Abstract:
The present teachings and illustrations describe a process for forming a plurality of conductive structures in or on a substrate. In one embodiment, the process comprises forming a plurality of recesses in or on the substrate, wherein the plurality of recesses include recesses having different dimensions. In addition, the process further comprises (i) forming a conductive layer which at least partially fills the plurality of recesses and (ii) treating the conductive layer to improve the conductive properties of the conductive layer. Moreover, the process still further comprises (iii) sequentially repeating acts (i) and (ii) until each of the recesses of the plurality of recesses are filled to a desired dimension and such that the conductive material in the recesses of smaller dimension are more uniformly adhered to the bottom surfaces of the recesses.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application is a continuation of U.S. patent application Ser. No. 10/651,765, filed Aug. 29, 2003, entitled “INTERMEDIATE ANNEAL FOR METAL DEPOSITION”, which is entirely incorporated herein by reference. 

   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to semiconductor technology and, in particular, relates to fabrication processes for conductive layers on substrates. 
   2. Description of the Related Art 
   Conventional fabrication of conductive structures, such as patterned interconnects, typically involves forming recesses, trenches, or vias in or on a substrate, and then filling or overfilling these features with various conductive materials, such as copper, poly-silicon, metal, or various metal alloys. Sometimes excessive conductive material, such as overfill or overburden, is removed by planarization using, for example, chemical mechanical polishing or the like to thereby form isolated conductive structures, such as traces, vias, wires, and/or wire bonding pads. Such metalization processes can sometimes avoid photolithographic mask and etching processing of conventional metal line definition. 
   In one such process, recessed features, such as trenches, vias, and wire bonding pads, are formed in an insulating substrate, such as an interlayer dielectric (ILD) layer, using reactive ion etching (RIE). In addition, electrochemical deposition (ECD) is sometimes used to deposit copper or various other conductive materials to a sufficient thickness to fill these features so as to form the desired conductive structures. In certain circumstances, a seed layer can first be deposited as part of the deposition process. In other circumstances, the deposition of copper material is preceded by the deposition of a thin barrier layer, which inhibits diffusion of copper into the underlying substrate or ILD layer. Moreover, the copper deposition is typically followed by annealing the copper by heating the wafer to a temperature between approximately 100° and 500° C. (e.g., 200° C.). 
   Unfortunately, defects can be introduced at various stages of processing (e.g., RIE, seed/barrier deposition, ECD, and CMP). In many cases, some of these defects can be removed with annealing processes. However, the excessive overburden of copper material above the conductive structures can create stresses during the annealing process, which can cause a multitude of defects and adversely impact the electrical characteristics of the copper material. For example, stresses created by the thermal cycling of heating and cooling during annealing can cause the copper material to lift off from a portion of the recessed trench or via, thereby creating voids, which can inhibit the conductive properties of the copper material. 
   In addition, conductive structures are typically formed in or on a substrate, including ILD layers, at various widths or pitches, wherein a via, for example, can be classified as a “smaller” recessed feature and a wire bonding pad, for example, can be classified as a relatively “larger” recessed feature. In general, conventional metalization techniques deposit or form a single layer of copper material on the substrate so as to simultaneously fill the “smaller” and “larger” recessed features, which results in excessive overfill or overburden of copper material above the “smaller” recessed feature or via. 
   Moreover, subsequent annealing of the copper layer can cause the copper material to flow at elevated temperatures. In general, the coefficient of thermal expansion (CTE) for copper is typically greater than the CTE for substrate materials including ILD layers. Thus, during annealing, copper material expands more than the substrate material at elevated temperatures. Unfortunately, the expansion forces of the copper and substrate material can cause copper to flow out of the “smaller” features. Typically, excessive overburden or thickness of copper material results in increased expansive stresses. Once cooled, the copper and substrate materials contract. In general, copper contracts more than the substrate due to the difference in the CTE. Therefore, the copper can shrink in the “smaller” features and the overburden can contract as well such that an excessive overburden of copper above the “smaller” features results in a larger contracting volume, which results in larger contracting forces pulling the copper out of the “smaller” features. 
