Abstract:
A method for forming high-density self-aligned contacts and interconnect structures in a semiconductor device. A dielectric layer thick enough to contain both interconnect and contact structures is formed on a substrate. A patterned hardmask is formed on the dielectric layer to define both the interconnect and contact structures. The openings for interconnect features are first formed by partially etching the dielectric layer selective to the hardmask. A second mask (e.g., a resist) is used to define the contact openings, and the dielectric layer is etched through the second mask, also selective to the hardmask, to expose the diffusion regions to be contacted. The patterned hardmask is used to help define the contact openings. Conductive material is then deposited in the openings which results in contacts and interconnects that are self-aligned. By first forming the openings for both interconnect and contacts, savings in processing steps may be obtained.

Description:
FIELD OF THE INVENTION  
         [0001]    The present invention relates to the manufacture of semiconductors and more specifically relates to the manufacture of dynamic random access memory (DRAM) arrays.  
         BACKGROUND OF THE INVENTION  
         [0002]    The integration of semiconductor devices for very large semiconductor integration (VLSI) requires that the devices first be fabricated so that they are electrically isolated from each other. Ultimately, these devices must be electrically interconnected to provide the desired circuit functionality. Thus, interconnection structures (e.g. wiring, word lines (WLs), bit lines (BLs), etc.) and contact structures, between the interconnection structures and the semiconductor devices, must also be formed.  
           [0003]    Semiconductor memory chips, such as dynamic random access memory (DRAM), typically include array regions, including arrays of memory cells, as well as support regions, which include logic devices that provide support functionality. As dimensions shrink to 110 nm and below, DRAM technologies face several critical challenges. The cell design must be “friendly” for lithography and all the use of self-alignment techniques in the array. For example, misalignment of interconnection and contact structures can result in problems such as leakage or shorts, and increased resistance, affecting both functionality and performance.  
           [0004]    Conventional methods of forming contacts and interconnection structures involve multiple processing steps, including lithographic masks for contacts and interconnection features at the minimum lithographic dimensions (i.e. minimum feature size). Processes involving masks having minimum feature sizes are relatively costly, and the difficultly of achieving overlay of such features without misalignment between different processing levels increases.  
           [0005]    An example of a conventional wiring and contact layout in an array region is illustrated in the plan view shown in FIG. 8A, where source/drain diffusion regions (active areas AA)  110  on a substrate is oriented along a vertical lines, and word lines  130  are formed over the substrate, running horizontally across the diffusion regions  110 . Wiring lines  120  (such as bit lines) might be laid out to run parallel and overlaying the diffusion regions  110 . Although it is preferable for the wiring lines  120  to be aligned over the diffusion regions  110 , typically there will be some misalignment, as illustrated in FIG. 8A. Note that the illustrations are not intended to be drawn to scale, and the misalignments shown are exaggerated for illustration purposes. Contact via holes  150  may be laid out to define contact structures for connecting the wiring to diffusion regions of devices (not shown) that are formed in the substrate.  
           [0006]    Referring to the cross-section views along lines A-A′ in FIG. 8B and along line B-B′ in FIG. 8C, the contact structures  150  and wiring structures  120  formed by conventional processes are illustrated. Typically, contact structures  150  are formed in a dielectric layer  210  formed over the devices in the substrate  10 , for example, by a damascene process. Following that, wiring structures  120  may be formed within another dielectric layer  211 , again using methods known in the art, such as a damascene method. However, this sequential method of first forming the contact structures and then forming the wiring structures suffers from two disadvantages. First, there may be overlay misalignments that can result in potential functional problems and require design tolerances that tend to limit the minimum size of devices and thereby limiting densities. Such design tolerances contribute to process costs. In addition, each additional step in the processing adds significant costs.  
           [0007]    Many different layouts for array regions may be formed, depending on the device type and other factors. For example, for some layouts, line-type contact structures may be appropriate, such as illustrated in FIG. 9A, in which the wiring lines  120  and the contact regions  150  are both arranged in a linear fashion overlaying the linear diffusion region  110 . Once again, misalignment may occur, as shown in FIG. 9A and the associated cross-sections along lines A-A′ and B-B′ in FIGS. 9B and 9C, respectively.  
