JP2010129590A - Substrate cleaning method and electrostatic charging suppression effect monitor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To easily and accurately monitor electrostatic charging suppression effect by a cleaning liquid when a substrate is cleaned with the liquid having higher conductivity than pure water so as to prevent electrostatic charging of the substrate. <P>SOLUTION: A substrate cleaning method includes portioning out part of the cleaning liquid, bringing it into contact with a model piece of the same material with the substrate to be cleaned, and measuring the electrostatic potential of the model piece to monitor an electrostatic charging state of the substrate. An electrostatic charging suppression effect monitor includes: a liquid contacting means for bringing the cleaning liquid into contact with the model piece of the same material with the substrate to be cleaned; and an electrostatic potential measuring means for measuring the electrostatic potential of the model piece brought into contact with the cleaning liquid by the liquid contacting means. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a method for cleaning a substrate that requires a high degree of cleanness, such as a silicon wafer for semiconductors, a glass substrate for flat panel displays, and a fluororesin-coated substrate, and a monitor for monitoring the charge suppression effect of liquid for substrate cleaning.

  Conventionally, ultrapure water or the like has been used for cleaning electronic component substrates. However, when ultrapure water is used for cleaning, because of its high specific resistance, the substrate is subject to friction due to friction with the substrate to be cleaned and nozzles. The cleaning substrate may be charged. When the substrate is charged, if the substrate has a fine circuit pattern, the circuit may be destroyed. In addition, dust and particles easily adhere to the substrate due to the generation of static electricity.

  In order to prevent this, conventionally, a very small amount of conductivity imparting substance, for example, water in which carbon dioxide gas is dissolved to increase conductivity, so-called carbonated water, is used for substrate cleaning (for example, patented water). Reference 1). The carbonic acid concentration of the carbonated water is usually 1 to 50 mg / L, which is an extremely low concentration, for the purpose of imparting conductivity.

  When cleaning a substrate using a liquid having higher conductivity than ultrapure water such as carbonated water (hereinafter sometimes referred to as “cleaning liquid”), the antistatic effect of this liquid on the substrate was confirmed, It is important to reflect the results in the cleaning conditions. For example, the higher the carbonate concentration of carbonated water used for cleaning, the higher the conductivity, and thus the higher the charge-suppressing effect. However, increasing the carbonate concentration of carbonated water used leads to an increase in the amount of carbonate consumption and the cleaning cost. This is not preferable. Therefore, it is desirable to perform washing using a low concentration carbonated water after obtaining a sufficient charge suppression effect. To this end, the carbonate concentration of carbonated water is increased by confirming the charge suppression effect of carbonated water. It is desirable to control.

Conventionally, the following method has been adopted as a method for confirming the effect of suppressing charging by a cleaning liquid such as carbonated water.
(1) Measure the conductivity or specific resistance (reciprocal of conductivity) of the liquid used for cleaning, and estimate the charge-suppressing effect from its conductivity.
(2) Directly measure the electrostatic potential of the substrate being cleaned by the liquid, that is, the substrate being cleaned.
JP 11-26412 A

  The method based on the measured conductivity or specific resistance value of the cleaning liquid indirectly estimates the charge suppression effect from the conductivity of the cleaning liquid, and does not necessarily reflect the actual charge suppression effect. . In this case, for example, in cleaning using carbonated water, it is common to control the specific resistance value of carbonated water to about 0.2 MΩ · cm. The concentration was about 15 mg / L, and it was determined that carbonated water having a lower carbonic acid concentration had no charge-suppressing effect, and the carbonic acid concentration of cleaning carbonated water could not be further reduced.

  Although the method of directly measuring the electrostatic potential of the substrate being cleaned is a reliable method, it is not possible to measure the electrostatic potential of the surface of the substrate to be cleaned in a system that is frequently operated, such as loading and unloading the substrate. It is difficult in practice.