   The contraction or shrinkage of the overburdened copper layer can cause the copper material to lift off from portions of the “smaller” recessed feature or via, thereby creating a void between the copper layer and portions of the “smaller” recessed feature. Therefore, there currently exists a need to improve the processing techniques associated with forming conductive structures so as to improve the physical and electrical characteristics thereof. 
   SUMMARY OF THE INVENTION 
   The aforementioned needs may be satisfied by a process for forming a plurality of conductive structures in a substrate. In one embodiment, the process may comprise forming a plurality of recesses in the substrate, wherein the plurality of recesses include recesses having different dimensions In addition, the process may further comprise (i) forming a conductive layer which at least partially fills the plurality of recesses and (ii) treating the conductive layer to improve the conductive properties of the conductive layer. Moreover, the process may still further comprise (iii) sequentially repeating acts (i) and (ii) until each of the recesses of the plurality of recesses are filled to a desired dimension and such that the conductive material in the recesses of smaller dimension are more uniformly adhered to the bottom surfaces of the recesses. 
   In one aspect, the process may further comprise forming a seed layer on the substrate so as to overlie the recesses, wherein forming the conductive layer may comprise forming the conductive layer on the seed layer. In addition, forming the seed layer comprises depositing a seed layer with conductive material selected from the group consisting of copper, nickel, and cobalt. Also, forming the seed layer comprises depositing a seed layer having a thickness of at least less than approximately 3000 A. 
   In another aspect, forming a conductive layer comprises depositing a conductive material in the plurality of recesses selected from the group consisting of copper, nickel, and cobalt. In addition, forming a conductive layer comprises depositing a layer of conductive material using electrochemical deposition (ECD). Also, forming a plurality of recesses comprises forming at least one recess sized to receive a contact via or small pitch/width line and at least one recess sized to form a wire bonding pad. 
   In still another aspect, forming a plurality of recesses in the substrate includes recesses having different widths such that sequentially repeating acts (i) and (ii) until each of the recesses of the plurality of recesses are filled to a desired width and such that the conductive material in the recesses of smaller width are more uniformly adhered to the bottom surfaces of the recesses. In addition, forming a plurality of recesses comprises forming at least one first recessed region having a first range of width between approximately 0.05-0.35 μm and forming at least one second recessed region having a second range of width between approximately 0.45 μm or greater. 
   In still another aspect, treating the conductive layer comprises annealing the conductive layer at a temperature of approximately 200° C. for approximately 30 minutes. In addition, treating the conductive layer comprises annealing the conductive layer with a temperature gradient between approximately 160-220° C. for approximately 30-90 minutes. Also, treating the conductive layer comprises annealing the conductive layer with a temperature range between approximately 100-500° C. 
   The aforementioned needs may also be satisfied by a process for forming a plurality of conductive structures on a substrate. In one embodiment, the process may comprise forming a plurality of recesses in the substrate, wherein the plurality of recesses include recesses having different widths. In addition, the process may further comprise (i) forming a layer of copper material which at least partially fills the plurality of recesses and (ii) treating the layer of copper material to improve the conductive properties thereof. Moreover, the process may still further comprise (iii) sequentially repeating acts (i) and (ii) until each of the recesses of the plurality of recesses are filled to a desired width and such that the copper material in the recesses of smaller width are more uniformly adhered to the bottom surfaces of the recesses. 
   The aforementioned needs may also be satisfied by a fabrication method for forming conductive interconnects on a substrate. In one embodiment, the method may comprise forming at least one first recessed region to a first width in the substrate and forming at least one second recessed region to a second width in the substrate, wherein the second width is at least greater than the first width. In addition, the method may further comprise forming a first conductive layer so as to at least fill the first recessed region to a first fill width and annealing the first conductive layer. Moreover, the process may still further comprise forming a second conductive layer on the first conductive layer after annealing the first conductive layer so as to at least fill the second recessed region to a second fill width, wherein filling the second recessed region to the second fill width over fills the first recessed region and annealing the second conductive layer, and wherein the previous anneal of the first conductive layer inhibits separation of the conductive material from the lower surface of the first recessed region during the anneal of the second conductive layer. 
   These and other objects and advantages of the present invention will become more fully apparent from the following description taken in conjunction with the accompanying drawings. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  illustrates one embodiment of a substrate having a surface with first and second recessed features formed therein. 
       FIG. 2  illustrates the deposition of a seed layer on the substrate. 
       FIG. 3  illustrates the deposition of a first conductive layer on the seed layer. 
       FIG. 4  illustrates the application of a first annealing process to the first conductive layer. 
       FIG. 5  illustrates the deposition of a second conductive layer on the first conductive layer. 
       FIG. 6  illustrates the application of a second annealing process to the second conductive layer. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
   Reference will now be made to the drawings wherein like numerals refer to like parts throughout.  FIGS. 1-6  illustrate an improved method for plating interconnects on a substrate so as to reduce the adverse effects of stresses and interface voids caused by annealing. These improvements and other aspects of the present teachings will be described in greater detail herein below with reference to the drawings. 
     FIG. 1  illustrates one embodiment of a substrate  100  having a surface  102  with first and second recessed features  110 ,  112  formed therein adjacent the substrate surface  102 . In one embodiment, the first recessed feature  110  may comprise a relatively “smaller” type of recessed feature having a first width or pitch  116 , such as a generally known via or Damascene structure. In addition, the second recessed feature  112  may comprise a relatively “larger” type of recessed feature having a second width or pitch  118  that is at least greater than the first width  116 , such as a recess for a generally known wire bonding pad. It should be appreciated by those skilled in the art that the widths of the features  110 ,  112  may vary in magnitude without departing from the scope of the present teachings and should not be limited to the illustrated embodiment. In general, features of differing widths are a concern, which also may include array lines and power bus lines. 
   In general, formation of the recessed features  110 ,  112  may comprise a generally known photo-mask pattern and etch technique that is adapted to etch the substrate  100  below the surface  102  thereof to a desirable dimension, such as width, so as to define the shape or contour of features  110 ,  112 . In one embodiment, the recessed features  110 ,  112  may be formed in the substrate  100  with reactive ion etching (RIE). In addition, as illustrated in  FIG. 1 , the recessed features  110 ,  112  may vary in size and width depending on the particular application or implementation such that, in one embodiment, the second recessed feature  112  is etched with a greater width than the first recessed feature  110 . In one aspect, as illustrated in  FIG. 1 , the shape or contour of the recessed features  110 ,  112  may resemble a substantially rectangular shape. However, it should be appreciated by those skilled in the art that the shape or contour of the recessed features  110 ,  112  may comprise various other types of shapes or contours, such as circular, elliptical, cylindrical, triangular, etc., without departing from the scope of the present teachings. 
   In one embodiment of the present teachings, the first recessed feature  110  may comprise a “smaller” recessed region, such as a line, trace, trench, or via, having a width of at least less than approximately 0.45 microns (μm). In another embodiment, the “smaller” first recessed feature  110  may comprise a range of widths between approximately 0.05-0.35 μm. In addition, the “smaller” first recessed feature  110  may be defined in terms of “smaller” recessed area or volume having varying dimensional characteristics of length and depth (not shown) along with the previously defined widths. Therefore, in one aspect, it should be appreciated by those skilled in the art that the dimensional characteristics of the “smaller” first recessed feature  110 , including the length, width, and depths or range of lengths, widths, and depths, may vary in magnitude depending on the particular application or implementation without departing from the scope of the present teachings. 
   Moreover, the second recessed feature  112  may comprise a “larger” recessed region, such as a recess for a wire bonding pad, having a range of widths between approximately 0.45-500 μm. In addition, the “larger” second recessed feature  112  may be defined in terms of “larger” recessed area or volume having dimensional characteristics of length and depth (not shown) along with the previously defined widths. Therefore, in one aspect, it should also be appreciated by those skilled in the art that the dimensional characteristics of the “larger” second recessed feature  112 , including the length, width, and depths or range of lengths, widths, and depths, may vary in magnitude depending on the particular application or implementation without departing from the scope of the present teachings. 
   In another embodiment of the present teachings, the substrate  100  may be referred to as interlayer dielectric (ILD) and may comprise an insulative material, such as borophosphosilicate glass (BPSG) or various other generally known field oxide materials. In addition, the substrate  100  may comprise at least a portion of a conventional silicon wafer, but can more generally encompass structures comprising semiconductive material or variations thereof, including, but not limited to, bulk semiconductor materials such as a semiconductor wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). Moreover, the term “substrate” or “ILD” may also encompass any various supporting or layered structures, including, but not limited to, oxide or semiconductive structures, layers, or substrates. Furthermore, when reference is made to the substrate  100  within the following description, previous processing steps may have been utilized to form regions, structures, or junctions in or on its base oxide or semiconductor structure or foundation. 
   Further, in one embodiment, the substrate  100  may comprise one or more generally known conductive vias, plugs, traces, or contacts (not shown) that abut at least a portion of the features  110 ,  112 . It should be appreciated that the one or more vias, plugs, traces, or contacts define one or more node regions (not shown) and may comprise a generally known electrical interconnect between the substrate  100  and one or more circuit components (not shown), such as a transistor or various other types of circuit components. In addition, it should also be appreciated that the features  110 ,  112  may be positioned in any region relative to the substrate  100  without departing from the scope of the present teachings. 
     FIG. 2  illustrates the deposition or plating of a seed layer  120  on the substrate  100  so as to overlie the substrate surface  102  and the features  110 ,  112  formed therein. In one embodiment, the seed layer  120  may comprise a layer of conductive material, such as copper, nickel, or cobalt, that provides an atomically-smooth and cohesive interface that encourages the correct grain growth during the subsequent bulk fill processing steps. In addition, the formation of the seed layer  120  comprises a conformal deposition or superfilling of conductive material, such as copper, nickel, or cobalt, using, for example, an electrochemical deposition (ECD) technique to a sufficient thickness  122 . It should be appreciated by those skilled in the art that various other conductive materials may be used without departing from the scope of the present teachings. In addition, it should also be appreciated that various other conformal deposition or plating processes, such as chemical vapor deposition (CVD), plasma enhanced CVD (PECVD), or the like, may be used to deposit the seed layer  120  to the sufficient thickness  122  without departing form the scope of the present teachings. Moreover, in one embodiment, the thickness  122  of the seed layer  120 , for example, is at least less than approximately 3000 A. Additionally, the deposition or plating of the seed layer  120  on the substrate  100  is considered optional and, therefore, the thickness  122  of the seed layer  120  may comprise a range between approximately 0-3000 A. 
   Advantageously, the seed layer  120  can also improve the effectiveness of the subsequent bulk fill. In one aspect, it should be appreciated that deposition of the first conductive layer  120  is optional such that the seed layer  120  may or may not be formed or deposited prior to the subsequent processing steps as disclosed herein without departing from the scope of the present teachings. It should also be appreciated that the thickness  122  of the seed layer  120  may vary in magnitude depending on the particular application or implementation without departing from scope of the present teachings. Moreover, it should also be appreciated that various other deposition or plating techniques, such as sputtering or vacuum evaporation, may be used to form the seed layer  120  without departing from the scope of the present teachings. 
     FIG. 3  illustrates the deposition or plating of a first conductive layer  130  on the seed layer  120  so as to fill the first recessed feature  110  and at least partially fill the second recessed feature  112 . In one embodiment, the formation of the first conductive layer  130  comprises a conformal deposition of conductive material, such as copper, nickel, or cobalt, using, for example, an ECD technique to a sufficient thickness  132 . In general, the “smaller” recessed features  110  tend to fill before the “larger” recessed features  112 , which may be related to the method of deposition. In one aspect, the “smaller” recessed features  110  fill fast from the bottom up, while the “larger” recessed features fill conformally. For example, a “smaller” or less wide recessed feature  110  may fill in approximately 20 seconds, and a “larger” or wider recessed feature  112  may fill in approximately 1.5 to 2.5 minutes. As with the deposition of the seed layer  120 , it should be appreciated that various other conformal deposition or plating processes, such as CVD, PECVD, or similar technique, may be used to deposit the first conductive layer  130  to the sufficient thickness  132 . In addition, it should also be appreciated by those skilled in the art that various other conductive materials may be used without departing from the scope of the present teachings. 
   In one embodiment, the deposition or plating of the first conductive layer  130  may be performed with accelerators, such as disulfides, suppressors, such as polyethylene glycol, and/or levelers in a generally known manner so as to reduce the “overburden” of the first conductive layer  130  on the substrate  100 . In general, accelerator molecules are relatively small and promote deposition because they fit into small areas and accumulate, and suppressor molecules are relatively large and inhibit deposition. In one aspect, it should be appreciated that the thickness  132  of the first conductive layer  130  may vary in magnitude depending on the particular application or implementation without departing from scope of the present teachings. Moreover, it should also be appreciated that various other deposition or plating techniques, such as sputtering, vacuum evaporation, or the like, may be used to form the first conductive layer  130  without departing from the scope of the present teachings. 
     FIG. 4  illustrates a first annealing process  140  that is applied to the first conductive layer  130  so as to improve the physical and electrical characteristics thereof. For example, the first annealing process  140  may be applied to the first conductive layer  130  to relieve stresses, increase grain sizes, drive-off impurities, and improve conductivity. In addition, since defects can be introduced into the first conductive layer  130  during deposition, some of these defects can be removed therefrom with the first annealing process  140 . For example, stresses created by the thermal cycling of heating and cooling can cause the conductive material of the first conductive layer  130  to lift from a portion of the substrate  100  adjacent the “smaller” first feature  110  thereby creating a void or gap therebetween. 
   However, in the present teachings, deposition and annealing of the first conductive layer  130  are the initial processing steps in a multi-step plating process to form a conductive structure  170  as illustrated in  FIGS. 5 ,  6 . Therefore, the first conductive layer  130  can be deposited or plated with less overfill or overburden than the prior art technique. With less of an overburden of conductive material, such as copper, nickel, or cobalt, above the first recessed feature  110 , the first annealing process  140  can advantageously reduce stresses that can cause adverse defects in the grain structure or void regions between the layer  130  and the substrate  100 . In addition, the first annealing process  140  can more uniformly adhere the conductive material of the first conductive layer  130  to the interior surfaces of at least the “smaller” first recessed feature  110  to thereby provide, for example, improved conduction therebetween. It should be appreciated that interior surfaces may include side and bottom or lower surfaces without departing from the scope of the present teachings. 
   In one embodiment, the first annealing process  140  may comprise a batch annealing process in a vertical furnace. In addition, the first annealing process  140  may comprise a rapid thermal annealing (RTA) process or variation thereof. Also, in one embodiment, the first annealing process  140  may be performed in a temperature of approximately 200° C. for approximately 30 minutes. Moreover, the first annealing process  140  may be performed, for example, with a temperature gradient between approximately 160-220° C. for approximately 30-90 minutes. In general, the temperature range for the first annealing process  140  may vary, for example, between approximately 100-500° C. It should be appreciated by those skilled in the art that the temperature range and temporal range of the first annealing process  140  may vary without departing from the scope of the present teachings. 
     FIG. 5  illustrates the deposition or plating of a second conductive layer  150  on the annealed first conductive layer  130  so as to form a conductive structure  170 . In one embodiment, as illustrate in  FIG. 5 , the second conductive layer  150  is deposited or plated on the first conductive layer  130  in a manner so as to overlie the first recessed feature  110  and fill at least the remaining portion of the second recessed feature  112 . In one embodiment, the formation of the second conductive layer  150  comprises a bulk fill of conductive material, such as copper, nickel, or cobalt, using, for example, an electrochemical deposition (ECD) technique to a sufficient thickness  152 . In one aspect, it should be appreciated that the thickness  152  of the second conductive layer  150  may vary in magnitude depending on the particular application or implementation without departing from scope of the present teachings. Moreover, as with the formation of the first conductive layer  130 , it should also be appreciated that various other deposition or plating techniques, such as CVD, PECVD, sputtering, vacuum evaporation, or the like, may be used to form the second conductive layer  150  without departing from the scope of the present teachings. Furthermore, it should also be appreciated by those skilled in the art that various other conductive materials may be used without departing from the scope of the present teachings. 
     FIG. 6  illustrates a second annealing process  160  that is applied to the second conductive layer  150  so as to improve the physical and electrical characteristics thereof in a manner similar to the discussion related to the first conductive layer  130  in  FIG. 4 . For example, in one embodiment, the second annealing process  160  is applied to the second conductive layer  150  to relieve stresses and increase the conductivity in a manner as previously described with reference to  FIG. 4 . In addition, it should be appreciated by those skilled in the art that the second annealing process  160  may be performed within similar scope to that of the first annealing process  140  as previously described in  FIG. 4  without departing from the scope of the present teachings. 
   In one aspect, the differing coefficients of thermal expansion (CTE) of deposited conductive structures, having conductive material such as copper, nickel, or cobalt, and the underlying wafer or substrate, having insulative material such as BPSG, can contribute to the production of defects by the annealing process in the prior art. However, according to the present teachings, by depositing the conductive layers  130 ,  150  in a multi-step plating and annealing process as disclosed herein, the resultant conductive structure  170  may comprise less grain defects and void regions to thereby provide improved physical and electrical characteristics. In one aspect of the present teachings, the first annealing process  140  serves as an intermediate annealing step interposed between the deposition or plating of the first and second conductive layers  130 ,  150 . In addition, the second annealing step  160  serves as a subsequent annealing step after the deposition or plating of the second conductive layer  150 . Advantageously, the layering and subsequent annealing of each layer  130 ,  150  forms an improved conductive structure  170  having improved physical and electrical characteristics. 
   Typically, copper and various other conductive materials, such as nickel and cobalt, have a different coefficient of thermal expansion (CTE) than many substrate materials so stresses can occur upon heating and/or cooling the “overburdened” structures as part of the annealing process. For example, when heated during the anneal, a copper “overburden” acts as a cap and stresses can be formed by the different expansions of the copper and the substrate material. During the anneal, the copper relaxes to relieve the stresses. In addition, the crystalline grains of copper experience Ostwald ripening in which some copper grains grow at the expense of other copper grains to minimize the overall free energy of the film. Upon cooling after the anneal, stresses are again formed by the different contraction of the copper and substrate material. In addition, the copper “overburden” and the copper structures can respond differently to the annealing process, thereby creating defect-inducing stresses. Certain embodiments of the present teachings as described herein reduce the stresses and interface voids caused by annealing the conductive structures after deposition thereof. Advantageously, by applying one or more deposition and annealing processes to form on or more conductive layers  130 ,  150  as disclosed herein, an improved conductive structure  170  can be formed with improved physical and electrical characteristics including improved adherence of conductive materials to recessed features formed in or on the substrate  100 . 
   Although the above-disclosed embodiments of the present invention have shown, described, and pointed out the fundamental novel features of the invention as applied to the above-disclosed embodiments, it should be understood that various omissions, substitutions, and changes in the form of the detail of the devices, systems, and/or methods illustrated may be made by those skilled in the art without departing from the scope of the present invention. Consequently, the scope of the invention should not be limited to the foregoing description, but should be defined by the appended claims.