           [0008]    Divakaruni et al. (U.S. Pat. No. 6,245,651) proposed a method for creating self-aligned borderless contacts in which a first dielectric layer is formed in both the array and support regions, and then an etch stop layer is formed over the support region. The array regions include gate stacks in the first dielectric layer, and diffusion regions between the gate stacks in the substrate, to which bitline contacts are to be formed. A second dielectric layer is then deposited over the array region and the support region, which includes the etch stop layer in the support region. The second dielectric layer is patterned to define the interconnect structures. Etching of the second dielectric layer is performed to form the interconnect structures in both the array and support regions. The etch stop layer in between the first and second dielectric layers stops the etching in support region, but allows further etching in the array region to form the contacts, which are borderless to the gate stacks and provide contact to the diffusion regions. Subsequently, the contacts and interconnect structures may be filled with a conductive material, for example, using a damascene process. However, the method of Divakaruni et al. has the disadvantage that the buried etch stop layer in the support region produces topographical anomolies that makes removal of excess conductive material difficult in the planarization step of the damascene process. In addition, the use of separate dielectric and etch stop layers in the method of Divakaruni et al. adds complexity to the processing, and tends to increase costs.  
           [0009]    In view of the foregoing discussion, there is a need for a process for fabricating contact and interconnect structures in high-density regions of a semiconductor chip (such as in a memory array) to reduce the misalignment of contacts and interconnection structures. In addition, there is a need to reduce the cost of such processes by reducing the number of steps in the process and/or reduce the complexity and cost of masks used in such processing.  
         SUMMARY OF THE INVENTION  
         [0010]    The present invention addresses the above-described need by providing a method for forming high-density self-aligned contacts and interconnect structures in a semiconductor device. A dielectric layer thick enough to contain both interconnect and contact structures is formed on a substrate. A patterned hardmask is formed on the dielectric layer to define both the interconnect and contact structures. The openings for interconnect features are first formed by partially etching the dielectric layer selective to the hardmask. A second mask (e.g., a resist) is used to define the contact openings, and the dielectric layer is etched through the second mask, also selective to the hardmask, to expose the diffusion regions to be contacted. The patterned hardmask is used to help define the contact openings. Conductive material is then deposited in the openings which results in contacts and interconnects that are self-aligned. By first forming the openings for both interconnect and contacts, savings in processing steps may be obtained.  
           [0011]    In accordance with the present invention, a method for forming a semiconductor device comprising the steps:  
           [0012]    providing a substrate including a support region and an array region having an array device diffusion region;  
           [0013]    depositing a dielectric layer on said substrate;  
           [0014]    forming a patterned hardmask on said dielectric layer, said patterned hardmask having a first opening that overlays at least a portion of said array device diffusion region;  
           [0015]    partially etching said dielectric layer selective to said hardmask through said first opening to form a first recess in said dielectric layer;  
           [0016]    forming a second mask having a second opening at least partially overlapping a portion of said first recess; and  
           [0017]    subsequently etching said dielectric layer selective to said hardmask through said second opening and through said portion of said first recess,  
           [0018]    so that said portion of said first recess is extended through said dielectric layer to form a second recess so that a corresponding portion of said array device diffusion region is exposed.  
           [0019]    In accordance with another aspect of the present invention, the interconnect structures of the support region may be formed at the same time as the interconnect structures in the array region.  
           [0020]    In accordance with another aspect of the present invention, after formation of the interconnect structures, the support region may be protected, for example, by a block mask, during the formation of the contact features in the array region. Subsequently, the contact features in the support region may be formed separately.  
           [0021]    In accordance with the present invention, a semiconductor device is provided having a substrate including a device diffusion region;  
           [0022]    a dielectric layer on said substrate;  
           [0023]    a contact structure formed in said dielectric layer;  
           [0024]    an interconnect structure formed in said dielectric layer over said contact structure,  
           [0025]    so that said contact structure is in contact with said device diffusion region and in contact with said interconnect structure and wherein said contact structure and said interconnect structure are aligned with each other.  