  For this reason, a highly practical technique that can accurately confirm the effect of suppressing the charge on the cleaning substrate by a simple method is desired.

  The present invention has been made in view of the above-described conventional situation, and provides a substrate cleaning method and a charge suppression effect monitoring monitor capable of easily and accurately confirming the charge suppression effect of a cleaning substrate by a cleaning liquid. With the goal.

  As a result of intensive studies to solve the above problems, the present inventors brought a cleaning liquid into contact with a model piece made of the same material as that of the substrate to be cleaned, and an electrostatic potential generated by the contact between the model piece and the cleaning liquid was increased. By measuring, it was found that the charge suppression effect of the liquid can be confirmed easily and accurately, and the present invention has been completed based on this finding.

  The substrate cleaning method of the present invention (Claim 1) is a substrate cleaning method in which a substrate is cleaned with a liquid having higher conductivity than ultrapure water. The charging state of the substrate is monitored by contacting with a piece and measuring the electrostatic potential of the model piece.

  According to a second aspect of the present invention, in the substrate cleaning method of the first aspect, the liquid is carbonated water.

  According to a third aspect of the present invention, there is provided a monitoring monitor for electrification suppression effect, comprising: a liquid contact means for contacting a liquid having higher conductivity than ultrapure water with a model piece made of the same material as the substrate; And an electrostatic potential measuring means for measuring the electrostatic potential of the model piece in contact with the model piece.

  According to a fourth aspect of the present invention, there is provided the monitoring monitor for charging suppression effect according to the third aspect, wherein the model piece is installed with an inclined plate surface, and the liquid contact means is an intermediate portion in the inclination direction of the plate surface of the model piece. The electrostatic potential measuring means is an electrostatic electrometer installed facing the upper side in the inclined direction with respect to the intermediate portion of the substrate. To do.

  According to the present invention, the cleaning liquid is brought into contact with the model piece made of the same material as the cleaning substrate, and the electrostatic potential generated by the contact between the model piece and the cleaning liquid is measured. Can be confirmed easily and accurately.

  For this reason, it is possible to perform effective substrate cleaning by monitoring the charging suppression effect by the cleaning liquid and reflecting the result in the cleaning conditions. For example, the concentration of the conductivity-imparting substance in the cleaning liquid to be used can be reduced within a range in which the charge suppressing effect can be sufficiently obtained, and the cleaning cost can be reduced.

  In the present invention, carbonated water is effective as the cleaning liquid (claim 2). Further, in the monitor for monitoring the effect of suppressing electrification of the present invention, specifically, the model piece is installed with the plate surface inclined, and the cleaning liquid is poured toward the middle of the inclination direction of the plate surface of the model piece. It is preferable that the liquid contact means is provided so as to be applied, and the electrostatic potential measuring means is provided facing the upper side in the inclination direction from the middle part of the model piece. The position measurement can be performed (claim 4).

  Embodiments of a substrate cleaning method and a charge suppression effect monitoring monitor according to the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a schematic diagram showing an embodiment of a monitoring monitor for electrification suppression effect of the present invention. In the figure, 1 is a housing, 2 is a model piece, 3 is an electrostatic potential meter, 4 is a liquid supply pipe for cleaning, Reference numeral 5 denotes a drain pipe.

  In FIG. 1, a plate-shaped model piece 2 is installed in the housing 1 with its plate surface 2 </ b> A inclined with respect to a horizontal plane, and the water supply pipe 4 is in the middle of the inclined plate surface 2 </ b> A of the model piece 2. The cleaning liquid is inserted into the housing 1 so that the cleaning liquid can be poured toward the portion (hereinafter, the position on the plate surface 2A of the model piece 2 where the cleaning liquid is poured) Sometimes referred to as “point”.)

  In addition, the electrostatic electrometer 3 is installed facing the upper side in the tilt direction from the liquid injection point.

