Abstract:
A plasma processing operation uses a gas mixture of N 2  and H 2  to both remove a photoresist film and treat a low-k dielectric material. The plasma processing operation prevents degradation of the low-k material by forming a protective layer on the low-k dielectric material. Carbon from the photoresist layer is activated and caused to complex with the low-k dielectric, maintaining a suitably high carbon content and a suitably low dielectric constant. The plasma processing operation uses a gas mixture with H 2  constituting at least 10%, by volume, of the gas mixture.

Description:
FIELD OF THE INVENTION 
   The invention relates most generally to semiconductor devices with reduced capacitance loading due to the use of a low-k dielectric, and a method for manufacturing such semiconductor devices. 
   BACKGROUND 
   The escalating requirements for high-density and performance associated with ultra large scale integration (ULSI) semiconductor devices require responsive changes in interconnection technology. Low dielectric constant (low-k) interlevel dielectric (ILD) materials have been found effective in mitigating RC (resistance capacitance) propagation delays to reduce power consumption and crosstalk. Materials which show promise as low-k ILDs include various carbon-containing materials. Such carbon-containing low-k dielectric materials include various polymers with carbon occupying a position in the backbone of the polymer. Typical of such carbon-containing polymers are benzocyclobutene (BCB), methyl silsesquioxane (MSQ), Flare-R®, Silk®, JSR, Orion, and Black Diamond®. Although materials having a dielectric constant of less than about 3.9 are considered low-k dielectric materials, as integrated circuit devices and interconnect technologies continue to scale smaller, low-k dielectric materials with even lower dielectric constants have become useful, and it is increasingly popular and advantageous to use materials having dielectric constants less than or equal to 3, i.e., k≦3. The challenges posed by the increasingly fragile and higher carbon content of the k≦3 materials impact plasma technology used in the manufacture of semiconductor devices because the Si—CH 3 , Si—C, and other carbon bonds in the low-k dielectric material are susceptible to be attacked by plasma processing. 
   Conventional methods often employ a plasma treatment of the low-k dielectric film after it is formed, to improve mechanical properties such as hardness and to reduce susceptibility to subsequent plasma attack. Following the plasma treatment, conventional photoresist patterning is carried out, the low-k dielectric film is etched and the photoresist film removed. The organic photoresist film is conventionally removed in a dry plasma process that uses oxygen. Plasma excitation during the stripping process results in atomic oxygen which oxidizes the organic photoresist into gases such as CO, CO 2  and H 2 O that are easily removed from the stripping chamber by conventional pumping. This stripping process undesirably degrades the low-k dielectric material because the oxygen used in the stripping process also combines with carbon from the low-k dielectric film, disrupts existing carbon bonds, and causes the carbon to leach out of the low-k dielectric film. The loss of carbon undesirably causes the dielectric constant of the film to increase. Another shortcoming of this conventional method is that the post-deposition plasma treatment only treats the top surface of a low-k dielectric film after deposition and does not treat surfaces of the film that become exposed during the subsequent etching process used to form trenches, vias, contacts and other openings in the low-k dielectric material. 
   It would therefore be desirable to provide a method for manufacturing a semiconductor device that overcomes the above shortcomings and does so in an efficient, streamlined processing sequence. 
   SUMMARY OF THE INVENTION 
   To address these and other needs, and in view of its purposes, an aspect of the invention provides a method for stripping photoresist and treating a dielectric to prevent dielectric constant degradation using a single plasma operation. The method comprises providing a dielectric over a substrate, forming a photoresist film over the dielectric before treating the dielectric with a plasma, patterning the photoresist film, etching at least an opening in the dielectric, and stripping the patterned photoresist film and treating the dielectric with carbon in a single plasma operation. Process conditions of the stripping and the treating are controlled to cause carbon from the photoresist to at least one of penetrate and complex with the dielectric film. The single plasma operation may use a gas mixture of N 2  and H 2  in which the H 2  concentration is larger than 10%. 
   In another aspect, provided is a method for stripping photoresist and treating a carbon-containing dielectric to prevent dielectric constant degradation, in a single plasma operation. The method comprises providing a carbon-containing dielectric over a substrate, forming a photoresist film over the carbon-containing dielectric before treating the carbon-containing dielectric with a plasma, patterning the photoresist film and etching at least an opening in the carbon-containing dielectric, and stripping the patterned photoresist film and treating the carbon-containing dielectric with carbon in a single plasma operation that includes a gas mixture of H 2  and N 2 . The gas mixture may contain a greater volume of H 2  than N 2  in an exemplary embodiment. 
   In another aspect, provided is a method for stripping photoresist and treating a carbon-containing dielectric to prevent dielectric constant degradation in a single plasma operation. The method comprises providing a carbon-containing dielectric over a substrate, forming a photoresist film over the carbon-containing dielectric before treating the carbon-containing dielectric with a plasma, patterning the photoresist film and etching at least an opening in the carbon-containing dielectric, and stripping the patterned photoresist film and forming a protective layer on the carbon-containing dielectric in a single plasma operation. The protective layer comprises at least one of an Si—N material and an Si—O—N material. 

   
     BRIEF DESCRIPTION OF THE DRAWING 
     The present invention is best understood from the following detailed description when read in conjunction with the accompanying drawing. It is emphasized that, according to common practice, the various features of the drawing are not necessarily to scale. On the contrary, the dimensions of the various features are arbitrarily expanded or reduced for clarity. Like numerals denote like features throughout the specification and drawing, which include the following cross-sectional views. 
       FIG. 1  shows an exemplary opening in a low-k dielectric film and illustrates the plasma treatment/photoresist stripping process; and 
       FIG. 2  shows the structure of  FIG. 1  after the photoresist film has been removed and the surfaces of the low-k material treated. 
   

   DETAILED DESCRIPTION 
   An aspect of the invention provides a plasma operation that both strips photoresist and treats the surface of a low-k dielectric material, avoids carbon leaching and maintains a suitably low dielectric constant and suitably low RC characteristics. 
   A low-k dielectric film may be formed on any of various semiconductor devices. Conventional formation methods may be used and the low-k dielectric film may advantageously have a dielectric constant no greater than 3, but other dielectric constants up to 3.9 may be used in other exemplary embodiments. The low-k dielectric film may be a carbon-containing film that includes bonds such as Si—CH 3  and Si—C bonds, but other carbon bonds may be included depending on the composition and nature of the low-k dielectric film. The low-k dielectric film may include various thicknesses and some suitable materials that may be used as the low-k material are BCB, MSQ, Flare-R®, Silk®, JSR, Orion, Black Diamond®, other similarly available commercial materials, various polymers and polyimides, carbon-doped SiO 2 , and other carbon-containing dielectric materials. The low-k dielectric material may be an interlevel dielectric used in various applications. Various openings such as vias, contact openings, and trenches for damascene interconnect lines, may subsequently be formed in the low-k dielectric material. An aspect of the invention is that a plasma treatment is not performed on the low-k dielectric film after deposition: rather; the low-k dielectric film is coated with a photosensitive patterning medium prior to the low-k dielectric film undergoing any plasma treatment. In one exemplary embodiment, a photoresist film is formed over the top surface of the low-k dielectric film and an anti-reflective coating (ARC) may optionally be formed between the low-k dielectric film and the photoresist. Conventional ARC and photoresist materials may be used. The photoresist is a carbon-containing, organic material. Various photoresists having various thicknesses may be used. 
   Conventional photoresist patterning techniques are used and followed by conventional etching techniques to form openings in the low-k dielectric film and to form the exemplary structure shown in  FIG. 1 . The openings may be contact openings, vias, trenches, dual damascene trenches, and the like.  FIG. 1  shows exemplary opening  2  formed in low-k dielectric film  4  after the patterning and etching processes have been carried out. The structure also includes optional ARC layer  8  and photoresist film  6 , each as described above. Low-k dielectric film  4  is as described above and includes top surface  14 , which has not yet been subjected to plasma treatment, and sidewall surfaces  16  that were exposed during the etching process. An aspect of the invention provides a plasma operation that both removes photoresist film  6  and treats the surfaces  14  and  16  of low-k dielectric film  4  as they become exposed. The use of this single plasma operation to both strip photoresist and treat the low-k dielectric material simplifies the processing sequence and reduces cycle time. The tool used to perform the plasma processing operation may be a reactive ion etcher, a microwave plasma tool, an ICP (Inductively Coupled Plasma) etching tool, a magnetically enhanced reactive ion etcher, downstream strippers or other tools that are commercially available to perform plasma processing operations by generating and controlling plasmas. Plasma  10  is generated within the processing chamber and in the vicinity of substrate  18 . During the plasma processing operation, a bias may be applied to substrate  18  causing the energized plasma species to be directed towards the surface of substrate  18 . The plasma processing operation may include a gas mixture of N 2  and H 2 . The volumetric concentration of H 2  gas in the gas mixture may exceed 10%. In one embodiment, the gas mixture may contain more H 2  than N 2  by volume. The volume percentage of N 2  in the gas mixture may range from 10-70% by volume in various exemplary embodiments and the volume percentage of H 2  in the gas mixture may range from 30-90 volume % in various exemplary embodiments. The pressure may range from 5-10 torr in one exemplary embodiment, but other pressures may be used. The source power for the plasma may range from 1000-1500 Watts, but other powers may be used in other exemplary embodiments. The bias power applied to substrate  18  may be 400 Watts or less in various exemplary embodiments. The temperature during the plasma processing operation that both strips photoresist  6  and treats the exposed surfaces of low-k dielectric film  4 , may range from room temperature (about 25° C.) to about 200° C. During this plasma processing operation, the photoresist may be stripped/removed at a rate of around 3500 Å/minute, but the photoresist removal rate may vary and will depend on the particular process parameters as well as the photoresist material. 
   The plasma processing operation also treats the exposed surfaces of the low-k dielectric material  4  such as surfaces  14  and  16  shown in  FIG. 2  which illustrates the structure after the photoresist and optional ARC material have been removed. The plasma processing conditions are chosen to enable plasma  10  to cause carbon from the photoresist material that is being removed, to penetrate low-k dielectric film  4  and complex with materials in the low-k dielectric film to maintain a suitably high carbon content and, therefore, a suitably low dielectric constant. The photoresist film therefore acts as a carbon source. The carbon from the photoresist material forms bonds with the materials within dielectric film  4  and reduces low-k damage. Carbon leaching from low-k dielectric film  4  is prevented. Pore sealing of the low-k dielectric material is accomplished by the single plasma operation. The plasma processing operation treats low-k dielectric film  4  by forming a thin layer  20  on surfaces  14  and  16  whereas a bulk treatment performed prior to etching would leave sidewall surfaces  16  untreated. The applicants have found, through XPS analysis, that thin layer  20  formed on surfaces  14  and  16  may be Si—N and Si—O—N type structures similar to silicon nitride and silicon oxynitride, respectively, but other silicon, oxygen, and nitrogen-containing structures may be formed. Protective thin layer  20  may be a material that includes at least one of Si—N and Si—O—N type materials. Protective thin layer  20  protects the low-k material against future plasma damage, prevents subsequent carbon leaching, and has also been found to improve mechanical properties such as hardness. Depending on the thickness of the photoresist film being removed, various times may be used for the plasma processing operation and a generous overetching time may be used after the conclusion of the photoresist removal, to insure the appropriate plasma treatment of the low-k dielectric material that occurs when the photoresist is removed and the low-k dielectric surfaces exposed. 
   The preceding merely illustrates the principles of the invention. It will thus be appreciated that those skilled in the art will be able to devise various arrangements which, although not explicitly described or shown herein, embody the principles of the invention and are included within its spirit and scope. Furthermore, all examples and conditional language recited herein are principally intended expressly to be only for pedagogical purposes and to aid in understanding the principles of the invention and the concepts contributed by the inventors to furthering the art, and are to be construed as being without limitation to such specifically recited examples and conditions. Moreover, all statements herein reciting principles, aspects, and embodiments of the invention, as well as specific examples thereof, are intended to encompass both structural and functional equivalents thereof. Additionally, it is intended that such equivalents include both currently known equivalents and equivalents developed in the future, i.e., any elements developed that perform the same function, regardless of structure. 
   This description of the exemplary embodiments is intended to be read in connection with the figures of the accompanying drawing, which are to be considered part of the entire written description. In the description, relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivatives thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. 
   Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.