Semiconductor device manufacturing: process – Having magnetic or ferroelectric component
Reexamination Certificate
2002-05-23
2003-11-18
Everhart, Caridad (Department: 2825)
Semiconductor device manufacturing: process
Having magnetic or ferroelectric component
C257S295000, C361S321100, C365S065000, C374S177000
Reexamination Certificate
active
06649424
ABSTRACT:
BACKGROUND OF THE INVENTION
FIELD OF THE INVENTION
The invention relates to a method for fabricating an integrated semiconductor circuit. The circuit has an integrated capacitor with a first electrode, a second electrode and an electrically insulating dielectric or ferroelectric disposed between the first electrode and the second electrode. The capacitor is formed on a semiconductor substrate, and the dielectric or ferroelectric is heated and thereby converted into a strongly polarizable phase.
Such methods are used for fabricating semiconductor circuits having integrated capacitors, in particular memory circuits. The capacitors contain either a dielectric having a high dielectric constant or a ferroelectric as a strongly polarizable medium disposed between the electrodes.
Strongly dielectric materials having a dielectric constant &egr;>100, preferably in a range from 200 to 300, are used in order to produce high-capacitance capacitors in the smallest possible space.
Ferroelectrics, in contrast, on account of their remanent polarization, are used for fabricating nonvolatile memories.
The ferroelectric and dielectric properties of the capacitor materials used are known. In contrast, incorporating the materials into integrated semiconductor circuits poses difficulties.
The ferroelectrics or dielectrics—usually substances with a perovskite structure (such as e.g. oxides of many alloys)—are usually not formed until a material that has initially been deposited in amorphous form onto a semiconductor substrate is heated to a temperature of 550-800° C., usually above 700° C., because the strongly polarizable ferroelectric or dielectric phase forms only above this temperature.
During the fabrication of integrated semiconductor circuits, a first electrode is applied to the semiconductor substrate. At this point in time, the transistors are already fabricated and are provided with contact connections, so-called plugs, at least below the first electrodes of the capacitors. The contacts produce the electrical connection between the transistor and the capacitor.
After the deposition of the metal layer intended for the production of the bottom electrode of all the capacitors to be formed, the dielectric is applied to the semiconductor substrate and subsequently heated. The dielectric and ferroelectric materials require a heat treatment of up to an hour for the conversion into the strongly polarizable phase. The entire semiconductor substrate is exposed to the crystallization temperature over this long period of time, as a result of which undesired changes to structures already fabricated can arise.
The heat treatment is carried out in an oxygen-containing atmosphere, preferably in a pure oxygen atmosphere. The oxygen supplied supports the oxidation and thus promotes the formation of the ferroelectric or strongly dielectric crystal lattice. During the heat treatment, oxygen can diffuse within the semiconductor substrate.
In order that the semiconductor structures situated below the first electrode, which is usually composed of platinum and is therefore inert with respect to oxygen, are not attacked and oxidized by diffusing oxygen, below the first electrode a thin layer is provided as an oxygen barrier, which is intended to prevent the further diffusion into deeper regions of the semiconductor circuit. As a result, the plugs that are situated between the first electrode and an underlying transistor and produce the electrical connection are intended to be protected against oxidation.
However, at the crystallization temperatures of usually above 700° C. that are necessary for perovskite and are required for the conversion into the strongly polarizable phase, the oxygen barrier is no longer able to stop diffusing oxygen. Above this temperature, titanium nitride and tungsten nitride, for example, oxidize and thus become non-conducting and pervious to oxygen. Below this temperature, too, oxygen cannot be completely stopped, the barrier effect becoming stronger, the lower the crystallization temperature employed.
In order to protect the integrated semiconductor circuit as well as possible from oxidation during the heat treatment, the temperature for the crystallization of the dielectric or ferroelectric is therefore lowered. Although this advantageously reduces the diffusion of oxygen into the integrated semiconductor circuit, it nonetheless leads to a large loss of remanent polarization in the dielectric or ferroelectric. The conversion into the ferroelectric phase does not commence at all below a minimum temperature—which is about 650° C. for example for strontium bismuth tantalate.
In the case of dielectrics, a heat treatment to an insufficient extent leads to a lower dielectric constant of the dielectric. As a consequence thereof, capacitors cannot store the envisaged charge or have to be made larger than is actually necessary.
Thus, the reduction of the oxygen diffusion is obtained at the expense of a loss of remanent polarization or a loss of storage density attained.
Other efforts are directed toward finding such barrier materials that are particularly stable at high temperatures, i.e. which do not oxidize or become pervious even at the desired crystallization temperature. However, barrier materials having the desired properties are still not known.
SUMMARY OF THE INVENTION
It is accordingly an object of the invention to provide a method for fabricating an integrated semiconductor circuit having a strongly polarizable dielectric or ferroelectric that overcomes the above-mentioned disadvantages of the prior art methods of this general type, which, during the heating of the dielectric or ferroelectric reliably prevents diffusion of oxygen into the integrated semiconductor circuit without losing part of the remanent polarization in the ferroelectric.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method for fabricating an integrated semiconductor circuit. The method includes providing a semiconductor substrate and forming an integrated capacitor on the semiconductor substrate. The integrated capacitor has a first electrode, a second electrode, and an electrically insulating layer disposed between the first electrode and the second electrode. The step of forming the integrated capacitor includes depositing an electrically insulating material being either a dielectric or a ferrroelectric, on an intermediate carrier. The intermediate carrier with the electrically insulating material is heated for converting the electrically insulating material into a strongly polarizable phase. The electrically insulating material is detached from the intermediate carrier. The electrically insulating material is comminuted into particles and the particles are applied to the semiconductor substrate for forming the electrically insulating layer of the integrated capacitor.
In the case of the method mentioned in the introduction, the object is achieved by virtue of the fact that the dielectric or ferroelectric material is deposited on an intermediate carrier and is heated on the intermediate carrier, is detached again from the intermediate carrier, and is comminuted into small particles and applied in the form of the particles to the semiconductor substrate.
The invention is based on a partial deviation from the fundamental layer concept which provides a deposition always of whole layers and, if appropriate, the patterning thereof on the semiconductor substrate. According to the invention, the dielectric or ferroelectric material is not deposited as a layer on the semiconductor substrate, but rather is first provided separately in amorphous form and heated principally separately from the semiconductor substrate, i.e. preferably individually, to the required crystallization temperature. In the process, the dielectric or ferroelectric is converted into the strongly polarizable phase but does not yet have the configuration required for application to the semiconductor substrate. Therefore, after heating, the dielectric or ferroelectric material is comminuted into
Hartner Walter
Mört Manfred
Schindler Günther
Weinrich Volker
Everhart Caridad
Greenberg Laurence A.
Infineon - Technologies AG
Lee Calvin
Locher Ralph E.
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