Patent Publication Number: US-2007113975-A1

Title: Plasma reaction chamber assemblies

Description:
TECHNICAL FIELD  
      The invention pertains to methods of enhancing selectivity of silicon dioxide relative to one or more organic materials, and further pertains to reaction chamber configurations.  
     BACKGROUND OF THE INVENTION  
      Semiconductor processing frequently involves etching of silicon-oxide-containing materials, such as, for example, silicon dioxide, borophosphosilicate glass (BPSG), etc. Semiconductor processing also frequently involves patterning etched materials with organic photoresist masking materials. Organic photoresist materials can be either positive or negative photoresists, and can include, for example, novolac and cyclized synthetic rubber resin. A difficulty which can occur in etching silicon-oxide-containing materials results from limited selectivity of present etch methods for silicon-oxide-containing materials relative to organic masking materials. Such difficulty is described with reference to  FIGS. 1-3 .  
      Referring first to  FIG. 1 , a semiconductor wafer fragment  10  is illustrated. Wafer fragment  10  comprises a substrate  12  having a silicon-oxide-containing layer  14  thereover. Substrate  12  can comprise, for example, monocrystalline silicon lightly-doped with a p-type background dopant. To aid in interpretation of the claims that follow, the terms “semiconductive substrate” and “semiconductor substrate” are defined to mean any construction comprising semiconductive material, including, but not limited to, bulk semiconductive materials such as a semiconductive wafer (either alone or in assemblies comprising other materials thereon), and semiconductive material layers (either alone or in assemblies comprising other materials). The term “substrate” refers to any supporting structure, including, but not limited to, the semiconductive substrates described above.  
      Layer  14  can comprise, for example, silicon dioxide; can consist essentially of silicon dioxide, or can consist of silicon dioxide. Also layer  14  can comprise a doped silicon oxide, such as, for example, BPSG.  
      A patterned masking layer  16  is shown formed over silicon-oxide-containing layer  14 . Masking layer  16  can comprise, for example, an organic photoresist material, and can be patterned by photolithographic processing.  
      Referring to  FIG. 2 , wafer fragment  10  is subjected to etching conditions which etch into silicon-oxide-containing material  14  to form an opening  18  extending therein. A suitable etch for silicon-oxide-containing material  14  is a plasma etch utilizing one or more of CF 4 , C 2 F 6 , H 2 , C 3 F 8 , and CHF 3 .  FIG. 2  shows a thickness of masking layer  16  reduced during the etching of oxide layer  14 . Such reduction in thickness occurs due to non-selectivity of the etch conditions for oxide material  14  relative to masking material  16 . Generally, the etching conditions will have some selectivity for oxide layer  14 , in that the material of oxide layer  14  will etch faster than will the material of organic masking layer  16 . However, the selectivity is not absolute, and accordingly some of the organic material of layer  16  etches during the etching of the silicon oxide of layer  14 .  
      Referring to  FIG. 3 , wafer fragment  10  is shown after continued etching of layer  14 . Such continued etching has removed layer  16  ( FIG. 2 ) from over layer  14 . Such removal of layer  16  can be problematic in further processing steps.  
      It would be desirable to develop alternative methods for etching silicon-oxide-containing materials with enhanced selectivity for the silicon-oxide-containing materials relative to organic materials.  
     SUMMARY OF THE INVENTION  
      In one aspect, the invention encompasses a method of enhancing selectivity of etching silicon dioxide relative to one or more organic substances. A material comprising one or more elements selected from Group VIII of the periodic table is provided within a reaction chamber; and a substrate is provided within the reaction chamber. The substrate has both a silicon-oxide-containing composition and at least one organic substance thereover. The silicon-oxide-containing composition is plasma etched within the reaction chamber. The plasma etching of the silicon-oxide-containing composition has increased selectivity for the silicon oxide of the composition relative to the at least one organic substance than would plasma etching conducted without the material in the chamber.  
      In another aspect, the invention encompasses a plasma reaction chamber assembly. The assembly comprises at least one interior wall, and at least one liner along the at least one interior wall. The liner comprises one or more of Ru, Fe, Co, Ni, Rh, Pd, Os, W, Ir, Pt and Ti. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      Preferred embodiments of the invention are described below with reference to the following accompanying drawings.  
       FIG. 1  is a diagrammatic, fragmentary, cross-sectional view of a semiconductor wafer at a preliminary processing step of a prior art method.  
       FIG. 2  is a view of the  FIG. 1  wafer fragment shown at a prior art processing step subsequent to that of  FIG. 1 .  
       FIG. 3  is a view of the  FIG. 1  wafer fragment shown at a prior art processing step subsequent to that of  FIG. 2 .  
       FIG. 4  is a flow chart diagram of a first embodiment method of the present invention.  
       FIG. 5  is a flow chart diagram of a second embodiment method of the present invention.  
       FIG. 6  is a diagrammatic, cross-sectional view of a reaction chamber apparatus which can be utilized in methodology of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
      This disclosure of the invention is submitted in furtherance of the constitutional purposes of the U.S. Patent Laws “to promote the progress of science and useful arts” (Article 1, Section 8).  
      The invention encompasses methods for increasing selectivity of silicon oxide etching relative to organic materials. One embodiment of the present invention is described with reference to  FIG. 4 . At an initial step  100  a material comprising one or more elements from Group VIII of the periodic table (i.e., one or more of Fe, Co, Ni, Ru, Rh, Pd, Os, Ir, and Pt) is provided within a reaction chamber. The material can consist essentially of one or more elements selected from Group VIII of the periodic table, or can consist of one or more elements selected from Group VIII of the period table.  
      One method of forming the material within a reaction chamber is to place a mass comprising one or more elements selected from Group VIII of the periodic table within the reaction chamber. Such mass can be in the form of a liner which is fabricated outside of the reactor and subsequently placed within the reaction chamber. Alternatively, the mass can be in the form of a material which is subjected to etching within the chamber. Such etching can cause compositions comprising one or more Group VIII elements to be expelled from the mass and deposited as a second mass along an interior of the reaction chamber.  
      After the material comprising the one or more Group VIII elements is provided within the reaction chamber, a silicon-oxide-containing composition is etched within the chamber. Suitable silicon-oxide-containing compositions include, for example, silicon dioxide and BPSG. In particular embodiments, the etched composition can consist essentially of silicon dioxide, or can consist of silicon dioxide.  
      Although the invention is described above with reference to forming a material comprising one or more Group VIII elements within a reaction chamber prior to etching a silicon-oxide-containing composition within the reaction chamber, it is to be understood that the Group VIII element can also be provided during the etching of the silicon-oxide-containing component. For instance, if a semiconductor wafer comprises both silicon dioxide and a Group VIII material thereon during etching of the silicon-oxide-containing material, the Group VIII element will be provided within the chamber at the same time that the silicon-oxide-containing composition is provided within the chamber.  
      It has been experimentally determined that the inclusion of one or more Group VIII elements within a reaction chamber can increase selectivity of a plasma etch for a silicon-oxide-composition relative to an organic material. For instance, if ruthenium is provided within a reaction chamber during a plasma etch of silicon dioxide, a selectivity of an etch for silicon dioxide relative to a photoresist can be enhanced. For purposes of interpreting this disclosure and the claims that follow, the term “selective” refers to an etch which is faster with respect to one material than to another, and enhancement of selectivity indicates that the difference in the relative etch rates is increased. A particular experiment is described below as Example 1.  
      There are several mechanisms by which enhancement of selectivity for a silicon-oxide-containing material relative to an organic material can be enhanced. One mechanism is that reactive species such as mono-atomic oxygen and mono-atomic fluorine are removed. For instance, the Group VIII elements provided within the reaction chamber can catalyze recombination of mono-atomic oxygen (which can be formed in a reaction chamber during an etch of a silicon-oxide-comprising material) with other materials to reduce a concentration of mono-atomic oxygen within a reaction chamber. As mono-atomic oxygen is highly reactive, and accordingly relatively non-selective for silicon-oxide-comprising materials to organic materials, increased selectivity can be achieved by reducing the mono-atomic oxygen concentration. If two mono-atomic oxygen species are recombined together, the result is diatomic oxygen (O 2 ). Alternatively, mono-atomic oxygen can be recombined with components other than monoatomic oxygen within a reaction chamber.  
      Another species which is highly reactive in reaction chambers is mono-atomic fluorine. The Group VIII elements can catalyze recombination of mono-atomic fluorine with other species to reduce a concentration of mono-atomic fluorine within a reaction chamber. If two mono-atomic fluorines are combined together, the result is diatomic fluorine (F 2 ). Alternatively, mono-atomic fluorine can be combined with carbon-containing materials to form HCF 3 , CF 4 , etc.  
      Another mechanism by which enhancement of selectivity for a silicon-oxide-containing material relative to an organic material can be enhanced with Group VIII elements is that the elements may modify organic materials to decrease an etch rate of the organic materials.  
       FIG. 5  shows a flow chart diagram of a particular embodiment of the present invention wherein a liner is provided within a reaction chamber. Specifically, the first step of  FIG. 5  is to provide a liner which comprises tungsten, platinum, titanium and/or one or more elements from Group VIII of the periodic table within a reaction chamber. Such liner will be formed outside of the reaction chamber, and subsequently inserted within the reaction chamber. The metallic components of the liner can increase selectivity of a plasma etch for silicon-oxide-containing components relative to organic materials. For instance, it has been experimentally determined that tungsten can increase such selectivity. Particular experimental conditions are described with reference to Example 2 below.  
      Step  210  of  FIG. 5  indicates that a silicon-oxide-containing material (specifically silicon dioxide) is etched within the reaction chamber after the liner is inserted.  
       FIG. 6  illustrates an exemplary apparatus  300  which can be utilized in the process of  FIG. 5 . Specifically, apparatus  300  comprises a reaction chamber  310  having sidewalls  312 . Reaction chamber  310  also has an orifice  314  extending into the chamber and an orifice  316  extending out of the chamber. A source of plasma gases  318  is provided outside of chamber  310 , and gases are flowed from source  318  into chamber  310 . Source  318  can comprise, for example, one or more of CF 4 , CHF 3 , H 2  and C 2 F 6 . Although only a single source  318  is shown, it is to be understood that multiple sources can be provided, and multiple gases flowed into chamber  310 . Outlet  316  is coupled with a pump  320  which removes gases from chamber  310  to maintain a flow of gases through chamber  310 , and also to maintain a desired pressure within chamber  310 . A substrate  322  is shown provided within chamber  310 . Substrate  322  can be retained within substrate  310  on a substrate holder (not shown). Substrate  322  is shown coupled to a bias.  
      Also shown within chamber  310  is a focusing ring  324 . Focusing ring  324  is utilized to focus reactive components from a plasma (not shown) which would be formed within chamber  310  for etching a silicon-oxide-material (not shown) associated with substrate  322 . The chamber  310  described thus far can comprise conventional materials, and a conventional construction. Accordingly, sidewalls  312  can comprise, for example, quartz or ceramic materials (such as, for example, alumina).  
      Apparatus  300  differs from conventional apparatuses, however, in that one or more liners  330  are provided within reaction chamber  310 . Reaction chamber  310  can comprise a circular construction, and accordingly, liner  330  can comprise a cylindrical shape configured to slip within chamber  310  and along sidewalls  312 . Alternatively, liner  330  could comprise other shapes, and can be provided within other interior regions of chamber  310  than along sidewalls  312 . Liner  330  is preferably formed of one or more of Ru, Fe, Co, Ni, Rh, Pd, Os, W, Ir, Pt, and Ti. Accordingly, liner  330  can enhance selectivity of an etch for a silicon-oxide-containing composition relative to organic materials. Exemplary compositions of liner  330  are elemental forms of one or more of the Group VIII elements, tungsten, platinum and titanium; or alloy forms of one or more of the Group VIII elements and/or one or more of tungsten, platinum and titanium.  
      Liner  330  can also consist of, or consist essentially of, one or more of the Group VIII elements and/or one or more of tungsten, platinum and titanium.  
      It is noted that a liner is different than merely being a coating on a sidewall of a reactor. Specifically, a “liner” is defined hereby to comprise a material which is formed outside of a reaction chamber, and subsequently inserted within a reaction chamber, and accordingly does not encompass deposits formed during etching of materials within the reaction chamber.  
     EXAMPLE 1  
      A first wafer comprising ruthenium in the form of ruthenium metal or ruthenium oxide is provided within a reaction chamber, and etched to form a ruthenium deposit along an interior of the chamber. Subsequently, a wafer comprising silicon dioxide and an organic photoresist material (specifically, the photoresist can be, for example, deep UV or I-line photoresist) is provided within the chamber. The silicon dioxide is etched utilizing a plasma etch comprising CF 4 , CHF 3  and argon. It is found that the selectivity of the etch for silicon dioxide is enhanced relative to a selectivity which would exist in the absence of the ruthenium deposit. Specifically, it is found that the selectivity for silicon dioxide relative to the photoresist is 3.5:1 in the presence of the ruthenium deposit, whereas a selectivity of silicon dioxide relative to photoresist is measured to be 3:1 in the absence of the ruthenium deposit.  
     EXAMPLE 2  
      A liner comprising tungsten in the form of tungsten metal is provided within a reaction chamber. Subsequently, a wafer comprising silicon dioxide and an organic photoresist material is provided within the chamber. The silicon dioxide is etched utilizing a plasma etch comprising CF 4  and CHF 3 .  
      In compliance with the statute, the invention has been described in language more or less specific as to structural and methodical features. It is to be understood, however, that the invention is not limited to the specific features shown and described, since the means herein disclosed comprise preferred forms of putting the invention into effect. The invention is, therefore, claimed in any of its forms or modifications within the proper scope of the appended claims appropriately interpreted in accordance with the doctrine of equivalents.