Abstract:
A method for making a semiconductor structure, includes patterning a photoresist layer to form both a zero marks pattern and a well implant mask pattern. The photoresist layer is on a region of a substrate.

Description:
This application claims the benefit of provisional application Ser. No. 60/227,121 filed Aug. 22, 2000. 
    
    
     BACKGROUND 
     The present invention relates to methods for the formation of zero marks on semiconductor devices. 
     Zero marks facilitate alignment of layers in semiconductor devices. They can be located on the periphery of the device or, alternatively, in every diode field. Typically, the zero marks are formed first and are carried along during further structure formation. 
     In FIGS.  1 ( a )- 1 ( d ) is shown a traditional approach to the formation of zero marks and isolation structures. First, an oxide layer  104  is formed on a silicon substrate  102 . Then, a first photoresist  106  layer is spun on the surface of the oxide layer  104 , resulting in the structure shown in FIG.  1 ( a ). 
     Next, the first photoresist layer  106  is patterned to form a zero marks mask. Afterwards, an etch is performed through the exposed portions of the oxide layer  104  and into the silicon substrate  102  to form a set of zero marks  108 , as shown in FIG.  1 ( b ). 
     The first photoresist layer  106  is then stripped, and a second photoresist layer  110  is spun over the surface of the structure and patterned to form a deep well mask. Subsequently, an etch is performed to remove the exposed portions of the oxide layer  104  and form a photomasking “hole”  112  over the active region, illustrated in FIG.  1 ( c ). Unlike the prior etch to form the zero marks  108 , the silicon substrate  102  is not typically penetrated. 
     Ion implantation is then performed over the photomasking “hole” to form a deep P or N well  114 , as shown in FIG.  1 ( d ). Finally, the second photoresist layer  110  is stripped and the surface is cleaned, to form the structure shown in FIG.  1 ( e ). 
     BRIEF SUMMARY 
     In one aspect, the present invention concerns a method for making a semiconductor structure, comprising patterning a photoresist layer to form both a zero marks pattern and a well implant mask pattern. The photoresist layer is on a region of a substrate. 
     In a second aspect, the present invention is a semiconductor structure, comprising a substrate and a photoresist layer on a region of the substrate. The photoresist layer has been patterned to form both a zero marks pattern and a deep well mask pattern. 
     Definitions 
     The term “substrate” refers to any semiconductor material conventionally known to those of ordinary skill in the art. Examples include silicon, gallium arsenide, germanium, gallium nitride, aluminum phosphide, and alloys such as Si 1−x Ge x  and Al x Ga 1−x As, where 0≦×≦1. Many others are known, such as those listed in Semiconductor Device Fundamentals, on page 4, Table 1.1 (Robert F. Pierret, Addison-Wesley, 1996). Preferably, the semiconductor substrate is silicon, which may be doped or undoped. 
     The term “oxide” refers to a metal oxide conventionally used to isolate electrically active structures in an integrated circuit from each other, typically an oxide of silicon and/or aluminum (e.g., SiO 2  or Al 2 O 3 , which may be conventionally doped with fluorine, boron, phosphorus or a mixture thereof, preferably SiO 2  or SiO 2  conventionally doped with 1-12 wt % of phosphorous and 0-8 wt % of boron). 
     The term “dielectric layer” refers to any dielectric material conventionally known to those of ordinary skill in the art. Examples include conventional oxides, nitrides, oxynitrides, and other dielectrics, such as borophosphosilicate glass (BPSG), borosilicate glass (BSG), phosphosilicate glass, spin-on glass (SOG), silicon oxide, P-doped silicon oxide (P-glass), and silicon nitride, for example SiO 2 , Si 3 N 4 , Al 2 O 3 , SiO x N y , etc. When the dielectric layer is an oxide layer, it preferably has a thickness of 10 to 999 Å, more preferably a thickness of 100 to 300 Å. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Various other objects, features and attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed description when considered in connection with the accompanying drawings in which like reference characters designate like or corresponding parts throughout the several views and wherein: 
     FIGS.  1 ( a )- 1 ( e ) illustrate a series of successive edge-on views for preparing a semiconductor structure with zero marks and a deep N or P well according to a conventional approach; and 
     FIGS.  2 ( a )- 2 ( d ) illustrate a series of successive edge-on views for preparing a semiconductor structure similar to that shown in FIG.  1 ( e ) according to the present invention. 
    
