Classifications

• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01H—ELECTRIC SWITCHES; RELAYS; SELECTORS; EMERGENCY PROTECTIVE DEVICES
  • H01H3/00—Mechanisms for operating contacts
  • H01H3/02—Operating parts, i.e. for operating driving mechanism by a mechanical force external to the switch
  • H01H3/14—Operating parts, i.e. for operating driving mechanism by a mechanical force external to the switch adapted for operation by a part of the human body other than the hand, e.g. by foot
• • H—ELECTRICITY
  • H01—ELECTRIC ELEMENTS
  • H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
  • H01L28/00—Passive two-terminal components without a potential-jump or surface barrier for integrated circuits; Details thereof; Multistep manufacturing processes therefor
  • H01L28/40—Capacitors
  • H01L28/55—Capacitors with a dielectric comprising a perovskite structure material
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
  • Y10T29/00—Metal working
  • Y10T29/43—Electric condenser making
  • Y10T29/435—Solid dielectric type

Definitions

• the present invention relates to integrated circuits, and more particularly, to methods for isolating Si ⁇ 2 layers from PZT, PLZT and platinum structures therein.
• the silicon chip has become a symbol of modem electronics.
• Semiconductor- based devices dominate the digital electronic world, and new applications of such devices are continually being created. As these applications demand greater optimization, semiconductor devices are developed which are both smaller and faster than their predecessors.
• Capacitance itself is related to the surface area and thickness of the capacitor, with larger and thinner capacitor surfaces providing a higher capacitance. Since there are practical limits to the minimum thickness of the capacitor, miniaturization of capacitors leads to lower capacitance and thereby a shorter period between refreshes. Since there is a minimum acceptable refresh period, some means for regaining the capacitance lost to size reduction is needed.
• One method for increasing the capacitance without increasing the physical dimensions of the capacitor is to utilize a material having a high dielectric constant to separate the plates of the capacitor.
• ferroelectric materials are known to have very high dielectric constants.
• Ferroelectrics such as lead zirconate titanate (PZT) and lead lanthanum zirconate titanate (PLZT) are particularly attractive in this regard, as thin films of these materials may be deposited on integrated circuits.
• PZT lead zirconate titanate
• PLAT lead lanthanum zirconate titanate
• dielectric constants in excess of 100 are routinely achieved.
• a typical ferroelectric capacitor consists of a bottom electrode, a PLZT dielectric layer, and a top electrode.
• the electrodes are typically constructed from Platinum.
• An array of such capacitors is constructed by patterning the bottom electrodes, depositing a PLZT film over the bottom electrodes, and then depositing a top layer of Platinum which is etched to form the individual top electrodes.
• the top surface of such a structure includes regions with exposed PLZT material and exposed areas of Platinum.
• the top surface of this structure is normally coated with Si ⁇ 2 which provides protection from scratching and acts as an interlayer dielectric for isolating metal interconnects from the top and bottom electrodes.
• Metal interconnects to the top and bottom electrodes are typically provided by etching via holes in the SiO 2 layer.
• the silicon in the SiO 2 can react with the ferroelectric materials in those regions in which the materials in question are in contact. This can lead to degraded performance from the capacitor. In addition, the capacitor may show aging effects as a result of the interaction in question. Finally, the Si ⁇ 2 layer has a tendency to crack when placed in contact with the Platinum electrodes. A cracked SiO 2 layer is a poor substrate on which to deposit the metal interconnects.
• the present invention comprises an improved integrated circuit construction technique and the structures produces thereby.
• the SiO 2 layer is separated from the platinum or ferroelectric regions by a substantially insulating layer of material that is substantially inert with respect to the ferroelectric material.
• the preferred insulating materials are TiO 2 , ZrO 2 , MgO, PZT, or PLZT.
• the oxide materials are preferably produced by depositing a layer of the corresponding metal, patterning the metallic layer, and then oxidizing the metallic layer in place.
• Figure 1 is a top view of a prior art capacitor array.
• Figure 2 is a cross-sectional view of the capacitor array shown in Figure 1
• FIGS. 3(A)-(G) are cross-sectional views of a capacitor array constructed according to the present invention at various stages in the construction process. Detailed Description of the Invention
• FIG. 1 and 2 illustrate a typical prior art ferroelectric capacitor array.
• Figure 1 is a top view of an integrated circuit 10 having four capacitors. The top electrodes of the capacitors are shown at 12, 14, 16, and 18.
• Figure 2 is a cross-sectional view of circuit 10 through line 22-32. The bottom electrodes corresponding to electrodes 12, 14, 16, and 18 are shown at 26-29, respectively.
• Circuit 10 is typically constructed by depositing a platinum layer on the surface of a silicon substrate 25. The platinum layer is then etched to form the individual bottom electrodes. A layer of ferroelectric material 24 is then deposited over electrodes 26-29.
• the ferroelectric material is preferably composed of PLZT.
• a second platinum layer is then deposited on top of layer 24. This layer is then etched to form top electrodes 12, 14, 16, and 18. A layer 23 of SiO 2 is then deposited over the top electrodes. Layer 23 provides scratch resistance and an insulating surface on which to deposit various conductors for connecting the capacitors to other circuit elements. Via holes 11 are then etched in layer 23 to provide access to the top electrodes. The bottom electrodes are accessed through via holes 13 which connect to extensions 17 of the bottom electrodes through via holes in PLZT layer 24.
• This prior art design has two problems. ' First, the SiO 2 reacts with the PLZT material in regions such as region 30 shown in Figure 2. This reaction degrades the performance of the capacitors, and can also result in aging effects. Second, layer 23 often exhibits cracks which appear to start at locations in which the edge of the platinum electrodes come in contact with layer 23. Typical cracks are shown at 15 and 32. Such cracks are unacceptable.
• the present invention avoids these problems by introducing an isolation layer between the SiO 2 and the surfaces having exposed PLZT material or exposed platinum.
• the isolation layer is constructed from a material that is sufficiently more inert to reactions with PLZT or PZT than SiO to avoid the problems from such interactions.
• the material must have high resistivity to prevent shorting of the platinum electrodes.
• the preferred material is TiO 2 .
• Zr0 2 , MgO, and a number of compositions of PZT or PLZT can be used for this purpose.
• PZT or PLZT compositions are utilized for the isolation layer, the process of etching via holes through the isolation layer becomes more difficult. In these case, ion milling is the preferred etching technique.
• FIGS 3(A)-(G) are cross-sectional views of a semiconductor substrate at various stages in the construction of an array of PLZT capacitors on the surface of a silicon substrate 206 utilizing a TiO 2 isolation layer.
• the capacitor array is to be constructed on top of a SiO 2 layer 203 which isolates components in the silicon substrate 206 from the capacitor array.
• a 1000 A thick layer 204 of titanium is first deposited on SiO 2 layer 203. This layer will be used to generate the first TiO 2 isolation for isolating the array from SiO 2 buffer layer 203.
• a 1000 A layer 202 of platinum is deposited on layer 204.
• This layer is masked and etched by conventional techniques to form the bottom electrodes 205 of the capacitor array as shown in Figure 3(B). If via holes are needed for connecting the electrodes of the capacitor array to the circuitry on substrate 206, these via holes are preferably opened at this stage of the construction as the titanium layer is more easily etched at this point. Such etching is conventional in the semiconductor arts, and hence will not be discussed in more detail here.
• layer 204 is oxidized by heating in an O 2 atmosphere at 650° C. This operation generates TiO 2 in the exposed regions as shown at 207 in Figure 3(C). It should be noted that any remaining metallic titanium will be located under the platinum electrodes and will be separated from substrate 206 by the SiO 2 layer 203.
• a layer 208 of PLZT material is then deposited. This layer is deposited using a conventional sol-gel process. PLZT layer 208 is then masked and etched using a conventional buffered-oxide-etch HC1 solution. This step is provides via holes for making connections to bottom electrodes 205 which serve the same function as via holes 13 shown in Figure 1. Once the PLZT layer is patterned, a 1000 A layer of platinum is deposited on PLZT layer 208. This layer is masked and etched to form the top electrodes 209 of the capacitor array.
• a 100 A layer of titanium is then deposited over the exposed portions of the PLZT layer 220 and top electrodes 209. This layer is then masked and etched using buffered-oxide-etch to open via holes 207 for making connections to the top electrodes and corresponding via holes for making connections through the via holes in the PLZT layer described above. This patterning operation is performed before oxidizing the titanium layer because etching TiO 2 is very difficult.
• titanium layer 220 is then oxidized by heating in an O2 atmosphere at 650° C for 20 minutes to form TiO 2 layer 231.
• an SiO 2 layer 240 is deposited over layer 231 and etched to form via holes for making electrical connections to the electrodes. Exemplary via holes are shown at 241 in Figure 3(G).
• titanium may be replaced by magnesium or zirconium in the above described process provided the oxidization times are suitably reduced.
• the TiO 2 layer may be replaced by a layer comprising a. PZT or PLZT material whose composition provides the electrical insulating characteristics in question.

