Abstract:
A method of etching a dielectric layer comprising the following steps. A structure having the dielectric layer formed thereover is provided. A patterned photoresist layer that may be a non-aromatic positive patterned photoresist layer is formed over the dielectric layer. The patterned photoresist layer is used as a mask while etching the dielectric layer with an etching gas comprising a fluorocarbon, and may also further comprise O 2 , while modulating one or both select powers on and off with a duty cycle or wave form. The select powers being selected from the group consisting of an RF power and a bias power.

Description:
[0001]    This Patent Application is a Continuation-in-Part of attorney docket number TSMC 01-189, filed as U.S. patent application Ser. No. 09/953523, filed on Sep. 17, 2001, which is hereby incorporated by reference in its entirety. 
     
    
     
       FIELD OF THE INVENTION  
         [0002]    The present invention relates generally to semiconductor fabrication and more specifically to dielectric etching processes using patterned photoresist masks.  
         BACKGROUND OF THE INVENTION  
         [0003]    As shown in FIG. 1, ArF light (wavelength 193 nm) or F2 laser (wavelength 157 nm) patterned photoresist (resist)  120  formed over structure  100  is susceptible to being damaged by plasma etching resulting in resist tilting during etching of polysilicon or metal layers.  
           [0004]    Such profile tilting is strongly correlated to the electron-temperature and ion flux and does not permit a good profile or critical dimension (CD) control. It is very difficult to totally resolve this problem by traditional plasma etching because it is difficult to independently control the total flux, electron temperature and other process trends. The resist has a non-aromatic structure, i.e. without phenyl rings in the structure.  
           [0005]    This tilting shown in FIG. 1 is believed to be caused by a synergistic effect from: (i) low mechanical strength of deep ultraviolet (DUV) resist under directional plasma etching; (ii) enhanced sidewall bombardment by ion due to the resist charging; and (iii) electrostatic distortion due to the resist charging.  
           [0006]    Based upon this proposed mechanism of tilting, several approaches to improve the etching condition have been proposed: (i) reduce power or use reactive ion etch (RIE) etcher to reduce the electron temperature; (ii) lower the wafer temperature; (iii) add a hydrogen containing source to neutralize the surface negative charging on the resist; and (iv) increase the bias power to minimize the ion deviation and residence time in the plasma. Even though these approaches can improve DUV resist tilting, the tilting has yet to be totally resolved due to the intrinsic limitation of the inherent high electron temperature.  
           [0007]    U.S. Pat. No. 6,136,723 to Nagase describes a method of fabricating a semiconductor device using a KrF deep ultraviolet (DUV) resist and a fluorocarbon etch.  
           [0008]    U.S. Pat. No. 5,770,097 to O&#39;Neill et al. describes a method of controlling etch selectivity.  
           [0009]    U.S. Pat. No. 5,705,443 to Stauf et al. describes a plasma-assisted dry etching process for etching of a metal containing material layer on a substrate to remove the metal containing material from the substrate.  
           [0010]    U.S. Pat. No. 5,614,060 to Hanawa describes a process and apparatus for patterning a masked metal layer to form a layer of metal interconnects for an integrated circuits structure which removes metal etch residues while inhibiting or eliminating erosion of the photoresist mask.  
           [0011]    The Journal of Vacuum Science &amp; Technology B article entitled “Pulse-Time-Modulated ICP Etching” by Ohtake et al., Vol. 18, No. 5 (2000), pages 2495 to 2499, discloses a inductively coupled plasma (ICP) etching system and method of patterning photoresist using KrF eximer light.  
         SUMMARY OF THE INVENTION  
         [0012]    Accordingly, it is an object of an embodiment of the present invention to provide an improved method of etching dielectric layers while using patterned photoresist masks.  
           [0013]    Other objects will appear hereinafter.  
           [0014]    It has now been discovered that the above and other objects of the present invention may be accomplished in the following manner. Specifically, a structure having the dielectric layer formed thereover is provided. A patterned photoresist layer that may be a non-aromatic positive patterned photoresist layer is formed over the dielectric layer. The patterned photoresist layer is used as a mask while etching the dielectric layer with an etching gas comprising a fluorocarbon, and may also further comprise O 2 , while modulating one or both select powers on and off with a duty cycle or wave form. The select powers being selected from the group consisting of an RF power and a bias power.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    The present invention will be more clearly understood from the following description taken in conjunction with the accompanying drawings in which like reference numerals designate similar or corresponding elements, regions and portions and in which:  
         [0016]    [0016]FIG. 1 schematically illustrates photoresist tilting after prior art plasma etching.  
         [0017]    FIGS.  2  to  4  schematically illustrate a preferred embodiment of the present invention.  
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     Brief Summary of the Invention  
       [0018]    In a key feature of the present invention, using an etching gas including/comprising a fluorocarbon, and which may also include/comprise O 2 , pulse modulation is used to reduce the electron temperature without substantially affecting the etching conditions and performance while etching dielectric layers using a DUV mask. The input RF signal and/or the bias is modulated on (plasma-on state) and off (plasma-off state) with a duty cycle so that the electron temperature is reduced during the plasma-off state. Another key factor is that a hydrogen (H) atom as a plasma species containing source enhances the method of the present invention.  
       Initial Structure  
