JP3926076B2 - Thin film pattern forming method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for forming a thin film comprising a semiconductor, an insulator, a conductor, etc. on a semiconductor substrate or an insulating substrate, and in particular, a silicon-based semiconductor thin film or a silicon oxide-based insulator on a semiconductor substrate or a glass substrate. The present invention relates to a thin film forming method suitable for forming a thin film or the like.
[0002]
[Prior art]
Semiconductor devices that have been widely used to date, such as silicon-based MOS devices, have an active layer inside a silicon wafer, and a MOS (Metal-Oxide) by forming a gate electrode on a thermally oxidized surface oxide film. -Semiconductor (metal-oxide film-semiconductor) structure. Inside the silicon wafer, the impurity diffusion layer is locally controlled using an ion implantation method or the like, and there are few examples of using a local structural change such as an island structure. On the other hand, gate electrodes, metal wirings, and the like formed on the silicon wafer require signal transmission between desired elements, and are thus formed in a predetermined pattern shape such as a line shape or an island shape. In general, such pattern formation is performed by the following procedure.
[0003]
1) A desired thin film is formed on the entire surface of the substrate, 2) A photoresist is applied to the surface, 3) A desired area is exposed using a stepper, and 4) The exposed area is developed to form a photoresist pattern. 5) Etching the thin film exposed in the opening using the photoresist pattern as a mask. 6) Stripping and cleaning the photoresist.
[0004]
In the method as described above, for example, unnecessary portions of the metal thin film formed on the entire surface of the substrate are selectively removed by a photolithography process and an etching process, which not only wastes material but also increases the number of processes. Have problems such as. As means for solving these problems, a technique of locally forming a metal thin film by a laser CVD method using an organometallic raw material has been tried.
[0005]
Furthermore, along with the rise of SOI (semiconductor-oxide film-insulator) devices and the practical use of large-area devices represented by active matrix liquid crystal displays, not only the wiring metal materials described above, but also the silicon semiconductor layer that becomes the active layer Patterning has become necessary. For example, in an amorphous silicon thin film transistor used for an active matrix liquid crystal display, 1) formation of amorphous silicon nitride and amorphous silicon film on the entire surface of the substrate by plasma CVD using silane gas as a raw material, 2) coating a photoresist on the surface, 3 ) Exposure of desired area using stepper, 5) development of exposed area to form photoresist pattern, 6) etching of amorphous silicon film exposed in opening using photoresist pattern as mask, 7) stripping of photoresist, Steps such as cleaning are sequentially performed.
[0006]
Also in the above process, unnecessary portions are selectively removed by a photolithography process and an etching process, and problems such as waste of materials and an increase in the number of processes are the same as those of the wiring materials already described. In addition, while the above-described semiconductor element is manufactured from a substrate of about 6 inches, a large number of chips are manufactured, the display device has a size of 20 inches diagonally, so the amount of thin film discarded by removal is also large. Increase dramatically.
[0007]
[Problems to be solved by the invention]
As means for solving the above problems, Japanese Patent Application Laid-Open No. 4-160624 uses a difference in etching rate between amorphous silicon and crystalline silicon after recrystallizing a desired pattern region of an amorphous silicon thin film. A technique for etching only an amorphous silicon region to form a pattern made of crystalline silicon has been proposed. By adopting such a method, there is an advantage that the photoresist process can be omitted. However, since the silicon-based thin film is removed after being formed on the entire surface, there still remains a problem that the raw material is consumed more than necessary.
[0008]
SUMMARY OF THE INVENTION An object of the present invention is to provide a thin film forming method capable of omitting the photolithography process and the etching process and reducing the amount of raw materials used.
[0009]
Another object of the present invention is to provide a new method for forming a semiconductor element and a liquid crystal element by applying a common technique to the formation of both an insulating thin film and a conductive thin film.
[0010]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides the following first to third thin film forming methods.
[0011]
1) A thin film comprising: a step of selectively applying a fluid raw material on a substrate to form a desired pattern; and a step of solidifying the desired pattern on the substrate to form a solidified pattern. Forming method.
