Abstract:
A process enables plasma etching of materials that do not contain silicon. The process is particularly suitable for the side wall passivation of chromium layers in masks for fabricating semiconductor components. The plasma contains oxygen and/or nitrogen, and at least one silicon-donating compound is introduced into the plasma. This allows efficient passivation of side walls.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a plasma-etching process using an oxygen-containing and/or nitrogen-containing plasma for side wall passivation.  
           [0003]    When materials are being patterned or structured in the semiconductor industry, it is often necessary for certain regions of a structure to be covered by passivation layers during etching processes. The passivation layers are used to protect underlying layers from the etching medium.  
           [0004]    This causes a problem in particular during the production of masks that include chromium layers. During the plasma etching of chromium layers in the production of masks (e.g. COG, chrome-on-glass), the chromium layer is usually patterned by way of a plasma etching process. In the present context, the term plasma etching is understood as meaning any process which, from a plasma, effects the removal of material. These include, for example, reactive ion etching (RIE), wherein, in addition to ion bombardment, reactive components of the gas atmosphere used are also active. Reactive ion etching allows in particular anisotropic etching. ICP (inductively coupled plasma) processes are also included in the term plasma etching. Furthermore, combinations of RIE and ICP processes are also possible.  
           [0005]    To enable the chromium to be converted into a volatile compound during the etching of chromium masks, relatively large amounts of oxygen have to be added to the etching gas (chlorine). In this case, the high oxygen content in the plasma prevents the formation of polymers with which side wall passivation is otherwise achieved. Furthermore, a resist layer which is used during the patterning of the chromium layer is laterally attacked by the oxygen radicals which are present.  
           [0006]    Hitherto, it has been attempted to solve this problem by adjusting the resist-etching rate. The resist-etching rate is partially isotropic, and consequently determines the uniformity of the final dimension (CD uniformity) and the dimension loss (CD bias).  
           [0007]    A drawback in this context is that effective flank protection cannot be achieved in this way.  
         SUMMARY OF THE INVENTION  
         [0008]    It is accordingly an object of the invention to provide a plasma-etching method for non-silicon materials which overcomes the above-mentioned disadvantages of the heretofore-known devices and methods of this general type and with which side wall passivation can be achieved in an effective way.  
           [0009]    With the foregoing and other objects in view there is provided, in accordance with the invention, a plasma-etching process, which comprises:  
           [0010]    providing a quartz substrate with a chromium layer;  
           [0011]    generating a plasma containing at least one of oxygen and nitrogen for side wall passivation; and  
           [0012]    introducing at least one silicon-donating compound into the plasma; and  
           [0013]    etching the chromium layer in a fabrication of a semiconductor component.  
           [0014]    In accordance with an added feature of the invention, the at least one silicon-donating compound is a gaseous molecule of the following empirical formula: SiA x H y , where  
           [0015]    x=0, . . . , 4;  
           [0016]    y=0, . . . , 4; and  
           [0017]    x+y=4 and  
           [0018]    A=Cl or A=F.  
           [0019]    In accordance with an additional feature of the invention, the at least one silicon-donating compound is a gaseous molecule of SiH 4 , SiCl 4 , SiF 4 , and/or SiH 2 Cl 2 .  
           [0020]    The introduction of at least one silicon-donating compound into the plasma allows a reaction with oxygen molecules or ions and/or nitrogen molecules and/or ions which are present in the plasma.  
           [0021]    The SiO 2  or SiO 2 -like compounds or nitride compounds which form are uncharged and therefore deposited on the surface of the treated material.  
           [0022]    In an advantageous configuration of the invention, at least one silicon-donating compound is a gaseous molecule in accordance with the following empirical formula: SiA x H y , where  
           [0023]    x=0, . . . , 4,  
           [0024]    y=0, . . . , 4  
           [0025]    x+y=4 and  
           [0026]    A=Cl or A=F,  
           [0027]    in particular SiH 4 , SiCl 4 , SiF 4  or SiH 2 Cl 2 .  
           [0028]    It is advantageous for in each case two hydrogen atoms in one of these silicon-donating compounds to be substituted by an oxygen molecule, with SiCl 2 O in particular being advantageous, the silicon-donating compound being in gas form under operating conditions.  
           [0029]    When a trench structure is being etched in the material, after the at least one silicon-donating compound has been added, a side wall of the trench structure is advantageously coated with an SiO 2  layer and/or an SiO 2 -like layer and/or with a nitride layer for the purpose of side wall passivation. The SiO 2  and/or SiO 2 -like compounds and/or the nitride compounds are detached again from the surfaces which lie transversely with respect to the electric field and on which the ions impinge with a particularly high level of energy, while a passivation layer remains in place on the side walls.  
           [0030]    SiO 2  layers and/or SiO 2 -like layers and/or nitride layers which have been deposited on a base of the trench structure are advantageously removed by charged particles in the plasma.  
           [0031]    It is also advantageous if the SiO 2  layers and/or the SiO 2 -like layers and/or the nitride layers are removed during cleaning and/or resist stripping of the material.  
           [0032]    Other features which are considered as characteristic for the invention are set forth in the appended claims.  
           [0033]    Although the invention is illustrated and described herein as embodied in a process for the plasma etching of materials which do not contain silicon, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.  
