Patent Publication Number: US-2018033643-A1

Title: Methods and apparatus for using alkyl amines for the selective removal of metal nitride

Description:
FIELD 
     Embodiments of the present disclosure generally relate to methods and apparatus for using alkyl amines for the selective removal of metal nitrides. 
     BACKGROUND 
     Metal nitride materials such as titanium nitride (TiN) and tantalum nitride (TaN) are commonly used in the semiconductor industry for many semiconductor applications, such as a masking material or as a barrier material. However, selectively removing a metal nitride masking material without harming other structures, for example exposed or underlying dielectric or metal layers, is very difficult. The problem of selectively removing a metal nitride masking material without harming other structures becomes even more difficult where solution based or plasma based approaches are not feasible and/or desirable. 
     Accordingly, the inventors have developed improved methods and apparatus for removing a metal nitride selectively with respect to exposed or underlying dielectric or metal layers. 
     SUMMARY 
     Methods and apparatus for removing a metal nitride selectively with respect to exposed or underlying dielectric or metal layers are provided herein. In some embodiments, a method of etching a metal nitride layer atop a substrate includes: (a) oxidizing a metal nitride layer to form a metal oxynitride layer (MN 1-x O x ) at a surface of the metal nitride layer, wherein M is one of titanium or tantalum and x is an integer from 0.05 to 0.95; and (b) exposing the metal oxynitride layer (MN 1-x O x ) to a process gas, wherein the metal oxynitride layer (MN 1-x O x ) reacts with the process gas to form a volatile compound which desorbs from the surface of the metal nitride layer. 
     In some embodiments, a method of etching a titanium nitride layer atop a substrate includes: exposing a titanium nitride layer to a process gas formed by vaporizing a process solution comprising diethylamine and water, wherein the titanium nitride layer reacts with the process gas to form a volatile compound which desorbs from the surface of the titanium nitride layer. 
     In some embodiments, an apparatus for etching a metal nitride layer atop a substrate apparatus for etching a metal nitride layer atop a substrate includes: a reactor body comprising a processing volume to hold a liquid process solution, a body flange at a first end, and a first heater embedded within or coupled to the reactor body at a second end opposite the first end to heat the liquid process solution; a reactor lid comprising a lid flange at a first end configured to mate with the body flange; a circumferential clamp configured to clamp the reactor body to the reactor lid at the lid flange and the body flange; a vacuum chuck embedded within the reactor lid and configured to hold a substrate within the processing volume such that a metal nitride layer disposed on the substrate faces a bottom of the processing volume; a second heater embedded within or coupled to the reactor lid and configured to heat the substrate; and an exhaust system coupled to the reactor body to remove process byproducts from the processing volume. 
     Other embodiments and variations of the present disclosure are discussed 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. The appended drawings illustrate only typical embodiments of the disclosure and are therefore not to be considered limiting of the scope, for the disclosure may admit to other equally effective embodiments. 
         FIG. 1  depicts a flowchart of a method of etching a metal nitride layer atop a substrate in accordance with some embodiments of the present disclosure. 
         FIGS. 2A-C  depicts the stages of etching a metal nitride layer atop a substrate in accordance with some embodiments of the present disclosure. 
         FIG. 3  depicts a cross-sectional view of an apparatus suitable to perform methods for etching a metal nitride layer atop a substrate in accordance with some embodiments of the present disclosure 
     
    
    
     To facilitate understanding, identical reference numerals have been used, where possible, to designate identical elements that are common to the figures. The figures are not drawn to scale and may be simplified for clarity. Elements and features of one embodiment may be beneficially incorporated in other embodiments without further recitation. 
