JP2008296122A - Method of forming thin film using liquid material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To efficiently form a thin film having a large area using an inkjet system instead of the conventional film forming method of a sputter method or a transfer printing system. <P>SOLUTION: An even liquid film is formed by filling up a base plate surface with circles depicted by a landing diameter D of a liquid material ejected from an inkjet, and disposing liquid drops by the inkjet at the centers of the circles so as to interconnect liquid drops each other. Further, a disposition for efficiently filling up the base plate surface with the circles depicted by the landing diameter D is given by a conditional formula. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for forming a thin film by discharging droplets onto a substrate and drying and baking a liquid film formed by the droplets.

  Flat panel displays typified by liquid crystal display devices are rapidly increasing in size and price.

  FIG. 12 is a cross-sectional view illustrating the structure of a liquid crystal display device. The liquid crystal display device is roughly divided into a TFT substrate 1202 and a CF substrate 1201. Between the TFT substrate 1201 and the CF substrate 1202, there is a spacer 1204 for keeping a gap between the substrates, and the gap is filled with liquid crystal 1205. On the TFT substrate 1202, gate wiring, source drain wiring, TFT, pixel ITO, etc. (not shown) are formed on an upper layer 1207 of the glass substrate 1206, and an alignment film 1208 is further formed thereon.

  On the CF substrate 1201, a black matrix, a color filter, a flattening film, etc. (not shown) are formed on the upper layer 1210 on the glass substrate 1209, and a transparent conductive film 1211 as a counter electrode is formed thereon.

  An alignment film 1212 is formed on the transparent conductive film 1211. Further, a polarizing plate 1213 is attached to the surfaces of the TFT substrate and the CF substrate.

  In the above structure, a process for forming a thin film is frequently used.

  In particular, wirings, transparent conductive films, and the like are formed using a sputtering apparatus which is a vacuum apparatus and then patterned using photolithography. The alignment film is formed by transferring an alignment film solution onto a substrate using a transfer method and then baking it.

  In the film formation by the sputtering apparatus, the problem is that the sputtering apparatus is enlarged, the cost is increased, and the material use efficiency is lowered as the substrate is enlarged.

  In the alignment film formation, since the alignment film liquid is transferred using a transfer roller, the size of the transfer roller increases due to the increase in size of the substrate, the adhesion of foreign matter on the substrate due to contact with the roller, and the product size changes. There is a problem that it takes time to change the model.

  Development of a new film formation method that meets these issues is desired, and a method for forming a film with a functional ink material by using an inkjet method that is non-contact and has high on-demand properties for such needs. Is being considered.

  Japanese Unexamined Patent Application Publication Nos. 2004-146796 and 2004-290959 describe a method of forming a film pattern using an ink jet method.

JP 2004-146796 A JP 2004-290959 A

  The ink jet method does not require a huge vacuum chamber unlike a sputtering apparatus, so that it can easily cope with an increase in the size of the substrate, and has excellent points as a film forming method because it is highly on-demand and non-contact.

  The prior arts disclosed in the cited documents 1 and 2 describe the formation of a film pattern using an ink jet. However, a method for efficiently forming a thin film with a large area is not described.

  An object of the present invention is to obtain a film forming method using an ink jet method, a film forming device, and an electro-optical device using a thin film formed by using this film forming method instead of the conventional vacuum device and transfer method. It is in.

  A liquid material for forming a target thin film is discharged using an inkjet head having a plurality of nozzles arranged in a line at a constant pitch. The inkjet head is scanned relative to the substrate while ejecting liquid droplets made of the liquid material at predetermined time intervals from the nozzle. Thereby, droplets are arranged in a matrix on the substrate. If the surface state of the substrate and the physical properties of the droplet are appropriately controlled, the droplet spreads in a circle with a diameter determined by the contact angle and the volume of the droplet. If the nozzle pitch, the nozzle scanning speed, and the discharge time interval are appropriately selected, the droplets spread in a circular shape are connected together to form a liquid film on the substrate. The method for forming the liquid film without unevenness is as follows.

