WO2008060069A1

WO2008060069A1 - Method for cleaning a substrate

Info

Publication number: WO2008060069A1
Application number: PCT/KR2007/005633
Authority: WO
Inventors: Dae Hee Gimm
Original assignee: Mujin Electronics Co., Ltd
Priority date: 2006-11-14
Filing date: 2007-11-09
Publication date: 2008-05-22
Also published as: TW200822195A; TWI361451B; KR20080043444A; KR100862911B1; CN101536158B; CN101536158A

Abstract

The present invention discloses the method for cleaning a substrate by dispensing to substrate an azeotropic mixture which is easily evaporated at the room temporature after producing the azeptropic mixture by controling the mixture ratio of a deionized water (DIW) and a liquid whose surface tenstion is lower than the surface tension of water. The method includes rotating the substrate, dispensing a cleaning liquid to the surface of the rotating substrate, producing an azeotropic mixture by mixing a deionized water with a liquid whose surface tension is lower than the surface tension of water, dispensing the azeotropic mixture to the surface of the rotating substrate and finishing drying by providing the substrate with an inert gas.

Description

Description METHOD FOR CLEANING A SUBSTRATE

Technical Field

[1] The present invention relates to a method of cleaning a substrate or a wafer in a process for producing a semi-conductor, and more specifically, to a method of producing an azeotropic mixture and using it in cleaning a substrate. Background Art

[2] The performance, credibility and yield of an integrated circuit are influenced by the wafer used in production, or by unnecessary physical/chemical impurities remaining on the surface of an element after production.

[3] When the minimum line width of an element becomes smaller enough to reach a sub- micron domain, the technology of cleaning a wafer surface clearly prior to the oxidation and pattern formation is required more significantly. The technology of cleaning the surface of a semiconductor wafer is roughly classified into wet chemical cleaning method, dried cleaning method, vapor method, etc., and the wet chemical cleaning method have been commonly used. Amongst the wet chemical cleaning methods, an RCA cleaning method comprising standard clean 1 (SC-I) and standard clean 2 (SC-2) has been most widely used. Generally, the wet cleaning of a silicone wafer is performed by soaking approximately 50-100 wafers collectively in a cleaning liquid such as SC-I or SC-2 and rinsing them in a deionized water (DI water). Ebwever, such process of soaking wafers collectively in a cleaning liquid has a problem that it is unavoidably slow because the process relies upon the flow passing through the wafers which are at pause to be rinsed.

[4] Thus, there had been an increasing need for cleaning and rinsing a wafer more quickly as a shorter period of time is required for the preparation of a semiconductor integrated circuit.

[5] Accordingly, U.S. Patent Application No. 09/892,130 discloses a method of improving a wafer rinse in a device for cleaning a single wafer. According to this method, a wafer is exposed to a cleaning liquid and is made to rotate at a high speed, and then, a deionized water is dispensed or sprayed to the rotating wafer for the purpose of removing the cleaning liquid from the wafer. The centrifugal force of the rotating wafer further improves the wafer rinse.

[6] However, even when the wafer rotates at a high speed, the deionized water swells in the center of the wafer due to the weak the centrifugal force and the surface tension of the deionized water, and the film of the deionized water becomes thinner toward the circumference of the wafer because of the centrifugal force.

[7] At this time, the chemicals of high concentration are diffused in the deionized water very quickly; thus, although rinsing with the deionized water is effective at the beginning of the rinsing process, the diffusion rate decreases as time passes by and the swollen deionized water in the center of the wafer remains.

[8] To solve the above problem, U.S. Patent Application M). 09/892,130 provides a method of dispensing a solution (either in a liquid or gas form) whose surface tension is lower than the surface tension of water, e.g., isopropyl alcohol (IPA), to a wafer after a chemical dispense and/or a deionized water dispense. According to this method, chemicals are removed by a deionized water having a high solubility thereto at the initial stage of rinsing, and the layer of the swollen deionized water in the center of the wafer is reduced by an IPA at the final stage of rinsing, thereby accelerating a diffusion.

[9] As another example, it discloses a method of spraying an IPA vapor or a liquid before dispensing a deionized water for rinse after a chemical dispense. As another example, it discloses a method of administering an IPA liquid at one point of the wafer through a nozzle and at the same time, dispensing a deionized water at another point of the wafer through another nozzle.

