Abstract:
An apparatus including a capacitor formed between metallization layers on a circuit, the capacitor including a bottom electrode coupled to a metal layer and a top electrode coupled to a metal via wherein the capacitor has a corrugated sidewall profile. A method including forming an interlayer dielectric including alternating layers of dissimilar dielectric materials in a multilayer stack over a metal layer of a device structure; forming a via having a corrugated sidewall; and forming a decoupling capacitor stack in the via that conforms to the sidewall of the via.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
   This application is a divisional of U.S. patent application Ser. No. 10/185,798, filed Jun. 27, 2002 now U.S. Pat. No. 6,737,699. 

   BACKGROUND 
   1. Field 
   An integrated circuit decoupling capacitor and more specifically, an on-chip decoupling capacitor. 
   2. Background 
   The operation of low power, high speed integrated circuits can be affected by the electrical noise generated by the continuous switching of the transistors located in the circuit. It is well known that the inductive noise of an integrated circuit can be reduced by connecting decoupling capacitors to the circuit. Decoupling capacitors placed on power-consuming circuits are able to smooth out voltage variations with the stored charge on the decoupling capacitor. The stored charge is used as a local power supply to device inputs during signal switching stages, allowing the decoupling capacitor to mitigate the effects of voltage noise induced into the system by parasitic inductance. 
   Typically, a decoupling capacitor is placed in the same package as the chip. Unfortunately, this arrangement is costly to manufacturer, and the long lead lines from the power-consuming circuit to the capacitor electrodes contributes a substantial inductance. Such off-chip decoupling capacitors, however, are not sufficient for very high speed microprocessor applications. The voltage drop across an inductor may be described by the relationship L di/dt, where L is inductance and di/dt represents the change in current through a circuit over a period of time. Implicit in the di/dt is a frequency component (omega), so as frequency goes up, inductance becomes more and more a factor for power distribution. The frequency dependent L di/dt voltage drop makes the off-chip capacitors generally unusable with gigahertz switching circuits unlike low frequencies for which voltage drops are dominated by resistance. 
   Some efforts have been made to integrate decoupling capacitors as part of the gate dielectric processing step. A portion of the active silicon area is used to deposit the gate dielectric for use as a decoupling capacitor. An advantage to this is that there are no additional processing steps involved with it. Disadvantages include the decoupling capacitor takes up high-value real estate on the chip as the capacitors compete for valuable chip area that could be used for building additional circuits. Also the capacitor made with a gate oxide designed for very high transistor performance generally has a great deal of leakage. These gate decoupling capacitors also generally have associated parasitic resistance from the relatively low silicon conductivity that entails an additional resistance-capacitance (RC) time constant for charge extraction. Although it is possible to integrate gate capacitors within the chip&#39;s circuit elements, due to the limited area in which to build these capacitors, the overall capacitive decoupling that they provide is also limited. 
   Another approach to decoupling capacitor fabrication is a decoupling capacitor that may be fabricated between metal layers in an integrated circuit. In a representative chip architecture having seven metal layers, for example, the capacitor may be fabricated between metal six (n−1) layer and metal seven (n) layer. Advantages to this embodiment include that there is little no additional real estate (area) on the chip consumed for fabrication of the decoupling capacitor, and the decoupling capacitor directly bridges the on-chip power grid being representatively up to 10 microns, according to current technologies, from the integrated circuit element it is supporting with a very low inductance per unit length due to the tight spacing of the power and ground lines. One problem with locating the decoupling capacitor between metal layers is that, in the example given, approximately 30 percent of the metal six layer is devoted to power supply. This limits the total amount of decoupling capacitance that can be provided on-chip per layer, because total capacitance available is generally a function of the total area dedicated to capacitor plates. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various embodiments are illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like references indicate similar elements. It should be noted that references to “an” or “one” embodiment in this disclosure are not necessarily to the same embodiment, and such references mean at least one. 
       FIG. 1  is a cross-sectional schematic illustration of one embodiment of a corrugated conformal decoupling capacitor stack. 
       FIG. 2  is a cross-sectional schematic illustration of one embodiment of a substrate having an interlayer dielectric of alternating layers of dielectric material. 
       FIG. 3  is a cross-sectional schematic illustration of the structure of  FIG. 2  having corrugated vias in the interlayer dielectric layer. 
       FIG. 4  is a cross-sectional schematic illustration of the structure of  FIG. 3  having a conformal decoupling capacitor stack formed thereon; 
       FIG. 5  is a cross-sectional schematic illustration of the structure of  FIG. 4  with a conformal capacitor stack in a selected via. 
       FIG. 6  is a cross-sectional schematic illustration of the structure of  FIG. 5  with a passivation layer formed on the structure. 
       FIG. 7  is a cross-sectional schematic illustration of the structure of  FIG. 6  with a blanket passivation formed on the structure. 
       FIG. 8  is a cross-sectional schematic illustration of the structure of  FIG. 7  with vias and trenches formed therein. 
       FIG. 9  is a cross-sectional schematic illustration of the structure of  FIG. 8  with a via metal and a metal layer formed on the structure. 
       FIG. 10  is cross-sectional schematic illustration of one embodiment of an alternate embodiment of a decoupling capacitor stack. 
       FIG. 11  is a cross-sectional schematic illustration of another embodiment of a corrugated capacitor stack decoupling capacitor. 
       FIG. 12  is a flow diagram representing one method of fabricating the structure according to  FIG. 2  to  FIG. 9 . 
   

