Abstract:
In one aspect, a method is provided which includes ( 1 ) providing a substrate including a photoresist layer and an additional layer which may be a potential source of contaminants, and ( 2 ) preventing a release of contaminants from the additional layer, wherein preventing the release of contaminants from the additional layer protects the photoresist layer from exposure to contaminants from the additional layer. Numerous other aspects are provided.

Description:
[0001]    The present application claims priority from U.S. Provisional Patent Application Ser. No. 60/951,181, filed Jul. 20, 2007 and titled “Methods and Apparatus to Prevent Contamination of a Photoresist Layer on a Substrate” (Docket No. 7791/L), which is hereby incorporated by reference herein in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates generally to electronic device fabrication, and more particularly to methods and apparatus to prevent contamination of a photoresist layer on a substrate, such as a photoresist layer. 
       BACKGROUND OF THE INVENTION 
       [0003]    During certain electronic device fabrication processes, portions of a substrate may be coated with a photoresist layer to generate a pattern (e.g., a two-dimensional pattern) on a substrate. Portions of a photoresist layer exposed to radiation, such as ultraviolet light, change in chemical properties in comparison with non-exposed portions. This enables a pattern of exposed versus non-exposed portions to be generated in a photoresist layer. It has been found that various factors may affect the physical and/or chemical properties of photoresist. Accordingly, a need exists to improve control over such factors to provide for suitable patterning of a photoresist layer. 
       SUMMARY OF THE INVENTION 
       [0004]    In a first aspect of the invention, a method is provided which includes (1) providing a substrate including a photoresist layer and an additional layer which may be a potential source of contaminants, and (2) preventing a release of contaminants from the additional layer, wherein prevention of the release of contaminants from the additional layer protects the photoresist layer from exposure to contaminants from the additional layer. 
         [0005]    In another aspect of the invention, an apparatus is provided which includes a substrate having (1) a photoresist layer, (2) an additional layer which may be a source of contaminants and (3) a cap layer formed over the additional layer, wherein the cap layer prevents a release of contaminants from the additional layer, protecting the photoresist layer from exposure to contaminants from the additional layer. 
         [0006]    Other aspects of the present invention will become more fully apparent from the following detailed description, the appended claims and the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWING(S) 
         [0007]      FIG. 1  is a cross sectional view of an exemplary substrate including a photoresist layer. 
           [0008]      FIG. 2  is a cross sectional view of an exemplary substrate as provided in accordance with an embodiment of the present invention. 
           [0009]      FIG. 3  is a cross sectional view of an exemplary substrate provided in accordance with an additional embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0010]    It has been found that photoresist layers used to pattern substrates are often sensitive to the presence of contaminants. In particular, the chemical properties of photoresist may be adversely affected by exposure to such contaminants. It has been found that additional layers of a substrate (i.e., aside from the photoresist layer) may act as a source of contaminants to the photoresist layer, depending on their composition. In accordance with the invention, a photoresist layer is protected from such sources of contamination to prevent exposure of the photoresist layer to the contaminants, thus avoiding adverse influences that the contaminants may have on the photoresist layer. 
         [0011]    According to embodiments of the invention, a substrate may be processed such that a layer of the substrate that is a potential source of contamination is covered with a protective layer (a ‘cap layer’) which prevents contaminants from leaking, migrating, outgassing or otherwise being released from the potentially contaminating layer. In this manner, the photoresist layer is protected from potential sources of contamination. The cap layer may be formed by a process that adds material (e.g., deposition) to the substrate. Additionally or alternatively, the cap layer may be formed by processing the substrate such that material is removed from one or more layers of the substrate (e.g., the potentially contaminating layer). 
         [0012]      FIG. 1  is a cross sectional view of an exemplary substrate  100 . The substrate  100  includes a photoresist layer  102  formed on a dielectric layer  104  (e.g., an oxide layer such as SiO 2 , a low K dielectric such as a carbon doped oxide, or another dielectric). The dielectric layer  104  is, in turn, formed on a base layer  108 . As shown, a feature, such as a through-hole or via  106  extends vertically through a portion of the photoresist layer  102  and the dielectric layer  104 , terminating at the base layer  108 . Although three layers  102 ,  104 ,  108  are depicted in  FIG. 1 , this is merely for purposes of illustration and the inventive concepts disclosed herein apply equally to substrates that include a larger or smaller number of layers. 
