Patent Publication Number: US-2019198392-A1

Title: Methods of etching a tungsten layer

Description:
FIELD 
     Embodiments of the present disclosure generally relate to device manufacture and, in particular, etching tungsten in a feature such as a trench or via. 
     BACKGROUND 
     Tungsten is a material solution for fabrication of devices such as integrated circuits, contact, and BEOL (back end of the line) interconnect fill applications in the 10/7 nm nodes and beyond. Tungsten (W) is often disposed within or atop dielectric layers such as SiN or SiO dielectric layers, however, the inventors have observed difficulty obtaining a desired smooth surface of locally planarized tungsten within features including a dielectric layer such as a trench or via. Further, the inventors have observed that dry etch of tungsten is problematic in that dry etch is often selective towards the dielectric layer leading to faster etching of the dielectric layer over tungsten resulting in unacceptable trenches having uneven tungsten surfaces disposed therein. Moreover, the inventors have observed that uneven surfacing, such as dishing of the top tungsten layer surface within a feature, limits additional processing and downward scaling of tungsten features (e.g., interconnects). 
     Accordingly, the inventors have provided an improved method for etching tungsten disposed within or atop a substrate such as a dielectric layer. 
     SUMMARY 
     Methods for etching tungsten are provided herein. In some embodiments, a method of etching tungsten, includes: leveling a first top surface of a tungsten layer within a feature and atop a top surface of a substrate; and etching the tungsten layer with a hydrogen peroxide and one of a strong acid or a strong base to remove a first portion of the tungsten layer from atop the substrate to form a second top surface of a tungsten layer at a level below the top surface of the substrate. 
     In some embodiments, a method of etching tungsten, includes: planarizing a top surface of a tungsten layer having a portion disposed within a feature and a portion protruding from the feature to form a first level top surface on the portion protruding from the feature, wherein the portion disposed within the feature is disposed upon a dielectric layer; and contacting the first level top surface with an etch solution including an oxidizing agent and one of a strong acid or strong base for a time sufficient to etch the portion protruding from the feature to form a second top surface within the feature, wherein the second top surface is substantially level. 
     In some embodiments, a method of etching tungsten, includes: contacting a substantially level first top surface of a tungsten layer having a portion disposed within a feature with hydrogen peroxide and one of a strong acid or a strong base for a time sufficient to etch the tungsten layer to form a second top surface within the feature, wherein the second top surface is substantially level. 
     In some embodiments, a method of etching tungsten, includes: contacting a substantially level first top surface of a tungsten layer having a portion disposed within a feature with hydrogen peroxide for a time sufficient to etch the tungsten layer to form a second top surface within the feature, wherein the second top surface is substantially level. 
     In some embodiments, a method of etching a tungsten layer disposed on a substrate, including: contacting a substantially level first top surface of a tungsten layer with hydrogen peroxide, and optionally one of a strong acid or a strong base for a time sufficient to etch the substantially level first top surface of the tungsten layer to form a substantially level second top surface within a feature disposed in the substrate. 
     In some embodiments, a method of etching tungsten, including: planarizing a top surface of a tungsten layer disposed atop a substrate and above a feature formed in a dielectric layer of the substrate to form a first level top surface of the tungsten layer above the feature; and contacting the first level top surface of the tungsten layer with an etch solution comprising an oxidizing agent and one of a strong acid or strong base for a time sufficient to etch the first level top surface of the tungsten layer to form a second level top surface of the tungsten layer within the feature. 
     Other and further embodiments of the present disclosure are described below. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of the present disclosure, briefly summarized above and discussed in greater detail below, can be understood by reference to the illustrative embodiments of the disclosure depicted in the appended drawings. However, the appended drawings illustrate only typical embodiments of the disclosure and are therefore not to be considered limiting of scope, for the disclosure may admit to other equally effective embodiments. 
         FIG. 1  depicts a flow diagram of a method for etching tungsten in a feature of a semiconductor device in accordance with embodiments of the present disclosure. 
         FIGS. 2A-2D  respectively depict stages of fabrication of etching tungsten in features of a semiconductor device in accordance with embodiments such as  FIG. 1  of the present disclosure. 
     
    
    
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof. 
     DETAILED DESCRIPTION 
     The inventors have observed that tungsten deposited within a feature may be advantageously formed with level, smooth layers within a feature via a metal fill and/or process including a wet etch in accordance with the present disclosure. Reducing or eliminating dishing and non-level layering within a feature leads to device yield increase, reduced manufacturing costs, and an increase in uniformity across a plurality of features during the formation of a semiconductor device. Increased uniformity enhances application of additional process layers as manufacturing continues. Thus, embodiments of the present disclosure may advantageously be used during different CVD and ALD processes or devices that may be subjected to further processing. In some embodiments, methods of the present disclosure advantageously provide tungsten films or layers having significantly improved level layer formation, such as a flat top surface within a feature, and production level throughput. 
       FIG. 1  is a flow diagram of a method  100  processing a substrate in accordance with some embodiments of the present disclosure. The method  100  is described below with respect to the stages of processing a substrate as depicted in  FIGS. 2A-2D . 
     The method  100  is typically performed on a substrate  200  provided to a processing volume of a process chamber. In some embodiments, as shown in  FIG. 2A , the substrate  200  includes one or more features such as trench  210 , (one shown in  FIGS. 2A-D ) to be filled in with a tungsten layer  225 , the trench  210  extending towards a base  214  of the substrate  200 . Although the following description is made with respect to one feature, the substrate  200  may include any number of features (such as a plurality of trenches  210 , vias, self-aligning vias, self-aligned contact features, duel damascene structures, and the like) as described below or may be suitable for use in a number of process applications such as dual-damascene fabrication processes, self-aligned contact feature processing, and the like. Non-limiting examples of features suitable for etching in accordance with the present disclosure include trenches such as trench  210 , vias, and duel-damascene type features, and features disclosed in U.S. Pat. No. 6,403,491 to Liu et al., entitled Etch Method Using a Dielectric Etch Chamber With Expanded Process Window. 
     Accordingly, substrate  200  may be any suitable substrate having one or more features such as via, self-aligning via, duel-damascene, or trench such as trench  210  formed in the substrate  200 . In embodiments, substrate  200  may include one or more of silicon (Si), silicon oxide, such as silicon monoxide (SiO) or silicon dioxide (SiO 2 ), silicon nitride (such as SiN), or the like. In non-limiting embodiments, the substrate  200  may be a trench  210  formed in a dielectric layer, thus the dielectric layer may be substrate  200  or made of the same materials as described above such as SiN, SiO, and the like. In addition, the substrate  200  may include additional layers of materials or may have one or more completed or partially completed structures or devices formed in, on or under the substrate  200  (not shown). In embodiments, substrate  200  is a dielectric layer which may include additional substrate layering surrounding the dielectric layer or substrate  200  (not shown in  FIGS. 2A-2D ). In embodiments, a low-k material may be suitable as a substrate or layer thereof (e.g., a material having a dielectric constant less than silicon oxide, or less than about 3.9), or the like. In embodiments, the substrate or one or more layers thereof may include, for example, a doped or undoped silicon substrate, a III-V compound substrate, a silicon germanium (SiGe) substrate, an epi-substrate, a silicon-on-insulator (SOI) substrate, a display substrate such as a liquid crystal display (LCD), a plasma display, an electro luminescence (EL) lamp display, a light emitting diode (LED) substrate, a solar cell array, solar panel, or the like. In some embodiments, the substrate  200  include a semiconductor wafer. 
     In embodiments, the substrate  200  may not be limited to any particular size or shape. The substrate may be a round wafer having a 200 mm diameter, a 300 mm diameter or other diameters, such as 450 mm, among others. The substrate  200  can also be any polygonal, square, rectangular, curved or otherwise non-circular workpiece, such as a polygonal glass substrate used in the fabrication of flat panel displays. 
     In some embodiments, features such as trench  210  may be formed by etching the substrate  200  using any suitable etch process. In embodiments, suitable feature(s) for use in accordance with the present disclosure include one or more high aspect ratio trench(es) having a width of less than 20 nanometers. In some embodiments, the trench  210  is defined by one or more sidewalls  220 , a bottom surface  222  and upper corner(s)  224 . In some embodiments, the trench  210  may have a high aspect ratio, e.g., an aspect ratio between about of about 5:1 and about 20:1. As used herein, the aspect ratio is the ratio of a depth of the feature to a width of the feature. In embodiments, the trench  210  has a width  226  less than or equal to 20 nanometers, less than or equal to 10 nanometers, or a width  226  between 5 to 10 nanometers. 
     In some embodiments, features such as one or more vias may be formed by etching the substrate  200  using any suitable etch process. In embodiments, suitable feature(s) for use in accordance with the present disclosure include one or more vias having a width of less than 20 nanometers. In some embodiments, via may include one or more sidewalls with a space between the one or more sidewalls. In embodiments, via may include self-aligning structures such as features described in U.S. Pat. No. 9,343,272 to Pandit, et al., and entitled Self-aligned process. 