     DETAILED DESCRIPTION 
     Methods and apparatus for etching a metal nitride selectively with respect to exposed or underlying dielectric or metal layers are provided herein. In some embodiments, the inventive methods described herein advantageously provide an innovative method of etching a metal nitride, utilized as a masking material, selectively with respect to exposed or underlying dielectric or metal layers, for example BLACK DIAMOND® dielectric material available from Applied Materials, Inc. of Santa Clara, Calif. (hereinafter “Black Diamond” or “BD”) or silicon dioxide layers (e.g. SiOx). The inventive methods described herein may also be used in other semiconductor manufacturing applications where etching a metal nitride may be necessary. In some embodiments, an amine-based solution is vaporized and applied to a metal nitride material to selectively etch the metal nitride material from the top of structures without harming, for example, underlying or exposed Black Diamond, silicon dioxide, and/or copper (Cu) structures. 
       FIG. 1  is a flow diagram of a method  100  of etching a metal nitride layer atop a substrate in accordance with some embodiments of the present disclosure.  FIGS. 2A-2C  are illustrative cross-sectional views of the substrate during different stages of the processing sequence of  FIG. 1  in accordance with some embodiments of the present disclosure. The inventive methods may be performed in a suitable reactor vessel, such as the reactor vessel discussed below with respect to  FIG. 3 . 
       FIG. 3  depicts a cross-sectional view of a reactor vessel  300  suitable for performing method  200 . The reactor vessel  300  is a closed loop controlled system using materials for the wetted parts of the reactor vessel  300  that are compatible with chemicals utilized in method  200  described below. The reactor vessel  300  depicted in  FIG. 3  comprises a reactor body  302  and a reactor lid  304 . The reactor body  302  and the reactor lid  304  comprise suitable openings for the addition of sensors, power, and vacuum inputs as described below. The reactor body  302  comprises a processing volume  306 . The processing volume  306  holds a suitable liquid process solution  318  used in the method  100  described below. In some embodiments, the processing volume  306  can hold up to about 200 to about 300 ml of a suitable liquid process solution  318 . 
     The reactor body  302  and the reactor lid are made of material suitable for withstanding the temperature and pressures utilized in the method  200  described below. In some embodiments, the reactor body  302  and the reactor lid are made of stainless steel (SST) material coated with, for example Teflon or Magnaplate 10K. The coating can be selected based on the compatibility with the chemicals, temperatures, and pressures utilized in the method  200 . The reactor body  302  comprises a body flange  322  at a first end  324 . The reactor lid  304  comprises a lid flange  326  at a first end  328  configured to mate with the body flange  322 . The body flange  322  is clamped with the lid flange  326  and having a leak proof O-ring  330  seal. The body flange  322  has a chamfered back-surface  356 . The lid flange  326  has a chamfered back-surface  358 . The body flange  322  and the lid flange  326  are mated by a circumferential clamp  332  tightened by a bolt  334  around the chamfered back-surfaces  356 ,  358 . 
     Cooling channels  336  are added in the vicinity of the O-ring  330  to protect the O-ring  330  from high temperatures. Cooling channels  336  are also provided on the top of the reactor lid  304  to maintain the outer reactor lid  304  temperature below about 70° C. for safety purposes. Suitable inlets  344  and outlets  346  are coupled to the cooling channels  336  to supply and remove a cooling fluid such as water from the cooling channels  336 . The outside walls  338  of the reactor body  302  are covered with an insulation jacket  340  to avoid condensation of process gases and protection from high temperature surfaces. 
     A vacuum chuck  308 , coupled to a vacuum source  360 , is embedded within the reactor lid  304  and configured to hold the substrate  314  within the processing volume  306 . The vacuum chuck  308  holds the substrate  314  such that the metal nitride layer disposed on the substrate  314  faces the bottom  316  of the processing volume  306 . 
     The liquid process solution  318  within the processing volume  306  is heated using, for example, a first heater  310  embedded within or coupled to the reactor body  302  at a second end  362 . The first heater  310  is coupled to a suitable power supply (not shown). The first heater  310  heats the liquid process solution  318  to a temperature sufficient to vaporize the solvent. 
     In some embodiments, the substrate  314  is heated using, for example, a second heater  312  embedded within or coupled to the reactor lid  304 . The second heater  312  is coupled to a suitable power supply (not shown). In some embodiments, the first heater  310  and the second heater  312  may be at the same temperature. In some embodiments, the first heater  310  and the second heater  312  may be at different temperatures. In some embodiments, the first heater may be at a temperature of about 25 degrees Celsius to about 300 degrees Celsius. In some embodiments, the second heater is at a higher temperature than the first heater to avoid condensation of vapors onto the substrate  314 . In some embodiments, the second heater  312  is at a temperature that is about 10 to about 15 degrees greater than the first heater temperature. 
     In some embodiments, the reactor lid  304  is clamped to a top portion of the reactor body  302  to seal the processing volume  306 . In some embodiments, the reactor body  302  is also heated using for example heating coils within the reactor body  302 . Heating the reactor body  302  prevents condensation of vapors onto the interior surface walls  320  of the processing volume  306 . 
     The liquid process solution  318  is injected inside the processing volume  306  through an opening  342  in the reactor body  302 . A manual valve  364  is used to drain out the liquid process solution  318  from the processing volume  306 . 
     A closed loop controlled exhaust system  348  coupled to the reactor body  302  takes a feedback from a pressure transducer  350  setting to trigger a pneumatic valve  352  to releases byproducts of the method  200  to, for example a scrubber, via the overpressure line  354 . A temperature loop feedback is maintained by thermocouples  354  &amp; an over temperature switch  366  with heater controller. 
     The method  100  begins at  102 , and as depicted in  FIG. 2A , by oxidizing a metal nitride layer  204  atop a substrate  202 . The substrate  202  may be any suitable substrate, such as a semiconductor wafer. Substrates having other geometries, such as rectangular, polygonal, or other geometric configurations may also be used. In some embodiments, the substrate  202  may include a first layer  216 . The first layer  216  may be a base material of the substrate  202  (e.g., the substrate itself), or a layer formed on the substrate. For example, in some embodiments, the first layer  216  may be a layer suitable for forming a feature within the first layer  216 . For example, in some embodiments, the first layer  216  may be a dielectric layer, such as silicon oxide (SiO2), silicon nitride (SiN), a low-k material, or the like. In some embodiments, the low-k material may be carbon-doped dielectric materials (such as carbon-doped silicon oxide (SiOC), BLACK DIAMOND® dielectric material available from Applied Materials, Inc. of Santa Clara, Calif., or the like), an organic polymer (such as polyimide, parylene, or the like), organic doped silicon glass (OSG), fluorine doped silicon glass (FSG), or the like. In some embodiments, the first layer  216  may be a copper layer. 
     In some embodiments, the metal nitride layer  204  is titanium nitride (TiN) or tantalum nitride (TaN). In some embodiments, the metal nitride layer  204  is deposited using any suitable deposition process known in the semiconductor manufacturing industry, such as a physical vapor deposition (PVD) process or a chemical vapor deposition (CVD) process. In some embodiments, the metal nitride layer may be a masking layer used for forming features, such as vias or trenches in underlying layers. Oxidation of the metal nitride layer  204  forms a metal oxynitride layer (MN 1-x O x )  208  at a surface  214  of the metal nitride layer  204 , where M is one of titanium or tantalum and x is an integer from 0.05 to 0.95. 
     In some embodiments as depicted in  FIG. 2A , the metal nitride layer  204  is oxidized by exposing the metal nitride layer  204  to an oxygen-containing gas  206 . In some embodiments, the oxygen containing gas is oxygen (O 2 ) gas or ozone (O 3 ) gas or combination thereof. In some embodiments, the oxygen-containing gas  206  is provided at a flow rate of about 2 sccm to about 20 sccm for about 2 to about 30 seconds. 
     Next, at  104  and as depicted in  FIG. 2B , the metal oxynitride layer (MN 1-x O x )  208  is exposed to a process gas  210 . The reaction of the process gas  210  and the metal oxynitride layer (MN 1-x O x )  208  forms a volatile compound  212  atop the metal nitride layer  204  which desorbs from the surface  214  of the metal nitride layer  204 . The volatile compound  212  desorbs from the surface  214  of the metal nitride layer  204  at the temperature at which the process gas  210  is formed, accordingly a separate anneal process is unnecessary to desorb the volatile compound  212 . In some embodiments, the process gas  210  is produced by heating a liquid process solution within the reactor vessel  300  to at least the boiling point of the liquid process solution. In some embodiments, the process solution comprises an etchant precursor of secondary amines having the formula R 1 R 2 NH wherein R 1  and R 2  can be an alkyl group such as methyl, ethyl, propyl, or butyl. In some embodiments, the etchant precursor is diethylamine, tert-butylamine, ethyldenediamine, triethylamine, dicyclohexylamine, hydroxylamine, dipropylamine, dibutylamine, butylamine, isopropylamine, or propylamine. 
     In some embodiments, the liquid process solution is heated to a temperature of at least the boiling point of the liquid process solution or in some embodiments to a temperature of at least above the boiling point of the liquid process solution. A person of ordinary skill in the art will understand that the maximum temperature to which the liquid process solution is heated is limited by the decomposition temperature of the selected etchant precursor molecule. For example in some embodiments, the process solution comprising diethylamine, which has a boiling point of about 55 degrees Celsius, is heated to a temperature of about 80 to about 175 degrees Celsius. For example, in some embodiments, the process solution comprising dicyclohexylamine, having a boiling point of about 255 degrees Celsius, is heated to a temperature of up to about 300 degrees Celsius. The inventors have also observed that increasing the volume of the etchant precursor, for example from about 5 ml to about 30 ml, and utilizing higher temperatures to vaporize the process solution (though still limited by decomposition temperature of the selected etchant precursor molecule), results in an increase in the pressure within the reactor vessel  300  which improves the etch rate of the metal nitride layer  204 . The inventors have observed that a pressure range of about 1 atmosphere (atm) to about 10 atm, for example about 7 atm improves the etch rate of the metal nitride layer  204 . In some embodiments, the metal oxynitride layer (MN 1-x O x )  208  is exposed to the process gas  210  for about 10 to 1200 seconds, for example for about 10 to about 300 seconds, for example for about 60 to about 1200 seconds. 
     In some embodiments, the oxidation of the metal nitride layer  204  is done within the reactor vessel  300  without exposure to the oxygen-containing gas as described above (i.e., in-situ oxidation). In in-situ oxidation embodiments, the metal nitride layer is not exposed to an initial oxygen-containing gas. Instead, the liquid process solution comprises a mixture of the etchant precursor and water. In some embodiments, the liquid process solution consists of, or consists essentially of, a mixture of the etchant precursor and water. In some embodiments, the liquid process solution comprises about 0.1 wt. % to about 5 wt % of water and the balance etchant precursor. The inventors have observed that the addition of water within the liquid process solution the process gas  210  shown in  FIG. 2B  can advantageously oxidize and etch the metal nitride layer  204  in a single step and furthermore improve the etch rate of the metal nitride layer  204  as compared to an initial oxidation of the metal nitride layer  204  oxidation via exposure to the oxygen-containing gas. For example, performing an in-situ oxidation results in an metal nitride layer  204  etch rate of about 3 to 4 angstroms/minute, whereas a separate oxidation step results in a lower metal nitride layer  204  etch rate. 
     In some embodiments, the method  100  can be repeated to etch the metal nitride layer  204  to a predetermined thickness. For example, in some embodiments, the method  100  is repeated to completely, or substantially completely, etch the metal nitride layer  204  without damaging the underlying first layer  216 . 
     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.