           [0026]    In yet another aspect according to the present invention, the semiconductor device includes an array region and a source region. For example, the array region may be an array of memory cells, such as dynamic random access memory (DRAM) cells. In another aspect, the devices in the array region may be vertical devices, or may be planar devices.  
           [0027]    In yet another aspect according to the present invention, the device diffusion region is associated and corresponds to a gate stack having an encapsulating material (e.g., a dielectric), where the device diffusion region is adjacent to the encapsulating material so that the contact structure is borderless to the encapsulating material of the gate stack.  
           [0028]    The novel features believed to be characteristic of this invention are set forth in the appended claims. The invention itself, however, as well as other objects and advantages thereof, may be best understood by reference to the following detailed description of an illustrated preferred embodiment to be read in conjunction with the accompanying drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0029]    [0029]FIG. 1A illustrates a plan view of an array region layout.  
         [0030]    [0030]FIG. 1B illustrates a plan view of an array region layout, including a mask for a contact region.  
         [0031]    FIGS.  2 A- 2 C illustrates cross-sectional views of a semiconductor substrate at a processing stage of one embodiment in accordance with the present invention.  
         [0032]    FIGS.  3 A- 3 C illustrates cross-sectional views of a semiconductor substrate at a subsequent processing stage of one embodiment in accordance with the present invention.  
         [0033]    FIGS.  4 A- 4 C illustrates cross-sectional views of a semiconductor substrate at a subsequent processing stage of one embodiment in accordance with the present invention.  
         [0034]    FIGS.  5 A- 5 C illustrates cross-sectional views of a semiconductor substrate at a subsequent processing stage of one embodiment in accordance with the present invention.  
         [0035]    FIGS.  6 A- 6 C illustrates cross-sectional views of a semiconductor substrate at a subsequent processing stage of one embodiment in accordance with the present invention.  
         [0036]    FIGS.  7 A- 7 C illustrates cross-sectional views of a semiconductor substrate at a subsequent processing stage of one embodiment in accordance with the present invention.  
         [0037]    [0037]FIG. 8A illustrates a plan view of a prior art layout including contact via regions.  
         [0038]    FIGS.  8 B- 8 C illustrates cross-sectional views of the layout of FIG. 8A.  
         [0039]    [0039]FIG. 9A illustrates a prior art plan view of a layout including line-type contact regions.  
         [0040]    FIGS.  9 B- 9 C illustrates cross-sectional views of the layout of FIG. 9A. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0041]    In the following descriptions of the preferred embodiments of the invention, a method is described for forming contacts that are self-aligned to interconnect structures and reduces processing costs. Reference is made to the drawings to illustrate the method according to the present invention, which are not necessarily drawn to scale.  
         [0042]    Referring to FIG. 1A, a plan view of a layout in a memory array region (for example, a DRAM memory array) on a substrate of a semiconductor chip. Source/drain regions  110  in the substrate (which are typically doped regions, also known as active area, or AA regions  110 ) are laid out in this embodiment in a linear fashion, for example, by using a line-type mask. Memory cells (not shown) are formed along the AA regions  110  at or near the intersection of the AA regions  110  and the word lines  130 . Note that in some embodiments, the word lines  130  may function as gate conductors at the intersection with the diffusion regions  110 . Thus, in accordance with the present invention, gates stacks  130  that are encapsulated in a dielectric  115  are associated with the source/drain diffusion regions  110 , and referred to hereinafter interchangeably with word lines  130 . The word lines  130  may be laid out essentially orthogonally to the orientation of the diffusion regions  110 , but could also be laid out to cross the AA patterns  110  (which are lines in this example, but could take arbitrary paths in other embodiments) at other angles. Isolation regions  140  are formed in the substrate between the diffusion regions  110 . Wiring lines (such as bitlines)  120  are typically formed over the devices formed in and on the substrate. The wiring lines  120  are preferably laid out to be aligned with the diffusion regions  110 , but typically there is some overlay misalignment between the wiring lines  120  and the AA or diffusion lines  110 , as illustrated in FIG. 1A. The present invention provides a method for forming contacts between the wiring lines  120  and the diffusion lines  110  that are self-aligned to the wiring lines  120  which minimizes problems caused by misalignment of contacts and reduces processing costs compared to prior methods.  
