIG. 3(   c ). Subsequent to the formation of the decap trench  76 , the Si substrate sidewalls and bottom of the trench  76  are doped to form an outdiffused portion of the outer electrode of the capacitor. This step implements an outdiffusion process and results in the formation of an outdiffused plate  85  forming a highly doped portion of the capacitor outer electrode beneath the buried oxide layer  70 . The trench sidewall doping can be accomplished by either of the following methods: 1) an N+ type dopant  60  angled ion implantation as shown in  FIG. 3(   d )(i); 2) an N+ gas-phase doping  61  of N type dopant, e.g., P or As dopants, as shown in  FIG. 3(   d )(ii); and, 3) an N+ doped glass deposition  62  and anneal as shown in  FIG. 3(   d )(iii). It is understood that, in alternative embodiments, the process steps for forming the outdiffused plate may be omitted. Whether the outdiffused plate  85  is formed or not, the next step is the process of forming the thin capacitor dielectric layer  82 —that is, an oxide or a nitride, such as SiN, that conforms to the trench sidewalls and bottom. Thus, as shown in  FIG. 3(   e ) and as described in detail herein with respect to  FIGS. 1 and 2 , a resist strip is first performed and then the node process is performed. Next, as shown in  FIG. 3(   f ) and as described herein with respect to  FIGS. 1 and 2 , a highly N doped polysilicon fill is performed to construct the decap inner electrode  75 .  FIG. 3(   f ) shows the N+ poly fill  75  in the decap trench  76 . It is understood that, as part of this process, a CMP is performed and a top portion of the polyfill is then recessed to the top surface of the active silicon layer  72 . 
   Then, as shown in  FIG. 3(   g ), after the trench process, the process proceeds to form a Bitline contact adjacent to the trench, which comprises steps of punching through an adjacent STI (or insulator) area(s)  71   a ,  71   c  and stopping the etch on the bottom substrate, i.e., it only has to etch the thickness of the active silicon layer  72  and the BOX layer  70 . According to processes of record for BI module, the etched area(s)  83  is(are) typically filled with intrinsic (undoped) Si  93  as shown in  FIG. 3(   g ) and a CMP is performed to planarize and recess each of the filled i-Si regions to the surface of the active Si layer  72 . It is understood that the steps for recessing the N+ polysilicon fill forming decap inner electrode  75  and the i-Si may be performed in the same process step. Then, as shown in  FIG. 3(   h ), an N-well implant step to form decap outer electrode  95  is performed in the manner such as described herein with respect to  FIGS. 1 and 2 . The substrate contacts (plugs) adjacent to the trench decap are to be used to bias the outer electrode of the trench decap. Since the substrate contacts polysilicon plugs  93  are undoped, for the substrate contacts within the trench decap macro, these would necessarily need to be doped N-type. This can be accomplished by N+ doping the Source/Drain regions in the active Silicon layer  72  by ion implantation later in the process. However, within the N-well ion implant mask (not shown), the implants for the substrate contacts (plugs) may be further doped if the N+ source/drain diffusions are insufficient to dope the entire poly plug. If necessary, N-type ion implants may then be targeted to depths below the active Si layer  72 , e.g., corresponding to the middle of the BOX, for example, to guarantee that the whole substrate contact is doped. This ion implantation may be performed during the following N-well ion implantation step or thereafter. Thus, to connect the trenches and make them amenable to voltage biasing, the deep N-well implant—like the one used in eDRAM processing, is performed. Doses in the range of 10 13 /cm 2 –10 14 /cm 2 , for example, should provide enough conduction to bias the outer plate (e.g., 100 Ω/sq–1000 Ω/sq). The projected range of the N-well implant would only need to be one that is on the order of the SOI and BOX thickness (e.g., about 2000 Å depth). If Phosphorus (P) is used as the N-well dopant, accelerating energies of 200 keV may be sufficient. Since the N-well mask is unique to the trench decap macro, other than N-type dopants may be implanted into the substrate contacts  93  to make them more conductive. Thus, as shown in the  FIG. 3(   h ), after an oxide deglaze, pad SiN etch process, and N-well ion implantation steps, the resulting structure  100  illustrates N+ poly plugs  93  contacting the N-well implant  95  which is connected to the outdiffused portion  85  of the outer DT capacitor electrode. 
