JP3940742B2 - Cleaning method - Google Patents

Description

The present invention relates to a cleaning method and a cleaning apparatus, and more particularly to a cleaning method and a cleaning apparatus capable of peeling and removing an organic film such as a photoresist on a precision substrate such as a semiconductor substrate or a liquid crystal substrate at room temperature.

Conventionally, in a wet process of manufacturing a semiconductor device or a liquid crystal display, the photoresist removal is performed at a high temperature of 100 to 150 ° C. by mixing sulfuric acid and hydrogen peroxide solution in a stock solution. Alternatively, a method is used in which an organic solvent having a high concentration is treated at a high temperature, and then the organic solvent adhering to the precision substrate is further treated with another organic solvent. In addition, when ion implantation or reactive ion etching is performed using a photoresist as a mask, a large amount of ions are irradiated on the photoresist surface, and the photoresist material itself is almost carbonized (carbonized). The remaining photoresist is removed by chemicals after burning and removing the carbonized photoresist portion by a plasma treatment method using plasma, ultraviolet light (UV) and ozone gas.

However, in the method using sulfuric acid / hydrogen peroxide, because of the high temperature treatment using high concentration chemicals, the operability of the cleaning liquid and silicon wafer transfer is poor, and the hydrogen peroxide in the cleaning liquid is decomposed. In addition to complicated management, a large amount of chemical vapor and water vapor is generated, and a large amount of clean air is required to remove them, and a facility for removing chemical vapor from exhaust air is required. In addition, there are disadvantages that the cost of power, the cost of equipment, and the like become expensive, and that it costs more for the treatment of waste chemicals such as sulfuric acid.

Even in the method using an organic solvent, since the high-temperature treatment is performed, the operability is poor and the waste liquid treatment is also troublesome. Whether it is sulfuric acid / hydrogen peroxide solution or organic solvent treatment, the removal mechanism is dissolution of the photoresist. Therefore, since all of the photoresist coated with a thickness of 1 to 2 μm is dissolved on almost the entire surface of the substrate such as a semiconductor, there is also a drawback that the removal chemical solution is extremely deteriorated.

The plasma processing method has a drawback in that contaminants such as metals and fine particles contained in the photoresist remain on the wafer after processing.

The present invention solves the problems of conventional cleaning methods and apparatuses, and removes organic coatings such as photoresist on precision substrates such as semiconductor substrates and liquid crystal substrates at room temperature instead of dissolving them. An object of the present invention is to provide a cleaning method having extremely excellent characteristics such as that the cleaning liquid does not deteriorate for a long time, has a high cleaning effect, and hardly generates chemical vapor or water vapor, so that the apparatus is miniaturized and simplified.

The present inventors have reduced the damage to precision substrates, for example, underlying materials and pattern shapes, and saved organic resources in a conventional organic film removal technique such as photoresists that can save resources and achieve zero emissions. It has been found that it is effective to carry out peeling and removal in place of the film dissolution and removal method.

In other words, the conventional method for dissolving and removing organic coatings by high-temperature treatment using high-concentration chemicals generates a large amount of harmful chemical vapor and water vapor. As a result, the precision substrate is damaged, and there are many problems such as a decrease in manufacturing yield and a decrease in product reliability.

However, in the organic film removal technology, by reducing the contact angle of the cleaning liquid used on the surface of the organic film, it becomes possible to perform organic film removal cleaning by the peeling removal method from organic film removal cleaning by the conventional dissolution removal method. The chemical solution used to reduce the contact angle on the coating surface is a low-concentration organic solvent, and the cleaning temperature is near room temperature, so resources can be saved, zero emissions are possible, and a cleaning method that addresses environmental issues The present inventors have clarified that this is possible.

The method of cleaning according to 請 Motomeko 1, the organic solvent was diluted with pure water, the cleaning solution was added ammonium fluoride or a metal halide salt, and carrying out organic coating removal.

Further, the cleaning method according to claim 2 is characterized in that the organic film is removed by a cleaning liquid to which hydrofluoric acid for etching the substrate material under the organic film is added.

The cleaning method according to claim 3 is characterized in that the organic film is removed in a sealed atmosphere .

The cleaning method according to claim 4 is characterized in that the organic film is a photoresist after ion implantation or / and reactive ion etching .

The cleanup method of claim 5, characterized in that the organic solvent used is isopropyl alcohol.

Since the present invention is a cleaning method capable of peeling and removing an organic film such as a photoresist on a precision substrate such as a semiconductor substrate, a liquid crystal glass substrate, and a magnetic disk at room temperature, the cleaning liquid may include metal ions, particles, and other organic solvents. Thus, an extremely high cleanliness that only a very small amount of impurities such as these are contained is required, and an organic solvent that is currently purified and easily available for electronic materials is isopropyl alcohol.

Therefore, by using isopropyl alcohol as the organic solvent, it is possible to provide a cleaning liquid that maintains the cleanliness required for a precision substrate, and thus a cleaning liquid that is very easy to use as a cleaning liquid for electronic device parts can be obtained.

The cleaning method according to claim 6 is characterized in that the metal halide salt is potassium fluoride and / or potassium chloride.

