Abstract:
A method of forming a self-aligned non-volatile device, includes, in part: forming trench isolation regions, forming a well between the trench isolation, forming a second well above the first well, forming a first oxide layer above a first portion of the second well, forming a first dielectric, a first polysilicon gate, and a second dielectric layer, respectively, above the first polysilicon layer, forming a first spacer above the body region and adjacent the first polysilicon layer, forming a second oxide layer above a second portion of the second well not covered by the first spacer, forming a second polysilicon gate layer above the second oxide layer, the first spacer and a portion of the second dielectric layer, removing the second polysilicon layer and the layers below it that are exposed in a via formed using a mask, thereby forming self-aligned source/drain regions.

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present application is related to copending application Ser. No. 10/447,715, filed on May 28, 2003, entitled “Method Of Manufacturing Non-Volatile Memory Device”, assigned to the same assignee, and incorporated herein by reference in its entirety. 
     The present application is also related to copending application Ser. No. 10/394,417, filed on Mar. 19, 2003, entitled “Non-Volatile Memory Device”, assigned to the same assignee, and incorporated herein by reference in its entirety. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to semiconductor integrated circuits. More particularly, the invention provides a semiconductor memory that has integrated non-volatile and static random access memory cells. Although the invention has been applied to a single integrated circuit device in a memory application, there can be other alternatives, variations, and modifications. For example, the invention can be applied to embedded memory applications, including those with logic or micro circuits, and the like. 
     Semiconductor memory devices have been widely used in electronic systems to store data. There are generally two types of memories, including non-volatile and volatile memories. The volatile memory, such as a Static Random Access Memory (SRAM) or a Dynamic Random Access Memory (DRAM), loses its stored data if the power applied has been turned off. SRAMs and DRAMs often include a multitude of memory cells disposed in a two dimensional array. Due to its larger memory cell size, an SRAM is typically more expensive to manufacture than a DRAM. An SRAM typically, however, has a smaller read access time and a lower power consumption than a DRAM. Therefore, where fast access to data or low power is needed, SRAMs are often used to store the data. 
     Non-volatile semiconductor memory devices are also well known. A non-volatile semiconductor memory device, such as flash Erasable Programmable Read Only Memory (Flash EPROM), Electrically Erasable Programmable Read Only Memory (EEPROM) or, Metal Nitride Oxide Semiconductor (MNOS), retains its charge even after the power applied thereto is turned off. Therefore, where loss of data due to power failure or termination is unacceptable, a non-volatile memory is used to store the data. 
     Unfortunately, the non-volatile semiconductor memory is typically slower to operate than a volatile memory. Therefore, where fast store and retrieval of data is required, the non-volatile memory is not typically used. Furthermore, the non-volatile memory often requires a high voltage, e.g., 12 volts, to program or erase. Such high voltages may cause a number of disadvantages. The high voltage increases the power consumption and thus shortens the lifetime of the battery powering the memory. The high voltage may degrade the ability of the memory to retain its charges due to hot-electron injection. The high voltage may cause the memory cells to be over-erased during erase cycles. Cell over-erase results in faulty readout of data stored in the memory cells. 
     The growth in demand for battery-operated portable electronic devices, such as cellular phones or personal organizers, has brought to the fore the need to dispose both volatile as well as non-volatile memories within the same portable device. When disposed in the same electronic device, the volatile memory is typically loaded with data during a configuration cycle. The volatile memory thus provides fast access to the stored data. To prevent loss of data in the event of a power failure, data stored in the volatile memory is often also loaded into the non-volatile memory either during the configuration cycle, or while the power failure is in progress. After power is restored, data stored in the non-volatile memory is read and stored in the volatile memory for future access. Unfortunately, most of the portable electronic devices may still require at least two devices, including the non-volatile and volatile, to carry out backup operations. Two devices are often required since each of the devices often rely on different process technologies, which are often incompatible with each other. 
     To increase the battery life and reduce the cost associated with disposing both non-volatile and volatile memory devices in the same electronic device, non-volatile SRAMs and non-volatile DRAMs have been developed. Such devices have the non-volatile characteristics of non-volatile memories, i.e., retain their charge during a power-off cycle, but provide the relatively fast access times of the volatile memories. As merely an example,  FIG. 1  is a transistor schematic diagram of a prior art non-volatile DRAM  10 . Non-volatile DRAM  10  includes transistors  12 ,  14 ,  16  and EEPROM cell  18 . The control gate and the drain of EEPROM cell  18  form the DRAM capacitor. Transistors  12  and  14  are the DRAM transistors. Transistor  16  is the mode selection transistor and thus selects between the EEPROM and the DRAM mode. 
