Abstract:
A method for protecting an alignment mark on a semiconductor substrate, includes forming a dielectric layer on the semiconductor substrate having the alignment mark, forming a cap oxide film on the dielectric layer, wherein the cap oxide film is formed to have a regular thickness and an additional thickness, etching a portion of the dielectric layer and the cap oxide film to expose the semiconductor substrate to thereby form a via hole, filling the via hole with a metal, and performing a chemical mechanical polishing process with the metal and the cap oxide film to form a via contact.

Description:
[0001]    The present application claims priority under 35 U.S.C. 119 to Korean Patent Application No. 10-2006-0083917 (filed on Aug. 31, 2006), which is hereby incorporated by reference in its entirety. 
       BACKGROUND 
       [0002]    In relatively highly integrated semiconductor devices, a planarization process (e.g. Chemical Mechanical Polishing (CMP)) may be important in Ultra Large Scale Integration (ULSI). Accordingly, alignment technology with relatively high reliability on a planarized wafer may be important in micro lithography. 
         [0003]    An alignment mark, as illustrated in example  FIG. 1 , may need to satisfy a minimum width (X) and step height (Y) for sensing in a lithography process. However, an alignment mark may not be able to be sensed if it has a step height smaller than a minimum step height, which may be due to dishing and/or erosion in a CMP process. Accordingly, in manufacturing processes (e.g. ULSI manufacturing processes), there is a need to sense, by an alignment sensor, an alignment mark having a very small step height on a wafer processed by CMP. 
       SUMMARY 
       [0004]    Embodiments relate to a method for protecting an alignment mark that minimizing damage to an alignment mark after a chemical mechanical polishing (CMP) process. 
         [0005]    In embodiments, a method of protecting an alignment mark on a semiconductor substrate includes at least one of the following steps: Forming a dielectric layer on and/or over the semiconductor substrate having the alignment mark. Forming a cap oxide film on and/or over the dielectric layer, wherein the cap oxide film has a regular thickness and an additional thickness. Etching a portion of the dielectric layer and the cap oxide film to expose the semiconductor substrate to form a via hole. Filling the via hole with a metal. Performing a chemical mechanical polishing process with the metal and the cap oxide film to form a via contact. 
     
     
       DRAWINGS 
         [0006]    Example  FIG. 1  illustrating an alignment mark. 
           [0007]    Example  FIGS. 2A to 2D  illustrate a procedure of protecting an alignment mark when forming a via contact, in accordance with embodiments. 
           [0008]    Example  FIG. 3  illustrates parameters of a metal layer, a dielectric layer, and a cap oxide film deposited over a semiconductor substrate, in accordance with embodiments. 
           [0009]    Example  FIGS. 4A to 4E  illustrating profiles for a Laser Step Alignment (LSA) mark, in accordance with embodiments. 
           [0010]    Example  FIGS. 5A to 5E  illustrate profiles for an ASML mark having a relatively large pattern density, in accordance with embodiments. 
           [0011]    Example  FIG. 6  illustrates a photograph of images of an LSA mark and an ASML mark after a main CMP and a touch up CMP are performed, in accordance with embodiments. 
           [0012]    Example  FIG. 7  illustrates a photograph of an image of a Field Image Alignment (FIA) mark, in accordance with embodiments. 
           [0013]    Example  FIG. 8  illustrates an indication of a signal being sensed from an alignment mark in a lithography process, in accordance with embodiments. 
       
    
    
     DESCRIPTION 
       [0014]    Example  FIGS. 2A to 2D  are process cross-sectional diagrams illustrating a procedure for protecting an alignment mark when forming a via contact, in accordance with embodiments. As illustrated in example  FIG. 2A , dielectric layer  202  (e.g. a BoroPhospho Silicate Glass (BPSG)) may be formed on and/or over semiconductor substrate  200 , in accordance with embodiments. Dielectric layer  202  may be for forming a via contact. Semiconductor substrate  200  may include alignment mark  200   a . Alignment mark  200   a  may include of a cap oxide film (SiH4) and/or a Pre-Metal Dielectric (PMD). A CMP process may be performed to planarize dielectric layer  202 . 
         [0015]    As illustrated in example to  FIG. 2B , a cap oxide film  204  (e.g. SiH4) may be deposited on and/or over the planarized dielectric layer  202 , in accordance with embodiments. In embodiments, cap oxide film  204  may have a regular thickness  204   b  and an additional thickness  204   a . Regular thickness  204   b  may be a nominal height that is normally deposited when forming a cap oxide film during a semiconductor manufacturing process. Additional thickness  204   a  may be a supplementary height deposited in addition to the regular thickness  204   b . For example, a regular thickness  204   b  of the cap oxide film  204  may be approximately 2000 Å on and/or over planarized dielectric layer  202 , in accordance with embodiments. Additional thickness  204   a  may be between approximately 25% and approximately 35% of regular thickness  204   b . The total thickness of cap oxide film  204  may be between approximately 2500 Å and approximately 2700 Å, in accordance with embodiments. 
         [0016]    In embodiments, cap oxide film  204  (having a regular thickness and an additional thickness) may be formed by a single deposition. In embodiments, cap oxide film  204  may be formed by two depositions (e.g. one deposition for regular thickness  204   b  and one deposition for additional thickness  204   a ). Cap oxide film  204  may be formed relatively thick compared to a normal thickness of a cap oxide film by having additional thickness  204   a , which may prevent damage to alignment mark  200   a  in a subsequent planarization process, in accordance with embodiments. 
         [0017]    As illustrated in example  FIG. 2C , dielectric layer  202  and cap oxide film  204  may be selectively etched to form a via hole, in accordance with embodiments. The via hole may be formed by coating and patterning a photoresist on and/or over cap oxide film  204 . The patterned photoresist may be used as an etch mask in a photolithography process that forms the via hole. 
         [0018]    As illustrated in example  FIG. 2D , a metal layer (e.g. tungsten (W)) may be deposited to fill the via hole, in accordance with embodiments. A CMP process may be performed using dielectric layer  202  as a polishing stopper. A CMP process may remove a portion of the metal layer and cap oxide film  204  may be substantially completely removed to forming via contact C. A CMP process may include a main CMP process and a touch up CMP process. A main CMP process may polish the metal layer. A touch up CMP process may polish cap oxide film  204  and the metal layer. 
         [0019]    There may be variations of a profile for alignment mark  200   a  depending on the thickness of the cap oxide film  204  and the parameters of a CMP process that forms via contact C. Example  FIG. 3  illustrates conditions of dielectric layer  202 , cap oxide film (SiH4)  204 , and metal layer (W) deposited on and/over semiconductor substrate  200 . 
         [0020]    Example  FIGS. 4A to 4D  illustrate profiles of alignment marks  200   a , in accordance with embodiments. In  FIGS. 4A to 4D , the solid line classifies the thickness of the cap oxide film  204  after a main CMP process, based on the conditions illustrated in example  FIG. 3 , in accordance with embodiments. In  FIGS. 4A to 4D , the dotted line classifies the thickness of cap oxide film  204  after a touch up CMP (‘TUP CMP’), based on the conditions illustrated in example  FIG. 3 , in accordance with embodiments. In embodiments, a LSA (laser step alignment) mark (e.g. available from NIKON Corporation, Japan) may be employed to form alignment mark  200   a.    
         [0021]    Example  FIG. 4A  illustrates a profile for a LSA mark with a process of reference (POR), in accordance with embodiments. Example  FIG. 4B  illustrates a profile of a LSA mark when the thickness of metal layer (W) is changed from approximately 1600 Å to approximately 2500 Å, in accordance with embodiments. Example  FIG. 4C  illustrates a profile of a LSA mark when the thickness of a cap oxide film (SiH4) is changed from approximately 1500 Å to approximately 2000 Å, in accordance with embodiments. Example  FIG. 4D  illustrates a profile of a LSA mark when the thickness of a metal layer (W) is changed from approximately 1600 Å to approximately 3000 Å, in accordance with embodiments. Example  FIG. 4E  illustrate a step height according to conditions illustrated in  FIG. 3 , in accordance with embodiments. In other words,  FIG. 4E  illustrates variations of the thickness of a POR, a cap oxide film (SiH4), and a metal layer (W) after a main CMP and a touch up CMP (‘TUP CMP’), including a difference (delta) between the thicknesses, in accordance with embodiments. 
         [0022]      FIGS. 5A to 5E  illustrate a profile of an ASML mark (e.g. available from ASML, Netherlands), in accordance with embodiments. An ASML may have a relatively large pattern density and may be used as alignment mark  200   a . Example  FIG. 5A  illustrates a profile of an ASML mark with the process of reference (POR) of  FIG. 3 , in accordance with embodiments. Example  FIG. 5B  illustrates a profile of an ASML mark when the thickness of metal layer (W) is changed from approximately 1600 Å to approximately 2500 Å, in accordance with embodiments. Example  FIG. 5C  illustrates a profile of an ASML mark when the thickness of a cap oxide film (SiH4) is changed from approximately 1500 Å to approximately 2000 Å, in accordance with embodiments. Example  FIG. 5D  illustrates a profile of an ASML mark when the thickness of a metal layer (W) is changed from approximately 1600 Å to approximately 3000 Å, in accordance with embodiments. Example  FIG. 5E  illustrates variations thicknesses of a POR, a cap oxide film (SiH4), and a metal layer (W) after a main CMP (indicated by a solid line in  FIGS. 5A through 5D ) and a touch up CMP (‘TUP CMP’) (indicated by a dotted line in  FIGS. 5A through 5D ), including differences (delta) between thicknesses, in accordance with embodiments. 
         [0023]    In embodiments illustrated in example  FIGS. 5A to 5E , when an ASML mark is used as alignment mark  200   a , a gap between pitches is relatively constant after a main CMP and a touch up CMP (‘TUP CMP’), when cap oxide film  202  is formed thicker by about 500 Å. An erosion thickness after a touch up CMP may be within a range of about 2000 Å to 3000 Å, which is greater by approximately three to four times than an LSA mark having a low pattern density. 
         [0024]    Example  FIG. 6  shows images of a LSA mark and a ASML mark after a main CMP and a touch up CMP, in accordance with embodiments. As illustrated in example  FIG. 6 , an ASML mark may have a relative large pattern density compared to an LSA mark, as shown by the ASML mark being more discolored than the LSA mark. 
         [0025]    Example  FIG. 7  shows an image of an FIA (field image alignment) mark (e.g. available from NIKON Corporation, Japan), under each condition after a touch up CMP, in accordance with embodiments. As illustrated in  FIG. 7 , when a thickness of a cap oxide film (SiH4) increases, an alignment mark is most distinct. When a thickness of the metal layer (W) increases, a difference between an alignment mark and a POR may be relatively small. 
         [0026]    As illustrated in example  FIG. 8 , it may be checked whether a signal can be sensed from an alignment mark in an M1 PEP (lithography) process on a condition basis, in accordance with embodiments. In embodiments, a signal may be sensed from an alignment mark when a cap oxide film (SiH4) is greater than approximately 2000 Å. In embodiments, a signal may not be sensed from an alignment mark when a metal layer (W) has a relatively large thickness. 
         [0027]    In embodiments, a cap oxide film may be formed relatively thick (e.g. by a predetermined additional thickness more than a regular thickness) prior to a CMP process. In embodiments, a relatively thick cap oxide film may minimize damage to an alignment mark during CMP, which may maximize semiconductor manufacturing yield. 
         [0028]    It will be obvious and apparent to those skilled in the art that various modifications and variations can be made in the embodiments disclosed. Thus, it is intended that the disclosed embodiments cover the obvious and apparent modifications and variations, provided that they are within the scope of the appended claims and their equivalents.