JP2003347261A - Cleaning device and cleaning method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cleaning device and a cleaning method capable of effectively removing even a substance having low solubility in a supercritical fluid. <P>SOLUTION: A cleaning device is composed of a cleaning chamber in which a substrate is arranged in the vertical direction or the direction inclined from a horizontal level and a supercritical fluid feeding part which supplies the supercritical fluid in the cleaning chamber. The substrate is arranged in the direction inclined from the horizontal level when treating the substrate with the supercritical fluid. Consequently, even a substance being hardly soluble in the supercritical fluid is easily removed from the substrate due to a difference in specific gravity between the supercritical fluid and the substance. <P>COPYRIGHT: (C)2004,JPO

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a cleaning apparatus and a cleaning method for cleaning a substrate, and more particularly, to a cleaning apparatus and a cleaning method for cleaning a substrate using a supercritical fluid in a supercritical state.

[0002]

2. Description of the Related Art A supercritical fluid may be used for cleaning a substrate such as a semiconductor wafer. For example, after treating the substrate with a chemical solution or the like, the substrate is washed with a supercritical fluid, and then the substrate is dried. The supercritical fluid has an intermediate property between gas and liquid, and can penetrate into fine parts, and therefore has a strong detergency. Further, by releasing the supercritical state after cleaning, the supercritical fluid is evaporated, and the substrate can be dried quickly.

[0003]

However, there is a case where a chemical solution (or a subsequent rinsing solution) has low solubility in a supercritical fluid. In such a case, it is difficult to completely remove the chemical solution or the like from the substrate even if the substrate is washed with a supercritical fluid. The present invention has been made to solve such a problem, and an object of the present invention is to provide a cleaning apparatus and a cleaning method capable of effectively removing even a substance having low solubility in a supercritical fluid.

[0004]

(1) In order to achieve the above object, a cleaning apparatus according to the present invention comprises: a cleaning chamber for arranging a substrate in a vertical direction or a direction inclined from horizontal; And a supercritical fluid supply unit for supplying a fluid. When treating a substrate with a supercritical fluid, the substrate is arranged in a direction inclined from horizontal. Even a substance that is hardly soluble in the supercritical fluid is easily removed from the substrate due to a difference in specific gravity from the supercritical fluid.

(2) The cleaning method according to the present invention includes a supercritical fluid processing step of processing the substrate with a supercritical fluid in a state where the substrate is arranged in a vertical direction or a direction inclined from horizontal. Since the substrate is arranged in a vertical direction or a direction inclined from the horizontal, even a substance that is hardly soluble in the supercritical fluid is easily removed from the substrate due to a difference in specific gravity from the supercritical fluid.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS (First Embodiment) Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. FIG. 1 is a block diagram showing a cleaning apparatus 10 according to the present invention. As shown in FIG. 1, the cleaning device 10 includes a fluid supply unit 12, a pressure generator 14, a chemical liquid supply unit 16, a solvent supply unit 18, a pressure vessel 20, and an impurity removing unit 22, and includes a chemical liquid Lm, a solvent S
A substrate such as a semiconductor wafer W (hereinafter, referred to as a wafer W) is cleaned using o and the supercritical fluid Fs. The fluid supply unit 12 (and the pressure generator 14), the chemical solution supply unit 16, and the solvent supply unit 18 are respectively connected via valves 24-28.
It is connected to a supply pipe 30 leading to the pressure vessel 20.
Further, a return pipe 34 for returning the fluid F to the fluid supply unit 12 via the pressure vessel 20, the valve 32, and the impurity removing unit 22 is provided. The supply pipe 30 and the return pipe 34 constitute a circulation system 36 for circulating the supercritical fluid Fs.

