Classifications

• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10B—ELECTRONIC MEMORY DEVICES
  • H10B12/00—Dynamic random access memory [DRAM] devices
  • H10B12/30—DRAM devices comprising one-transistor - one-capacitor [1T-1C] memory cells
  • H10B12/31—DRAM devices comprising one-transistor - one-capacitor [1T-1C] memory cells having a storage electrode stacked over the transistor
• • H—ELECTRICITY
  • H10—SEMICONDUCTOR DEVICES; ELECTRIC SOLID-STATE DEVICES NOT OTHERWISE PROVIDED FOR
  • H10B—ELECTRONIC MEMORY DEVICES
  • H10B12/00—Dynamic random access memory [DRAM] devices
  • H10B12/30—DRAM devices comprising one-transistor - one-capacitor [1T-1C] memory cells

Definitions

• This disclosure relates to semiconductor fabrication and more particularly, to a device and method including array structures formed in support areas of a memory device to reduce topography therebetween.
• memory devices and in particular dynamic random access memories include an architectures composed of two major parts: 1) an array of memory cells made of transistors and capacitors as well as minimal amplifying circuitry and 2) a large support region (typically about 20-40% of the total chip area) that provides power supplies, read-write control logic, redundancy circuits and other circuitry needed for operating the memory device.
• the capacitors are made of a stack, typically about 0.3 -1.5 microns in thickness, which includes a lower electrode (EL) , a dielectric medium, and an upper common electrode plate (PL) . This stack is typically formed after a first metal (bitline level), but prior to all other metallization levels.
• Semiconductor device 10 includes stacked capacitor structures or stacks 12 formed in an array region 14.
• Stacks 12 include a lower electrode 16, a dielectric medium or capacitor dielectric 18 and an upper common electrode plate 20.
• a support region 22 is included on device 10 and includes support circuitry for operating device 10.
• Support region 22 shows a portion of a first metal layer 24 which is formed at the same time as bitlines 26 in array region 14.
• a dielectric layer 28 is formed over stacks 12 in array region 14 and over support region 22.
• a via 25 down to metal line 24 is illustratively formed through dielectric layer 28.
• a topographical feature or topography 30 is formed.
• Topography 30 disturbs the definition and formation of features of critical dimension on subsequent levels of processing. This effect is predominant at the edge of array region 14 and can be enhanced by underlying topography of first metal layer 24. This effect is responsible for memory cell failures and reliability problems for components at the edge of array regions 14.
• a semiconductor memory device in accordance with the present invention, includes a substrate having a major surface including an array region and a support region.
• the array region includes memory cell structures having a first height above the major surface of the substrate.
• the support area includes dummy structures formed therein having a second height above the major surface.
• a dielectric layer is formed over the memory cell structures in the array region and the dummy structures in the support region such that a top surface of the dielectric layer is substantially planar wherein topographical features are substantially eliminated on the dielectric layer across the array region and the support region.
• the memory cells may include stacked capacitors and the dummy structures may include at least a portion of the components employed for the stacked capacitors. Variations in topography between support regions and array regions less than 10 times a minimum feature size are preferably eliminated by the present invention.
• the dummy structures may include one of a dielectric material and a conductive material .
• the dummy structures may include at least one of a lower stacked capacitor electrode and an upper stacked capacitor electrode.
• the dielectric layer may be gradually transitioned between the array region and the support region by dummy structures of gradually decreasing height above the major surface .
• the dummy structures may be spaced apart between about 1 to about 20 minimum feature sizes apart for a given technology.
• the dummy structures may include conductive materials and the dummy structures preferably electrically float to prevent grounding.
• the dummy structures may be tied to a common ground or held at a constant potential with respect to ground.
• the second height may be dependent on a position within the support region.
• the semiconductor device may further include a plurality of first metal lines in the support region disposed in a first direction and a plurality of second metal lines disposed in a different layer from the first metal lines, the second metal lines disposed substantially perpendicular to the first direction, and the dummy structures are preferably oriented to prevent adjacent first metal lines and adjacent second metal lines from covering a same dummy structure.