     In some embodiments the substrate  200  comprises or consists of a dielectric layer of material described above such as silicon oxide, silicon monoxide (SiO), silicon dioxide (SiO 2 ), silicon nitride (such as SiN), or the like and shaped having an opening  211 , a surface opposite the opening such as bottom surface  222 , and sidewalls  220  between the opening  211  and bottom surface  222 , i.e., the surface opposite the opening  211 . 
     An underlayer (not shown in  FIG. 2A-D ) may optionally be deposited on substrate  200  and within the feature such as trench  210  in a process chamber configured to deposit a layer. The underlayer can be a layer conformably formed along at least a portion of the sidewalls  220  and/or bottom surface  222  of a feature such as trench  210  such that a substantial portion of the feature prior to the deposition of the layer remains unfilled after deposition of the layer. In some embodiments, the underlayer may be formed along the entirety of the sidewalls  220 , such as two sidewalls, and bottom surface  222  of the trench  210 . The underlayer may be a wetting layer provided to enhance the adherence of a metal layer disposed upon the underlayer. 
     Referring to  FIG. 2B , a tungsten layer  225  is shown deposited atop the substrate  200  and within a feature such as trench  210 . In embodiments, tungsten layer  225  includes tungsten or a tungsten alloy. In some embodiments, the tungsten layer  225  may also include, however, other metals, tungsten alloys, and dopants, such as nickel, tin, titanium, tantalum, molybdenum, platinum, iron, niobium, palladium, nickel cobalt alloys, doped cobalt, and combinations thereof. In embodiments, the tungsten and tungsten-containing material is substantially pure tungsten, or tungsten with no more than 1, 2, 3, 4, or 5% impurities. In embodiments, the tungsten layer  225  is a tungsten film or tungsten-containing film resulting from the CVD and ALD processing and may include a pure tungsten (W), tungsten nitride (WN), tungsten silicide (W k Si l ), or tungsten oxide (W n O m ) film, wherein k, l, m, and n are integers which inclusively range from 1 to 6. In embodiments, tungsten containing carbon species may be avoided, for example, tungsten carbide (WC), tungsten carbonitride (WCN) or the like may be excluded and not used to form tungsten layer  225 . 
     In some embodiments, as shown in  FIG. 2B , the tungsten layer  225  is deposited atop a bottom surface  222  of the substrate  200  and within the trench  210  formed in the substrate  200 . The tungsten layer  225  may be deposited using any suitable deposition process(es) or processing chamber. For example, one suitable non-limiting example of a processing chamber may include the OLYMPIA™ brand ALD system available from Applied Materials, Inc. of Santa Clara, Calif. Other suitable process chambers may similarly be used. 
     In some embodiments, the tungsten is pretreated by heating the tungsten to at least 450 degrees Celsius prior to depositing into the feature such as trench  210 . In embodiments, the tungsten is heated to form tungsten with an increased grain size and increased hardness factor within the feature. In some embodiments tungsten is preselected by heating substantially pure tungsten, pure tungsten, tungsten alloy, or tungsten material to above 400 degrees Celsius such as at least 450 degrees Celsius; and forming the tungsten layer atop a dielectric layer such as substrate  200 , wherein the dielectric layer is disposed within the feature. In embodiments, the tungsten layer is formed of pretreated tungsten, wherein the pretreated tungsten has an increased hardness value and increase grain size compared to non-pretreated tungsten. Suitable process conditions for depositing tungsten layer  225  include process conditions, such as temperature suitable to heat the substrate at a temperature in the range from about 450 degrees C. to about 600 degrees C., or in the range from about 450 degrees C. to about 500 degrees C. In embodiments, the process chamber for depositing tungsten is maintained at a pressure in the range from about 1 Torr to about 150 Torr, or in the range from about 5 Torr to about 90 Torr. 
     In some embodiments, tungsten is deposited into the feature by chemical vapor deposition (CVD). Non-limiting examples of CVD processes suitable for deposition of the tungsten layer  225  are disclosed in commonly-owned U.S. Pat. No. 7,405,158, issued Jul. 29, 2008 to Lai et al. 
     In some embodiments, the thickness of the tungsten layer  225  is predetermined to fill a gap in a feature such as a trench, via, self aligned via, duel damascene structure, or the like. In embodiments, the shape of the tungsten layer  225  is substantially uniform and fills the feature at least to the top surface  240  of the substrate  200 . In embodiments, tungsten layer  225  completely fills the feature to overfill trench  210 . As shown in  FIG. 2B , a first portion  228  of the tungsten layer  225  is shown as overburden extending above the top surface  240  of the substrate  200  and atop the top surface  240  of the substrate  200 . In some embodiments, tungsten layer  225  is deposited within a feature such as a via or trench  210  and atop substrate  200  such that overburden is deposited on the field region or top surface  240  of substrate  200 . In embodiments, a first top surface  242  of the tungsten layer  225  is at a level above the top of the feature such as trench  210  or top surface  240  of the substrate  200 . As shown in  FIG. 2B , a first portion  228  of the tungsten layer  225  may include the first top surface  242  of the tungsten layer  225  having a rough or non-flat surface. A second portion  229  of the tungsten layer  225  fills the feature such as trench  210  from the bottom surface of first portion  228  of the tungsten layer  225  to the bottom surface  222  of the feature such as trench  210 . 
     Referring to  FIG. 1  at  104 , embodiments of the present disclosure include leveling a first top surface of a tungsten layer within a feature and atop a top surface of a substrate. For example, in some embodiments, first top surface  242  of tungsten layer  225  as shown in  FIG. 2B  is leveled to form first level top surface  248  of the tungsten layer  225  as shown in  FIG. 2C . First level top surface  248  of the tungsten layer  225  is flat or substantially flat, such that is sits upon an imaginary horizontal line above the feature such as a via or trench  210 . Leveling the first top surface  242  of the tungsten layer at  225  within the feature and atop the top surface of substrate  200  may be performed by chemical mechanical planarization (CMP) techniques and the like. In embodiments, first level top surface  248  of the tungsten layer  225  is flat or substantially flat, and also has a smooth surface. 
     In embodiments, planarizing the first top surface  242  of the tungsten layer  225  having a portion (such as second portion  229 ) disposed within a feature such as trench  210  and a portion (such as first portion  228  of the tungsten layer  225  described above) protruding from the feature, may form, as shown in  FIG. 2C , a first level top surface  248  of the tungsten layer  225  on the protruding portion such as the first portion  228  of the tungsten layer  225  described above. In some embodiments, the first level top surface  248  of the tungsten layer  225  is disposed upon a dielectric layer as described above. In embodiments, leveling of first top surface  242  includes planarizing the first portion of the tungsten layer atop the substrate to form a first level top surface  248  of the tungsten layer  225  above the top surface  240  of the substrate  200 . 
     Referring to  FIG. 2C , the first level top surface  248  of the tungsten layer  225  is formed as a level or substantially level surface free of rough or jagged deformities. In embodiments, the first level top surface  248  of the tungsten layer  225  is characterized as flat, or free of rough or dished shapes. Further, the first level top surface  248  of the tungsten layer  225  is shaped as a flat plane horizontal to a base plane. In some embodiments, the first level top surface  248  of the tungsten layer  225  is shaped as a straight or flat surface positioned horizontally from, or parallel to, base  214  and/or bottom surface  222 . 
     In embodiments, etching in accordance with the present disclosure is performed on the first level top surface  248  which may be a substantially level top surface of the tungsten layer  225 . Referring to  FIG. 1  at  106  and  FIG. 2D , tungsten etch in accordance with the present disclosure removes tungsten from atop substrate  200  or dielectric layer and the first level top surface  248  of the tungsten layer  225 , to form a level below the top surface  240  of the substrate  200 . In some embodiments etching the first level top surface of the tungsten layer includes contacting the first level top surface  248  with an oxide, peroxide such as hydrogen peroxide, and/or one of a strong acid or a strong base to remove the first portion  228  of the tungsten layer  225  from atop the substrate  200  to form a second top surface  260  of the tungsten layer  225  at a level below the top surface  240  of the substrate  200  and within the feature. In some embodiments, etching the first level top surface  248  of the tungsten layer  225  includes contacting the first level top surface  248  with a hydrogen peroxide and one of a strong acid or a strong base to remove the first portion  228  of the tungsten layer  225  from atop the substrate  200  to form a second top surface  260  of the tungsten layer  225  at a level below the top surface  240  of the substrate  200 . In some embodiments etching the first level top surface of the tungsten layer includes contacting the first level top surface  248  with an oxide, peroxide such as hydrogen peroxide to remove the first portion  228  of the tungsten layer  225  from atop the substrate  200  to form a second top surface  260  of the tungsten layer  225  at a level below the top surface  240  of the substrate  200  and within the feature. In some embodiments, etching the first level top surface  248  of the tungsten layer  225  includes contacting the first level top surface  248  with a hydrogen peroxide to remove the first portion  228  of the tungsten layer  225  from atop the substrate  200  to form a second top surface  260  of the tungsten layer  225  at a level below the top surface  240  of the substrate  200 . In embodiments, etching is for a time sufficient to etch the tungsten layer to form a substantially level, or substantially flat, second top surface  260  of the tungsten layer  225  within the feature. In embodiments, the second top surface  260  is free of rough or jagged deformities. In embodiments, the second top surface  260  is characterized as flat, or free of rough or dished shapes. Further, the second top surface  260  is shaped as a flat plane horizontal to, or parallel to, a base plane (such as the general plane of the substrate). In some embodiments, the second top surface  260  is a straight or flat surface positioned horizontally from, or parallel to, base  214  and/or bottom surface  222  within the feature. 
     In some embodiments, the depth of the formation of second top surface  260  of the tungsten layer  225  may be controlled by, e.g. adjusting the etch duration. In some embodiments, the landing or depth of the second top surface  260  may be controlled or lowered within the feature such as trench  210  by extending the amount of time the etch solution (e.g., combination of peroxide and acid or base) is in contact with tungsten layer  225 . In embodiments, the landing or depth of the second top surface  260  may be lowered within the feature such as trench  210  be lengthening the amount of time the etch solution (e.g., hydrogen peroxide and HCl) is in contact with tungsten layer  225 . Non-limiting examples of suitable times sufficient to etch the tungsten layer to form, for example, a substantially level second top surface  260  within the feature include 1 second to 5 minutes, 1 second to 1 minute, 30 seconds to 1 minute, 10 seconds to 50 seconds, 20 seconds to 40 seconds, 30 seconds to 35 seconds, or about 30 to 40 seconds. 
     In embodiments, etching is characterized as an in situ wet etch, where the oxide constituent, and acid constituent or base constituent of the wet etch solution are added together to contact the first level top surface  248  of the tungsten layer  225  together. In embodiments, the etch is characterized as an in situ wet etch, for example where an oxide constituent such as hydrogen peroxide, and acid constituent are added simultaneously. In embodiments, the etching is characterized as highly selective towards the tungsten layer over the dielectric layer. In some embodiments, oxidant such as peroxide (e.g., hydrogen peroxide) is added in amounts sufficient to oxidize the top layer of tungsten upon or within the feature such as when the oxidant contacts the tungsten. 
     In some embodiments, acid such as HCL is added in amounts sufficient to etch oxidized tungsten. Non-limiting examples of acid includes dilute acid, concentrated acid, or acids solutions containing about 1% to about 90% acid. In embodiments, a strong acid such as an acid that completely ionizes in water to give one or more protons per acid molecule may be suitable for use in accordance with the present disclosure. In embodiments, suitable strong acids for use in accordance with the present disclosure include acid having a pH of 3 or lower. One non-limiting example of a suitable acid for use in accordance with the present disclosure is hydrochloric acid (HCl). 
     In some embodiments, base is added in amounts sufficient to etch oxidized tungsten. In embodiments, a strong base such as a base that completely ionizes in water to give hydroxide ions (OH—) may be suitable for use in accordance with the present disclosure. In embodiments, suitable strong bases for use in accordance with the present disclosure include base having a pH of 12 or higher. In embodiments, a base such as NH 4 OH may be added in amounts sufficient to etch oxidized tungsten. Non-limiting examples of base includes dilute base, concentrated base, or basic solutions containing about 1% to about 90% base. In embodiments, a strong base is NH 4 OH. 
     In some embodiments, hydrogen peroxide is suitable for use as an etching solution. For example, a method of etching tungsten, includes: leveling a first top surface of a tungsten layer within a feature and atop a top surface of a substrate; and etching the tungsten layer with a hydrogen peroxide etching solution to remove a first portion of the tungsten layer from atop the substrate to form a second top surface of a tungsten layer at a level below the top surface of the substrate. Further, some embodiments, include a method of etching tungsten, including: planarizing a top surface of a tungsten layer having a first portion disposed within a feature and a second portion protruding from the feature to form a first level top surface on the second portion, wherein the first portion is disposed upon a dielectric layer; and contacting the first level top surface with an etch solution including, or consisting of hydrogen peroxide for a time sufficient to etch the second portion to form a second level top surface on the first portion within the feature. In embodiments, the hydrogen peroxide etching solution is an aqueous solution of hydrogen peroxide, including concentrations of at least 35%, at least 50%, or at least 70%. 
     In embodiments, the etch rate of the tungsten layer is 1 nm/min to 50 nm/min, 1 nm/min to 10 nm/min, 1 nm/min to 5 nm/min. 
     In embodiments, etching may be terminated by removing the etch solution, washing the one or more features, and drying the feature filled substrate. For example, washing may be performed by contacting the feature filled substrate with water. Drying may be performed under gas such as argon, or nitrogen. 
     While the foregoing is directed to embodiments of the present disclosure, other and further embodiments of the disclosure may be devised without departing from the basic scope thereof.