Abstract:
A method for fabricating an integrated device with reduced plasma damage is disclosed, including providing a substrate, forming a structural layer on the substrate, forming a photoresist layer on the structural layer, and performing an etching process to the structural layer, wherein the photoresist layer is conductive to reduce plasma damage during the etching process.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    This invention generally relates to a process for the fabrication of integrated devices and more particularly to a process for the fabrication of integrated devices with reduction of damage from plasma. 
         [0003]    2. Description of the Related Art 
         [0004]    For the fabrication of the integrated devices which are on the market at present, the monocrystalline silicon wafers are subjected to a plurality of physical and chemical treatments which make it possible to define the topographies of the integrated electronic circuits. 
         [0005]    In particular, for definition of electronic components in submicrometric technologies, extensive use is made of a process technique which is known as plasma etching, which makes it possible to etch thin films, which can be made of conductive materials and dielectric materials. 
         [0006]    A known example of the application of the plasma etching technique is illustrated in  FIGS. 1A-1C , in which a portion of a wafer  100  comprises a substrate  102  of semiconductor material and a structural layer  104  on top of the substrate  102 . The structural layer  104  can for example be a layer of dielectric material, a layer of polycrystalline silicon, or a layer of metallization, which is intended to be defined by means of plasma etching. 
         [0007]    As illustrated in  FIG. 1B , on top of the structural layer  104 , a mask layer  106  is produced in order to protect the portions which are not to be removed. In particular, the mask layer  106  is produced from a known material such as photoresist or resist material. 
         [0008]    As illustrated in  FIG. 1C , after the plasma etching has been carried out, a defined layer  108  is obtained. Referring to  FIG. 2 , during the plasma etching, an equal quantity of positive ions and electrons is directed towards the wafer  100 , but in individual areas of the wafer  100  there are two mechanisms which lead to plasma damage to the wafer  100  i.e. lack of uniformity of the plasma  202  and a high electrical field, as a result of which more negative than positive charges reach certain areas on the wafer  100 , whereas in other areas the contrary applies. The high electrical field from the plasma  202  in the chamber  204  leads the positive charges  206  on the structural layer  104  of sensitive material to be etched recall electrons from the substrate  102  (supported by a holder  208 ) beneath, thus giving rise to a passage of current and electrical field in the structural layer  104  of the devices. The electric currents which pass through the thin oxides of electronic devices can cause damage, modifying their properties and giving rise to problems of functioning of the devices themselves, or reducing their reliability over a period of time. Specifically, the semiconductor dimension is getting smaller and the gate oxide is thinner, so that the plasma  202  damage is getting worse. 
       BRIEF SUMMARY OF INVENTION 
       [0009]    The invention provides a method for fabricating an integrated device with reduced plasma damage, comprising providing a substrate, forming a structural layer on the substrate, forming a conductive photoresist layer on the structural layer, wherein the conductive photoresist layer is formed by doping a photoresist material with a conductive polymer, and performing an etching process to the structural layer. 
         [0010]    The invention provides a method for fabricating an integrated device with reduced plasma damage, comprising providing a substrate, forming a structural layer on the substrate, forming a photoresist layer on the structural layer, and performing an etching process to the structural layer, wherein the photoresist layer is conductive to reduce plasma damage during the etching process. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0011]    The invention can be more fully understood by reading the subsequent detailed description and examples with references made to the accompanying drawings, wherein, 
           [0012]      FIG. 1A  to  FIG. 1C  show a conventional method for fabricating an integrated device. 
           [0013]      FIG. 2  shows a mechanism of plasma damage during etching. 
           [0014]      FIGS. 3A-3B  shows an intermediate cross section of a method for fabricating a integrated device of an embodiment of the invention. 
           [0015]      FIG. 4  shows a mechanism of reducing plasma damage of an embodiment of the invention. 
           [0016]      FIG. 5  shows an intermediate cross section of a method for fabricating conductive photoresist layer of an embodiment of the invention. 
       
    
    
     DETAILED DESCRIPTION OF INVENTION 
       [0017]    It is understood that specific embodiments are provided as examples to teach the broader inventive concept, and one of ordinary skill in the art can easily apply the teaching of the present disclosure to other methods or apparatus. The following discussion is only used to illustrate the invention, not limit the invention. 
         [0018]    Reference throughout this specification to “one embodiment” or “an embodiment” means that a particular feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, the appearances of the phrases “in one embodiment” or “in an embodiment” in various places throughout this specification do not necessarily all refer to the same embodiment. Furthermore, the particular features, structures, or characteristics may be combined in any suitable manner in one or more embodiments. It should be appreciated that the following figures are not drawn to scale; rather, these figures are merely intended for illustration. 
         [0019]      FIG. 3A  illustrates schematically a wafer  301 , formed by a substrate  302  of monocrystalline silicon, superimposed by a structural layer  304  to be etched. The structural layer  304  to be etched may be one of a number of materials, including silicon dioxide, silicon nitride, BPSG, epitaxy, or other layers to be etched during the manufacturing of a semiconductor chip. A photosensitive mask layer  306  is formed on top of the structural layer  304  to be etched. Referring to  FIG. 3B , the device is then subjected to plasma etching, for definition of the geometry of the structural layer  304  and then the photosensitive mask layer  306  is removed. Referring to  FIG. 4 , during this etching, the wafer  301  is placed in an isolated chamber  312  with plasma produced by coil  314 , wherein the plasma comprises electrons and positive ions. The photosensitive mask layer  306  is conductive, and it allows the electrons which have become stationary on the upper portion of the photoresist mask layer  306  to move, and recombine with the positive charges which have already reached the structural layer  304  to be etched. This prevents the formation of parasitic electric currents, which are damaging to the electronic device, and thus prevents damage from plasma. In other words, the conductive photosensitive mask layer  306  can be polarized to be a shade layer protecting the structural layer  304  and/or the substrate  302  (supported by a holder  310 ) thereunder from electrical field damage generated from plasma. In an example, the conductive photosensitive mask layer  306  is formed from adding conductive polymer into a photoresist, wherein the conductive polymer can be Trans-Polyacetylene, Polythiophene, Polyisothianaphthene, Polyaniline, Polypharaphenylene, Polypharaphenylene-vinylene, or Polycarbazole. 
         [0020]    According to the embodiment, as illustrated in  FIG. 5 , a photosensitive masking layer  406  made of non-conductive material (for example photoresist material) is initially produced. Then, before the plasma etching step, a conductive polymer material  408  is doped into the photosensitive masking layer  406  to function as an ion trapper to reduce plasma damage during the etching process. In an example, the conductive polymer material  408  is doped in the same isolated chamber in which the plasma etching is carried out, at a pressure which is lower than atmospheric pressure, for example 10-1000 mTorr, and with a gas flow of 10-400 sccm (standard cube centimeters per minute). 
         [0021]    It is also possible to dope the conductive polymer material  408  in a chamber different from that in which the plasma etching takes place. 
         [0022]    The features of the process described for fabrication of electronic devices are apparent from the foregoing description. In particular, the fact is emphasized that it makes it possible to reduce, or even eliminate, damage from plasma, owing to the fact that it permits recombination of the electric charges which are separated during the etching. 
         [0023]    In addition, it is particularly advantageous in the case when the structural layer  304  to be etched is the metallization layer used to define the electrical connections between the components of the integrated circuit. However, it can also advantageously be used in the case of isolating layers or regions of semiconductor material, whether these are produced on top of the substrate  302 , or belong to the substrate  302  itself. Additional, the structural layer  304  can be a gate layer with a gate oxide layer thereunder. 
         [0024]    The method for etching a layer with conductive photoresist layer has many advantages. First, a conductive photoresist layer can be formed by doping conductive polymers into a standard photoresist layer, which an easier process and can be integrated into a standard integrated circuit process. Second, the conductive photoresist layer has a similar chemical structure as a conventional photoresist layer, which can be removed by plasma ash. Third, the method for etching a layer with a conductive photoresist layer can reduce plasma damage during the etching process. 
         [0025]    While the invention has been described by way of example and in terms of the preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments. It is intended to cover various modifications and similar arrangements (as would be apparent to those skilled in the art). Therefore, the scope of the appended claims should be accorded the broadest interpretation so as to encompass all such modifications and similar arrangements.