JP6705083B2 - Plasma cleaning apparatus and plasma cleaning method - Google Patents

Description

The present invention relates to a technique for plasma-cleaning an object to be cleaned (specifically, a white LED package for lighting, for example).

In the post-process of semiconductor manufacturing, steps such as die bonding for mounting a semiconductor chip on a substrate such as epoxy resin, wire bonding for connecting electrodes with metal wires, and molding for sealing the chip with resin are performed. At each stage of the process, the surface needs to be cleaned and modified to improve the quality of the product. These cleanings are often performed by plasma cleaning, which is a cleaning method that does not require drying and can be performed at a low temperature (around room temperature). For this plasma cleaning, oxygen (O ₂ ) plasma that can clean organic contaminants by a chemical reaction is often used.

Also in the manufacturing process of the white LED package for lighting or the like, each process of die bonding, wire bonding and molding is similarly performed, and it is necessary to clean the surface at each stage in the series of processes. However, in the white LED package, there is a circumstance that silver (Ag) plating is used for the case electrode in order to reflect light efficiently, and therefore oxygen plasma cannot be used for plasma cleaning. Oxygen plasma has a strong oxidizing effect, so if the white LED package is plasma-cleaned with this, silver on the surface will oxidize and turn black, and plating may peel off due to oxidation.

Since oxygen plasma cannot be used, argon (Ar) plasma is often used for plasma cleaning of white LED packages. However, silver has the property of being more easily sputtered than other materials such as gold. Therefore, if the white LED package is plasma cleaned with argon plasma, even if the energy of the argon plasma is suppressed to a low level, the surface silver will be slightly It will be sputtered. If silver is sputtered, the sputtered silver may be redeposited on the protective film or the like of the LED chip, causing a decrease in illuminance and an increase in leak current.

Therefore, there has been proposed a technique of performing plasma cleaning of a white LED package with a plasma gas (water (H ₂ O) plasma) generated by converting water vapor (H ₂ O) into plasma (Patent Document 1). It has been found that water plasma can be used to sufficiently clean organic contaminants without oxidizing silver as in oxygen plasma and without spattering silver as in argon plasma. In addition, water vapor is a safe gas and has the advantage of being easy to handle.

JP 2015-160192 JP

As described above, plasma cleaning using water plasma is a cleaning target in which a substance that is easily oxidized or sputtered is present on the surface (for example, a cleaning target that contains silver on the surface, such as a white LED package). ) Is very effective as a method of cleaning. However, since the water plasma contains atomic hydrogen, an object to be cleaned is exposed to the atomic hydrogen in plasma cleaning using the water plasma. Atomic hydrogen has the function of forming a high resistance film on the object to be cleaned (so-called hydrogen passivation), so if the plasma processing time is longer than the time required for cleaning, a high resistance film is formed on the object to be cleaned. As a result, the characteristics of the cleaning target may change.

The problem to be solved by the present invention is to provide a technique capable of appropriately plasma-cleaning an object to be cleaned without changing its characteristics.

The present invention made to solve the above problems is a plasma cleaning apparatus,
A plasma cleaning chamber in which the object to be cleaned is placed,
A water introducing section for introducing water into the plasma cleaning chamber,
A plasma forming unit that forms water plasma by converting water introduced into the plasma cleaning chamber into plasma,
An analyzer for measuring the amount of a predetermined substance present in the plasma cleaning chamber,
A control unit that determines the end timing of the plasma cleaning based on the measurement data obtained from the analyzer, and terminates the plasma cleaning at the determined end timing,
Equipped with.

In this configuration, when water plasma is formed in the plasma cleaning chamber to plasma-clean the object to be cleaned, the amount of a predetermined substance present in the plasma cleaning chamber is measured by the analyzer, and the obtained measurement data is obtained. Based on this, the end timing of the plasma cleaning is determined.
The “predetermined substance” here is, for example, one or more substances selected from various substances exemplified in (i) to (iii) below.
(I) Substances derived from plasma formed in the plasma cleaning chamber (specifically, in the above configuration in which water plasma is formed in the plasma cleaning chamber, atomic hydrogen (H), hydroxyl radical (OH) , Atomic oxygen (O), etc.)
(Ii) Substances derived from the object to be cleaned (for example, silver (Ag) or its compound when the object to be cleaned contains silver on the surface)
(Iii) A substance derived from a substance attached to the cleaning target (specifically, for example, a monoxide generated by a reaction between an organic substance attached to the cleaning target and a plasma-derived substance). Carbon (CO), carbon dioxide (CO ₂ ), etc.)
By observing the amount of a certain substance existing in the plasma cleaning chamber, it becomes possible to understand what kind of chemical reaction is progressing in the plasma cleaning chamber, and atomic hydrogen is a high resistance film on the cleaning target. The plasma cleaning can be ended at the timing before the formation of the film is started. Therefore, the cleaning target can be appropriately plasma cleaned without changing the characteristics of the cleaning target.

According to the plasma cleaning using the water plasma, for example, when silver is contained on the surface of the object to be cleaned, it is possible to remove organic stains adhering to the object to be cleaned with almost no generation of silver oxide. . Further, according to the plasma cleaning using water plasma, when silver oxide is present on the surface of the object to be cleaned from the beginning (that is, before the plasma cleaning is performed), not only the organic contaminants are removed but also the surface is cleaned. The silver oxide of can be reduced back to silver. The inventors of the present invention have speculated the reason as follows.
That is, the inventors of the present invention monitored the type and amount of substances existing in the plasma cleaning chamber when plasma cleaning a cleaning object containing silver on the surface with water plasma, as a result, water plasma It was confirmed that hydroxyl radicals, atomic hydrogen, and atomic oxygen were present in the plasma cleaning chamber in which was generated. Then, the inventors measured how the amount of each of these substances changes with time as the plasma cleaning progresses, and based on the measurement result, the plasma cleaning chamber was operated in the following manner during the plasma cleaning. It was possible to infer that the chemical reactions (1) to (3) had occurred.
(1) Chemical Reaction in which Atomic Oxygen and Hydroxyl Radical Combine with Organic Soil Attached to Cleaning Object The organic contamination is removed from the cleaning object by this chemical reaction. That is, the atomic oxygen and the hydroxyl radicals in the plasma cleaning chamber contribute to the removal of organic contaminants on the cleaning target.
(2) A chemical reaction in which atomic oxygen and hydroxyl radicals bond with silver (so-called oxidation).
2Ag＋O→Ag ₂ O
2Ag + 2OH → Ag ₂ O + H ₂ O
2Ag + OH → Ag ₂ O + (1/2)H ₂
This chemical reaction oxidizes the silver contained on the surface of the object to be cleaned to generate silver oxide. In other words, atomic oxygen and hydroxyl radicals in the plasma cleaning chamber contribute to the removal of organic contaminants, but also cause silver oxidation.
(3) Chemical reaction in which atomic hydrogen and silver oxide are bonded (so-called reduction)
Ag ₂ O＋H→2Ag＋OH
Ag ₂ O＋2H→2Ag＋H ₂ O
This chemical reaction reduces the silver oxide generated on the surface of the object to be cleaned. In other words, the atomic oxygen and hydroxyl radicals contained in the water plasma contribute to the removal of organic contaminants, while causing the oxidation of silver.The generated silver oxide is generated by the atomic hydrogen contained in the water plasma. It is reduced and returned to silver. Therefore, as a result, it is considered that the organic contaminants adhering to the cleaning target can be removed with almost no generation of silver oxide. Further, even when silver oxide is present on the surface of the object to be cleaned from the beginning, the silver oxide is reduced by atomic hydrogen contained in water plasma to return to silver. It is considered that the silver oxide on the surface can be returned to silver while removing the.

Further, preferably, in the plasma cleaning device,
The control unit,
The timing at which the consumption amount of atomic oxygen existing in the plasma cleaning chamber per unit time becomes equal to or less than a predetermined value is determined as the end timing.

Here, the “predetermined value” is preferably a sufficiently small value (for example, a value that is small enough to assume that the consumption amount has become almost zero).
During the plasma cleaning, as described above, in the plasma cleaning chamber, a chemical reaction occurs in which atomic oxygen is combined with the organic contaminants adhering to the object to be cleaned, and the organic contaminants adhering to the object to be cleaned occur. It is presumed that the consumption of atomic oxygen per unit time will be almost zero if the above disappears. According to the above configuration, the plasma cleaning is ended at the timing when the consumption amount is sufficiently small, so that the plasma cleaning can be ended when the organic contaminants are sufficiently removed. Therefore, it is possible to prevent the characteristics of the object to be cleaned from changing due to the plasma processing time being longer than the time required for cleaning. Further, the throughput of the plasma cleaning apparatus can be improved by suppressing the plasma processing time to a necessary minimum.

Further, preferably, in the plasma cleaning device,
The control unit,
The timing at which the amount of at least one of carbon monoxide and carbon dioxide existing in the plasma cleaning chamber per unit time is equal to or less than a predetermined value is determined as the end timing.

Also in this case, it is preferable that the “predetermined value” is a sufficiently small value (for example, a small value that the consumption amount can be regarded as almost zero).
During the plasma cleaning, as described above, in the plasma cleaning chamber, a chemical reaction occurs in which atomic oxygen and hydroxyl radicals combine with organic contaminants adhering to the cleaning target, and this chemical reaction causes carbon monoxide. Since carbon dioxide and carbon dioxide are generated, it is presumed that the amount of carbon monoxide, carbon dioxide, or both generated per unit time will be almost zero if the organic contaminants attached to the cleaning target are eliminated. According to the above configuration, the plasma cleaning is ended at the timing when the amount of generation is sufficiently small, so that the plasma cleaning can be ended when the organic contaminants are sufficiently removed. Therefore, it is possible to prevent the characteristics of the object to be cleaned from changing due to the plasma processing time being longer than the time required for cleaning. Further, the throughput of the plasma cleaning apparatus can be improved by suppressing the plasma processing time to a necessary minimum.

Preferably, in the plasma cleaning device,
The surface of the cleaning object contains silver,
The control unit,
The timing when the consumption amount of atomic hydrogen existing in the plasma cleaning chamber per unit time becomes equal to or less than a predetermined value is determined as the end timing.