[10] Also, it discloses a method of heating the deionized water at the temperature higher than a room temperature, for example, at 60-70⁰C, to accelerate a diffusion of chemicals by supplying heat energy to the deionized water.

[11] Also, it discloses a method of rotating a wafer at a speed higher than the speed during the wafer rinsing, or applying a nitrogen gas to the wafer, after rinsing, to dry the wafer.

[12] Hwever, although the prior art had already disclosed the method of using a deionized water and a liquid whose surface tension is lower than the surface tension of water (e.g., isopropyl alcohol) for cleaning a substrate, it has not yet published the method of easing the drying process when cleaning a substrate at a room temperature, by properly adjusting the mixing ratio of a deionized water and an isopropyl alcohol.

[13] In this regard, the present inventor has found that the processes of cleaning, rinsing and drying a substrate can be more effectively done at a room temperature by using an azeotropic mixture, which is produced by mixing a deionized water with a liquid whose surface tension is lower than the surface tension of water (in particular, isopropyl alcohol), in a process of cleaning a substrate. [14] Accordingly, the present invention provides a method of producing an azeotropic mixture by mixing, in a suitable ratio, a deionized water which is applied in the process of cleaning a semiconductor with a liquid whose surface tension is lower than the surface tension of water and using thus-produced azeotropic mixture to clean a substrate more effectively at a room temperature. Disclosure of Invention Technical Problem

[15] The object of the present invention is to provide a method of producing an azeotropic mixture capable of easily vaporizing at a lower temperature than the vaporizing temperatures of a deionized water and of an IPA, by properly adjusting the mixing ratio of a deionized water which is used in cleaning a semiconductor and a liquid whose surface tension is lower than the surface tension of water, and also a method of using the azeotropic mixture to clean a substrate effectively.

[ 16] Another object of the present invention is to provide a method of producing an azeotropic mixture of a deionized water having a constant compositional ratio and a liquid whose surface tension is lower than the surface tension of water, by using an inline static mixer attached to the dispenser of a device for cleaning a semiconductor, and using the azeotropic mixture to clean a substrate effectively.

Technical Solution

[17] To achieve the foregoing objects, the present invention provides a method of producing an azeotropic mixture that can easily vaporize at a room temperature by properly adjusting the mixing ratio of a deionized water and a liquid whose surface tension is lower than the surface tension of water so as to rinse the substrate surface during cleaning. Also, the present invention further provides a method of cleaning a wafer by dispensing the aforesaid azeotropic mixture to the wafer.

[18] The method of cleaning a substrate according to the present invention comprises the steps of: rotating a substrate; dispensing a cleaning liquid to the surface of the rotating substrate; producing an azeotropic mixture by mixing a deionized water with a liquid whose surface tension is lower than the surface tension of water; and dispensing the azeotropic mixture to the surface of the rotating substrate, wherein the boiling point of the azeotropic mixture is lower than the boiling points of the deionized water and of a liquid to be mixed.

[19] Preferably, the method of cleaning a substrate according to the present invention further comprises a step of striking the center of the rotating substrate with a gas, or dispensing the vapor of a liquid whose surface tension is lower than the surface tension of water to the rotating substrate, after the step of dispensing an azeotropic mixture.

[20] Preferably, the method of cleaning a substrate according to the present invention further comprises a step of dispensing both a gas and the vapor of a liquid whose surface tension is lower than the surface tension of water to the rotating substrate at the same time, after the step of dispensing an azeotropic mixture.

[21] Preferably, the azeotropic mixture applied in the method of cleaning a substrate according to the present invention is produced and provided by an in-line static mixer.

[22] Preferably, according to the method of cleaning a substrate of the present invention, the influx of impurities from the outside of a chanber can be stopped by a film of nitrogen gas which is formed by supplying the nitrogen gas from the upper part of the charrber around the circumference of the inner space of the charrber where the cleaning the substrate is performed.

Advantageous Effects

[23] The present invention can clean a wafer effectively by use of an azeotropic mixture that can easily vaporize at a relatively lower temperature than the vaporizing temperature of the deionized water and liquid, the azeotropic mixture being produced by suitably adjusting the compositional ratio of the deionized water which is used in cleaning a substrate and a liquid whose surface tension is lower than the surface tension of water.

