Patent Publication Number: US-6984874-B2

Title: Semiconductor device with metal fill by treatment of mobility layers including forming a refractory metal nitride using TMEDT

Description:
This application is a divisional of U.S. application Ser. No. 10/280,427, filed on Oct. 25, 2002 now U.S. Pat. No. 6,812,139, issued Nov. 2, 2004, which is a continuation of U.S. application Ser. No. 09/428,159, filed on Oct. 27, 1999, now U.S. Pat. No. 6,482,735 B1, issued Nov.  19, 2002, which is a divisional of U.S. application Ser. No.  09/248,499, filed on Feb. 10, 1999, now U.S. Pat. No. 6,057,231, issued May 2, 2000, which is a divisional of U.S. application Ser. No. 08/942,811, filed on Oct. 2, 1997, now U.S. Pat. No. 6,054,768, issued Apr.  25, 2000, all of which are incorporated herein by reference.   

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to a high-aspect ratio contact in a semiconductor device and a method of forming the same. In particular, the present invention relates to formation of a contact in a semiconductor device with a refractory metal and a refractory metal nitride liner that assists in filling of a contact hole in which the contact is situated. More particularly, the present invention relates to an aluminum or aluminum alloy-filled contact plug that fills a contact hole in a semiconductor device that is lined with a titanium layer and at least one titanium nitride layer. The titanium and the first of the at least one titanium nitride layers are formed by chemical vapor deposition. Subsequently formed titanium nitride layers, if any, are formed by physical vapor deposition (PVD). 
   2. Background Technology 
   In the microelectronics industry, a substrate refers to one or more semiconductor layers or structures that include active or operable portions of semiconductor devices. In the context of this document, the term “semiconductor substrate” is defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive material such as a semiconductive wafer, either alone or in assemblies comprising other materials thereon, and semiconductive material layers, either alone or in assemblies comprising other materials. The term “substrate ” refers to any supporting structure including, but not limited to, the semiconductive substrates described above. 
   In the fabrication of semiconductor devices, metal contacts are formed over semiconductor substrates that have been processed to form devices connected to each other to form integrated circuits. In particular, aluminum and aluminum alloy lines have been deposited into vias and other recesses such as trenches and contact corridors. This method of metallization is used generally in the microelectronics industry. However, as devices have been miniaturized due to requirements for a higher device density on a semiconductor substrate and a smaller device, the recesses to be filled have higher aspect ratios, where an aspect ratio is the depth of the recess divided by the width thereof. 
   One need for higher aspect ratio recesses is the formation of deeper contacts where, for example, a stacked capacitor for a dynamic random access memory (DRAM) is formed and then covered over by a dielectric layer. For such a stacked DRAM capacitor, a contact with an aspect ratio greater than 5:1 would need to be formed in two steps using known prior art processes. Such prior art processing produces a conductive structure having two interconnect halves with a physical seam therebetween. Typically, the two interconnect halves have a width or cross-sectional footprint of about 0.35 microns or smaller. Alignment of the small footprint interconnect halves is problematic at best, and fabrication yield with such a process prerequisite is undesirable. Also undesirable is an increased resistivity caused by the physical seam between the two interconnect halves. 
   Difficulties have been encountered in depositing aluminum lines and contacts by conventional sputtering processes when submicron high-aspect ratio recesses are to be filled. As a recess is made smaller and deeper (i.e., higher aspect ratio), the bottom and sides of the recess will receive less sputtered target material than the opening to the recess. Additional sputtering will result in a detrimental phenomena known as bread loafing where a layer of sputtered target material closes off the opening to the recess. Thus over time, the bottom and sides of the recess receive inadequate amounts of the sputtered metal material and the sputtered metal material overhangs and closes over the opening to the recess before the recess is substantially filled. 
   While the aluminum and the silicon in the semiconductor substrate must be electrically connected, it has become useful to use intermediate layers to provide better electrical connection to the silicon and to provide a metallurgical barrier between silicon and aluminum to prevent spiking of the aluminum into the silicon. Spiking can interfere with the performance and reliability of the integrated circuit. Conventionally, one method which has been used to accomplish the metallurgical barrier has been to form a layer of titanium over a semiconductor substrate at the interconnect-exposed site. Titanium silicide is then formed at the interconnect-exposed site and a titanium nitride layer is formed elsewhere, in that the titanium layer is exposed to a nitrogen atmosphere. While this method forms a metallurgical barrier between silicon and aluminum to prevent spiking, it often is inadequate to form the titanium nitride barrier because of the competing simultaneous formation of titanium silicide and titanium nitride at the titanium region that covers the exposed semiconductor substrate site. 