         [0043]    In accordance with the present invention, a substrate  10  is provided at an intermediate stage in which devices may be formed in both an array region  910  and a support region  920 . FIG. 2A shows a cross-sectional view along the direction of line B-B′ of FIG. 1 extending through the array region  910  and support region  920 . In the array region  910 , doped portions of the substrate  10  form the diffusion regions  110 . Isolation trenches  140  containing a dielectric material such as silicon oxide have been formed. A support device  230  is formed in the support region  920  having support device diffusion regions  111 . Array devices (not shown), are formed in the array region having diffusion regions  110 . The array devices, such as memory cells, are required to be densely packed. The memory cells may include planar or trench-type (vertical) devices. Word lines  130  are formed in a layout that intersects the layout of the diffusion regions  110 , as shown in the cross-section in FIG. 2B along the line A-A′ of FIG. 1A. The word lines  130  may be formed within a dielectric material  115 , such as silicon nitride, which provides protection from shorts which may occur during the contact etch. In order to integrate the array devices into a circuit, contacts must be formed between the array device diffusion regions  110  and circuit wiring.  
         [0044]    Referring to FIG. 3A, an interlevel dielectric layer  210  (ILD) is formed on the surface of the substrate  10 . The ILD  210  may be formed from materials such as silicon oxide, borosilicate (BSG), phospho-silicate (PSG), and borophosphosilcate glass (BPSG), among others, and could include a combination of layers of such materials. The ILD layer  210  is preferably planarized, for example, by chemical mechanical polishing (CMP) or by applying the ILD using a spin-on technique. A hardmask layer  220  is formed on the surface of the ILD  210 . The hardmask  220  may be formed from materials such as polysilicon, silicon nitride, silicon carbide or other materials that have high etch selectivity relative to the ILD etch. A resist layer  430  is formed on the hardmask layer  220  and is patterned to provide openings  250  for interconnects (wiring) in the array region and openings  270  for wiring in the support region. Note that, in this example, because of the high density of devices in the array region, which require features at or near the minimum feature size that the lithographic process can resolve, the interconnects in the array region are designed to have dimensions at or near the minimum feature size. However, the use of minimum feature size is not typically a requirement for wiring in the support regions. The openings  250  for interconnects in the array region are preferably aligned with the diffusion regions  110 , but as a practical matter, some misalignment always occurs. Cross-sections along lines A-A′ and B-B′ at this stage of the process are illustrated in FIGS. 3B and 3C, respectively.  
         [0045]    The hardmask  220  is then patterned according to the resist patterning. The patterned hardmask  220  is now used as the mask for subsequent etching of the dielectric layer  210 . At this stage, the resist  430  may be optionally stripped off, or may be left on during the next etching step of the ILD layer  210 , which may be preferable for cost effectiveness. The ILD layer  210  is then partially etched, selective to the resist  430  (and to the hardmask  220  if the resist  430  has been removed) to form the features  280  that will be used for wiring lines in both the array region  910  and in the support region  920 , as illustrated in FIG. 4A. At this stage, the ILD layer  210  is partially etched to form openings  280  which define the interconnect (wiring) structures, so that array devices and wordlines  130  remain covered by the ILD layer  210  in the array region  910  as shown in the A-A′ cross-section in FIG. 4B. The resulting cross-section along the B-B′ line is shown in FIG. 4C.  
