Abstract:
A method for processing a substrate includes providing a substrate including a metal layer, a dielectric layer arranged on the metal layer, and at least one of a via and a trench formed in the dielectric layer; depositing a metal using chemical vapor deposition (CVD) during a first deposition period, wherein the first deposition period is longer than a first nucleation period that is required to deposit the metal on the metal layer; stopping the first deposition period prior to a second nucleation delay period, wherein the second nucleation period is required to deposit the metal on the dielectric layer; performing the depositing and the stopping N times, where N is an integer greater than or equal to one; and after the performing, depositing the metal using CVD during a second deposition period that is longer than the second nucleation delay period.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of U.S. Provisional application Ser. No. 61/386,791, filed on Sep. 27, 2010. The entire disclosure of the above application is incorporated herein by reference. 
     FIELD 
     The present disclosure relates to systems and methods for filling a via from bottom up using selective tungsten deposition. 
     BACKGROUND 
     The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
     Semiconductor substrates often include features such as vias that are filled with a conductive material to allow interconnection of conductive layers. For example, some substrates may include an interlayer dielectric (ILD) arranged on a tungsten layer. A via may be defined in the ILD to allow connection to the tungsten layer. The via needs to be filled with a conductive material such as tungsten to allow connection to the tungsten layer. Usually, it is important for the connection to have low resistance to minimize power dissipation and heat. 
     A conformal fill approach may be used to fill the via. This approach grows tungsten film from both side walls of the via. As a dimension between the side walls shrinks, the tungsten grain growth is limited. As a result, the resistivity of the film is limited. Also, a seam can be created in a center of the via. The seam limits the volume filled with tungsten and compromises via resistance. 
     SUMMARY 
     This section provides a general summary of the disclosure, and is not a comprehensive disclosure of its full scope or all of its features. 
     A method for processing a substrate includes providing a substrate including a metal layer, a dielectric layer arranged on the metal layer, and at least one of a via and a trench formed in the dielectric layer; depositing metal using chemical vapor deposition (CVD) during a first deposition period, wherein the first deposition period is longer than a first nucleation period that is required to deposit the metal on the metal layer; stopping the first deposition period prior to a second nucleation delay period, wherein the second nucleation period is required to deposit the metal on the dielectric layer; performing the depositing and the stopping N times, where N is an integer greater than or equal to one; and after the performing, depositing the metal using CVD during a second deposition period that is longer than the second nucleation delay period. 
     In other features, the metal comprises tungsten. The metal layer comprises tungsten. The method includes depositing a nucleation layer prior to the first deposition period. The nucleation layer comprises one of fluorine-free tungsten layer and a tungsten/tungsten-nitride layer. The nucleation layer has a thickness between 2 Angstroms and 30 Angstroms. 
     In other features, the method includes performing a growth interruption treatment to interrupt growth of the metal on the dielectric layer after the stopping and before at least one of another one of the N times and the second deposition period. The growth interruption treatment comprises performing an ammonia soak during a soak period. Alternately, the growth interruption treatment comprises performing a flourine soak during a soak period. 
     In other features, the method includes depositing a nucleation layer prior to the first deposition period. The method includes performing a sputter etch process prior to the first deposition period to at least partially remove the nucleation layer in the via at a contact bottom. 
     A method for processing a substrate includes providing a substrate including a metal layer, a dielectric layer arranged on the metal layer, and at least one of a via and a trench formed in the dielectric layer; depositing metal using physical vapor deposition (PVD); depositing the metal using chemical vapor deposition (CVD) during a second deposition period, wherein the second deposition period is longer than a first nucleation period required to deposit the metal on the metal layer; stopping the second deposition period prior to a second nucleation delay period, wherein the second nucleation delay period is required to deposit the metal on the dielectric layer; performing the CVD depositing and the stopping N times, where N is an integer greater than or equal to one; and after the performing, depositing the metal using CVD during a third deposition period that is longer than the second nucleation delay period. 
     In other features, the metal comprises tungsten. The metal layer comprises tungsten. The method includes depositing a nucleation layer prior to the first deposition period. The nucleation layer comprises one of fluorine-free tungsten layer and a tungsten/tungsten-nitride layer. The nucleation layer has a thickness between 2 Angstroms and 30 Angstroms. 