It has been reported that residues of potassium, fluorine, and chlorine (substances remaining on the surface of precision substrates as cleaning residues) are relatively easy to clean and remove. These compounds, potassium fluoride and / or potassium chloride, have been reported. By using it, the organic film can be peeled and removed in a short time, and the residue can be easily cleaned after the peeling and removal.

The concentration of hydrofluoric acid is preferably 0.05 to 0.5 wt%, and ammonium fluoride is preferably 0.6 to 6.5 wt%.

The concentration of potassium fluoride is preferably 0.05 to 10 wt%, and the concentration of potassium chloride is preferably 0.5 to 10 wt%.

The effects of the invention according to the present invention will be described. The present invention is characterized in that an organic film is removed with a cleaning liquid in which an organic solvent is diluted with pure water and ammonium fluoride or a metal halide salt is added. By adding hydrofluoric acid that etches the underlying substrate material or ammonium fluoride, potassium fluoride, or potassium chloride to improve the penetration of the cleaning liquid into the precision substrate and organic coating interface, ion implantation or / and An extremely high cleaning effect can be obtained even after a process such as reactive ion etching where the photoresist material itself is almost carbonized and difficult to remove.

In addition, since the chemicals used are few and the concentration is low, it also addresses environmental problems.

Furthermore, since almost no chemical vapor or water vapor is generated, the size of the device can be simplified and the occupied area of the device can be reduced, so that space can be saved, and the cost of manufacturing factories such as semiconductor devices and liquid crystal displays can be reduced. Can contribute.

Hereinafter, embodiments of the present invention will be specifically described in detail, but the present invention is not limited thereto.

As a result of various investigations on the types and concentrations of chemicals used in the organic film removal cleaning method for photoresists such as photoresist after ion implantation and reactive ion etching of precision substrates such as semiconductor substrates and liquid crystal substrates, the present inventors A completed example is shown in FIG. 1 and FIG.

FIG. 1 shows a cleaning apparatus that removes and removes photoresist using an immersion method. First, a cleaning liquid 502 in which any one or more of hydrofluoric acid, ammonium fluoride, potassium fluoride, or potassium chloride is mixed with a solution of an organic solvent diluted with pure water is prepared, and a cleaning liquid storage tank 506 is prepared. To supply. The cleaning liquid is pressurized by the pump 507 and sent to the membrane degassing device 508. After the dissolved gas in the cleaning liquid is removed, the cleaning liquid is sent to the inner tank 501 of the cleaning tank.

The concentration of hydrofluoric acid in the cleaning liquid 502 is preferably 0.05 to 0.5 wt%, and the concentration of ammonium fluoride is preferably 0.6 to 6.5 wt%. Moreover, the compounding quantity of potassium fluoride is preferably 0.05 to 10 wt%, and the compounding quantity of potassium chloride is preferably 0.5 to 10 wt%.

On the other hand, the pure water 504 is degassed by the membrane degassing device 509, cooled to a desired temperature by the heat exchanger 510, and this cooling pure water can also be recovered and reused.

An ultrasonic transducer 505 is attached to the outer wall of the outer tank 503. The wafer to which the photoresist is attached is immersed in the inner tank 501, and the photoresist is removed by irradiating the ultrasonic wave with the ultrasonic vibrator 505.

More specifically, by applying a voltage to the ultrasonic vibrator 505, ultrasonic waves oscillated from the ultrasonic vibrator 505 are irradiated to the cleaning solution 502 via the outer tank 503, the pure water 504, and the inner tank 501. In addition, due to the synergistic effect of the ultrasonic wave and the cleaning solution component, the photoresist on the precision substrate is peeled and removed very effectively at a temperature near room temperature.

The level sensor 511 attached to the inner tank 501 is for controlling the liquid level, and the level sensor 512 attached to the outer tank is for preventing the ultrasonic vibrator from cooking empty.

The cleaning liquid is returned to the tank 506 through the filter 514 by the pump 513. The photoresist peeled from the wafer is removed by a filter 514. In the example shown in the figure, two series of filters are arranged in two stages. When the removal rate decreases, the filter series is switched. For example, a filter that removes photoresist particles of 0.5 μm or more may be used as the front-stage filter, and a filter that removes particles of 0.05 μm or more may be used in the latter stage.

Regarding the reason for cooling the pure water 504 to a desired temperature, the inventors of the present invention preferably set the temperature of the cleaning liquid 502 to 15 to 40 ° C., more preferably 20 with respect to the dependency of the cleaning effect on the cleaning liquid temperature. It was found that ˜35 ° C. is more preferable. When the temperature exceeds 40 ° C., the photoresist dissolves and appears to be firmly adsorbed to the precision substrate, so that the removal effect is reduced. Further, even in a low temperature range, the surface tension of the cleaning liquid increases and the liquid does not easily penetrate the interface between the photoresist and the precision substrate, so that the removal effect is reduced. However, in the cleaning method of the present invention, the temperature of the cleaning liquid is not limited, and in this example, an example in which the heat exchanger 510 is attached so that the desired removal effect can be appropriately adjusted. Show. Since there are already various commercially available cleaning liquid temperature control devices, any means may be used for temperature control.

Further, the degree of increase in the cleaning liquid temperature varies depending on conditions such as ultrasonic power, frequency, and irradiation time. There are various methods for keeping the temperature within a predetermined range. For example, as shown in this example, pure water 504 may be circulated between a constant temperature bath and a heat exchanger 510. Moreover, it is effective to suppress the temperature rise by intermittently irradiating ultrasonic waves.

The ultrasonic frequency is preferably in the range of 0.8 to 10 MHz. When the frequency is lower than 0.8 MHz, cavitation is likely to occur, and the shape destruction of the fine element processed on the semiconductor substrate or the like may occur. Cavitation does not occur at 0.8 MHz or higher, and sound pressure (vibration acceleration) increases at higher frequencies, and the effect of removing the photoresist becomes higher, which is preferable. A large device is required. However, in the cleaning method of the present invention, the ultrasonic frequency is not limited, and appropriate adjustments may be made so as to obtain a desired removal effect, and a necessary apparatus may be arranged.

Further, the present inventors have found that there is a high photoresist removing effect near the liquid surface, and it is more preferable to raise and lower the precision substrate during cleaning. Thereby, the photoresist removal effect is further improved. The reason for this is that at the liquid level, a high cleaning liquid flow velocity can be obtained by ultrasonic waves, and the combined wave (standing wave) of the straight wave and reflected wave on the liquid surface becomes dense near the interface. It is considered that the cleaning effect is enhanced due to the formation of active parts.

Further, it is more preferable that the precision substrate is swung left and right so that the sound wave is uniformly irradiated and the cleaning effect is further enhanced.

Further, since it is a well-known fact that the removal effect of the photoresist can be further enhanced by providing scratches on the photoresist surface in advance, it is preferable to scratch the photoresist surface before removing the photoresist. As a method of scratching, for example, a method of tracing with a fine needle, a method of spraying fine ice (ice scrub method), a treatment with ozone water (5 to 20 ppm), or a photoresist by irradiating ozone water with ultrasonic waves There are methods to roughen the surface. The scratch is preferably formed as deep as possible within a range that does not damage the substrate surface. Further, the effect of removing the photoresist can be enhanced by forming a pattern instead of forming the scratch as described above.

The pure water used in this example is preferably suppressed as much as possible depending on the type of precision substrate to be cleaned. When removing the photoresist from the semiconductor substrate, dust having a particle diameter of 0.05 μm or more is used. Of ultrapure water having a specific resistance value of 18 MΩ · cm or more and a TOC (total organic carbon) or silica value of 1 ppb or less.

Note that the deionized water 504 used in FIG. 1 is preferably degassed in order to efficiently propagate ultrasonic waves. Also, it is preferable to use a degassed cleaning liquid 502 as well. When the ultrasonic frequency is 2 MHz, the gas component in pure water is preferably 2.5 ppm or less, and more preferably 1.5 ppm or less. When the ultrasonic frequency is 2 MHz or more, the gas component in pure water is 1 ppm or less, more preferably 100 ppb or less.

Although this example shows a cleaning device having a two-tank configuration, the configuration is not limited, and a single-tank configuration may be provided with a vibrator attached to the outer wall, and ultrasonic waves may be directly applied to the cleaning liquid. In this case, as described above, it is preferable to keep the temperature constant by intermittently irradiating ultrasonic waves or circulating a cleaning liquid between the thermostat.

Further, the number and position of the vibrators are not limited, and it is preferable to provide the necessary number of the best places on the side wall, bottom surface, top surface, etc. of the tank. In addition, it is preferable to remove the photoresist in the cleaning solution with a filter during the circulation process.

Next, FIG. 2 shows an example of a cleaning apparatus that performs single-wafer photoresist stripping removal by spraying a cleaning solution. First, a cleaning liquid in which any one or more of hydrofluoric acid, ammonium fluoride, potassium fluoride, or potassium chloride is mixed with an organic solvent solution diluted with pure water is prepared, and the cleaning liquid storage tank 601 is prepared. Supply. The cleaning liquid in the tank 601 is pressurized by the pump 602 and sent to the membrane deaerator 603 to remove the dissolved gas contained in the cleaning solution.

The degassed cleaning liquid is sent to the cleaning nozzle 605, and ultrasonic waves are irradiated by the ultrasonic vibrator 606 and supplied to the precision substrate. A cleaning solution is then supplied and photoresist removal is performed.

Note that the precision substrate is held on the turntable 604 and is rotatable. Thereby, the photoresist is efficiently removed by the synergistic effect with the action of the centrifugal force by spraying the cleaning solution irradiated with ultrasonic waves onto the rotating precision substrate surface.

The washing drainage liquid is stored in the recovery tank 607, pressurized by the pump 608, removed the photoresist peeled off by the filter 609, returned to the tank 601, and reused.

