JPH10335294A - Device and method for cleaning substrate and semiconductor device manufactured by the cleaning method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve effectiveness for eliminating the particles of a substrate in supersonic cleaning with dissolved oxygen in a washing liquid and other dissolved gases which is reduced, for example, by vacuum dearation in advance to prevent a natural oxide film from formed generated in the substrate. SOLUTION: A cleaning tank 21 for cleaning a substrate, a means 22 for supplying the cleaning liquid to the cleaning tank 21, a ultrasonic vibration generation means 25 for transferring vibrations to the cleaning liquid, a means 32 for reducing the pressure of a region including the surface of the cleaning liquid, and a shield 31 for encircling the region, including the surface of the cleaning liquid and maintaining a reduced pressure are provided. The substrate is subjected to ultrasonic cleaning, while the pressure of the region including the surface of the cleaning liquid is being reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a substrate cleaning apparatus, a cleaning method and a semiconductor device manufactured by using the method, and more particularly, to dissolved oxygen and other dissolved substances in a cleaning liquid for preventing generation of an oxide film on a substrate. The present invention also relates to a technique for improving the particle removal rate of a substrate even in ultrasonic cleaning with a reduced gas.

[0002]

2. Description of the Related Art In general, in a process of treating a substrate such as a semiconductor wafer, a cleaning step of the substrate is performed for the purpose of removing organic substances, metal impurities, particles, natural oxide films, etc. which cause defects in semiconductor devices. Is provided.

[0003] Conventionally, in such a cleaning step, in general, ultrasonic cleaning as physical cleaning has been used in combination with chemical cleaning in order to remove particles (fine particles). At present, among these ultrasonic cleanings, conventional general-purpose ultrasonic cleaning (28 kHz) is used.
So-called megahertz ultrasonic cleaning (megasonic cleaning) using a frequency of 500 kHz or more has come to be the mainstream in place of 〜100 kHz). This is due to the necessity of removing particles smaller than quarter-micron size, as well as the necessity of removing fine particles of quarter micron size or less, as well as the destruction of the substrate crystal, It responds to the demand for suppression of destruction induction and uniform cleaning of the substrate surface ("Megasonic generation and cleaning" Clean Technology 1996.
6. ).

On the other hand, in order to suppress the growth of a natural oxide film, in the process of producing ultrapure water used as a cleaning solution in the above-mentioned cleaning process, a vacuum is used to reduce dissolved oxygen which causes the formation of a natural oxide film. It is common to perform degassing. Also in such vacuum degassing, with the miniaturization of the above-mentioned design rules, there is a situation where it is increasingly required to improve the degassing performance and further reduce the dissolved oxygen as compared with the conventional one. In this way, the ultrapure water after the dissolved gas (dissolved oxygen, dissolved nitrogen, etc.) has been sufficiently reduced is provided as a cleaning liquid for particle removal during megahertz cleaning.

Conventionally, there has been a demand for improving the performance of vacuum degassing of ultrapure water to suppress the growth of such a native oxide film.
The two requests to improve the rate of removal of the tickle were not contradictory. That is, when ultrapure water with sufficiently reduced dissolved gas is used for megahertz ultrasonic cleaning, cavitation caused by the dissolved gas is not generated as much. At present, it is not established yet how the particles on the wafer are removed by the ultrasonic cleaning, but it is generally said that the particles are detached by the vibration of water molecules by ultrasonic waves. Was a popular belief. For this reason, it has been conventionally considered that the presence of cavitation hinders the propagation of the pressure wave caused by the vibration of the water molecule. Therefore, suppressing the occurrence of cavitation is directly related to the improvement of the particle removal rate. Because it was supposed to be linked to
Here, cavitation refers to a phenomenon in which a gas contained in a liquid is separated to form bubbles, thereby generating cavities in the flowing liquid. In addition to the amount, the pressure applied to the liquid, the temperature of the liquid, and the like can be cited as variables.

However, recently, in megahertz ultrasonic cleaning, cavitation itself effectively functions for particle removal, that is, it is necessary to generate cavitation for efficient particle removal. It turned out to be.

The experimental data shown in FIG. 4 suggests the need for such cavitation. That is, FIG.
Shows the correlation between the dissolved nitrogen concentration in pure water as a cleaning solution and the number of particles increased on the wafer. Specifically, an 8-inch wafer on which about 200 particles are adsorbed is subjected to ultrasonic cleaning (ultrasonic frequency: 850 MHz, irradiation for 10 minutes) using pure water in which the nitrogen concentration is controlled under atmospheric pressure. Is a graph showing the increase / decrease number of particles in the case of performing the above, and the more the increase number becomes negative, the higher the effect of particle removal is. From this, it can be seen that the higher the concentration of nitrogen, one of the dissolved gases in pure water, the smaller the particles on the substrate, and therefore the more cavitation excited by the dissolved gas is generated. Thus, it can be said that particle removal is performed accordingly.