[0012]
In the first invention method, for example, a desired pattern of the liquid material is formed by selectively applying the liquid material on the substrate by ejecting and flying small droplets of the liquid material a plurality of times in a predetermined direction. Thus, the lithography process and the etching process are omitted. For the ejection and flight of the above-mentioned small droplets, a plurality of droplets are selectively ejected simultaneously using a droplet ejection means having a plurality of ejection ports for ejecting a liquid material in a predetermined direction and a supply port for the material liquid. Is preferred. As the droplet discharge means, one utilizing a vaporization / volume expansion phenomenon due to heating of a liquid material or one caused by mechanical vibration by a piezo element or the like can be used.
[0013]
As the fluid raw material, in addition to the liquid as described above, a mixture of liquid and fine particles, fine particles having high fluidity, and the like can be used. It is necessary to appropriately adjust the surface tension and viscosity of the liquid on the substrate so that the pattern formed after application and before the solidification step does not collapse. When solid fine particles are used, pattern collapse can be prevented by charging the substrate and the solid fine particles in advance.
[0014]
The film thickness of the formed thin film pattern is preferably controlled to a film thickness of, for example, about 1 μm. In order to obtain a desired film thickness and pattern size by ejecting and flying droplets, conditions such as the ejection port size, ejection pressure, and the moving speed of the substrate or ejection means are appropriately controlled. After a thin film having a predetermined thickness or more is formed, the thickness can be reduced by polishing, ion milling, or the like. In the solidification step, drying of the liquid raw material by heat, melt solidification of fine particles, solid formation by chemical reaction, or the like can be used.
[0015]
2) A thin film forming method comprising a step of selectively applying a fluid raw material on a substrate to form a desired pattern, and a step of recrystallizing or amorphizing the desired pattern on the substrate.
[0016]
In the second invention method as well, droplet discharge and flight can be used. In a preferred embodiment of the method of the present invention, the liquid raw material is solidified on the substrate to form an amorphous thin film or a polycrystalline thin film. By irradiating these thin films with an energy beam such as a laser, an electron beam, or lamp light, it is possible to promote melting and recrystallization, thereby realizing crystallization of an amorphous thin film, high quality of a polycrystalline thin film, and single crystallization.
[0017]
3) A thin film forming method including a step of applying a liquid material on a substrate to form a liquid pattern, and a step of oxidizing or nitriding the liquid pattern.
[0018]
When a higher order silane represented by the general formula Si _n H _{2n + 2} (n> = 2) is used, it is easy to obtain a high-purity silicon thin film. In particular, trisilane Si ₃ H ₈ , tetrasilane Si ₄ H ₁₀ and higher higher silanes are easy to handle because they are liquid at room temperature. Since silanes have a feature that they easily react with the air or an oxidizing atmosphere, that is, are easily oxidized, a silicon oxide film is formed by applying a higher order silane and then exposing to an oxidizing atmosphere. After coating using a method such as spin coating, the entire surface of the substrate an oxide film by oxidizing, by oxidation after selectively applied by the droplet, it is possible to selectively form the oxide film.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
1-4, the present invention will be described in more detail based on exemplary embodiments of the present invention. 1A to 1D are cross-sectional views sequentially showing steps of a thin film forming method according to an embodiment of the present invention. First, the droplet 102 is made to fly and adhere on the substrate 101 (FIG. 1A) to form the liquid pattern 103 (FIG. 2B). The pattern size and film thickness are controlled by the unit amount and number of droplets that fly and adhere. A desired liquid pattern can be formed on the surface of the substrate 101 by moving the droplet discharge means relative to the substrate 101 or by moving the substrate 101 relative to the droplet discharge means. The liquid pattern thus formed is heated and dried to form the thin film 104 (FIG. 3C). Further, if necessary, the crystallized film 106 is formed by irradiating the entire surface of the substrate or a part thereof with the laser 105 (FIG. 4D).
[0020]
When a higher order silane represented by the general formula Si _n H _{2n + 2} (n> = 2) is used as the liquid used in the present embodiment, a high-purity silicon thin film can be easily obtained. In particular, trisilane Si ₃ H ₈ , tetrasilane Si ₄ H ₁₀ and higher higher silanes are easy to handle because they are liquid at room temperature. However, since it easily reacts with the air or an oxidizing atmosphere, the formation of the droplets is preferably performed in a nitrogen or inert gas atmosphere or a reduced pressure atmosphere. In the step of solidifying the liquid pattern by heating using higher-order silane, hydrogen atoms bonded to silicon atoms are released, and the silicon atoms are solidified by bonding in a disorderly manner. If a heating / cooling process of about 600 ° C. or higher where solid phase growth is observed in a finite time, a crystalline silicon thin film can be obtained because bonding is performed in a more stable bonding state. On the other hand, when a glassy substrate such as a liquid crystal display substrate is used, it is necessary to suppress the processing temperature to about 600 to 300 ° C. or lower, and therefore amorphous silicon is formed at the time of solidification by heat treatment at about 300 ° C. . In such a case, in order to form a crystalline silicon thin film, a laser recrystallization process using an excimer laser (XeCl, KrF, XeF, ArF, etc.), a YAG laser, an Ar laser, or the like is applied. In this case, even when a low softening point substrate such as glass is used, crystallization of amorphous silicon can be promoted.
[0021]
FIG. 2 is a diagram illustrating a droplet discharge unit. FIG. 2 (a) shows a sectional view of the discharge means alone. The raw material is supplied to the nozzle 201 from the supply port 204 side. For example, when tetrasilane Si ₄ H ₁₀ is used, the boiling point under 1 atm is about 108 ° C., and therefore, by heating the heater 202 to about 120 ° C., tetrasilane is formed in the region near the heater in the nozzle. Vaporizes and expands in volume. Since the liquid can flow out without resistance on the discharge port 203 side, the liquid tetrasilane existing in the vicinity of the discharge port is discharged and flies by the pressure due to vaporization and expansion. By arranging a plurality of nozzles as described above, droplets are supplied at high speed. FIG. 2 (b) is a perspective view of a droplet discharge means having such a structure. A drive circuit 206 for controlling the heating of the heater 202 is connected to the control means 208, and these are held on the drive circuit board 205. In the figure, the nozzles 201 are arranged in a one-dimensional array. However, it is possible to increase the processing speed by arranging the nozzle arrays in a two-dimensional array.
[0022]
As the droplet forming means, not only the method using the vaporization / volume expansion mechanism by heating shown in FIG. 2, but also a jetting mechanism by mechanical pressure using a piezo element, screen printing, intaglio printing, etc. can be used. . A silicon thin film and a silicon oxide thin film can be formed by using silicon fine particles, silicon oxide fine particles, or those obtained by dispersing them in a solvent as the fluid raw material. In such a case, an electrostatic latent image is formed on the substrate and developed using a charged material. Alternatively, a method may be used in which the electrostatic latent image formed on the photoreceptor is developed using the fine particles, and then the fine particle pattern is transferred onto the substrate.
[0023]
FIG. 3 shows an outline of the liquid pattern forming apparatus. A substrate 310 on which a thin film pattern is to be formed is introduced into the transfer chamber 305 through a gate valve 306. A transfer robot (not shown) is used for transfer. After the introduction of the substrate 310, the atmosphere in the transfer chamber 305 is replaced with a nitrogen atmosphere. After the replacement, the substrate 310 is further introduced into the process chamber 309 via the second gate valve 306. The substrate 310 is placed on the substrate stage 310 in the process chamber 309. The process chamber 309 is connected to the exhaust device 312 via a third gate valve, and is controlled simultaneously with the nitrogen introduction mechanism or the inert gas introduction mechanism (not shown), thereby purifying the atmosphere. The ejection device 308 moves while maintaining an appropriate gap on the substrate, thereby forming a desired pattern on the substrate. Further, the process chamber has a laser introduction window 307. By introducing laser light supplied from the laser oscillator 301 through the optical element 302 into the surface of the substrate 310, the patterned thin film is modified or crystallized. Laser light is also irradiated to the entire surface of the substrate by providing the moving means 303 in the optical element group. Although not shown in the figure, the laser light may be one having a uniform spatial intensity using a beam homogenizer or the like, or one having a desired beam pattern using a mask or the like.