  With this charge suppression effect monitoring monitor, a part of the cleaning liquid is collected during the substrate cleaning operation or prior to the substrate cleaning, and poured into the model piece 2 from the pipe 4 so that the cleaning liquid is By measuring the electrostatic potential generated in the model piece 2 by contacting and rubbing the model piece 2 with the electrostatic potentiometer 3 provided in the vicinity of the injection point, the charging suppression effect of the cleaning liquid to be used can be reduced. Can be confirmed.

  That is, if the measured value by the electrostatic potentiometer 3 is −10 to +10 kV and almost 0 kV, it can be confirmed that the cleaning liquid has a sufficient charge suppressing effect and is suitable for substrate cleaning. Further, when the measured value of the electrostatic electrometer 3 deviates significantly from, for example, −0.5 kV or less and 0 kV, it is evaluated that the cleaning liquid does not have sufficient charge suppression effect and is inappropriate for substrate cleaning. can do.

  The cleaning liquid poured onto the plate surface 2 </ b> A of the model piece 2 flows down the inclined plate surface 2 </ b> A of the model piece 2 and is discharged from the pipe 5.

  The substrate to be cleaned in the present invention is a silicon wafer for semiconductor, a glass substrate for flat panel display, a fluororesin coated substrate or the like, and the material thereof is silicon, glass, PFA (perfluoroalkoxy fluororesin), PTFE (polyethylene). There are no particular restrictions on the substrate coated with a fluororesin such as (tetrafluoroethylene), PFA, topcoat or the like.

  The model piece 2 is made of the same material as the substrate to be cleaned, and more specifically, is made of the same material as the surface to be cleaned of the substrate to be cleaned. Therefore, the substrate to be cleaned is a surface such as a fluororesin coated substrate. In the case of having a coating layer, the model piece does not necessarily have to be coated with a fluororesin in the same manner as the substrate, and may be a plate-shaped piece made of only a fluororesin that forms the coating layer.

  The size of the model piece 2 is not particularly limited, but the monitor of the present invention is not excessively large, and the dimensions of the plate surface are required to ensure handling and strength and to prevent measurement errors. Is preferably a plate having a thickness of about 30 to 100 mm × 30 to 100 mm and a thickness of about 3 to 5 mm.

  As shown in FIG. 1, the model piece 2 is provided with the plate surface 2 </ b> A inclined with respect to a horizontal plane. The inclination angle θ is preferably 20 to 60 °, particularly preferably about 30 to 50 °. Whether the tilt angle θ is too large or too small, the amount of electrostatic potential generated by the friction between the poured cleaning liquid and the plate surface of the model piece is not enough, There are cases where accurate electrostatic potential measurement cannot be performed due to insufficient simulation.

  Moreover, it is preferable that the pouring point of the cleaning liquid is approximately in the vicinity of the center of the inclined plate surface 2A of the model piece 2.

  The cleaning liquid is a liquid having higher conductivity than ultrapure water, and is usually prepared by dissolving a substance for imparting conductivity to ultrapure water. This conductivity imparting substance is preferably one that does not remain on the substrate after cleaning, and carbon dioxide gas is optimal. That is, carbonated water is preferable as the cleaning liquid.

  The carbonate concentration of carbonated water used for washing is usually about 1 to 50 mg / L, and the specific resistance is about 0.1 to 0.3 MΩ · cm. According to the present invention, the charge suppression effect of carbonated water is confirmed. Thus, after obtaining the required charge suppression effect, the carbonate concentration of carbonated water can be controlled to a sufficiently low value, for example, 1 to 5 mg / L, and the cleaning cost can be reduced by reducing the amount of carbon dioxide used. Can be reduced.

  There is no particular limitation on the rate at which the cleaning liquid is injected onto the model plate surface. However, even if the injection rate is too high or too low, electrostatic electricity due to friction between the cleaning liquid and the plate surface of the model piece can be obtained. Since the amount of generated potential is not sufficient, and the actual substrate cleaning situation cannot be sufficiently simulated, accurate electrostatic potential measurement may not be performed, so 0.1 to 1 L / min. It is preferable to set the degree.

  As the electrostatic electrometer 3, a commercially available electrostatic electrometer can be used, and the use conditions may be in accordance with the specifications of the electrostatic electrometer used.

  The material of the housing 1 is preferably a substrate that is in contact with the substrate by substrate cleaning, and usually PPS (polyphenylene sulfide), PEEK (polyetheretherketone), PFA, PE (polyethylene) or the like is used.

  Hereinafter, the present invention will be described more specifically with reference to examples.

<Example 1>
Using the apparatus shown in FIG. 1, the cleaning liquid was switched from ultrapure water to carbonated water, and the electrostatic potential of the model piece 2 was measured. The results are shown in FIG.

The materials, measuring equipment, conditions, etc. used in this example are as follows.
Housing material: PE
Model piece: PFA plate of 50 mm x 50 mm x 3 mm thickness Tilt angle of model piece: 45 °
Electrostatic potential meter: “STATIRON-D23” manufactured by Sicid Electrostatic Co., Ltd.
Supply amount of cleaning liquid: 0.5 L / min
Carbonate concentration in carbonated water: 1 to 5 mg / L (specific resistance value: 0.5 to 1.1 MΩ · cm)
Specific resistance value of ultrapure water: 18.2 MΩ · cm
Injection point: Near the center of the model piece

  The following is clear from FIG.

  Since ultrapure water has a high specific resistance value, charging occurs when it comes into contact with the model piece. Therefore, when the ultrapure water is supplied, the measured value of the electrostatic potential of the model piece is −1.0 kV or less and the model piece is charged. . On the other hand, carbonated water has electrical conductivity and does not easily charge the model piece. Therefore, when the water supply is switched from ultrapure water to carbonated water, the measured value of the electrostatic potential of the model piece is stabilized at approximately 0 kV, It was confirmed that no charging occurred.

As described above, in the conventional substrate cleaning with carbonated water, when the conductivity is confirmed from the specific resistance value of carbonated water and used for cleaning, carbonated water having a specific resistance value of about 0.2 MΩ · cm is required. In this case, the carbonate concentration of carbonated water is about 15 mg / L.
On the other hand, from the results of the above examples, it was confirmed that a sufficient charge suppression effect could be obtained even with carbonated water having a carbonate concentration of 1 to 5 mg / L. It can be seen that it can be reduced to about 1/3 or less.

It is a schematic diagram which shows embodiment of the charging suppression effect monitoring monitor of this invention. 3 is a graph showing the results of Example 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Case 2 Model piece 3 Electrostatic potential meter 4 Liquid supply pipe for washing 5 Drain pipe

Claims (4)

In a substrate cleaning method for cleaning a substrate with a liquid having higher conductivity than ultrapure water,
Substrate cleaning characterized in that a part of the liquid is separated, brought into contact with a model piece made of the same material as the substrate, and an electrostatic potential of the model piece is measured to monitor the charging state of the substrate. Method.   The substrate cleaning method according to claim 1, wherein the liquid is carbonated water. A liquid contact means for cleaning a substrate and contacting a liquid having higher conductivity than ultrapure water with a model piece of the same material as the substrate;
An electrification suppression effect monitoring monitor comprising: an electrostatic potential measurement unit that measures an electrostatic potential of a model piece that is in contact with the liquid by the liquid contact unit. In claim 3, the model piece is installed with the plate surface inclined.
The liquid contact means is provided so as to pour the liquid toward an intermediate portion in the inclination direction of the plate surface of the model piece,
The electrostatic charge measuring monitor according to claim 1, wherein the electrostatic potential measuring means is an electrostatic potential meter that is installed facing the upper side in the tilt direction with respect to the middle portion of the model piece.

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