   After the N-well process,  FIGS. 3(   i ) and  3 ( j ) illustrate the remaining processes to create the trench decap uses the POR MOL module. In  FIG. 3(   i ), the substrate contacts  93  and decap inner electrode poly  75  are silicided  96  and contacted by plugs  98  of a metal material, e.g., such as Tungsten (W). The process includes the formation of respective contact holes  97  implementing a dielectric film deposition (e.g., a nitride or BPSG) and a contact hole lithography patterning and etch as shown in  FIG. 3(   i ). M 1  and M 2  metallurgy is then used to follow and finish up the macro as shown in  FIG. 3(   j ). 
   What is described in  FIGS. 3(   a )– 3 ( j ) depict the easiest method in that trench decaps  100  can be integrated into existing SOI processing technology. 
   In a further embodiment, described herein with respect to  FIGS. 4(   a )– 4 ( j ), the deep trench decap  200  can be processed before the STI (standard) processing, i.e., does not require trench formation through STI. In the embodiment depicted in  FIG. 4(   a ), there is formed by process of record a thin active Silicon layer  112  atop a BOX layer  110  formed atop a Si-containing substrate  20 . As shown in  FIG. 4(   a ), a Pad nitride layer or nitride stack  114  is deposited above the thin active Si layer  112 . Then, as shown in  FIG. 4(   b )– 4 ( c ), a trench lithography, mask open, and Si RIE process is conducted. That is, as described herein with respect to  FIGS. 1 and 2  herein, a resist mask  115  and/or an optional hardmask (e.g., BSG), is patterned to expose a region  116  for forming a deep trench etch. Subsequent to the formation of the decap opening  116 , an etch process is performed through the opening in the mask to form a trench  126  that extends through the PAD layer  114 , thin active silicon layer  112  and through the thin BOX layer  110  to a depth of about 2 Im to 3 Im as shown in  FIG. 4(   c ). Subsequent to the formation of the decap trench  126 , the Si substrate sidewalls and bottom of the trench are doped to form an outdiffused portion of the outer electrode of the capacitor. This step results in the formation of an outdiffused plate  135  beneath the buried oxide layer  110  forming a highly doped portion of the capacitor outer electrode and implements an outdiffusion process. The trench sidewall doping can be accomplished by either of the following methods: 1) an N+ type dopant  60  angled ion implantation as shown in  FIG. 4(   d )(i); 2) an N+ gas-phase doping  61  of N type dopant, e.g., P or As dopants, as shown in  FIG. 4(   d )(ii); and, 3) an N+ doped glass deposition  62  and anneal as shown in  FIG. 4(   d )(iii). It is understood that, in alternative embodiments, the process steps for forming the outdiffused plate may be omitted. Whether the outdiffused plate  135  is formed or not, the next step is the process for forming the thin capacitor dielectric layer  142 —that is, an oxide or a nitride, such as SiN, that conforms to the trench sidewalls and bottom. Thus, as shown in  FIG. 4(   e ) and as described in detail herein with respect to  FIGS. 1 and 2 , any remaining resist strip is first performed and then the node process is performed. Next, as shown in  FIG. 4(   f ) and as described herein with respect to  FIGS. 1 and 2 , a highly N+ doped polysilicon fill is performed to construct the decap inner electrode  155 .  FIG. 4(   f ) shows the N+ poly fill  155  in the decap trench  126 . It is understood that, as part of this process, a CMP is performed and a top portion of the polyfill is then recessed to the top surface of the active silicon layer  112 . 
   In the next steps in the process flow, shown in  FIG. 4(   g ), a typical STI module process is performed to form two STI structures  131   a ,  131   b  located on either side of the decap inner electrode  155 . In the STI module process, each STI region is first patterned and formed by etching through a Pad nitride or nitride stack  114 , the thin active silicon layer  112  and through the thin BOX layer  110 . Etching of the BOX layer  110  is an optional step, and the STI may be formed at the top of the BOX layer, i.e., etched through to the bottom of the silicon layer  112 . The width of each STI region may be about 0.3 Im to 0.6 Im, however, the depth may range up to 500 Å to 1000 Å, but may range up to a depth up to 2500 Å. Each STI opening is filled with an oxide, e.g., LP-TEOS, and HDP oxide, as described herein. As shown in  FIG. 4(   g ), after the POR STI module and a pad Nitride strip step (not shown), a deep N-well implant step similar to the one used in eDRAM processing, is performed to form the N-well implant regions  145  under each STI region. Then, as shown in  FIG. 4(   h ), the Bitline lithography, mask open, and Si RIE process is conducted to form respective openings  141   a ,  141   b  at each formed STI structure  131   a ,  131   b  respectively. The etched openings  141   a ,  141   b  are used to form the metal substrate poly contacts to the decap outer electrode. In  FIG. 4(   i ), the resist  148  used to etch the STI regions in  FIG. 4(   h ) is removed (stripped) and a silicide layer, e.g., a metal silicide, is formed above the entire region of the trench capacitor and the adjacent active silicon regions  112   a ,  112   b . Silicide is additionally formed at the substrate contact regions (openings)  141   a ,  141   b . Then, a dielectric layer  150 , e.g., an oxide, or BPSG, is deposited, planarized, lithography patterned and etched to open up the capacitor electrode contact holes  153  above the formed silicide regions  156 . Then, in  FIG. 4(   j ) all of the contact holes  153  are filled with Tungsten or like conductive material to contact the Si underneath the BOX. Then normal BEOL (back-end-of-the-line) and MOL processing is performed to connect the formed Tungsten plugs to M 1 , M 2  metallurgy layers. Advantageously, with Tungsten metal contacts  163  formed as part of substrate contacts, the frequency response is higher than the decap structures created with the N+ polyfill contacts in the previous embodiment depicted in  FIGS. 3(   g )– 3 ( j ). It should be understood that it is possible to eliminate the N-well if there is enough thermal budget such that the outdiffused plate can reach the substrate N+ contact. Additionally, it has been shown that Phosphorus in high concentrations of Arsenic dopant will greatly accelerate the Phosphorus outdiffusion. An outer plate comprising of these two dopant materials (P and As) may be suitable to allow for the N-well elimination. 
   It should be understood that for some applications, the polarity of the electrodes in the decap devices in the embodiments described herein may be reversed, i.e., P-type dopants may be utilized in the process steps described, without much modification or undue experimentation. 
   As a measure to further reduce costs, the decap  300  of the present invention is implemented in a base logic process consistent with and compatible with logic processing methods and tool set as now described with respect to  FIGS. 5(   a )– 5 ( h ). In the embodiment depicted in  FIGS. 5(   a )– 5 ( h ), the decap trench is formed in the same processing steps as the formation of the STI regions. That is, the only extra added steps is the patterning and developing a resist layer  302  having an opening  316  upon a formed hard mask oxide layer  313 , a pad oxide layer  310  and/or pad nitride surface layer  312  formed above the Si substrate  320  as shown in  FIG. 5(   a ), and then etching a shallow decap trench  326  into the Si layer e.g., below the surface as shown in  FIG. 5(   b ). Then the layer of resist is stripped and the base processing for forming the STI region is performed. According to the STI base processing, a new mask is formed by patterning and developing a resist layer  330  including an opening  336  that is about the same width of the STI region to be formed as shown in  FIG. 5(   c ). Then, a further etch process, such as a Reactive Ion Etch (RIE) is performed to etch the Si substrate  320  to form STI trench region  340 . As a result of this processing, in the same STI etch step, the depth of decap trench is extended, i.e., more Si is being etched to a depth of about 2–3 μm to result in the decap trench structure  326 ′ as depicted in  FIG. 5(   d ). The trench structure shown in  FIG. 5(   d ) is then filled with a HD plasma oxide  327  or like dielectric material and planarized. Depending upon a particular application, the resulting structure will form a decap for example, with the formation of an underlying N-well region  350  and provision of a highly doped N-band layer  355  as shown in the structure of  FIG. 5(   e )( 1 ). Advantageously, the provision of N-band layer  355  effectively increases the decap capacitance, thus obviating the need for the formation of a heavily doped outdiffused plate as in the other embodiments described herein. Alternately, the structure may be used as an isolation region for isolating an N-well region  350  and a P-well region  360  shown in  FIG. 5(   e )( 2 ). Further to the forming of decap  300  of the present embodiment, the only other additional cost to the base logic processing is the addition of a second mask  370  as shown in  FIG. 5(   f ) which provides an opening  375  enabling a straight etch, e.g., RIE, to remove the HDP oxide present in the trench while leaving the HDP oxide portions  342 ,  343  of the formed STI. Once the HDP oxide is removed from the trench, the standard technology for forming the thin decap dielectric layer  382  is performed concurrently with a surface gate oxidation process, e.g., grown to a thickness ranging between 2.0 and 5.0 nm. Then, a standard gate polysilicon deposition process providing a conformal fill  385  of the decap trench is performed concurrent with base logic standard gate polysilicon deposition and the polyfill is doped with N+ material dopant (as described herein) to form the inner decap electrode. The resultant structure is shown in  FIG. 5(   g ). Preferably, this implantation of N+ dopant is also part of the standard logic N+ source and drain implant procedure. Advantageously, depositing the same dielectric material, e.g., an oxide, nitride, oxynitride, etc. used for the decap dielectric  382  at the time logic gate dielectric is deposited, incurs no additional cost as this is part of standard base processing. Likewise, the polysilicon fill  385  is deposited at the same time logic gate polysilicon is deposited according to standard logic base processing thus, incurring no additional cost. Then, in a subsequent processing step shown in  FIG. 5(   h ), the decap polysilicon fill layer is patterned and portions removed by etching the poly over the thin oxide regions and corresponding insulating spacers  395   a ,  395   b  are formed over the STI regions  342 ,  343  according to known techniques. Finally, active diffusion regions (e.g., source/drain implants)  390   a ,  390   b , e.g., having implanted N+ material dopant materials are formed according to standard processing and concurrently dope the poly  385  that contact the N+ doped N-band and N-well regions which form the outer decap electrode. 
     FIG. 5(   i ) depicts a conceptual top view schematic of a resultant formed decap trenches  300  pointing downward into the silicon for about 2 μm–3 μm deep forming a high capacitance structure in a small area  400 . It is understood that the amount of decoupling capacitance may be tailored according to number of trenches formed. For example, for a typical nitrided oxide dielectric of 2.2 nm in thickness, a trench that is 0.1 μm wide with a depth of 1.0 μm will result in approximately 25 fF/μm 2  of capacitance. Additionally depicted is the formed polysilicon  385 , underlying N-well  350 , active silicon region  398 , and STI  340  regions separating the active silicon. It is understood that spacers separating the outer edges of the polysilicon layers as shown in  FIG. 5(   h ) are omitted in  FIG. 5(   i ). It is further understood that the process and resulting decap structure of the embodiment depicted in  FIGS. 5(   a )– 5 ( h ) may be formed in a substrate having an underlying BOX (buried oxide) layer, however, there would be no N-band and additionally, no need for well-to-well isolation with SOI structure having a buried oxide. 
   The embodiment of the invention depicted in  FIGS. 5(   a )– 5 ( h ) provides a very simple increase in decoupling capacitance available for logic based processing and provides a simple well isolation for improved N+/P+ with no extra process cost. This synergy coupled with the low added process cost and growing need for on chip decoupling capacitance makes the approach of the present invention very attractive for 65 nm node applications and beyond. 
   While there has been shown and described what is considered to be preferred embodiments of the invention, it will, of course, be understood that various modifications and changes in form or detail could readily be made without departing from the spirit of the invention. It is therefore intended that the invention be not limited to the exact forms described and illustrated, but should be constructed to cover all modifications that may fall within the scope of the appended claims.