JP6551784B2 - Method and apparatus for managing carbonic acid concentration in resist stripping solution - Google Patents

Description

  The present invention relates to a method and an apparatus for managing the concentration of carbonic acid in a resist stripping solution used in a photolithography process, and in particular, when stripping a resist film having a novolak resin provided on a copper film with an alkaline solution. The present invention relates to a method and apparatus for managing carbonic acid concentration in a stripping solution.

  Photolithography processes are used to fabricate integrated circuits and are now also used to form thin film transistor circuitry for displays such as flat panels. In the etching, a resist film is formed into a shape of a pattern desired to be left or removed from the target thin film, the target thin film is processed by wet etching or dry etching, and the unnecessary resist film is then removed. In particular, the opportunity to process conductive lines by wet etching is very numerous at present.

  Conventionally, the conductive line was formed of aluminum. This is because the resist was able to be peeled off without affecting other films because of its high conductivity and relatively high resistance to alkaline solutions.

  However, when a large number of transistors are formed over a wide area, such as a flat panel, a material having higher conductivity than aluminum is required. Copper is inexpensive and has higher conductivity than aluminum, making it a suitable material for use in flat panels. However, since copper easily dissolves not only in an acidic solution but also in an alkaline solution, there is a problem that the copper film disappears in the resist stripping step.

  In response to this problem, Patent Document 1 shows a technique for reducing the damage to the copper film by adding an additive to the resist stripping solution and enabling the resist stripping of the copper film. Thereafter, in Patent Document 2, an alkaline stripping solution using an amine was proposed.

  Furthermore, a resist stripping solution having a tertiary amine, two types of polar solvents and water has been proposed. This resist stripping solution can strip the resist on the copper film without damaging the so-called positive resist containing the novolak resin formed on the copper film.

  On the other hand, Patent Document 4 has reported that when the concentration of carbonic acid in the resist stripping solution increases with respect to the lifetime of the resist stripping solution, the stripping force decreases. In Patent Document 4, when the concentration of carbonic acid in the resist stripping solution exceeds 3% by weight, the stripping force is considered to be reduced.

JP 2001-188363 A JP2012-113101A JP, 2012-225959, A JP 2003-122029 A

  The resist stripping solution containing a tertiary amine, two types of solvents and water can be suitably used for copper etching as described above. However, during use, the phenomenon that the surface of the copper film was roughened before the resist peeling force decreased was confirmed.

  It is known from experience that that the surface of the copper film is rough, although it does not occur that the copper film disappears or partially disappears, but that the copper film disappears or partially disappears. That is, the rough surface of the copper film is understood to be that the copper film is corroded from the surface.

  If the surface of the copper film is rough and uneven, the possibility of chemicals and water remaining in the recessed portions increases in the resist stripping process. When the chemical solution or water remains in the dent, there is a problem in that the remaining chemical solution or moisture expands due to heating in the film forming step after the peeling step, causing a problem such as film peeling.

  The present invention was conceived in view of the above problems, and when the carbonic acid component in the resist stripping solution rises, the electric conductivity rises, and the galvano current flows, so that the copper film dissolves little by little. It was concluded that this was the cause and the present invention was conceived. That is, the present invention provides a method and an apparatus for managing the carbonic acid concentration in a resist stripping solution for stably stripping a resist film containing a novolak resin on a copper film with the resist stripping solution.

More specifically, the carbon dioxide concentration management method in the resist stripping solution according to the present invention is as follows:
A resist film composed of novolak resin and naphthoquinone diazo formed on a copper film,
Tertiary amines,
Polar solvent,
A step of stripping with a resist stripping solution containing water;
Measuring the carbonic acid concentration in the resist stripping solution with an NDIR apparatus;
When the carbonic acid concentration in the resist stripping solution reaches 2000 ppm or more, the method further comprises the step of replacing at least a part of the resist stripping solution.