       FIG. 2  is a transistor schematic diagram of a prior art non-volatile SRAM  40 . Non-volatile SRAM  40  includes transistors  42 ,  44 ,  46 ,  48 ,  50 ,  52 ,  54 ,  56 , resistors  58 ,  60  and EEPROM memory cells  62 ,  64 . Transistors  48 ,  50 ,  52 ,  54  and resistors  58 ,  60  form a static RAM cell. Transistors  42 ,  44 ,  46 ,  56  are select transistors coupling EEPROM memory cells  62  and  64  to the supply voltage Vcc and the static RAM cell. Transistors  48  and  54  couple the SRAM memory cell to the true and complement bitlines BL and {overscore (BL)}. 
     EEPROM  18  of non-volatile DRAM cell  10  ( FIG. 1 ) and EEPROM  62 ,  64  of non-volatile SRAM cell  40  ( FIG. 2 ) may consume a relatively large semiconductor area and may thus be expensive. Moreover, they may also require a high programming voltage and thus may suffer from high-voltage related stress. Accordingly, a need continues to exist for a relatively small non-volatile memory device that, among other things, is adapted for use in a non-volatile SRAM or DRAM and consume less power than those known in the prior art. 
     While the invention is described in conjunction with the preferred embodiments, this description is not intended in any way as a limitation to the scope of the invention. Modifications, changes, and variations, which are apparent to those skilled in the art can be made in the arrangement, operation and details of construction of the invention disclosed herein without departing from the spirit and scope of the invention. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, a method of forming a self-aligned non-volatile semiconductor device, includes, in part, the steps of: forming at least two trench isolation regions in the semiconductor substrate, forming a first well between the two trench isolation regions, forming a second well between the two trench isolation regions and above the first well to define a body region, forming a first oxide layer above a first portion of the body region, forming a first dielectric layer above the first oxide layer, forming a first polysilicon layer—that forms a control gate of a non-volatile device—above the first dielectric layer, forming a second dielectric layer above the first polysilicon layer, forming a first spacer above the body region and adjacent said first polysilicon layer, forming a second oxide layer above a second portion of the body region that is not covered by the first spacer, forming a second polysilicon layer—that forms a guiding gate of the non-volatile device—above the second oxide layer, the first spacer and the second dielectric layer; forming a masking layer over the second polysilicon layer; forming a via positioned above the first portion of the body region in the masking layer, removing the second polysilicon layer, the second dielectric layer, the first polysilicon layer, the first dielectric layer, and the first oxide layer from regions exposed in the via to form self-aligned source/drain regions; forming a second spacer to define source and drain implant regions of the non-volatile device; and delivering n-type implants in the defined source and drain regions of the non-volatile device. 
     In some embodiments, the semiconductor substrate is a p-type substrate. In such embodiments, the first well is an n-well formed using a number of implant steps each using a different energy and doping concentration of Phosphorous. Furthermore, in such embodiments, the second well is a p-well formed using a number of implant steps each using a different energy and doping concentration of Boron. In some embodiments, the implant steps used to form the n-well and p-well are carried out using a single masking step. 
     In some embodiments, the first dielectric layer further includes an oxide layer and a nitride layer and the second dielectric layer is an oxide layer. Moreover, the thickness of the second oxide layer is greater than that of the first oxide layer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified transistor schematic diagram of a non-volatile DRAM, as known in the prior art. 
         FIG. 2  is a simplified transistor schematic diagram of a non-volatile SRAM, as known in the prior art. 
         FIG. 3  is a cross-sectional view of a non-volatile memory device, in accordance with one embodiment of the present invention. 
         FIG. 4  is a cross-sectional view of a semiconductor substrate in which an integrated circuit including the non-volatile memory device of  FIG. 3  is formed. 
         FIG. 5  is a cross-sectional view of the semiconductor structure of  FIG. 4  after a layer of pad oxide is formed thereon. 
         FIG. 6  is a cross-sectional view of the semiconductor structure of  FIG. 5  after a layer of nitride is deposited on the pad oxide. 
         FIG. 7  is a cross-sectional view of the semiconductor structure of  FIG. 6  after formation of trench isolation. 
         FIG. 8  is a cross-sectional view of the semiconductor structure of  FIG. 7  after the trench isolations are filled with dielectric materials. 