Also in this case, it is preferable that the “predetermined value” is a sufficiently small value (for example, a small value that the consumption amount can be regarded as almost zero).
During the plasma cleaning of the cleaning target containing silver on the surface, a chemical reaction of reducing silver oxide by atomic hydrogen occurs in the plasma cleaning chamber as described above, and when all the silver oxide is reduced, , It is assumed that the consumption of atomic hydrogen per unit time will be almost zero. Then, if the plasma treatment is continued even after the reduction of silver oxide is completed, it is considered that the chemical reaction of atomic hydrogen to form a high resistance film on the object to be cleaned may proceed. According to the above configuration, the plasma cleaning is terminated at the timing when the consumption amount becomes sufficiently small, so that the plasma processing is performed at the timing before the silver oxide is completely reduced and the high resistance film is formed on the cleaning target. Can be terminated.

Preferably, the plasma cleaning device is
When introducing water into the plasma cleaning chamber, an oxygen gas introducing unit that also introduces oxygen gas,
Further equipped with,
The plasma forming unit converts a mixed gas of water and oxygen gas into plasma.

According to this structure, the effect of cleaning organic contaminants can be enhanced by increasing the amount of atomic oxygen existing in the plasma cleaning chamber.
The inventors of the present invention turned each mixed gas having a different mixing ratio of water and oxygen gas into plasma, and measured the type and amount of the substance present in the plasma using an analyzer. As a result, it was found that as the concentration of oxygen gas in the mixed gas increased, the amount of atomic oxygen increased and the amounts of hydroxyl radical and atomic hydrogen decreased. It was also found that when the oxygen gas concentration exceeds 80%, the reduction rate of hydroxyl radicals and atomic hydrogen increases rapidly. Further, although the cleaning efficiency of organic contaminants is increased when the amount of atomic oxygen is increased, the oxidation of silver is also promoted. On the other hand, if the concentration of oxygen gas in the mixed gas is 80% or less, a sufficient amount is obtained. It was confirmed that since the atomic hydrogen of 1 is present in the plasma, the produced silver oxide can be sufficiently reduced by the atomic hydrogen. Therefore, in the above structure, the concentration (volume ratio) of the oxygen gas in the mixed gas is preferably 80% or less.

Preferably, in the plasma cleaning device,
The analyzer is an emission spectroscopic analyzer or a mass spectrometer.

According to the configuration in which the amount of the predetermined substance existing in the plasma cleaning chamber is measured by the emission spectroscopic analyzer or the mass spectrometer, the chemical reaction proceeding in the plasma cleaning chamber can be grasped in real time. Therefore, it is possible to appropriately end the plasma cleaning without causing a significant time lag from the time when the plasma cleaning chamber is in the state where the plasma cleaning should be ended. For example, if an attempt is made to grasp the chemical reaction that is progressing in the plasma cleaning chamber using an indicator that changes color by reacting with a specific chemical substance (for example, the indicator disclosed in JP2013-095765A), It takes a certain amount of time from when the substance is generated in the plasma cleaning chamber until the indicator discolors. Further, it is necessary to take out the indicator from the plasma cleaning chamber and check the discoloration. Therefore, it is likely that the end of plasma cleaning cannot be evaluated in situ. The above configuration does not cause such a delay.

The present invention is also applied to the plasma cleaning method.
The plasma cleaning method is
A step of introducing water into the plasma cleaning chamber in which the cleaning object is placed and plasmatizing it to form water plasma, and plasma cleaning the cleaning object with the water plasma,
Measuring the amount of a predetermined substance present in the plasma cleaning chamber with an analyzer, and determining the end timing of the plasma cleaning based on the obtained measurement data;
Ending the plasma cleaning at the determined end timing,
including.

According to the present invention, when water plasma is formed in the plasma cleaning chamber to plasma-clean an object to be cleaned, the amount of a predetermined substance present in the plasma cleaning chamber is measured by an analyzer, and the obtained measurement data is obtained. Based on this, the end timing of the plasma cleaning is determined. By observing the amount of a given substance existing in the plasma cleaning chamber, it becomes possible to understand what kind of chemical reaction is progressing in the plasma cleaning chamber, and atomic hydrogen has a high resistance to the cleaning target. The plasma cleaning can be ended at the timing before the formation of the film is started. Therefore, the cleaning target can be appropriately plasma cleaned without changing the characteristics of the cleaning target.

1 is a schematic configuration diagram of a plasma cleaning apparatus according to an embodiment. The figure which shows an example of the flow of the process performed with a plasma cleaning apparatus. The figure (a) which shows an example of the measurement data acquired from an analyzer when water plasma is formed in the processing space, and the measurement acquired from the analyzer when oxygen plasma is formed in the processing space. The figure (b) which shows an example of data. The figure which shows the time-dependent change of each luminescence intensity of atomic oxygen and carbon monoxide. The figure which shows the time-dependent change of each signal intensity of carbon dioxide and carbon monoxide. The figure which shows the time-dependent change of the emission intensity of atomic hydrogen.

Hereinafter, preferred embodiments of the present invention will be described with reference to the drawings.

<1. Device configuration>
FIG. 1 shows a schematic configuration diagram of a plasma cleaning apparatus 100 according to the embodiment. As is clear from this figure, the plasma cleaning apparatus 100 is a parallel plate type (capacitive coupling type) plasma processing apparatus.

The plasma cleaning apparatus 100 introduces water (specifically, water vapor which is gaseous water) into the plasma cleaning chamber 1 in which the processing space V in which the cleaning object 9 is placed is formed, and the processing space V. A water introducing part 2, an oxygen gas introducing part 3 for introducing oxygen gas into the processing space V, an exhaust part 4 for exhausting the processing space V, a pair of electrodes 5 and 6 arranged to face the processing space V, and a process. The analysis device 7 for measuring the type and amount of the substance existing in the space V and the control unit 8 for controlling these units are mainly provided.

The plasma cleaning chamber 1 is provided with a gas introduction port 11 for introducing gas into the processing space V and an exhaust port 12 for exhausting the processing space V. Pipes 22 and 32, which will be described later, are connected to the gas inlet 11. A pipe 42, which will be described later, is connected to the exhaust port 12. Further, the plasma cleaning chamber 1 is provided with an opening 13 for communicating the processing space V with the analyzer 7. When an emission spectroscopic analyzer is used as the analyzer 7, the opening 13 is formed of a material (eg, quartz) that transmits electromagnetic waves emitted from a predetermined substance (described later) existing in the processing space V. The window member 14 is fitted.

The water introduction part 2 includes a pipe 22 having one end connected to the gas introduction port 11 and the other end connected to the water supply source 21. In the middle of the pipe 22, a valve 23, a mass flow controller 24 that automatically adjusts the flow rate of the gas flowing through the pipe 22, and a vaporizer that vaporizes the introduced fluid (here, water is vaporized into water vapor) (vaporization) Device) 25. Each of these units 23, 24, 25 is electrically connected to the control unit 8, and the control unit 8 controls introduction and stop of water vapor into the processing space V.

The oxygen gas introduction unit 3 includes a pipe 32 having one end connected to the gas introduction port 11 and the other end connected to the oxygen gas supply source 31. A valve 33 and a mass flow controller 34 that automatically adjusts the flow rate of the gas flowing through the pipe 32 are provided in the middle of the pipe 32. Each of these units 33 and 34 is electrically connected to the control unit 8, and the control unit 8 controls the introduction and stop of the oxygen gas into the processing space V.

The exhaust unit 4 includes a pipe 42 having one end connected to the exhaust port 12 and the other end connected to an exhaust line. A valve 43 and a vacuum pump 44 are provided in the middle of the pipe 42. Each of these units 43 and 44 is electrically connected to the control unit 8, and the control unit 8 controls the exhaust of gas from the processing space V.

Electric power is supplied to one electrode 5 of the pair of electrodes 5 and 6 arranged opposite to each other in the plasma cleaning chamber 1 through an RF power source 51 and a capacitor 52 (hereinafter, this electrode 5 will be referred to as a “powered electrode”). 5"). The other electrode 6 is grounded (hereinafter, this electrode 6 is referred to as "ground electrode 6"). In this configuration, by supplying RF power to the powered electrode 5, the gas introduced into the processing space V is turned into plasma. In the plasma cleaning apparatus 100, the RIE (Reactive Ion Etching) mode in which the cleaning target 9 is mounted on the powered electrode 5 and the PE (Plasma Etching) mode in which the cleaning target 9 is mounted on the ground electrode 6 are used. Although plasma cleaning can be performed by selecting from two modes, in this embodiment, it is assumed that plasma cleaning is performed in the PE mode, for example. That is, the cleaning object 9 is placed on the ground electrode 6 as shown in FIG.

The analysis device 7 is a device that measures the type and amount of the substance existing in the processing space V, and is specifically formed by, for example, an optical emission spectroscopy analyzer. The electromagnetic waves emitted from the substance existing in the processing space V enter the spectroscope (not shown) of the analyzer 7 through the window member 14, and the electromagnetic waves spectrally separated for each wavelength are detected by the detector (not shown). The measurement data (see FIG. 3) indicating the type and amount (specifically, the emission wavelength and the emission intensity) of the substance existing in the processing space V is acquired by being detected. However, the analysis device 7 is not limited to the emission spectroscopic analysis device, and may be various other analysis devices. For example, it may be a mass spectrometer (for example, a quadrupole mass spectrometer). The analyzer 7 is electrically connected to the controller 8, and the measurement data acquired by the analyzer 7 is sent to the controller 8.

The control unit 8 has an end timing determining unit 81 that determines the timing (end timing) for ending the plasma cleaning based on the measurement data sent from the analyzer 7, and the plasma cleaning at the determined end timing. And an end control unit 82. The control unit 8 uses the personal computer as a hardware resource and executes the dedicated control/processing software installed in the personal computer to embody the functional blocks 81 and 82. be able to.

<2. Process flow>
FIG. 2 is a diagram showing an example of the flow of processing performed in the plasma cleaning apparatus 100. The cleaning target 9 here is, for example, a white LED package before resin encapsulation, in which a silver case electrode is exposed on the surface. However, the cleaning object 9 is not limited to the white LED package before resin sealing. However, in the plasma cleaning according to the following treatment mode, like the white LED package before resin sealing, there is a metal or the like that is easily oxidized on the surface, and a substance that is easily sputtered is exposed on the surface. It is especially suitable for cleaning existing objects.

First, the cleaning object 9 is carried into the plasma cleaning chamber 11 via a carry-in port (not shown), and placed on the ground electrode 6 (step S1). Then, the cleaning target 9 is fixed to the ground electrode 6 with an electrostatic chuck or the like.

When the cleaning object 9 is loaded, the loading port is closed and the plasma cleaning chamber 1 is sealed, and then the introduction of water vapor and oxygen gas into the processing space V is started. At the same time, the cleaning target 9 is connected to the exhaust port 12. The evacuation of the processing space V by the vacuum pump 44 is started (step S2). It should be noted that the introduction of oxygen gas is not essential and only the introduction of water vapor may be performed.

Then, the measurement (monitoring) by the analyzer 7 is started (step S3). That is, the analyzer 7 sequentially acquires, in real time, measurement data indicating the type and amount of the substance existing in the processing space V at each time, and sends the measurement data to the controller 8.

Subsequently, high frequency power is applied to the powered electrode 5 (step S4). As a result, the gas (specifically, a mixed gas of water vapor and oxygen gas) introduced into the processing space V is turned into plasma, and plasma of the mixed gas is generated above the cleaning target 9. When the oxygen gas is not introduced, the water vapor introduced into the processing space V is turned into plasma, and water plasma is generated above the cleaning object 9. Plasma cleaning (or water plasma) of the mixed gas is generated in the upper portion of the cleaning target 9, so that plasma cleaning of the cleaning target 9 proceeds.

FIG. 3A shows an example of measurement data acquired from the analyzer 7 when water plasma is formed in the processing space V. From this measurement data, when water plasma is formed in the processing space V, a relatively large amount of hydroxyl radicals, a relatively large amount of atomic hydrogen, and a relatively small amount of atomic oxygen are present in the processing space V. I understand. When plasma of a mixed gas of water vapor and oxygen gas is formed in the processing space V, it is considered that the amount of atomic oxygen further increases. The hydroxyl radicals and atomic oxygen present in the processing space V remove organic stains adhering to the cleaning target 9 (chemical reaction (1) described above). Further, while atomic oxygen and hydroxyl radicals also cause oxidation of silver (chemical reaction (2) described above), the generated silver oxide (and silver oxide originally present in the cleaning object 9) is: It is reduced by atomic hydrogen existing in the processing space V to return to silver (chemical reaction (3) described above). For this reason, the organic contaminants adhering to the cleaning target 9 are removed with almost no generation of silver oxide (or returning the silver oxide originally present in the cleaning target 9 to silver). It is thought that you can do it.

In FIG. 3B, as a comparative example, when only the oxygen gas is supplied to the processing space V to turn it into plasma (that is, when only oxygen plasma is formed), it is acquired from the analyzer 7. An example of the measured data is shown. Comparing FIG. 3A and FIG. 3B, hydroxyl radicals and atomic hydrogen do not exist when only oxygen plasma is formed in the processing space V, and water plasma is formed in the processing space V. It is understood that it exists only when Therefore, when only the oxygen gas is supplied to the processing space V, the atomic oxygen existing in the processing space V removes the organic contaminants adhering to the cleaning target 9, but the atomic hydrogen does not exist. Therefore, the oxidation of silver caused by atomic oxygen is not reduced. For this reason, the organic contaminants adhering to the cleaning object 9 are removed, and the silver on the surface of the cleaning object 9 is also oxidized.

While the plasma cleaning is in progress, in the control unit 8, how the end timing determination unit 81 changes the amount of the predetermined substance with time based on the measurement data acquired from the analyzer 7 (change with time). Is monitored and the end timing of the plasma cleaning is determined based on the mode of the change. A specific mode in which the end timing determination unit 81 determines the end timing will be described later.

When the end timing determination unit 81 determines that the end timing has arrived (YES in step S5), the end control unit 82 ends the plasma cleaning (step S6). Specifically, the termination control unit 82 closes the valves 23 and 33 to stop the supply of water vapor and oxygen gas, and stops the supply of high frequency power.

When the plasma cleaning is completed, the processing space V is returned to the atmospheric pressure, and the cleaning target 9 is carried out of the plasma cleaning chamber 11 (step S7).

<3. Determination of end timing>
As described above, when the measurement by the analyzer 7 is started, the acquired measurement data is sent to the control unit 8 one after another. The end timing determining unit 81 determines the amount of a predetermined substance (specifically, the emission intensity in the wavelength region corresponding to the predetermined substance (the analysis device 7 (In the case of an emission spectroscopic analyzer) or a change in signal intensity (in the case where the analyzer 7 is a mass analyzer) at a mass number corresponding to a predetermined substance), and the end timing of plasma cleaning is determined based on this. To do. However, as described above, this "predetermined substance" is derived from (i) plasma formed in the processing space V (specifically, plasma of a mixed gas of water vapor and oxygen gas or water plasma). At least one of the following substances, (ii) a substance derived from the cleaning target 9, or (iii) a substance derived from a substance attached to the cleaning target.
Hereinafter, three examples according to the mode in which the end timing determination unit 81 determines the end timing of the plasma cleaning will be described.

<Example 1>
In this embodiment, atomic oxygen, which is “(i) substance derived from plasma formed in processing space V”, and “(iii) substance derived from substance attached to cleaning target 9” At least one of certain carbon monoxide (CO) is a “predetermined substance”. That is, atomic oxygen, carbon monoxide, or both of them are set as the measurement target in the analyzer 7, and the end timing determination unit 81 monitors the time-dependent change in the amount of the target measurement target. The end timing of plasma cleaning is determined based on the above.

FIG. 4 shows measurement data obtained by using a plasma cleaning apparatus PC-300 manufactured by Samco Co., Ltd. as the plasma cleaning apparatus 100, and an emission spectrophotometer manufactured by Hamamatsu Photonics Co., Ltd. as the analysis apparatus 7 using a detection unit of product number C7460. It is a figure which shows the time-dependent change of each emission intensity of atomic oxygen (frequency: 777 nm) and carbon monoxide (frequency: 484 nm) acquired and specified based on the said measurement data.
In obtaining this data, plasma cleaning was performed under the following processing conditions. That is, the amount of water vapor introduced was 6 sccm, the amount of oxygen gas introduced was 14 sccm, and the pressure in the processing space V was maintained at about 12 Pa. Further, after 300 seconds from the start of the measurement by the analyzer 7, 250 W of high frequency power was applied to the powered electrode 5. A wafer having a photoresist (hydrocarbon) on its surface was used as the cleaning target 9.

As can be seen from FIG. 4, when the application of high-frequency power is started, luminescence from atomic oxygen is detected, and the luminescence intensity of atomic oxygen hardly changes for a while (time zone T1). Then, the emission intensity of atomic oxygen gradually increases at time t1 (time zone T2), and after time t2, the emission intensity of atomic oxygen becomes almost constant again (time zone T3).
On the other hand, after the emission of atomic oxygen is detected, the emission intensity of carbon monoxide gradually increases, and remains almost constant from a certain time. Then, the emission intensity of carbon monoxide gradually decreases at the same time as the time t1 at which the emission intensity of atomic oxygen starts to increase (time period T2), and the emission at the same time as the time t2 becomes the boundary. The emission intensity of carbon also becomes almost constant (time zone T3).

For some time after the application of high-frequency power is started (time period T1), a chemical reaction in which atomic oxygen decomposes organic substances (here, photoresist) on the wafer proceeds, and the atomic oxygen is added to the chemical reaction. It is considered that carbon monoxide is produced in the chemical reaction as the carbon is consumed. Further, in time period T2, it is considered that the consumption amount of atomic oxygen decreases and the production amount of carbon monoxide also decreases because the remaining amount of the photoresist has decreased. Then, in time period T3, it is considered that the consumption of atomic oxygen is zero and the production amount of carbon monoxide is also zero because the photoresist has completely disappeared. That is, the timing t2 at which the rate of change of the amount of atomic oxygen or carbon monoxide (specifically, the emission intensity) becomes zero (or a sufficiently small value) disappears from the wafer when the photoresist is almost completely decomposed. It can be estimated that the timing almost coincides with the timing. In fact, under the above processing conditions, the plasma cleaning is terminated and the wafer is unloaded from the plasma cleaning apparatus 100 at a time substantially coincident with the time t2 (specifically, about 600 seconds after the start of measurement by the analyzer 7). However, it was confirmed that the resist was completely removed from the surface of the wafer.

Therefore, the end timing determination unit 81 ends the plasma cleaning at this timing t2. Specifically, the end timing determination unit 81 determines whether or not the rate of increase of the atomic oxygen emission intensity gradually increases to zero after the emission intensity of atomic oxygen gradually increases (specifically, the increase rate is equal to or less than a predetermined value). Whether or not) is determined, and if a positive determination is obtained, the time is determined as the end timing. Alternatively, the end timing determination unit 81 determines whether or not the rate of decrease becomes substantially zero after the emission intensity of carbon monoxide gradually decreases (specifically, whether or not the decrease rate is equal to or less than a predetermined value. ) Is determined, and when a positive determination is obtained, the time is determined as the end timing.

By ending the plasma cleaning at such a timing t2, the plasma cleaning can be ended when the organic substances attached to the cleaning target 9 are sufficiently removed, and the plasma processing time is required for the cleaning. It is possible to prevent the characteristics of the cleaning object 9 from changing when the cleaning time is longer than the time. Further, the throughput of the plasma cleaning apparatus 100 can be improved by suppressing the plasma processing time to the necessary minimum.

<Example 2>
In this embodiment, at least one of carbon monoxide and carbon dioxide, which is “(iii) a substance derived from a substance attached to the cleaning target 9”, is a “predetermined substance”. That is, carbon monoxide, carbon dioxide, or both are set as the measurement target in the analyzer 7, and the end timing determination unit 81 monitors the change over time in the amount of the measurement target substance. Based on this, the end timing of the plasma cleaning is determined.

FIG. 5 shows measurement data obtained by using a plasma cleaning apparatus: PC-300 manufactured by Samco Co. as a plasma cleaning apparatus 100 and a quadrupole mass analyzer manufactured by Hyden: part number EQP analyzer series 1000 as an analyzer 7. FIG. 4 is a diagram showing a change over time of each signal intensity (count/second) of carbon dioxide (molecular weight 44) and carbon monoxide (molecular weight 28) identified based on the measurement data.
In obtaining this data, 125 W of high frequency power was applied to the powered electrode 5 60 seconds after the measurement by the analyzer 7 was started. The other processing conditions were the same as the processing conditions of Example 1. In addition, here, since the measurement of the analyzer 7 is performed every 60 seconds, the measurement value acquired 60 seconds after the start of measurement is plotted at the time “0”. Further, carbon dioxide and carbon monoxide detected at this time “0” are considered to be background concentrations of these substances in the processing space V. That is, the carbon dioxide and carbon monoxide detected at this time “0” are not derived from the plasma treatment.

As can be seen from FIG. 5, when application of high-frequency power is started, increases in carbon dioxide and carbon monoxide are detected, and the signal intensity of each substance hardly changes for a while (time zone T11). Then, at time t11, the signal intensities of carbon dioxide and carbon monoxide gradually weaken (time zone T12), and after time t12, the signal intensities of carbon dioxide and carbon monoxide become almost constant (time zone). T13).

For a while after the application of high-frequency power is started (time period T11), a chemical reaction of decomposing organic substances (here, photoresist) on the wafer proceeds, and carbon dioxide and carbon monoxide are generated in the chemical reaction. Is considered to have been generated. Further, in time period T12, it is considered that the production amounts of carbon dioxide and carbon monoxide are also reduced because the remaining amount of the photoresist has decreased. Then, in time zone T13, it is considered that the production amount of carbon dioxide and carbon monoxide is zero because the photoresist has completely disappeared. That is, at the timing t12 when the rate of change of the amount of carbon dioxide or carbon monoxide (specifically, the signal intensity) becomes zero (or a sufficiently small value), almost all the photoresist is decomposed and disappeared from the wafer. It can be estimated that the timing is almost the same. In fact, under the above processing conditions, the plasma cleaning is terminated and the wafer is unloaded from the plasma cleaning apparatus 100 at a time substantially coincident with the time t12 (specifically, about 550 seconds after the measurement by the analyzer 7 is started). However, it was confirmed that the resist was completely removed from the wafer surface.
Although the time from the start of application of the high frequency voltage to the timing t12 in the second embodiment is longer than the time from the start of application of the high frequency voltage to the timing t2 in the first embodiment, It is considered that the high frequency power was set to 250 W in the first embodiment, while it was set to 125 W in the second embodiment, and the ashing speed decreased.

Therefore, the end timing determination unit 81 ends the plasma cleaning at this timing t12. Specifically, the end timing determination unit 81 determines whether or not the rate of decrease becomes substantially zero after the signal intensity of carbon dioxide or carbon monoxide gradually decreases (specifically, a predetermined value). It is determined whether or not), and if a positive determination is obtained by this, the time is determined as the end timing.

By ending the plasma cleaning at such a timing t12, the plasma cleaning can be ended when the organic substances attached to the cleaning target 9 are sufficiently removed, as in the first embodiment. It is possible to prevent the characteristics of the cleaning object 9 from changing when the time is longer than the time required for cleaning. Further, the throughput of the plasma cleaning apparatus 100 can be improved by suppressing the plasma processing time to the necessary minimum.

<Example 3>
In this embodiment, atomic hydrogen, which is “(i) a substance derived from plasma formed in the processing space V”, is a “predetermined substance”. That is, atomic hydrogen is the measurement target in the analyzer 7, and the end timing determination unit 81 monitors the change over time in the amount of atomic hydrogen and determines the end timing of plasma cleaning based on this.

In the same manner as in Example 1, FIG. 6 uses a plasma cleaning apparatus PC-300 manufactured by Samco Co., Ltd. as the plasma cleaning apparatus 100, and an emission spectrophotometer manufactured by Hamamatsu Photonics Co., Ltd. as an analysis apparatus 7: a detection unit of product number C7460 FIG. 3 is a diagram showing a change over time in the emission intensity of atomic hydrogen (frequency: 657 nm), which was obtained based on the measurement data obtained by using the above-mentioned measurement data.
When acquiring this data, high frequency power was applied to the powered electrode 5 5 seconds after the start of measurement by the analyzer 7. The cleaning object 9 was a silver frame for LEDs that was oxidized to such a degree that the surface was black. The other processing conditions were the same as the processing conditions of Example 1.

As can be seen from FIG. 6, when application of high-frequency power is started, light emission from atomic hydrogen is detected, and the emission intensity of atomic hydrogen continues to increase gradually for a while (time zone T21). Then, at time t21, the emission intensity of atomic hydrogen becomes almost constant (time zone T22).

It is considered that a chemical reaction (reduction reaction) in which atomic hydrogen reduces silver oxide on the flame is progressing for a while after the application of high-frequency power is started (time zone T21). This reduction reaction starts from the peripheral portion of the silver oxide formed in the frame and gradually proceeds toward the central portion, so that the reduced area becomes smaller as time passes. Therefore, it is considered that the consumption amount of atomic hydrogen decreases as time passes (that is, the emission intensity of atomic hydrogen gradually increases). Then, in the time zone T22, it is considered that the consumption amount of atomic hydrogen is zero because all of the silver oxide is reduced. That is, it is estimated that the timing t21 at which the rate of change of the amount of atomic hydrogen (specifically, the emission intensity) becomes zero (or a sufficiently small value) almost coincides with the timing at which almost all silver oxide disappears from the frame. it can. In fact, under the above processing conditions, the plasma cleaning was terminated at the time substantially coincident with the time t21 (specifically, about 55 seconds after the start of the measurement by the analyzer 7), and the frame was carried out from the plasma cleaning apparatus 100. However, it was confirmed that all the silver oxide on the frame surface was reduced and returned to silver.

Therefore, the end timing determination unit 81 ends the plasma cleaning at this timing t21. Specifically, the end timing determination unit 81 determines whether or not the rate of increase of the atomic hydrogen emission intensity is gradually increased to zero after the emission intensity of atomic hydrogen is gradually increased (specifically, it is equal to or less than a predetermined value). Whether or not) is determined, and if a positive determination is obtained, the time is determined as the end timing.

By ending the plasma cleaning at such a timing t21, it is possible to end the plasma treatment at a stage before the reduction of silver oxide is completed and before the high resistance film is formed on the cleaning object 9.

<4. Modification>
In the above embodiment, the “predetermined substance” to be measured by the analyzer 7 is not limited to the ones exemplified above. For example, the hydroxyl radical may be the measurement target, and the end timing determination unit 81 may monitor the change over time in the amount of the hydroxyl radical and determine the end timing of the plasma cleaning based on this. Specifically, based on the rate of change of the emission intensity (or signal intensity) of the hydroxyl radicals, whether or not the consumption amount of the hydroxyl radicals has become almost zero (specifically, a value equal to or less than a predetermined value Whether or not) is determined, and if a positive determination is obtained, the time may be determined as the end timing.

The end timing determination unit 81 may combine the above-described first to third embodiments to determine the end timing. For example, the end timing determination unit 81 performs the determination according to the first exemplary embodiment and the determination according to the third exemplary embodiment in parallel, and selects the first (or the second) of the timing t2 and the timing t21. The arrival timing may be determined as the end timing.

In the above-described embodiment, the water (steam) in a gaseous state is introduced into the processing space V, but the water introduced into the processing space does not necessarily have to be in a gaseous state. It may be water, water in the form of ice mist, or the like.

1 Plasma Cleaning Chamber 2 Water Introducing Section 3 Oxygen Gas Introducing Section 4 Exhaust Section 5 Powered Electrode 6 Grounding Electrode 7 Analyzing Device 8 Control Section 9 Cleaning Target 11 Gas Inlet 12 Exhaust 13 Open 14 Window Member 21 Water Supply Source 31 Oxygen Gas supply sources 22, 32, 42 Pipes 23, 33, 43 Valves 24, 34 Mass flow controller 25 Vaporizer 44 Vacuum pump 51 RF power supply 52 Condenser 81 End timing determination unit 82 End control unit V Processing space 100 Plasma cleaning device

Claims (4)

A plasma cleaning chamber cleaned object that contains silver is located inside the surface,
A water introducing section for introducing water into the plasma cleaning chamber,
A plasma forming unit that forms water plasma by converting water introduced into the plasma cleaning chamber into plasma,
An analyzer for measuring the amount of a predetermined substance present in the plasma cleaning chamber,
A control unit that determines the end timing of the plasma cleaning based on the measurement data obtained from the analyzer, and terminates the plasma cleaning at the determined end timing,
Equipped with
The control unit,
The timing when the consumption amount of atomic oxygen existing in the plasma cleaning chamber per unit time is equal to or less than a predetermined value, and the consumption amount of atomic hydrogen existing in the plasma cleaning chamber per unit time is predetermined. of the timing value becomes less than or equal to a plasma cleaning device that determine said end timing of the timing arrive earlier. The plasma cleaning apparatus according to claim 1 , wherein
When introducing water into the plasma cleaning chamber, an oxygen gas introducing unit that also introduces oxygen gas,
Further equipped with,
The plasma forming unit converts a mixed gas of water and oxygen gas into plasma.
Plasma cleaning device. The plasma cleaning apparatus according to claim 1 or 2, wherein
The analyzer is an emission spectroscopic analyzer or a mass spectrometer,
Plasma cleaning device. A step of introducing water into a plasma cleaning chamber in which a cleaning object containing silver on the surface is placed to form a plasma by water and plasma cleaning the cleaning object with the water plasma;
Measuring the amount of a predetermined substance present in the plasma cleaning chamber with an analyzer, and determining the end timing of plasma cleaning based on the obtained measurement data;
Ending the plasma cleaning at the determined end timing,
Only including,
The step of determining the end timing, the timing when the consumption amount of atomic oxygen existing in the plasma cleaning chamber per unit time is equal to or less than a predetermined value, and the atomic hydrogen existing in the plasma cleaning chamber A plasma cleaning method , wherein among the timings when the consumption amount per unit time is equal to or less than a predetermined value, the timing that arrives earlier is determined as the end timing .

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