JP5514667B2 - Spin coating method - Google Patents

Description

  The present invention relates to a spin coating method for coating a coating liquid while rotating a semiconductor wafer, a flat panel display (FPD) substrate, or the like.

  In order to form a resist film or the like by applying a coating solution such as a resist solution to a substrate such as a semiconductor wafer or a glass substrate for a flat panel display (FPD), a spin coater is used. In general, the spin coater is a chuck that rotates the substrate while holding the substantially central portion of the back surface of the substrate, a dispenser that drops a resist solution or the like onto the substrate held by the chuck, and is scattered from the surface of the substrate by the rotation of the substrate. And a cup portion for receiving a resist solution or the like. Holding the substrate with a chuck, dropping a resist solution or the like onto the substrate while rotating or standing still, and rotating the substrate at a predetermined rotation speed, a resist film having a film thickness corresponding to the rotation speed is obtained. Formed on a substrate. At this time, since the resist solution or the like on the substrate is scattered at a considerable speed and collides with the cup portion, mist due to a solvent such as the resist solution or a solid content is generated. When the generated mist floats in the cup part and adheres to the substrate surface, local variations occur in the film thickness of the resist film, etc., resulting in defects in subsequent processes, and particles are generated. An exhaust port is provided in the lower part, and the inside of the cup part is exhausted through this. In order to reduce defects and particles, methods and apparatuses for controlling the exhaust have been proposed (for example, Patent Documents 1 and 2).

Japanese Patent No. 3512270 Japanese Patent No. 3703281

  In the spin coater, in order to sufficiently suck the mist floating in the cup part, if the exhaust amount of the exhaust inside the cup part is excessively increased, the centrifugal pump effect due to the rotation of the substrate is combined, especially in the region near the periphery of the substrate. The solvent such as the resist solution easily evaporates. As a result, the film thickness of the resist film or the like is increased in a region near the periphery. Such a tendency becomes more prominent as the size of the substrate increases. Further, according to the study of the inventors of the present invention, turbulent flow is likely to occur in the region near the peripheral edge of the substrate due to the increase in the substrate size. ), That is, it has been found that unevenness in film thickness occurs.

  The present invention is made by the above circumstances, and provides a spin coating method capable of maintaining a uniform film thickness of a resist film or the like particularly in a region near the periphery of the substrate.

According to one aspect of the invention,
A raw material chemical solution for a film formed on a substrate having a diameter of 450 mm held by the substrate rotation holding unit is dropped onto the substrate, and the cup is surrounded by a predetermined portion within a range of 500 to 900 rpm while exhausting the cup portion surrounding the substrate A spin coating method for forming the film by rotating at a rotational speed of
And forming the film using the cup portion while exhausting the first cup emissions, the first substrate having a diameter of 450mm at the predetermined rotational speed,
Forming the film on a second substrate having a diameter of 450 mm at the predetermined rotational speed while evacuating the cup portion with a second cup displacement;
Based on the first cup displacement, the film thickness of the film formed on the first substrate, the second cup displacement, and the film thickness of the film formed on the second substrate, Obtaining a rate of change of the film thickness with respect to the cup displacement of the cup portion;
Determining a target cup displacement based on the obtained rate of change;
While exhausting the cup portion at the determined the target cup emissions, see containing and forming the film at the predetermined rotational speed to a third substrate with a diameter of 450 mm,
The film thickness of the film formed on the first substrate is a film thickness in a region closer to the periphery than the center of the first substrate, and the film thickness of the film formed on the second substrate is A spin coating method is provided which is a film thickness in a region corresponding to the region of the first substrate in the second substrate .

  According to the embodiment of the present invention, there is provided a spin coating method capable of maintaining a uniform film thickness of a resist film or the like particularly in a region near the periphery of the substrate.

