Semiconductor device manufacturing: process – Formation of semiconductive active region on any substrate – Amorphous semiconductor
Reexamination Certificate
1999-09-21
2001-08-21
Christianson, Keith (Department: 2813)
Semiconductor device manufacturing: process
Formation of semiconductive active region on any substrate
Amorphous semiconductor
Reexamination Certificate
active
06277714
ABSTRACT:
FIELD OF THE INVENTION
This invention relates to a method for inducing selective crystallization of an amorphous semiconductor and more particularly, to a method which uses a “metal” printing action to provide crystallization seed sites from which crystallization in a semiconductor layer commences and from which large grains can be produced.
BACKGROUND OF THE INVENTION
Displays, photovoltaics, microelectronics, and MEMS (microelectro-mechanical devices) employ polycrystalline silicon (poly-Si) films. There is a need to be able to fabricate such poly-Si films at low temperatures, using low-cost processing techniques. Poly-Si is used in thin film transistors (TFTs) for the active channel region because of its relatively high mobility and in solar cells for the same reason; i.e., its high carrier mobility.
Low resistance metal/poly-Si silicide materials are also needed for the source and drain contact or contact finger regions of TFTs and for the contact regions of solar cells. Such silicides offer low resistance, chemical stability, and relatively low temperatures of formation. Low resistance metal silicides, formed with poly-Si also are useful as resistors and interconnects in displays, microelectronics, and MEMS, if the metal/poly-Si silicide regions can be readily isolated. Such metal silicide regions can also be subsequently used to initiate electrochemical or electroless deposition of additional metallic layers. In such case, the metal/poly-Si silicide can serve as a foundation for subsequent depositions for further tailoring of resistance.
Metal silicides are currently fabricated by reacting co-deposited or sequentially deposited silicon and metal or by a deposited metal film with a silicon substrate or film. This is often done by vacuum depositing the metal, patterning it lithographically, and then reacting the metal with the silicon substrate, using an elevated temperature process.
Thin film poly-Si films can be directly deposited or deposited in amorphous silicon (a-Si) form and then crystallized into poly-Si films. In the latter approach, crystallization of the a-Si into poly-Si can be achieved by various methods: laser crystallization, solid phase crystallization, and metal induced solid phase crystallization. The metal induced crystallization (MIC) SPC process has been also used to make poly-Si devices in a pre-determined pattern to cause selective crystallization with a low thermal budget. For poly-Si films produced by MICSPC, the metals (e.g., Pd, Ni, Cr or Mo) have been physically deposited in vacuum or from solution. See, for example, U.S. Pat. Nos. 5,147,826 and 5,275,851.
Regardless of the method used to fabricate poly-Si films, the resulting grain size of the poly-Si film plays a crucial role in determining the performance of a device. Grain size affects critical device parameters such as carrier mobilities in transistors, thin film transistors (TFTs), solar cells, detectors; on/off ratio of transistors and TFTs; switching speed of transistors and TFTs; and efficiencies of solar cells. However, none of the methods used to produce thin film poly-Si (including the as-deposited approach), has been able to produce grain sizes larger than on the order of tens of microns (e.g., 10~50 &mgr;m), i.e., see Lee et al., Appl. Phys. Lett. 66, 1671 (1995).
There is a need for a low cost, low temperature method for inducing crystallization in amorphous semiconductors. Also there is a need to produce large crystals during such a crystallization procedure.
SUMMARY OF THE INVENTION
The invention is a low-cost, pressure-printing method that transfers a metal pattern to an amorphous semiconductor layer. Application of the metal pattern, using heat and applied pressure, results in a patterned poly-crystalline semiconductor region, or in the event that the semiconductor is silicon and the metal is a silicide-former, the application results in a patterned metal/poly-crystalline silicide region. The method further uses the printed metal region (i) to catalyze the MIC process adjacent to the metallized region to produce poly-Si therein and to simultaneously form silicide contacts at the printed region, or ii) to form pre-selected metal silicide regions isolated by non-crystallized and non-silicided a-Si (for resistor and interconnect applications). In the latter case, the non-silicided regions of silicon can be subsequently oxidized after or during silicidation, thereby forming an ideal isolating medium; i.e., SiO
2
. In either case, the printed metal layer plays the key role of inducing crystallization at a low anneal temperature.
The method of the invention induces crystallization in an amorphous semiconductor layer, and includes the steps of: a) producing a patterned metal layer on a first substrate, the metal layer exhibiting a weak level of adherence to the first substrate; b) pressing the metal layer into physical contact with the amorphous semiconductor layer; c) applying heat to the metal layer and amorphous semiconductor layer to cause a reaction therebetween and a crystallization of the amorphous semiconductor that is juxtaposed to the metal. The reaction also causes a greater level of adherence to occur between the metal layer and the amorphous semiconductor than the weak level of adherence between the metal layer and the first substrate, allowing the metallization to adhere to the semiconductor when the first substrate is removed.
REFERENCES:
patent: 5147826 (1992-09-01), Liu et al.
patent: 5254484 (1993-10-01), Hefner et al.
patent: 5264072 (1993-11-01), Mukai
patent: 5275851 (1994-01-01), Fonash et al.
patent: 5843811 (1998-12-01), Singh et al.
Bae Sanghoon
Fonash Stephan J.
Christianson Keith
Ohlandt Greeley Ruggiero & Perle L.L.P.
The Penn State Research Foundation
LandOfFree
Metal-contact induced crystallization in semiconductor devices does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Metal-contact induced crystallization in semiconductor devices, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Metal-contact induced crystallization in semiconductor devices will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2546975