# US 7,745,822 B2 · Thin film transistor and thin film transistor substrate including a polycrystalline semiconductor thin film having a large heat capacity part and a small heat capacity part > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 7,745,822 B2 - Document ID: US7745822B2 - Status: Granted - Kind: B2 - Application number: 10/558,073 - Filed: 2004-03-15 - Published: 2006-11-02 - Granted: 2010-06-29 - Earliest claimed: 2003-06-27 - Assignees: NEC Corporation - Inventors: Hiroshi Okumura - Web page: https://patentgrep.com/patent/US7745822B2 ## CPC - H10P 14/3816: {Pulsed laser beam} - H10D 30/0314: {of lateral top-gate TFTs comprising only a single gate} - H10D 30/0321: {comprising silicon, e.g. amorphous silicon or polysilicon} - H10D 30/6704: {having supplementary regions or layers in the thin films or in the insulated bulk substrates for controlling properties of the device} - H10D 30/6706: {for preventing leakage current (TFTs characterised by the properties of the source or drain H10D30/6713)} - H10D 30/6715: {characterised by the doping profiles, e.g. having lightly-doped source or drain extensions} - H10D 30/6731: {Top-gate only TFTs} - H10D 30/6745: {Polycrystalline or microcrystalline silicon} - H10D 30/6757: {characterised by the structure of the channel, e.g. transverse or longitudinal shape or doping profile (TFTs having channel structures for preventing kink or snapback effects H10D30/6708; TFTs having lightly-doped source or drain extensions H10D30/6715)} - H10D 62/40: Crystalline structures - H10D 86/00: Integrated devices formed in or on insulating or conducting substrates, e.g. formed in silicon-on-insulator [SOI] substrates or on stainless steel or glass substrates - H10D 86/0227: {using structural arrangements to control crystal growth, e.g. placement of grain filters} - H10D 86/471: {having different architectures, e.g. having both top-gate and bottom-gate TFTs} - H10D 86/60: wherein the TFTs are in active matrices - H10P 14/2922: {being non-crystalline insulating materials, e.g. glass or polymers} - H10P 14/3238: {being insulating materials} - H10P 14/3241: {being conductive materials} - H10P 14/3244: {Layer structure} - H10P 14/3251: {consisting of three or more layers} - H10P 14/3411: {Silicon, silicon germanium or germanium} - H10P 14/3456: {Polycrystalline} - H10P 14/3808: {using laser beams} - H10P 14/382: {Scanning of a beam} - H10P: GENERIC PROCESSES OR APPARATUS FOR THE MANUFACTURE OR TREATMENT OF DEVICES COVERED BY CLASS H10 - H10D: INORGANIC ELECTRIC SEMICONDUCTOR DEVICES ## Abstract A TFT and the like capable of realizing performances such as a low threshold voltage value, high carrier mobility and a low leak current easily. A TFT consists of a polycrystalline Si film having a small heat capacity part and a large heat capacity part, and the small heat capacity part is used at least as a channel part. The polycrystalline Si film is formed of a crystal grain film through laser annealing of an energy density with which the small heat capacity part melts completely but the large heat capacity part does not melt completely. Since the channel part is formed of large crystal grains grown from the boundaries between the small heat capacity part and the large heat capacity parts, it is possible to realize performances such as a low threshold voltage value, high carrier mobility and a low leak current by using a typical laser annealing device. ## Claims ### Claim 1 A thin film transistor comprising: a polycrystalline semiconductor thin film including a large heat capacity part having a large heat capacity and a small heat capacity part having a small heat capacity, in which the small heat capacity part is used at least as a channel part, wherein the polycrystalline semiconductor thin film is formed of a crystal grain film by laser annealing of an energy density with which the small heat capacity part melts completely to form a microcrystalline structure, but the large heat capacity part does not melt completely so that there is an absence of any microcrystalline structure in said large heat capacity part, wherein the small heat capacity part is interposed between two large heat capacity parts, and crystal grain films in two aligned rows are provided, which are grown from boundaries between the large heat capacity parts and the small heat capacity parts to the small heat capacity part side to thereby contact each other, wherein an edge part in a channel width direction of the small heat capacity part used as a channel is positioned inside an edge part in a channel width direction of the large heat capacity part, and a portion of the small heat capacity part in the channel width direction is outside the edge part of the large heat capacity part, wherein distances between the large heat capacity parts facing each other across the small heat capacity part are different, and the polycrystalline semiconductor thin film includes a short distance region and a long distance region corresponding to the distances between the large heat capacity parts, wherein, in the short distance region, the polycrystalline semiconductor thin film includes a grain boundary formed by collision, at a point where the small heat capacity part is divided in two parts, of the large crystal grains which are crystal-grown toward different directions from the large heat capacity parts facing each other, and wherein the polycrystalline semiconductor thin film includes said grain boundary formed at the crystal growth edge by growth and collision of the large crystal grains in the long distance region. ### Claim 2 (depends on 1) The thin film transistor, as claimed in claim 1, wherein the crystal grain film of the small heat capacity part is formed by laser annealing of an energy density not less than a microcrystallization threshold with which the small heat capacity part melts completely, and the crystal grain film of the large heat capacity part is formed by laser annealing of an energy density less than a microcrystallization threshold at which the large heat capacity part does not melt completely. ### Claim 3 (depends on 1) The thin film transistor, as claimed in claim 1, wherein the crystal grain film of the small heat capacity part is formed by laser annealing of an energy density not less than a microcrystallization threshold at which the small heat capacity part melts completely but less than an ablation threshold, and the crystal grain film of the large heat capacity part is formed by laser annealing of an energy density not less than a polycrystallization threshold but less than a microcrystallization threshold at which the large heat capacity part does not melt completely. ### Claim 4 (depends on 1) The thin film transistor, as claimed in claim 1, wherein the small heat capacity part is formed of a crystal grain film which is crystal-grown from a seed crystal grain of the large heat capacity part. ### Claim 5 (depends on 1) The thin film transistor, as claimed in claim 1, wherein a film thickness of the large heat capacity part of the polycrystalline semiconductor thin film is thick, and a film thickness of the small heat capacity part of the polycrystalline semiconductor thin film is thin, and a ratio of the film thickness of the small heat capacity part to the film thickness of the large heat capacity part is set to a range between 1:1.5 and 1:8. ### Claim 6 (depends on 1) The thin film transistor, as claimed in claim 1, wherein a lower layer film is formed solely on a substrate of a region where a semiconductor thin film of the large heat capacity part is formed, and the lower layer film directly contacts the semiconductor film. ### Claim 7 (depends on 1) The thin film transistor, as claimed in claim 1, wherein the crystal grain film forming the small heat capacity part is grown from a boundary between the large heat capacity part and the small heat capacity part to the small heat capacity part side. ### Claim 8 (depends on 1) The thin film transistor, as claimed in claim 1, wherein the channel part is formed in each of the crystal grain films in two rows. ### Claim 9 (depends on 1) The thin film transistor, as claimed in claim 1, wherein the small heat capacity part is formed to be interposed between two large heat capacity parts, and the two large heat capacity parts are formed independently. ### Claim 10 (depends on 1) A thin film transistor substrate in which a thin film transistor of a low threshold voltage formed of a thin film transistor according to claim 1, and a thin film transistor of an intermediate threshold voltage in which a polycrystalline film or a microcrystalline film is used as a channel part, are provided on a same substrate. ### Claim 11 (depends on 1) A thin film transistor substrate in which a thin film transistor of a low threshold voltage formed of a thin film transistor according to claim 1, a thin film transistor of an intermediate threshold voltage in which a polycrystalline film or a microcrystalline film is used as a channel part, and a thin film transistor of a high threshold voltage in which an amorphous film is used as a channel part, are provided on a same substrate. ### Claim 12 (depends on 1) The thin film transistor according to claim 1, wherein the channel part comprising the small heat capacity part is formed to have a length of not more than 5 μm. ### Claim 13 (depends on 1) The thin film transistor according to claim 1, further comprising one of a metal film, a silicide metal film, or a nitride metal film between said large heat capacity part and said substrate, said metal film, said silicide metal film, or said nitride metal film being absent between said small heat capacity part and said substrate. ### Claim 14 (depends on 6) The thin film transistor, as claimed in claim 6, wherein the lower layer film is formed of a film having a large heat capacity such as a metal film, a silicide metal film or a nitride metal film. ### Claim 15 (depends on 7) The thin film transistor, as claimed in claim 7, wherein the channel part is formed in the crystal grain film. ### Claim 16 (depends on 7) The thin film transistor, as claimed in claim 7, wherein the crystal grain film of the small heat capacity part is formed of a crystal grain film of a large diameter and a crystal grain film of a fine diameter. ### Claim 17 (depends on 16) The thin film transistor, as claimed in claim 16, wherein an impurity introducing region is formed in a region including the crystal grain film of the fine diameter. ### Claim 18 (depends on 17) The thin film transistor, as claimed in claim 17, wherein a low-concentration impurity introducing region is formed in a region including the crystal grain film of the fine diameter. ### Claim 19 (depends on 10) The thin film transistor substrate, as claimed in claim 10, wherein a thin film integrated circuit formed of the thin film transistors having different threshold voltages is provided. ### Claim 20 (depends on 10) A liquid crystal display device having a thin film transistor substrate according to claim 10. ### Claim 21 (depends on 10) An organic electroluminescent display device having a thin film transistor substrate according to claim 10. ### Claim 22 (depends on 10) A mobile telephone having a thin film transistor substrate according to claim 10. ### Claim 23 (depends on 10) A personal digital assistant having a thin film transistor substrate according to claim 10. ### Claim 24 (depends on 10) An electronic apparatus having a thin film transistor substrate according to claim 10. ### Claim 25 (depends on 11) The thin film transistor substrate, as claimed in claim 11, wherein a thin film integrated circuit formed of the thin film transistors having different threshold voltages is provided. ### Claim 26 A thin film transistor comprising: a polycrystalline semiconductor thin film including a large heat capacity part having a large heat capacity and a small heat capacity part having a small heat capacity, in which the small heat capacity part is used at least as a channel part, wherein the polycrystalline semiconductor thin film is formed of a crystal grain film by laser annealing of an energy density with which the small heat capacity part melts completely but the large heat capacity part does not melt completely, the small heat capacity part is so formed as to be interposed between two adjacent large heat capacity parts, wherein distances between said two adjacent large heat capacity parts facing each other across the small heat capacity part varies so that a distance across said small heat capacity part is not constant, the polycrystalline semiconductor thin film includes a short distance region and a long distance region corresponding to the distances between the large heat capacity parts, wherein, in the short distance region, the polycrystalline semiconductor thin film includes a grain boundary formed by collision, at a point where the small heat capacity part is divided in two parts, of the large crystal grains which are crystal-grown toward different directions from the large heat capacity parts facing each other, and wherein the polycrystalline semiconductor thin film includes said grain boundary formed at the crystal growth edge by growth and collision of the large crystal grains in the long distance region. ### Claim 27 A thin film transistor comprising: a substrate; a polycrystalline semiconductor thin film including a large heat capacity part having a first heat capacity and a small heat capacity part having a smaller heat capacity, in which the small heat capacity part is used at least as a channel part; and a metal film between said large heat capacity part and said substrate, said metal film being absent between said small heat capacity part and said substrate, the polycrystalline semiconductor thin film is formed of a crystal grain film by laser annealing of an energy density with which the small heat capacity part melts completely to form a microcrystalline structure, but the large heat capacity part does not melt completely so that there is an absence of any microcrystalline structure in said large heat capacity part, wherein the small heat capacity part is interposed between two large heat capacity parts, and crystal grain films in two aligned rows are provided, which are grown from boundaries between the large heat capacity parts and the small heat capacity parts to the small heat capacity part side to thereby contact each other, wherein distances between the large heat capacity parts facing each other across the small heat capacity part are different, and the polycrystalline semiconductor thin film includes a short distance region and a long distance region corresponding to the distances between the large heat capacity parts, wherein, in the short distance region, the polycrystalline semiconductor thin film includes a grain boundary formed by collision, at a point where the small heat capacity part is divided in two parts, of the large crystal grains which are crystal-grown toward different directions from the large heat capacity parts facing each other, and wherein the polycrystalline semiconductor thin film includes said grain boundary formed at the crystal growth edge by growth and collision of the large crystal grains in the long distance region.