    
     DETAILED DESCRIPTION 
     With the present invention it is possible to eliminate the separate zero-mask step, by forming the zero marks mask concurrently with the well implant mask. This reduces the total number of steps needed to form semiconductor devices. 
     FIGS.  2 ( a )- 2 ( d ) illustrate a series of successive edge-on views for preparing a semiconductor structure similar to that shown in FIG.  1 ( e ) according to the present invention. First, a dielectric layer  204  is formed on a substrate  202 . Then, a photoresist layer  206  is applied on the surface of the dielectric layer  204 , resulting in the structure shown in FIG.  1 ( a ). Preferably, the substrate  202  is a single crystal silicon and the dielectric layer  204  is thermally grown oxide. 
     The photoresist layer  206  is then patterned to form both a zero marks mask and a deep well mask. Afterwards, an etch is performed through the exposed portions of the dielectric layer  204  and into the substrate  202  to form a set of zero marks  208 , a photomasking “hole”  212 , a zero marks recess  213 , and a photomasking “hole” recess  211 , as shown in FIG.  2 ( b ). Unlike conventional approaches, where the photomasking hole is not recessed at all, the depth of the photomasking hole recess  211  is typically similar to the depth of the zero marks recess  213 , with a variation of up to 5-10%. The zero marks recess should be sufficiently deep to allow the zero marks to be detected in subsequent alignment steps. The depth of both the zero marks recess and the photomasking hole recess is preferably 20 to 2000 Å, more preferably 800 to 1200 Å. 
     Ion implantation is then performed over the photomasking hole  212  to form a deep P or N well  214 , illustrated in FIG.  2 ( c ). Finally, the photoresist layer  206  is stripped and the surface is cleaned, to form the structure in FIG.  2 ( d ). 
     Because zero marks facilitate alignment of layers in semiconductor devices, they are typically formed first and are carried along during further structure formation. Consequently, subsequent processing steps leading to the formation of isolation regions should not remove the zero marks. Since the invention concerns the concurrent formation of a zero marks mask with a well implant mask, subsequent operations leading to the structures in FIGS.  2 ( c )- 2 ( d ) are optional. While still further processing steps are contemplated by the invention, processing can be terminated at any point after the formation of the zero marks/well implant mask. 
     The invention makes it possible to eliminate the separate zero-mask step, by forming the zero marks mask concurrently with the well implant mask. This reduces the total number of steps needed to form semiconductor devices. 
     The present invention contemplates the situation where the zero marks are located on the periphery of the semiconductor device, as well the situation where zero marks are located in one or more diode fields. While in FIGS.  2 ( a )- 2 ( d ) the zero marks are shown adjacent to the active regions on the substrate, it is understood that distances between features in these figures are not necessarily drawn to scale. Hence, the figures are intended to encompass arrangements where the zero marks are adjacent to the active regions, as well as arrangements where the zero marks are spatially removed from the active regions (e.g. where the active regions are located on the interior of the substrate surface and the zero marks are located on the periphery). 
     The individual processing steps for use in the present invention are well known to those of ordinary skill in the art, and are also described in Encyclopedia of Chemical Technology, Kirk-Othmer, Volume 14, pp. 677-709 (1995); Semiconductor Device Fundamentals, Robert F. Pierret, Addison-Wesley, 1996; and Microchip Fabrication 3 rd  edition, Peter Van Zant, McGraw-Hill, 1997. 
     The dielectric layer may be deposited by conventional methods known to those of ordinary skill in the art, such as by spin-on methods, sintering (which may further include sol-gel oxide formation), chemical vapor deposition, etc. A glass layer deposited by a chemical vapor deposition technique may be subject to a glass reflow step (e.g., by heating) to smooth, densify and further improve the contact between the protection layer and the substrate. 
     Etching of deposited films may be conducted by conventional methods known to those of ordinary skill in the art. The specific etching methods and materials depend on the material being removed, the resist material and the compatibility of the etching material with the existing structure. Selection of suitable etching materials, resist materials and etching conditions is within the level of ordinary skill in the art. 
     The semiconductor structures of the present invention may be incorporated into a semiconductor device such as an integrated circuit, for example a memory cell such as an SRAM, a DRAM, an EPROM, an EEPROM etc.; a programmable logic device; a data communications device; a clock generation device; a nonvolatile memory device, etc. Furthermore, any of the semiconductor devices may be incorporated into an electronic device (e.g. a computer, an airplane, a mobile telephone, or an automobile). 
     The present invention contemplates the situation where the zero marks are located on the periphery of the semiconductor device, as well the situation where zero marks are located in one or more diode fields. 
     Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein.