JP2000173965A - Cleaning method by high-speed shear flow - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently remove contaminations attaching to the surface of a substance to be cleaned, by generating a shear flow of a constant velocity gradient or more having a controlled range and distribution along the surface of the substance. SOLUTION: This cleaning method peels minute contaminations attaching to the surface of a material to be cleaned 2, cutting their bonding with the material surface, and prevents the removed contaminations from reattaching to the surface of the material by a high-speed shear flow, by arranging the material 2 and a high-pressure nozzle 1 at a specified interval in a processing bath containing mainly super pure water, and generating a high-speed shear flow of the pure water jetted from the high-pressure nozzle in the vicinity of the surface of the substance.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for producing a high-speed shear flow of ultrapure water, particularly in the vicinity of the surface of an object to be cleaned such as a semiconductor wafer.
The present invention relates to a cleaning method using a high-speed shear flow capable of completely removing fine foreign matter attached to the surface of an object to be cleaned.

[0002]

2. Description of the Related Art Conventionally, there are chemical cleaning and physical cleaning as a cleaning method for removing foreign substances adhering to the surface of an object to be cleaned. In particular, since electronic circuits having a submicron order fine pattern are formed on the surface of a semiconductor wafer, metal contamination on the surface has a great effect on device performance, deteriorates yield, and hinders cost reduction. become.
Therefore, various cleaning methods have been proposed and put to practical use.

[0003] Typical examples of chemical cleaning include cleaning with acid or hydrogen fluoride, and chlorofluorocarbon cleaning which is a problem due to destruction of the ozone layer. In addition, typical examples of physical cleaning include:
Ultrasonic cleaning in ultrapure water, a method of cooling or heating the object to be cleaned, and shrinking and expanding the attached fine particles to peel off from the surface of the object to be cleaned, and the like.

However, foreign substances are fine particles, foreign atoms, organic
In the case of inorganic molecules, ions, etc., it is necessary to remove the foreign particles firmly adhered by the interaction (a kind of chemical bond) at the interface of the object to be cleaned without damaging the surface of the object to be cleaned. It is not easy and conventional cleaning methods are not effective. That is, in the case of chemical cleaning, the surface of the object to be cleaned is corroded by the cleaning liquid, and in the case of physical cleaning, the surface of the object to be cleaned is damaged. In addition, the foreign matter once removed from the surface of the object to be cleaned may reattach to the surface, which is extremely difficult.

[0005]

SUMMARY OF THE INVENTION The inventor of the present invention requires a shear flow having a predetermined strength or more on a surface of an object to be cleaned in order to remove fine particles attached to the surface of the object to be cleaned with chemical bonding. That is, the need for a shear flow above a certain velocity gradient was theoretically predicted and confirmed in experiments.

[0006] In view of the above situation, the present invention seeks to solve the problem by generating a shear flow having a controlled range and distribution over a predetermined velocity gradient along the surface of the object to be cleaned. The above-mentioned problems can be solved at once, and fine foreign substances that are difficult to remove by ultrasonic cleaning in water can be completely removed, and the removed foreign substances re-attach to the surface of the object to be cleaned. Another object of the present invention is to provide a high-speed shearing flow cleaning method capable of preventing cleaning and performing cleaning with high efficiency.

[0007]

According to the present invention, in order to solve the above-mentioned problems, an object to be cleaned and a high-pressure nozzle are arranged at a predetermined interval in a processing tank mainly composed of ultrapure water. By generating a high-speed shear flow of ultrapure water sprayed from a high-pressure nozzle near the surface of the object to be cleaned, fine foreign matter adhering to the surface of the object to be cleaned is cut off by bonding to the surface of the object to be cleaned. At the same time, a high-speed shearing flow cleaning method has been established which prevents the removed foreign matter from re-adhering to the surface of the object to be cleaned by the high-speed shearing flow.

Here, the cleaning effect can be further enhanced by using a cleaning liquid in which a chemical solution that does not adhere to the cleaning object is mixed with ultrapure water and spraying the cleaning liquid from the high-pressure nozzle onto the surface of the cleaning object. . When the high pressure nozzle has a circular hole, point cleaning can be performed. When the high pressure nozzle has a slit hole, line cleaning can be performed, and the surface of the object to be cleaned can be uniformly cleaned over a wide area.

In the cleaning method of the present invention, the recovery means is disposed on the downstream side of the high-speed shear flow generated by the high-pressure nozzle, and the ultrapure water containing foreign matters is recovered to prevent re-adhesion. Especially preferred for.

[0010]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, in order to remove fine particles adhering to a surface of an object to be cleaned along with a chemical bond, a shear flow intensity (velocity gradient) is required on the surface of the object to be cleaned. Or estimated. When ZrO ₂ fine particles having a particle size of 0.1 μm are adsorbed on the Si (100) surface in ultrapure water, and a shear flow of ultrapure water of various strengths acts on this surface, the fine particles are removed from the Si surface. The state of removal was observed with an optical microscope. As a result, it was found that when the velocity gradient exceeded about 5 m / sec · μm, effective removal of fine particles proceeded. From this result, it was found that the washing requires a shear flow at a speed gradient or higher, but the lower limit is expected to vary depending on the material of the object to be washed and the type and particle size of the attached fine particles.

According to the present invention, a high-pressure nozzle is used to spray ultrapure water or a cleaning liquid obtained by mixing a chemical solution not adhering to an object to be cleaned with ultrapure water onto the surface to be cleaned of the object to be cleaned, thereby forming a shear flow along the surface to be cleaned. The cleaning is performed by cutting off the chemical bond between the attached fine particles and the atoms on the surface of the object to be cleaned and removing the attached fine particles from the surface of the object to be cleaned. Then, the flow of the ultrapure water or the cleaning liquid jetted from the high-pressure nozzle was calculated in the vicinity of immediately below the nozzle by numerical calculation using a fluid analysis model.

In the analysis model, the nozzle is axially symmetrical at right angles to the surface of the object to be cleaned, and Navier's
Stokes equation of motion was solved numerically by the difference method. The calculation is as follows: the hole diameter of the nozzle is 0.1 mmφ, the outer diameter is 2 m
mφ, and the gap between the nozzle tip and the surface of the object to be cleaned is 1
mm and 2 mm. The supply pressure of the fluid to the nozzle was 1000 atm. At each gap, a pressure distribution, a flow distribution in a nozzle hole direction (Z-axis direction) and a radial direction (R direction) were obtained. FIG. 1 shows the results when the gap is 1 mm, and FIG. 2 shows the results when the gap is 2 mm.

From this calculation result, it is understood that the pressure loss due to the viscosity of the fluid in the analysis region is about 50 atm. At the inflow section, a flow (about 450 m / sec) in the direction of the nozzle hole corresponding to a dynamic pressure of about 950 atm is generated (see FIG. 1 (a)). The vehicle decelerates after traveling almost straight to about 75 μm from the object surface. At that time, the dynamic pressure is converted into a static pressure near the surface of the object to be cleaned, and after a static pressure of about 950 atm is generated (see FIG. 1 (b)), the dynamic pressure is converted back to the dynamic pressure as a radial flow. (Figure 1
(c)). The radial flow occurs in a very thin layer along the surface of the object to be cleaned (approximately 2 mm from the surface of the object to be cleaned).
(In the range of 5 μm), it has been found that the shear flow on the surface of the object to be cleaned required for cleaning can be generated very effectively. In the case of a gap of 1 mm and 2 mm,
Almost the same flow occurs, which indicates that the gap control is extremely easy. In these conditions,
Even when the gap is 1 mm or 2 mm, the maximum velocity gradient on the surface of the object to be cleaned is about 100 m / sec · μm.

Next, the details of the present invention will be further described with reference to the accompanying drawings. 3 and 4 show a conceptual structure of the high-pressure nozzle, in which a cleaning liquid or ultrapure water is jetted from the tip of the high-pressure nozzle 1 to create a predetermined shear flow on the surface of the article 2 to be cleaned. Here, when only ultrapure water is ejected from the high-pressure nozzle 1, a cleaning liquid in which ultrapure water and a chemical solution are mixed is supplied.

FIG. 3 shows a structure in which ultrapure water is jetted from the jet port 3 of the high-pressure nozzle 1. FIG. 3 (a) shows a vertical direction in which the jet port 3 is oriented at right angles to the surface of the article 2 to be cleaned. FIG. 3B shows an oblique incidence type in which the direction of the ejection port 3 is inclined with respect to the surface of the object 2 to be cleaned. Here, when the ejection port 3 is a circular hole, it is possible to clean the entire surface of the cleaning object 2 by continuously forming point-like cleaning marks formed in a minute area on the cleaning surface, In particular, cleaning can be performed intensively in a portion where a large amount of foreign matter is attached, and when the jet port 3 is a slit hole, linear cleaning can be performed on the cleaning surface, and the cleaning target 2 having a large area can be cleaned. The surface can be uniformly cleaned in a short time.

Further, ultrapure water or a cleaning liquid obtained by mixing ultrapure water and a chemical liquid is jetted from the jet port 3 of the high-pressure nozzle 1 onto the surface of the object 2 to be cleaned, and the removed foreign substances are put on the flow of the ultrapure water. It is desirable that the foreign matter be immediately and efficiently collected before re-adhering to the surface of the cleaning object 2. This conceptual diagram is shown in FIG. FIG. 4 (a) shows a recovery means in which a ring-shaped recovery plate 4 is arranged at a fixed interval around the tip of a high-pressure nozzle 1 of a vertical incidence type, and is disposed between the high-pressure nozzle 1 and the recovery plate 4. Ultrapure water or cleaning liquid is allowed to flow. Also,
FIG. 4B shows a collecting means in which a collecting plate 4 is partially disposed at a certain interval downstream of the ultrapure water or the cleaning liquid of the oblique incidence type high-pressure nozzle 1.

Next, a system for supplying high-pressure ultrapure water to the high-pressure nozzle 1 will be briefly described with reference to FIG. A plunger pump is used as the pressure generating pump 10. In addition, if the ultrapure water for cleaning is directly pressurized by a pump, contamination of particles and the like generated in sliding parts in the pump becomes a problem. Therefore, the ultrapure water for cleaning is passed through a diaphragm or blow made of PTFE or SUS. The system which pressurizes water is adopted. Pressurizing parts 11 and 12 of ultrapure water are 2
The city water is pressurized to a predetermined pressure by one plunger pump 10 and the pressure is
It branches into a flow path and is connected to the pressurizing units 11 and 12 via valves 14 and 15, respectively. On the other hand, the ultrapure water for cleaning is connected from the ultrapure water supply device 16 to the pressurizing units 11 and 12 via valves 17 and 18, respectively. And
Each of the pressurizing parts 11 and 12 has a PTFE or SUS inside.
City water and ultrapure water are separated by diaphragms 19 and 20 made of
Ultrapure water is pressurized by the pressure of city water through the diaphragms 19 and 20, and the ultrapure water pressurized by the pressurizing units 11 and 12 is supplied to the valve 2.
The two are merged via the nozzles 1 and 22 and supplied to the high-pressure nozzle 1. A drain valve 23 is provided between the valve 14 and the pressurizing unit 11, and a drain valve 24 is provided between the valve 15 and the pressurizing unit 12. All these valves employ electromagnetic valves and can be opened and closed by a computer.

The operation of the high-pressure ultrapure water supply system is as follows. First, the ultrapure water supply device 16 produces ultrapure water having substantially the same pressure as the atmospheric pressure. Since it is difficult to continuously pressurize the ultrapure water, in the above-described system, the ultrapure water is alternately pressurized from atmospheric pressure to a predetermined pressure by the two pressurizing units 11 and 12, and the high-pressure nozzle 1 is pressurized. , High-pressure ultrapure water is continuously supplied. That is, in the system of one pressurizing unit 11, the valves 14 and 21 are opened, and the valves 17 and 23 are closed to supply pressurized city water into the pressurizing unit 11, and the diaphragm 19 in the pressurizing unit 11 is supplied. The pressurized ultrapure water is supplied to the high-pressure nozzle 1 through the
2 is closed, valves 18 and 24 are opened, and ultrapure water is supplied from the ultrapure water supply device 16 into the pressurizing unit 12 while draining city water from the pressurizing unit 12. Here, after opening the valve 24 to return the inside of the pressurizing section 12 to the atmospheric pressure, the valve 18 is opened so that the ultrapure water supply device 16 does not break down under pressure. Next, the valves 18 and 24 are closed, the valve 15 is opened to supply the pressurized city water into the pressurizing section 12, and the ultrapure water is pressurized to reach the supply pressure. , 1
4, the valve 23 is opened to drain the city water in the pressurizing unit 11 and the inside of the pressurizing unit 11 is brought to the atmospheric pressure. From 16, ultrapure water is supplied into the pressurizing section 11. Thereafter, this is a repetition, and the opening / closing timing of each valve is controlled by a computer, and high-pressure ultrapure water is continuously supplied to the high-pressure nozzle 1.
It is supplied to.

Next, FIG. 6 shows an example of a cleaning apparatus employing the high-speed shear flow cleaning method of the present invention. The cleaning device 100 has a cleaning tank 101 filled with ultrapure water at an upper part, and a driving mechanism unit 1 having a built-in XY-θ driving system at a lower part.
The cleaning tank 101 and the drive mechanism 102 are separated from each other by a partition wall 103 made of a non-magnetic material so that the inside of the cleaning tank 101 is not contaminated by particles or the like generated from a sliding portion of the drive system. In the washing tank 101, a high-pressure nozzle 1 connected to a Z-axis driving system 104 is provided at an upper part, and a sample table 105 provided horizontally and rotatably by ultrapure water static pressure support is provided at a lower part. The object to be cleaned 2 is fixed and is opposed to the high-pressure nozzle 1. The drive mechanism 102 includes an X-axis drive system 106 and a Y-axis drive system 10.
7 has an XY table 108 which is provided so as to be horizontally movable, and the XY table 108 is provided with a θ-axis drive system 109. The permanent magnet 110 fixed to the lower surface of the sample stage 105 and the permanent magnet 1 fixed to the θ-axis drive system 109
11 are opposed to each other via the partition 103 and are magnetically coupled to each other, and the displacement by the XY-θ drive system is changed by the permanent magnet 111,
The light is transmitted to the sample stage 105 via the permanent magnet 110.
As described above, the high-pressure nozzle 1 and the object to be cleaned 2 can be relatively displaced in the XYZ-θ-axis directions by the respective driving systems, and the object to be cleaned 2 is formed into a predetermined shape by the high-pressure nozzle 1. It can be washed.

