Coating method

Abstract: A fluid application apparatus of the present invention includes a rotatable substrate holding mechanism (4), a photoresist liquid supply portion (5) and a motor mechanism (26). The photoresist liquid supply portion (5) supplies resist fluid to a region smaller than the entire region of the substrate surface while moving in the horizontal direction relative to the substrate holding mechanism (4). The motor mechanism (26) rotates the substrate holding mechanism (4) to diffuse the resist fluid over the entire surface of the substrate and form a resist layer having a predetermined thickness.

Description: BACKGROUND OF THE INVENTION A) FIELD OF THE INVENTION The present invention relates to a coating method for coating a surface of a substrate with a predetermined liquid, such as a photoresist liquid. for coating a surface of a substrate. B) DESCRIPTION OF THE RELATED ART There are numerous devices for coating a substrate, such as a rectangular glass substrate, with a photoresist liquid in order to manufacture a liquid crystal display (LCD). For instance, the devices shown in JP-A-Hei 4-61955, and JP-A-Hei 1-135565 apply liquid to a substrate. In such devices, the substrate is horizontally held by a rotatable chuck The photoresist liquid is dropped down on the central portion of the upper surface of the substrate through a supply nozzle while the substrate is held in a stationary position by the chuck. Thereafter, the rotatable chuck is rotated thus rotating the substrate. As the substrate rotates, the photoresist liquid is spread over the whole area of the upper surface of the substrate by centrifugal force generated by the rotation of the substrate. Some of the photoresist fluid is thrown from the substrate's center by the centrifugal force, scatters around the periphery and is wasted. The quantity of photoresist fluid necessary to form a photoresist layer having a predetermined thickness on a substrate surface can be calculated based upon the thickness and size of the substrate. However, in the above described devices, such calculations are, for the most part, meaningless because of the amount of wasted liquid lost due to scattering around the periphery of the substrate during rotation. According to a method known from US-A-4 451 507 the treating liquid is discharged onto the substrate through a point-like nozzle movable across the substrate. A coating method known from DE-A-27 46 519 is also based on point-like nozzles. From JP-A-63 209769 it is known to drip a coating solution onto a substrate in the vicinity of the center thereof and to spread the coating solution by spinning the substrate. SUMMARY OF THE INVENTION One object of the present invention is provide a method which can apply a liquid, forming a thin layer of a predetermined liquid on the surface of a substrate using a minimal amount of liquid to reduce the amount of waste liquid in comparison with the prior art devices. Another object of the present invention is to provide a coating method which can form a thin layer of a predetermined liquid on the surface of a substrate by using a minimal amount of liquid to decrease waste as compared to prior art methods. The coating method according to the invention is as defined in claim 1. These and other objects, features. aspects and advantages of the present invention will become more fully apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings where like reference numerals denote corresponding parts throughout, in which: BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic diagram, part section of coating device, having a movable nozzle, in accordance with a preferred embodiment of the present invention for coating a rectangular substrate; Fig. 2 is a fragmentary, part section, perspective view of the nozzle used with the coating device depicted in Fig. 1 on an enlarged scale; Fig. 3 is cross-section view taken along the line III-III in Fig. 2, looking in the direction of the arrows; Fig. 4 is a block diagram showing a controller connected to various portions of the coating device depicted in Fig. 1; Fig. 5 is a flowchart showing operational steps of the coating device depicted in Fig 1; Fig. 6 is a flowchart showing the coating step depicted in the flowchart in Fig 5; Fig. 7 is a top view showing positions of the nozzle of the coating device with respect to the substrate; Fig. 8 is a view of the coating device showing the nozzle retracted away from the substrate during rotation of the substrate; Fig. 