• the first height and the second height are preferably substantially equal.
• Another semiconductor memory device in accordance with the present invention, includes a substrate having a major surface including an array region and a support region.
• the array region includes memory cell structures having a first height above the major surface of the substrate, and the support area includes conductive structures formed therein having a second height above the major surface.
• the conductive structures are employed by support circuitry in the support region.
• a dielectric layer is formed over the memory cell structures in the array region and the conductive structures in the support region such that a top surface of the dielectric layer is substantially planar wherein topographical features are substantially eliminated on the dielectric layer across the array region and the support region.
• the memory cells may include stacked capacitors and the conductive structures may include at least a portion of the components employed for the stacked capacitors.
• the conductive structures may include at least one of a lower stacked capacitor electrode and an upper stacked capacitor electrode.
• the dielectric layer may be gradually transitioned between the array region and the support region by conductive and dielectric structures of gradually decreasing height above the major surface.
• the dummy structures may be tied to a common ground or held at a constant potential with respect to ground. Variations in topography between support regions and array regions less than 10 times a minimum feature size are preferably eliminated by the present invention.
• the dummy structures may be spaced apart between about 1 to about 20 minimum feature sizes apart for a given technology.
• the conductive structures may electrically float to prevent grounding.
• the dummy structures may be tied to a common ground or held at a constant potential with respect to ground.
• the second height may be dependent on a position within the support region.
• the semiconductor device may further include a plurality of first metal lines in the support region disposed in a first direction and a plurality of second metal lines disposed in a different layer from the first metal lines, the second metal lines disposed substantially perpendicular to the first direction.
• the conductive structures • are preferably oriented to prevent adjacent first metal lines and adjacent second metal lines from covering a same conductive structure.
• the first height and the second height may be substantially equal for the structures.
• the conductive structures may be employed to connect different metal layers.
• the conductive structures may be employed to electrically shield a first conductive layer from a second conductive layer.
• the conductive structures may employed to provide interconnects substantially parallel to the major surface for support region circuitry.
• a method for maintaining a substantially planar transition for a dielectric layer between support regions and array regions on a semiconductor chip includes providing a semiconductor memory device including a substrate with a major surface having an array region and a support region. An array of devices is formed in the array region including memory cell structures having a first height above the major surface of the substrate. Dummy memory cell structures (which include at least portions of the memory cell structures) are formed in the support area having a second height above the major surface. A dielectric layer is formed over the memory cell structures in the array region and the dummy memory cell structures in the support region such that a top surface of the dielectric layer is substantially planar wherein topographical features are substantially eliminated on the dielectric layer across the array region and the support region.
• the memory cell structures may include stacked capacitors and the dummy memory cells structures in the support area may include at least a portion of the components employed for the stacked capacitors.
• the dielectric layer may be gradually transitioned between the array region and the support region by forming dummy memory cell structures of gradually decreasing height above the major surface.
• the method may further include the step of providing a spacing between dummy memory cell structures in the support region wherein the spacing is between about 1 and 20 minimum feature sizes for a given technology.
• the method may also include the steps of providing a plurality of first metal lines in the support region disposed in a first direction and a plurality of second metal lines disposed in a different layer from the first metal lines, the second metal lines disposed substantially perpendicular to the first direction, and orienting the dummy memory cell structures in the support region to prevent adjacent first metal lines and adjacent second, metal lines from covering a same memory cell structure in the support area.
• the first height and the second height for the structures may be substantially equal .
• FIG. 1 is a cross-sectional view of a prior art semiconductor memory device having a topographical feature
• FIG. 2 is a cross-sectional view of a semiconductor memory device having reduced topography after introduction of structures in a support region in accordance with the present inven ion;
• FIG. 3 is a cross-sectional view of a semiconductor memory device having a gradually reduced topography after introduction of structures of different heights in a support region in accordance with the present invention
• FIGS. 4A and 4B illustrate the impact of spacing of structures on a dielectric layer formed over the structures
• FIGS. 5 and 6 schematically depict offsets provided for conductive structures to reduce capacitive coupling between metal lines in accordance with the present inven ion;
• FIG. 7 is a cross-sectional view of a semiconductor device showing contacts for connecting different metal layers in accordance with the prior art
• FIG. 8 is a cross-sectional view of a semiconductor device showing contacts for connecting different metal layers which employ support region structures formed in accordance with the present invention
• FIG. 9 is a cross-sectional view of a semiconductor device showing support region structures formed in accordance with the present invention employed for shielding between different metal layers.
