Patent Publication Number: US-2006016786-A1

Title: Method and apparatus for removing SiC or low k material film

Description:
BACKGROUND OF THE INVENTION  
      1. Field of the invention  
      The present invention relates to a method and apparatus for removing silicon carbide (SiC) or low dielectric (low k) material film, In particular, the present invention relates to a method and apparatus to remove the SiC or low k material thin film on recycling control-wafers by oxidation and etching.  
      2. Description of Relative Prior Art  
      SiC and low k dielectric films are widely used in interconnection of the back end process of semiconductor manufacturing and are not easy to etch by chemical etching. The control-wafer can not be recycled by removing the deposited SiC or low k dielectric film from the substrate by wet etching. Traditionally the SiC or low k dielectric film is removed by chemical mechanical polishing (CMP). Though it is simple, the cost is high and need a longer time to remove it. Furthermore, part of the substrate may also be consumed. This will decrease the lifetime of the substrate, and may affect the recycling efficiency of the control-wafers.  
      In the Taiwanese patent publication No. 464977, proposed a SiC removing method. After forming a layer of silicon nitride (Si 3 N 4 ) and a layer of SiC film, the SiC is etched with high density plasma, till the remaining thickness of the Si 3 N 4  approaches 500 Å, then using the remaining Si 3 N 4  to be the under-layer for the deposition of another layer of SiC film. Wherein the etch time of the high density plasma is 1 to 3 minutes longer then the deposition time of the SiC. The operation condition of the high density plasma is the temperature of the reaction chamber, which is between 350° C. to 450° C., the pressure is between 4 mtorr to 8 mtorr, the flow rate of the hydrogen is between 300 sccm to 800 sccm, the frequency and power of the low frequency RF power source is 1 MHz, 3000 watts. Also proposed a forming method of the SiC control-wafer, wherein the remaining Si 3 N 4  layer is removed by acidic liquid, which includes 49% of HF. It also proposes a method for recycling the silicon wafer by repeat forming and removing steps of SiC. The disadvantage of this method may need a long process time and a lot of power consumption. High cost and the need of Si 3 N 4  layer are additional drawbacks.  
      The Taiwanese patent publication No. 465022 proposed a dielectric thin film removing method. By using oxygen plasma to treat the control-wafer to form a dielectric film of silicon-rich oxide layer, then forms a layer of dielectric thin film, and then removes the dielectric thin film by immerse the silicon control-wafer in a solution of NH 4 OH and H 2 O 2  to transform the surface of the dielectric film to be hydrobolic, finally removes the dielectric film by HF solution to remove the film. The disadvantage of this method is that the growth of an extra silicon dioxide, which increases the dielectric constant; furthermore, this method may not be applied to other dielectric film from a control-wafer.  
     OBJECT OF THE INVENTION  
      It is therefore an object of the invention to provide a method and apparatus to remove the silicon carbide (SiC) or low dielectric constant (low k) dielectric film from a control-wafer, which need a shorter time, less power and lower cost to remove the films.  
      It is another object of the invention to provide a method and apparatus to remove SiC or low k dielectric film from a control-wafer, to increase the lifetime of the control-wafer.  
      It is yet a further object of the invention to provide a method and apparatus to remove SiC or low k dielectric film from a control-wafer, which may apply to most of the low k dielectric.  
     DISCLOSURE OF THE INVENTION  
      In order to achieve the above object, a first aspect of the present invention teaches a method and apparatus for removing the silicon carbide (SiC) or low dielectric constant (low k) material film from a control-wafer, wherein the SiC or the low k dielectric film is formed on a substrate. The method is mainly by treating the SiC or the low k dielectric film with a high temperature oxidation to transform the SiC or the low k dielectric film to an oxide layer, and then remove the oxide layer by wet etching.  
      Said high temperature oxidation may be wet oxidation or dry oxidation, and can completely oxidize the SiC or the low k dielectric film at temperatures above 400° C. The high temperature oxidation process of the present invention, for example, is a high temperature furnace, a rapid thermal processing (RTP). The oxide may be removed by etching with HF contained solutions, such as buffered HF. It may also be dry etching, such as plasma etching.  
      Said substrate can be silicon substrate or other substrate of suitable material. Said material of low k dielectric may be carbon doped oxide (CDO), porous carbon doped oxide (PCDO), silicon-base inorganic material such as HSQ, MSQ, CVD-Black Diamond, CVD-Carol, Orion™ flowfill™, etc, and the same silicon-base inorganic material with nano-hole structure. Said oxide layer generally is silicon dioxide.  
      Another aspect of the present invention teaches an apparatus for removing said silicon carbide or low k dielectric film, said apparatus mainly including a high temperature processing unit such as a high temperature furnace or a rapid thermal processing (RTP), which providing the SiC or the low k film enduring a high temperature process to transform the film into oxide, also including an etching unit with etch solution that can remove said oxide.  
      Said high temperature processing unit is a high temperature furnace or RTP equipment, and said etching unit is a wet bench, such as a single wafer spin etching and cleaning bench, a batch etching and cleaning bench or a plasma dry etching apparatus. Said high temperature processing unit and said etching unit may be installed as one apparatus or separately installed, or formed a cluster tools. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The foregoing and other advantages of the invention will be more fully understood with reference to the description of the best embodiment and the drawing wherein:  
       FIG. 1  to  FIG. 3  illustrates the process of the method for removing all the silicon carbide or low k dielectric film of the present invention.  
       FIG. 4  to  FIG. 6  illustrates the process of the method for removing part of the SiC or the low k dielectric film of the present invention. 
    
    
     DISCRIDTION OF THE PREFERRED EMBODIMENTS  
       FIG. 1  to  FIG. 3  illustrate the process of the method for removing all the silicon carbide or low k dielectric film of the present invention, wherein the low k dielectric film  21  or the SiC layer  22  is formed on a substrate  1 . As shown in  FIG. 1 , after treating with high temperature oxidation, the low k dielectric film  21  or the SiC layer  22  is transformed into silicon dioxide layer  3 , as shown in  FIG. 2 . Then the silicon dioxide layer  3  is removed by wet etching, as shown in  FIG. 3 , such that the silicon substrate can be used again.  
       FIG. 4  to  FIG. 6  illustrate the process of the method for removing part of the SiC or the low k dielectric film of the present invention, wherein the low k dielectric film  21  or the SiC layer  22  is deposited on a silicon control-wafer  1 , as shown in  FIG. 4 , After oxidation, part of the low k material film  21  or the SiC layer  22  is transformed into silicon dioxide layer  3 , as shown in  FIG. 5 , this silicon dioxide layer is removed by etching, as shown in  FIG. 6 .  
      The dry oxidation or wet oxidation transforms the SiC into SiO 2 , The oxidation reaction equations of the SiC is as follow: 
 
SiC+2O 2 →SiO 2 +CO 2    (1) 
 
SiC+4H 2 O→SiO 2 +CO 2 +4H 2    (2) 
 
      From the experiment results, we know that the oxidation rate of SiC in wet oxide is faster than that in dry oxide. The thickness of the oxide can be modeled with the Deal-Grove model as the following equation: 
 
 X   0   2   +AX   0   =Bt    (3) 
 
      Where X 0  is the thickness of the oxide layer, t is the oxidation time, A and B are constant. B is also a parabolic constant of oxidation (i.e. when X 0  is thick, X 0   2 =Bt), B/A is the linear constant of oxidation (i.e. when X 0  is thin, X 0 =Bt/A). Refer to  FIG. 7  and  FIG. 8 ,  FIG. 7  illustrates the relation between the thickness (in nm) of dry oxidation and the required oxidation time per unit thickness t/X 0  (in min/nm);  FIG. 8  illustrates the relation between the thickness (in nm) of wet oxidation and the required oxidation time per unit thickness t/X 0  (in min/nm). From equation (3), the value of A and B can be obtained from these charts of  FIG. 7  and  FIG. 8 .  
     Embodiment 1  
      Supplies dry oxide in an oxidation furnace to perform oxidation with four different temperatures. The results are shown in  FIG. 7 , the values of A and B are obtained as in Table 1  
               TABLE 1                          Results of dry oxidation of SiC                                 Temperature   550° C.   650° C.   750° C.   850° C.                                         A(nm)   4.28   15.17   15.57   32.05       B(nm)   7.60   23.64   44.31   127.56                  
 
      From table 1, even by dry oxidation, at temperature of 550° C., the value of B is still as high as 7.6, which is faster than the oxidation of silicon.  
     Embodiment 2  
      Supplied wet oxide in an oxidation furnace to process oxidation with three different temperature, the results are shown in  FIG. 8 , the values of A and B are obtained as in Table 2  
               TABLE 2                          Results of wet oxidation of SiC                                     Temperature   650° C.   750° C.   850° C.                                                 A(nm)   116.18   78.47   64.27           B(nm)   406.73   574.53   1379.29                      
 
      Form table 2, the oxidation rate of wet oxidation is much higher than that of dry oxidation. Although the oxidation temperature is above 650° C. in the present embodiment, it can obtain an efficient oxidation rate as at temperature low as 400° C.  
     Embodiment 3  
      By using a vertical furnace of ASM advance 400 to perform wet (H 2 +O 2 ) oxidation, the flow rate of H 2  is 4 slm, the flow rate of 02 is 4 slm, the temperature is 950° C., the thickness of the SiC is 70 nm, oxidation time is 2 hours, the SiC is completely oxidized, the silicon substrate is also partly oxidized. The results are shown in table 3:  
               TABLE 3                          The oxidation Results of a 70 nm SiC film oxidizing at 950° C.                                     method   SiC#1   SiC#2   SiC#3   SiC#4   Si                                             SiC thickness (nm)   70.0   70.0   70.0   70.0   0       SiC thickness (nm)   376.9   389.5   409.9   390.5   350.5       Tolerance   3.37   6.41   6.70   7.89   12.40       Particles (&gt;0.2 μm)   36   43   112   73   132                  
 
      The number of particles in this table is the particle on the surface of the wafer after etching, and is measured by a KLA Tencor SP1. The particle is less then the cleanliness of a clean room.  
      The surface of the silicon substrate is observed by an atomic force microscopy (ASM) after etching, it shows that the surface is very smooth. The average root-mean-square roughness is as low as 0.300 nm.  
     Embodiment 4  
      The low dielectric constant materials of carbon doped oxide (CDO) and porous carbon doped oxide (PCDO) are oxidized by dry oxidation in an oxidation furnace. 360 nm of CDO and 180 nm of PCDO are oxidized at 950° C., then is removed with dilute HF.  
      The etching process of the present invention can be performed in a single wafer spin etching and cleaning bench or a wet etching apparatus.  
      Although specific embodiments of the invention have been disclosed, it will be understood by those having skill in the art that minor changes can be made to the form and details of the specific embodiments disclosed herein, without departing from the spirit and the scope of the invention. The embodiments presented above are for purposes of example only and are not to be taken to limit the scope of the appended claims.