   One prior art solution to this inadequate prior art method has been to form the titanium silicide barrier layer first and then to sputter additional titanium nitride over the titanium silicide or titanium silicide/titanium nitride layer. In this way, a sufficient thickness of titanium nitride may be formed to provide a desired thickness in a barrier layer. 
   As stated, sputtered layers of titanium nitride have been used in integrated circuits as barrier layers for recesses, such as contact holes, vias, and interconnects. Sputter deposited titanium nitride, however, is not very conformal and its step coverage within high-aspect ratio recesses is poor. As such, there results an unacceptably thin or discontinuous titanium nitride barrier layer for a high-aspect ratio recess. 
   As aspect ratios have been increasing for recesses in microelectronic devices, the need for substantial recess filling with sputtered aluminum and aluminum alloy metallization material has proved inadequate in spite of improved titanium nitride barrier layers. While high pressure and/or high temperature aluminum reflow recess filling techniques have been developed, a substantially filled recess having an aspect ratio exceeding 5:1 has been difficult or impractical to achieve. 
   It has been proposed to form a titanium nitride layer in the recess by chemical vapor deposition (CVD), for example, by using titanium tetrachloride (TiCl 4 ) in the presence of NH 3 , H 2 , and Ar. Although the TiCl 4  CVD process has improved reflow techniques, substantially filled recesses with aspect ratios greater than about 5:1 have been elusive. One problem that has been experienced is that aluminum reflow requires a substantially pristine refractory metal nitride surface, whereas interstitial titanium nitride layer impurities incident to the TiCl 4  CVD process have caused the aluminum to become impure. As a result, aluminum loses its relatively low-friction flowing or sliding ability over the impure titanium nitride layer. 
   Methods have been proposed to drive the interstitial impurities out of the titanium nitride layer by using thermal energy, but the thermal limit or budget of the fabrication process must be monitored so as avoid a yield decrease. Additionally, it has been observed that a thermal cleansing of the titanium nitride layer leaves significant voids in the titanium nitride layer that also resists flow of the aluminum thereacross. Attempts have been made to “stuff” the interstices in the titanium nitride layer with nitrogen. Even with a stuffing technique, however, substantially filled recesses with aspect ratios that exceed 5:1 are not readily realized. 
   What is needed is a method of lining and substantially filling a high-aspect ratio recess with aluminum metallization or equivalents in microelectronic device fabrication where the aspect ratio of the recess exceeds 5:1. What is also needed is a method of forming a high-aspect ratio structure that allows for a taller microelectronic component, such as a taller stacked DRAM capacitor, where the interconnect to the stacked DRAM capacitor is unitary and formed by a single recess filling process. 
   SUMMARY OF THE INVENTION 
   The present invention relates to a substantially filled recess in a semiconductor structure, where the recess has a height-to-width aspect ratio in a range from about 6:1 to about 10:1, and where the width is about 0.35 microns or smaller. The process steps and achieved structure in accordance with an embodiment of the invention comprise an interconnect in a recess having an aspect ratio that exceeds about 6:1. The recess, for example, can be a via, a trench, a contact corridor, or a combination thereof. In a first embodiment of the present invention, the recess is a contact hole that is substantially filled by first performing a surface pre-cleaning of the contact hole followed by degassing. Following degassing, a refractory metal layer is formed, and a refractory metal nitride layer is formed on the refractory metal layer. A heat treatment step, preferably by rapid thermal processing (RTP), is used to secure a refractory metal silicide contact upon semiconductor material such as silicon at the bottom of the contact hole. 
   At least two alternative methods may be carried out after heat treatment. In a first alternative, a high-temperature NH 3  treatment is carried out to remove undesirable impurities within the contact hole and to replace the impurities in the refractory metal nitride layer with more nitrogen. In the second alternative, a second refractory metal nitride layer is formed by PVD upon the first refractory metal nitride layer. In either alternative, a metallization layer is deposited within the contact hole. Preferably, aluminum is used in a fast metallization deposition technique and alternatively, by use of elevated temperatures to substantially fill the contact hole with aluminum. High pressure and temperature can also be used in combination in the inventive method to substantially fill the contact hole with aluminum. 
   In yet another embodiment of the present invention, the steps of precleaning, degassing, and deposition of a refractory metal layer are accomplished as set forth above. Deposition of the first refractory metal nitride layer is accomplished using trimethylethylenediamine tris (dimethylamino) titanium (TMEDT). Use of TMEDT allows for a higher density of titanium and nitrogen to form in the contact hole than that achieved in previous metal-organic deposition techniques. The aspect ratio achieved by a TMEDT-deposited refractory metal nitride layer and the subsequent deposition of a second refractory metal nitride layer by PVD may exceed 8:1. 
   Following filling of the contact hole, residual surface metallization may be entirely removed by techniques, such as etchback, or by a planarization technique, such as chemical mechanical planarization (CMP). Partial CMP of the surface metallization may be carried out, wherein a portion of the surface metallization remains to be patterned and treated to form metallization lines. CMP of the surface metallization assists in preventing unwanted reflective characteristics. 
   These and other features of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In order to illustrate the manner in which the above-recited and other advantages of the invention are obtained, a more particular description of the invention briefly described above will be rendered by reference to specific embodiments thereof which are illustrated in the appended drawings. The accompanying drawings, although illustrative of the inventive methods and structures, are not to be construed as dimensionally precise as to both methods and structures. Understanding that these drawings depict only typical embodiments of the invention and are not, therefore, to be considered limiting of its scope, the invention will be described and explained with additional specificity and detail through the use of the accompanying drawings in which: 
       FIG. 1  is an elevational cross-section illustration of a semiconductor structure having a trench above a contact hole, where the contact hole terminates at an exposed surface on an active area. 
       FIG. 1A  is an elevational cross-section illustration of an alternative embodiment of FIG.  1 . 
       FIGS. 1B through 1D  are partial top plan views of alternative embodiments of a semiconductor structure having a trench above a contact hole. 
       FIG. 2  is an illustration of the semiconductor structure depicted in  FIG. 1  in which a refractory metal layer has been deposited that covers the trench, the contact hole, and the exposed active area surface. 
       FIG. 3  illustrates further processing of the semiconductor structure depicted in  FIG. 2 , in which a first refractory metal nitride layer has been deposited substantially conformably over the refractory metal layer, and a heat treatment has induced formation of a refractory metal silicide layer upon the exposed surface of the active area at the terminal end of the contact hole. 
       FIG. 4  illustrates further processing of the semiconductor structure depicted in  FIG. 3 , including formation of a metallization layer to cover the opening to the trench and contact hole. 
       FIG. 5  illustrates further processing of the semiconductor structure depicted in  FIG. 4 , and also illustrates an article of manufacture embodiment achieved by the inventive method, wherein the trench and contact hole have been substantially filled with a metallization layer by the inventive method to form a contact plug, and wherein a selected thickness of the metallization layer remains above the trench upon the semiconductor structure. 
       FIG. 6  is an elevational cross-section illustration of processing according to the inventive method for recess filling according to another embodiment of the inventive method, wherein the recess is a contact hole having a refractory metal layer that lines the wall of the contact hole within a semiconductor structure, the refractory metal layer having been superposed by a first and a second refractory metal nitride layer, and wherein a metallization layer has been formed that substantially covers over the opening to the contact hole. 
       FIG. 7  illustrates further processing of the structure depicted in  FIG. 6 , wherein the contact hole has been substantially filled with the metallization layer to form a contact plug by increased pressure and/or temperature, and wherein a selected thickness of the metallization layer remains above the contact hole upon the semiconductor structure. 
   

   DETAILED DESCRIPTION OF THE INVENTION 
   The present invention relates to formation of a metal-filled recess in a semiconductor structure, where the recess has a height-to-width aspect ratio in a range from about 6:1 to about 10:1, and where the width is about 0.35 microns or smaller. The inventive method is carried out by formation of preferred liner layers within the recess and by force-filling the recess with a metallization layer that flows over and moves across the preferred liner layers to facilitate substantial filling of the recess.  FIGS. 1 through 5  are cross-sectional views of a semiconductor structure being subjected to process steps in accordance with an embodiment of the invention, wherein an inventive interconnect is formed as part of the semiconductor structure. 
   In  FIG. 1 , a semiconductor structure  10  is illustrated, comprising a semiconductor substrate  12  and an active area  22 . A dielectric layer  14  has been deposited over, by way of non-limiting example, a gate stack that is generally seen at reference numeral  20 . Gate stack  20  is situated upon semiconductor substrate  12 . Alternatively, semiconductor structure  10  (and semiconductor substrate  12  therein) may, for example, comprise a polysilicon layer formed over other layers of a semiconductor structure to provide electrical contact to an active device. Semiconductor structure  10  may also comprise some other type of polysilicon-connecting interconnecting structure. 
   In dielectric layer  14 , etching has formed a trench  16  and a contact hole  18 . Semiconductor structure  10  has a first exposed surface  40  that includes the surface-defining trench  16  and contact hole  18  with an exposed surface  52  on active area  22  at the bottom of contact hole  18 . Dielectric layer  14  has a top surface above a recess, where the recess includes trench  16  and contact hole  18 . Contact hole  18  extends from an exposed portion of semiconductor substrate  12  to terminate at an opening to contact hole  18  below the top surface of dielectric layer  14 . Trench  16  is elongated and extends from a trench opening at the top surface of dielectric layer  14  to terminate at the contact hole opening below the top surface of dielectric layer  14 . 
   Two alternative embodiments for the respective dimensions of trench  16  and contact hole  18  are contemplated. In the first alternative seen in  FIG. 1 , the opening to trench  16  has a width that is wider than the width of the opening to contact hole  18 , and trench  16  has a length that is substantially parallel to semiconductor substrate  12 , which length can exceed the width of the opening to contact hole  18 .  FIG. 1B  shows a top plan view of FIG.  1 . In the second alternative seen in  FIG. 1A , the opening to trench  16  has a width that is equal to the width of the opening to contact hole  18 , and trench  16  has a length that is substantially parallel to semiconductor substrate  12 , which length is greater than the width of the opening to contact hole  18 .  FIG. 1C  is a top plan view of FIG.  1 A.  FIG. 1D  is a top plan view of a contact hole extending from first exposed surface  40  to exposed surface  52  on active area  22 , where the width of the opening to contact hole  18  is shorter than the length of trench  16  and wider than the width of trench  16 . Processing of the structures seen in  FIGS. 1A-1D  are contemplated to be as would the processing for the structures seen in  FIGS. 2-7 . In general, the invention contemplates that the width of the trench can be less than or equal to the width of the opening to the contact hole. The length of the trench, however, must be greater than the width of the opening to the contact hole. 
   In a first embodiment of the present invention, trench  16  and contact hole  18  are filled by first performing a surface pre-cleaning upon semiconductor structure  10 . Precleaning can be by an HF dip, for example, in a 100:1 aqueous solution for about 30 seconds. The HF dip is followed by a degassing process in which semiconductor structure  10  is placed in a chamber in where it is subjected to a vacuum and elevated temperatures. 
   Following the degassing process, a first layer is formed upon first exposed surface  40 . The first layer is seen in  FIG. 2  as a refractory metal layer  24  that is composed of titanium, although other refractory metals could also used. Deposition of refractory metal layer  24  is preferably accomplished by chemical vapor deposition (CVD). The thickness of the refractory metal is dependent upon the specific application for forming a contact to the active area within the recess. A preferred thickness range of refractory metal layer  24  when refractory metal layer  24  comprises titanium, is from about 0 Å to about 400 Å, a more preferred thickness is from 100 Å to about 300 Å, and a most preferred thickness is about 200 Å. 
     FIG. 3  illustrates a first metal nitride layer  26  formed by CVD. First metal nitride layer  26  may be formed in the same chamber used for formation of refractory metal layer  24  and can be composed of refractory metal nitrides of titanium, cobalt, tungsten, and the like. First metal nitride layer  26  may be formed. Care must be taken that refractory metal layer  24  does not prematurely form a refractory metal silicide layer  30  which is needed later on in the fabrication process to form a desired metallurgical junction. 
   Following formation of first metal nitride layer  26 , a heat treatment, preferably by rapid thermal anneal (RTA), causes a reaction of active area  22  with the silicon in semiconductor substrate  12  of exposed surface  52  so as to form refractory metal silicide layer  30  at the bottom of contact hole  18 . As such, refractory metal silicide layer  30  forms a metallurgical junction between semiconductor substrate  12  and the eventual contact plug that will fill contact hole  18 . In the processing of semiconductor structure  10 , wherein refractory metal layer  24  is comprised substantially of titanium and wherein at least first metal nitride layer  26  is comprised substantially of titanium nitride, RTA preferred temperature is in a range from about 100° C. to about 660° C. for a processing time in a range from about 10 seconds to about 60 seconds. 
   Impurities that may exist within a wall  50  of first metal nitride layer  26  that lines trench  16  and contact hole  18  can be removed by an ammonia high-temperature treatment. Such impurities can be introduced to wall  50  incident to formation of first metal nitride layer  26 . The high-temperature treatment effectively displaces impurities on wall  50  with more nitrogen from the ammonia gas in the ammonia high-temperature treatment. The ammonia high-temperature treatment is preferably conducted at temperatures in a range from about 100° C. to about 500° C., more preferably in a range from about 200° C. to about 400° C., and most preferably about 300° C. Ammonia treatment may be carried out with or without conventional plasma assistance. 
   Following the ammonia high-temperature treatment, an aluminum layer  28  seen in  FIG. 4  is deposited over trench  16  and contact hole  18 . With respect to underlying materials, for example, Al, an AlCuSi alloy, or AlCu alloy can be deposited over titanium nitride. As can be seen in  FIG. 4 , aluminum layer  28  does not substantially fill contact hole  18 . A preferred thickness of the deposited aluminum layer  28  is in a range from about 0.5 micrometers to about 2.0 micrometers, or more preferably about 0.5 micrometers to about 1.7 micrometers. 
   Preferably, aluminum layer  28  is formed by a fast metallization deposition technique, such as a fast alloy physical vapor deposition (PVD) technique. The process for forming aluminum layer  28  can also be accompanied by elevated temperatures. Preferable conditions for the deposition of aluminum layer  28  can be set forth in two (2) protocols. In a first protocol for PVD formation of aluminum layer  28 , the energy range is from about 0.5 kW to about 5 kW, preferably from about 1 kW to about 3.5 kW, and most preferably from about 1 kW to about 2 kW. Also in the first protocol, the temperature during the PVD process is in a range from about 350° C. to about 600° C., more preferably from about 400° C. to about 575° C., and most preferably from about 450° C. to about 550° C. In a second protocol for the PVD formation of aluminum layer  28 , the energy range is from about 10 kW to about 14 kW, preferably about 11 kW to about 13 kW, and most preferably about 12 kW. Also in the second protocol, the temperature during the PVD process is in a range from about 400° C. to about 550° C., more preferably from about 450° C. to about 510° C., most preferably about 480° C. 
     FIG. 5  illustrates an achieved article of manufacture that, by way of non-limiting example, is a bit line that extends from a trench to active area  22  between two gate stacks  20 . Substantial filling of trench  16  and contact hole  18  with aluminum layer  28  is realized by the preferred liner layers of refractory metal layer  24  and first metal nitride layer  26  which are low in impurities. These preferred liner layers, in combination with high pressure and high temperature, allow aluminum layer  28  to realize a relatively low-friction flowing or sliding motion into trench  16  and contact hole  18  so as to substantially fill the same. In a preferred embodiment where the refractory metal layer is Ti and first metal nitride layer  26  is TiN treated with a high-temperature ammonia treatment, both trench  16  and contact hole  18  are substantially filled at a temperature of about 520° C. and at a pressure of about 750 atmospheres, which temperature and pressure is held for a duration of about four minutes. 
   For the trench over contact hole structure known as a dual damascene structure seen in  FIG. 5 , second refractory metal nitride layer  32 , as seen in  FIG. 6  or  7 , can be formed upon first metal nitride layer  26 , and is preferably formed from titanium nitride in a thickness range of from about 1,500 Å to about 2,500 Å, more preferably from about 1,750 Å to about 2,250 Å, and most preferably about 2,000 Å. Aluminum layer  28 , as seen in  FIG. 4 , is formed correspondingly in a thickness range from about 1.2 microns to about 2.2 microns, more preferably from about 1.5 microns to about 1.9 microns, and most preferably about 1.7 microns. 
     FIG. 6  illustrates, by way of non-limiting example, partial formation of a contact plug in a high-aspect ratio contact hole  18 . Following a degassing process as described above, a second refractory metal nitride layer  32  is formed substantially over first metal nitride layer  26 .  FIG. 6  illustrates further processing of contact hole  18  wherein second refractory metal nitride layer  32  is formed by PVD. In  FIG. 6 , semiconductor structure  10  has been built up with refractory metal layer  24  that is in contact with dielectric layer  14 . Upon refractory metal layer  24 , first metal nitride layer  26  has been formed upon a second upper surface  42  of refractory metal layer  24 . Upon first metal nitride layer  26 , second refractory metal nitride layer  32  has been deposited by PVD and substantially covers a third upper surface  44  of first metal nitride layer  26 . It can be seen that second refractory metal nitride layer  32  has thereupon a fourth upper surface  46 . PVD formation of second refractory metal nitride layer  32 , under conditions used in the present invention, cause it to be thicker above dielectric layer  14  than along the vertical walls of contact hole  18 , although it may be as thick at the bottom of contact hole  18  above refractory metal silicide layer  30 . Various conventional PVD techniques can be used to achieve a uniform thickness of second refractory metal nitride layer  32 , including “long throw” collimator techniques, and the like. 
   Following PVD formation of second refractory metal nitride layer  32 , aluminum layer  28  is formed over contact hole  18  as seen in FIG.  6 . Pressure filling of contact hole  18  is accomplished according to the method of the present invention as set forth previously. Preferably, recesses will be substantially filled with aluminum or alloys thereof under the inventive method by applying for a duration in a range from about 1 second to about 500 seconds at least one of pressure in the range of from about 450 atmospheres to about 1,050 atmospheres and heat in the range of from about 100° C. to about 700° C. 
   For the partial contact plug structure seen in  FIG. 6 , second refractory metal nitride layer  32  is preferably formed from titanium nitride in a thickness range from about 1,000 Å to about 2,000 Å, more preferably about 1,250 Å to about 1,750 Å, and most preferably about 1,500 Å. Aluminum layer  28  is formed correspondingly in a thickness range from about 0.8 microns to about 1.6 microns, more preferably from about 1.0 microns to about 1.4 microns, and most preferably about 1.2 microns. 
   After aluminum layer  28  has substantially filled a recess, as shown in either of  FIG. 5  or  7  at  34 / 36  or  34 , respectively, surface metallization  38  may be entirely removed by techniques, such as etchback, or a planarizing process, such as chemical mechanical planarization (CMP). Partial CMP of surface metallization  38  may be carried out, wherein a portion of surface metallization  38  remains to be patterned and further treated to form metallization lines having a fifth upper surface  48 . CMP of surface metallization  38  assists in preventing unwanted reflective characteristics of surface metallization  38  when it is not substantially planar. 
   In another embodiment of the present invention, formation of the first metal nitride layer  26  is accomplished by the use of titanium tetrachloride (TiCl 4 ) in the presence of NH 3 , H 2 , and Ar. More preferably, an organometallic complex of titanium called tetrakis(dimethylamino) titanium (TDMAT) is used. TDMAT allows for a denser occurrence of both titanium and nitrogen in a titanium nitride layer according to formation of first metal nitride layer  26 . TDMAT may be used in any embodiment of the present invention for CVD formation of first metal nitride layer  26 . Other organometallic complexes may be used in the present invention with varying degrees of titanium and nitrogen density achieved in forming first metal nitride layer  26 . The embodiment uses a degas step to remove any unwanted elements or compounds that reside in wall  50 , whereas the first embodiment uses an NH 3  high-temperature treatment to remove impurities from wall  50 . 
   In yet another embodiment of the present invention, the steps of precleaning, degas, and deposition of refractory metal layer  24  are accomplished as set forth above. Deposition of first metal nitride layer  26  is accomplished using trimethylethylenediamine tris(dimethylamino) titanium (TMEDT). Use of TMEDT allows for a higher percentage of titanium and nitrogen in a denser occurrence to deposit than in previous metal-organic deposition techniques. The aspect ratio of recesses that can be achieved when first metal nitride layer  26  is formed by TMEDT and the subsequent deposition of second refractory metal nitride layer by PVD, or the subsequent NH 3  treatment, can exceed about 6:1, for example about 7:1, about 8:1, about 9:1, and about 10:1. The first metal nitride layer preferably has a thickness from about 100 Å to about 500 Å. 
   Use of TMEDT may be applied in any embodiment of the present invention to assist in achieving a high-aspect ratio recess. TMEDT or TDMAT or a combination thereof may be used as set forth above. For example, a ratio of about 10:1 TMEDT:TDMAT may be used. Other preferred ratios include about 8:1, 6:1, 4:1, 2:1, 1:1, 1:2, 1:4, 1:6, 1:8, and about 1:10. 
   Although  FIGS. 5 and 7  illustrate distinct layers, such as refractory metal layer  24 , first metal nitride layer  26  and second refractory metal nitride layer  32 , it is understood that processing of semiconductor structure  10  may make residual signs of these layers difficult to detect when forensically examined due to processing that causes intermixing of these layers with neighboring structures. 
   The present invention may be embodied in other specific forms without departing from its spirit or essential characteristics. The described embodiments are to be considered in all respects only as illustrative and not restrictive. The scope of the invention is, therefore, indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are to be embraced within their scope.