JPH07201795A - Cleaning method - Google Patents

Abstract

PURPOSE:To provide a cleaning method which brings no contamination from a cleaning means nor damage of a substrate because the substrate and ice particles have a fluid intervene CONSTITUTION:A substrate 3 is dipped in a liquid such as a liquid organic compound having a solidification point lower than the solidification point of water and mixed with ice particles 26, so that the ice particles 26 are made to collide with the substrate 3 at a temperature of under the solidification point of water.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for cleaning a substrate, and more specifically, a substrate for an electronic device, a semiconductor wafer, a liquid crystal substrate, a photomask,
The present invention relates to a method for cleaning dust, particles, foreign matters, etc. (hereinafter referred to as “dust”) such as particles and films attached to a glass substrate or the like.

[0002]

2. Description of the Related Art Dust having a diameter of about 0.2 to 10 μm adhered to a substrate as described above cannot be completely removed by ultrasonic washing with a frequency of about 27 to 40 kHz or strong agitation. It was generally practiced to remove dust by rubbing with. Currently 100 diameter
The method of rubbing the surface of the substrate with a brush scrubber having a brush of molybdenum, nylon, etc. of up to 300 μm to remove the attached dust is the mainstream. Specifically, as shown in FIG. 7, the brush 4 is moved in the diametrical direction of the substrate 3 while rotating the substrate 3 held on the rotary table 1 through the O-ring 2 and vacuum-adsorbed to move the substrate surface to the surface. The pure water 6 is jetted from the nozzle 5 which is rubbed and simultaneously moves integrally with the brush 4, and the pure water 6 is jetted from the nozzle 7 provided separately to wash away the dust. In addition, 8 is a holding rod which incorporates the rotating shaft of the brush 4, and 9 is a valve.

By the way, de-ionized water = D
The ultrasonic vibration applied to the substrate immersed in (IW) may destroy the device on the substrate due to the cavity generated in the liquid even if the intensity is about 5 cabins. No such cleaning method has been put to practical use for cleaning.

In recent years, so-called ice scrubber cleaning for cleaning semiconductor devices using fine particle ice produced by freezing pure water has been studied. In this method, fine particles of ice are sprayed onto the surface of the substrate to remove dust.

[0005]

With the recent increase in the degree of integration of semiconductor devices and the like, it has become a problem that the brush becomes a contamination source of the substrate. That is, the surface of a recent IC substrate has a fine pattern of 0.3 to 1.0 μm.
An electronic element pattern, a wiring pattern, etc. are formed in m line and space. These fine electronic element patterns use a high-purity substance that substitutes for the brush in order to prevent contamination due to the friction of the brush. Development is desired.

On the other hand, the ice scrubber system does not cause contamination because the cleaning substance is ice made from pure water, but in order to enhance the cleaning effect, it is necessary to increase the collision energy of the fine ice particles with the substrate. There is a jet of ice particles at high speed using air as a medium. As a result, the device may be damaged.

Therefore, it is an object of the present invention to provide a cleaning method that does not cause contamination from the cleaning means and that does not damage the substrate because the particles of the substrate and the ice mediate the fluid. To do.

[0008]

In order to achieve the above object, the present invention provides a substrate having a freezing point lower than the freezing point of water and immersing in a liquid in which fine particles of ice are mixed. There is provided a substrate cleaning method, which comprises cleaning the substrate by colliding the ice particles with the substrate at the following temperature.

The structure of the present invention will be described in detail below. In the present invention, it is ice fine particles that remove dust from the substrate, and in order to make this ice fine particle form a scrubber system using a liquid instead of the air injection scrubber system, the ice fine particles are mixed with the liquid. ing. Here, as the liquid,
For example, isopropyl alcohol (IPA) (mp = -8
9.5 ° C .; bp = 82.4 ° C.), this is cooled to a range of −5 to −15 ° C., and when ice particles are mixed in an appropriate amount, the ice particles can be dissolved in isopropyl alcohol. It is possible to achieve a state in which solidification does not occur.

Besides isopropyl alcohol, methyl alcohol (mp = −97.78 ° C .; bp = 64.65)
° C), ethyl alcohol (mp = -114.1 ° C; bp
= 78.3 ° C), water 5% by volume balance ethyl alcohol mixed solution (bp = 78.2 ° C), acetone (-94.82)
C .; bp = 56.5.degree. C.), 50% by volume of water, the balance acetone mixed solution and the like can also be used.

The particle size of the ice particles used in the present invention must be selected according to the line and space dimensions of the pattern formed on the substrate. If this particle size is too small, it is difficult to remove large dust, and conversely, if it is too large, the ability to collide with the details of the fine pattern and remove dust decreases. The center particle size of the ice fine particles is preferably 1 to 150 μm.
And more preferably about 10 times the particle size corresponding to the width of the line and space. The ice is preferably pure water frozen. A method for producing fine ice particles using pure water is described in, for example, Applied Physics, Vol. 59, No. 11 (1990), 1509-15.
The method described on page 10 can be used.

The ratio of ice and liquid is appropriately determined so that the cleaning efficiency is high, but it is preferable that the former is 10 to 30% by weight and the latter is the balance.

Next, in order to perform scrubbing cleaning with a liquid mixed with ice particles, it is necessary to make the ice particles collide with the substrate immersed in the mixed liquid. Or agitate: Vibrate or shake the liquid container: Agitate while flowing the liquid: Apply ultrasonic vibration at a frequency that hardly causes cavitation, that is, vibration using megasonics to the liquid: Mixing ice particles The liquid is circulated in the container by a pump: during this circulation, the flow velocity of the liquid is pulsatingly changed or reversed, or the carrier on which the substrate is set is swung up and down or left and right; the wafer surface contains ice. It can be performed by means of kinetic energy generating / applying means such as spraying alcohol with stirring.

In the present invention, when the liquid is not water but substantially a liquid organic compound, it is possible to prevent the substrate from being oxidized, and there is an advantage that a natural oxide film is suppressed as much as possible.

[0015]

The operation of the liquid scrubber cleaning system of the present invention has the following features. (A) Since the substrate is rubbed with ice particles in the liquid, a fluid having a higher viscosity than an ice scrubber as an air medium becomes a shock absorber for collision, and damage to the elements on the substrate surface is reduced. (B) Since the substrate is immersed in the liquid, not only the element formation surface of the substrate but also the back surface is cleaned. As a result, it is possible to prevent contamination due to dust on the back surface. Furthermore, the substrates can be cleaned one by one, or several substrates can be batch processed to increase the throughput. (C) Since the cleaning temperature is 0 ° C. or lower, the organic matter such as the resist film adhered to the substrate is solidified and shrunk to be easily removed. Also, since the vapor pressure of the liquid is low due to the low temperature, there is little risk of fire. (D) When an organic compound other than water, such as alcohol, is used as the liquid, the substrate does not come into contact with water, so that no natural oxide film is formed on the substrate. Even when water and an organic compound are mixed, an increase in the thickness of the natural oxide film can be suppressed. Embodiments of the present invention shown in the drawings will be described below.

[0015]

EXAMPLE A specific example of an apparatus for carrying out the cleaning method according to the present invention will be shown. FIG. 1 shows an apparatus for cleaning the megasonic oscillator 20 by means of energy generating / applying means. In the figure, 1, 2 and 3 are those shown in FIG. In the direction of the arrow, a mixture of ice particles in isopropyl alcohol cooled to −20 ° C. is supplied to the megasonic oscillator 20, where they are sufficiently uniformly mixed by ultrasonic vibration and then passed through the nozzle 25. The substrate 3 is jetted. The ice particles 26 and the water droplets 27 are jetted toward the substrate 3 from the left and right. In addition, it is preferable that the entire apparatus including the members 1, 2, 3, 20, 25, etc. be arranged in a temperature-controlled room.

FIG. 2 shows an embodiment in which a general liquid cleaning apparatus is applied to practice the method of the present invention. Reference numeral 10 is a container for containing and processing the wafer 3, 11 is a receiving tank for temporarily collecting the liquid and ice particles overflowing from the container 10, 12 is a wafer holding jig, and 13 is a holding jig 12 which is detachably held in the container 10. A fixed support arm, 14 is a pump connected to the receiving tank 11 via a pipe 19, 15 is a storage tank, and 17 is a container 10.
It is a supply pipe part for circulating ice particles and liquid.
Reference numeral 25 is a valve that can be switched to discharge the ice particles and the liquid to the drain when the cleaning is completed.

FIG. 3 is a perspective view of a holding jig for the wafer 3. The wafer 3 has two U grooves 12a on the side wall of the holder.
And that it is supported at three points on the bottom support bar 18 (where a U groove (not shown) is formed). A gap is formed between the wafers 3 except at these supporting points, and ice particles rub against the surface of the wafer 3 through the gap and pass through while colliding with the wafer surface. After that, the liquid is evaporated by a method such as blowing nitrogen gas. Alternatively, it is easy to dry the surface of the wafer substrate by using the IPA vapor cleaner which is now widely used.

A method of operating the apparatus shown in FIG. 2 will be described below. In the direction of the arrow, a mixture of isopropyl alcohol and ice fine particles 26 cooled to −20 ° C. is supplied into the container 10 by opening the valve 28. At this time the valves 22 and 2
The valves 4 and 25 are closed and the valves 23 and 29 are opened. Once the vessel 10 has been filled with the ice-liquid mixture,
The valve 28 is closed, the pump 14 is driven to circulate the mixture in the flow path, and when the flow is stable, the wafer 3 is put into the container 10 for cleaning. During cleaning, the temperature of the ice-liquid mixture is adjusted in the storage tank 15, and the ice-liquid mixture is spilled from the container 10 into the receiving tank 11 to circulate in the cleaning system. After a desired time has passed, the wafer 3 is left as it is, the valves 23 and 29 are closed, the valves 22 and 24 are opened, and cleaning with pure water is performed. After completion of washing with water, the wafer 3 is taken out.

FIGS. 4 to 6 show an apparatus for generating and applying cleaning energy by directly attaching the megasonic oscillator 20 to a quartz tank, and the apparatus elements common to FIGS. 1 and 2 have the same reference numerals. Is shown. The megasonic oscillator 20 that is currently used in IC production facilities and that is generally operated at a frequency of 800 kc to 1.4 MHz can be used. By vibrating the liquid, ice particles are generated along with the liquid. The substrate is vibrated so that the ice particles collide with the substrate surface. In this device, the holding portion 21 is made of a material such as a soft rubber that does not scratch the wafer 3 at the tip of the wafer support arm 13. Further, the liquid and the ice particles overflowing from the part 11a of the receiving tank are collected in a tank (not shown).

[0020]

Since the present invention is configured as described above, it is possible to clean the substrate surface without inducing secondary contamination of the substrate surface or destruction of elements, which contributes to the electronic industry. There is a lot to do. further,
When an organic compound is used and a liquid containing no water or only a small amount is used, a natural oxide film is hard to be formed on the silicon surface. Therefore, it is considered that it is effective for removing dust from fine recesses as in the cleaning performed after etching the electrode contact window.

[Brief description of drawings]

FIG. 1 is a drawing showing an example of a cleaning apparatus for carrying out the method of the present invention.

FIG. 2 is a drawing showing an example of a cleaning apparatus for carrying out the method of the present invention.

FIG. 3 is a view of the wafer holder used in FIG.

FIG. 4 is a view showing an example of a cleaning apparatus for carrying out the method of the present invention using megasonics.

5 is a cross-sectional view taken along the line AA of FIG.

6 is a cross-sectional view taken along the line BB of FIG.

FIG. 7 is a diagram illustrating a conventional cleaning method.

[Explanation of symbols]

 1 Rotating Table 3 Substrate 4 Brush 5 Nozzle 6 Pure Water 10 Container 11 Receiving Tank 12 Wafer Retaining Treatment 14 Pump 15 Storage Tank 26 Ice Particles

Claims (2)

[Claims] 1. A substrate is immersed in a liquid having a freezing point lower than the freezing point of water and mixed with fine particles of ice, and the fine particles of ice are made to collide with the substrate at a temperature not higher than the freezing point of water. A cleaning method comprising cleaning the substrate. 2. The cleaning method according to claim 1, wherein the liquid is substantially a liquid organic compound.