         FIG. 9  is a cross-sectional view of the semiconductor structure of  FIG. 8  after formation of an n-well and a p-well defining a body region in which the non-volatile device of  FIG. 3  is formed. 
         FIG. 10  is a cross-sectional view of the semiconductor structure of  FIG. 9  after a second n-well is formed adjacent the first n-well and p-well. 
         FIG. 11  is a cross-sectional view of the semiconductor structure of  FIG. 10  after formation of various layers thereon. 
         FIG. 12  is a cross-sectional view of the semiconductor structure of  FIG. 11  after a photo-resist mask has been formed to define the control gate of the non-volatile device, in accordance with one embodiment of the present invention. 
         FIG. 13  is a cross-sectional view of the semiconductor structure of  FIG. 12  following etching steps and oxide spacer formation steps. 
         FIG. 14  is a cross-sectional view of the semiconductor structure of  FIG. 13  after a second-well a third n-well and various gate oxide layers have been formed. 
         FIG. 15  is a cross-sectional view of the semiconductor structure of  FIG. 14  after a second poly layer has been deposited and photo-resist masks have been formed to define gate regions of high-voltage and low-voltage NMOS and PMOS transistors as well as the guiding gates of a pair of non-volatile devices. 
         FIG. 16  is a cross-sectional view of the semiconductor structure of  FIG. 15  after various etching steps are carried out to form the gate regions of high-voltage and low-voltage NMOS and PMOS transistors as well as the guiding gates of a pair of non-volatile devices. 
         FIG. 17  is a cross-sectional view of the semiconductor structure of  FIG. 16  after a photo-resist mask has been formed to separate the guiding gates of the pair of non-volatile devices and to define their respective LDD regions. 
         FIG. 18  is a cross-sectional view of the semiconductor structure of  FIG. 17  after LDD implants. 
         FIG. 19  is a cross-sectional view of the semiconductor structure of  FIG. 18  after formation of a second oxide spacer layer. 
         FIG. 20  is a cross-sectional view of the semiconductor structure of  FIG. 19  after formation of a Salicide layer and source/drain implant steps. 
         FIG. 21  is a cross-sectional view of the semiconductor structure of  FIG. 20  after layers of nitride and oxide have been deposited thereon. 
         FIG. 22  is a cross-sectional view of the semiconductor structure of  FIG. 21  after formation of Tungsten plugs and first metal layer. 
         FIG. 23  is a cross-sectional view of the semiconductor structure of  FIG. 22  after formation of a second metal layer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to the present invention, an improved method of forming a non-volatile memory device is provided. Although the invention has been applied to a single integrated circuit device in a memory application, there can be other alternatives, variations, and modifications. For example, the invention can be applied to embedded memory applications, including those with logic or microcircuits, and the like. 
       FIG. 3  is a cross-sectional view of some of the regions of non-volatile memory device  200  (hereinafter alternatively referred to as device  200 ), in accordance with the present invention. Device  200  which is formed in, e.g., a p-type semiconductor substrate or a p-well formed in an n-type semiconductor substrate, includes, in part, a guiding gate  152   a , a control gate  124 , n-type source/drain regions  166  formed in p-well  114 . Control gate  124 , which is typically formed from polysilicon, is separated from p-type substrate or p-well layer  114  via oxide layer  118 , nitride layer  120  and oxide layer  122 . Guiding gate  152   a , which is also typically formed from polysilicon, is separated from substrate  206  via layer  136 . Layer  136  may be an oxide layer or oxinitride layer or any other dielectric layer. Guiding gate  152   a  partially extends over control gate  124  and is separated therefrom via oxide layer  126 . A sequence of steps adapted to manufacture device  200  is described below. In the following, it is understood that similar elements or regions in the drawings are identified with similar reference numerals. Moreover, after various regions or elements in a drawing are identified with their respective reference numerals, the subsequent drawings may omit those reference numerals for simplification purposes. 
       FIG. 4  shows a semiconductor substrate  100  in which the non-volatile device  200  shown in  FIG. 3  is formed. In the exemplary embodiment described above, substrate  100  is a p-type substrate. It is understood that in other embodiments, substrate  100  may be an n-type substrate. To form non-volatile device  200 , a layer of pad oxide  102  having a thickness in the range of, e.g., 60–1000 Å, is grown on substrate  100  using conventional thermal oxidation processes, as shown in  FIG. 5 . Next, as shown in  FIG. 6 , a layer of silicon-nitride  104  having a thickness in the range of, e.g., 500–1500 Å, is deposited on pad oxide layer  102 . It is understood that the various layers and spacings shown in the Figures are not drawn to scale. Next, using conventional masking and etching steps, shallow trenches  106  are formed in substrate  100 , thereby forming structure  505  as shown in  FIG. 7 . It is understood that in some embodiments, isolation regions formed using conventional locos isolation (not shown) techniques may be used in place of trenches  106 . 