  The substrate surface is filled with a circle determined by the landing diameter D of the liquid material for forming the thin film, and the droplets are arranged by ink jet so as to arrange the droplets at the center of the circle. Thereby, the droplets are connected to each other, and a liquid film without unevenness can be formed. The liquid film is dried and fired to form a desired thin film.

  Moreover, this invention is a thin film formation method which makes the method of filling up a board | substrate efficiently with the circle | round | yen of the diameter D formed by an impact diameter as follows.

The nozzle pitch of the ink-jet head having a plurality of nozzles and P _2, the relationship of the pitch P ₂ and diameter D P ₂ <D · · · · (a)
The inkjet head is selected, the substrate surface treatment, or the liquid physical properties are adjusted so that Furthermore the discharge gap and P ₁ with respect to the scanning direction. In general, the nozzle is inclined by θ ₁ with respect to the scanning direction in order to adjust the ink ejection pitch. With the above configuration, first, one row of droplets is discharged from the nozzle row onto the substrate.

Next, the discharge pitch P ₂ is determined according to the condition shown in the following formula (b), and the next droplet is discharged. By repeating this, the droplets are arranged without gaps.

  According to another aspect of the present invention, there is provided a method of manufacturing an electronic device using a thin film produced by using the thin film forming method.

  According to the present invention, there is provided an electronic apparatus using a thin film formed by using the thin film forming method.

  Further, the present invention is characterized in that the above-mentioned method for efficiently filling the substrate with a circle having a diameter D formed by the landing diameter is incorporated in a control device, and a liquid film is formed by this droplet arrangement method. Inkjet device.

  In the present invention, since film formation conventionally performed by a vacuum apparatus can be performed by applying and baking a liquid material using an ink jet apparatus, the apparatus cost can be reduced.

  For film formation performed by the transfer method, there are effects such as improvement of quality by non-contact and shortening of model switching time by direct use of CAD data.

  In addition, since the droplet placement method can be performed efficiently, film formation with high material use efficiency and high throughput becomes possible.

  Furthermore, since quantitative droplet arrangement design is possible, the film formation condition design by ink jet can be performed efficiently.

  Due to the above effects, the cost for manufacturing a liquid crystal display device or the like can be reduced by reducing the equipment cost for film formation, improving the throughput, and improving the yield by improving the quality.

  Embodiments of the present invention will be described including the results of previous studies.

FIG. 2 is a configuration diagram of an ink jet apparatus 201 for explaining a droplet discharge method using an ink jet method. In FIG. 2, 202 is a substrate, 203 is a table for mounting and moving the substrate, 204 is an ink jet head, and 205 is a control device for controlling the jet head 204 and the table 203. The substrate 202 is fixed to the table 203 by vacuum suction or the like. The jet head 204 has a plurality of nozzles (not shown) at a pitch P ₂ in one row. A droplet 207 is ejected from the nozzle according to a predetermined signal. The table 203 has an encoder (not shown) and is configured to generate a pulse 206 at every predetermined distance as the table moves.

  The operation of the inkjet apparatus 201 having this configuration will be described.

  The inkjet head 204 is fixed, and the table 203 scans in the direction of the arrow 208. As the table 203 moves, a pulse is generated from the encoder, and a droplet is ejected from the nozzle at the timing of this pulse.

As a result, it is possible to drop liquid droplets in a matrix form at positions corresponding to the intersection points 301 of the lattice shown in FIG. In the lattice of FIG. 3, the unit of the horizontal axis is the nozzle pitch P ₂ , and the unit of the vertical axis is the distance P ₁ that travels between pulses generated by scanning the table. Although discharge is possible with respect to the intersection point 301, ON / OFF of discharge is determined by data in the control device 205. The pattern resolution that can be formed by inkjet is determined by the nozzle pitch P ₂ and the dropping pitch P ₁ in the table scanning direction.

If you want to increase the resolution with respect to the nozzle direction, move the head in the nozzle row direction, a droplet is dropped in the middle of the pitch P _2.

The width W of the film that can be formed by this ink jet discharge is in a range represented by pitch P ₂ × (n−1), where n is the number of nozzles. In order to increase the discharge width W, the necessary number of nozzles may be arranged.