     In other features, the method includes performing a growth interruption treatment to interrupt growth of the metal on the dielectric layer after the stopping and before at least one of another one of the N times and the third deposition period. The growth interruption treatment comprises performing an ammonia soak for a soak period. Alternately, the growth interruption treatment comprises performing a flourine soak for a soak period. 
     In other features, the PVD comprises directional PVD. Alternately, the PVD comprises non-directional PVD. The method includes depositing a nucleation layer prior to the first deposition period. The method includes performing a sputter etch process to etch the metal from sidewalls of the via prior to the second deposition period and the third deposition period. The method includes depositing a nucleation layer prior to the first deposition period. The method includes performing a sputter etch process to etch the metal from a field of the substrate, the trench and sidewalls of the via prior to the second deposition period and the third deposition period. 
     Further areas of applicability will become apparent from the description provided herein. The description and specific examples in this summary are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1  is a graph illustrating tungsten thickness as a function of deposition time over various underlying materials; 
         FIGS. 2A-2B  are cross-sectional views illustrating deposition of tungsten in a via using one fill approach according to the present disclosure; 
         FIG. 2C  is a flowchart illustrating a method for depositing tungsten in the via of  FIGS. 2A-2B ; 
         FIGS. 3A-3C  are cross-sectional views illustrating deposition of tungsten in a via using another fill approach according to the present disclosure; 
         FIG. 3D  is a flowchart illustrating a method for depositing tungsten in the via of  FIGS. 3A-3C ; 
         FIG. 4  illustrates a relationship between resistance and tungsten thickness using conformal and bottom-up fill approaches; 
         FIGS. 5-6  illustrate normalized via resistance for conformal and bottom-up fill approaches; 
         FIG. 7  illustrates deposition thickness as a function of time (or selectivity) both with and without a fluorine free tungsten (FFW) nucleation layer; 
         FIG. 8  illustrates resistance as a function of thickness both with and without a fluorine free tungsten (FFW) nucleation layer; 
         FIGS. 9A-9C  are cross-sectional views illustrating deposition of tungsten in a via using another fill approach according to the present disclosure; 
         FIG. 9D  is a flowchart illustrating a method for depositing tungsten in the via of  FIGS. 9A-9C ; 
         FIGS. 10A-10C  are cross-sectional views illustrating deposition of tungsten in a via using another fill approach according to the present disclosure; 
         FIG. 10D  is a flowchart illustrating a method for depositing tungsten in the via of  FIGS. 10A-10C ; 
         FIGS. 11A-11C  are cross-sectional views illustrating deposition of tungsten in a via using another fill approach according to the present disclosure; and 
         FIG. 11D  is a flowchart illustrating a method for depositing tungsten in the via of  FIGS. 11A-11C . 
     
    
    
     DETAILED DESCRIPTION 
     The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
     The present disclosure utilizes selective growth of a metal such as but not limited to chemical vapor deposition tungsten (CVD-W) to at least partially fill a via using a bottom-up approach. The selective growth is followed by non-selective growth in the trench and/or field. 
     The growth of a metal such as but not limited to CVD-W has a different nucleation delay on metal substrates (such as tungsten (W), copper (Cu) and other materials) as compared to interlayer dielectric (ILD). Usually, the nucleation delay on the metal substrate is shorter than on the ILD. The nucleation delay differences can be used to allow selective growth on the metal substrate. The present disclosure utilizes the selectivity to allow tungsten growth from a contact bottom (usually metal) while limiting the growth from the dielectric side walls. Using this approach leads to bottom-up fill of the via and elimination of the seam. 
     In some implementations, a nucleation layer can be used before the selective CVD-W growth. The nucleation layer may include fluorine-free tungsten (FFW) layer, a low temperature pulsed nucleation layer tungsten-tungsten nitride (PNL)-W/WN layer, or another suitable nucleation layer. The nucleation layer may be sufficiently thin such that it does not compromise the selectivity. For example only, the FFW layer may have a thickness from 2-30 angstroms (Å). 
     In some implementations requiring additional thickness, a growth interruption treatment can be used to interrupt growth of CVD-W on the ILD. For example only, the growth interruption treatment may include an ammonia (NH 3 ) soak to interrupt the growth on the ILD. Fluorine treatment may also be used. The deposition of tungsten resumes after the growth interruption treatment. This pattern can be repeated until the desired thickness is achieved. 
     To enhance selectivity and maintain low resistivity, a large H 2  to WF 6  ratio may be applied during the CVD-W nucleation. This can be achieved either in CVD mode or pulsed nucleation layer (PNL) mode where H 2  flows continuously while WF 6  pulses. This approach can also be used in a barrier first fashion. Using the approach described herein allows bottom-up fill while maximizing tungsten grain and eliminating seams associated with conformal growth. This approach can be performed on Novellus Altus® DirectFill™ systems (Fluorine-free tungsten, preclean+tungsten nitride (WN), or preclean+PNL) with minimal hardware modifications. 
     Non-limiting exemplary implementations are set forth below for further illustration. Referring now to  FIG. 1 , tungsten (W) thickness is shown as a function of deposition time over various underlying materials. As can be seen, tungsten growth starts on FFW/W more quickly than on FFW/ILD. In other words, the nucleation delay of CVD-W is longer on FFW/ILD as compared to FFW/W. The present disclosure describes systems and methods that take advantage of the nucleation delay to selectively grow CVD tungsten and allow bottom up fill of vias. As can be seen, the selective growth approach described herein allows approximately 150 angstroms (Å) of tungsten growth on FFW/W before tungsten growth begins on the FFW/ILD. 
     In some implementations, the CVD-W growth is started and continued for a predetermined selectivity period that is less than a predetermined period that would allow FFW/ILD growth. Then, CVD-W growth is terminated and the growth interruption treatment is performed to interrupt growth on FFW/ILD. CVD-W growth is then initiated again on FFW/W and continued for a period of less than or equal to the predetermined selectivity period. CVD-W growth can then proceed to non-selective growth. In some implementations, non-selective growth refers to CVD-W growth for periods longer than the predetermined selectivity period (without interruption), although other non-selective growth approaches may be used. Alternatively, growth can be interrupted again using the growth interruption treatment. The pattern can be repeated until a desired thickness is achieved. 
     Referring now to  FIG. 2A , deposition of tungsten in a via using one fill approach according to the present disclosure is shown. A substrate  20  includes a tungsten layer  24 . The tungsten layer  24  may comprise low resistivity tungsten (LRW). An interlayer dielectric (ILD)  22  is arranged on the tungsten layer  24  to define a field  26 , a trench  28 , and/or a via  30 . A nucleation layer  32  may be deposited on the field  26 , the trench  28  and/or the via  30 . For example only, the nucleation layer  32  may comprise fluorine free tungsten (FFW) having a thickness from 2-30 angstroms (Å). For example only, the FFW may have a thickness of 5 Å. 
     After depositing the nucleation layer  32 , CVD-W  38  is deposited in the via  30  using a selective fill approach. In other words, the tungsten is grown using CVD-W and terminated prior to growth on the ILD. A growth interruption treatment may be performed and then the CVD-W growth may be initiated again. One or more CVD-W and growth interruption steps may be used to achieve a desired thickness. When the desired thickness is reached, non-selective CVD-W growth may be initiated. Non-selective CVD-W growth may comprise CVD-W growth for a period longer than the predetermined selectivity periods, although other methods may be used. 
     Referring now to  FIG. 2C , a method  50  for depositing tungsten in the via of  FIGS. 2A-2B  is shown. A substrate is provided at  52 . The substrate includes ILD and tungsten areas that define a field, a trench and/or a via. At  56 , the nucleation layer  32  is deposited on the field  26 , trench  28  and/or via  30 . 
     At  58 , selective CVD-W growth is initiated. At  60 , the method determines whether the desired thickness has been reached. If false, the method uses a growth interruption treatment to interrupt growth on FFW/ILD and the method returns to  58 . When  60  is true, the method initiates nonselective CVD-W growth at  64 . In some implementations, the nonselective CVD-W growth fills the via and trench regions and may extend above the field to create overburden and allow subsequent processing. For example, the subsequent processing may include chemical mechanical polishing (CMP). 