         [0013]    The photoresist layer  102  may comprise a photosensitive material which changes in physical and/or chemical properties in response to exposure to radiation, such as visible or ultraviolet light. The photoresist material may comprise organic molecules, resins and/or polymers (e.g., polyhydroxy-styrene-based polymers). The photoresist layer  102  may be formed on the substrate  100  using a number of techniques including spin coating. When spin coating is employed, the thickness of the photoresist layer  102  may be controlled by a spin rate of the substrate  100 , for example. Other suitable techniques may be employed to deposit the photoresist layer  102  on the substrate  100  to achieve a desired thickness. Exemplary photoresist layer thicknesses range from about 800 to 5000 angstroms, although other thicknesses may be used. 
         [0014]    As noted, the photoresist layer  102  may be employed during patterning processes in which a precisely defined pattern (e.g., a two-dimensional pattern) may be formed in the photoresist layer  102 . In some embodiments, a pattern may be generated by transmitting light through a mask having an inscribed pattern onto an unexposed photoresist layer. The pattern inscribed in the mask, or a reverse image of the pattern inscribed in the mask, is thereby transferred to the photoresist layer  102 . After exposure, the photoresist layer  102  may be developed in a suitable developing solution to complete image transfer to the photoresist. The patterning of the photoresist layer  102  enables features such as via  106  to be formed at precisely determined locations on the substrate  100  in subsequent procedures such as etching, for example. 
         [0015]    The dielectric layer  104  may comprise a silicon oxide (SiO) layer, such as silicon dioxide, a low K dielectric or any other layer having suitable electrical and/or physical properties. For example, in some embodiments, the dielectric layer  104  may comprise a carbon-doped silicon oxide layer. In one particular embodiment, the dielectric layer  104  may include a low K dielectric having a thickness of about 200 angstroms to 1 micron, although other thicknesses may be used. 
         [0016]    As noted above, the via  106 , which, in the embodiment depicted comprises a through-hole extending through the photoresist and dielectric layers  102 ,  104  may be generated subsequent to patterning of the photoresist layer  102 . As shown in  FIG. 1 , the via  106  may have vertical sidewalls. In some embodiments, the sidewalls of the via  106  may be tapered or otherwise shaped. 
         [0017]    In one or more embodiments, the base layer  108  may comprise a SiCN layer, although any suitable material may be employed. The base layer  108  may be employed to isolate one or more layers and/or materials (not shown) situated below the base layer  108 , as an etch stop, or for any other suitable purpose. 
         [0018]    The base layer  108  may act as a source of contaminants to the photoresist layer  102  directly through ‘outgassing’ of particles from the base layer  108  to the photoresist layer  102  (shown by curved arrows A 1  in  FIG. 1 ) and/or indirectly, by migration of particles from the base layer  108  through the dielectric layer  104  to the photoresist layer  102  (shown by straight arrows A 2  in  FIG. 1 ). It is noted however, that other layers of the substrate  100  may act as a source of contaminants which may adversely affect the photoresist layer  102 , alternatively or in addition to the base layer  108 . 
         [0019]    The contamination may affect various physical and/or chemical properties of the photoresist material in layer  102 , including, for example, solubility and pH level. For example, portions of the photoresist layer  102  may become basic (i.e., pH greater than 7) due to exposure to contaminants. 
         [0020]    As stated, contamination may have an adverse affect on the properties of the photoresist layer  102 . For example, due to changes in the pH and/or solubility in the photoresist layer  102 , residues of photoresist material may remain after operations intended to completely remove the photoresist layer  102  (e.g., developing and/or cleaning procedures). The remnant residues may adversely impact the electrical properties (e.g., resistance) of portions of the substrate  100  and devices formed therein. 
         [0021]    Referring to  FIG. 2 , a cross sectional view of a substrate  200  provided in accordance with an embodiment of the present invention is shown. As depicted in  FIG. 2 , the substrate  200  may include layers and features similar to those of the exemplary substrate  100  discussed above with reference to  FIG. 1 , including a photoresist layer  202 , a dielectric layer  204 , a via  206  and a base layer  208 . The same layer thicknesses described with reference to  FIG. 1 , or any suitable layer thicknesses, may be used. 
