Abstract:
This invention discloses a planarization method for semiconductor device. The planarization method includes the steps of: providing a semiconductor substrate in which metal patterns are formed with various pattern densities; depositing a porous oxide layer over the semiconductor substrate so as to cover the metal patterns; plasma-treating surface of the porous oxide layer; and polishing the plasma-treated porous oxide layer by chemical mechanical polishing.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a planarization method for semiconductor device, more particularly to a planarization method for semiconductor device capable of obtaining the global planarization with a selective CMP by simply performing surface treatment at an O 3 -TEOS layer. 
     2. Description of the Related Art 
     As the integrity of integrated circuits increases, a global planarization of interlayer dielectric by using CMP (Chemical Mechanical Polishing) is became necessary to meet the requirements of lithography process. The CMP is a planarization method by performing simultaneously a chemical reaction due to slurry and a mechanical process due to polishing pad. This method has an advantage of global planarization at a wide range of region that is impossible for the conventional BPSG(Boron-Phosphorous-Silicate-Glass) reflow or the SOG(Spin-On-Glass) etch-back, also the CMP is able to perform a low temperature planarization. 
     Meanwhile, at the manufacturing of integrated circuits, when the spacing between patterns is small, for example the spacing is below 0.3 μm, gap filling matter is raised as a problem to be solved. And as solutions, HDP-CVD(High Density Plasma Chemical Vapor Deposition) manner, spin-on polymer coating manner and deposition of O 3 -TEOS(Ozon-Tetra Ethyl Ortho Silicate) layer having excellent surface mobility have been proposed. 
     However, since the O 3 -TEOS layer used to achieve the gap filling performance has a porous structure, an annealing step is further required to increase density of the O 3 -TEOS layer after the deposition step. Although the density is increased by the annealing step, its layer quality is still inferior to that of a thermal oxide. Therefore, according to those results of CMP on the O 3 -TEOS layer, a dishing is occurred at the regions of wide spacing between patterns. This dishing is also found not only in the O 3 -TEOS layer but also in oxide layers and metals such as tungsten. 
     In the aspect of planarity, global planarity is affected by feature height, size, layout, density and polishing condition such as polishing mechanical parameters, pad and slurry. When the active area is wide and feature height is high, it is difficult to get planarized surface without additional scheme as mentioned above. 
     The CMP provides not the global planarity but excellent local planarity. Therefore, a selective CMP has been proposed to obtain excellent global planarity without occurring dishing. The selective CMP is believed to be a very useful polishing method of achieving global planarization since selective CMP uses polishing selectivity of materials to be polished simultaneously. 
     FIGS. 1A to  1 C are sectional views illustrating a planarization method for semiconductor device in prior art using the selective CMP. 
     Referring to FIG. 1A, metal patterns  2  are formed on a semiconductor substrate  1  by an etching process using a hard mask layer  3 . Those metal patterns  2  are formed to get pattern densities that are various depending on regions. An O 3 -TEOS layer  4  having excellent gap filling characteristics is deposited over the semiconductor substrate  1 . At this time, deposition thickness of the O 3 -TEOS layer  4  is thicker at a portion having the metal pattern  2  than at a portion not having the metal pattern  2 . And the deposition thickness is also thicker at a portion having high pattern density than at a portion having low pattern density. A BN layer or SiN layer, more preferably a BN layer  5  is formed on the O 3 -TEOS layer  4  by a conventional plasma system having various depositing RF power. 
     Referring to FIG. 1B, the BN layer  5  is polished by the CMP step. Herein, the EN layer  5  over a region where the metal pattern  2  is formed, is polished while the BN layer  5  over wide range of regions where no metal pattern  2  is formed, is not polished and remained. 
     Referring to FIG. 1C, the O 3 -TEOS layer  4  and the remained BN layer  5  are continuously polished by the CMP step until the hard mask layer  3  is exposed. As a result, global planarization is accomplished. Herein, as known in the art, the BN layer  5  has high polishing selectivity with respect to oxide layers or metals. For instance, the polishing rate of the BN layer  5  is slower than that of the oxide layers and metals. Accordingly, during the CMP step, the O 3 -TEOS layer  4  is rapidly removed while the BN layer  5  is slowly removed. Therefore, the global planarization is obtained without occurring dishing at the wide range of region where no metal pattern  2  is formed. 
     However, the above described selective CMP requires additional BN depositing step thereby increasing manufacturing cost and decreasing production yield. Furthermore, device characteristics may be degraded by particles generated during the deposition step. 
     SUMMARY OF THE INVENTION 
     Therefore, the object of the present invention is to provide a planarization method for semiconductor device capable of obtaining the global planarization with a selective CMP without occurring any cost increase, degraded production yield or particle generation. 
     To accomplish the foregoing object of the present invention, the planarization method comprises following steps of: providing a semiconductor substrate in which metal patterns with various pattern densities are formed; depositing a porous oxide layer over the semiconductor substrate so as to cover the metal patterns; plasma-treating surface of the porous oxide layer; and polishing the plasma-treated porous oxide layer. 