• FIGS. 10A-B is a cross-sectional view of other semiconductor device structures showing contacts for connecting different metal layers for reducing resistance of a metal structure by employing support region structures formed in accordance with the present invention.
• the present invention includes forming array region structures in support region areas to reduce topographical features in the transition between the two regions .
• the present invention proposes a number of ways to reduce this topography by formation of structures, such as lower electrode patterns and/or upper electrode patterns in the support region when the memory array includes stacked capacitor structures. These patterns may be either dummy shapes without further functionality or may be integrated in the support circuitry and function with the support circuitry. Preferred embodiments of the present invention will now be illustratively described with reference to the figures and in terms of a stacked capacitor semiconductor memory device .
• Device 100 includes an array region 102 and a support region 104.
• Array region 102 includes memory cells which comprise access transistors (not shown) and stacked capacitors 106.
• Lower electrodes 110 of stacked capacitors 106 are connected to the access transistors.
• Bitlines 105 are formed with a first metal layer 108.
• Stacked capacitors 106 include a lower electrode 110, a dielectric medium 112 and an upper electrode 114. During the formation processes for stacked capacitors 106, all or some of the components of the stacked capacitors 106 may also be patterned in support area 104. As shown in FIG.
• lower electrodes 110 and dielectric medium 112 are formed in support region 104 to form dummy structures 119.
• a dielectric layer 118 is formed atop device 100 which includes a reduced topography after introduction of lower electrode 110 and dielectric medium 112 patterns in support region 104.
• topographies of less than about 10 times a minimum features size are eliminated.
• Lower electrode 110 patterns in support region 104 are formed such that Cl contacts, which are to be formed in vias 120 in later steps, are not affected by the placement of lower electrode 110 patterns.
• An upper surface 122 of dielectric layer 118 is significantly more planar than the prior art topography shown in FIG. 1. If these patterns are dummy patterns without any functionality in the circuitry, their dimension and arrangement can be optimized for a given device design. It is to be understood that although the lower electrode pattern is used to reduce topography other structures may be formed in addition to or as a substitute for the lower electrode pattern.
• lower electrodes 110, dielectric medium 112 and or upper electrodes 114 may also be employed alone or in any combination in the pattern in support area 104, or simple dielectric pads may be employed.
• the area next to array region 102 can be filled by decreasing the height of the features gradually to form a transition region between support region 104 and array region 102.
• Patterns next to the array can be formed using lower electrode 110, dielectric medium 112 and upper electrode 114 structures or stack 130.
• stacks 132 which include lower electrode 110 and dielectric medium 112.
• stacks 132 are lower electrodes 110 (upper electrodes 114 may also be employed or any other structures which provide a desired height) . As illustrated in FIG.
• the topography of a dielectric layer 136 is then smoothed to provide a gradual transition between array region 102 and support area 104. While the entire height difference remains the substantially the same, the sharp step at the array edge is avoided. (See FIG. 1) .
• structures formed in support area 104 will be referred to as stacks 130, stacks 132 or lower electrodes 110.
• distances between structures formed in support region 104 are to be maintained above a predetermined threshold value.
• a dielectric surface 138 follows the topography of the surface of stacks 132 which is not conformal (see FIG. 4A) .
• Stacks 132 are separated by a distance d x in FIG. 4A.
• d x is below the threshold value d th - I n this way, surface 132 of dielectric layer 118 is at a nearly uniform height h over stacks 132.