     After shallow trenches  106  are formed, a layer of oxide having a thickness of, e.g., 150 Å, is grown over structure  505 . This oxide is also grown in trenches  106 . Next, a layer of TEOS having a thickness of, e.g., 5000–10,000 Å is deposited on the oxide. This TEOS layer is also deposited in trenches  106 . Thereafter, using a planarization technique, such as chemical-mechanical polishing (CMP), the resulting structure is planarized.  FIG. 8  shows the resulting structure  510  after the planarization process. As is seen from  FIG. 8 , as all the layers overlaying substrate  100 , except for the oxide layer  108  and TEOS layer  110  formed in trenches  106 , are removed. 
     Next, as shown in  FIG. 9 , using conventional photo-resist patterning and etching steps, n-well  112  and p-well  114  are formed. As seen from  FIG. 9 , n-well  112  is deeper than and formed before p-well  114 . In some embodiments, a Phosphorous implant with a concentration of 2.0e 13  atoms/cm 2  and using an energy of 1.5 Mega-electron volts is used to form n-well  112 . In such embodiments, three to six separate Boron implants are used to form p-well implant  114 . The first Boron implant is made using a concentration of 2.0e 13  atoms/cm 2  and an energy of 600 Kilo-electron volts. The second Boron implant is made using a concentration of 1.0e 13  atoms/cm 2  and an energy of 300 Kilo-electron volts. The third Boron implant is made using a concentration of 4.0e 13  atoms/cm 2  and an energy of 160 Kilo-electron volts. The fourth Boron implant is made using a concentration of 6.0e 13  atoms/cm 2  and an energy of 70 Kilo-electron volts. The fifth Boron implant is made using a concentration of 1.0e 13  atoms/cm 2  and an energy of 300 Kilo-electron volts. The above phosphorous and Boron implants are performed using the same masking step. 
     Because, the Phosphorous implant is performed using a relatively high energy, relatively few Phosphorous impurities may remain in p-well  114 . Therefore, in accordance with the present invention, advantageously very few Boron impurities in p-well  114  are neutralized (i.e., compensated) by the phosphorous impurities. After the above implants, a thermal anneal is performed at the temperature of, e.g., 1000–1050° C. for a period of, e.g., 30 seconds. The resulting structure  515  is shown in  FIG. 9 . 
     Next, as shown in  FIG. 10 , a second n-well  116  is formed adjacent n-well  112  and p-well  114 . N-well  116  that extends to the surface of substrate  100  has a depth that is substantially the same as the combined depth of n-well  112  and p-well  114 . The resulting structure  520  is shown in  FIG. 10 . As is seen from  FIG. 10 , n-well  116  and deep n-well  112  are connected in substrate  100 . 
     Next, as shown in  FIG. 11 , a layer of thermal oxide  118  having a thickness in the range of, e.g., 15–40 Å, is grown over structure  520 . Thereafter, a layer of nitride  120  having a thickness in the range of, e.g., 40–120 Å, is formed over oxide layer  118 . Next, a layer of CVD oxide  122  having a thickness in the range of, e.g., 40–70 Å, is deposited over nitride layer  120 . Thereafter, during a densification step, the resulting structure is heated to a temperature of, e.g., 700–850° C. for a period of, e.g., 0.5 to 1 hour. After the densification step, a layer of polysilicon (alternatively referred to herein below as poly)  124  having a thickness in the range of, e.g., 1500–3000 Å is deposited over CVD oxide layer  122 . Poly layer  124  may be doped in-situ or using other conventional doping techniques, such as ion implantation Thereafter, a layer of nitride-oxide layer  126  having a combined thickness in the range of, e.g., 500–1500 Å is formed over ploy layer  124 . The thickness of oxide layer in the oxide-nitride layer  126  may be between, e.g., 100–200 Å.  FIG. 11  shows structure  525  that is formed after the above growth and deposition steps are performed on structure  520 . 