In the cleaning apparatus 100, the same amount of ultrapure water injected from the high-pressure nozzle 1 and ultrapure water flowing into the cleaning tank 101 from the ultrapure water static pressure support of the sample stage 105 is used. A system is provided for separating ultrapure water from the cleaning tank 101 by liquid phase separation, and the extracted ultrapure water is sent to the static pressure support unit again after the impurity concentration is reduced to the limit by a purification device. This system makes it possible to remove even trace amounts of metal ions and the like eluted from the structure in the cleaning tank 101.

[0021]

According to the high-speed shear flow cleaning method of the present invention as described above, it is possible to completely remove atomic-level foreign substances which are difficult to remove by ultrasonic cleaning in water or the like. In addition, foreign substances can be removed to prevent foreign substances from re-adhering to the surface of the object to be cleaned, cleaning can be performed with high efficiency, and a predetermined flow can be generated only in a necessary area. Since it is possible to perform cleaning with a sufficiently large gap, gap control for stabilizing the flow is extremely easy and stable against disturbance such as mixing of coarse particles.

[Brief description of the drawings]

FIG. 1 shows a simulation result of a pressure and a velocity component when ultrapure water is jetted from a high-pressure nozzle to a surface of an object to be cleaned at a right angle with a gap of 1 mm, and FIG.
(b) shows the pressure distribution, and (c) shows the velocity component in the R direction.

FIG. 2 shows a simulation result of pressure and velocity components when ultrapure water is jetted from a high-pressure nozzle at a right angle to the surface of an object to be cleaned with a gap of 2 mm.
(b) shows the pressure distribution, and (c) shows the velocity component in the R direction.

FIGS. 3A and 3B are simplified cross-sectional views showing the concept of a high-pressure nozzle that directly injects a cleaning liquid. FIG. 3A shows a vertical incidence type, and FIG. 3B shows an oblique incidence type.

FIG. 4 is a simplified cross-sectional view showing a nozzle structure having a function of recovering ultrapure water or a cleaning liquid after cleaning, and FIG. 4 (a) is a structure in which a recovery plate is arranged around a vertical incidence type high pressure nozzle. (B) shows a structure in which a collecting plate is disposed downstream of the oblique incidence type high pressure nozzle.

FIG. 5 is a simplified piping diagram of a high-pressure ultrapure water supply system.

FIG. 6 is a partially cutaway perspective view showing a cleaning apparatus employing the method of the present invention.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 high-pressure nozzle 2 object to be washed 3 spout 4 recovery plate (recovery means) 10 pump 11, 12 pressurizing unit 13 regulator 14, 15, 17, 18, 21, 22, 23, 24 valve 16 ultrapure water supply device 19, 20 diaphragm 100 cleaning apparatus 101 cleaning tank 102 drive mechanism section 103 partition wall 104 Z-axis drive system 105 sample table 106 X-axis drive system 107 Y-axis drive system 108 XY table 109 θ-axis drive system 110, 111 permanent magnet

Claims (5)

[Claims] An object to be cleaned and a high-pressure nozzle are disposed at a predetermined interval in a processing tank mainly composed of ultrapure water, and an ultrapure nozzle sprayed from a high-pressure nozzle near a surface of the object to be cleaned. By generating a high-speed shear flow of water, fine foreign substances adhering to the surface of the object to be cleaned are cut off by bonding to the surface of the object to be cleaned, and the removed foreign objects are removed by the flow of the high-speed shear flow. A cleaning method using high-speed shear flow, wherein re-adhesion to a surface is prevented. 2. The cleaning method using a high-speed shear flow according to claim 1, wherein a cleaning solution obtained by mixing a chemical solution that does not adhere to the object to be cleaned with ultrapure water is used, and the cleaning solution is sprayed from a high-pressure nozzle onto the surface of the object to be cleaned. 3. The cleaning method using a high-speed shear flow according to claim 1, wherein the ejection port of the high-pressure nozzle is a circular hole. 4. The cleaning method according to claim 1, wherein the ejection port of the high-pressure nozzle is a slit hole. 5. The cleaning method using a high-speed shear flow according to claim 1, wherein a recovery means is disposed downstream of the high-speed shear flow generated by the high-pressure nozzle to recover the cleaning liquid.