         [0022]    As depicted in  FIG. 2 , an additional cap layer  210  is formed between the base layer  208  and the dielectric layer  204 . In this embodiment, the base layer  208  is assumed to be a potential source of contamination for the photoresist layer  202 . The cap layer  210  may comprise a thin film formed over the base layer  208  using various techniques including plasma treatment and/or deposition (e.g., physical vapor deposition (PVD), chemical vapor deposition (CVD) and plasma-enhanced chemical vapor deposition (PECVD)). Thus, the cap layer  210  may be formed using depository or non-depository processes. In some embodiments, the cap layer  210  may have a thickness sufficient to prevent diffusion of material covered by the cap layer  210  into the dielectric layer  204  (e.g., particularly when the dielectric layer  204  is a porous low K material such as a carbon doped oxide). Exemplary cap layer thicknesses range from about 50 to 500 angstroms for PECVD deposited oxide, although other thicknesses may be used. 
         [0023]    In one or more embodiments, the material of the cap layer  210  may comprise a thin oxide layer, such as silicon oxide or silicon dioxide, and/or another nitrogen-free dielectric layer. Additionally or alternatively, the cap layer  210  may be formed by treating the surface of the base layer  208  to stabilize the surface (e.g., to stabilize and/or remove the species, such as nitrogen, that may contaminate the photoresist layer  202 ). In the case of a SiCN base layer, such a plasma treatment may form a nitrogen-free or nitrogen-reduced SiC layer which effectively caps the underlying SiCN material. For example, exposure of a SiCN layer to a helium or similar plasma may remove carbon and nitrogen atoms from a top surface region of the layer. 
         [0024]    In one embodiment, the cap layer  210  may be formed by removal of material from the base layer  208 . For example, a cap layer  210  comprising SiC may be formed from a SiCN base layer  208  by removal of nitrogen (N) from the SiCN during plasma treatment or another suitable process. A combination of surface treatment of the base layer  208  and deposition of capping material may be used to form the cap layer  210 . 
         [0025]      FIG. 3  is a cross sectional view of another exemplary substrate  300  provided according to an embodiment of the present invention which includes a number of intermediate layers. The substrate  300  may include a photoresist layer  302 , a low k dielectric layer  304  and a base layer  308  similar to the layers described in  FIGS. 1 and 2 . A cap layer  310 , which may be similar to the cap layer  210  described above with respect to  FIG. 2 , may be formed directly over the base layer  308  between the base layer  308  and the low k dielectric layer  304 . In addition, the substrate  300  may include a silicon oxide layer  312  or other layer formed on top of the low k dielectric layer  304 , and an anti-reflective layer  314  or other layer formed over the silicon oxide layer  312  directly under the photoresist layer  302 . The depicted layers  302 ,  304 ,  308 ,  310 ,  312 ,  314  are exemplary and a larger or smaller number of layers may be provided. 
         [0026]    In one embodiment, the base layer  310  may comprise SiCN having a thickness of about 50 nanometers, although other materials and thicknesses may be used. 
         [0027]    As noted above, the base layer (e.g.,  108 ,  208 ,  308 ) may not be the only potential source of contamination within a substrate. Thus, according to the present invention, additional cap layers may be formed over other potentially contaminating layers (e.g., silicon oxide layer  312 ) to prevent outgassing or migration of chemical species from such layers that may adversely affect the properties of the photoresist layer (e.g.,  102 ,  202 ,  302 ). 
         [0028]    The foregoing description discloses only exemplary embodiments of the invention. Modifications of the above disclosed apparatus and methods which fall within the scope of the invention will be readily apparent to those of ordinary skill in the art. For instance, in some embodiments, combinations of processes may be employed. For example, a wash may be employed in combination with a plasma treatment to prevent contamination of the photoresist layer. 
         [0029]    Accordingly, while the present invention has been disclosed in connection with exemplary embodiments thereof, it should be understood that other embodiments may fall within the spirit and scope of the invention, as defined by the following claims.