[24] The present invention can clean a wafer effectively by use of an azeotropic mixture of a deionized water having a constant compositional ratio and a liquid whose surface tension is lower than the surface tension of water, the azeotropic mixture being produced by an inline static mixer attached to the dispenser of the device for cleaning a semiconductor. Brief Description of the Drawings

[25] Fig. 1 is a sectional view of an example of a single device for cleaning a substrate according to the present invention of the method for cleaning a substrate.

[26] Fig. 2 is a sectional view of an example of a device for fixing a substrate used in the method of cleaning a substrate according to the present invention.

[27] Fig. 3 is a sectional view of an example of an in-line static mixer used in a device for cleaning a single substrate to produce an azeotropic mixture by mixing a deionized water with an isopropyl alcohol.

[28] ^■& Reference mxrbers of the main elements of the drawings [29] 100: device for fixing a substrate

[30] 102: substrate (or wafer)

[31] 104, 106: dispenser

[32] 108: in-line static mixer

[33] 110, 114: flowmeter

[34] 112, 116: spike pump

[35] 120: chamber

Mode for the Invention

[36] Hereinbelow, the preferable examples of the present invention will be described in more details with reference to the drawings attached.

[37] Fig. 1 is a sectional view of an example of a device for cleaning a single substrate to which the method of cleaning a substrate according to the present invention is applied.

[3S] As shown in Fig. 1, the device 10 for cleaning a substrate which is used in the method of cleaning a substrate according to the present invention comprises: a substrate-fixing device 100; also called 'chuck') for fixing a substrate 102 in the upper part and rotating it; a dispenser 104, 106 for dispensing a cleaning liquid, a deionized water for rinse, etc. to the surface of the rotating substrate; an in-line static mixer (108), which is connected to the dispenser 106, for mixing the liquids (e.g., a deionized water and an isopropyl alcohol) to be dispensed to the surface of the substrate 102 to produce an azeotropic mixture; a flowmeter 110, 114, which is connected to the in-line static mixer, for regulating the flow of liquids flowed into the in-line static mixer; a spike pump 112, 116 for supplying liquids to the in-line static mixer; and a chamber 120 for performing a substrate cleaning seperated by the external environment.

[39] Also, a curtain film of nitrogen gas is formed by supplying the nitrogen gas from the upper part of the charrber 120 around the circumference of the inside of charrber 120 in which the substrate cleaning is being performed, thereby preventing the influx of impurities from the outside of the charrber.

[40] Hereinbelow, one example of the device 100 for fixing a substrate used in the device

10 for cleaning a substrate according to the present invention is specifically described with reference to Fig. 2.

[41] Fig. 2 is a sectional view of an example of a device for fixing a substrate used in the device for cleaning a substrate according to the present invention.

[42] As shown in Fig. 2, the device 200 (chuck) for fixing a substrate according to one example of the present invention comprises: an upper plate 21 comprising a porous plate 23 on which a plurality of holes 25 are distributed irregularly and evenly; a lower plate 22, which is connected to the bottom of the upper plate 21, for establishing a gas storage 26 in which gases flowed into through a spindle frcm the outside of the chuck 200 are stored; a wafer supporter 24 for fixing a substrate by being attached closely to the side of the substrate; and a sensing element comprising a sensor for sensing the existence and rough position of a wafer in the center of the porous plate 23, wherein the porous plate 23 is round- shaped and is positioned in the center of the upper plate 21.

[43] When a gas, e.g., a nitrogen gas, outflows from the gas storage 25 positioned between the upper plate 21 and the lower plate 22 toward the substrate through the plural holes 25 of the porous plate 23, the substrate attached to the top of the upper plate 21 floats up due to the pressure of the outflowed gas, and the side of the floated substrate is fixed by a substrate supporter 24.

[44] Also, as shown in Fig. 2, the plural holes 25 formed on the porous plate 23 are distributed in an irregular and even manner like the shape of a foamy sponge. The porous plate 23 consists of a high-functional plastic showing the most excellent chemical resistance, a poly tetra fluoro ethylene (PTFE), which is commonly known as "Teflon"; thus, it does not react with chemicals used in the wafer treatment and does not produce any impurities.