     Next, using standard photo-resist deposition, patterning and etching steps, photo-resists masks  128  are formed over oxide-nitride layer  126 . As seen on  FIG. 12 , photo-resists mask  128  includes one continuous piece. The resulting structures  530  is shown in  FIG. 12 . Mask  128  is subsequently used to define the control gates of the non-volatile devices formed in substrate  100 . As described below, one masking step is used to form the control gate and two masking steps are used to form the guiding gate of the non-volatile device. 
     Next, using conventional etching techniques, such as reactive ion etching, all the various layers grown or deposited on substrate  100 , namely layers  118 ,  120 ,  122 ,  124  and  126  are removed from substantially all regions down to the surface of substrate  100  except for the regions positioned below masks  128 . Thereafter, photo-resist masks  128  are also removed. Next, a layer of gate oxide  130  is thermally grown. In some embodiments, gate oxide layer  130  has a thickness in the range of, e.g., 100–200 Å. As is known to those skilled in the art, during this thermal oxidation, portions of polysilicon layer  124  are also oxidized, thereby causing the formation of rounded oxide regions  132 , commonly referred to as spacers or parts thereof. Structure  535  of  FIG. 13  shows the result of performing these steps on structure  530 . It is understood that the drawings do not show some of the intermediate steps involved in forming structure  535  from structure  530 . 
     Next, using conventional anisotropic etching techniques, oxide layer  130  overlaying substrate  100  is removed as a result of which spacers  132  are also partially etched. Next, using conventional masking and ion implantation steps, highly doped p-well region  140  is formed (see  FIG. 14 ). In some embodiments, three to five separate Boron implants are used to form p-well implant  140 . If four Boron implants are used, the first Boron implant is made using a concentration of, e.g., 1–3.3e 12  atoms/cm 2  and an energy of 20 Kilo-electron volts (Kev). The second Boron implant is made using a concentration of, e.g., 5–6.5e 12  atoms/cm 2  and an energy of 70 Kev. The third Boron implant is made using a concentration of, e.g., 2.5–3.4e 12  atoms/cm 2  and an energy of 180 Kev. The fourth Boron implant is made using a concentration of, e.g., 2–3.5e 13  atoms/cm 2  and an energy of 500 Kilo-electron volts. 
     Next using conventional masking and ion implantation steps, highly doped n-well region  142  is formed (see  FIG. 14 ). In some embodiments, three to five separate Phosphorous implants are used to form n-well implant  24 . If four Phosphorous implants are used, the first Phosphorous implant is made using a concentration of, e.g., 5.7e 12  atoms/cm 2  and an energy of 50 Kev. The second Phosphorous implant is made using a concentration of, e.g., 6.6e 12  atoms/cm 2  and an energy of 150 Kev. The third Phosphorous implant is made using a concentration of, e.g., 5.0e 12  atoms/cm 2  and an energy of 340 Kev. The fourth Phosphorous implant is made using a concentration of, e.g., 4.0e 13  atoms/cm 2  and an energy of 825 Kilo-electron volts. After the above implants, a thermal anneal is performed at the temperature of, e.g., 1000° C. for a period of, e.g., 10 seconds. 
     Thereafter using several masking steps, three layers of oxide thickness each having a different thickness are thermally grown. In the surface regions identified with reference numeral  134 , the oxide layer has a thickness in the range of, e.g., 15–60 Å. The semiconductor substrate underlaying oxide layer  134  is used to form core transistors having relatively high speed. In the region identified by reference numeral  136 , the oxide layer has a thickness in the range of, e.g., 60–80 Å. The semiconductor substrate underlaying oxide layer  136  and overlaying p-well  114  is used to form devices adapted to operate with voltages substantially similar to the Vcc voltage (i.e., 3.3 volts), such as input/output transistors. In the region identified by reference numeral  138 , the oxide layer has a thickness in the range of, e.g., 120–250 Å. The semiconductor substrate underlaying oxide layer  138  is used to form high-voltage transistors, such as high-voltage charge pump devices. The process of making multiple, e.g. 3, layers of oxide each with a different thickness is known to those skilled in the art and is not described herein. In some other embodiments, oxide layers  136  and  138  have the same thickness in the range of, e.g., 120–250 Å. Structure  540  of  FIG. 14  shows the result of performing these steps on structure  535  of  FIG. 13 , in accordance with the present invention. It is understood that the drawings do not show some of the intermediate steps involved in forming structure  540  from structure  535 . 
     Next, as shown in  FIG. 15 , a layer of polysilicon  144  having a thickness in the range of, e.g., 1000–3200 Å, is deposited. Thereafter using standard photo-resist masking and patterning techniques, photo-resists masks  146  are formed over polysilicon layer  144 . Structure  545  of  FIG. 15  shows the result of performing these steps on structure  540  of  FIG. 14 . 