[0024]
FIG. 4 is a plan view showing a case where the liquid pattern forming apparatus of the above embodiment is combined with another process apparatus. Load / unload chamber C1, plasma CVD chamber C2, substrate heating chamber C3, hydrogen or oxygen plasma processing chamber C4, and laser irradiation / coating chamber C5 via gate valves GV1 to GV6 (GV6 is a reserve), respectively, and substrate transfer chamber Connected to C7. Each process chamber includes gas introduction devices gas1 to gas7 and exhaust devices vent1 to vent7. The processing substrates sub2 and sub6 introduced from the load / unload chamber are transferred to each process chamber by a transfer robot provided in the substrate transfer chamber. In the laser irradiation / coating chamber C5, a liquid thin film pattern is formed by coating means (not shown) and then solidified by heating. Next, the laser beam supplied through one or both of the first beam line L1 and the second beam line L2 is shaped by the laser synthesis optical devices opt1 and opt2, and is applied to the substrate surface via the laser introduction window w1. Irradiate.
[0025]
By using the apparatus as described above, it is possible to prevent the substrate from being released into the atmosphere when forming a laminated structure with the plasma CVDSiO ₂ film, so that a clean interface can be formed.
[0026]
A second embodiment will be described with reference to FIGS. The liquid droplets 102 fly and adhere to the substrate 101 (FIG. 1A) to form a liquid pattern 503 (FIG. 2B). The pattern size is controlled by the unit amount and the number of droplets that fly and adhere. A desired droplet pattern 504 is formed on the surface of the substrate 101 by moving the droplet discharge means relative to the substrate or moving the substrate 101 relative to the droplet discharge means. At this time, in controlling the pattern size and the film thickness, the parameters are sufficiently set in consideration of the viscosity of the droplet, the surface tension on the substrate, the size of the island film to be produced, and the like. Here, when a film thicker than a desired film thickness is formed, or as shown in FIG. 5 (b), when the unevenness is formed on the upper surface in the cross-sectional shape when the pattern 504 is solidified, the surface The flattening step is performed. As shown in FIG. 5C, the planarization process is performed by forming an oxide film 505 on the upper portion and then polishing and removing the surface of the solidified pattern 504 simultaneously with the oxide film by a chemical mechanical polishing method. Do. Further, the entire surface of the substrate or a part thereof may be irradiated with the laser 105 as necessary. The flattening means is selected according to the material, such as chemical etching, mechanical polishing, or ion milling.
[0027]
Next, a third embodiment of the present invention will be described with reference to FIGS. 6A to 6D each show a part of a thin film transistor manufacturing process. A thin film pattern 604 is formed on the substrate 101 on which an appropriate substrate cover film is deposited by applying a liquid raw material in an island shape (FIG. 5A). Next, a crystalline silicon film 605 is formed through a heating / solidification step at 300 ° C. and a laser recrystallization step ((b) in the figure). Next, a trisilane (Si 3 H ₈ ) film 606 that is a liquid raw material is formed by a spin coating method ((c) in the figure). The spin conditions are set so as to obtain a desired film thickness. After coating is completed, annealing is performed at a temperature of 600 ° C. in a reduced-pressure oxygen atmosphere. By doing so, trisilane is oxidized to form an oxide film 607 (FIG. 4D). As a result, a silicon film pattern 605 covered with the oxide film 607 is formed. Next, a thin film transistor is formed through formation of a gate electrode, impurity implantation into the source / drain region, annealing, formation of a wiring metal, and the like.
[0028]
FIG. 7 is a schematic cross-sectional view of an apparatus for actively forming an oxide film. Power is supplied to the high-frequency electrode RF2 from a high-frequency power source RF1 (high frequency of 13.56 MHz or higher is suitable). Plasma is formed between the electrode RF3 with gas supply hole and the high-frequency electrode, and the radical formed by the reaction passes through the electrode with gas supply hole and is guided to the region where the substrate is disposed. By using a gas containing oxygen as the source gas, oxygen radicals are supplied onto the surface of the substrate sub2. At this time, another gas may be introduced by the planar gas introducing device RF4 without being exposed to plasma, and a silicon oxide film can be formed by introducing silane or the like. That is, as shown in the figure, the oxide film forming apparatus includes an exhaust device ven2, a gas introduction device gas2, an oxygen line gas21, a helium line gas22, a hydrogen line gas23, a silane line gas24, a helium line gas25, and an argon line gas26. Yes. The substrate holder S2 can be heated from room temperature to about 500 ° C. with a heater or the like. As the form of the oxygen radical supply apparatus as described above, not only the parallel plate type RF plasma CVD apparatus as described above, but also a method using no plasma such as low pressure CVD or atmospheric pressure CVD, microwave or ECR (Electron Cyclotron Resonance). It is also possible to use a plasma CVD apparatus using the effect. In addition, a nitride film can be formed by using a raw material containing nitrogen instead of oxygen.