[45] The size and nurber of the holes 25 formed on the porous plate 23 can be adjusted; the size is preferably 5-800/M and the volune of the hole 25 is preferably 5-90% volume of the porous plate 23. Also, the gases outflowed through the holes 25 are sprayed with an irregular directionality toward the wafer.

[46] In the present example, the upper plate 21 comprises only one porous plate 23 having a round shape, but the porous plate 23 can take any shapes such as a polygon, etc., and also, multiple porous plates may be arranged in a point- symmetry form with respect to the center of the chuck 10.

[47] According to the method of cleaning a substrate of the present invention, the substrate 102 floats up and is made to rotate by flowing out a nitrogen gas through the porous plate 23 by using the aforementioned chuck 100. Usually, SC-I and SC-2 are used as a cleansing liquid of a semiconductor and these liquids are sprayed to the surface of the rotating substrate 102 to rinse the surface. According to the method of cleaning a substrate of the present invention, the process of applying a cleaning liquid to the substrate 102 and the process of rinsing the substrate are done in the same device 10.

[48] According to one example of the method of cleaning a substrate of the present invention, in order to rinse the substrate 102, a mixed solution of a deionized water (DIW) and an isopropyl alcohol (IPA), which is in the state of an azeotropic mixture, is dispensed to the surface of the substrate 102 by a dispenser 106 while the chuck 100 rotates the substrate 102 to which a cleaning liquid such as SC-I and SC-2 is sprayed.

[49] Generally, the deionized water has a high solubility in ionic pollutants and the purchase and treatment thereof do not cost much, and also, it is effective in eliminating the pollutants because at the initial step of rinsing, the chemicals of high concentration remaining on the substrate quickly spread into the deionized water and decrease. For this reason, the deionized water is widely used in the process of cleaning a substrate.

[50] However, when applying a deionized water to a substrate which has been coated with a cleaning liquid or an etching liquid, etc. for rinse, the centrifugal force generated by the rotation of the substrate becomes stronger toward the circunference of the substrate, and thus the film of the deionized water formed on the surface of the substrate gets thinner toward the circunference; however, the centrifugal force is relatively weak in the center of the substrate, and this is why the deionized water film swells in the center. That is, the centrifugal force by the rotation of the substrate makes the deionized water film get thinner toward the circunference of the substrate, while the center of the substrate where the centrifugal force is weak swells due to the surface tension of the deionized water.

[51] As stated in the above, the spreading of pollutants into the deionized water gradually decreases as time passes by, and the deionized water swells in the center of the substrate. Therefore, for more effective rinsing and drying of a substrate, it is necessary to reduce the swollen portion of the deinozed water formed in the center of the substrate.

[52] According to the method of cleaning a substrate of the present invention, an azeotropic mixture is prepared by mixing a deionized water liquid (1) and an isopropyl alcohol (IPA: (CH3)2CHOH) liquid (1) in a proper ratio, and this azeotropic mixture is applied to the surface of the substrate in order to rinse the substrate.

[53] While the isopropyl alcohol is less soluble in ionic pollutants than water, the surface tension thereof is lower than the surface tension of water; thus, when the isopropyl alcohol is mixed with a deionized water, the whole surface tension of the mixture is lowered than that of water, and as a result, the swollen portion of the deinozed water formed in the center of the substrate is reduced.

[54] Also, the isopropyl alcohol can produce an azeotropic mixture that cannot be turned into a pure one by eliminating a moisture by distillation. Azeotropic mixture refers to a liquid mixture which is in the state of a solution capable of generating azeotropy. Generally, the composition of a vapor, which is in an qeuivalent state with a solution in which two liquid ingredients are mixed, differs from the composition of the solution thereof. This fact is applied when distilling a mixture solution of liquids into each ingredient liquid. When a solution is distilled, the composition of a vapor generally differs from the composition of the original solution, and one ingredient exceeds the other ingredient. Thus, as for the composition of the solution itself, the concentration of the other ingredient gradually increases and the boiling point of the solution accordingly elevates continuously.

[55] However, a solution having a certain composition exhibits a property of a pure liquid; that is, during distillation, the composition of the solution is identical to the composition of the vapor and thus the ingredients constituting the solution remain unchanged, continuing boiling at a particular temperature. Like this, in a mixture solution of liquids, the boiling that occurs at a certain temperature without changing the composition is called "azeotropy" and the temperature (boiling point) in which azeotropy occurs is called "azeotropic point".

[55] As stated earlier, a mixture solution of liquids having a particular composition capable of generating azeotropy is called "zeotropic mixture", and this azeotropic mixture is divided into "the lowest azeotropic mixture" whose azeotropy occurs at a lowest boiling point of the solution system and "the highest azeotropic mixture" whose azeotropy occurs at a highest boiling point.

[57] According to the present invention, an azeotropic mixture is produced at a mixture ratio of an isopropyl alcohol liquid to a deionized water wherein the mixture ratio is between 10-90 : 90-10; preferably, when the ratio of an isopropyl alcohol liquid to a deionized water is roughly 95.6 : 4.4, azeotropy occurs at 80.4⁰C under 1 pressure at which the boiling point is lower than the boiling point of water (99.97⁰C) and that of isopropyl alcohol (82.3⁰C), and this is the lowest azeotropic mixture of a deionized water and an isopropyl alcohol.

[53] Therefore, by dispensing an azeotropic mixture of an isopropyl alcohol and a deionized water to a rotating substrate, the process of cleaning the substrate, especially rinsing and drying, can be significantly improved thanks to the three effects that follow. Specifically, first, the coating film of a deionized water and an isopropyl alcohol liquid formed on the surface of a substrate becomes thinner toward the cir- cunference of the substrate due to the centrifugal force by the rotation of the substrate.

[59] Next, the surface tension of an isopropyl alcohol is lower than the surface tension of water, which causes the whole surface tension of a mixture of the deionized water and isopropyl alcohol to be lowered; as a result, the film formed by the deionized water and isopropyl alcohol on the surface of the substrate is thinner than the film formed only by the deionized water, and in particular, the thickness of the swollen portion of the film appearing in the center of the substrate can be reduced. Also, when a deionized water is mixed with an isopropyl alcohol in a suitable ratio, an azeotropic mixture having a lower boiling point is produced, and thus the vaporization at a room temperature can occur more easily. As a result, the process of rinsing and drying the substrate while cleaning it are further improved.

[60] Also, according to the method of cleaning a substrate of the present invention, only a small quantity of isopropyl alcohol is used and thus a rather expensive isopropyl alcohol can be chosen.

[61] Also, according to the method of cleaning a substrate of the present invention, with a small amount of isopropyl alcohol, a watermark remaining on the substrate can be effectively prevented.

[62] Preferably, as shown in Fig. 1, the method of cleaning a substrate of the present invention may further comprise a step of striking a nitrogen gas to the center of the substrate 102 by a dispenser 104 after the step of dispensing an azeotropic mixture of a deionized water and an isopropyl alcohol to the surface of the substrate 102. Striking a nitrogen gas adds a physical force to the swollen portion of the substrate and thus can lessen the thickness of the swollen portion in the center of the substrate, together with an isopropyl alcohol liquid nixed with a deionized water.

[63] Also, preferably, the vapor of an isopropyl alcohol may be added to the center of the substrate 102 by a dispenser 104 after dispensing an azeotropic mixture of a deionized water and an isopropyl alcohol to the surface of the substrate 102, in order to reduce the thickness of the swollen portion formed in the center of the substrate. At this time, the isopropyl alcohol added to the center of the substrate 102 dissolves into the deionized water and thereby reduces the surface tension, and as a result, the thickness of the center of the surface of the substrate decreases.

[64] Also, preferably, the vapors of nitrogen gas and of isopropyl alcohol may be added at simultaneously to the center of the substrate 102 by a dispenser 104 after dispensing an azeotropic mixture of a deionized water and an isopropyl alcohol to the surface of the substrate 102, in order to reduce the thickness of the swollen portion formed in the center of the substrate.

[65] Fig. 3 is a sectional view of an example of an in-line static mixer used in a single device for cleaning a substrate in order to produce an azeotropic mixture by mixing a deionized water and an isopropyl alcohol.

[66] As shown in Fig. 3, the inline static mixer 108 is a device for producing an azeotropic mixture by receiving an isopropyl alcohol liquid (IPA (I)) which is supplied by a spike punp 112 and the flow of which is controlled by a flowmeter 110, a deionized water (DIW (I)) which is supplied by a spike pump 116 and the flow of which is controlled by a flowmeter 114 and mixing the two.

[67] In the case of adopting a pre-nixing system and supplying a mixture of a deionized water and an isopropyl alcohol from the outside of the device, it requires a bigger size of device and the steam pressure of the deionized water becomes different from that of the isopropyl alcohol with the lapse of time in the mixing tank of the device; consequently, the compositional ratio of the deionized water and isopropyl alcohol change.

[68] As a result, the optimum compositional ratio of the deionized water and isopropyl alcohol cannot be maintained and thus it is impossible to produce the azeotropic mixture having the lowest boiling point.

[69] Therefore, as shown in Fig 1, the device 10 used in the method of cleaning a substrate of the present invention is equipped with an inline static mixer 108 for mixing a deionized water and an isopropyl alcohol in the device 10.

[70] Generally, the inline static mixer 108 is a device in which several elements 302, fixed consecutively from right to left inside the tube, generate a successive mixing to fluids which are passing through while converting the fluid of a laminar flow to the fluid of a turbulent flow, in order to mix two or more fluids, gases and pulverulent bodies effectively. The inline static mixer plays the three roles of dividing, direction- reversing and mixing by dividing the flow of fluids, reversing its direction and converting it during the transmission in a tube, and thereby achieves a fine mixing. Therefore, using an inline static mixer 108 can help improve the productivity because while attaining better mixing effects, it makes the management of the whole mixing process easier through the simplification, continuation, and reduction in time together with cutting back the production costs (e.g., by saving energy). And the effect can be achieved no matter where the inline static mixer is attached.

[71] By adopting the inline static mixer as mentioned above, the method of cleaning a substrate according to the present invention can clean the substrate more effectively by dispensing an azeotropic mixture to the surface of the substrate while maintaining the compositional ratio of the azeotropic mixture of the deionized water and isopropyl alcohol to be constant without regard to the lapse of time.

[72] The above descriptions on the examples are provided so that those skilled in the art could freely practice the present invention. Various modifications to those examples would be apparent to those skilled in the art, and general principles defined herein may be applicable to other examples without going beyond the idea and scope of the present invention. Hence, the present invention is not limited to the examples disclosed herein, but encompasses a widest scope of equivalencies which are in accordance with the principles and novel features disclosed in the present invention.

Claims

[1] A method for cleaning a substrate, said method comprising the steps of: rotating the substrate; dispensing a cleaning liquid to the surface of the rotating substrate; producing an azeotropic mixture by mixing a deionized (DI) water with a liquid whose surface tension is lower than the surface tension of water; dispensing the azeotropic mixture to the surface of the rotating substrate; and finishing drying by providing the substrate with an inert gas (N2, Ar, Ne, etc. ) , wherein the boiling point of the azeotropic mixture is lower than the boliling point of the deionized water and the liquid whose surface tension is lower than the surface tension of water.

[2] The method of claim 1, wherein the liquid whose surface tension is lower than the surface tension of water is Protic Polar Solvents, especially

CnH2n+lOH(n=l~10).

[3] The method of claim 1, wherein the azeotropic mixture is provided by an in-line static mixer.

[4] The method of claim 1, further comprising providing a nitrogen gas from the upper part of the chanter around the circumference of inner space of the charrber where the cleaning the substrate is performed to form a film of the nitrogen gas.

[5] The method of any one of claims 1 to 4, further comprising striking the center of the rorating substrate with a gas after dispensing the azeotropic mixture.

[6] The method of claim 5, wherein the gas is nitrogen.

[7] The method of any one of claims 1 to 4 further including dispensing the vapor of liquid whose surface tension is lower than the surface tension of water to the rotating substrate, after dispensing the azeotropic mixture. [8] The method of claim 7, wherein the liquid whose surface tension is lower than the surface tension of water is isopropyl alcohol. [9] The method of any one of claims 1 to 4 further including dispensing a gas and the vapor of the liquid whose surface tension is lower than the surface tension of water to the rotating substrate, after dispensing the azeotropic mixture. [10] The method of claim 9, wherein the gas is nitrogen and the liquid whose surface tension is lower than the surface tension of water is Protic Polar Solvents, especially CnH2n+lOH(n=l~10).