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• Engineering & Computer Science (AREA)
• Power Engineering (AREA)
• Chemical & Material Sciences (AREA)
• Materials Engineering (AREA)
• Computer Hardware Design (AREA)
• Microelectronics & Electronic Packaging (AREA)
• Semiconductor Integrated Circuits (AREA)
• Semiconductor Memories (AREA)
• Crystals, And After-Treatments Of Crystals (AREA)
• Local Oxidation Of Silicon (AREA)

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Citations (4)

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• 1992
  • 1992-03-03 US US07/845,064 patent/US5212620A/en not_active Expired - Lifetime
• 1993
  • 1993-02-18 DE DE69318294T patent/DE69318294T2/de not_active Expired - Fee Related
  • 1993-02-18 AU AU37745/93A patent/AU668925B2/en not_active Ceased
  • 1993-02-18 JP JP5515703A patent/JPH07504783A/ja active Pending
  • 1993-02-18 CA CA002129838A patent/CA2129838C/en not_active Expired - Fee Related
  • 1993-02-18 EP EP93906973A patent/EP0629312B1/en not_active Expired - Lifetime
  • 1993-02-18 WO PCT/US1993/001469 patent/WO1993018530A1/en active IP Right Grant
• 1994
  • 1994-09-02 KR KR940703073A patent/KR100300681B1/ko active
  • 1994-09-02 KR KR1019940703073A patent/KR950700598A/ko not_active IP Right Cessation

Patent Citations (4)

Non-Patent Citations (1)

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