It is a schematic diagram which shows the spin coating apparatus suitable for implementation of the spin coating method by embodiment of this invention. It is a time chart (an example) at the time of use of the spin coater of FIG. It is explanatory drawing explaining the striation which may occur in the area | region near the periphery of the board | substrate of the resist film spin-coated, and its generation | occurrence | production. It is a graph which shows the suitable range of the rotational speed of a board | substrate for every board | substrate size. It is a flowchart which shows the spin coating method by embodiment of this invention. It is a graph which shows an example of the film thickness distribution in the area | region near the periphery of the board | substrate of the resist film spin-coated. It is explanatory drawing explaining the measurement jig | tool which measures the cup displacement in the spin coater of FIG. It is explanatory drawing explaining the pressure sensor which measures the cup displacement in the spin coater of FIG.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the accompanying drawings. In all the accompanying drawings, the same or corresponding members or parts are denoted by the same or corresponding reference numerals, and redundant description is omitted. Also, the drawings are not intended to show the relative ratio between members or parts. Accordingly, specific thicknesses and dimensions should be determined in light of the following non-limiting embodiments.

  An example of a spin coater suitable for carrying out the spin coat method according to the embodiment of the present invention will be described with reference to FIG. This spin coating apparatus may be incorporated in a coating and developing apparatus.

  As shown in the figure, the spin coater 10 includes a spin chuck 11 that holds and rotates the wafer W substantially horizontally, a cup 12 that is disposed so as to surround the wafer W on the spin chuck, and a horizontal position above the spin chuck 11. And a dispenser 13 that is movably disposed and supplies a coating liquid to the wafer W held by the spin chuck 11.

  The spin chuck 11 is coupled to the rotation drive unit 14 via the shaft 10a, can be moved up and down by the rotation drive unit 14, and can be rotated around the vertical axis. The spin chuck 11 is provided with a suction conduit (not shown) opened on the upper surface thereof, and this suction conduit is connected to a vacuum mechanism (not shown) through the shaft 10a. The wafer W placed on the upper surface of the substrate is sucked and held.

  The cup 12 has a generally cylindrical shape with a bottom, and the upper opening 12 a has a diameter larger than the diameter of the wafer W. An annular protrusion 12 b that protrudes inward is provided on the inner peripheral wall of the cup 12. The protrusion 12b is provided to control the airflow in the cup 12, and the upper surface of the protrusion 12b is at the same height as the surface of the wafer W held by the spin chuck 11, and the inner peripheral end of the protrusion 12b. And the edge of the wafer W held by the spin chuck 11 are maintained at a predetermined interval. The cup 12 has a guide portion 12 c that is disposed on the back side of the wafer W held by the spin chuck 11. Guide part 12c has apex part 12cA which adjoins the back surface of wafer W, and extends cyclically, and inclined part 12cS which inclines below from here downward. The inclined portion 12cS guides the coating liquid supplied onto the wafer W, the rinsing liquid that cleans the coating liquid that has come around the back surface of the wafer W, and the like to the outside of the cup 12 and downward. In addition, the inclined portion 12cS provides an air flow path for the airflow flowing through the cup 12 together with the above-described protruding portion 12b.

  Further, a waste liquid pipe 12d is connected to the bottom of the cup 12, through which a coating liquid, a rinsing liquid, and the like are discharged. In addition, two exhaust pipes 12e are connected to the bottom of the cup 12 inside the waste liquid pipe 12d. These exhaust pipes 12e merge on the downstream side, and are connected to an exhaust system (not shown) via an exhaust amount adjuster 15. The displacement adjuster 15 has a damper 15a, and the flow rate of the airflow flowing through the exhaust pipe 12e is adjusted by the opening of the damper 15a. With this configuration, as indicated by the solid line arrow in FIG. 1, an airflow with a controlled exhaust amount flowing from the opening 12a of the cup 12 to the exhaust pipe 12e through the gap between the protrusion 12b and the wafer W is generated. Formed in the cup 12.

  The dispenser 13 can reciprocate between a home position above and outside the cup 12 and a dispensing position above and substantially at the center of the wafer W held by the spin chuck 11 by a driving mechanism (not shown). In the example shown, the dispenser 13 is in the dispensing position. The dispenser 13 is connected to a coating solution supply system that supplies a coating solution such as a resist solution. With such a configuration, the dispenser 13 is retracted to the home position when the wafer W is loaded / unloaded, and after the wafer W is held by the spin chuck 11, the dispenser 13 moves to the upper part of the wafer W and substantially to the center. A coating solution is supplied to W.