[0007] The supercritical fluid Fs is in a pressure or pressure range exceeding a critical point (the limit pressure or temperature at which gas is compressed and liquefied, and gas does not liquefy at a pressure or temperature exceeding this limit). Fluid. The supercritical fluid Fs generally has the following properties. -It has an intermediate property between gas and liquid, and can penetrate fine parts. -The diffusion coefficient is high and the dissolved contaminants can be dispersed quickly. -Evaporation can be performed almost instantaneously by releasing the supercritical state (normally, returning to normal temperature and normal pressure). -Since there is no phase boundary between gas and liquid (the two phases of gas and liquid do not coexist), there is no surface tension. By cleaning the substrate with the supercritical fluid Fs having such properties, it becomes possible to remove contaminants that have entered the fine pattern details on the substrate. Further, by releasing the supercritical state after cleaning, the substrate can be dried quickly. Furthermore, since there is no surface tension, a fine pattern on the substrate is not destroyed by the surface tension when the substrate is dried (so-called pattern collapse).

The conditions for selecting the supercritical fluid Fs are as follows.・ It is easy to realize supercritical state (critical temperature and critical pressure are as close as possible to normal temperature and normal pressure) ・ High safety ・ Inexpensive and economical Carbon, sulfur dioxide, nitrous oxide, ethane, propane, chlorofluorocarbon and the like can be mentioned. Of these, carbon dioxide (carbon dioxide)
It is almost harmless (non-toxic) to living organisms, has a critical point of 31 ° C. and 70 atm, is relatively easy to realize, and is inexpensive and easily available. For this reason, in the present embodiment, carbon dioxide (carbon dioxide) is used as the material of the supercritical fluid Fs, but other substances can be used as the material of the supercritical fluid Fs as necessary.

The fluid supply section 12 is a supply means for supplying a fluid F which is a source of the supercritical fluid Fs. When carbon dioxide is used as the supercritical fluid Fs, the fluid supply unit 12 can be configured using a gas cylinder of carbon dioxide or the like. The pressure generator 14 applies a pressure exceeding the critical pressure Pc to the fluid F supplied from the fluid supply unit 12 to supercritical fluid F in a supercritical state.
s, for example, a high-pressure pump. In this embodiment, since carbon dioxide is used as the supercritical fluid Fs, a pressure of 70 atm or more, for example, about 100 atm is generated. In order to generate a supercritical state, not only pressure but also temperature are important factors. For this reason, a heating unit (heater) (not shown) is provided in the pressure generator 14 so that the fluid F supplied from the fluid supply unit 12 is heated to the critical temperature T.
Heat to a temperature above c. In this embodiment, since carbon dioxide is used as the supercritical fluid Fs, the temperature of the fluid F is set to 31 ° C. or higher, for example, about 40 ° C. As described above, the pressure generator 14 constitutes a supercritical fluid supply unit that supplies the supercritical fluid Fs together with the fluid supply unit 12 (and further with the heating unit).

The chemical supply section 16 supplies a chemical Lm (in some cases, a plurality of chemicals) for cleaning the substrate. Inside the chemical solution supply section 16, a chemical solution storage tank for storing the chemical solution Lm is installed. When supplying a plurality of types of chemicals Lm, the supplied chemicals Lm can be switched by switching a plurality of chemicals storage tanks. There are various methods for cleaning the substrate, such as cleaning with a resist stripper for removing (dissolving) the resist, and RCA cleaning for removing particles (particulate impurities) and metal impurities from the substrate. The chemical supply unit 16 can supply a chemical such as an organic solvent, an acid, or an alkali corresponding to these methods.

The solvent supply section 18 is provided with a solvent (solvent) S for rinsing (rinsing) the substrate washed with the chemical solution.
o. The solvent So dissolves the components of the chemical liquid Lm, and thereby the chemical liquid L supplied from the substrate by the chemical liquid supply unit 16.
Remove m. Hereinafter, in the present embodiment, a case where pure water is used as the solvent So will be considered. However, if necessary, the solvent So
It is also possible to use an organic solvent or the like.