For the cleaning nozzle 605, the angle between the nozzle and the precision substrate is preferably about 45 °. The nozzle outlet may be circular and may be reciprocated in the radial direction of the substrate, or may be a line nozzle having a linear outlet in the radial direction of the substrate and a narrow outlet in the circumferential direction. The size of the nozzle outlet is preferably set to be larger than the wavelength of the ultrasonic wave in the cleaning solution so that the ultrasonic wave can pass efficiently. For example, when 0.95 MHz ultrasonic waves are used, the size of the blowout port is preferably 1.5 mm or more and 2 mm or less. In order to further enhance the cleaning effect, a plurality of nozzles may be arranged to spray the cleaning solution onto the substrate surface.

Further, when applying the photoresist while rotating the substrate, the photoresist may sag from the front surface to the back surface. Therefore, in order to remove the photoresist adhering to the back surface, the organic solvent is diluted with pure water so that the contact angle on the surface of the organic film is 40 ° or less, and the organic film underlayer is applied to enhance the removal effect of the organic film. Cleaning the backside of precision substrates using hydrofluoric acid that etches the substrate material and cleaning fluids containing ammonium fluoride, potassium fluoride, and potassium chloride to improve penetration of the cleaning solution into the precision substrate and organic coating interface By doing so, it is preferable to reduce the influence of contamination on other process equipment. In the backside cleaning, a cleaning nozzle may be arranged at a lower part of the cleaning apparatus so as to be perpendicular to or inclined with respect to the turntable.

The components of the cleaning solution of this example are preferably adjusted to the above-mentioned concentrations, and measures are also taken to improve the photoresist removal effect with regard to cleaning solution temperature control and filter installation and piping for circulation. It is preferable to take.

Further, prior to the cleaning method using the cleaning apparatus shown in FIGS. 1 and 2 of this example, it is effective to further enhance the photoresist removing effect by performing a pretreatment with an organic solvent.

That is, the cleaning step is divided into two steps. In the first step, the precision substrate having the organic coating adhered to the organic solvent is immersed, and in the second step, the contact angle on the surface of the organic coating of the present invention is 40 °. Dilute the organic solvent with pure water to reduce the organic film's exfoliation and removal effect, so that the hydrofluoric acid that etches the substrate material under the organic film and the penetration of the cleaning solution into the precision substrate / organic film interface In order to improve, the photoresist is removed using a cleaning liquid to which ammonium fluoride, potassium fluoride, potassium chloride or the like is added.

Here, as the organic solvent in the first step, isopropyl alcohol, dimethyl sulfoxide and the like are effective, and 100% isopropyl alcohol is particularly preferable. Further, it is preferable that the treatment atmosphere of the first step is sealed and the moisture is 1 ppm or less. Note that the first step may use not only immersion but also a shower method or a spray method.

The present invention is suitable for removing various photoresists, and TSMR-8900 (manufactured by Tokyo Ohka Kogyo Co., Ltd.), which has high heat resistance and is difficult to remove, has an extremely high removal effect. It is also effective for an i-line photoresist, an excimer laser photoresist, and an electron beam photoresist.

In addition, the present invention is not limited to photoresists, but can be used to remove various organic polymer coatings such as paints and adhesives, coatings of machine oils (including those baked into polymers), surfactants and dyes. Needless to say, it can be applied.

EXAMPLES The present invention will be specifically described below with reference to examples, but it goes without saying that the present invention is not limited to these examples.

Using the cleaning apparatus of FIG. 1, the relationship between the concentration of hydrofluoric acid in the cleaning solution and the time until the photoresist was removed was examined.

As the cleaning solution, 100% isopropyl alcohol was added to ultrapure water (at this time, the isopropyl alcohol concentration was set to 20 wt% corresponding to the variable amount of hydrofluoric acid), and then 50 wt% hydrofluoric acid. Hydrofluoric acid was added to adjust the hydrofluoric acid concentration, and ultrasonic waves were applied. The temperature of the cleaning liquid was maintained at 25 ° C. by circulating the pure water 504 in FIG. 1 between the thermostats. The frequency of the used ultrasonic wave is 0.95 MHz.

In this example, a silicon plate having a diameter of 33 mm coated with a photoresist by the following procedure was used as the precision substrate.

A silicon substrate having a diameter of 33 mm was pre-baked at 150 ° C. for 5 minutes, and then hexamethyldisilazane (HMDS) was applied for 1 minute and 30 seconds. Next, a photoresist (TSMR-8900) was applied at 800 rpm for 2 seconds and 3000 rpm for 40 seconds to apply the photoresist to a thickness of 1.0 to 1.3 μm. Thereafter, baking for drying the photoresist was performed at 90 ° C. for 1 minute and 30 seconds, followed by rinsing with ultrapure water for 1 minute, and post baking was performed at 130 ° C. for 5 minutes to solidify the photoresist.

The photoresist was removed using each cleaning solution in which the concentration of hydrofluoric acid (HF) was changed, and the relationship between the concentration of hydrofluoric acid (HF) and the treatment time was examined. The results are shown in Table 1. In addition, the processing time in a table | surface measures the film thickness of the photoresist on a precision board | substrate beforehand, measures the time until a photoresist residue disappears using optical microscope observation as a removal time, and with respect to 1 micrometer thickness of photoresist. This is a value converted as the removal processing time.

As can be seen from Table 1, the photoresist can be removed even with isopropyl alcohol and ultrapure water, but the treatment time can be greatly shortened by mixing hydrofluoric acid (HF), particularly at a concentration of 0.05 to 0.5 wt%. It was found that the removal effect was further improved in the range.

Although the details of these reasons are not clear, the present inventors have found that the cleaning solution is a photoresist because the mechanism for removing the photoresist of the present invention is not removal by dissolution of the conventional photoresist, but removal by peeling. It was assumed that the adhesion between the photoresist and the precision substrate surface was extremely reduced by penetrating the interface between the photoresist and the precision substrate, and further etching the substrate material under the organic film with hydrofluoric acid.

Using the cleaning apparatus of FIG. 1, the relationship between the concentration of ammonium fluoride in the cleaning solution and the time until the photoresist was removed was examined.

In addition, as a cleaning solution, 100% isopropyl alcohol was added to ultrapure water (at this time, the isopropyl alcohol concentration was set to 20 wt% corresponding to variable ammonium fluoride), and then 30 wt% ammonium fluoride. Was added to adjust the ammonium fluoride concentration.

The removal conditions were the same as in Example 1 except that ammonium fluoride (NH 4 F) that did not etch the silicon oxide film was used instead of hydrofluoric acid that etched the silicon oxide (SiO 2) film. The photoresist was removed using each cleaning solution in which the concentration of ammonium fluoride (NH 4 F) was changed, and the relationship between the concentration of ammonium fluoride (NH 4 F) and the processing time was examined. The results are shown in Table 2. The processing time calculation method in the table is the same as that in the first embodiment.

As a comparative example, conventional cleaning was performed at 130 ° C. using sulfuric acid / hydrogen peroxide solution. The results are shown in Table 3.

Regarding the removal effect of the photoresist, the ammonium fluoride (NH4F) concentration dependency is the same as that of hydrofluoric acid (HF), and the effect is improved when the concentration is increased. It was confirmed that the effect was obtained. Although the cleaning of this embodiment can be performed at room temperature using a low concentration of chemicals, it has excellent removal ability compared to conventional sulfuric acid / hydrogen peroxide treatment that requires high temperature treatment. There was found. This is probably because the removal by the sulfuric acid / hydrogen peroxide treatment is removal by dissolution, whereas the removal of the present invention is peeling removal.

Using the cleaning apparatus of FIG. 1, the relationship between the concentration of potassium fluoride in the cleaning solution and the time until the photoresist was removed was examined.

In addition, 100% isopropyl alcohol was added to ultrapure water as the cleaning solution (at this time, the isopropyl alcohol concentration was set to 20 wt% corresponding to variable potassium fluoride), and then potassium fluoride powder was added. Then, the potassium fluoride concentration was adjusted.

Removal conditions were the same as in Example 1 except that potassium fluoride (KF) was used instead of hydrofluoric acid. The photoresist was removed using each cleaning solution in which the concentration of potassium fluoride (KF) was changed, and the relationship between the concentration of potassium fluoride (KF) and the treatment time was examined. The results are shown in Table 4. The processing time calculation method in the table is the same as that in the first embodiment.

About the removal effect of the photoresist, the dependency on the concentration of potassium fluoride (KF) is the same as that of hydrofluoric acid (HF), and the effect is improved when the concentration is increased, and a high removal effect is obtained at 0.05 wt% or more. I was able to confirm. When a cleaning solution having a potassium fluoride (KF) concentration of 10 wt% or more was used, precipitation of potassium fluoride (KF) salt was confirmed in the cleaning apparatus. This is probably because the vapor of the cleaning solution adhered to the inner wall of the cleaning device and dried during the removal of the photoresist. Since such precipitates cause recontamination from the cleaning apparatus to the precision substrate, it was confirmed that the potassium fluoride (KF) concentration is preferably 0.05 to 10 wt%.

Using the cleaning apparatus shown in FIG. 1, the relationship between the concentration of potassium chloride in the cleaning solution and the time until the photoresist was removed was examined.

In addition, 100% isopropyl alcohol was added to ultrapure water as the cleaning solution (at this time, the isopropyl alcohol concentration was set to 20 wt% corresponding to variable potassium chloride), and then potassium chloride powder was added. The potassium chloride concentration was adjusted.

The removal conditions were the same as in Example 1 except that potassium chloride (KCl) was used instead of hydrofluoric acid. The photoresist was removed by using each cleaning solution in which the concentration of potassium chloride (KCl) was changed, and the relationship between the concentration of potassium chloride (KCl) and the treatment time was examined. The results are shown in Table 5. The processing time calculation method in the table is the same as that in the first embodiment.

Regarding the removal effect of photoresist, the dependency on potassium chloride (KCl) concentration is the same as that of hydrofluoric acid (HF), and the effect is improved when the concentration is increased. A high removal effect can be obtained at 0.5 wt% or more. Was confirmed. When a cleaning solution having a potassium chloride (KCl) concentration of 10 wt% or more was used, precipitation of potassium chloride (KCl) salt was confirmed in the cleaning apparatus as in Example 3. Therefore, it was confirmed that the potassium chloride (KCl) concentration is preferably 0.5 to 10 wt%.