           [0034]    The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0035]    [0035]FIG. 1 is a diagrammatic sectional side view of a part of a mask for the fabrication of semiconductor components prior to an etch;  
         [0036]    [0036]FIG. 2 is a diagrammatic and schematic view of a part of the mask shown in FIG. 1 during an etch using the process according to the invention;  
         [0037]    [0037]FIG. 3 is a diagrammatic view of the part of the mask shown in FIG. 2 following the etch using the process according to the invention;  
         [0038]    [0038]FIG. 4 is a diagrammatic view of the part of the mask shown in FIG. 3 after resist stripping and cleaning steps. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0039]    Referring now to the figures of the drawing in detail and first, particularly, to FIG. 1 thereof, there is shown a structure in section, the structure being used in the fabrication of a mask for semiconductor manufacture. FIG. 1 represents the state of the assembly prior to the etch.  
         [0040]    In this state, a chromium layer  31  is arranged on a quartz substrate  30 . This chromium layer  31  is to be patterned in a plasma-etching process, a resist layer  32  (photoresist) being arranged above parts of the chromium layer. The resist layer  32  has trench structures  20 , at which a plasma  10  (cf. FIG. 2) is to etch the chromium layer  31  in order to produce a pattern. Regions of the chromium layer  31  which are covered by the resist layer  32  are not etched.  
         [0041]    [0041]FIG. 2 illustrates the etching operation using the process according to the invention.  
         [0042]    According to the invention, the plasma  10  contains a silicon donor, i.e., a silicon-donating compound  1 , namely gaseous SiH 4 . Alternatively, or even additionally, it is also possible to use gaseous SiCl 4 , SiF 4  or SiH 2 Cl 2  as silicon-donating compounds. Also, each of these silicon-donating compounds  1  can be used on its own in the process according to the invention. In general terms, the molecule of the silicon-donating compound  1  can be built up in accordance with the following empirical formula: SiA x H y , where  
         [0043]    x=0, . . . , 4  
         [0044]    y=0, . . . , 4 and  
         [0045]    x+y=4 and  
         [0046]    A=Cl or A=F.  
         [0047]    Therefore, chlorine-containing or fluorine-containing silicon compounds are suitable. Alternatively, it is also possible to use gaseous compounds of this nature if two hydrogen atoms are replaced by an oxygen atom, such as for example SiCl 2 O, provided that the compound is gaseous under the process conditions (silicon dioxide, SiO 2  is accordingly ruled out).  
         [0048]    Furthermore, the plasma  10  contains uncharged molecules (e.g. Cl 2 O 2 ) and ions (O + , Cl + , O 2   + ). In the present example, the oxygen in the plasma  10  is used as a reaction partner for the silicon during the formation of passivation layers. As an alternative or in addition it is also possible for nitrogen in the plasma  10  to be used as a reaction partner.  
         [0049]    The electric field which forms in the plasma perpendicular to the substrate causes the ionized particles to be diverted substantially vertically toward a base  23  of the trench structure  31 . This is symbolically indicated in FIG. 2 by arrows at the corresponding ions.  
         [0050]    The uncharged particles, in particular the silicon-donors  1 , move randomly in the field, i.e. they impinge in particular on the side walls  21  of the trench structure  20 . However, some of these particles will also impinge on the base  23  or the top side of the resist layer  32 .  
         [0051]    The silicon-donating compounds  1  are broken down in the plasma  10 , the silicon which is released combining with the oxygen which is present in the plasma  10 . Since there is sufficient oxygen in the plasma, small quantities of the silicon-donating compound  1  are sufficient.  
         [0052]    SiO 2  compounds and/or SiO 2 -like compounds  2  are formed as a product of the reaction. These are in principle deposited on the top side of the resist layer  32 , the side walls  21  of the resist layer  32  and on the base  23 .  
         [0053]    The ions that are generated in the plasma  10 , however, impinge vertically on the top side of the resist layer  32  and the base  23  with an energy which can be adjusted, so that the compounds deposited there comprising SiO 2  and/or SiO 2 -like compounds are removed again in situ. The deposits of SiO 2  and/or SiO 2 -like compounds on the side walls  21 , however, are not affected by the vertically impinging ions, since only very small quantities of these ions impinge on the side walls  21 , which are likewise substantially vertical. Scattered ions and neutral particles which impinge on the side walls  21  do not have sufficient kinetic energy to effect removal, or the density of the particles is too low. Therefore, the resist is not recessed back, and the etching flank which is produced into the layer of chromium  31  is also protected.  
         [0054]    Therefore, the result is the formation of side wall passivation  22  comprising SiO 2  and/or SiO 2 -like compounds on the side walls  21  of the resist layer  32  and on etched regions of the chromium layer  31 . This is indicated in FIG. 2 by the thick lines.  
         [0055]    Therefore, an anisotropic etch without loss of dimensions is possible.  
         [0056]    Typical operating parameters for a plasma etch of this type for chromium layers are:  
                                                           Pressure:   10   mTorr           Cl 2  flow:   20   sccm           O 2  flow:   10   sccm           He flow:   40   sccm           SiH 4  flow:   2   sccm           magnetic flux density:   0.5   mT           RF power:   50   W           ICP power:   300   W                      
 
         [0057]    The process described can be regarded as a combination of RIE (reactive ion etching) and ICP (inductively coupled plasma) processes.  
         [0058]    [0058]FIG. 3 shows the situation after the etching. The chromium layer  31  has been partially etched and patterned. The side walls  21  are covered with a side wall passivation  22 .  
         [0059]    [0059]FIG. 4 then shows the state after the resist stripping and cleaning. The resist layer  32  and the side wall passivation  22  have been removed. Only the patterned chromium layer  31  remains in place on the quartz substrate  30 .  
         [0060]    The execution and implementation of the invention is not restricted to the preferred exemplary embodiments described above. Rather, there are a number of conceivable variants which make use of the process according to the invention even in embodiments which are of fundamentally different configuration but which nevertheless incorporate the basic concepts of the novel process.