     Next, using conventional reactive ion etching (RIE) steps, polysilicon layer  144  and oxide layer  134 ,  136  and  138  are removed from all regions except those positioned below masks  146 . Structure  550  of  FIG. 16  shows the result of performing these steps on structure  545  of  FIG. 15 . Poly gate  148  is shown as overlaying gate oxide layer  134  formed above p-well  142 . Poly gate  150  is shown as overlaying gate oxide layer  134  formed above n-well  140 . Poly gate  154  is shown as overlaying gate oxide layer  138  formed above p-well  114 . Poly gate  156  is shown as overlaying gate oxide layer  138  formed above n-well  116 . Poly gates  148  and  150  respectively form the gates of low-voltage high-speed PMOS and NMOS transistors. Poly gates  154  and  156  respectively form the gates of high-voltage NMOS and PMOS transistors. Poly gate  152  forms the guiding gates of a pair of non-volatile devices and each is shown as overlaying, in part, gate oxide layer  136  formed below it. 
     Next, using known photo-resist deposit and patterning techniques, photo-resist masks  158  are formed to form via  160 . Structure  555  of  FIG. 17  shows the result of performing these steps on structure  550  of  FIG. 16  after formation of via  160 . Thereafter, layers  118 ,  120 ,  122 ,  124  and  126  disposed in via  160  and underlaying polysilicon layer  152  are etched from structure  555  using standard etching step (see  FIG. 18 ). 
     Next, using several masking steps, low voltage p-type lightly doped (LDD) regions  162 , low-voltage n-type LDD regions  164 , intermediate voltage n-type LDD regions  166 , high voltage n-type LDD region  168 , and high voltage p-type LDD region  170  are formed. The resulting structure  560  is shown in  FIG. 18 . 
     Next, as shown in  FIG. 19 , using conventional processing steps, side-wall spacers  172  are formed. In some embodiments, each side-wall spacer  172  is made from oxide and each has a thickness in the rage of, e.g., 300–1500 Å. Thereafter, several p +  and n +  masking steps are performed to form p +  source/drain regions  174 , n +  source/drain regions  176 , n +  source/drain regions  178 , and p +  source/drain regions  180 . In some embodiments, the doping concentration of Boron used to form p +  source/drain regions  174  is the same as that used to form p +  source/drain regions  180 . In some other embodiments, the doping concentration of Boron used to form p +  source/drain regions  174  is different from that used to form p +  source/drain regions  180 . In some embodiments, the doping concentration of Arsenic used to form n +  source/drain regions  176  is the same as that used to form n +  source/drain regions  178 . In some other embodiments, the doping concentration of Arsenic used to form n +  source/drain regions  176  is different from that used to form n +  source/drain regions  178 . The resulting structure  565  is shown in  FIG. 19 . 
     Next, Salicide is deposited over structure  565 . Thereafter, a high-temperature anneal cycle is carried out. As is known to those skilled in the art, during the anneal cycle, Salicide reacts with silicon and polysilicon, but not with silicon-nitride or silicon-oxide. In the resulting structure  570 , which is shown in  FIG. 20 , Salicided layers are identified with reference numeral  182 . 
     Next, a layer of nitride  184  is deposited over structure  570  and a layer of oxide  186  is deposited over nitride layer  184 , as shown in  FIG. 21 . 
     Next, vias are formed in nitride layer  184  and oxide layer  186  to expose the underlaying Salicide layers. Thereafter, a barrier metal, such as Titanium-nitride  188  is sputter-deposited partly filling the vias. Next, Tungsten  190  is deposited over Titanium-nitride layer to fills the remainder of the vias. The deposited Tungsten is commonly referred to as Tungsten Plug. Next, using a CMP technique, the Tungsten deposited structure is planarized. Next, a metal such as Aluminum or Copper is deposited and patterned over the planarized structure. The resulting structure  580  is shown in  FIG. 22 . As is seen from  FIG. 22 , each via has disposed therein a Titanium-Nitride layer  188  and Tungsten layer  190 . The deposited and patterned Al or Copper layers are identified with reference numeral  192 . 
     The description above is made with reference to a single metal layer. However, it is understood that additional metal layers may be formed over metal layers  192  in accordance with known multi-layer metal processing techniques. For example,  FIG. 23  shows structure  580  after it is processed to include a second metal layer  194  that is separate from metal layer  192  via layers of dielectric materials.