During the past decade there has been a rapid growth of interest in poly-Si for the active device layer in thin film transistors (TFTS) for active matrix flat-panel displays. Whilst the early work, demonstrating the high carrier mobility of these devices, employed processing temperatures of approximately 1000 degrees C and quartz susbtrates, this was soon followed by the investigation of lower-temperature processes which were compatible with the use of glass substrates. Some of the key aspects of this work are reviewed in this article: the preparation of the material by direct deposition and by crystallization from a-Si precursors, the characterization of the defect-induced trapping states within the material and their passivation, and the present understanding of the TFT leakage current mechanisms. This work is put into the context of the requirements for active matrix liquid-crystal displays, and, with the understanding and control of poly-Si which has been achieved to date, its application in this area can be expected to increase rapidly in the coming years.

https://iopscience.iop.org/article/10.1088/0268-1242/10/6/001/pdf

Polycrystalline silicon thin film transistors

In producing a thin film transistor, after an amorphous silicon film is formed on a substrate, a nickel silicide layer is formed by spin coating with a solution (nickel acetate solution) containing nickel as the metal element which accelerates (promotes) the crystallization of silicon and by heat treating. The nickel silicide layer is selectively patterned to form island-like nickel silicide layer. The amorphous silicon film is patterned. A laser light is irradiated while moving the laser, so that crystal growth occurs from the region in which the nickel silicide layer is formed and a region equivalent to a single crystal (a monodomain region) is obtained.

Method for producing semiconductor device

It is an object to provide a highly reliable semiconductor device with good electrical characteristics and a display device including the semiconductor device as a switching element. In a transistor including an oxide semiconductor layer, a needle crystal group provided on at least one surface side of the oxide semiconductor layer grows in a c-axis direction perpendicular to the surface and includes an a-b plane parallel to the surface, and a portion except for the needle crystal group is an amorphous region or a region in which amorphousness and microcrystals are mixed. Accordingly, a highly reliable semiconductor device with good electrical characteristics can be formed.

Oxide semiconductor film and semiconductor device

Hydrogenated nanocrystalline silicon (nc-Si:H) films were deposited by using 13.56MHz plasma-enhanced chemical vapor deposition at 260°C by means of a silane (SiH4) plasma heavily diluted with hydrogen (H2). The high-quality nc-Si:H film showed an oxygen concentration (CO) of ∼1.5×1017at.∕cm3 and a dark conductivity (σd) of ∼10−6S∕cm, while the Raman crystalline volume fraction (Xc) was over 80%. Top-gate nc-Si:H thin-film transistors employing an optimized ∼100nm nc-Si:H channel layer exhibited a field-effect mobility (μFE) of ∼150cm2∕Vs, a threshold voltage (VT) of ∼2V, a subthreshold slope (S) of ∼0.25V∕dec, and an ON∕OFF current ratio of ∼106.

High-mobility nanocrystalline silicon thin-film transistors fabricated by plasma-enhanced chemical vapor deposition

A technique for forming a film of material (12) from a donor substrate (10). The technique has a step of introducing energetic particles (22) in a selected manner through a surface of a donor substrate (10) to a selected depth (20) underneath the surface, where the particles have a relatively high concentration to define a donor substrate material (12) above the selected depth and the particles for a pattern at the selected depth. An energy source such as pressurized fluid is directed to a selected region of the donor substrate to initiate a controlled cleaving action of the substrate (10) at the selected depth (20), whereupon the cleaving action provides an expanding cleave front to free the donor material from a remaining portion of the donor substrate.

Controlled cleavage process using pressurized fluid

We report a novel growth method of polysilicon thin films on glass substrates at a low temperature (450°C) by plasma chemical vapor deposition (PCVD) using SiH4/SiF4 mixture gases. In this method, the conventional low-cost glass substrates such as Corning 7059 may be used because of the low deposition temperature. Furthermore, the conventional vacuum chamber with its base pressure of ~1×10-4 Pa, which is usually thought to be inadequate for high-quality Si growth because of its many impurities, can be used since the growing surface of polysilicon is in-situ chemically cleaned by SiF4 plasma. The polysilicon films obtained on glass show strong (100) preferred orientation. A grain size as large as 250 nm is obtained in a film with 700 nm thickness. The field-effect mobility of 44 cm2/Vs has been achieved in a thin-film transistor (TFT) using this polysilicon film.

In-Situ Chemically Cleaning Poly-Si Growth at Low Temperature

Thin film transistors were fabricated using polycrystalline silicon (poly-Si) film which were directly deposited on Corning 7059 glass substrates by plasma chemical vapor deposition method at very low temperature of 450°C. No annealing procedure was carried out in the fabrication process. The dependences of the crystallinity and the electrical properties on the poly-Si film thickness were investigated for three kinds of films deposited under different conditions. These dependences on the film thickness were found to be strongly influenced by the deposition condition, especially the reaction gas pressure. By choosing optimum poly-Si deposition condition carefully, high performance TFTs have been fabricated by this novel method.

Low Temperature Fabrication of poly-Si TFTs Using in-Situ Chemically Cleaning Method

According to the present invention, a polycrystalline silicon thin film with a large crystal grain size is formed on a substrate, other than single crystalline silicon, e.g. on a glass substrate with a low strain point, by plasma CVD or photo CVD, and the polycrystalline silicon thin film thus obtained has a high (100) orientation percentage and a low (220) orientation percentage, a low hydrogen content, a low fluorine content in the film, and a large crystal grain size. It has excellent flatness and is suitable for microstructure fabrication and for the manufacture of a thin film transistor. Because a thin film transistor with a large area can be produced, it is also usable for many applications such as liquid crystal display. By introducing a high concentration of dopant into the interface region between the polycrystalline silicon film and the substrate, the growth of the polycrystalline grain is enhanced because the high concentration of dopant becomes the nucleus for crystal growth.

Polycrystalline silicon thin film and transistor using the same

PURPOSE:To uniformly form a semiconductor film of few defects by a low temperature film forming means which film is constituted of a polymer film provided with a texture trench, by forming a polymer film layer on the surface of a master by a spin-coating method, and baking the polymer film layer. CONSTITUTION:A master 3 for a substrate is mounted on a spinner. While the master 3 is rotated, solution wherein polyimide monomer is dissolved in methyl ethyl ketone is dripped on the master 4 surface. After a polymer film layer is peeled from the master 3 for a substrate, the polymer film layer on which etch-pits of the master 3 are transferred is baked. Thus a polymer film substrate 4 is manufactured. A polymer film substrate provided with a texture trench wherein the crest part and the valley part are worked in a curved surface can be simply and surely manufactured, and the photoelectric conversion efficiency of an obtained photoelectric transducer can be improved.

Manufacture of substrate for photoelectric transducer

PURPOSE: To form a polycrystalline silicon thin film of a predetermined thickness by repeating the steps of growing a silicon film by a plasma CVD method using mixture gas of silane and silane fluoride, hydrogen plasma processing the silicon film, and accelerating the crystallization. CONSTITUTION: A glass substrate is held in a holder in a vacuum chamber of a plasma CVD apparatus, mixture gas of SiH 4 /SiF 4 /H 2 = 1 : 30 : 100 is discharge decomposed under the condition of 250°C, 0.1W/cm 2 , 2Torrs, a film of 50Å is deposited, then gas in the vacuum chamber of the same apparatus is stored in H 2 of 100scm, discharged under the condition of 0.2W/cm 2 , 500 mTorrs for 5min, and hydrogen plasma processed. A cycle of depositing a silicon film and hydrogen plasma processing is repeated 20 times, and a polycrystalline silicon thin film of 1,000Å thick is formed. Then, crystal grain size of the obtained thin film becomes 400 - 600Å, and the crystal grain size of the thin film under the same conditions without hydrogen plasma processing is 200 - 300Å. COPYRIGHT: (C)1992,JPO&Japio

Tatsuro Nagahara

Papers

In-Situ Chemically Cleaning Poly-Si Growth at Low Temperature

Low Temperature Fabrication of poly-Si TFTs Using in-Situ Chemically Cleaning Method

Polycrystalline silicon thin film and transistor using the same

Manufacture of substrate for photoelectric transducer

Method of growing polycrystalline silicon thin film