  The spin chuck 11, the cup 12, the dispenser 13, and the like are housed in a housing 16. The housing 16 is provided with a transfer port 16a for the wafer W, and the wafer W is carried in and out via the transfer port 16a by a transfer arm (not shown). In addition, a shutter 16b that can be opened and closed is provided at the transport port 16a. The shutter 16b is closed except when the wafer W is carried in and out of the housing 16 by the transport mechanism, and a substantially sealed space is formed in the housing 16. A fan filter unit (FFU) 16 c is provided on the inner upper portion of the housing 16. The FFU 16c is connected to the clean gas supply system via the gas supply path 16d, whereby the clean gas from the clean gas supply system is supplied into the housing 16 as a downward flow, and thus the interior of the housing 16 is clean. Maintained in the environment.

  The spin coating device 10 is provided with a control unit 17. The control unit 17 is electrically connected to the rotation drive unit 14, the spin chuck 11, the flow rate adjustment unit 15, and the like, and controls them. The control unit 17 is configured by a computer, and controls each component or member of the spin coater 10 according to a computer program for performing a coating liquid coating operation. The computer program is stored in the storage unit 17b via the storage medium 17a such as a flexible disk, a portable hard disk, a memory card, a compact disk (CD), a digital versatile disk (DVD), and installed in the control unit 17. . Further, a user interface 17c is connected to the control unit 17, and through this, a computer program can be selected, the computer program can be updated, recipe parameters (application conditions), and the like can be input.

  FIG. 2 is a time chart of the rotation speed of the wafer W (spin chuck 11) in the coating rotation apparatus 10. As shown in FIG. 2, after a predetermined time (15 seconds in the illustrated example) has elapsed since the wafer W was held on the spin chuck 11, the rotation W 14 causes the wafer W to pass through the spin chuck 11. Rotating at the rotation speed, the coating liquid is supplied onto the wafer W (coating liquid supply step). After the supply, the rotation speed of the wafer W is temporarily reduced, and a so-called reflow step is performed. This is performed in order to cover the unevenness with a coating liquid when device elements such as wirings, contact holes, vias, and insulating layers are formed and the surface of the wafer W has unevenness. Thereafter, the rotation speed of the wafer W is increased, and a coating liquid drying step is performed (about 35 seconds in the illustrated example). In this step, the coating liquid on the wafer W is spread by the centrifugal force accompanying the rotation of the wafer W, and the solvent in the coating liquid is dried, so that a film having a thickness corresponding to the rotation speed is formed on the wafer W. Is done. Next, the rotation speed of the wafer W is reduced, and the back surface cleaning (BSR) for cleaning the coating solution that has entered the back surface of the wafer W with a rinse solution, and the coating solution for the peripheral edge of the front surface of the wafer W with the rinse solution, etc. A cleaning step including edge cleaning (EBR) is performed, and finally, a drying step is performed in which the rotational speed is increased again to dry the rinse liquid or the like used in the cleaning step. Thus, film formation on the wafer W is completed, and the wafer W is unloaded from the coating rotation device 10.

  The rotation speed in the drying step varies depending on the size of the wafer even when, for example, films having the same film thickness are obtained using the same coating solution. Specifically, when trying to obtain a film having the same film thickness, the wafer rotation speed tends to decrease as the wafer size increases. This is because a large centrifugal force acts on the coating liquid supplied onto the wafer as the diameter of the wafer increases.

  According to the study by the present inventors, for example, when a resist film is formed on a wafer having a diameter of 450 mm, the linear velocity at the periphery of the wafer is relatively large even if the rotation speed of the wafer is lowered, so that it is close to the periphery of the wafer. It was found that turbulent flow is likely to occur in the region. As shown in FIG. 3A, when the wafer W is rotated, a centrifugal pump effect is generated, and an airflow AF that is attracted to the surface of the wafer W from above the wafer W and flows outward along the surface of the wafer W is generated. Arise. Such airflow AF flows as a laminar flow in the region near the rotation center C of the wafer W, but the flow velocity increases as it approaches the region near the periphery of the wafer W and flows as a turbulent flow. As a result, a laminar flow region, a turbulent flow region, and a transition region that gradually changes from laminar flow to turbulent flow are formed above the wafer W. Here, in the turbulent flow region, the coating liquid on the wafer W may spread non-uniformly due to the influence of non-uniform air resistance due to the turbulent flow. In the region, a striation S is generated as schematically shown in FIG. This can be recognized by the difference in the interference color of the coating film (a streak pattern having a different interference color from the surroundings is observed).

  According to the results of the study by the inventors on the rotation speed of the wafer that does not generate turbulent flow, as shown in FIG. 4, in the case of a wafer having a diameter of 200 mm, the rotation speed is about In the range of 2000 to about 3500 revolutions per minute (rpm), for a 300 mm diameter wafer, the rotational speed is in the range of about 1000 to 1800 rpm, and for a 450 mm diameter wafer, the rotational speed is Preferably, the rotational speed is in the range of about 500 to 900 rpm.

  However, even if the wafer is rotated at such a rotational speed and the occurrence of striation can be suppressed, there is a problem that the film thickness is increased particularly in a region near the periphery of the wafer having a diameter of 450 mm. . The reason for this is that since the size of the wafer is large, it takes a relatively long time for the coating solution supplied on the wafer to spread, and the solvent in the coating solution evaporates while the coating solution spreads, which is substantially This is thought to be because the concentration of solid components increases. Further, the evaporation of the solvent is promoted because the air flow in the region near the periphery of the wafer becomes faster due to the relatively large centrifugal pump effect, and is also promoted by the exhaust in the cup.

  Hereinafter, a spin coating method according to an embodiment of the present invention based on the above examination will be described with reference to FIGS. 1 and 5. In this description, the case where the above-described spin coater 10 is used, a silicon wafer having a diameter of 450 mm is used as the wafer W, and a resist solution is used as the coating solution will be described.

First, a single wafer (referred to as a wafer W1 for convenience) is used, and a resist film is formed on the wafer W1 (step S501). Specifically, using a transfer arm (not shown) having a fork at the tip, the wafer W1 is loaded into the spin coater 10 through the feed port 16a of the casing 16 of the spin coater 10, and the wafer W1 is spun. Hold above the chuck 11. Next, the spin chuck 11 is lifted by the rotation drive unit 14, and the wafer W1 is received by the spin chuck 11 and sucked to hold the wafer W1. Next, the spin chuck 11 is lowered and the wafer W <b> 1 is accommodated in the cup 12. The opening degree of the damper 15a of the flow regulator 15 is adjusted by the instruction signal from the control unit 17, and the exhaust amount of the airflow flowing through the exhaust pipe 12e is the first cup exhaust amount (1.25 m ³ / min in this example). Set to Next, the wafer W1 is rotated at a predetermined rotation speed by the spin chuck 11, and the dispenser 13 is moved to the upper center of the wafer W to supply a predetermined amount of resist solution onto the wafer W1. Subsequently, a resist film having a predetermined film thickness is formed on the wafer W1 in accordance with the reflow step, the drying step, and the cleaning step described with reference to FIG.

  Next, the film thickness of this resist film is measured (step S502). This measurement can be performed by, for example, a film thickness meter using light interference. An example of the measured thickness distribution of the resist film is shown in FIG. In FIG. 6A, the film thickness in the range from the periphery of the wafer W1 (diameter 450 mm) to 50 mm is standardized by the average film thickness. As shown in the figure, it can be seen that the resist film becomes thicker as it approaches the periphery of the wafer W1. In particular, at a point of several mm from the periphery of the wafer W1, it is about 25 nm thicker than the average film thickness.

Next, a resist film is formed on this wafer W2 using another wafer (for convenience, referred to as wafer W2) (step S503). At this time, except that the exhaust amount of the cup 12 is set to a second cup exhaust amount (0.9 m ³ / min in this example), the same conditions as those for forming the resist film on the wafer W1 in step S501 and A resist film is formed by the procedure.

  Then, the thickness of the resist film formed on the wafer W2 is measured in the same manner as in step S503 (step S504). The result is shown in FIG. As shown in the drawing, compared with the resist film formed on the wafer W1, an increase in film thickness in the region near the periphery of the wafer is suppressed. This is because the evaporation of the solvent in the resist solution is suppressed by reducing the displacement of the cup 12, that is, the resist solution is removed from the periphery of the wafer W2 without significantly increasing the solid component concentration in the resist solution. It can be considered that it has spread to.

Subsequently, from the above result, the rate of change of the film thickness in the region near the periphery of the wafer with respect to the cup displacement is calculated (step S505). Specifically, the difference in resist film thickness at the same point between wafer W1 and wafer W2 is obtained and divided by the difference in cup exhaust amount. Assuming that the value of the rightmost point (about 3 mm from the wafer edge) in each graph of FIG. 6 is used as the film thickness, the difference in film thickness is 23.1-12. The difference in the cup displacement is 1.25-0.9 = 0.35 m ³ / min. Therefore, the change rate of the film thickness is about 30.9 nm / (m ³ / min).

Next, the cup exhaust amount is determined based on this result (step S506). For example, if the device formation region on the wafer is inside 5 mm from the periphery of the wafer (edge exclusion 5 mm), and the allowable value of the resist film thickness in that region is 15 nm, for example, the cup The displacement may be determined to be about 0.76 m ³ / min.

  After determining the cup exhaust amount as described above, a resist film is formed on one or more wafers (for example, a wafer for manufacturing an integrated circuit (IC)) with the cup exhaust amount (step S507). For example, when the cup exhaust amount parameter in the recipe is changed using the user interface 17c (FIG. 1), an instruction signal is transmitted from the control unit 17 to the flow rate regulator 15 according to the recipe, and the determined cup exhaust amount is realized. The damper 15a is set to the angle.

  As described above, according to the spin coating method according to the embodiment of the present invention, the change rate of the film thickness with respect to the cup exhaust amount, particularly in the region near the periphery of the wafer, is obtained, and the cup exhaust amount is determined based on this Since the film thickness in the region near the periphery of the wafer is controlled, a uniform film can be formed.

  The film thickness used to determine the rate of change in film thickness is measured at a position about 3 mm from the periphery of the wafer in the above example. However, the present invention is not limited to this. For example, in the region closer to the periphery than the center of the wafer. To measure. Specifically, for example, it is preferable to measure the film thickness in a region on the peripheral side from the midpoint of the center and peripheral edge of the wafer, which is thicker than the average film thickness of the film on the wafer. Further, it is preferable that the measurement position of the film thickness is determined in consideration of edge exclusion. Furthermore, the number of film thickness measurement points is not limited to one point. For example, the film thickness is measured at a plurality of points along a circle 7 mm inside from the periphery of the wafer, and the average value is used for calculating the change rate of the film thickness. You may do it. However, it goes without saying that the wafer W1 and the wafer W2 should be measured at the same position.

  In the above example, the resist film formation and the film thickness measurement were performed twice using the wafers W1 and W2, but the resist film formation and the film thickness measurement were performed using the third wafer W3. The change rate of the film thickness may be calculated using the result. In this way, it becomes possible to make the film thickness more accurate.

  Further, the above steps S501 to S506 need not be performed every time the film is formed in step S507. In step S507, for example, the film may be formed on all the wafers for one lot.

Next, a method for measuring the cup displacement will be described.
Referring to FIG. 7, a pressure sensor 18a is attached to the back surface of the guide portion 12c of the cup 12 at a position facing the opening of the exhaust pipe 12e. As the pressure sensor, any one of a semiconductor diaphragm type, a capacitance type, an elastic diaphragm type, a piezoelectric type (including a semiconductor piezo type), a vibration type, a Bourdon tube type, and a bellows type may be used. it can. Considering the mounting position, a semiconductor piezo-type or semiconductor diaphragm-type pressure sensor is preferable. When the pressure sensor 18a is attached to the illustrated position, the pressure applied to the pressure sensor 18a is measured by the airflow flowing into the exhaust pipe 12e through the air flow path formed by the protruding portion 12b and the guide portion 12c. The pressure sensor 18a is electrically connected to the controller 18b. The controller 18b receives a signal from the pressure sensor 18a, converts the magnitude of this signal into a pressure value, and displays it. On the other hand, the exhaust pipe 12e is provided with a flow meter (not shown) downstream of the flow rate controller 15. As this flow meter, for example, a mass flow meter can be used. As a preliminary experiment, the instruction signal output from the control unit 17 to the flow rate controller 15 is variously changed as a variable, and the pressure measured by the pressure sensor 18a and the displacement measured by the flow meter each time the change is made. And record. Thereby, a conversion table (graph) between the displacement and the pressure is acquired. If this conversion table is prepared, the cup displacement can be measured by the pressure sensor 18a without using a flow meter.