   DETAILED DESCRIPTION 
     FIG. 1  is a cross-sectional schematic illustration of one embodiment of a portion of a die or chip having at least one corrugated stacked capacitor between conductors. Structure  200  includes substrate  205  that is, for example, a semiconductor substrate or a semiconductor film having devices formed thereon. Overlying substrate  205  are typically multiple conductive (e.g., “metal”) layers (e.g., seven metal layers) that serve or reference (e.g., power/ground) to link various devices on substrate  205 . The metal layers are patterned into one or more “lines” at each level. Substrate  205  and the metal layers or lines are typically isolated from one another by dielectric material layers, referred to as interlayer dielectric (ILD) material. 
   Interlayer dielectric  210  and interlayer dielectric layer  280  generally refer to the various ILD material layers that electrically isolate the various structural elements on substrate  205  circuit from one another while providing mechanical support for various elements that might be associated with the metal lines. In one embodiment, metal line  230  (e.g., metal layer six) is shown making direct contact to metal line  241 . This direct contact is made through via  338 . Metal line  243  is connected to metal line  230  through via  342 . Vias  342  and  338  are formed in a dielectric material layer comprising, in one example described herein, alternating layers of dielectric materials having dissimilar etch rates. 
   Referring to  FIG. 1 , alternating layers of dielectric materials  215  and  217  are shown stacked in on metal line  230 , and as is shown here allowing access to metal line  230  from metal lines  243  and metal line  241 . Alternating layers of dielectric material  217  and  215  having dissimilar etch rates are shown having different widths (x direction widths as viewed) within vias  342  and  338 . The different widths of alternating layers of dielectric materials  217  and  215  produce a corrugation in the vertical surfaces of vias  342  and  338 . 
   It is to be understood that although  FIG. 1  is a two dimensional drawing, the drawing represents a three dimensional figure. Thus, in various embodiments vias  342  and  338  may be circular, square or rectangular. Vias  342  and  338  thus define an opening in dielectric materials  217  and  215 . The corrugated surface of vias  342  and  338  may therefore be on all vertical sides of the interior surface of the via (e.g., different x and z direction widths). The corrugations of alternating layers of dielectric materials  217  and  215  within vias  342  and  338  increase the surface area of the vertical surface of vias  342  and  338 . 
     FIG. 1  also shows a decoupling capacitor formed in and around via  342 . Decoupling capacitor stack  240  includes (as viewed in the inset) top electrode  214 , dielectric material  216  and bottom electrode  218 . Referring to  FIG. 1 , decoupling capacitor stack  240  fills the surface area of via  342 , and in one embodiment covers, as viewed, the top of uppermost alternating layer of dielectric material, in this example dielectric material  217 . Decoupling capacitor stack  240  is conformally formed on the vertical surfaces of via  342 . As a result of the corrugated configuration of via  342 , the total capacitive area of the decoupling capacitor stack is increased as compared to capacitors formed in a linearly-edged via. 
   Passivation layer  220  shown in  FIG. 1  covers the exposed surface of decoupling capacitor stack  240  and alternating layers of dielectric materials  217  and  215 . A conductive material, such as tungsten or copper fills each of via  338  and via  342  to couple metal line  241  and metal line  243 , respectively, to metal line  230 . Via  342  makes a decoupled connection between metal line  230  and metal line  243 . In one embodiment, metal line  241  represents a V CC , and metal line  243  represents a V SS  metal line. 
     FIGS. 2-9  show one technique for forming the structure illustrated in  FIG. 1 .  FIG. 12  is a flow chart representing a flow scheme described with reference to  FIGS. 2-9 .  FIG. 2  shows metal line  230  resting on and in interlayer dielectric  210  on substrate  205 . A top surface of metal line  230  and interlayer dielectric  210  may be planarized (e.g., by way of a chemical-mechanical polish) to achieve a uniform smoothness. Alternating layers of dielectric materials  215  and  217  are deposited on a surface of metal line  230  and interlayer dielectric  210  ( FIG. 12 , block  1301 ). The number of alternating layers of dielectric materials  215  and  217  is determined by the design parameters of the circuit. For instance, an increased stack height (e.g., more dielectric layers) tends to increase decoupling capacitance. However, increasing stack also tends to increase the capacitance for signal lines and increase delay. In the embodiment illustrated, there are three alternating layers of dielectric materials. The first deposited layer is a layer of dielectric material  217  and the final deposited layer is a layer of dielectric material  215 . Dielectric material  217  and dielectric material  215 , in one embodiment, having dissimilar etch characteristics at least for a particular etch chemistry. Representatively, dielectric material  217  and dielectric material  215  are selected such that for a selected etch chemistry, one material may be etched to the exclusion of the other or at a rate significantly greater than the other. In one embodiment, layer of dielectric material  217  may be a layer of silicon nitride (Si 3 N 4 ) and layer of dielectric material  215  may be a layer of silicon oxide (SiO 2 ) deposited respectively by chemical vapor deposition. 
     FIG. 3  is a cross-sectional schematic illustration of the structure of  FIG. 2  following, in one embodiment, forming corrugated vertical surface vias in alternating layers of dielectric materials  215  and  217 . Alternating layers of dielectric material  215  and  217  are etched with an anisotropic vertical etch to create a via hole to metal line  230  in this view ( FIG. 12 , block  1302 ). In one embodiment (where dielectric material  217  is Si 3 N 4  and dielectric material  215  is SiO 2 ), this vertical anisotropic etch may be performed by an O 2 /CH 3  plasma etch. The etch rate is on the order of about 2:1 (SiO 2 :Si 3 W 4 ). After anisotropically etching the vias into formation, an isotropic etch may then be used to form the corrugations in the vertical services of the vias resulting in corrugated vias  238  and  242  ( FIG. 12 , block  1303 ). The isotropic etch has differential etch rates depending on which material it desired to etch. In a buffered hydrofluoric acid liquid etch, the selectivity of the silicon nitride and the silicon oxide etch ratios will be approximately 100 to one. That is the silicon oxide will etch a 100 times faster then the silicon nitride in the buffered hydrofluoric acid. Thus, layers of dielectric material  215  would etch more rapidly then layers of dielectric material  217  to form the corrugations or wider lateral openings in dielectric material  215  than dielectric material  217  as shown in  FIG. 3 . One etch system that would provide this differential etch rate would be buffered hydrofluoric acid (HF). 
     FIG. 4  is a cross-sectional schematic illustration of the structure of  FIG. 3  following, in one embodiment, deposition of decoupling capacitor stack  240  ( FIG. 12 , block  1304 ). As is shown in  FIG. 1 , decoupling capacitor stack  240  comprises top electrode  214 , dielectric (capacitive) material  216  and bottom electrode  218 . Decoupling capacitor stack  240  is deposited, in this embodiment, such that each layer of the stack conforms to all of the surfaces presented for deposition including the corners and edges of corrugated vertical surfaces in vias  238  and  242 . 