• the density of stack 132 patterns next to array region 102 may be defined such that the pattern's density gradually decreases and finally ends in a stack-free area. This results in a smoothed topography at the surface of the dielectric layer
• d th may depend on the material of dielectric layer or other factors, such as the height of the features.
• d th may be about IF where F is a minimum feature size for a given technology. In preferred embodiments, d 2 is between about 1 and about 20 minimum features sizes for a given technology.
• optimization of fill pattern geometry and arrangement are employed, in accordance with the invention, to enhance the effects of a smooth topographical transition from the high a density array to the support area.
• the geometry and arrangement of the stack or structure fill patterns can be optimized with respect to the subsequent topography as well as capacitance impact due to the addition of metal features .
• the capacitance impact is addressed first.
• the structures are preferably:
• Structures 142 preferably include stacks 130, stack 132 and/or lower electrode 110. It is contemplated that dielectric structures may be used as structures 142. In this case, structures 142 are not subject to the electrical guidelines as illustratively set forth above. It is contemplated that structures 142 may include shapes other than rectangles or squares .
• the minimization of coverage of adjacent structures 142 may be realized by defining regularly repeated structures 142 with a certain offset in both X and Y directions .
• the angle is between about 5 to about 75 degrees, and more preferably between about 30 degrees to about 60 degrees such that metal line pairs 140 and 141 have a minimized capacitive coupling between each pair due to conductive structures.
• shapes or structures 142 are preferably:
• Structure patterns may be employed in a functional way within support regions. The following will describe several illustrative applications of functional structures in accordance with the present invention.
• a conventional device 200 having capacitor contacts 202 connecting to a diffusion region 201 of an access transistor 204 in an array region 203.
• Access transistor 204 includes a gate 206 for enabling conduction through transistor 204.
• transistor 204 connects a bitline 208 and contact 202.
• Contact 202 connects to a lower electrode 210 which is capacitively coupled to a common electrode or upper electrode 212.
• a support area 214 includes a metal layer 216 (preferably the same metal layers used to form bitlines 208) .
• Metal layer 216 may be designated as layer M0.
• Metal layer 216 is connected to an upper metal layer 218 through a dielectric layer 220 by a contact 219, also referred to as a Cl contact.
• the upper metal layer may be an Ml layer.
• a topographical feature 222 is shown as described for the prior art with reference to FIG. 1.
• the present invention includes the use of structure 302 patterns for support circuitry.
• Structures 302 may be employed for conducting straps, e.g. to bridge over metal lines on other metal levels. Structures 302 are connected at some point over their length at a location 301 (shown in phantom lines) .
• Contact 304 connects an M0 metal line 305 to structure 302. Structure 302' is connected to structure 302 and to contact 306. Contact 306 is connected to metal line 308 (Ml) thereby creating a bridge which connects line 305 to line 308.
• shielding between metal layers 320 and 322 may be achieved in support region 326. This is accomplished by connecting a lower electrode 324 to a fixed potential (e.g. the potential used for a common plate in the array region) .
• contacts (CC) 402 may be formed on a metal line 404
• a line can be formed similarly to the modified CC contact depicted in FIG. 8 but may be composed of line-shaped features.
• Contact 402 may be a cylinder shape. However, bar shaped contacts 403 may be employed as well and employed with layer 404 for a horizontal interconnect. Also, horizontal interconnects
• Ml layer 408 is connected to lower (or upper) electrodes 406 by contacts 410 (e.g., Cl contacts) .
• contacts 410 e.g., Cl contacts
• a horizontal interconnect may be realized by employing a bar shaped contact 412 (e.g., Cl contacts) .
• the horizontal bar shaped contacts 403 and 412 extend into the page as a line shaped feature while contacts 402 and 410 are cylindrical contacts. Other configurations and combinations are contemplated as well.

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• 2001
  • 2001-06-20 WO PCT/US2001/019684 patent/WO2001099160A2/en not_active Ceased
  • 2001-06-20 TW TW090114976A patent/TW494565B/zh not_active IP Right Cessation
  • 2001-06-20 EP EP01952175A patent/EP1292986A2/de not_active Withdrawn

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