The pressure vessel 20 includes a substrate (in this embodiment,
A container for placing the wafer W) therein and performing cleaning using a chemical solution, a solvent, and further a supercritical fluid Fs;
The internal space S corresponds to the cleaning room according to the present invention. The pressure vessel 20 can withstand the pressure generated by the pressure generator 14, and the supercritical fluid Fs can maintain the supercritical state inside the pressure vessel. The pressure vessel 20 has an opening / closing section (not shown) so that the wafer W can be loaded and unloaded into the pressure vessel 20. Further, the pressure vessel 20 has an inflow port and an outflow port respectively above and below the pressure vessel. The fluid such as the supercritical fluid Fs flows in from the inlet above the wafer W and flows out from the outlet below.

In the pressure vessel 20, the main surface of the wafer W is arranged in a vertical direction or along a direction inclined from horizontal. FIG. 2 is a schematic diagram showing the direction of the wafer W in the pressure vessel 20. The main surface 42 is inclined at an angle θ (0 ° <θ <180 °) with respect to the horizontal direction. Examples of the angle θ include 45 ° to 135 °, 60 ° to 120 °, and 80 °.
° to 100 °. The reason why the wafer W is inclined from the horizontal direction is that the solvent So can be easily removed from the wafer W due to a difference in specific gravity between the solvent So and the supercritical fluid Fs. This is shown below. In the present embodiment, the supercritical fluid Fs and the solvent So are pure water and carbon dioxide, respectively. Therefore, the specific gravity of the solvent So is larger than that of the supercritical fluid Fs. While the specific gravity of pure water is approximately 1, the specific gravity of the supercritical fluid Fs composed of carbon dioxide is about 0.2 to 0.8. Therefore, the solvent S having a large specific gravity
o tends to settle down (downward in the vertical direction). Therefore, by tilting the wafer W, the solvent S
o is easily removed. The greater the difference in specific gravity, the easier the removal of the solvent So from the wafer W. For this purpose, for example, it is conceivable to reduce the specific gravity by setting the pressure P and temperature T of carbon dioxide in a range close to the critical state.

The surface to be cleaned is not the main surface 42, but may be the main surface 44 on the back surface or both the main surfaces 42 and 44. Considering that the solvent So precipitates, the main surface 44 facing downward in the vertical direction is easier to remove the solvent So than the main surface 42 facing upward in the vertical direction. However, even if the main surface 42 facing upward is inclined from the horizontal, the solvent So can be easily removed. In order to uniformly clean both of the main surfaces 42 and 44, it is preferable to direct the wafer W in the vertical direction. This is because the angle conditions of both the main surfaces 42 and 44 match. However, even if the angle θ at this time deviates slightly from 90 ° (for example, θ is 80 ° or more and 100 ° or less), the main surfaces 42 and 44
Uniformity of both cleanings is ensured.

The impurity removing section 22 is a kind of filter for removing impurities, particularly the solvent So, contained in the supercritical fluid Fs. The solvent So having a relatively large specific gravity is allowed to settle at the bottom, and the supercritical fluid Fs having a relatively small specific gravity is sent from the outlet to the return pipe 34. In the impurity removing section 22 and the return pipe 34, the supercritical fluid Fs
The supercritical state is released, and the normal fluid F may be used. The valves 24 to 26 are two-way valves for selecting (switching) a fluid to be supplied to the pressure vessel 20 from the supercritical fluid Fs, a chemical solution, and a solvent. The valve 32 removes the liquid flowing out from the outlet of the pressure vessel 20 to the impurity removing section 2.
This is a three-way valve for selecting whether to send to the cleaning device 2 or to discharge the cleaning device 10 out of the system.

The cleaning process referred to here generally refers to a process for removing contaminants from the object to be cleaned. For example, after the wafer W is dry-etched, or after the dry-etching and further ashing, it is considered unnecessary. It can be used to remove a resist as a mask or an etching residue. Further, it can also be used for a normal pre-cleaning process performed before the wafer film forming process or the like.

(Operation of Cleaning Apparatus 10)
The operation of 0 will be described. FIG. 3 is a flowchart illustrating an example of an operation procedure of the cleaning device 10. As shown in the figure, the cleaning procedure by the cleaning apparatus 10 includes loading of the wafer W (step S11), chemical treatment of the wafer W (step S11).
12), rinsing processing of wafer W (step S13), supercritical fluid processing of wafer W (step S14), wafer W
(Step S15). Hereinafter, steps S11 to S15 will be described in detail.

(1) An unprocessed wafer W is loaded into the cleaning apparatus 10 (step S11). Specifically, an opening / closing unit (not shown) of the pressure vessel 20 is opened,
The wafer W is carried into the pressure vessel 20. Then, the wafer W is held and fixed in a vertical direction or a direction inclined from horizontal. FIG. 1 shows an example in which the wafer W is held in a vertical direction as an example. After holding the wafer W, the pressure vessel 20 is closed in a liquid-tight manner, and the interior space S is closed.

(2) The wafer W in the pressure vessel 20 is cleaned with a chemical (step S12). The valve 26 is opened to allow the chemical to flow into the pressure vessel 20 from the chemical supply unit 16. As a result, the wafer W in the pressure vessel 20 is processed by the chemical. The chemical solution flowing out of the pressure vessel 20 is discharged from the valve 32 to the outside of the system.

In removing the resist, a resist stripping solution is used as a chemical. The resist stripping solution includes those mainly containing organic sulfonic acid, those mainly containing alkylene glycol, and highly polar solvents (dimethyl sulfoxide,
There are various resist stripping solutions such as those mainly composed of dimethylformamide, etc., and mixtures of polar solvents (γ-butyrolactone, N-dimethylformamide, etc.) and amino alcohols, which can be used properly.

RCA cleaning can be used to remove particles and metal impurities. The RCA cleaning uses ammonia-hydrogen peroxide (APM) and hydrochloric acid-hydrogen peroxide (HPM). The former removes particles adsorbed on the surface simultaneously by etching the oxide, and the latter removes metal deposits. RCA cleaning is A
The steps of PM cleaning, pure water rinsing, HF dip, pure water rinsing, HPM cleaning, and pure water rinsing are sequentially performed. That is, in the case of RCA cleaning, there are three types of chemicals supplied by the chemical supply unit 16, APM, HF, and HPM, and rinsing with pure water is performed between the treatments with the respective chemicals.
For this rinsing process, pure water can be supplied from the solvent supply unit 18 for use.

(3) Rinse processing of wafer W (step S
13). The valve 26 is closed, the valve 28 is opened, and the solvent So flows from the solvent supply unit 18 into the pressure vessel 20. As a result,
The wafer W in the pressure vessel 20 is cleaned by the solvent (rinse liquid) So. The solvent So flowing out of the pressure vessel 20 is discharged from the valve 32 to the outside of the system. The cleaning with the solvent So is for removing the chemical used in the chemical processing from the wafer W, and the solvent that dissolves the components of the chemical Lm is used as the solvent So. As described above, pure water is used as the solvent So. In the RCA cleaning, the cleaning with pure water is performed three times for convenience, but here, the rinsing process () immediately before the final drying is referred to.

(4) Supercritical fluid processing of wafer W (step S14). The valve 28 is closed, the valve 24 is opened, and the supercritical fluid Fs flows into the pressure vessel 20 from the fluid supply unit 12 via the pressure generator 14. Further, the valve 32 is switched to the impurity removing section 22 side. As a result, the wafer W in the pressure vessel 20 is cleaned by the supercritical fluid Fs. On the other hand, the supercritical fluid Fs flowing out of the pressure vessel 20 is returned to the fluid supply unit 12 from the return pipe 34 via the valve 32 and the impurity removing unit 22, and is reused. When the processing of the supercritical fluid on the wafer W is completed, the valves 24 and 32 are closed and the pressure inside the pressure vessel 20 is set to the normal pressure. The supercritical fluid Fs evaporates instantaneously, and the wafer W can be dried quickly.

The above-described cleaning with the supercritical fluid Fs is for removing the solvent So used for the rinsing process from the wafer W and drying it quickly. FIG. 4 is a cross-sectional view illustrating a process in which the solvent So is removed from the wafer W by cleaning with the supercritical fluid Fs. FIG. 4A shows the solvent S
“o” indicates the wafer W immediately after the rinsing process. The solvent So adheres to the surface of the wafer W. FIG.
(B) and (C) show the initial state of the processing of the wafer W with the supercritical fluid Fs and the state where the processing has progressed, respectively.
In (B), the solvent So remains in the groove of the wafer W, but the specific gravity of the solvent So is larger than the supercritical fluid Fs, and the wafer W is inclined from the horizontal (in the present embodiment, the vertical direction is set). Therefore, the solvent So settles below the wafer W and is removed. FIG. 4D shows a state where the supercritical fluid Fs is released from the supercritical state and the wafer W is dried.
Since the solvent So is removed from the wafer W in (C), the solvent So does not affect the drying of the wafer W.
Therefore, a stain such as a watermark described later does not easily occur.

The solvent So removed from the wafer W is settled and held in the impurity removing section 22 due to its specific gravity, and only the supercritical fluid Fs having a relatively small specific gravity is supplied through the return pipe 34 to the fluid supply section. Return to 12. This prevents the solvent So from being mixed into the supercritical fluid Fs that is returned from the return pipe 34 and reused (supplied again from the fluid supply unit 12).

FIG. 5 is a cross-sectional view showing a process of performing supercritical cleaning while keeping the wafer W horizontal as a comparative example. 5A to 5D show a state in which supercritical cleaning is performed immediately after the rinsing treatment with the solvent So, a state in which a supercritical fluid is evaporated after the supercritical cleaning, and a state in which the wafer W
, Respectively. As shown in FIG. 5B, the solvent S remains in the groove of the wafer W even by the supercritical cleaning.
o may remain. This is because the solvent So is a supercritical fluid Fs
It is easy to occur when it is difficult to dissolve. For example, water is only about 0.1% soluble in supercritical carbon dioxide. In such a case, the supercritical fluid Fs and the solvent So have a relationship like water and oil, and the effect of cleaning with the supercritical fluid Fs cannot be improved. For this reason, the solvent So tends to accumulate in the wafer W, especially in the vicinity of the groove.

As a result, as shown in FIG. 5C, the solvent So may remain even when the supercritical fluid Fs evaporates. When the solvent So evaporates, it becomes a watermark Wm on the wafer W, which may adversely affect devices (malfunctions) formed from the semiconductor substrate. The watermark Wm is a pattern (stain) formed by particles contained in droplets remaining on the surface of the wafer W when the solvent (water or the like) evaporates in the final stage of drying, and is critical to the device yield. Have a significant effect. In FIG. 4, since the wafer W is tilted, the solvent So having a large specific gravity is easily removed from the wafer W.

The watermark Wm tends to occur when the wafer W is hardly wetted by the solvent So (when the solvent So is water, it is hydrophobic). This is because it is easy to dry the wafer W while the solvent remains in a lump (water droplet) on the wafer W. (Conversely, when the wafer W is hydrophilic, the water on the wafer W is thin. Therefore, the watermark Wm is unlikely to occur). For this reason, the wafer W may be made a hydrophilic surface in order to prevent the generation of the watermark Wm. In the present embodiment, the case where the wafer W is hydrophilic is shown, but even when the wafer W is hydrophobic, the solvent So (water in this embodiment) is removed from the wafer W by tilting the wafer W. You can do it effectively.

(4) The cleaning apparatus 1 cleans the wafer W after the cleaning processing.
It is carried out from inside 0 (step S14). Specifically, the opening / closing section (not shown) of the pressure vessel 20 is opened to release the fixation of the wafer W, and the wafer W subjected to the cleaning process is carried out of the pressure vessel 20 using a wafer transfer device (not shown).

According to the present embodiment described above, by tilting the wafer W, the solvent S which is hardly soluble in the supercritical fluid Fs is formed.
Even if it is o, removal of the solvent So from the wafer W can be promoted.

(Other Embodiments) The embodiments of the present invention are not limited to the above-described embodiments, and can be extended and modified. Extended and modified embodiments are also included in the technical scope of the present invention. For example, the object is not limited to a semiconductor wafer, and a general substrate including a glass substrate and the like can be used. In addition, in both cases where the substrate is easily wetted by the solvent or hardly wet (water is hydrophilic or hydrophobic), the removal of the solvent from the substrate can be promoted by tilting the substrate. In the present embodiment, the supercritical fluid flows from above the wafer W, but may flow from below the wafer W. In the present embodiment, the solvent and the supercritical fluid are a combination of water (pure water) and carbon dioxide, but other combinations may be used. In this case, the specific gravity of the solvent may be smaller than that of the supercritical fluid, but in such a case, it is effective to tilt the substrate. It should be noted that another cleaning material (such as an organic solvent) may be mixed with the supercritical fluid to improve the cleaning power.

[0032]

As described above, according to the present invention, it is possible to provide a cleaning apparatus and a cleaning method capable of effectively removing even a substance having low solubility in a supercritical fluid.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a cleaning apparatus according to the present invention.

FIG. 2 is a schematic diagram illustrating a direction of a wafer W in a pressure vessel.

FIG. 3 is a flowchart showing an example of an operation procedure of the cleaning device.

FIG. 4 is a cross-sectional view illustrating a process in which supercritical cleaning is performed while the wafer W is tilted.

FIG. 5 is a cross-sectional view illustrating a process in which supercritical cleaning is performed while the wafer W is kept horizontal.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Cleaning apparatus, 12 ... Fluid supply part, 14 ... Pressure generator, 16 ... Chemical supply part, 18 ... Solvent supply part, 20 ... Pressure vessel, 22 ... Impurity removal part, 24, 26, 28, 32 ...
Valve, 30 ... supply pipe, 34 ... return pipe, 36 ... circulation system, 42, 44 ... main surface

Claims (10)

[Claims] 1. A cleaning apparatus, comprising: a cleaning chamber for disposing a substrate in a vertical direction or a direction inclined from horizontal, and a supercritical fluid supply unit for supplying a supercritical fluid into the cleaning chamber. 2. The cleaning apparatus according to claim 1, wherein the cleaning chamber has an inflow port and an outflow port through which a fluid flows above and below the substrate, respectively. 3. An impurity removing section for removing impurities from a supercritical fluid used for cleaning in the cleaning chamber, and a return path for returning the supercritical fluid passing through the impurity removing section to the supercritical fluid supply section. The cleaning device according to claim 1, further comprising: 4. A cleaning apparatus further comprising: a chemical solution supply unit for supplying a chemical solution into the cleaning chamber; and a solvent supply unit for supplying a solvent for dissolving the chemical solution supplied by the chemical solution supply unit to the cleaning chamber. The cleaning device according to claim 1. 5. The cleaning apparatus according to claim 1, wherein the supercritical fluid is carbon dioxide in a supercritical state. 6. The cleaning apparatus according to claim 3, wherein the solvent and the impurities are both water. 7. A supercritical fluid processing step of processing a substrate with a supercritical fluid in a state where the substrate is arranged in a vertical direction or a direction inclined from horizontal. 8. A chemical treatment step of treating the substrate with a chemical solution before the supercritical fluid treatment step; a rinsing treatment step of treating the substrate treated in the chemical solution treatment step with a solvent that dissolves the chemical solution; The cleaning method according to claim 6, further comprising: 9. The cleaning method according to claim 7, further comprising: an impurity removing step of removing impurities from the supercritical fluid used in the processing in the supercritical fluid processing step. 10. The cleaning method according to claim 7, further comprising: after the supercritical fluid processing step, a drying step of drying the substrate processed in the supercritical fluid processing step.