News Column

Patent Issued for Thin Film Resistor

September 3, 2014



By a News Reporter-Staff News Editor at Electronics Newsweekly -- From Alexandria, Virginia, VerticalNews journalists report that a patent by the inventors Mieczkowski, Van (Apex, NC); Gurganus, Jason (Raleigh, NC), filed on September 27, 2013, was published online on August 19, 2014.

The patent's assignee for patent number 8810355 is Cree, Inc. (Durham, NC).

News editors obtained the following quote from the background information supplied by the inventors: "Thin film resistors are generally resistors that are formed on a semiconductor substrate using a thin-film deposition process. An exemplary thin film resistor 10 is illustrated in FIG. 1. As depicted, the thin film resistor 10 is formed on a substrate 12 and is shown having metallic interconnects 14 extending from either side of the thin film resistor 10. The substrate 12 may be formed from a wafer and is used as a foundation on which one or more semiconductor devices, such as transistors and diodes, are formed. The interconnects 14 are used to connect either side of the thin film resistor 10 to other electrical components, such as other resistors, inductors, capacitors, transistors, diodes, and the like in an overall circuit that is formed at least in part on the substrate 12. While the interconnects 14 are shown on either side of the thin film resistor 10, the interconnects 14 may be provided entirely or substantially above and below the thin film resistor 10.

"In certain applications, the resistance provided between the interconnects 14 by the thin film resistor 10 is critical to the overall performance of the circuit in which the thin film resistor 10 resides. The circuit may be designed to require a resistor with very tight tolerances, and if the resistance provided by the thin film resistor 10 falls outside of a set tolerance, the circuit may not perform as desired. As such, it is important to form the thin film resistor 10 such that the resistance provided between the interconnects 14, or two other contact points, is highly controllable and repeatable during fabrication of the overall circuit on the substrate 12.

"Unfortunately, the material from which thin film resistor 10 is formed is prone to oxidizing, and oxidation occurs before the interconnects 14 are formed during the fabrication process. The oxidation results in an oxide layer 16 forming over the exposed surface of the thin film resistor 10 before the interconnects are formed. The oxide layer 16 effectively raises the interlevel contact resistance between the thin film resistor 10 and the interconnects 14, and as a result, the actual resistance provided between the interconnects 14 by the thin film resistor 10 can be significantly different than the desired resistance. While the oxide layer 16 may be removed using various acid-based cleaning steps, such cleaning steps may unintentionally erode or harm other structures that were previously formed on the substrate.

"Further, semiconductor fabrication generally involves numerous deposition, etching, and cleaning iterations as the various layers and devices are formed on the substrate 12. As such, numerous etching and cleaning steps may be required after the thin film resistor 10 is formed. These etching and cleaning steps may erode portions of the thin film resistor 10. Erosion of the thin film resistor 10 also has a significant impact on the resistance provided by the thin film resistor 10 between the interconnects 14.

"Accordingly, there is a need for a technique that will substantially protect thin film resistors 10 from the undesirable effects of oxidation during fabrication, such that the thin film resistors 10 can be repeatedly formed to provide resistances within relatively tight tolerances. There is a further need for a technique that will substantially protect thin film resistors 10 from erosion during fabrication."

As a supplement to the background information on this patent, VerticalNews correspondents also obtained the inventors' summary information for this patent: "The present disclosure relates to a thin film resistor that is formed on a substrate along with other semiconductor devices to form all or part of an electronic circuit. The thin film resistor includes a resistor segment that is formed over the substrate and a protective cap that is formed over the resistor segment. The protective cap is provided to keep at least a portion of the resistor segment from oxidizing during fabrication of the thin film resistor and other components that are provided on the semiconductor substrate. As such, no oxide layer is formed between the resistor segment and the protective cap. Contacts for the thin film resistor may be provided at various locations on the protective cap, and as such, are not provided solely over a portion of the resistor segment that is covered with an oxide layer.

"In one embodiment, the thin film resistor may be formed on the substrate by depositing a resistor material to form a resistor layer and then depositing a protective cap material over the resistor layer to form a protective cap layer prior to any subsequent fabrication process that would cause the resistor material to oxidize. The thin film resistor is formed by removing unwanted portions of the resistor layer and the protective cap layer, wherein the removal of these layers may take place in the same removal process or different removal processes. The removal processes may include etching, lift-off, or like removal processes. In one embodiment, the subsequent fabrication process that would cause the resistor material to oxidize is an ashing process.

"In this embodiment, the resistor material is deposited under vacuum and the protective cap material is deposited prior to releasing the vacuum. In essence, the protective cap material of the thin film resistor forms a protective cap and has a first surface such that a first interconnect may be formed having a first end in contact with at least a first portion of the first surface. A second interconnect may also be formed having a second end in contact with at least a second portion of the first surface, wherein a majority of current flowing through the thin film resistor will flow through a resistor segment formed by the resistor material.

"In certain embodiments, the resistor material is prone to oxidation, and the protective cap material is not prone to oxidation. The protective cap material may include or consist essentially of platinum. The resistor material may include one of a group consisting of nickel, chromium, and nichrome. In certain embodiments, a thickness of the protective cap material of the thin film resistor is less than about 15% of a combined thickness of the protective cap material and the resistor material. In certain embodiments, a thickness of the resistor material of the thin film resistor is greater than about 85% of a combined thickness of the protective cap material and the resistor material. For example, the resistor material of the thin film resistor may between about 800 and 1000 Angstroms thick while the protective cap material may be less than about 100 Angstroms thick.

"Those skilled in the art will appreciate the scope of the disclosure and realize additional aspects thereof after reading the following detailed description in association with the accompanying drawings."

For additional information on this patent, see: Mieczkowski, Van; Gurganus, Jason. Thin Film Resistor. U.S. Patent Number 8810355, filed September 27, 2013, and published online on August 19, 2014. Patent URL: http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO1&Sect2=HITOFF&d=PALL&p=1&u=%2Fnetahtml%2FPTO%2Fsrchnum.htm&r=1&f=G&l=50&s1=8810355.PN.&OS=PN/8810355RS=PN/8810355

Keywords for this news article include: Cree Inc., Electronics, Semiconductor.

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Source: Electronics Newsweekly


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