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  Method and apparatus forming crystallized semiconductor layer, and method for manufacturing semiconductor apparatusUSPTO Application #: 20060040436Title: Method and apparatus forming crystallized semiconductor layer, and method for manufacturing semiconductor apparatus Abstract: A method for forming a crystallized semiconductor layer includes preparing a non-single-crystal semiconductor layer in which at least one crystal seed is formed, and irradiating with an energy ray the non-single-crystal semiconductor layer having the crystal seed formed therein to allow a crystal to laterally grow from the crystal seed in the non-single-crystal semiconductor layer, irradiation of the energy ray is carried out by positioning to at least a part of the crystal seed an area having a minimum intensity value of the energy ray, the energy ray having a confirmation that an area having a maximum intensity value of the energy ray is continuously reduced to the area having the minimum intensity value in an irradiated surface. (end of abstract) Agent: Oblon, Spivak, Mcclelland, Maier & Neustadt, P.C. - Alexandria, VA, US Inventors: Yoshitaka Yamamoto, Mikihiko Nishitani, Masato Hiramatsu, Masayuki Jyumonji, Yoshinobu Kimura USPTO Applicaton #: 20060040436 - Class: 438166000 (USPTO) Related Patent Categories: Semiconductor Device Manufacturing: Process, Making Field Effect Device Having Pair Of Active Regions Separated By Gate Structure By Formation Or Alteration Of Semiconductive Active Regions, On Insulating Substrate Or Layer (e.g., Tft, Etc.), Having Insulated Gate, Including Recrystallization Step The Patent Description & Claims data below is from USPTO Patent Application 20060040436. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is based upon and claims the benefit of priority from prior Japanese Patent Application No. 2003-158136, filed Jun. 3, 2003, the entire contents of which are incorporated herein by reference. BACKGROUND OF THE INVENTION [0002] 1. Field of the Invention [0003] The present invention relates to a method for forming a crystallized semiconductor layer which is crystallized from a non-single-crystal semiconductor layer by using laser beams, a method for manufacturing a semiconductor apparatus, an apparatus for forming a crystallized semiconductor layer, and a method for manufacturing a display apparatus. [0004] 2. Description of the Related Art [0005] As well known, a thin film semiconductor device such as a thin film transistor (TFT) has a substrate in which a semiconductor layer consisting of a semiconductor substance such as silicon is formed on a base substance consisting of an insulating material such as quartz glass. In the semiconductor layer of this substrate, a channel area is defined between a source area and a drain area formed to be separated from each other. A gate electrode is provided on the channel area through an insulating film. [0006] The semiconductor layer is generally formed of amorphous silicon or polycrystalline silicon. In a TFT using a substrate having a layer of amorphous silicon, a mobility of electrons or holes is very low. For example, since the electron mobility is usually (not more than approximately 1 cm.sup.2/Vsec), an operating speed of the TFT is slow. As a result, such a TFT in hardly be used in an apparatus which requires a high-speed operation. [0007] A semiconductor layer in which a channel area is formed of a polycrystalline silicon film is recently in heavy usage for the purpose of increasing the mobility. This polycrystalline silicon film is composed of many crystal grains having a very small particle size. Therefore, when it is operated as a semiconductor circuit apparatus, crystal grain boundaries become an obstacle for a flow of electrons, and there is a limit in improvement of the mobility. [0008] Therefore, there has been examined acquisition of a thin film semiconductor device with the mobility being increased by reducing or eliminating the crystal grain boundary in the channel area by increasing a size of the crystal grain of the polycrystal silicon film, and further reducing or eliminating an obstacle for an electron flow. For example, there has been attempted formation of a thin film TFT which realizes the mobility of approximately 100 cm.sup.2/Vsec by heating a polycrystal silicon film in a high-temperature furnace in order to increase a particle size and thereby growing crystal grains having a particle size of approximately 1 .mu.m. In order to crystallize the amorphous silicon to have a large particle size and form a TFT in this manner, a heat treatment at a high temperature which is not less than 600.degree. C. is required. Therefore, a quartz glass plate which can withstand a high temperature but is expensive must be used as an insulating substrate, and an inexpensive glass plate (e.g., a soda glass plate) cannot be used. Therefore, such a TFT becomes expensive and has a drawback that it is hard to be used in display apparatus or the like for a large-screen TV receiver which uses many TFTs. [0009] Thus, there has been developed a method for crystallizing non-single-crystal silicon by a laser annealing process without using a high-temperature heat treatment step. For example, there have been proposed some attempts in which silicon of an amorphous silicon film or a polycrystal silicon film is crystallized or re-crystallized by irradiating the film with an excimer laser beam in order to obtain a polycrystal silicon layer composed of crystal grains with a large particle size, and they have been put into practical use. According to such methods, crystal grains can be increased in size even if an inexpensive glass plate is used as a substrate. [0010] However, even in a crystallization method using an excimer laser beam or the like, a particle size of obtained crystal grains is approximately 1 .mu.m at the maximum level, and the particle size is uneven (e.g., Jpn. Pat. Appln. KOKAI Publication No. 2001-127301). This cited reference discloses a series of operations that a zonal amorphous silicon film is polycrystallized by a fusion re-crystallization method, an amorphous silicon film is further deposited thereon and this is crystallized by using a solid phase growth method. This prior art method is a technique which first forms a crystal of a zonal polycrystal film composed of many small crystal grains, grows a crystal in a horizontal direction by using this as a crystal seed in order to obtain a polycrystal film having a crystal with a large grain size. [0011] Even this proposed method is not satisfactory. That is because an acquired maximum crystal grain size is approximately 1000 nm (i.e., 1 .mu.m), the particle size is uneven and it is suggested that irregularities in mobility become large (see FIGS. 2 to 5 in the above-described cited reference). [0012] Furthermore, as a problem which has passed unnoticed in the conventional polycrystal semiconductor device, there is a problem in a crystal grain arrangement conformation in a layer. That is, in the conventional polycrystal semiconductor layer, the crystal grain arrangement conformation in a two-dimensional direction is completely random, and aligning the crystal grains has not been attempted. The randomness of the crystal grain arrangement and the uneven particle size produce irregularities in characteristics of thin film transistors, and bring a serious drawback to performances of an apparatus to be used for the following reasons. [0013] In an arrangement of a transistor circuit in a thin film semiconductor device, many unit circuits must be aligned regularly and systematically, e.g., in a geometrical arrangement conformation. If a crystal particle size or a crystal arrangement of a polycrystal layer which is a base of formation of circuits is uneven, unit circuits are formed over crystal grains with various particle sizes or arrangements. This brings a result that the mobility or the electron passage conformation differs depending on each unit circuit, and adversely affects performances of the thin film semiconductor apparatus. For example, if there are irregularities in characteristics of each unit circuit, the entire apparatus must be designed with low-level characteristics as a basis. BRIEF SUMMARY OF THE INVENTION [0014] It is an object of the present invention to provide a method for forming a crystallized semiconductor layer in which crystallized grain formation positions are aligned and electron or hole mobility characteristics are also unified, a method for manufacturing a semiconductor apparatus, an apparatus for forming a crystallized semiconductor layer and a method for manufacturing a display apparatus. That is, in a thin film semiconductor apparatus in which a unit electrical circuit is arranged in accordance with each crystallized grain having a large particle size, irregularities in mobility of electrons or holes are improved. [0015] The inventors of the present invention have developed a technique by which positions where crystallized crystal grains are generated are aligned in good order by irradiating a non-single-crystal semiconductor layer deposited on a substrate of glass or the like with a regular energy line or ray or a laser beam having a predetermined energy ray irradiation intensity distribution. That is, in this technique, at least one crystal seed is formed or regularly arranged in a non-single-crystal semiconductor layer in advance, and an energy ray is applied in such an irradiation intensity distribution conformation as that at least a part of this crystal seed is not melted but the portion of the non-single-crystal semiconductor film adjacent to the crystal seed is melted, thereby aligning the crystal grain generation positions in good order. Here, "application of an energy ray in such an irradiation intensity distribution conformation as that at least a part of this crystal seed is not melted but the portion of the non-single-crystal semiconductor film adjacent to the crystal seed is melted" means that an area of the energy ray having a minimum value of an irradiation intensity, which continuously varies from an area of the energy ray having a maximum value of the same to the area having the minimum value, is positioned to the crystal seed, and the energy ray or rays are applied. The present inventors have found that using a crystal phase initial film having a so-called crystal orientation plane of (110) or (111) as the crystal seed can obtain matching of crystal orientations of generated crystal grains, and reached the present invention. [0016] Providing a crystal seed to a semiconductor layer before applying the energy ray to the non-crystal semiconductor layer can hasten start of crystallization of the semiconductor layer, prolong a crystallization advancing time, and thereby have a good impact on an increase in particle size of generated crystal grains or arrangement of a crystal grain boundary in order. In order to hasten start of the crystal growth, there are known application of an energy ray such as a laser beam and a reduction in a period of a supercooling state (i.e., a state in which semiconductor is not solidified even if it enters a state which is not more than its melting point) which is generated by heat conduction to a glass substrate involved by this application. As a result, the crystallization advancing time must be prolonged. As means for reducing the period of the supercooling state, there has been widely carried out provision of a head conduction control film such as made of silicon oxide (SiO.sub.2) between a glass substrate and a semiconductor layer in order to lower heat conduction to the glass substrate. In order to sufficiently lower heat conduction to the glass substrate by using such a heat conduction control film, the heat conduction control film must have the porosity. Although providing the porous film is effective for reducing heat conduction, the strength of the manufactured thin film semiconductor device may be possibly lowered due to the brittleness derived from the porosity, and there is a problem that the quality of the semiconductor film formed on the porous film is deteriorated. [0017] The present inventors have discovered that arranging the crystal seed or seeds in the semiconductor layer in advance can hasten start of a crystal growth on an early stage before the semiconductor enters the excessive supercooling state, even if the porous heat conduction control film or the like is not used. Thus, there may be obtained an increase in particle size of crystal grains or arrangement of the crystal grain boundary in order. [0018] Therefore, a method for forming a crystallized semiconductor layer according to a first aspect of the present invention, comprises a method for forming a crystallized semiconductor layer comprising: preparing a non-single-crystal semiconductor layer in which at least one crystal seed is formed; and irradiating with an energy ray the non-single-crystal semiconductor layer having the crystal seed formed therein to allow a crystal to laterally grow from the crystal seed in the non-single-crystal semiconductor layer, wherein irradiation of the energy ray is carried out by positioning to at least a part of the crystal seed an area having a minimum intensity value of the energy ray, the energy ray having a confirmation that an area having a maximum intensity value of the energy ray is continuously reduced to the area having the minimum intensity value in an irradiated surface. [0019] In particular, it was found that using a crystal seed or seeds having a so-called crystal plane orientation of (110) or (111) as a crystal seed, crystal plane orientations of respective generated crystal grains are matched to have a plane orientation of (110) or (111), which greatly contributes to an improvement in performances of a manufactured thin film semiconductor device in addition to the effect of hastening start of crystallization. That is, even if a semiconductor layer in which single crystal grains with a large particle size are arranged in good order is obtained and a thin film semiconductor device in which a unit electrical circuit is arranged in accordance with a crystal grain is acquired, irregularities in crystal plane orientations of respective generated crystal grains cause the mobility of each unit electrical circuit to slightly differ, and an improvement in mobility of the entire apparatus may thereby possibly become insufficient. Further, when irregularities occur in opening values with which currents are caused to flow, performances of the entire circuits may be deteriorated. [0020] However, when a crystal seed having a crystal orientation plane of (110) or (111) is used as a crystal seed which is arranged in the semiconductor layer in advance, growth directions of the crystal are two-dimensionally defined, and the crystal plane orientations of the generated crystal grains are defined to a plane orientation of (110) or (111). As a result, the mobility of the electrical circuit arranged in accordance with each crystal grain is unified, thereby obtaining a high-performance thin film semiconductor device in which the mobility is sufficiently improved. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING Continue reading... 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