  Moreover, as shown in FIG. 8, if the conversion table of the wind speed measured with the wind speed measuring jig 19 and the flow rate measured with the above-mentioned flowmeter is calculated | required using the wind speed measuring jig 19, a wind speed measurement will be carried out. It is possible to determine the cup displacement from the wind speed measured by the jig 19. As shown in the drawing, the wind speed measuring jig 19 has a diameter capable of closing the opening 12a of the cup 12, and has a measuring portion 19a in the central opening. The measurement part 19a has an impeller, for example. When the airflow passes through the central opening of the wind speed measuring jig 19 placed on the cup 12, the impeller rotates by the airflow, and the wind speed of the airflow is measured by the control unit 19c according to the rotational speed.

  The displacement of the cup 12 is not limited to that measured by the pressure sensor 18a or the flow velocity measuring jig 19. You may measure using the above-mentioned flow meter provided in the exhaust pipe 12e. Of course, the exhaust amount of the cup 12 does not have to be an absolute amount, and may be an index value (alternative value) indicating the exhaust amount. For example, the rate of change of the film thickness with respect to the instruction signal output from the control unit 17 to the flow rate adjuster 15 may be obtained, and the magnitude of the instruction signal may be adjusted based on this to make the film thickness uniform.

  Further, although the case where a resist film is mainly formed has been described, a raw material coating solution is supplied to the wafer, such as an antireflection film or a spin-on dielectric (SOD) film (including a spin-on glass film), and the wafer is rotated. In the case where a film is formed by this, the present invention can be applied. Further, the present invention can be applied not only to a semiconductor wafer but also to a glass substrate for a flat panel display.

  The present invention is not limited to the above-described embodiments, and various modifications and changes can be made without departing from the scope of the claims.

  DESCRIPTION OF SYMBOLS 10 ... Spin coating apparatus, 11 ... Spin chuck, 12 ... Cup, 12d ... Waste liquid pipe, 12e ... Exhaust pipe, 13 ... Dispenser, 15 ... Exhaust amount regulator, 15a ... damper, 16 ... casing, 16a ... transport port, 16c ... fan filter unit (FFU), 17 ... control unit.

Claims (4)

A raw material chemical solution for a film formed on a substrate having a diameter of 450 mm held by the substrate rotation holding unit is dropped onto the substrate, and the cup is surrounded by a predetermined portion within a range of 500 to 900 rpm while exhausting the cup portion surrounding the substrate A spin coating method for forming the film by rotating at a rotational speed of
And forming the film using the cup portion while exhausting the first cup emissions, the first substrate having a diameter of 450mm at the predetermined rotational speed,
Forming the film on a second substrate having a diameter of 450 mm at the predetermined rotational speed while evacuating the cup portion with a second cup displacement;
Based on the first cup displacement, the film thickness of the film formed on the first substrate, the second cup displacement, and the film thickness of the film formed on the second substrate, Obtaining a rate of change of the film thickness with respect to the cup displacement of the cup portion;
Determining a target cup displacement based on the obtained rate of change;
While exhausting the cup portion at the determined the target cup emissions, see containing and forming the film at the predetermined rotational speed to a third substrate with a diameter of 450 mm,
The film thickness of the film formed on the first substrate is a film thickness in a region closer to the periphery than the center of the first substrate, and the film thickness of the film formed on the second substrate is A spin coating method , which is a film thickness in a region corresponding to the region of the first substrate in the second substrate . Forming the film on a fourth substrate having a diameter of 450 mm at the predetermined rotational speed while evacuating the cup portion with a third cup displacement;
In the step of obtaining the rate of change , the first cup displacement, the film thickness of the film formed on the first substrate, the second cup displacement, and the second substrate are formed. 2. The rotation according to claim 1, wherein the rate of change is acquired based on the third cup displacement and the thickness of the film formed on the fourth substrate in addition to the thickness of the film. Application method. The spin coating method according to claim 1 or 2 , wherein the target cup exhaust amount is measured by a pressure sensor disposed at an exhaust port of the cup portion. The target cup exhaust amount, the is determined based on the air flow sensor is Ru arranged on the upper end of the cup portion, the spin coating method according to claim 1 or 2.

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