   In one embodiment, decoupling capacitor stack  240  may be deposited by atomic layer chemical vapor deposition (ALCVD) in a processing chamber. In one embodiment, bottom electrode  218  of capacitor stack  240  is deposited first and may be made from either titanium nitride (TiN) or tantalum nitride (TaN) at a thickness on the order of 100 Å. ALCVD processes deposit one atomic layer at a time, therefore, exposed surfaces would be saturated with one chemical constituent either tantalum (Ta), titanium (Ti) or nitrogen (N) in an environment which would allow that constituent to bond to the exposed surface layer. The excess of that original constituent would then be swept away, for example, by a gas flow. The chemical composition of the chamber would then be altered to deposit the second constituent of the binary compound (e.g., TiN or TaN) on the monolayer of the first constituent, in this case nitrogen. These alternating atomic layers of metal and nitrogen would continue to be deposited until a sufficient thickness of TiN or TaN is formed on all exposed surfaces of integrated circuit structure  200 . 
   To form a titanium nitride (TiN) layer, a precursor chemistry of titanium chloride (TiCl 4 ) is used to saturate the surface. The TiCl 4  would be cracked to produce two chlorine molecules (Cl 2 ) which leave the exposed surface of the structure and exit the chamber through an exhaust, and one titanium (Ti) atom which bonds the surface. As long as there is surface free of Ti, the Ti continues to deposit. Once the surface is saturated with Ti, deposition ceases. Ti tends not to deposit on Ti. The surface is then ready for deposition of nitrogen. 
   Ammonia (NH 3 ) is saturated over the exposed Ti surface. The ammonia cracks to produce nitrogen (N) atoms which bond to the Ti surface and hydrogen (H 2 ) gas which leaves the surface and exits through the chamber&#39;s exhaust. Once the Ti surface is saturated with nitrogen, the nitrogen deposition tends to cease. This process is repeated until the TiN layer is sufficiently thick, for example, on the order of 100 Å. 
   When bottom electrode  218  has been deposited to satisfactory thickness, dielectric material  216  is then deposited on bottom electrode  218 . In one embodiment, dielectric material  216  is tantalum pentoxide (Ta 2 O 5 ). Tantalum pentoxide like bottom electrode  218  would be deposited one element at a time. In one embodiment, the first element to be deposited would be tantalum (Ta) and the surface would be saturated with tantalum in such condition as to allow the tantalum to bond to bottom electrode  218 . The precursor would be tantalum (TaCl 5 ) pentachloride. The excess TaCl 5  is then swept away and a saturating layer of oxygen (O) is deposited on the monolayer of tantalum. The oxygen precursor may be water (H 2 O). This process would repeat itself until sufficient thickness of tantalum pentoxide is deposited uniformly on all exposed areas of bottom electrode  218 . In one embodiment, a thickness of dielectric material  216  of tantalum pentoxide is on the order of 50 angstroms (Å). 
   Once sufficient thickness of dielectric material  216  is deposited on bottom electrode  218 , top electrode  214  is deposited on dielectric material  216 . A suitable material for top electrode  214  includes, but is not limited to, titanium nitride or tantalum nitride. In such example, the deposition would proceed similar to that of bottom electrode  218 . Alternating layers of the tantalum or titanium and nitrogen would proceed until sufficient thickness of top electrode  214  had been deposited forming coupling capacitor stack  240 . A representative thickness of top electrode  214  is on the order of 100 Å. 
     FIG. 5  is a cross-sectional schematic illustration of the structure of  FIG. 4  following, in one embodiment, the removal of capacitor stack  240  from via  238 . In this example, via  242  has decoupling capacitor stack  240  fabricated therein while via  238  allows for direct metallic contact to metal line  230 . Decoupling capacitor stack  240  is removed from those areas of structure  200  where its presence is not desired. One way to remove capacitor stack material is through a photolithographic process to expose the material desired to be removed and etching with a suitable chemistry or chemistries to remove the capacitor stack material. 
     FIG. 6  is a cross-sectional schematic illustration of the structure of  FIG. 5  following the passivation of the surface of the structure. In this example, passivation layer  220  of a dielectric material such as silicon nitride (Si 3 N 4 ) is deposited over the exposed surfaces and conforms to the corrugations of via  238  and any corrugations remaining in via  242  with the capacitor stack  240  ( FIG. 12 , block  1305 ). 
     FIG. 7  is a cross-sectional schematic diagram of the structure of  FIG. 6  following introduction of interlayer dielectric layer  280 . In one embodiment, interlayer dielectric layer  280  is deposited (e.g., by chemical vapor deposition) over the entire structure. A suitable dielectric material for interlayer dielectric layer  280  is SiO 2  deposited to a layer thickness on the order of 1 micron. Following deposition, the superior (as viewed) exposed surface of interlayer dielectric  210  may be planarized such as by a chemical-mechanical polish. 
     FIG. 8  is a cross-sectional schematic illustration of the structure of  FIG. 7  following the formation of vias and trench openings (e.g., when following a Damascene process) in interlayer dielectric layer  280 . Vias  338  and  342 , respectively, are formed, for example, by photolithographic and etch processes, in areas at least partially aligned, in this example, with via  238  and via  242 , respectively (see, e.g.,  FIG. 6 ). Trenches  345  and  350  are etched into interlayer dielectric layer  280  to a depth suitable for a portion of a metallization layer or line. Via  342  defines an opening through a interlayer dielectric layer  280  to decoupling capacitor stack  240 . Via  338  forms an opening to metal line  230 . 
     FIG. 9  is a schematic cross-section illustration of the structure of  FIG. 8  following the introduction of conductive (e.g., metal) material to form metal lines  243  and  240  ( FIG. 12 , block  1306 ). A suitable material in the described process is copper or a copper alloy. It is appreciated that vias  338 ,  342  and trench  345 ,  350  may first be lined with one or more barrier materials. Metal line  243  forms a decoupling contact with metal line  230  through decoupling capacitor stack  240  by way of conductive via  342 . Metal line  241  makes a direct metallic contact to metal line  230  through conductive via  338 . In the embodiment where metal line  230  is a V CC  line, metal line  241  is a V CC  transmission line, and metal line  243  may be a V SS  transmission line. Metal line  243  also contacts decoupling capacitor stack  240 . This configuration tends to improve strapping (or lower resistance) of the electrode (e.g., top electrode as viewed). 
   A metallization process that is sometimes referred to as a full Damascene process has been described in relation to forming a metal layer or line. Various other embodiments contemplate among other possible processes, including a partial Damascene process whereby a plug (e.g., tungsten plug) is formed in a via and a copper material is deposited in a trench in an interlayer dielectric, or formation of a conductive via in an interlayer dielectric material and depositing and patterning metal lines (e.g., an aluminum or aluminum alloy material) on a surface of the interlayer dielectric. 
     FIG. 10  is a cross-sectional schematic illustration of a contemplated embodiment of the structure formed according to  FIGS. 2-9 . In this embodiment, metal line  230 A, a V SS  line, is decouply connected to metal line  243  which is a V CC  line via the decoupling capacitor stack  240  (including top electrode  214 , dielectric material  216  and bottom electrode  218 ). Multiple vias are etched through interlayer dielectric  210  placed over metal line  230 A and the decoupling capacitor stack is conformally deposited within these vias. Metal line  230 B and metal line  241  define a V SS . 
     FIG. 11  is a cross-sectional schematic illustration of one embodiment of an enhanced area vertical decoupling capacitor stack. A series of alternating metal depositions are formed in via  1252  on metal line  1230 . In one embodiment, metal layers  1212  comprise a metal while metal layers  1215  comprise a metal nitride compound. The metal/metal nitride compound may consist of tantalum or titanium/tantalum nitride or titanium nitride. Layers  1212  and  1215  are deposited and patterned of altering widths (x and z direction widths) with, in this example, layers  1215  being wider in an x-direction than layers  1215 . Layers  1212  and  1215  may be patterned in this manner by photolithographic and etch techniques. By using different materials for layer  1212  and layer  1215 , the layers may be selectively patterned. Once the alternating metal nitride via stack is deposited to a sufficient thickness, a differential etch is used to create the corrugations in the side of the stack. Decoupling capacitor stack  1240  is then conformally deposited on the surface of the stack, including on the corrugated surface of the stack. Interlayer dielectric layer  1280  is deposited to surround the stack and the capacitor and a via is etched through interlayer dielectric layer  1280  to allow placement of via metal  1242 . 
   Table 1 illustrates the enhancement of capacitive area in a decoupling capacitor using a corrugated surface structures such as described herein. Column one in Table 1 describes the number of layers of alternating dielectric material deposited on a metal line. Column two displays the area multiplier of that number of layers of alternating dielectric material given a 500 Å undercut. Column three gives the area multiplier associated with that number of layers given a 1000 Å undercut. The data in Table 1 is premised on an embodiment having vias with an area of one by one square micron and a depth of approximately one micron. 
   In an embodiment where there are 100 vias over a 20 micron by 20 micron area a planer capacitor (that is a capacitor having no vias) would have a capacitive area of 400 square microns. The capacitive area of the decoupling capacitor generated by hauling 100 one by one micron vias with a depth of one micron would be equal to 400 square microns plus the product of (four sides per via×one square micron per side×100 vias) which would equal 800 square microns. In the embodiment where the vias are corrugated with for example, 10 layers of alternating interlayer dielectric material and a 1000 Å undercut, Table 1 discloses area multiplier for this embodiment of two. The total capacitive area available in this embodiment is calculated by adding 400 square microns from the planer capacitor to the product of (four sides per via×one square micron per side×the area enhancement factor of two×100 vias) this product is 800 square microns which added to 400 square microns gives a total capacitive are available of 1200 square microns. 
   
     
       
             
             
             
           
             
             
             
           
         
             
               TABLE 1 
             
             
                 
             
             
               Number of layers 
               500 Å undercut 
               1000 Å undercut 
             
             
                 
             
           
           
             
                 
             
           
        
         
             
               2 
               1.1 
               1.2 
             
             
               4 
               1.2 
               1.4 
             
             
               6 
               1.3 
               1.6 
             
             
               8 
               1.4 
               1.8 
             
             
               10 
               1.5 
               2.0 
             
             
               12 
               1.6 
               2.2 
             
             
               14 
               1.7 
               2.4 
             
             
               16 
               1.8 
               2.6 
             
             
               18 
               1.9 
               2.8 
             
             
               20 
               2.0 
               3.0 
             
             
                 
             
           
        
       
     
   
   In the preceding detailed description, the invention is described with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made thereto without departing from the broader spirit and scope of the invention as set forth in the claims. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.