     According to the present invention, an O 3 -TEOS layer or PECVD oxide layer is used as porous oxide layer. 
     Further, according to the present invention, N 2 O or NH 3  gas is used as a plasma source gas during the plasma-treating step of the porous oxide layer, so that the surface of porous oxide layer is nitrified. 
     Also, according to the present invention, Ar, He or Ne gas is used as a plasma source gas during the plasma-treating step of the porous oxide layer, so that the surface of porous oxide layer is hardened. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other objects and advantages of the invention will become apparent upon reading the following detailed description and upon reference to the accompanying drawings in which: 
     FIGS. 1A to  1 C are cross-sectional views illustrating a planarization method for semiconductor device in prior art. 
     FIGS. 2A to  2 D are cross-sectional views illustrating a planarization method for semiconductor device of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The planarization method of this invention reutilizes the shortcoming i.e. the porosity of O 3 -TEOS layer. In other words, the surface of O 3 -TEOS layer is nitrified or hardened by the plasma-treating step, such that the polishing rate of the O 3 -TEOS layer is different between a surface portion and a bulk portion, thereby obtaining excellent global planarity. 
     FIGS. 2A to  2 D are cross-sectional views illustrating a planarization method for semiconductor device of the present invention. Detailed description is as follows. 
     Referring to FIG. 2A, metal patterns  12  having various pattern densities are formed on a semiconductor substrate  12 . The metal patterns  12  are formed by an etching process using a hard mask layer  13  as an etching mask similar to that of the conventional methods. A porous oxide layer  14  such as O 3 -TEOS layer having excellent gap filling characteristic is formed over the semiconductor substrate  11  so as to cover the metal patterns  12 . A deposition thickness of the O 3 -TEOS layer  14  is thicker at a portion having the metal pattern  12  than at a portion not having the metal pattern  12 . And the deposition thickness is also thicker at a portion having high pattern density than at a portion having low pattern density. As a porous oxide layer, an oxide layer deposited according to the PECVD process can be used instead the O 3 -TEOS layer  14 . 
     Referring to FIG. 2B, the O 3 -TEOS layer  14  is plasma-treated by a plasma source gas such as N 2   0  or NH 3 . During the plasma-treating step, a shrinking in the surface of the O 3 -TEOS layer  14  is occurred owing to a radical bombardment and the radicals fill voids on the film surface, thereby nitrifying the surface of the O 3 -TFOS layer  14 . As a result, there is formed a surface layer  14   a  made of nitride having polishing selectivity with respect to the O 3 -TEOS layer  14  on the surface of the O 3 -TEOS layer  14 . Since the surface layer  14   a  made of nitride is formed by plasma-treating the O 3 -TEOS layer  14 , no further deposition step for forming the surface layer  14   a  made of nitride and no particle generation due to the deposition step is occurred. 
     Referring to FIG. 2C, the O 3 -TEOS layer  14  is annealed to increase its density, and then the O 3 -TEOS layer  14  including the surface layer  14   a  made of nitride is polished according to the CMP step. At this time, the surface layer  14   a  formed on the metal pattern  12  and at a portion of high density is removed, while the surface layer  14   a  formed at wide range of regions where no metal pattern  12  is formed is remained. 
     Referring to FIG. 2D, the remained surface layer  14   a  and the O 3 -TEOS layer  14  are continuously polished according to the CMP step until the hard mark layer  13  is exposed. Herein, as mentioned above, since the nitride layer has relatively slow polishing rate compared with that of oxide layer, the polishing rate of the surface layer  14   a  made of nitride is slower than that of bulk of the O 3 -TEOS layer  14 . Accordingly, without occurring dishing at the wide range of regions where no metal pattern  12  is formed, global planarization is obtained. 
     Therefore, according to the present invention, excellent global planarization with a selective CMP step is provided without occurring additional BN layer deposition step since the surface layer made of nitride is formed at the surface of O 3 -TEOS layer by plasma-treating the surface of the O 3 -TEOS layer. 
     In another embodiment of the present invention, instead using the plasma nitride source gas such as N 2   0  or NH 3 , Ar is used as a plasma source gas. Also He or Ne can be used as a plasma source gas. In this case, as the O 3 -TEOS layer is plasma-treated by Ar, He or Ne gas, voids on the surface of the O 3 -TEOS layer are removed, and at the same time Ar ions are filled in the voids thereby hardening the surface of the O 3 -TEOS layer. Herein, He or Ne ions can be filled in the voids. At this time, the hardened O 3 -TEOS layer surface has a polishing selectivity with respect to a bulk of the same, for example the hardened surface has a slow polishing rate compared with that of the bulk. 
     Accordingly, when the O 3 -TEOS layer having the hardened surface is polished by the CMP step, owing to the difference of polishing rate between the hardened O 3 -TEOS layer surface and the bulk, excellent global planarization is obtained without occurring dishing at wide range of regions where no metal pattern is formed as described in the previous embodiment of the present invention. 
     Although preferred embodiments of the present invention are described and illustrated, various other modifications will be apparent to and can be readily made by those skilled in the art without departing from the scope and spirit of the present invention.