  The contents of the study conducted to form a thin film using the ink jet apparatus having the above configuration will be described.

  FIG. 4 shows a state where one drop of the liquid material is ejected onto the substrate 401 by ink jet and landed. A landing droplet is shown at 402. When ejecting droplets by the inkjet method, the droplet diameter is as small as several tens of μm, and the factors that determine the shape of the liquid that has landed on the substrate are the variations in surface energy depending on the position of the substrate surface, the surface tension of the liquid, the substrate And wettability between liquids. By adjusting the surface appropriately with respect to the liquid to be ejected, a substantially perfect landing shape as shown in FIG. 4 can be obtained.

  The landing droplets when the lattice shown in FIG. 3 is a square lattice with equal vertical and horizontal pitches are as shown in FIG. When forming a liquid film, it is considered that these landed droplets are connected to each other and flattened by the action of surface tension, whereby a liquid film is formed. Considering the unit for forming the liquid film in FIG. 5A, it can be generalized by considering the connection state of four landing droplets as shown in FIG. 5B.

  The connection state of the four landing droplets can be classified into five types shown in the table of FIG. Each state is represented by a relational expression of a connected state and a pitch P between droplets and a landing diameter D. State No1 represents the state where the landed droplets are separated from each other, State No2 is in a state of contact, No3 is a state where the droplets overlap each other, and State No4 is a state where the central gap 601 between the droplets in No3 is eliminated , No5 represents a state where the droplets overlap at the center 602 between the droplets. For these states, experiments were conducted to confirm the actual liquid film formation status for No1, No3, and No5 except for No2 and No4, which are the boundary states of the connections. FIG. 7 shows an observation photograph of the experimental results corresponding to the connected state. The liquid used for ejection is obtained by dispersing nanoparticles in an organic solvent, and the viscosity, surface tension, etc. are adjusted for inkjet. The substrate was also cleaned prior to the experiment to remove organic contamination. The landing state of the droplet shows a state close to a perfect circle equivalent to FIG.

  In the result of state No. 1, the shape indicated by 701 is the landing mark remaining at the landing position, and exhibits unevenness reflecting the discharge position as a whole. The thin dots 702 arranged in a matrix in the result of the state No3 are those in which the gap 601 at the center of the state No3 in FIG. 6 remains uneven. In the result of state No5, regular unevenness does not occur and a substantially uniform liquid film is formed.

  From the above results, the condition for forming a uniform liquid film without unevenness is the droplet shown in state No. 3 in the combination of circles composed of droplet circles upon landing (hereinafter referred to as landing circles) shown in FIG. There is no gap 601 between them. Accordingly, the discharge pitch and the placement condition of the landing circle having the diameter D when the liquid film formation without unevenness is performed at a square pitch are expressed by the following formula (c).

  When arrangement conditions other than the square pitch are examined as a method of filling the plane with the landing circle, arrangement conditions as shown in FIG. 8 also exist. Therefore, a general arrangement condition for filling the landing circle without gaps was obtained.

Generalization was performed on the condition that ejection was performed by inkjet. FIG. 9A is a schematic diagram showing a part of the arrangement of the inkjet head nozzles. Reference numeral 901 indicates a nozzle, and an arrow 900 indicates a direction in which the head and the substrate move relatively. The row of the plurality of nozzles 901 is inclined by θ _{1 with} respect to the moving direction. FIG. 9 (2) shows a landing circle row formed by the nozzle row of FIG. 9 (1). FIG. 1 shows four combinations extracted as elements constituting a liquid film from the landing circle.

In FIG. 1, the landing circles indicated by 901 and 902 indicate two landing circles of a droplet row ejected along the direction of the landing center 906 shown in FIG. Circles denoted by reference numerals 903 and 904 indicate two landing circles of a droplet row discharged along the direction of the discharge position center 907 discharged next to the landing center 906. When the conditions under which these four landing circles 901 to 904 can be arranged without a gap are obtained, they can be expressed by combinations of equations 103 and 104. In FIG. 1, D represents a landing diameter, P ₂ represents a nozzle pitch, and P ₁ represents a discharge pitch.

  In FIG. 1, Formula 103 is a condition in which the landing circles 901 and 902 overlap each other and the intersection 101 of the landing circles exists. Expression 104 is a condition for overlapping the intersection 101 of the landing circles 901 and 902 on the inside of the landing circle 904. Due to the symmetry of the figure, it is also a condition that the intersection 102 of the landing circles 903 and 904 is arranged inside the landing circle 901. By arranging the landing circles according to the conditions of equations 103 and 104, the plane can be filled without gaps.

  Next, an example of film formation using the conditions of equations 103 and 104 will be described.

  FIG. 10 shows a film forming process flow. A glass substrate is used as the substrate. First, the substrate surface is cleaned, and further organic contamination on the substrate surface is removed by ultraviolet irradiation. As a method for removing contamination from the substrate surface, plasma treatment, treatment of etching glass such as dilute hydrofluoric acid, or the like may be used.

Next, the liquid material used for film formation is ejected by inkjet, and the landing diameter D on the substrate is obtained. The nozzle pitch P ₂ is a value determined by selecting the ink jet head. First, it is checked whether the landing diameter D and the nozzle pitch P ₂ have a relationship of D <P ₂ . If this relationship is not satisfied, a head with a larger landing diameter or a smaller nozzle pitch is selected. As a method for increasing the landing diameter, there are methods such as increasing the piezo voltage and increasing the discharge amount, or increasing the wettability of the liquid material to the substrate. In inkjet discharge, the nozzle is tilted at an angle θ ₁ in order to adjust the discharge pitch with respect to the moving direction. The value of the discharge pitch P _{1 is obtained from} the values of D, P ₂ , and θ ₁ using the formula (b). The value of the discharge pitch P ₁ obtained here often has a fraction. Further, the value of the ejection pitch in the ink jet apparatus is determined by the value of the moving resolution on the apparatus side. Accordingly, the actual discharge pitch P _1M is set to a value that is an integral multiple of the moving resolution smaller than P ₁ obtained by the equation (b).

As a specific example, when the landing diameter D = 240 μm, the nozzle pitch P ₂ = 200 μm, and the nozzle inclination θ = 20 °, P ₁ is calculated to be 193.07 μm. If the moving resolution of the nozzle is 10 μm, P _1M is 190 μm or less. FIGS. 11 (1) and 11 (2) show the arrangement of the landing circles obtained for two types of P _1M of 190 μm and 170 μm. The figure shows the scale ratios closely matched.

When P _1M is 190 μm and 170 μm, the 190 μm overlap part 1101 is smaller than the 170 μm overlap part 1102, and when P _1M is 190 μm, it does not overlap due to variations in the landing diameter D, discharge position accuracy, etc. Cases may also arise. Therefore, it is necessary to determine P _1M with a margin so that the landing circles overlap in consideration of various errors.

The liquid is ejected at the pitch P _1M and a droplet is disposed on the substrate. The arranged droplets cover the entire coating area.

  Immediately after landing, irregularities exist, but a flat liquid film is formed on the liquid surface in several minutes (depending on the type of liquid material) due to surface tension.

  After evaporating the solvent by drying, the thin film is completed by baking at the required temperature.

  By using the present invention, it is possible to apply the liquid material while confirming the overlap amount of the landing circles. Therefore, the overlap amount is not increased unnecessarily, and efficient droplet arrangement is possible. Thereby, a high-quality film without unevenness can be formed efficiently.

  In the structure of the liquid crystal display shown in FIG. 12, gate wirings, source / drain wirings, and pixel electrodes (not shown) formed on the TFT substrate are formed by sputtering and then patterned by photolithography. The alignment film is formed by applying an alignment film solution and baking it. The same applies to the pixel electrode and alignment film of the CF substrate.

  Typical wiring materials such as gate, source, drain, etc. are Cr, Al, Ti, etc. in the sputtering method, but the liquid material for forming the conductive film is one in which Ag nanoparticles are dispersed in a solvent. is there. Specifically, there is Ag nanometal ink made by ULVAC Material. This material can be applied and baked under appropriate conditions to form a conductive thin film that can be used as a wiring material, and can also be patterned using a photolithography method.

  As for transparent conductive films, the sputtering method uses a lot of ITO. As a liquid material, nano-sized ITO fine particles are dispersed in a solvent, or a precursor of a transparent conductive material such as ITO (ITO by heating, light irradiation, etc.). Etc.). These liquid materials are coated, dried, and fired under appropriate conditions to obtain a transparent conductive film close to the sputtering method, and the pixel electrode can be formed by patterning by a photolithography method.

  In addition, the alignment film is formed using a liquid material, and can be applied by adjusting the physical properties suitable for inkjet application. Therefore, an equivalent alignment film can be formed.

  The thin film in the liquid crystal display device described above can be formed according to the process shown in FIG.

  In addition to a liquid crystal display device, a thin film having a large area can be formed in a process as a device structure such as a PDP, electronic paper, or a solar cell, and used for manufacturing an electronic device to be used.

Since the ink jet apparatus has a configuration as shown in FIG. 2, it is possible to discharge droplets from the ink jet head in synchronization with scanning of the substrate. Landing that can be formed of a liquid material by incorporating a function for calculating the P ₁ and P _1M in accordance with the above equation (b) in the control device, and having a configuration in which the scanning pitch can be controlled to P _{1M based} on the calculation result. An ink jet apparatus that can efficiently cover the entire surface of the application region with a circle can be configured.

  The thin film forming method according to the present invention provides a method for efficiently forming a thin film without unevenness using an inkjet, and can be applied to all products to which a thin film that can be formed from a liquid material is applied.

An explanatory view and a relational expression related to a droplet arrangement method of the present invention. The block diagram explaining an inkjet system. Explanatory drawing of the droplet discharge position by an inkjet. Droplets ejected onto a substrate by inkjet. Explanatory drawing which shows the state of the droplet discharged on the board | substrate from the several nozzle of inkjet. The table | surface which shows the relationship figure and relational expression of the connection relation of the droplet discharged on the board | substrate. The experimental result regarding the connection relation of FIG. Connection relationship of droplets discharged on the substrate (state other than square pitch). The schematic diagram showing the relationship between an inkjet head nozzle arrangement | positioning and a discharge result position. The film-forming process flow by the droplet arrangement | positioning of this invention. The droplet arrangement | positioning figure by the droplet arrangement | positioning method of this invention. FIG. 14 is a cross-sectional view illustrating a structure of a liquid crystal display device.

Explanation of symbols

  103, 104 ... Formula, 202 ... Substrate, 204 ... Inject head, 205 ... Control device, 402 ... Landing droplet, 901-904 ... Landing circle.

Claims (5)

  In a method of forming a thin film by applying, drying, and baking a liquid material on a substrate by an inkjet method, the liquid material is discharged onto the substrate by inkjet, and the diameter of a droplet spread in a circle on the substrate is defined as D. A liquid film is formed by placing a droplet at the center of a circle that is filled with a circle with no gaps by combining the circles of D, and the liquid film is dried and baked to form a thin film. Thin film forming method. 2. The thin film forming method according to claim 1, wherein a nozzle pitch is set to P in an ink jet head provided with a plurality of nozzles at equal intervals, as a method of ejecting droplets by an ink jet method and efficiently filling and arranging the substrate. _The diameter of the liquid material discharged from the nozzle in a circular shape on the substrate is D, and the straight line connecting the centers of the nozzles of the inkjet head is θ ₁ with respect to the scanning direction of the inkjet head and the substrate. When the discharge pitch in the scanning direction with respect to the substrate is P ₁ , the droplets are arranged by determining the values of the variables D, P ₂ and P _{1 so} that the following expressions (a) and (b) are satisfied. The thin film forming method according to claim 1.

  A method for manufacturing an electronic device, characterized in that a thin film prepared by using the thin film forming method according to claim 2 is used.   An electronic apparatus using a thin film produced by using the thin film forming method according to claim 2.   An ink jet apparatus, wherein the droplet placement method according to claim 2 is incorporated in a control device, and a liquid film is formed by the droplet placement method.

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