Moreover, the carbonic acid concentration management device in the resist stripper according to the present invention is
A resist film composed of novolak resin and naphthoquinone diazo formed on a copper film,
Tertiary amines,
Polar solvent,
A device for managing the concentration of carbonic acid in a resist stripping solution used for a resist stripping device that is stripped while being circulated and used from a reservoir for storing a resist stripping solution containing water,
A pipe for sample acquisition for taking out the resist stripping solution in the reservoir;
An NDIR device connected to the sample acquisition pipe;
The apparatus is characterized by comprising a control device for transmitting a signal for replacing a part of the resist stripping solution when the carbonic acid concentration in the resist stripping solution measured by the NDIR apparatus reaches 2000 ppm or more.

  In the carbonic acid concentration management method in the resist stripping solution according to the present invention, when the carbonic acid component concentration in the resist stripping solution reaches 2000 ppm or more, at least a part of the resist stripping solution is replaced. Therefore, the carbonic acid component in the resist stripping solution is always less than 2000 ppm. To be maintained. Therefore, even if the resist film having a novolac resin formed on the copper film is peeled off, the roughness of the copper film can be suppressed.

  Further, the carbonic acid component in the resist stripping solution is measured using a non-dispersive infrared absorber. Therefore, the sensitivity is very high, and even if the resist component dissolved in the resist stripping solution increases, the measurement can be continued with the same accuracy.

It is a figure which shows the structure of a resist stripping apparatus and the carbonic acid concentration management apparatus in the resist stripping solution which concerns on this invention. It is a figure which shows the structure of NDIR apparatus. It is a graph which compares the measurement precision of NDIR and electrical conductivity. It is the photograph which carried out the SEM observation of the corrosion state of the surface of a copper film in the case where the carbonic acid density | concentration in a resist stripping solution is 20 ppm, and 2000 ppm.

  Hereinafter, a carbon dioxide concentration management method and management apparatus in a resist stripping solution according to the present invention will be described with reference to the drawings. The following description shows one embodiment of the present invention, and modifications and implementations can be made without departing from the spirit of the present invention.

  FIG. 1 shows a configuration of a carbon dioxide concentration management device in a resist stripping solution according to the present invention. The carbonic acid concentration management device 1 in the resist stripping solution may be a part of the resist stripping device 50. The resist stripping apparatus 50 includes a conveyor 54 for transporting the object 62, a reservoir 52 for resist stripping solution provided below the conveyor 54, and a shower pipe 56 disposed from the reservoir 52 to above the conveyor 54. A shower 58 for spraying a resist stripping solution on the object 62 to be processed and a pump 60 provided in the middle of the shower pipe 56 are included.

  The carbonic acid concentration management device 1 in the resist stripping solution includes a sample acquisition pipe 12 that delivers the stripping solution from the storage unit 52, an NDIR device 10 connected to the pipe, and a control device connected to the NDIR device 10. Have fourteen. Further, the display device 16 may be connected to the control device 14.

  The sample acquisition pipe 12 is for acquiring a part of the resist stripping solution from the shower pipe 56 or the reservoir 52 of the resist stripping apparatus 50. Therefore, one end of the sample acquisition pipe 12 may be connected to at least one of the storage section 52 and the shower pipe 56. In addition, even if it is the sample of resist stripping liquid acquired from any place, it may be said that the resist stripping liquid in the storage part 52 was acquired. In the resist stripping device 50, the resist stripping solution is circulating.

  The other end of the pipe 12 for sample acquisition is connected to an NDIR (Non Dispersive Infra Red) device (non-dispersive infrared absorption device) 10. As well known, the NDIR device 10 is a device that measures the amount of absorption without dispersing light. FIG. 2 shows a simple principle. The sampled resist stripping solution is introduced into the gas generating cell 20. Into the gas generating cell 20, a strong inorganic acid solution is injected in advance.

  In the gas generation cell 20, bubbling is performed with an inert gas or the like in a state where the resist stripping solution and the inorganic strong acid solution are mixed. The carbonic acid component in the resist stripping solution becomes carbon dioxide gas by the inorganic strong acid solution in the gas generating cell 20, vaporizes, and is stored in the head space 20 h of the gas generating cell 20. It is introduced into the absorption chamber 24 together with the carrier gas.