9 is a top view showing the relationship between a substrate and the nozzle in a coating device not claimed. Fig. 10 is a top view similar to Fig. 9, showing the relationship between a substrate and the nozzle: a) during rotation of the substrate; and b) after rotation of the substrate with the head moved away from the substrate; Fig. 11 is a top view similar to Fig. 9, showing an embodiment not claimed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In Fig. 1, a photoresist coating device is depicted in a preferred embodiment of the invention and includes a substrate processing portion (1), a photoresist liquid apply portion (2) and a motor mechanism (26). In the coating device, a photoresist liquid is applied and a coating process carried out to coat a rectangular substrate P as shown in Figs. 2 and 8. The substrate processing portion (1), shown in Fig. 1, includes a substrate holding mechanism (4) that holds a rectangular shaped substrate P using a plurality of vacuum suction holes (not shown), and retains the substrate P such that the longest side of the substrate P is held in a first direction d 1 (see Fig. 2). The substrate processing portion (1) also includes a photoresist liquid supply portion (5) that supplies photoresist liquid to the substrate P retained by the substrate holding mechanism (4) as will be described further below. The substrate holding mechanism (4) is freely rotatable by motor mechanism (26). The motor mechanism (26) rotates the substrate holding mechanism (4). A cup shaped spatter guard (6) is located at the outside of the substrate holding mechanism (4) such that the rim is above the periphery of the substrate P to prevent scattering of the photoresist liquid during rotation of the substrate due to centrifugal force. As shown in Figs. 1, 2 and 8, the photoresist liquid supply portion (5) has a supply nozzle (7). The length of the nozzle (7) is disposed over the short side of the rectangular substrate P in a second direction d 2 perpendicular to the first direction d 1 . As shown in Fig. 3, the cross section of the nozzle (7) is shaped like an inverted house. The bottom surface of the nozzle (7) is tapered to form an elongated point along the length of the nozzle at its lowest, most central point. The nozzle (7) is formed with a liquid path which includes a liquid supply inlet (31a), a storing chamber (31), and a liquid supply outlet (31b), as shown in Fig. 3. At the end of the liquid supply outlet (31b) and at the length-wise tip of the nozzle (7), there is formed a slit shaped opening (20). The opening (20) is generally shorter than the width of the short side of the substrate P. The nozzle (7) is supported on a movable frame (9) via a nozzle support arm (8). The nozzle support arm (8) is movably supported on the movable frame (9) to move selectively up and down relative to the substrate P. The movement guide (10) extends along the first direction d 1 and supports movement frame (9) such that the movable frame (9), along with the support arm (8) and nozzle (7), can move freely in the first direction d 1 . Accordingly, the nozzle (7) moves along the upper surface of the substrate P in the first direction d 1 in order to supply photoresist liquid to a predetermined region smaller than the entire region of the upper surface of the substrate P. As is shown in Fig. 3, inside the nozzle (7) is formed the liquid storing chamber (31), liquid supply inlet (31a) and the liquid supply outlet (31b). The liquid storing chamber (31 ) is formed with a width wider than outlet (31b) and the opening (20). The purpose of pro viding the liquid storing chamber (31 ) is to evenly diffuse the photoresist liquid supplied from a photoresist liquid supply pipe (16) (described below) through the nozzle (7) and on to the substrate P. As shown in Fig. 1, the photoresist liquid apply portion (2) has a liquid tank (12), a pressure tank (11) and a pressure pipe (13). The liquid tank (12) storing photoresist liquid to be supplied, is disposed within the pressure tank (11). The pressure tank (11) is sealed to be airtight. The pressure pipe (13) connects the top of the pressure tank (11) to a nitrogen gas source (not shown). On the pressure pipe (13) is attached a 3-way supply/discharge valve (14) and a regulator (15) which are respectively arranged along the pressure pipe 13 a shown in Fig. 1. The 3-way valve (14) allows for nitrogen gas to be selectively supplied to the pressure tank (11) or expelled from it, as is shown in Fig. 1. One end of the photoresist liquid supply pipe (16) protrudes into the liquid tank (12), extending close to the bottom. The other end of the supply pipe (16) is connected to the nozzle (7). In a mid-portion of the photoresist liquid supply pipe (16) between the liquid tank and the nozzle (7) a flowrate meter (17) and photoresist liquid supply valve (18) are disposed. As shown in Fig. 4, the coating device includes a controller (23) which includes a microprocessor or a microcomputer. Connected to the controller (23) are the substrate holding mechanism (4) which includes a vacuum chuck, the nozzle support arm (8) and a drive portion of the movably frame (9), the 3-way supply/discharge valve (14), the photoresist liquid supply valve (18) and the motor mechanism (26). Also, various sensors (not shown) are connected to the controller (23) and other I/O apparatus, which detect the position of the nozzle support arm (8) and the movable frame (9). The operation of the coating device is explained in the flowcharts shown in Figs. 5 to 7. For instance, the controller may be programmed to perform the steps described below. In step S1 of Fig. 5 the settings for the entire coating device are initialized. Next, in step S2 a transport mechanism (not shown) transports the substrate P to the substrate holding mechanism (4). After the substrate P is transported into position, the substrate P is held by vacuum suction by the substrate holding mechanism (4) in step S3. The coating process is carried out in step S4, shown in Fig. 6. Entering step S4, the nozzle (7) is moved to a predetermined start position at step S10 in Fig. 6. Here, the nozzle (7) is arranged at a predetermined distance from one edge of the substrate P, as shown in Fig. 7. In step S11, photoresist liquid is released from the slit (20) of the nozzle (7) to the substrate P. At the start of this supply operation, the controller (23) adjusts the 3-way valve (14) to the supply setting and further opens the photoresist liquid supply valve (18) to supply photoresist liquid from the liquid tank (12) to the nozzle (7). In step S12, the movement of the movable frame (9), support arm (8) and nozzle (7) begins horizontally relative to the movement guide (10) and, as shown in Fig. 2 and 3, photoresist liquid D is applied to the substrate P. In step S13 it is determined whether or not the nozzle (7) has moved in the first direction d 1 a predetermined distance from right edge of substrate P. Upon reaching the predetermined distance, the 3-way valve (14) is switched to cut off the flow of nitrogen gas into the pressure tank (11), and the photoresist liquid supply valve (18) is closed stopping the supply of photoresist liquid D in step S14. In step S15, movement of the nozzle (7) is stopped. Then, as shown in Fig. 6, the nozzle (7) is moved to a predetermined protective position away from the substrate P so as not to interfere with subsequent operations in step S16. In step S17, the motor mechanism (26) rotates the substrate holding mechanism (4), and the substrate P, at a low speed in a direction shown by the arrow in Fig. 8. The substrate P is then rotated continuously for a predetermined time period. During this time, centrifugal force is created by the rotation of the substrate holding mechanism (4), the centrifugal force affecting the photoresist liquid D on the upper surface of the substrate P moving the fluid D in an outer peripheral direction. As a result, the photoresist liquid D diffuses evenly about the entire surface region of the substrate P forming a generally uniform photoresist liquid layer on the upper surface of the substrate P with an even thickness. The rotation of the substrate P is continued until a predetermined time has passed. Once the predetermined time has passed, the rotation of the motor mechanism (26) is stopped in step S19. Once rotation is stopped, the operation returns to the main routine in Fig. 5. In step S5 of Fig. 5, the vacuum suction of substrate holding mechanism (4) is released. Thereafter, the transport mechanism (not shown) transfers the coated substrate P out and away from the substrate holding mechanism (4). Then the operation returns to step S2 and waits for the arrival of the next substrate P In the above described embodiment of this invention, it is provided for the substrate P to be rectangular. In an alternate embodiment shown in Fig. 9 and not belonging to the invention, it is preferable for the substrate W to be disc shaped. In the alternate embodiment with the disc shaped substrate W, a nozzle (41) is disposed over a rotatable substrate holding mechanism (40). The nozzle (41) has a slit (42), the length of which is shorter than the diameter of a disc-shaped substrate W. Here, as shown in Fig. 10 (a), the nozzle supplies a photoresist liquid (D) to a specified region smaller than the entire surface of the substrate W while the substrate holding mechanism (40) is rotated at a relatively low speed. When the liquid coating process is complete, the nozzle (41) is retracted to a predetermined position away from the substrate so as not to interfere with subsequent steps, and the substrate holding mechanism (40) is rotated at a relatively high speed. As shown in Fig. 10 (b), centrifugal force distribute the photoresist liquid D over the entire surface of the substrate W resulting in a photoresist layer having a predetermined thickness. In another embodiment not belonging to the invention, the slit (20) of the nozzle (7) may be replaced with a plurality of needle-like liquid supply portions arranged in the longitudinal direction on the tip of the nozzle (7) or similarly with a plurality of narrow liquid supply holes H as is shown in Fig. 11. In the coating method of the present invention, the rotation of the substrate holding mechanism causes movement of photoresist liquid D applied to the surface of the substrate P. However, the liquid is supplied to a region of the surface of the substrate that is smaller than the entire region of the substrate surface. The rotation of the substrate P causes the photoresist liquid D to evenly cover the entire surface of the substrate and a relatively small amount of excess liquid may be thrown from the substrate surface due to the rotation of the substrate P. Consequently, even though the amount of photoresist liquid applied to the surface of the substrate P is small, photoresist liquid can be diffused over the entire surface of the substrate, creating a photoresist layer having a specified thickness. With the simple construction of the liquid supply nozzle of the present invention, liquid can be easily supplied at a specified region. Further, as the substrate is rectangular, the coating device may be of simpler construction providing a method for moving the nozzle over the surface of the substrate, as opposed to a movable substrate holding portion. Moreover, when the nozzle has a liquid storing chamber the liquid can be more evenly supplied. In the coating method, as the substrate is rectangular, by supplying the liquid over the upper surface of the substrate in a single direction, liquid can easily be supplied to an entire specified surface. Various details of the invention may be changed without departing from its scope. The foregoing description of the embodiments according to the present invention is provided for the purpose of illustration only, and not for limiting the invention as defined by the appended claim.

Claims: A coating method for coating a surface of a rectangular substrate with a predetermined treating liquid, comprising the steps of: disposing a rectangular substrate in a horizontal position; carrying out a liquid discharging operation onto a horizontal surface of the substrate by discharging thereon a predetermined treating liquid through a liquid supply nozzle having an outlet formed as an elongated slit (20) extending in parallel to said surface and perpendicularly to a first edge of said substrate over a length shorter than the width of the substrate taken in the direction perpendicular to said first edge, while moving the nozzle relative to the substrate in a direction parallel to said first edge of the substrate, said discharging of said treating liquid onto the substrate being started at a distance away from a second edge of the substrate that is perpendicular to said first edge and is stopped a distance ahead of a third edge of the substrate that is parallel to said second edge, and spinning the substrate with the treating liquid discharged thereon about a vertical axis after the discharging operation has been completed.

Inventors: KINOSE KAZUO, OKETANI TAIMI, YAMAMOTO TOMOO, YONEZAWA TAKESHI, KINOSE, KAZUO, OKETANI, TAIMI, YAMAMOTO, TOMOO, YONEZAWA, TAKESHI, KINOSE, KAZUO, C/O DAINIPPON SCREEN MFG. CO., LTD., YONEZAWA, TAKESHI, C/O DAINIPPON SCREEN MFG CO LTD
Applicants: DAINIPPON SCREEN MFG, SHARP KK, DAINIPPON SCREEN MFG. CO., LTD., SHARP KABUSHIKI KAISHA
Application year: 1995
Main classification: B05D1
IPC codes: H01L21, B05D1, B05C11, G03F7