       [0019]    Accordingly as shown in FIG. 2, structure  10  is understood to possibly include a semiconductor wafer or substrate, active and passive devices formed within the wafer, conductive layers and dielectric layers (e.g., inter-poly oxide (IPO), intermetal dielectric (IMD), etc.) formed over the wafer surface. The term “semiconductor structure” is meant to include devices formed within a semiconductor wafer and the layers overlying the wafer.  
         [0020]    Dielectric layer  14  is formed over structure  10  to a thickness of preferably from about 500 to 10,000 Å and more preferably from about 1000 to 6000 Å. Dielectric layer  14  may be a single layer or multi-layer and is preferably comprised of a low-k material such as nitride, oxide or oxynitride, silicon nitride (SiN), silicon oxide, silicon oxynitride (SiON), oxide/SiN or SiON/oxide for example.  
         [0021]    Optionally, anti-reflective coating (ARC) layer  12  may be formed over dielectric layer  14 . ARC layer  12  has a thickness of preferably from about 200 to 2000 Å, more preferably from about 300 to 1500 Å and most preferably from about 300 to 900 Å. ARC layer  12  is preferably formed of an organic material, oxynitride, nitride or TiN and is more preferably formed of an organic material or oxynitride.  
         [0022]    Photoresist layer  16  is formed over ARC layer  12 /dielectric layer  14  to a thickness of preferably from about 0.05 to 0.80 μm and more preferably from about 0.10 to 0.40 μm. Photoresist layer  16  is preferably either a positive non-aromatic photoresist or a negative non-aromatic photoresist. Positive, non-aromatic photoresist layer  16  is preferably comprised of ether, ester, acrylic, fluorocarbon or having a cyclic aliphatic structure. Negative, non-aromatic photoresist layer  16  is preferably comprised of acrylate polymer, cyclic olefin polymer, fluoro polymer, silicon polymer or cyano polymer and is more preferably acrylate polymer or cyclic olefin polymer.  
       Patterning of Photoresist Layer  16   
       [0023]    As shown in FIG. 3, negative or positive (non-aromatic) photoresist layer  16  is exposed and patterned using a DUV mask  18  for negative photoresist layer  16  (and, as one skilled in the art would recognize, a DUV mask (not shown) complimentary to DUV mask  18  would be used to expose positive photoresist layer  16 ) with either ArF eximer light (wavelength 193 nm) or F2 eximer light (wavelength 157 nm) to form patterned photoresist layer  16 ′. Patterned photoresist layer  16 ′ overlies portions  20  of ARC layer  12 /dielectric layer  14 . Other wavelengths of light, or other patterning sources, may also be used such as UV light, e-beam or x-ray (the resist is also acrylate system).  
       Key Step of the Invention  
       [0024]    In a key step of the invention and as shown in FIG. 4, using an etching gas including: (1) a fluorocarbon; or (2) a fluorocarbon and O 2 ; to etch ARC layer  12 /dielectric layer  14  using patterned photoresist layer  16 ′ masking portions  20  of ARC layer  12 /dielectric layer  14  to form patterned ARC layer  12 ′/dielectric layer  14 ′, the input RF signal (RF power) and/or the bias power is/are modulated on (plasma-on state) and off (plasma-off state) with various duty cycles or wave forms to reduce the electron temperature during the plasma-off state without a significant change to the etching conditions. For example, a 30% ON duty cycle may be used. Both the RF signal and the bias are independently controlled.  
         [0025]    An optional additional hydrogen atom as a plasma species containing source gas further enhances the method of the present invention.  
         [0026]    The source RF power is preferably from about 10 to 60 MHz and the bias applied to the structure  10  is preferably from about 2 to 20 MHz.  
         [0027]    The fluorocarbon and O 2  containing etching gas preferably includes/comprises:  
         [0028]    (I) (a) O 2  supplied at preferably from about 0 to 70 sccm, more preferably from about 1 to 70 sccm and most preferably from about 10 to 30 sccm; and (b) C 4 F 8 , C 5 F 8 , C 4 F 6 , C 2 F 6 , CF 4 , C 3 F 8  or C 2 F 4  supplied at preferably from about 10 to 100 sccm and more preferably from about 20 to 40 sccm; and more preferably includes/comprises:  
         [0029]    II) (a) O 2  supplied at preferably from about 0 to 70 sccm, more preferably from about 1 to 70 sccm and most preferably from about 10 to 30 sccm.; and C 2 F 6 , CF 4  or C 4 F 8  supplied at preferably from about 10 to 100 sccm and more preferably from about 20 to 40 sccm.  
         [0030]    The fluorocarbon containing etching gas preferably includes/comprises C 4 F 8 , C 5 F 8 , C 4 F 6 , C 2 F 6 , CF 4 , C 3 F 8  or C 2 F 4 , more preferably includes/comprises C 2 F 6 , CF 4  or C 4 F 8  and is supplied at preferably from about 5 to 100 sccm and more preferably from about 10 to 40 sccm.  
         [0031]    The optional hydrogen containing gas preferably is comprised of HBr, CHF 3 , H 2 , CH 2 F 2 , or CH 3 F and is more preferably is comprised of CH 2 F 2  and is supplied at preferably from about 5 to 50 sccm and more preferably from about 10 to 40 sccm.  
         [0032]    The etching of ARC layer  12 /dielectric layer  14  is preferably carried out in a dielectric etcher or a poly etcher with inductive type high-density plasma (inductively coupled plasma (ICP)) or a capacitive-type low-density/medium density plasma and is more preferably carrier out in an ICP etcher.  
         [0033]    The input RF and/or bias waveform and power are adjusted until the DUV resist is not tilted by the fluorocarbon containing etching gas in accordance with the method of the present invention.  
         [0034]    Further processing may then proceed.  
       Advantages of the Present Invention  
       [0035]    The advantages of one or more embodiments of the present invention include avoiding the DUV resist tilting simply by adjusting the RF/bias power modulation cycle without dramatically changing the etching chemistry.  
         [0036]    While particular embodiments of the present invention have been illustrated and described, it is not intended to limit the invention, except as defined by the following claims.