As is apparent from Examples 3 and 4, it was found that an excellent photoresist removal effect can be obtained by using either potassium fluoride or potassium chloride. In particular, it has been found that potassium fluoride has a better photoresist removal effect than hydrofluoric acid and ammonium fluoride.

Although the details of these reasons are not clear, the present inventors have found that the cleaning solution is a photoresist because the mechanism for removing the photoresist of the present invention is not removal by dissolution of the conventional photoresist, but removal by peeling. It is assumed that the photoresist penetrates into the interface between the photoresist and the precision substrate, dissolves and expands the photoresist slightly, and extremely reduces the adhesion between the photoresist and the precision substrate surface.

Therefore, the present inventors have investigated the wettability of each cleaning liquid by using a contact angle meter, paying attention to the permeability (wetting property) of the cleaning liquid to the photoresist and the precision substrate interface. The results are shown in FIG.

FIG. 3 shows the contact angle of each cleaning solution on the photoresist surface. The contact angle of each cleaning solution to the photoresist is 30 ° compared to 32 ° for 30 wt% isopropyl alcohol / ultra pure water (IPA) and 28 ° for 30 wt% isopropyl alcohol / 5 wt% potassium chloride (IPA / KCl). % Isopropyl alcohol / 5 wt% potassium fluoride (IPA / KF) is as low as 18 °, and it can be seen that the wettability of the photoresist is highest when potassium fluoride is added.

As can be seen from Example 1, the reason why the photoresist that cannot be removed by removing only pure water can be removed by adding isopropyl alcohol is that the propyl alcohol obtained in this example is used. The results confirming the inventors' assumption that the cleaning liquid easily penetrates into the interface between the photoresist and the precision substrate due to the reduction of the contact angle due to the addition.

That is, it is known that organic coatings that cannot be peeled and removed with ultrapure water are generally hydrophobic, and the contact angle of ultrapure water is 72 ° (wetability). On the other hand, by adding 30 wt% isopropyl alcohol, the contact angle is halved to 32 °, and the improved permeability (wetting) makes it easier for the cleaning liquid to penetrate the interface between the organic coating and the precision substrate. It can be inferred that the removal and removal of can be performed.

Further, by adding 5 wt% potassium fluoride (KF), potassium chloride (KCl), or ammonium fluoride (NH 4 F) to 30 wt% isopropyl alcohol / ultra pure water, the contact angle is further reduced, and potassium fluoride. Since the lowest contact angle is obtained when (KF) is added, the result shows the best peeling effect of the organic coating compared to the other additive chemicals obtained in Example 3, and the photoresist and precision substrate It shows the ground that the higher the permeability to the interface, the higher the removal effect.

Further, in a solution obtained by adding 0.5 wt% hydrofluoric acid (IPA / HF) to 30 wt% isopropyl alcohol / ultra pure water, there is no difference in contact angle with 30 wt% isopropyl alcohol / ultra pure water (IPA). The reason why the excellent peeling effect is obtained is that the removal and removal effect is improved by etching the substrate material under the organic coating and the permeability of the cleaning liquid to the interface between the organic coating and the precision substrate. The results were supported by their guesses.

From this, the inventors' assumption that the higher the wettability, that is, the higher the permeability to the interface between the photoresist and the precision substrate, the higher the removal effect is obtained, was correct, and the above results were clarified. This is the first time by the present inventors.

In addition, TSMR-8900 is used as the photoresist material used in this example, but it has been confirmed that there is no difference in the contact angles of the above-mentioned solutions even in other photoresist materials. The removal removal effect by addition is obtained because the contact angle is 40 ° or less, so a solution prepared with an organic solvent (isopropyl alcohol) so that the contact angle is 40 ° or less is used as the organic film peeling removal cleaning solution. The basis of this invention is shown.

In this example, a MOS capacitor was fabricated using the cleaning method of the present invention, and capacitor characteristics were evaluated.

First, a manufacturing procedure of a MOS capacitor is shown below. A silicon wafer (Cz, n (100)) having a diameter of 33 mm is subjected to SPM (H 2 SO 4: H 2 O 2 = 4: 1) for 15 minutes, DHF (0.5 wt% HF) for 1 minute, and APM (NH 4 OH: H 2 O 2: H 2 O = 0). .05: 1: 5) for 10 minutes at 85 to 90 ° C. and then for 10 minutes with ultrapure water.

A field oxide film was formed by 600 nm wet oxidation, a 1 μm photoresist was formed in the same manner as in Example 1, and photolithography was performed on a pattern having a desired shape.

Subsequently, the field oxide film was etched with buffered hydrofluoric acid (LAL700 manufactured by Hashimoto Kasei Co., Ltd.) for 11 minutes and washed with ultrapure water for 10 minutes.

Next, the photoresist was removed by immersing in each cleaning solution for 160 seconds while irradiating ultrasonic waves (MS) of 0.95 MHz.

Each cleaning solution is 30 wt% isopropyl alcohol (IPA), 4.5 wt% potassium fluoride (KF), 4.8 wt% ammonium fluoride (NH 4 F), and 0.5 wt% hydrofluoric acid (HF), respectively. Adjusted. The immersion time of 160 seconds is the time for completely removing the photoresist.

Subsequently, after washing with SPM (10 minutes), DHF (1 minute), APM (10 minutes), and DHF (1 minute), it was immersed in ultrapure water containing 2 ppm ozone for 20 minutes to form a precursor. A gate oxide film (7.5 nm) was formed by dry oxidation at 900 ° C.

Next, p-type poly-Si for a gate electrode was formed to 500 nm by CVD, annealed at 850 ° C. for 30 minutes, and then washed with SPM (5 minutes) and ultrapure water (3 minutes). Next, photolithography was performed by the same method as described above, and poly-Si was etched using HF: HNO3: H2O (0.02: 1: 1). After that, the photoresist is removed by immersing in a cleaning solution for 160 seconds while irradiating ultrasonic waves (MS) in the same manner, and cleaning is performed with SPM (10 minutes), DHF (1 minute), and ultrapure water (3 minutes). It was.

Next, SiO 2 was formed by atmospheric pressure CVD at 400 ° C. for 18 minutes, and after patterning to a desired shape, Al 1 μm was formed by sputtering and patterned.

Through the above steps, a MOS capacitor having a gate electrode area of 1 × 10 −4 cm 2 and a gate oxide film thickness of 7.5 nm was produced.

With respect to the fabricated MOS capacitor, the dielectric strength voltage was measured using a parameter analyzer HP4145A manufactured by Hewlett Packard. The withstand voltage was a voltage value at which a current density of 10 −4 A / cm 2 flows. The results are summarized in Table 6.

Similarly, a MOSFET was manufactured, and the mobility was obtained from the ID in the saturation region and the slope of the graph of (VG−VTH) 2. ID is a drain current, VG is a gate voltage, and VTH is a threshold value. The results are also shown in Table 6.

As is clear from the above, the photoresist removal technology using the cleaning liquid of the present invention can be used in the manufacturing process of semiconductor devices that require microfabrication and high cleanliness. Therefore, it is a cleaning technology that can cope with environmental problems and can reduce the area occupied by the equipment and contribute to cost reduction because the chemical vapor and water vapor are hardly generated. It is clear that there is.

Further, in the MOS capacitor and the MOSFET prepared in this example, the cleaning liquid using potassium fluoride (KF) is more resistant to withstand voltage and movement than the cleaning liquid containing ammonium fluoride (NH 4 F) and hydrofluoric acid (HF). It has been found that the semiconductor device characteristics are excellent in terms of temperature.

For this reason, the present inventors pay attention to the fact that they depend on the damage to the precision substrate by the photoresist removing cleaning liquid of the present invention, and in this embodiment, each cleaning liquid is brought into the surface state of the silicon wafer. The effect was investigated.

First, a silicon wafer (Cz, n (100)) was immersed in DHF (0.5% HF) for 1 minute, then rinsed with ultrapure water for 10 minutes, washed with 2 ppm ozone-added ultrapure water for 10 minutes, Ultra pure water rinse was performed for 10 minutes.

Then, after being further immersed in DHF for 1 minute, it was immersed in each cleaning solution for 160 seconds while irradiating an ultrasonic wave (MS) of 0.95 MHz. The adjusted concentration of each cleaning solution is the same as in Example 6.

After cleaning, the surface roughness Ra of the silicon surface was measured at 30 points on the wafer surface by an atomic force microscope (AFM). The results are shown in Table 7.

As is clear from Table 7, the cleaning liquid containing potassium fluoride (KF) did not cause the most surface roughness of the silicon wafer, and the same value as the surface roughness of the silicon wafer before the investigation was maintained. On the other hand, it was found that the cleaning liquid containing ammonium fluoride (NH4F) and hydrofluoric acid (HF) was rougher than the cleaning liquid containing potassium fluoride (KF), and the variation in the surface was large.

That is, in Example 6, the reason why the cleaning liquid using potassium fluoride (KF) is superior to the cleaning liquid containing ammonium fluoride (NH 4 F) and hydrofluoric acid (HF) is that The present inventors have clarified that the inventors' assumption that it depends on the damage to the precision substrate by the photoresist removing cleaning liquid of the invention is correct.

In addition, as is clear from this example, in the cleaning process (resist removal process) for precision substrates such as semiconductor devices and liquid crystal displays that require microfabrication and high cleanliness, there are few chemical types to be used at low concentrations, A cleaning method that responds to environmental problems and can contribute to space saving and cost reduction with little generation of chemical vapor or water vapor uses a cleaning solution that is a mixture of isopropyl alcohol diluted with pure water and potassium fluoride. It is clear that it is most effective to irradiate with ultrasonic waves.

According to the present invention, that is, by irradiating the cleaning liquid with at least one kind of potassium fluoride, potassium chloride, hydrofluoric acid or ammonium fluoride mixed with isopropyl alcohol diluted with pure water with ultrasonic waves, An extremely high cleaning effect can be obtained by a cleaning method for removing an organic film such as a photoresist attached to a precision substrate.

The details of the reason why the high cleaning effect can be obtained are not completely clear at present, but are estimated as follows from the results of this example. First, isopropyl alcohol and potassium fluoride, potassium chloride, hydrofluoric acid or ammonium fluoride penetrate into the photoresist, especially the interface between the photoresist and the precision substrate, so that the photoresist is slightly dissolved and expanded. It is considered that the photoresist is peeled off by ultrasonic waves by extremely reducing the adhesion between the resist and the precision substrate surface.

Further, the chemical bond between the photoresist and the precision substrate surface is broken by radicals (H radicals, OH radicals) generated in the cleaning liquid by ultrasonic waves, and the peeling of the photoresist is promoted.

By using isopropyl alcohol, potassium fluoride, potassium chloride, hydrofluoric acid or ammonium fluoride is permeated into the interface between the precision substrate and the photoresist to expand the photoresist.

In addition, potassium fluoride, potassium chloride, hydrofluoric acid or ammonium fluoride enters the interface with isopropyl alcohol, slightly etches the precision substrate, pulls the photoresist away from the substrate, and the photoresist is peeled off by ultrasound. It is considered a thing.

The present invention is suitably applied particularly to the removal of a photoresist in a microfabrication process such as a semiconductor device or a liquid crystal display, and can provide a highly clean surface with a higher cleaning removal effect than a conventional removal method.

Furthermore, since the treatment is performed at around room temperature, it is excellent in handling and safety, and waste liquid treatment is easy. A room temperature wet cleaning technique that does not use any high-temperature high-concentration chemicals has already been developed by the present inventors (authored by Tadahiro Omi, Ultra Clean ULSI Technology, published in December 1995).

In addition, the present invention is not limited to photoresists, but can be used to remove various organic polymer coatings such as paints and adhesives, coatings of machine oils (including those baked into polymers), surfactants and dyes. Needless to say, it can be applied.

In addition, since organic film removal such as photoresist of the present invention is not dissolved by a conventional chemical solution but by peeling from the substrate surface, if the organic film such as removed photoresist is circulated and filtered, the organic film is filtered. Since all of them are removed, the cleaning liquid is hardly deteriorated and can be used for a long time.

Accordingly, the cleaning liquid after use in the cleaning apparatus of the present invention can be reused by passing it through the coarse performance filter, the medium performance filter, and the high performance filter sequentially. If two filter systems are provided, continuous operation is possible by sequentially switching and using the other filter system.

That is, the cleaning (resist removal) method and cleaning apparatus of the present invention are applied to environmental problems because they use a small number of chemicals and a low concentration. In addition, since almost no chemical vapor or water vapor is generated, the size of the device can be simplified and the occupied area of the device can be reduced, so that space can be saved, and the cost of manufacturing plants for semiconductor devices and liquid crystal displays can be reduced. Has been applied.

It is a conceptual diagram which shows an example of the washing | cleaning apparatus for enforcing the washing | cleaning method of this invention. It is a conceptual diagram which shows an example of the washing | cleaning apparatus for enforcing the washing | cleaning method of this invention. It is a graph which shows the contact angle of various washing | cleaning liquids and a photoresist.

Explanation of symbols

501 ... The inner tank of the washing tank,
502 ... Cleaning solution,
503 ... Outer tank,
504 ... pure water,
505 ... ultrasonic transducer,
506 ... Cleaning liquid storage tank,
507 ... Pump,
508 ... Membrane deaerator,
509 ... Membrane deaerator,
510 ... heat exchanger,
511 ... Level sensor,
512... Level sensor,
513 ... Pump,
514 ... Filter,
601 ... Cleaning liquid storage tank,
602 ... Pump,
603 ... Membrane deaerator,
604 ... turntable,
605 ... Cleaning nozzle,
606 ... ultrasonic transducer,
607 ... Recovery tank,
608 ... Pump,
609: Filter.

Claims (10)

Cleaning method the organic solvent was diluted with pure water, the cleaning solution was added ammonium fluoride or a metal halide salt, and carrying out organic coating removal. 2. The cleaning method according to claim 1, wherein the organic film is removed with a cleaning liquid to which hydrofluoric acid for etching the substrate material under the organic film is added. The cleaning method according to claim 1 or 2, wherein the organic coating is removed in a sealed atmosphere . The cleaning method according to claim 1, wherein the organic coating is a photoresist after ion implantation and / or reactive ion etching. The cleaning method according to any one of claims 1 to 4, wherein the organic solvent is isopropyl alcohol. The cleanup method of claim 1, the halogenated metal salt is characterized in that potassium fluoride and / or potassium chloride. The cleaning method according to claim 2, wherein a concentration of the hydrofluoric acid is 0.05 to 0.5 wt%. The cleaning method according to claim 1 , wherein the concentration of the ammonium fluoride is 0.6 to 6.5 wt%. The concentration of the potassium fluoride method of cleaning according to claim 6, wherein 0.05-10% der Rukoto. The concentration of the potassium chloride The method of cleaning according to claim 6, wherein 0.5-10% der Rukoto.

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