         [0046]    Next, the resist layer  430  is removed, if it has not already been removed, and a layer of resist is formed as a mask  540  over the support region  920 , which could be a block mask as shown in FIG. 5A. The patterned hardmask  220  remains in place. In addition, the contact areas  150  are defined by patterning the resist  540  appropriately in the array area. The pattern used to define contact regions in the array area will be dependent on the array device layout, and type of devices used, which could be, for example, planar devices or trench devices. For example, contact via holes  150  could be defined as illustrated in FIG. 8A using the mask material  540  patterned to expose the contact vias  150 . Alternatively, referring to FIG. 1B, contact regions could be defined by a line-type mask  540  as part of the mask  540  that blocks the support region, but which cross the openings in the patterned hardmask  220  to expose defined contact regions. Thus, line mask  540  would define the upper and lower boundaries of the contact regions, while the hardmask  220  will define the left and right boundaries of the contact regions. Such a line mask as in FIG. 1B may cross the wire line regions  120  and diffusion regions  110  at any appropriate angle, which is not necessarily at 90 degrees. A non-orthogonal angle may be preferable in cases when the underlying AA pattern is more complex than a simple alternating line and space pattern as depicted in the current example. In another possible embodiment of an array region layout, contact regions that are parallel to the wiring lines  120  and the diffusion regions  110  may be desired, and in such an embodiment, the patterned hardmask  220  alone will be sufficient to define the contact regions and no resist material  540  will be required to define the contacts in the array region  910 , requiring only a block mask  540  in the support region  920 . If the cross line-type mask  540  as illustrated in FIG. 1B is used, then the mask  540  will define contact openings  290  (which overlap interconnect openings  280 ) as shown in the cross-section along line A-A′ as shown in FIG. 5B, and the hardmask  220  will define the contact openings  290 / 280  along the line B-B′ as in the cross-section shown in FIG. 5C.  
         [0047]    In some layouts, devices may have been formed that have gate stacks  130 ,  230  including gate conductors  130 ,  230  encapsulated in an insulator  115 ,  215  and have corresponding source/drain regions  110 ,  111 , respectively. The encapsulating dielectric  115 ,  215  may be used as an aid in defining the boundaries of the contact openings  290  which result in contact structures  620  that are borderless to the encapsulated gate stacks ( 130 / 115 ,  230 / 215 ) and thus self-aligned to the source/drain regions  110 ,  111 . This is performed by etching the ILD  210  selective to the encapsulating dielectric  115 ,  215 , as is known in the art.  
         [0048]    The ILD dielectric layer  210  is then etched selective to the hardmask  220  and mask  540 , so that the diffusion region  110  is exposed within the contact openings  290 . The etching is preferably an anisotropic etch, such as a reactive ion etch (RIE). The resulting structure is illustrated in FIGS. 6A, 6B and  6 C.  
         [0049]    Subsequently, the mask  540  is removed. The wiring and contact openings may now be filled with conductive material  620 ,  740  using processes known in the art. For example, barrier layers (not shown) are typically formed in such openings to protect against undesirable interactions between the conductive material and adjacent materials. The conductive materials in the contact structure  620  and interconnect or wiring structure  740  could be the same or different conductive materials, depending on the application, but are shown separately here to illustrate that the contact structures  620  and the wiring (interconnect) structures  740  formed in accordance with the present invention are self-aligned. Conductive materials for the contact structures  620  could include, for example, tungsten, polysilicon, polysilicide or even stacked conductor combinations. Conductive materials for interconnect structures  740  may include tungsten, aluminum, or possibly copper. The hardmask layer  220  will be removed during this process, for example by planarization methods such as chemical-mechanical polishing (CMP) or an etchback method.  
         [0050]    The process in accordance with the present invention has, among other benefits, the formation of self-aligned contact and wiring structures, and also requires fewer process steps than conventional methods, thus reducing costs. The method of forming wiring and contact structures in accordance with the present invention is not restricted to the layouts illustrated in the embodiments discussed above, and are not restricted to any particular types of devices.  
         [0051]    It will be appreciated by those skilled in the art that the method and layout in accordance with the present invention is not limited to the embodiments discussed above. Accordingly, the invention is intended to encompass all such alternatives, modifications and variations which fall within the scope and spirit of the invention and the following claims.