[0029]
Further, since the above-described method is highly pure and suitable for forming a thick oxide film having a thickness of 1 μm or more, the following application is also possible. A glass substrate on which an active matrix liquid crystal display or an image sensor using a thin film transistor is formed contains a trace amount of alkali metal or the like. In order to prevent impurities such as alkali metals from diffusing from the substrate to the active layer silicon or the insulating film and its interface in the annealing process or the laser crystallization process, the substrate cover layer is used, and the silicon oxide film for the cover layer is used. Suitable as a manufacturing method. Process time can be shortened compared to conventional CVD deposition. On the other hand, an interlayer insulating film used in a semiconductor process, an active matrix TFT-LCD, or the like is often required to have flatness on the top. Even in such applications, the application of liquid material forms a flat surface, which is an excellent alternative.
[0030]
As described above, the present invention has been described based on the preferred embodiment examples. However, the thin film forming method of the present invention is not limited to the configuration of the above embodiment examples, and various modifications can be made. Modifications and changes are also within the scope of the present invention.
[0031]
【The invention's effect】
According to the thin film forming method of the present invention, since a thin film pattern can be formed by selectively supplying a fluid raw material onto a substrate, the number of steps of the manufacturing process can be reduced by omitting the photolithography step and the etching step, In addition, the amount of raw materials used can be reduced. Furthermore, for silicon-based thin films, high-performance semiconductor elements can be formed at low cost by applying the coating film oxidation technique to the insulating thin film formed by the thin film forming method of the present invention.
[Brief description of the drawings]
FIGS. 1A and 1B are cross-sectional views for each step sequentially showing a thin film forming method according to a first embodiment of the present invention. FIGS. 2A and 2B are a single discharge device used in the method of the present invention. FIG. 6 is a cross-sectional view showing the structure of FIG. 2 and a perspective view showing the structure of the ejection device arranged in an array.
FIG. 3 is a schematic plan view of a liquid pattern forming apparatus used in the method of the present invention.
FIG. 4 is a plan view of a composite apparatus including a liquid pattern forming apparatus used in the method of the present invention.
FIG. 5 is a cross-sectional view sequentially showing a thin film forming method according to a second embodiment of the present invention.
FIG. 6 is a cross-sectional view sequentially showing a thin film forming method according to a third embodiment of the present invention.
FIG. 7 is a schematic cross-sectional view of an oxygen radical supply device used in a third embodiment.
[Explanation of symbols]
101: substrate 102: droplet 103: liquid pattern 104: solidification pattern 105: laser 106: crystallized film 201: nozzle 202: heater 203: discharge port 204: supply port 205: drive circuit substrate 206: drive circuit 207: supply means 208: Control means 301: Laser oscillator 302: Optical element 303: Moving means 304: Optical path 305: Transfer chamber 306: Gate valve 307: Laser introduction window 308: Discharge device 309: Process chamber 310: Exhaust device 311: Substrate stage 312: Exhaust device 504: thin film pattern 604: liquid pattern 605: thin film pattern 606: trisilane film 607: oxide film

Claims (4)

A step of selectively applying droplets of a liquid material represented by Si _n H _{2n + 2} (n> = 2) on a substrate to form a desired liquid pattern, and applying the desired liquid pattern on the substrate And a step of forming a solidified pattern by solidifying into a thin film pattern forming method of a semiconductor element or a liquid crystal element . The method for forming a thin film pattern according to claim 1, wherein the step of forming the desired liquid pattern includes a step of ejecting and discharging droplets. 3. The method according to claim 1, further comprising a step of forming an oxide film over the entire surface of the solidified pattern, and a step of polishing the oxide film and the solidified pattern to form a solidified pattern having a desired thickness. Thin film pattern forming method. The thin film pattern forming method according to claim 1 , wherein the step of forming the solidified pattern includes a step of recrystallization or amorphization .

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