[0008] Here, the above two requirements, that is, the requirement for improving the performance of vacuum degassing of ultrapure water for suppressing the growth of the natural oxide film and the requirement for increasing the particle removal rate, are in a trade-off relationship. It was found out. That is,
If the precision of vacuum degassing of ultrapure water is improved to suppress the growth of the natural oxide film, the occurrence of cavitation is suppressed accordingly, and the improvement in the particle removal rate is sacrificed to some extent. A new problem has arisen.

FIG. 2 shows an example of a conventional general substrate cleaning apparatus.

A supply port 2 of ultrapure water used as a cleaning liquid is provided at the bottom of a quartz cleaning tank 1 for cleaning a substrate. The ultrasonic transmission tank 4 for transmitting the pressure to the inside of the cleaning tank 1 is provided. Also, at the bottom of the ultrasonic transmission tank 4, 5
An ultrasonic vibrator 5 for generating an ultrasonic wave of 00 kHz or more is provided.

Further, ultrapure water 6 used as a cleaning liquid is used.
In the ultrapure water production process, which is another process, vacuum degassing is sufficiently performed.

The megahertz ultrasonic cleaning based on such a configuration is performed as follows. That is, at the time of megahertz ultrasonic cleaning, first, a substrate such as a semiconductor wafer 3 to be cleaned is set in the cleaning tank 1. Then, ultrapure water 6 as a cleaning liquid is supplied from the ultrapure water supply port 2 to the cleaning tank 1.
The inside is supplied in an upward direction from below. In the conventional example of FIG. 2, the supplied ultrapure water 6 overflows as overflowing water 7 from the upper part of the cleaning tank 1, so-called an overflow rinse. When the ultrapure water 6 is supplied by overflow, the ultrasonic vibrator 5
Operates, and ultrasonic vibration is applied to the semiconductor wafer 3 to remove particles.

However, as described above, since the ultrapure water 6 is subjected to vacuum degassing and the dissolved gas is reduced, sufficient cavitation is generated even when ultrasonic vibration is applied during cleaning. I couldn't let it.

As described above, in the conventional substrate cleaning apparatus,
If ultrapure water that has been sufficiently degassed is used as a cleaning liquid, the occurrence of cavitation is suppressed accordingly in megahertz ultrasonic cleaning, and the particle removal rate cannot be sufficiently improved. is there.

That is, when the conventional substrate cleaning apparatus and the conventional cleaning method are used, there are two requirements, that is, a request for improving the performance of vacuum degassing for suppressing the growth of a natural oxide film and a request for improving the particle removal rate. The problem was that the two requirements could not be met at the same time.

[0016]

As described above, the present invention relates to the two prior arts, namely, a request for improving the performance of vacuum degassing for suppressing the growth of a native oxide film and a request for improving the particle removal rate. The purpose of the present invention is to solve the problem that the two requirements cannot be satisfied at the same time. The purpose is to prevent dissolved oxygen and It is an object of the present invention to provide a cleaning apparatus including an ultrasonic vibrator capable of sufficiently generating cavitation even in a state in which other dissolved gases are reduced and improving a particle removal rate of a substrate.

In addition, by preventing the dissolving of easily soluble gas from the atmosphere at the time of cleaning, the generation of a natural oxide film on the substrate can be prevented even after a long cleaning, and at the same time, the particle removal rate can be improved. It is to plan.

Another object of the present invention is to remove the fine particles having a size of quarter micron or less, suppress crystal destruction of the substrate, suppress the induction of electrostatic destruction, and reduce the surface of the substrate by changing the ultrasonic cleaning to megahertz ultrasonic cleaning. The purpose of the present invention is to achieve uniform cleaning of the substrate.

Another object of the present invention is to prevent the recontamination of the substrate by the desorbed particles mixed in the cleaning liquid by operating the pressure reducing device while supplying the cleaning liquid so as to overflow. It is to plan.

It is another object of the present invention to reduce the pressure during the ultrasonic cleaning by using a simple apparatus or method by maintaining the reduced pressure using an overflow cleaning solution.

Another object of the present invention is to provide a means for controlling a pressure by detecting a variable factor relating to the occurrence of cavitation, thereby realizing a pressure reduction by a control pressure optimal for removing particles.

Further, an object of the present invention is to prevent the formation of a natural oxide film on the substrate by sufficiently generating cavitation even in a state where the dissolved oxygen in the cleaning liquid has been reduced in advance, thereby allowing the substrate to pass through. An object of the present invention is to provide an ultrasonic cleaning method for a substrate, which can improve a removal rate of a tickle.

Further, the object of the present invention is also to sufficiently generate cavitation even in a state where dissolved oxygen in the cleaning solution is reduced in advance in order to prevent the formation of a natural oxide film on the substrate. Another object of the present invention is to provide a semiconductor device manufactured by using an ultrasonic cleaning method, which can improve the particle removal rate.