  The absorption chamber 24 is formed of a transparent member at one end and the other end, and enters light from the light source 28 that has passed through the slit 26 from one end. Here, the light from the light source 28 is introduced into the absorption chamber 24 without being dispersed. Light that has passed through the other end of the absorption chamber 24 is introduced into the measurement chamber 30. The measuring chamber 30 is divided into at least two chambers by a thin film 32.

  The chamber closer to the absorption chamber 24 is a carbon dioxide chamber 34 filled with carbon dioxide, and the other chamber is a capacity chamber 36 for detecting volume such as capacitance. The volume chamber 36 is provided with a terminal 38 t of a measuring device 38 for detecting a change in volume of the volume chamber 36.

  The light emitted from the light source 28 passes through the absorption chamber 24. At this time, if the absorption chamber 24 contains carbon dioxide, only the wavelength component that responds to carbon dioxide is absorbed according to the amount of carbon dioxide. The light that has passed through the absorption chamber 24 enters the carbon dioxide chamber 34 and heats and expands the carbon dioxide by the amount of light remaining in the wavelength component that carbon dioxide can absorb. That is, the NDIR apparatus 10 measures the amount of carbon dioxide gas by replacing the absorption of light with a change in volume. The measured amount of carbon dioxide is transmitted to the control device 14 by the signal Sc.

  Note that the NDIR apparatus 10 can remove moisture in the vicinity of carbon dioxide and the absorption band from the sample gas sent to the absorption chamber 24, and drive out the carbonic acid component in the resist solution. Selection of a carrier gas with a different absorption band is a point for accurate measurement. In FIG. 2, the example which provided the cooler 22 in the middle of the carbon-dioxide transfer piping 40 from the gas generation cell 20 to the absorption chamber 24 was shown.

  The operation of the carbon dioxide concentration management device 1 in the resist stripping solution having the above-described configuration will be described. Referring again to FIG. 1, the workpiece 62 is placed on the conveyor 54 and transferred into the resist stripping apparatus 50. The workpiece 62 is a substrate on which the steps of exposure and rinsing have been completed. Therefore, there is at least a copper film and a resist film formed on the copper film on the substrate. The resist film is composed of a mixture of novolak resin and naphthoquinone diazo (NQD).

  In the resist film, when exposed to light, naphthoquinone diazo changes to indene carboxylic acid and dissolves in an alkaline solution. Therefore, the resist film remaining on the copper film in the resist stripping process is a resist film which is a mixture of novolak resin and naphthoquinone diazo and which has been subjected to a heating process (baking process) in order to strengthen the resist film.

  In the resist stripping device 50, the resist stripping solution collected in the storage unit 52 is transferred by the pump 60 through the shower pipe 56 to the shower 58. Then, the resist stripping solution is discharged onto the object 62 from the shower 58. The discharged resist stripping solution strips the resist film on the workpiece 62 and returns to the storage unit 52. Thus, the resist stripping solution is delivered from the reservoir 52, and after stripping the resist film, returns to the reservoir 52 again. That is, it can be said that the resist stripping solution is circulated from the storage unit 52.

  The resist stripping solution is a mixture of a tertiary amine, two types of polar solvents, and water. Here, diethylene glycol monobutyl ether (BDG) and propylene glycol (PG) can be suitably used as the two polar solvents.

  Since the resist stripping solution is circulated, the concentration of the carbonic acid component gradually increases. Then, the surface of the copper film of the workpiece 62 becomes rough. Therefore, the concentration of the carbonic acid component is measured by the NDIR apparatus 10.

  More specifically, the NDIR apparatus 10 acquires the resist stripping solution from the reservoir 52 in accordance with an instruction from the controller 14. Acquisition of the resist stripping solution is carried out by transferring the resist stripping solution into the NDIR apparatus 10 through the pipe 12 for sample acquisition. The sample acquisition pipe 12 may be provided with a sample acquisition pump 13 in the middle.

  The NDIR apparatus 10 bubbles the sampled resist stripping solution with argon gas, and introduces the generated gas into the absorption chamber 24. Then, light is irradiated into the carbon dioxide chamber 34 through the absorption chamber 24 for a predetermined time. Then, the volume expansion of carbon dioxide in the carbon dioxide chamber 34 is measured by the change of the capacity chamber 36. The NDIR device 10 notifies the control device 14 of this volume expansion as a signal Sc.

  The control device 14 that has received the signal Sc determines whether or not the volume expansion of carbon dioxide (proportional to the carbonic acid component in the resist stripping solution) exceeds a predetermined threshold value. If the threshold value is exceeded, a caution signal Sw is transmitted to the effect that the copper film surface may be roughened. The transmission destination may be, for example, the display 16.

  The control unit (not shown) of the resist stripping apparatus 50 can perform a process of receiving this signal and replacing a part of the resist stripping solution.

  The carbonic acid concentration management device 1 in the resist stripping solution periodically detects the concentration of the carbonic acid component in the resist stripping solution in the reservoir 52. Therefore, the previous attention signal Sw is canceled when the concentration of the carbonic acid component in the resist stripping solution falls below the threshold value. Alternatively, a signal Sr that informs that the resist stripper can be used safely may be transmitted.

  As described above, according to the method for managing the carbonic acid concentration in the resist stripping solution and the resist stripping solution management apparatus according to the present invention, the carbonic acid component in the resist stripping solution can be maintained at less than 2000 ppm. It can be said that damage to the surface can be suppressed and is substantially avoided.

  Examples of the method and apparatus for managing the carbonic acid concentration in the resist stripper according to the present invention will be described below.

<Reason for using the NDIR device 10>
In the present invention, it is necessary to detect a trace amount of the carbonic acid component in the resist stripping solution. In such a case, there is also a method for measuring the electrical conductivity of the resist stripping solution. However, since the resist stripping solution is an alkaline solution, various ionic components are present therein, and it is not suitable for the measurement of a small amount. It confirmed in the following Example.

The resist stripping solution used has the following composition.
Tertiary amine (MDEA (N-methyldiethanolamine)) 1.5 mass%
Polar solvent (BDG (diethylene glycol monobutyl ether)) 40% by mass
Polar solvent (PG (propylene glycol)) 28.5% by mass
Water 30% by mass

Carbon dioxide gas was bubbled into the resist stripping solution. From the weight of the resist stripping solution before and after bubbling, the amount of carbon dioxide prepared in the resist stripping solution was defined as the CO ₂ blending value (ppm). Next, the amount of CO ₂ in the resist stripping solution is measured by the NDIR apparatus 10 (carrier gas is Ar gas), and the results of measurement of the electric conductivity are shown in FIG.

FIG. 3A shows the case where the NDIR apparatus 10 is used, and FIG. 3B shows the case where the electrical conductivity is measured. In both graphs, the horizontal axis represents the CO ₂ preparation value (ppm). The vertical axis in FIG. 3A is the measured CO ₂ value (ppm), and the vertical axis in FIG. 3B is the electrical conductivity (mS / m).

In the case of the NDIR device 10, good linearity is exhibited even when the CO ₂ content is less than 2000 ppm. On the other hand, in the case of electrical conductivity, if the blending ratio is less than 2000 ppm, the linearity is deteriorated. In addition, the change in electrical conductivity is small with respect to the CO ₂ preparation value, and the sensitivity is poor.

  In particular, in the examples described later, roughening was confirmed on the surface of the copper film when the carbonic acid component in the resist stripping solution was 2000 ppm. Therefore, in the management method (or management device) of the carbonic acid concentration in the resist stripping solution according to the present invention, it is desirable to measure the carbonic acid concentration using the NDIR apparatus 10.

<About roughness on copper film (corrosion evaluation)>
For some resist stripping solutions, the state of copper film roughness (hereinafter also referred to as “corrosiveness”) due to changes in carbonic acid concentration was confirmed by experiments.

  In each case, the resist used was 50% by mass of novolak resin and 50% by mass of naphthoquinone diazo.

  As a substrate for corrosive evaluation, a silicon thermal oxide film is formed to a thickness of 100 nm on a silicon substrate, a copper film is formed to a thickness of 300 nm on the silicon thermal oxide film by a sputtering method, and a Cu film sample is produced. did. This is called “Cu gate”. Similarly, a molybdenum film was formed to a thickness of 20 nm on a silicon thermal oxide film on a silicon substrate, and a copper film was subsequently formed to a thickness of 300 nm to prepare a Cu / Mo laminated film sample. . This is called "Cu / Mo gate". In addition, an aluminum film was formed to a thickness of 300 nm on the silicon thermal oxide film on the silicon substrate to prepare an Al film sample. This is called “Al gate”.

  On these evaluation samples, a resist patterned in a wiring shape was formed to a thickness of about 1 μm, and used as a substrate for corrosion evaluation. In other words, the corrosive evaluation substrate includes a Cu film, a Cu / Mo film, and an Al film formed on a silicon thermal oxide film on a silicon substrate, and a resist layer formed in a wiring shape thereon. Consists of. Note that these substrates for evaluating corrosion were subjected to heat treatment (baking treatment) at 140 ° C. for 5 minutes.

  Etching was performed by immersing these corrosive evaluation substrates in an etchant for copper film or aluminum film for just etching time. Thereafter, the substrate for corrosivity evaluation after etching was immersed in a sample resist stripping solution maintained at 40 ° C. for 2 minutes to strip the resist film. After the corrosive evaluation substrate immersed in the sample resist stripping solution for 2 minutes was washed and dried, the surface of the copper film was observed by SEM (Scanning Electron Microscope). The SEM observation conditions were 30 kV and a magnification of 30,000.

  The evaluation method was a round mark when no corrosion was observed in the copper film, the molybdenum film or the aluminum film by SEM observation, and a cross mark was observed when a clear corrosion or peeling of the film was observed.

  The judgment of just etching was made when the silicon thermal oxide film was visually confirmed from the start of etching.

  Next, the composition of the sample resist stripping solution will be shown. In addition, although the carbonic acid concentration in the composition is mass% (indicated in ppm), since it is added later, the amount is based on 100 mass% of other components. That is, the following composition exceeds 100 mass% when including carbonic acid concentration.

Example 1
Example 1 used the sample resist stripping solution with the following composition.
Tertiary amine (MDEA (N-methyldiethanolamine)) 5.0 mass%
Polar solvent (BDG (diethylene glycol monobutyl ether)) 40.0% by mass
Polar solvent (PG (propylene glycol)) 24.0% by mass
Water 31.0% by mass
Carbonate concentration 20 ppm

(Comparative example 1)
Comparative Example 1 was a sample resist stripping solution having the following composition.
Tertiary amine (MDEA (N-methyldiethanolamine)) 5.0 mass%
Polar solvent (BDG (diethylene glycol monobutyl ether)) 40.0% by mass
Polar solvent (PG (propylene glycol)) 24.0% by mass
Water 31.0% by mass
Carbon dioxide concentration 2000 ppm

(Example 2)
In Example 2, a sample resist stripping solution having the following composition was used.
Tertiary amine (MDEA (N-methyldiethanolamine)) 5.0 mass%
Polar solvent (BDG (diethylene glycol monobutyl ether)) 40.0% by mass
Polar solvent (PG (propylene glycol)) 20.6% by mass
Water 31.0% by mass
Additive (amino alcohol (MMA)) 1.9% by mass
Additive (sorbitol) 1.5% by mass
Carbonate concentration 20 ppm

(Comparative example 2)
Comparative Example 2 was used as a sample resist stripping solution with the following composition.
Tertiary amine (MDEA (N-methyldiethanolamine)) 5.0 mass%
Polar solvent (BDG (diethylene glycol monobutyl ether)) 40.0% by mass
Polar solvent (PG (propylene glycol)) 20.6% by mass
Water 31.0% by mass
Additive (amino alcohol (MMA)) 1.9% by mass
Additive (sorbitol) 1.5% by mass
Carbon dioxide concentration 2000 ppm

  The composition and results are shown in Table 1 for Example 1 or Example 2 and Comparative Example 1 or Comparative Example 2.

  Referring to Table 1, Example 1 and Comparative Example 1 have the same resist stripping solution composition, and the carbonic acid concentration differs between 20 ppm and 2000 ppm. As a result, when the carbonic acid concentration was 20 ppm as in Example 1, there was no problem in SEM observation. However, when the carbonic acid concentration was 2000 ppm, the surface of the copper film was obviously corroded and roughened. This is not a level at which the copper film itself peels off or dissolves and disappears.

  However, the roughening of the surface of the copper film adversely affects the adhesion to the film formed thereon, and eventually becomes the cause of peeling or disappearance. Therefore, in the state of 2000 ppm, it can be judged that it is better to replace at least a part of the resist stripping solution.

  Further, Example 2 and Comparative Example 2 have the same composition, and the carbonic acid concentrations are different, such as 20 ppm and 2000 ppm. Example 1 and Example 2 are the difference between the case where the additive is not contained and the case where the additive is contained. The results were the same as those in Example 1 and Comparative Example 1. That is, the surface of the copper film of Comparative Example 2 was corroded.

  FIG. 4 shows an SEM photograph at this time. FIG. 4A shows the case of the first embodiment. Since the case of Example 2 was also indistinguishable from the case of Example 1 by SEM photo observation, FIG. 4A shows the case of Examples 1 and 2. In all the photographs, the white arrow at the lower right indicates a length of 1 μm.

  When the carbonic acid concentration in the resist stripping solution was 20 ppm, the surface of the copper film was almost indistinguishable from the state after film formation. On the other hand, in the case of Comparative Example 1, the surface of the copper film was clearly uneven, and it was confirmed that corrosion was progressing. Further, in the case of Comparative Example 2 as well, although not as great as Comparative Example 1, asperity was clearly recognized in comparison with Examples 1 and 2, and it was confirmed that corrosion was progressing.

  The resist stripping solution according to the present invention can be suitably used in a method of controlling the concentration of carbonic acid in a resist stripping solution based on the composition of Cu, a tertiary amine, a polar solvent, and water.

DESCRIPTION OF SYMBOLS 1 Carbon dioxide concentration management apparatus in resist stripping solution 10 NDIR apparatus 12 Piping for sample acquisition 13 Sample acquisition pump 14 Control apparatus 16 Display 20 Gas generating cell 20 h Head space 22 Cooler 24 Absorption room 26 Slit 28 Light source 30 Measurement room 32 Thin film 34 carbon dioxide chamber 36 volume chamber 38 measuring instrument 38 t terminal 40 carbon dioxide transfer piping 50 resist stripping device 52 reservoir 54 conveyor 56 shower pipe 58 shower 60 pump 62 object Sc signal Sw signal Sr signal

Claims (4)

A resist film composed of novolak resin and naphthoquinone diazo formed on a copper film,
Tertiary amines,
Polar solvent,
A step of stripping with a resist stripping solution containing water;
Measuring the carbonic acid concentration in the resist stripping solution with an NDIR apparatus;
A method for managing a carbonic acid concentration in a resist stripping solution, comprising the step of replacing at least a part of the resist stripping solution when the carbonic acid concentration in the resist stripping solution reaches 2000 ppm or more. The tertiary amine is MDEA (N-methyldiethanolamine),
The polar solvent is BDG (diethylene glycol monobutyl ether);
2. The method for controlling the concentration of carbonic acid in a resist stripping solution according to claim 1, which is a mixed polar solvent with PG (propylene glycol). A resist film composed of novolak resin and naphthoquinone diazo formed on a copper film,
Tertiary amines,
Polar solvent,
A carbon dioxide concentration management device in a resist stripping solution for use in a resist stripping apparatus for stripping while being cyclically used from a reservoir storing a resist stripping solution containing water, comprising:
A pipe for sample acquisition for taking out the resist stripping solution in the reservoir;
An NDIR device connected to the sample acquisition pipe;
In the resist stripping solution, comprising a control device for transmitting a signal for exchanging a part of the resist stripping solution when the carbonic acid concentration in the resist stripping solution measured by the NDIR apparatus reaches 2000 ppm or more. Carbon dioxide concentration management device. The tertiary amine is MDEA (N-methyldiethanolamine),
The polar solvent is BDG (diethylene glycol monobutyl ether);
The carbon dioxide concentration control device in a resist stripping solution according to claim 3, which is a mixed polar solvent with PG (propylene glycol).