     Referring now to  FIGS. 3A-3C , another approach that is similar to that shown in  FIGS. 2A-2C  is shown. After depositing the nucleation layer  32 , a sputter etch process identified by arrows  70  is used to remove the nucleation layer  32  in the via  30  above the tungsten layer  24 . Then, the selective CVD-W growth is performed followed by nonselective CVD-W growth. 
     Referring now to  FIG. 3D , a method  80  for depositing tungsten in the via of  FIGS. 3A-3C  is shown. A substrate is provided at  82 . The substrate includes ILD and tungsten areas that define a field, a trench and/or a via. At  86 , the nucleation layer  32  is deposited. At  90 , after depositing the nucleation layer  32 , the method  80  etches the nucleation layer  32  in the via  30  above the tungsten layer  24 . At  92 , selective CVD-W growth is performed. 
     At  94 , if the CVD-W in the via  30  does not have sufficient thickness, CVD-W growth is interrupted at  96  using a growth interruption treatment to interrupt growth on FFW/ILD and the method continues at  92 . When a sufficient thickness is reached, nonselective CVD-W growth is performed at  98 . 
     Referring now to  FIG. 4 , relationships between resistance and tungsten thickness using a conformal approach and a bottom-up approach are shown. As can be appreciated, the bottom-up CVD-W approach has an improved grain structure as compared to the conformal approach. For example only, when filling a via (for example a 30 nm via), bottom-up CVD-W grain size can be as big as the feature size (e.g. 30 nm in this example). The conformal approach grains are limited to half of the feature (or 15 nm in this example). Due to the larger grain size to fill the same feature, the bottom-up approach would result in low via resistance. 
     Referring now to  FIGS. 5-6 , normalized via resistance for conformal and bottom-up approaches is shown. As can be appreciated, the bottom up approach has a lower normalized via resistance as compared to the conformal approach. 
     Referring now to  FIG. 7 , deposition thickness as a function of time (or selectivity) with and without the FFW nucleation layer is shown. Additional selectivity is provided when the CVD-W growth is performed directly on the tungsten layer (as shown in  FIGS. 3A-3D ). 
     Referring now to  FIG. 8 , resistance as a function of thickness with and without the FFW nucleation layer is shown. A lower resistance is provided when the CVD-W growth is performed directly on the tungsten layer after etching the FFW nucleation layer (as shown in  FIGS. 3A-3D ). 
     Referring now to  FIGS. 9A-9C , deposition of tungsten in a via using another fill approach according to the present disclosure is shown. A substrate  200  includes a tungsten layer  204  and an interlayer dielectric (ILD)  202  defining a field  206 , a trench  208 , and/or a via  210 . PVD-W  220  and  222  may be deposited on the field  206  using a directional physical vapor deposition (PVD) approach. Likewise, PVD-W  224  may be deposited on the trench  208  and PVD-W  226  may be deposited in the via  210   
     After depositing the PVD-W  220 ,  222 ,  224  and  226 , CVD tungsten  234  is deposited on the PVD-W  220 ,  222 ,  224  and  226  using a selective approach. When a sufficient thickness is reached, non-selective CVD-W growth is initiated and may continue until the non-selective CVD-W extends above the field to allow subsequent processing. 
     For example, the subsequent processing may include chemical mechanical polishing (CMP). For example only, a thickness of the PVD-W  226  in the via  210  may be 50 (Å). A thickness of the PVD-W  224  in the trench may be 100 (Å). A thickness of the PVD-W  220  and  222  may be 200 (Å). Other thicknesses may be used. 
     Referring now to  FIG. 9D , a method  248  for depositing tungsten in the via of  FIGS. 9A-9C  is shown. A substrate is provided at  250 . The substrate includes ILD and tungsten areas that define a field, a trench and/or a via. 
     At  256 , a directional PVD-W process is used to deposit tungsten on the field, trench and/or via. At  260 , selective CVD-W growth is initiated on the PVD-W. At  262 , the method determines whether the desired thickness has been reached. If false, the method interrupts growth on the ILD at  264  and the method returns to  260 . When the desired thickness is reached at  262 , the method initiates nonselective CVD-W growth at  266 . In some implementations, the nonselective CVD-W growth fills the via and trench regions and may extend above the field to allow subsequent processing. For example, the subsequent processing may include chemical mechanical polishing (CMP). 
     Referring now to  FIGS. 10A-10C , deposition of tungsten in a via using another fill approach according to the present disclosure is shown. A substrate  300  includes a tungsten layer  304  and an interlayer dielectric (ILD)  302  defining a field  306 , a trench  308 , and/or a via  310 . PVD-W  320  and  322  may be deposited on the field  306  using a non-directional physical vapor deposition (PVD) approach. Likewise, PVD-W  324  may be deposited on the trench  308  and PVD-W  326  may be deposited in the via  310 . PVD-W  321 ,  323  and  325  may be deposited on sidewalls. As can be appreciated, a thickness of the PVD-W layer is thinner on the sidewalls  321 ,  323  and  325  as compared to the PVD-W  320 ,  322 ,  324  and  326  on the field  306 , the trench  308 , and the via  310 . An etchback process may be performed. Since the PVD-W is thinnest on the sidewalls, the PVD-W is eliminated there first. 
     After the etchback process, tungsten  334  is deposited on the layers  320 ′,  322 ′,  324 ′ and  326 ′ (after etch) using a selective CVD approach. In other words, the tungsten is grown using one or more selective CVD-W growth and growth interruption steps. Then, non-selective CVD-W growth is initiated and may continue until the non-selective CVD-W extends above the field to allow subsequent processing. For example, the subsequent processing may include chemical mechanical polishing (CMP). 
     Referring now to  FIG. 10D , a method  350  for depositing tungsten in the via of  FIGS. 10A-10C  is shown. At  350 , a substrate is provided that includes ILD and tungsten layers that define features such as a field, trench and/or via. At  356 , PVD-W is deposited on the features such as the field, trench and/or via. At  360 , an etch process removes PVD-W. The etch is continued for a sufficient amount of time such that the PVD-W is removed from the side walls. At  362 , selective CVD growth is initiated. 
     At  364 , the method determines whether the desired thickness has been reached. If false, the method interrupts growth on the ILD at  366  and the method returns to  362 . When the desired thickness is reached at  364 , the method initiates nonselective CVD-W growth at  370 . In some implementations, the nonselective CVD-W growth fills the via and trench regions and may extend above the field to allow subsequent processing. For example, the subsequent processing may include chemical mechanical polishing (CMP). 
     Referring now to  FIGS. 11A-11C , deposition of tungsten in a via using another fill approach according to the present disclosure is shown. A substrate  400  includes a tungsten layer  404  and an interlayer dielectric (ILD)  402  defining a field  406 , a trench  408 , and/or a via  410 . PVD-W  420  and  422  may be deposited on the field  406  using a non-directional physical vapor deposition (PVD) approach. Likewise, PVD-W  424  may be deposited on the trench  408  and PVD-W  426  may be deposited in the via  410 . PVD-W  421 ,  423  and  425  may be deposited on sidewalls. An etchback process with selectivity in the field, sidewall and trench regions may be used to remove PVD-W at  420 ′- 425 ′. For example, fluorine radicals or fluorine gas may be used. 
     CVD-W  434  is deposited on the via  426  approach. In other words, the tungsten is grown using one or more selective CVD-W growth and growth interruption steps. Then, non-selective CVD-W growth is initiated and may continue until the non-selective CVD-W extends above the field to allow subsequent processing. For example, the subsequent processing may include chemical mechanical polishing (CMP). 
     Referring now to  FIG. 11D , a method for depositing tungsten in the via of  FIGS. 11A-11C  is shown. At  450 , a substrate is provided that includes ILD and tungsten layers that define features such as vias, trenches and/or fields. At  456 , PVD-W is deposited. At  460 , a selective etch process removes PVD-W from the side walls, trench and field but not completely from the via  410  (at  426 ′). At  462 , selective CVD growth is initiated. 
     At  464 , the method determines whether the desired thickness has been reached. If false, the method interrupts growth on the ILD surfaces at  466  and the method returns to  462 . When the desired thickness is reached at  464 , the method initiates nonselective CVD-W growth at  470 . In some implementations, the nonselective CVD-W growth fills the via and trench regions and may extend above the field to allow subsequent processing. For example, the subsequent processing may include chemical mechanical polishing (CMP). 
     The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification, and the following claims.