[0024]

In short, the apparatus of the present invention (claim 1) comprises a cleaning tank for cleaning a substrate, a cleaning liquid supply means for supplying a cleaning liquid to the cleaning tank, and an ultrasonic vibration applied to the cleaning liquid. Ultrasonic vibration generating means to be transmitted, decompression generating means for decompressing a region including on the cleaning liquid surface, and a shield surrounding the region including on the cleaning liquid surface and maintaining a decompressed state, at least comprising: Is what you do.

The term "reduced pressure" as used herein means that the pressure is reduced to the atmospheric pressure or less, but at least to the atmosphere in the clean room.

According to the above-described structure, by reducing the pressure in the region including the surface of the cleaning liquid during the ultrasonic cleaning, even if the amount of the dissolved gas in the cleaning liquid is small, it is more effective than under the atmospheric pressure.
More cavitation can be generated. In other words, it is possible to reduce the amount of dissolved gas such as oxygen in the cleaning liquid, thereby preventing natural oxide film from being generated on the substrate, and at the same time, generate desired cavitation, thereby improving the particle removal rate of the substrate. Become.

Similarly, by reducing the pressure in the region including the surface of the cleaning liquid during ultrasonic cleaning, the dissolution of easily dissolved gas in the atmosphere can be prevented, the low dissolved gas concentration can be maintained, and the specific resistance of the cleaning liquid can be prevented from deteriorating. Is done. In other words, even when the ultrasonic cleaning is performed for a long time, it is possible to suppress the generation of a natural oxide film on the substrate.

Further, in the invention according to claim 2, the ultrasonic generating means has an ultrasonic transmission tank and an ultrasonic vibrator, and the ultrasonic vibration is transmitted to the cleaning liquid via the ultrasonic transmission tank. By doing so, it is possible to obtain the same effect as the above-described device of claim 1.

According to a third aspect of the present invention, there is provided a substrate rotating means for rotating a mounted substrate, a cleaning liquid supply nozzle for discharging a cleaning liquid onto the substrate, and an ultrasonic wave for transmitting ultrasonic vibration to the cleaning liquid. The above-mentioned claim 1 comprising at least a vibration generating means, a shield for enclosing the substrate rotating means, the cleaning liquid supply nozzle and the ultrasonic vibration generating means, and a pressure reducing means for reducing the pressure inside the shield. It is possible to obtain the same effect as that of the device.

According to the fourth aspect of the present invention, the same effect as the above-described apparatus of the first aspect can also be obtained by connecting the reduced pressure generating means to the shield which maintains a reduced pressure state. Becomes possible.

Further, in the invention according to claim 5, the ultrasonic vibration generating means generates ultrasonic waves of 500 kHz or more to remove fine particles of quarter micron size or less and to remove crystal of the substrate. It is possible to suppress the destruction and the induction of the electrostatic destruction, and to achieve uniform cleaning of the substrate surface.

In the invention according to claim 6, the cleaning liquid supply means supplies the cleaning liquid so as to overflow into the cleaning tank, and the overflow of the cleaning liquid is performed simultaneously with the generation of the ultrasonic vibration. With this, the desorbed particles mixed in the cleaning liquid can be discharged from the upper portion of the cleaning apparatus, and the substrate can be constantly washed with the new cleaning liquid, thereby preventing re-contamination of the substrate due to the desorbed particles. Becomes possible.

In the invention according to claim 7, the overflow of the cleaning liquid is maintained in a reduced pressure state in a region including the surface of the cleaning liquid together with the shield, so that a dedicated pressure reduction for applying the reduced pressure during ultrasonic cleaning is performed. It is not necessary to increase the size of the apparatus, such as forming a chamber or the like outside the cleaning apparatus itself, and it is possible to realize decompression with a simple apparatus.

Further, in the inventions according to claims 8 and 9, a detecting means for detecting a variable element relating to the occurrence of cavitation and a signal for controlling the pressure in the shield based on the detection result are output to the decompression generating means. By providing at least the pressure control means, it is possible to transmit a pressure reduction value that cannot be set uniformly according to the situation, and to realize a pressure reduction by a control pressure optimal for particle removal. Here, the detection means specifically refers to a pressure sensor and a dissolved gas concentration sensor.

Further, the method of the present invention (claim 10) comprises a dissolved gas detecting means for detecting a dissolved gas concentration of the cleaning liquid,
At least pressure control means for outputting a signal for controlling the pressure in the shield based on the concentration detection result of the dissolved gas detection means to the pressure reduction generation means.

According to such a method, by reducing the pressure in the region including the surface of the cleaning liquid during ultrasonic cleaning, even if the amount of dissolved gas in the cleaning liquid is small, more cavitation can be achieved than in the case of the atmospheric pressure. Can be generated. In other words, it is possible to reduce the amount of dissolved gas such as oxygen in the cleaning liquid, thereby preventing natural oxide film from being generated on the substrate, and at the same time, generate desired cavitation, thereby improving the particle removal rate of the substrate. Become. Also,
Similarly, by reducing the pressure in the area including the cleaning liquid surface during ultrasonic cleaning, it is possible to prevent the dissolution of easily soluble gas in the atmosphere,
A low dissolved gas concentration is maintained, and the specific resistance of the cleaning liquid is prevented from deteriorating. In other words, even when the ultrasonic cleaning is performed for a long time, it is possible to suppress the generation of a natural oxide film on the substrate.
Here, the predetermined pressure refers to a pressure equal to or lower than the pressure in the cleaning device.

In the eleventh aspect of the present invention, the substrate is provided in a cleaning tank, and the cleaning liquid supplied to the substrate overflows from the cleaning tank, so that the desorbed particles mixed in the cleaning liquid. Can be discharged from the upper portion of the cleaning apparatus, and the substrate can be constantly cleaned with a new cleaning liquid, so that re-contamination of the substrate due to the desorbed particles can be prevented.

In the twelfth aspect of the present invention, the cleaning liquid is pure water that has been degassed under vacuum, so that the dissolved gas is reduced during cleaning, so that the effect of the present invention is reduced. It can be enjoyed without.

According to the thirteenth aspect of the invention, at least one of nitrogen, argon, helium and hydrogen rare gas is dissolved in the cleaning liquid, thereby deteriorating the specific resistance of ultrapure water. Without this, it is possible to generate more cavitations and further improve the particle removal rate.

Further, in the invention of claim 14, the reduced pressure state is controlled based on the pressure in the shield and the concentration of dissolved gas in the cleaning liquid, so that the reduced pressure state cannot be set uniformly. The value can be transmitted according to the situation, and pressure reduction by the optimal control pressure for particle removal can be realized.

Further, the semiconductor device of the present invention (claim 1)
5) a step of supplying a cleaning liquid to the substrate, a step of reducing the pressure in a region including the surface of the cleaning liquid, and a step of transmitting ultrasonic vibration to the cleaning liquid under reduced pressure to wash the substrate. It is characterized by being manufactured using at least a method of cleaning a substrate.

According to such a semiconductor device, by reducing the pressure in the region including the surface of the cleaning solution during the ultrasonic cleaning, even if the amount of dissolved gas in the cleaning solution is small, more cavitation than in the case of the atmospheric pressure is obtained. Can be generated. In other words, it is possible to reduce the amount of dissolved gas such as oxygen in the cleaning liquid, thereby preventing natural oxide film from being generated on the substrate, and at the same time, generate desired cavitation, thereby improving the particle removal rate of the substrate. Become. Similarly, by reducing the pressure of the region including the surface of the cleaning liquid during the ultrasonic cleaning, the dissolution of easily dissolved gas in the atmosphere can be prevented, the low dissolved gas concentration is maintained, and the specific resistance of the cleaning liquid is prevented from deteriorating. In other words, even when the ultrasonic cleaning is performed for a long time, it is possible to suppress the generation of a natural oxide film on the substrate. Therefore, a semiconductor device with improved reliability and yield can be obtained.

[0043]

BEST MODE FOR CARRYING OUT THE INVENTION

First Embodiment Hereinafter, the present invention will be described based on a first embodiment shown in the drawings. In FIG. 1, a substrate cleaning apparatus according to the present invention comprises:
Cleaning tank 21, ultrasonic transmission tank 24, decompression shield 31
, A pressure reducing device 32, a pulling device 34, and a pressure control device 35.

In this embodiment, a case where a semiconductor wafer is cleaned as one of the substrates will be described.
However, the object to be cleaned is not limited to this, and may be general substrates such as a base substrate and an exposure mask substrate for forming an integrated circuit.

In FIG. 1, a supply port 22 of ultrapure water used as a cleaning liquid is provided at the bottom of a quartz cleaning tank 21 for cleaning semiconductor wafers. Ultrapure water 26 is supplied upward from below.

Although the present embodiment is based on the premise of cleaning by the overflow rinsing method, the cleaning method is not limited to this, and a quick dump rinsing method is also possible. However, if the overflow rinsing method is used, the desorbed particles mixed in the cleaning liquid overflow from the upper part of the cleaning tank 21 and are discharged, so that the semiconductor wafer can always be cleaned with a new cleaning liquid.
It is possible to prevent recontamination of the semiconductor wafer by the particles after desorption.

An ultrasonic transmission tank 24 for transmitting ultrasonic waves to the inside of the cleaning tank 21 is provided around the cleaning tank 21.
An ultrasonic vibrator 25 for generating an ultrasonic wave of kilohertz or more and transmitting the ultrasonic wave into the cleaning tank 21 is provided.

In this embodiment, the cleaning tank 21 is a so-called indirect system in which the cleaning tank 21 is separately formed as an inner tank of the ultrasonic transmission tank 24. However, the configuration of both is not limited to this. An integrated so-called direct system is also possible. In such a case, a higher ultrasonic intensity can be obtained.

Further, ultrapure water 26 used as a cleaning liquid is used.
In the ultrapure water production process, which is another process, vacuum degassing is sufficiently performed.

It should be noted that the cleaning liquid is not necessarily limited to ultrapure water. In the case of ultrapure water, the effect of the present invention is reduced due to vacuum degassing. It can be enjoyed without.

Further, argon (A) is added to the ultrapure water.
If a rare gas such as r), helium (He), or hydrogen is added, more cavitation is generated without deteriorating the specific resistance of ultrapure water, and the particle removal rate can be further improved. .

A decompression shield 31 is provided above the cleaning tank 21 and the ultrasonic transmission tank 24 so as to surround them. In addition, as shown in FIG. 1, the term “surround” refers to a state where the surrounding area is covered so as to cover the upper part, and a state where the surrounding area is not in contact with the cleaning tank 21 and the ultrasonic transmission tank 24. The space between the pressure-reducing shield 31 and the ultrasonic transmission tank 24 is set to such an extent that the space can be filled and the pressure-reduced state can be maintained by overflowing flowing water 27 flowing from the upper part of the cleaning tank 21 through the upper part of the ultrasonic transmission tank 24. It is set.

In this embodiment, the overflow water 2
7, the pressure reduction state is maintained by sealing the inside of the pressure reduction shield.
However, the present invention is not limited to this.
1 can also be configured. However, by adopting a method of sealing the inside of the decompression shield with such overflow water, it is possible to maintain the decompression state similar to that of the decompression chamber with a simpler device configuration.

The pressure reducing shield 31 is formed by a duct 33
The pressure reducing device 32 is connected to the pressure reducing device 32, and has an inverter device 39, a motor (not shown) driven by the inverter device 39, and a blower 40 rotated by the motor. The inverter device 39
It is used to control the number of rotations of a motor for rotating the blower 40. The blower 40 is a decompression device 3
2 is rotatably fixed to the inside thereof.

The pulling device 34 is fixed to the upper part of the pressure reducing shield 31 and is configured to be able to move up and down together with the pressure reducing shield.

The pressure controller 35 includes a pressure sensor 36 provided on the inner wall of the pressure reducing shield 31 and a dissolved gas concentration sensor 3 provided on the inner wall of the ultrapure water supply pipe 28.
7 are separately connected by a signal line 38, and between one end of the pressure control device 35 and the pressure reducing device 32, pressure control information is also transmitted to the pressure reducing device 32. Are connected by a signal line 38.

The present embodiment can be applied to any of a multi-tank batch system and a single-tank batch system in the form of a semiconductor wafer cleaning tank.

In the cleaning method according to the present invention, the step of supplying the cleaning liquid to the substrate, the step of reducing the pressure in the region including the surface of the cleaning liquid, and the step of transmitting ultrasonic vibrations to the cleaning liquid under the reduced pressure state, And a step of cleaning the substrate.

Further, in the semiconductor device according to the present invention, the step of supplying the cleaning liquid to the substrate, the step of reducing the pressure in a region including the surface of the cleaning liquid, and the step of transmitting ultrasonic vibration to the cleaning liquid under the reduced pressure state A semiconductor device manufactured by using a method for cleaning a substrate, the method comprising:

The present embodiment is configured as described above, and its operation will be described below. When cleaning a semiconductor wafer using this embodiment, first, as shown in FIG. 1, a semiconductor wafer 23 to be cleaned is placed in a cleaning tank 21. Prior to the start of cleaning, the pulling device 34, which has been moving upward when the semiconductor wafer 23 is installed and removed, is moved downward, so that the decompression shield 31 is moved to the cleaning tank 21 and the ultrasonic transmission tank 24. Surround the upper part of.

Ultrapure water 26 as a cleaning liquid for semiconductor wafers
Is supplied from the ultrapure water supply port 22 to the inside of the cleaning tank 21 from below through the ultrapure water supply pipe 28. The supplied ultrapure water 26 flows outward from the upper edge of the cleaning tank 21 when the amount exceeding the capacity of the cleaning tank 21 is supplied. At a stage where the continuously supplied ultrapure water further exceeds the capacity of the ultrasonic transmission tank 24, a so-called overflow state occurs in which the ultrapure water flows further outward from the upper edge of the ultrasonic transmission tank 24. Ultrasonic transducer 25
Generates an ultrasonic wave in the case of the overflow state, and the pressure reducing device 32 is controlled to operate when the ultrasonic vibrator 25 is in a driving state. The pressure reducing device 32 changes the pressure by controlling the rotation speed of the blower 40 by the inverter device 39 included therein. It should be noted that a vacuum pump may be used instead of the blower 40 at all.

The air inside the decompression shield 31 is depressurized through the duct 33 by the rotation of the blower 40 of the decompression device 32. Since the overflow water seals the decompression shield 31 and the ultrasonic transmission tank 24, the pressure inside the decompression shield 31 is controlled and maintained at a predetermined decompression state.

Although the level of the overflow water 27 rises depending on the pressure in the pressure reducing shield 31, the overflow water 27 between the pressure reducing shield 31 and the ultrasonic transmission tank 24 is sucked and discharged by the pump 41 depending on the situation. You may.

The pressure in the reduced pressure shield in the reduced pressure state is notified by the pressure sensor 36 to the pressure control device 35 through the signal line 38. Further, the concentration of the dissolved gas of the ultrapure water supplied into the cleaning tank 21 is also notified to the pressure controller 35 by another dissolved gas concentration sensor 37 through another signal line 38. The pressure control device 35 includes:
The optimum set pressure in the decompression shield 31 is calculated from the values of these two fluctuation factors, and the signal line 38 is supplied to the decompression device 32.
, The optimum set pressure is notified. The pressure in the pressure-reducing shield is controlled to the optimum pressure for particle removal by the notified value.

The optimal pressure for particle removal is:
The control pressure in the pressure-reducing shield cannot be set unconditionally because it changes depending on the concentration of the dissolved gas in the ultrapure water supplied at that time. For this reason, such a detecting means is advantageous in that it can always provide an optimal pressure for particle removal.

According to the present embodiment, the following quantitative effects were obtained. That is, when the semiconductor device is cleaned by performing ultrasonic irradiation using ultrapure water having a dissolved nitrogen concentration of 10 ppm as a cleaning liquid by the conventional cleaning apparatus illustrated in FIG. 2, the ultrasonic irradiation is performed. However, cavitation hardly occurred, and the particle removal rate on the semiconductor wafer was only 20% or less. The saturated concentration of dissolved nitrogen in ultrapure water under atmospheric pressure is about 20 ppm.

In comparison with the above, similarly, using the ultrapure water having a dissolved nitrogen concentration of 10 ppm, the cleaning apparatus according to the present invention shown in FIG. 1 was used to perform ultrasonic irradiation at an ultrasonic frequency of 850 kHz. When cleaning the semiconductor wafer, the inside of the decompression shield was controlled to 50 kPa by the pressure controller 35. By applying such reduced pressure, the dissolved nitrogen in the ultrapure water is brought into a state close to supersaturation, and the dissolved nitrogen is easily foamed by irradiation of ultrasonic waves, cavitation occurs, and particles on the semiconductor wafer are removed. The rate was dramatically improved to 80% or more.

FIG. 5 is a graph showing a change in pressure inside the pressure reducing shield 31 using ultrapure water and a pressure change of 0.2 mm in this embodiment.
The removal rate of particles having a particle size of μm or more is observed. In this case, the removal rate sharply increases from 60 kPa, reaches 83% at 50 kPa, and is almost saturated at 40 kPa, with the removal performance of 95%. However, as described above, since the removal performance curve also changes depending on the dissolved gas concentration in the supplied ultrapure water, this is detected, and the inside of the pressure reduction shield is adjusted to the optimum pressure by the pressure control device 35. It is controlled.

FIG. 6 shows the relationship between the depth in the cleaning tank and the specific resistance of the ultrapure water in the prior art, and the relation between the depth in the cleaning tank and the specific resistance of the ultrapure water in the cleaning apparatus according to the present invention. From here, the cleaning apparatus according to the present invention prevents the dissolving of easily soluble gas in the atmosphere, such as CO ₂ , which affects the specific resistance of ultrapure water. In addition, it can be seen that the specific resistance of the ultrapure water does not deteriorate even in the region on the cleaning liquid level. Conventionally, even if vacuum degassing is performed in the ultrapure water manufacturing process, C is removed from the air again at the stage of cleaning the semiconductor wafer when using ultrapure water.
The dissolution of O ₂ and O ₂ in the ultrapure water liquid caused the formation of a natural oxide film. Although the specific resistance deterioration at the upper part of the liquid level is mainly caused by CO ₂ ,
It is easily understood that O ₂ is dissolved at the same time. However, in the present invention, by maintaining the area above the liquid surface in a reduced pressure state during cleaning, such O
₂ and CO ₂ are prevented from dissolving, so that the generation of a natural oxide film on the semiconductor wafer during cleaning is further suppressed than before.

Second Embodiment Next, a second embodiment will be described with reference to FIG.

In FIG. 3, the semiconductor wafer cleaning apparatus according to the present invention is constituted by a so-called single wafer type, and comprises a wafer chuck 52 and a cleaning liquid discharge nozzle 54.
, A waste liquid temporary storage tank 57, a decompression pump 59, and a decompression chamber 60.

The wafer chuck 52 is fixed to a wafer rotating motor 53 by a rotating shaft. When the semiconductor wafer 51 is mounted on the wafer chuck 52, the wafer chuck 52 rotates in a direction perpendicular to the rotating shaft. It is configured. Further, an ultrasonic vibrator 55 is fixed to the cleaning liquid discharge nozzle 54.

The entirety of the wafer chuck 52 and the cleaning liquid discharge nozzle 54 is opened and closed by a load lock 5 that can be opened and closed.
6 is encapsulated by a reduced pressure chamber 60.
The decompression pump 59 is connected to a decompression chamber 60 via a waste liquid temporary storage tank 57. A waste liquid valve 58 is formed in the lower part of the waste liquid temporary storage tank 57.

This embodiment is configured as described above, and its operation will be described below. When cleaning a semiconductor wafer using the apparatus of the present embodiment, first,
The left load lock 56 is opened, a semiconductor wafer is loaded, and the semiconductor wafer is set on the wafer chuck 52. Thereafter, the load lock 56 and the waste liquid valve 58 are closed, the inside of the decompression chamber 60 is closed, and the decompression pump 59 is operated to reduce the pressure inside the decompression chamber 60 to the atmospheric pressure or less. Subsequently, the semiconductor wafer 51 to be cleaned is rotated by operating the wafer rotation motor 53.

When the pressure in the decompression chamber 60 has been reduced to the set pressure, the cleaning liquid is discharged from the cleaning liquid discharge nozzle 54 onto the rotating semiconductor wafer 51, and ultrasonic waves are generated by the ultrasonic vibrator 55. I do.

At the stage when the cleaning of the semiconductor wafer is completed,
The discharge of the cleaning liquid, the ultrasonic oscillation, and the rotation of the semiconductor wafer are stopped, and the operation of the decompression pump 59 is stopped to return the inside of the decompression chamber 60 to the atmospheric pressure.

The right load lock 56 is opened, and the washed semiconductor wafer is carried out and delivered to the next step. The waste liquid valve 55 is opened, and the cleaning liquid stored in the waste liquid temporary storage tank 57 is discharged.

In this embodiment, similarly to the first embodiment, by providing the pressure sensor, the dissolved gas concentration sensor, and the pressure control device, it is possible to realize the decompression by the optimal control pressure for removing particles. it can.

According to the present embodiment, the same effects as provided by the first embodiment can be enjoyed even in a spin-on-wafer type cleaning apparatus that does not use a cleaning tank.

[0080]

As described above, according to the present invention,
The following effects are obtained.

That is, since the cleaning device provided with the ultrasonic vibrator is provided with a decompression device for reducing the area on the surface of the cleaning liquid to a pressure lower than the internal pressure of the cleaning device, more cavitation is generated than under the atmospheric pressure. Can be generated. Therefore, in order to prevent the formation of a natural oxide film on the substrate,
Cavitation can be sufficiently generated even in ultrasonic cleaning in a state where dissolved oxygen and other dissolved gases in the cleaning liquid are reduced in advance by vacuum degassing or the like. As a result, the effect of improving the particle removal rate of the substrate can be obtained.

At the same time, the dissolution of easily dissolved gas from the atmosphere during cleaning is prevented, and a low dissolved oxygen concentration is maintained, so that the effect of further preventing the formation of a natural oxide film on the substrate is obtained. Can be That is, under the atmospheric pressure, the occurrence of cavitation and the prevention of the natural oxide film, which are in a trade-off relationship, are simultaneously achieved. As a result, the efficiency of removing particles that cause defects in the semiconductor chip is increased, and the effect of improving the reliability and yield of semiconductor products is achieved.

Further, since the ultrasonic cleaning is performed by megahertz ultrasonic cleaning, in addition to removing fine particles having a size of quarter micron or less, crystal breakage of the substrate, suppression of electrostatic breakdown, and uniform cleaning of the substrate surface can be achieved. An effect that can be achieved is obtained.

Further, since the pressure is reduced while the cleaning liquid is supplied in an overflow manner, the effect of preventing re-contamination of the substrate by particles after desorption mixed in the cleaning liquid can be obtained.

Further, the reduced pressure state is maintained by the overflow cleaning liquid itself, so that the effect that the reduced pressure during the ultrasonic cleaning can be realized with a simple apparatus and method can be obtained. As a result, it is possible to suppress an increase in substrate cleaning cost due to the above-described effect of improving the yield of semiconductor products and to achieve an effect of improving the throughput in cleaning, and at the same time, to suppress an increase in the footprint of the cleaning apparatus. Thus, the effect of eliminating the influence on the reduction in the degree of freedom in designing the clean room can be achieved.

Further, since a means for controlling the pressure by detecting a variable element relating to the occurrence of cavitation is provided,
The effect of reducing the pressure by the optimal control pressure for removing the particles is obtained, which further contributes to the improvement in the yield of the semiconductor products.

As described above, according to the present invention, the efficiency of removing particles that cause defects in a semiconductor chip can be increased, and the reliability and yield of semiconductor products can be improved. This is an extremely effective invention.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view showing the configuration and operation of a first embodiment of a cleaning device according to the present invention.

FIG. 2 is a longitudinal sectional view showing the configuration and operation of a conventional semiconductor wafer cleaning apparatus.

FIG. 3 is a longitudinal sectional view showing the configuration and operation of a second embodiment of the cleaning device according to the present invention.

FIG. 4 is a graph showing a correlation between the dissolved nitrogen concentration in ultrapure water and the number of particles increased on a semiconductor wafer.

FIG. 5 is a graph showing the relationship between the pressure inside the pressure reduction shield and the particle removal rate of 0.2 μm or more in the first embodiment of the cleaning apparatus according to the present invention.

FIG. 6 shows a comparison between the relationship between the depth in the cleaning tank and the specific resistance of the ultrapure water in the prior art, and the relationship between the depth in the cleaning tank and the specific resistance of the ultrapure water in the cleaning apparatus according to the present invention. It is a graph.

[Explanation of symbols]

 1,21 Cleaning tank 2,22 Ultrapure water supply port 3,23,51 Semiconductor wafer 4,24 Ultrasonic transmission tank 5,25,55 Ultrasonic vibrator 6,26 Ultrapure water 7,27 Overflow flowing water More than 28 Pure water supply pipe 31 Pressure reducing shield 32 Pressure reducing device 33 Duct 34 Pulling device 35 Pressure control device 36 Pressure sensor 37 Dissolved gas concentration sensor 38 Signal line 39 Inverter device 40 Blower 41 Pump 52 Wafer chuck 53 Wafer rotating motor 54 Cleaning liquid discharge nozzle 56 Load Lock 57 Waste liquid temporary storage tank 58 Waste liquid valve 59 Pressure reducing pump 60 Pressure reducing chamber

Claims (15)

[Claims] A cleaning tank for cleaning a substrate; a cleaning liquid supply unit for supplying a cleaning liquid to the cleaning tank; an ultrasonic vibration generating unit for transmitting ultrasonic vibration to the cleaning liquid; A substrate cleaning apparatus comprising: a pressure reducing means for reducing the pressure; and a shield surrounding the area including the surface of the cleaning liquid and maintaining the reduced pressure. 2. The ultrasonic generator according to claim 1, further comprising an ultrasonic transmission tank and an ultrasonic transducer, wherein the ultrasonic vibration is transmitted to the cleaning liquid via the ultrasonic transmission tank. 1
A substrate cleaning apparatus as described in the above. 3. A substrate rotating means for rotating a mounted substrate; a cleaning liquid supply nozzle for discharging a cleaning liquid onto the substrate; an ultrasonic vibration generating means for transmitting ultrasonic vibration to the cleaning liquid; A substrate cleaning apparatus comprising: at least a unit, a shield for enclosing the cleaning liquid supply nozzle and the ultrasonic vibration generating unit, and a reduced pressure generating unit for reducing the pressure inside the shield. 4. The substrate cleaning apparatus according to claim 1, wherein said reduced pressure generating means is connected to said shield for maintaining a reduced pressure state. 5. The substrate cleaning apparatus according to claim 1, wherein said ultrasonic vibration generating means generates an ultrasonic wave of 500 kHz or more. 6. The cleaning liquid supply unit supplies a cleaning liquid to the cleaning tank so as to overflow, and the overflow of the cleaning liquid is performed simultaneously with the generation of the ultrasonic vibration. 6. The substrate cleaning apparatus according to any one of 2, 4, and 5. 7. The substrate cleaning apparatus according to claim 6, wherein the overflowing cleaning liquid maintains a reduced pressure state in a region including a surface of the cleaning liquid together with the shield. 8. The apparatus for cleaning a substrate, comprising: a pressure detection unit configured to detect a pressure in a region including a surface of the cleaning liquid; and a signal that controls a pressure in the shield based on a pressure detection result of the pressure detection unit. 8. The apparatus for cleaning a substrate according to claim 1, further comprising at least pressure control means for outputting to the reduced pressure generating means. 9. A substrate cleaning apparatus, comprising: a dissolved gas detecting means for detecting a dissolved gas concentration of the cleaning liquid; and a signal for controlling a pressure in the shield based on a concentration detection result of the dissolved gas detecting means, for reducing the pressure. 9. The apparatus for cleaning a substrate according to claim 1, further comprising at least pressure control means for outputting to the generation means. 10. A step of supplying a cleaning liquid to the substrate, a step of reducing the pressure in a region including the surface of the cleaning liquid, and a step of transmitting ultrasonic vibration to the cleaning liquid under reduced pressure to wash the substrate. A substrate cleaning method comprising at least: 11. The substrate cleaning method according to claim 10, wherein the substrate is set in a cleaning tank, and a cleaning liquid supplied to the substrate overflows from the cleaning tank. 12. The substrate cleaning method according to claim 10, wherein the cleaning liquid is pure water degassed under vacuum. 13. The cleaning solution contains nitrogen, argon,
13. The method for cleaning a substrate according to claim 10, wherein at least one of rare gases of helium and hydrogen is dissolved. 14. The substrate cleaning method according to claim 10, wherein the reduced pressure state is controlled based on a pressure in the shield and a concentration of a dissolved gas in the cleaning liquid. 15. A step of supplying a cleaning liquid to the substrate, a step of reducing the pressure in a region including the surface of the cleaning liquid, and a step of transmitting ultrasonic vibration to the cleaning liquid under reduced pressure to clean the substrate. A semiconductor device manufactured by using a method for cleaning a substrate having at least: