JPH1041262A - Cleaning method and method for manufacturing semiconductor device - Google Patents

Abstract

(57) [Problem] To remove contamination composed of metal and metal oxide / hydroxide without damaging metal wiring. It also facilitates waste liquid treatment. SOLUTION: The cleaning solution is water in which hydrogen gas is dissolved or an aqueous electrolyte solution in which hydrogen gas is dissolved. As the electrolyte aqueous solution, a field ionized water or a carbonic acid aqueous solution in which hydrogen gas is dissolved is used. Further, oxygen or hydrogen peroxide is added to these cleaning solutions. The ratio of the dissolution rate of the metal and its compound is optimally controlled for cleaning by adjusting the oxidation-reduction potential of the cleaning solution. In addition, since a neutral or weak acid cleaning solution can be effectively cleaned, waste liquid treatment is unnecessary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cleaning method for removing metals and their compounds attached to the surface of an object to be cleaned.

[0002] The step of cleaning and removing contaminants including metals and their compounds, for example, contaminants including iron, iron oxides and iron hydroxides, adhered to the surface of an object to be cleaned is performed by a semiconductor device manufacturing process or a magnetic process. It is often required in head manufacturing and maintenance processes.

In such a cleaning step, it is necessary to remove metals and metal compounds adhering to the surface of the object to be cleaned without corroding and damaging the fine wiring or metal thin film formed on the surface of the object to be cleaned. Further, it is desired that the cleaning liquid can be easily treated for waste liquid.

[0004] Therefore, in a cleaning method for removing contaminating metals and contaminant metal oxides, there is a demand for a method in which the corrosion of the metal thin film is small and the treatment of the waste liquid of the cleaning liquid is easy.

[0005]

2. Description of the Related Art In a semiconductor device manufacturing process, a process of cleaning a surface of an object to be cleaned, for example, a surface of a semiconductor substrate, with an oxidizing agent such as a mixed solution of ammonia and hydrogen peroxide is widely used. However, oxidizing agents cannot remove metal contaminants such as iron and its compounds.
For this reason, conventionally, it is common to add an acid cleaning step using a strong acid in order to remove metal contamination.

However, when a metal wiring or a metal thin film is formed on the surface of an object to be cleaned, the wiring and the thin film are corroded and damaged by acid cleaning, and the object to be cleaned on which the metal wiring or the metal thin film is formed is removed. It cannot be acid washed. Further, in the cleaning method using a strong acid, expensive equipment is required for treating the waste liquid of the acidic cleaning liquid. In addition, the surface of the metal wiring and the metal thin film is oxidized in the water washing after the acid washing, which may hinder the subsequent processing. In addition to using acid cleaning, there is also a means to remove metal contamination by electrolysis.
The field of application is severely limited because contaminants not on the electrodes are not removed.

[0007] A similar problem also occurs when removing the metal oxide generated on the surface of the metal thin film of the magnetic head. In a magnetic head, since a thin film of iron or an iron alloy is exposed to the atmosphere, it is necessary to remove metal oxides formed on the surface. At this time, acid cleaning with a strong acid cannot be used because the metal thin film is etched, so that it has been difficult to effectively clean and remove the metal oxide of the magnetic head.

[0008]

As described above, the conventional cleaning method for removing metal contamination by using a strong acid has a problem that a metal wiring or a metal thin film formed on the surface of an object to be cleaned is corroded and damaged. there were. In addition, there is a problem that the surface of the metal wiring or the metal thin film is oxidized in the water washing step after the acid washing. Further, there is a disadvantage that it is necessary to treat an acid cleaning solution composed of a strong acid as a waste liquid.

The present invention maintains a redox potential at a potential at which metal corrosion occurs by dissolving hydrogen gas in pure water or an aqueous electrolyte solution to convert metals, metal oxides and metal hydroxides into water. It is an object of the present invention to provide a cleaning method that removes as soluble, reduces corrosion of metal wiring and metal thin film, and effectively removes metal contamination, metal oxide contamination and metal hydroxide contamination. It is still another object of the present invention to provide a cleaning method that facilitates waste liquid treatment of a cleaning liquid.

[0010]

According to a first aspect of the present invention, there is provided a cleaning method comprising the steps of: forming a cleaning solution using water in which hydrogen gas is dissolved or an aqueous electrolyte solution in which hydrogen gas is dissolved; The second configuration is characterized in that the pH of the aqueous solution is set to 9 or less in the cleaning method of the first configuration, and the cleaning method of the third configuration is characterized in that a hydrogen gas-dissolved electric field ionized water is used. Alternatively, a cleaning solution is constituted by an aqueous solution of carbon dioxide in which hydrogen gas is dissolved, and a fourth configuration is characterized in that hydrogen peroxide is added to the cleaning solution in the cleaning method of the first, second or third configuration. A fifth aspect of the present invention is the cleaning method according to the first, second, or third aspect, characterized in that oxygen gas is dissolved in the cleaning solution, and the semiconductor device has a sixth aspect. The manufacturing methods of , Configured as further comprising a step of cleaning the semiconductor substrate using the cleaning method of the fourth or fifth configuration.

The inventor of the present invention has conducted intensive research on a method for cleaning surface contaminants including metal elements. As a result, the cleaning solution obtained by dissolving hydrogen gas in water or an aqueous electrolyte solution has a low corrosion of metal wiring and metal thin films. On the other hand, it was clarified by experiments that metal contamination, metal oxide and metal hydroxide contamination were effectively removed. The present invention has been made based on this fact. The reason why the aqueous solution in which hydrogen gas is dissolved effectively removes polluting metals and polluting oxides is explained as follows from the viewpoint of oxidation-reduction potential.

[0012] Figure 1 is a PH─ redox potential diagram of iron ─ iron oxide, the system comprising a passivation film consisting of 1 (a) is Fe ₂ O _3, FIG. 1 (b) Fe ₂ O ₃ shows a system including a passivation film made of ₃ and Fe ₃ O ₄ . FIG. 2 is a diagram showing the PH-oxidation-reduction potential of iron-iron hydroxide, and shows a system containing Fe (OH) ₃ and Fe (OH) ₂ . Note that the oxidation-reduction potential is represented by a potential with respect to a standard hydrogen electrode. The potentials at which the oxygen generation reaction and the hydrogen generation reaction by water electrolysis occur are indicated by dotted lines a and b in FIG. 1, respectively. These PH─ redox potential diagrams are well known as Pourbaix diagrams.

Referring to FIGS. 1 and 2, the iron oxidation / reduction reaction depends on the pH and the redox potential depending on the immunity region (a), the passivation region (b) and the corrosion (corrosio) region.
n) Classified as region c. In the system where Fe ₃ O ₄ is present, a region in contact with the insoluble region A of the passive region B is a region D in which a part of Fe ₃ O ₄ is formed. Similarly _, Fe
(OH) ₃ and Fe (OH) _in a system ₂ and is _present, the area in contact with the insoluble region Lee passivation region Russia some Fe (OH)
_The area e where ₂ is formed. The corrosion area of iron is iron.
In the iron iron oxide system, it does not exist in the range of PH10 to PH14, and in the iron-iron hydroxide system, it does not exist in the range of PH9 to PH12. It exists as a wedge-shaped region in a narrow range of oxidation-reduction potential along. At PH2 or less, since a corrosion region exists in a wide range of oxidation-reduction potential, iron, iron oxide or iron hydroxide is dissolved by the strong acid. As is well known, in order for iron to dissolve, the pH and redox potential must be in the corrosive region, and the further away from the boundary between the insoluble region a and the passive region b, iron oxide and iron hydroxide Dissolution of the material and iron is facilitated.

In the first configuration of the present invention, water in which hydrogen gas is dissolved or an aqueous electrolyte solution in which hydrogen gas is dissolved is used as a cleaning liquid. By dissolving the hydrogen gas, the oxidation-reduction potential of the cleaning liquid becomes close to the potential a at which the hydrogen generation reaction occurs, referring to FIG. For this reason, this cleaning solution easily enters the corroded area of iron even when the pH is near neutral. Therefore, water or an aqueous solution in which hydrogen gas is dissolved becomes a cleaning solution which is nearly neutral and dissolves iron and iron oxides. Since such a cleaning solution is close to neutral and close to the insoluble region, the metal dissolution rate is low, and the metal wiring and the metal thin film formed on the surface of the object to be cleaned by the cleaning are not damaged. However, iron fine particles having a large surface area are easily dissolved and removed.
In order to remove iron oxides and iron hydroxides, it is preferable that the conditions be away from the passive region b. From this viewpoint, it is desirable that the hydrogen gas is close to saturation.

In this configuration, the etching action for removing contamination and the washing step after etching are performed with the same cleaning liquid. Therefore, even during the washing with water, the oxidation-reduction potential is in the corroded region C, and no oxide or hydroxide is formed on the surface of the metal wiring and the metal thin film on the surface of the object to be washed. For this reason, a situation in which a passivation film is formed on the surface of a metal wiring or a thin film as in the case of ordinary water washing does not occur.

Of course, if the damage of the wiring or thin film on the surface of the object to be cleaned is not a problem, the cleaning solution according to the present invention can be a strong acid or strong alkali. Even in this case, by controlling the dissolution rate ratio of oxides and hydroxides to iron by dissolving hydrogen gas, contamination of iron, iron oxides and iron hydroxides without damaging metal wiring Optimum washing conditions can be selected to remove the water. In addition, the use of water or an aqueous solution in which hydrogen gas is dissolved in the water washing step after the acid washing can prevent the formation of a passive film during the water washing.

In the present invention, so-called pure water having high purity and high electric resistance used in the semiconductor industry can be used. In addition, a neutral non-electrolyte aqueous solution can be used if it does not hinder the cleaning. The electrolyte aqueous solution is preferably a weak acid which is easy to treat waste liquid and has little damage to the metal wiring and the metal thin film, for example, a carbonic acid aqueous solution and electrolytic ion water. In such a configuration, metal contamination can be washed and removed without using a strong acid or strong alkali, so that waste liquid treatment of the washing liquid is unnecessary or easy. Also, because it is more acidic than neutral water, it is easier to dissolve the contamination.

According to a second aspect of the present invention, in the cleaning method of the first aspect, the pH of the aqueous solution, ie, the cleaning liquid, is 9 or less. In this range, iron contamination can be reliably washed and removed by saturating the hydrogen gas. Although the above description is for iron, the cleaning liquid having the above-described structure has the same effect on nickel, cobalt, and manganese having the same region as iron in the PH─ redox potential diagram. Has the effect of

FIG. 3 shows the pH of nickel oxide / hydroxide.
─ It is an oxidation-reduction potential diagram. FIG. 4 is a diagram showing a PH reduction potential of lead oxide. A, B, and C in FIGS. 3 and 4 correspond to the insoluble region A, the passive region B, and the corrosion region C in FIG. 1, respectively. In the passivation region (b), nickel hydroxide and lead monoxide are stably present in the region in contact with the insoluble region (a), and in the other passive region (b), nickel oxide and lead dioxide are stably present.

Referring to FIG. 2, in the case of this type of metal, similarly to iron, a corrosion region C in which the range of the oxidation-reduction potential is narrowed like a wedge in a neutral region is formed. Is between a potential a for causing a hydrogen generation reaction and a potential b for causing an oxygen decomposition reaction. Therefore, in order to effectively clean such metal and oxide contaminations, it is necessary to control the hydrogen concentration and appropriately maintain the oxidation-reduction potential. That is, if the hydrogen concentration is high and the oxidation-reduction potential is low, the metal will not be dissolved, while if the hydrogen concentration is low, the oxidation-reduction potential will be high and the stable oxides or hydroxides will not be dissolved in the passive region b. .

In the fourth and fifth configurations of the present invention, hydrogen peroxide is added to the above-mentioned water or aqueous solution in which hydrogen gas is dissolved, or oxygen gas is dissolved. By dissolving the hydrogen peroxide or the oxygen gas, the redox potential changed to the negative side by dissolving the hydrogen gas is returned to the positive side. Since hydrogen gas is easily saturated, it is difficult to adjust the oxidation-reduction potential by controlling the hydrogen concentration. However, it is easy to adjust the oxidation-reduction potential by adding an oxidizing agent to a cleaning solution in which a large amount of hydrogen gas is dissolved. Therefore, the oxidation-reduction potential is set to P
Since it can be easily adjusted according to H, the corrosive region C as shown in FIGS. 3 and 4 is located between the potential a for causing the hydrogen generation reaction and the potential b for causing the oxygen decomposition reaction, and the cleaning solution saturated with hydrogen gas. In this case, appropriate cleaning is performed even for metals for which an appropriate oxidation-reduction potential cannot be obtained. Note that control is more reliable when using hydrogen peroxide that is stably present as a solution.

The above-described cleaning methods of the first to fifth constitutions are
By utilizing the present invention for cleaning a semiconductor wafer on which metal wiring or a thin film is formed, metal contamination can be removed without damaging the semiconductor device. Therefore, a highly reliable method for manufacturing a semiconductor device is provided.

[0023]

BEST MODE FOR CARRYING OUT THE INVENTION

(1) Cleaning Device FIG. 5 is a conceptual diagram of a cleaning device according to an embodiment of the present invention, and shows the cleaning device used in the embodiment of the present invention. Referring to FIG. 5, the cleaning apparatus includes a part for producing a cleaning liquid and a spin cleaning apparatus. The part that produces the cleaning solution
The mixer 1, the hydrogen injector 2, and the heater 3 are connected by a water pipe 6.

Pure water or an aqueous electrolyte solution supplied from a water supply port 6a provided at the end of the water distribution pipe 6 is supplied to the valves V1 and V1.
Whether to pass through the mixing device 1 is selected by opening and closing operations of 1a and V1b. Similarly, valves V2, V2a and V2
Whether or not to pass through the hydrogen injector 2 is selected by the opening and closing operation of b, and whether or not to pass through the heating device 3 is selected by opening and closing of the valves V3, V3a and V3b. The mixing device 1 adds a hydrogen peroxide solution to pure water or an aqueous electrolyte solution, and mixes with stirring. The hydrogen injector 2 dissolves the hydrogen gas by bubbling the hydrogen gas into the pure or electrolyte aqueous solution filled in the tank. Usually, the hydrogen concentration of the pure or aqueous electrolyte solution is saturated by bubbling. The heating device 3 heats the pure or electrolyte aqueous solution to a predetermined temperature. The pure water or the aqueous electrolyte solution supplied from the water supply port 6a is supplied to the hydrogen injection device 2,
In addition, it is converted into a cleaning liquid through one or both of the mixing device 1 and the heating device 3 as necessary.

The spin cleaning device 4 supports a wafer 7 to be cleaned on a support table rotating in a horizontal plane, and discharges a cleaning liquid from a discharge port 6b provided at the rear end of the water distribution pipe 6 and opening on the wafer 7. Then, the surface of the wafer 7 is cleaned. Such a spin cleaning device is the same as a conventional cleaning device. (2) Cleaning Effect Confirmation Test (Example 1) Example 1 is an example using a cleaning solution in which hydrogen is dissolved in pure water. Hydrogen gas was dissolved in pure water at a flow rate of 10 liters / minute using a hydrogen injection device to obtain a cleaning solution.
When the flow rate of the hydrogen gas was 10 to 100 sccm, the pH of the cleaning solution was 7, and the oxidation-reduction potential of the cleaning solution with respect to the standard hydrogen electrode was -300 mV to -400 mV.

The silicon wafer is cleaned with the cleaning liquid for 10 minutes using the spin cleaning apparatus 4 and the Fe wafer before and after cleaning is cleaned.
The change in wafer surface concentration of contamination was measured. as a result,
Iron contamination on the wafer surface is 2 × 10 ¹³ atoms / cm before cleaning.
² to a measurement limit of 1 × 10 ¹⁰ atoms / cm ² or less. The measurement of the iron contamination was performed by a total reflection X-ray fluorescence apparatus. Separately, as a result of cleaning a silicon wafer on the surface of which a pattern composed of an iron thin film, an Al thin film and a copper thin film was formed under the same conditions, the formation of a passivation film on the thin film surface was not observed under a microscope, and the thickness of the thin film was No change was observed.

Further, the cleaning liquid of Example 1 was heated to 60 ° C. by a heating device to clean the silicon wafer. At this time, the hydrogen concentration in the cleaning solution was 30 ppb. The cleaning results were the same as in Example 1 described above. (Embodiment 2) Embodiment 2 is an example using an aqueous electrolyte solution. Carbon dioxide was bubbled into pure water to dissolve the carbon dioxide, thereby obtaining an aqueous electrolyte solution having a pH of about 5.5. This aqueous electrolyte solution was used in place of the pure water of Example 1, and hydrogen gas was bubbled into a cleaning solution to clean the silicon wafer with the cleaning solution. The conditions of bubbling and washing are the same as in the first embodiment. The results were the same as in Example 1. (Embodiment 3) Embodiment 3 is an example in which a hydrogen peroxide solution is added. A 30% hydrogen peroxide solution was mixed using a pure mixing apparatus 1 at a flow rate of 10 liter / min, and the H ₂ O ₂ concentration was 0.0
An aqueous hydrogen peroxide solution of 1 to 1.0 g / liter is produced. Next, hydrogen gas was bubbled and saturated to obtain a cleaning solution, and the silicon wafer was cleaned using the spin cleaning device 4. As a result, the residual surface concentration of Fe and Ni contamination was below the measurement limit. (Embodiment 4) This is an example in which oxygen gas is dissolved in place of the hydrogen peroxide solution of Embodiment 3. Hydrogen gas is bubbled into pure water that has been previously degassed to reduce the dissolved oxygen concentration, and is dissolved to near saturation. Next, while measuring the oxidation-reduction potential, oxygen was dissolved until the oxidation-reduction potential reached 0.2 V to obtain a cleaning solution. When the silicon wafer was cleaned in the same manner as in Example 3, F
The same results as in Example 3 were obtained for e and Ni contamination.

[0028]

According to the present invention, the oxidation-reduction potential of the cleaning solution can be adjusted to a potential suitable for cleaning by dissolving hydrogen gas in the cleaning solution. It is possible to provide a cleaning method for effectively removing metal hydroxide and metal oxide contamination.

Further, by using a cleaning solution obtained by dissolving hydrogen gas in water or an aqueous solution of a weak acid, it is possible to provide a method for cleaning contamination of metals, metal hydroxides and metal oxides, which is easy to distribute water.

For this reason, it greatly contributes to the improvement of reliability and the reduction of equipment in the manufacture of semiconductor devices and the manufacture and maintenance of electronic equipment.

[Brief description of the drawings]

FIG. 1 PH-redox potential diagram of iron-iron oxide

FIG. 2 PH-redox potential diagram of iron-iron hydroxide

FIG. 3 PH-redox potential diagram of nickel oxide / hydroxide

FIG. 4 PH-redox potential diagram of lead oxide

FIG. 5 is a conceptual diagram of a cleaning apparatus according to an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Mixing device 2 Hydrogen injection device 3 Heating device 4 Spin washing device 6 Water distribution pipe 7 Wafer 8 Support base

Claims (6)

[Claims] 1. A cleaning method using water in which hydrogen gas is dissolved or an aqueous electrolyte solution in which hydrogen gas is dissolved as a cleaning liquid. 2. The cleaning method according to claim 1, wherein the pH of the aqueous solution is 9 or less. 3. A cleaning method using a field ionized water in which hydrogen gas is dissolved or an aqueous solution of carbonic acid in which hydrogen gas is dissolved as a cleaning liquid. 4. The cleaning method according to claim 1, wherein hydrogen peroxide is added to said cleaning liquid. 5. The cleaning method according to claim 1, wherein oxygen gas is dissolved in said cleaning liquid. 6. A method for manufacturing a semiconductor device, comprising a step of cleaning a semiconductor substrate using the cleaning method according to claim 1, 2, 3, 4, or 5.