US 10,093,834 B2  1  2  POLISHING COMPOSITION AND  POLISHING METHOD  TECHNICAL FIELD  BACKGROUND ART  Advantageous Effects of Invention  DESCRIPTION OF EMBODIMENTS  SUMMARY OF INVENTION  Technical Problem  Solution to Problem  The present invention relates to compositions for polish› ing (hereinafter polishing compositions) and methods for  polishing. The present invention particularly relates to a  method for polishing a layer containing elemental silicon, by  which a silicon compound other than the elemental silicon is  selectively polished while limiting the polishing rate of the  elemental silicon.  Manufacturing process of semiconductor devices include  a step of polishing an object made of elemental silicon ( e.g.,  polysilicon, single crystalline silicon, or amorphous silicon),  silicon compounds, metals or the like. In this step, when a  semiconductor to be manufactured includes a gate electrode  made of polysilicon and a silicon-based material other than  polysilicon surrounding the gate electrode, such a silicon› base material other than polysilicon, which may be silicon  nitride or silicon dioxide, is required to be polished prefer› entially. For instance, Patent Literature 1 proposes a polish- ing liquid capable of polishing a layer containing a silicon  material other than polysilicon quickly and limiting the  polishing of polysilicon. The polishing liquid proposed  contains colloidal particles, organic acid, and at least one  nonionic additive selected from nonionic surfactant and  nonionic hydrophilic resin. Such a polishing liquid, how› ever, does not have good washing efficiency because it  contains nonionic additive and the nonionic additive remains  after the polishing. Therefore this polishing liquid does not  satisfy user’s demand fully.  CITATION LIST  Patent Literature  PTL 1: JP 2009-289886 A  The present invention aims to provide a polishing com› position and a method for polishing to solve the problems of  the conventional techniques as stated above. According to  the present invention, when a polishing object including  elemental silicon, a silicon compound, metals and the like is  polished, the polishing rate of the elemental silicon, such as  polysilicon, single crystalline silicon, or amorphous silicon,  especially the polishing rate of polysilicon, can be limited,  and the silicon compound other than the elemental silicon,  such as a silicon nitride or silicon dioxide, can be selectively  polished.  To solve the above problems, a polishing composition  according to one embodiment of the present invention  includes: abrasives, an organic acid and a conjugate base of  this organic acid.  A polishing composition according to one embodiment  may include abrasives, an organic acid and a conjugate base  of the organic acid.  In the polishing compos1t10n in this embodiment, the  organic acid may have a value of pKa that is 0.3 or more and  6.0 or less, and the polishing composition may have a value  of pH that is equal to or higher than a value smaller than the  value of pKa of the organic acid by 1.0 unit and that is equal  to or lower than a value larger than the value of pKa by 1.5  units.  In the polishing composition in this embodiment, the  conjugate base of the organic acid may be at least one type  selected from ammonium salt, sodium salt and potassium  salt.  In the polishing composition in this embodiment, the  abrasives may be silica with an organic acid immobilized to  a surface of the silica.  In the polishing composition in this embodiment, content  of the abrasives may be 0.1 % by mass or more and 20.0%  by mass or less.  In the polishing composition in this embodiment, content  of the conjugate base of the organic acid may be 0.01 % by  mass or more and 10.0% by mass or less.  This polishing composition can be used for polishing a  substrate including elemental silicon, especially polysilicon.  A method for polishing according to another aspect of the  present invention includes polishing a polishing object using  the polishing composition according to the above embodi› ment. In this method for polishing, the polishing object may  be a substrate including polysilicon.  A polishing composition and a method for polishing of the  present invention are capable of, when a polishing object  includes elemental silicon, limiting the polishing rate of the  elemental silicon, especially polysilicon. According to the  polishing composition and the method for polishing, while  limiting the polishing rate of elemental silicon, especially  polysilicon, a silicon compound other than the elemental  silicon, such as a silicon nitride or silicon dioxide, can be  polished at a high polishing rate.  The following describes embodiments of the present  invention in details. A polishing composition of the present  embodiment can be prepared by mixing abrasives, organic  acid, and a conjugate base of the organic acid.  This polishing composition is suitably used for polishing  of an object such as elemental silicon, silicon compounds or  metals, e.g., for polishing the surface of a wiring substrate  made of silicon, containing elemental silicon, a silicon  compound, or metals, during the manufacturing process of a  semiconductor device. The polishing composition is particu› larly suitably used for polishing of a substrate containing  polysilicon. Elemental silicon includes polysilicon, single  crystalline silicon, and amorphous silicon. Polysilicon  includes typical polysilicon and modified polysilicon. Modi- fled polysilicon includes silicon doped with impurities such  as B or P in polysilicon. Silicon compounds include silicon  nitride, silicon oxide and silicon carbide. A silicon com› pound film includes a low-permittivity coat having specific  permittivity of 3 or less. This polishing composition enables  limiting of a polishing rate of the elemental silicon and  polishing of the silicon compounds other than the elemental  silicon at a high polishing rate. 