JPH08306651A - Alkaline cleaning composition and cleaning method using the composition - Google Patents

Abstract

PURPOSE: To suppress the adsorption of Al from a cleaning solution while enhancing the cleaning effect by blending fluoride ions exceeding a specific value with the alkaline cleaning solution. CONSTITUTION: A fluoride ions are normally added as hydrofluoric acid of fluoride although it may be added in any state. When the hydrofluoric acid is added, normally used as a water solution of 1-80wt.%, but as a fluoride, normally added as a fluoride or ammonium fluoride of organic alkali. At this time, the fluoride ion concentration in the whole solution of cleaning composition shall exceed 0.15mol/l preferably exceeding 0.20mol/l at the upper limit of 2.0mol/l. If the added amount does not exceed the lower limit, both sticking and removing effects will become insufficient. Furthermore, even if the added amount exceeds the upper limit, any exceptional effect can not be expected.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to an alkaline cleaning composition suitable for use as a cleaning agent for substrates.

[0002]

2. Description of the Related Art In recent years, fine processing technology typified by semiconductor integrated circuits has been increasingly improved in processing accuracy. Taking a dynamic random access memory (DRAM) as an example, it is currently a submicron design rule. Has been established as a mass production level technology.

In such a fine pattern, the impurity contamination existing on the substrate has a serious adverse effect on the electrical characteristics of the device, the processing accuracy, and the yield of the integrated circuit. Therefore, before the process susceptible to contamination such as oxide film formation and electrode metal film formation, or after the process where contamination is likely to occur conversely such as etching and ion implantation, each time,
It is customary to remove contaminants using acidic or alkaline detergents such as sulfuric acid, hydrochloric acid, ammonia, hydrogen peroxide. From the mid 1970s, RCA cleaning (W.Kern: RCA
Review (1970.6) pp.207-233, W. Kern and DAPuotine
n: RCA Review, 31, 187 (1970), etc.), a series of cleaning treatments using a cleaning solution in which an acidic or alkaline cleaning agent and hydrogen peroxide are mixed is widely used, and is the basis of wet cleaning.

Organic matter contamination and some metals such as Cu and A
It has a cleaning effect on g, etc., and has a remarkable cleaning effect especially on particulate contamination [ammonia + hydrogen peroxide +
Water] (SC-1 cleaning) is usually performed at 40 to 80 ° C. to activate the movement of fine particles, and the composition ratio is usually (30% by weight aqueous ammonia) :( 31% by weight hydrogen peroxide). Water): (water) = 0.05 to 1: 1: About 5 is used.

The [hydrochloric acid + hydrogen peroxide + water] cleaning (SC-2 cleaning), which is extremely effective in removing metal contamination, is usually used at a temperature of about 60 to 80 ° C., and its composition ratio is
(36 wt% hydrochloric acid): (31 wt% hydrogen peroxide solution):
It is used at (water) = 1: 1: 5.

In addition, [sulfuric acid + hydrogen peroxide] cleaning (SPM cleaning), which is excellent in cleaning organic contaminants such as resist residues, which are very difficult to remove, or diluted HF cleaning for removing a natural oxide film, etc. It is customary that the cleaning is performed by the combination of.

As the degree of integration of the integrated circuit is improved, the finer pattern and the more complicated unevenness are combined, and the allowable contamination level is becoming lower and lower than the contamination removal level required for the cleaning process. On the other hand, severe demands have been made. For this reason, the quality of the cleaning liquid is extremely strictly controlled, and not only the acid and alkali cleaning liquids themselves are highly purified, but also the supply system is being maintained by chemical manufacturers.

[0008]

A generally used RCA cleaning sequence is
For example, SPM cleaning → SC-1 cleaning → SC-2 cleaning → dilute HF cleaning, that is, it is customary to remove organic contaminants, particulate contaminants, metal contaminants, and natural oxide film in this order.

In a cleaning process using an acidic cleaning agent such as SC-2 cleaning or dilute HF cleaning, the zeta potentials of the particles in the liquid and the particles in the liquid are different from each other, so that they are susceptible to particle contamination.
Also, the ability to remove fine particles is poor. On the other hand, the smaller the size of the fine particles, the more the adhesion force to the wafer increases, and therefore the removal tends to be difficult. In other words, as the degree of integration increases and the pattern becomes finer, the degree to which the particulate removal capacity in the cleaning process contributes to the manufacturing yield becomes even greater, and in that sense, it is not so much to place the acid cleaning in the final step of the cleaning sequence. Not preferable.

Since the SC-2 cleaning is usually carried out at a high temperature of about 80 ° C., a large amount of hydrogen chloride gas is generated.
Hydrogen chloride gas is extremely corrosive, and there is a risk of causing metal contamination due to corrosion of equipment members and the like. In order to prevent gas leakage, it is usually necessary to install exhaust equipment around the SC-2 cleaning tank, which is one of the reasons for increasing the cost of the clean room.

Therefore, a method has been tried in which alkali cleaning such as SC-1 cleaning is used as the final step of the cleaning process and SC-2 cleaning is omitted. However, when it is washed with a conventional alkaline cleaning solution, it shows an excellent effect in removing fine particle contamination, but on the contrary, metal contamination is hardly removed, rather, it is contaminated from the equipment or environment and contained in a trace amount in the solution. Since the metal such as Fe and Al adheres, the recombination lifetime is shortened, and the electrical characteristics such as the breakdown voltage of the oxide film are deteriorated.

As an alkali cleaning method similar to SC-1 cleaning, a method using a mixed solution of organic alkali and hydrogen peroxide is known. For example, [tetramethylammonium hydroxide (TMAH) + hydrogen peroxide] (Japanese Unexamined Patent Publication No. 50-147284), [trialkyl (hydroxyalkyl) ammonium hydroxide + hydrogen peroxide] (Japanese Patent Publication No. 53-43012). ) And the like have been proposed, but in both cases, [alkali +
Hydrogen peroxide] has an excellent ability to remove fine particles, which is a characteristic of cleaning, but on the other hand, a large amount of Fe, Al, etc. adheres from the cleaning liquid,
The cleaning power for wafers contaminated with e, Al, etc. is also insufficient.

The method of trapping metal impurities as a stable water-soluble complex and inactivating it against the object to be cleaned is a conventional method when blending a general cleaning agent, and a specific complexation with these alkaline cleaning solutions is required. Several methods have been proposed for adding a chemical agent and cleaning the wafer. For example, Japanese Patent Laid-Open No. 5-
Japanese Patent No. 275405 discloses an example in which a chelating agent having at least one phosphonic acid group or a salt group thereof or an oxidant thereof, or condensed phosphoric acid or a salt thereof is added to an alkali cleaning solution for cleaning. Further, JP-A-5-259140 discloses an example in which a phosphonic acid-based chelating agent and a surfactant are added to a basic aqueous hydrogen peroxide solution for cleaning. However, when these cleaning liquids were used for cleaning, both had a slight effect of preventing adhesion of Fe and removing contaminants, but Al did not have a trapping ability as a complexing agent at all, and thus the normal SC-1 Adhesion to the same extent as the cleaning liquid was observed, and further improvement was desired.

In addition, an example of adding hydrofluoric acid to an SC-1 cleaning solution to clean a wafer has been reported (Sem
iconductor World, 1993.3, pp126-129), when adding about 4000 ppm of hydrofluoric acid to the SC-1 cleaning solution and making the pH acidic to 3.8, the amount of Fe, Al and other metals adhering decreases, but hydrofluoric acid It is known that there is no metal adhesion preventing effect in an alkaline cleaning liquid having a pH of 8.6, to which 2000 ppm (0.10 mol / l as a fluoride ion) is added.

As described above, the [alkaline + hydrogen peroxide] cleaning, which has an excellent effect on the cleaning of fine particles, does not have a sufficient cleaning effect on harmful metals such as Fe and Al as it is, and the complexing agent, etc. Even with the addition of the above additive, improvement in prevention of Al adhesion and cleaning has not yet been made.

[0016]

As a result of various studies to solve the above problems, the inventors of the present invention have found that the alkaline cleaning liquid contains fluoride ions in an amount of 0.15 mol / l or more so that The present invention has been reached by finding that it has a high cleaning effect while suppressing the adsorption of Al.

That is, the gist of the present invention lies in an alkaline cleaning composition containing 0.15 mol / l or more of fluoride ion, and a substrate cleaning method using the same. Hereinafter, the present invention will be described in detail.

The alkaline cleaning liquid in the present invention means p
It is a general term for cleaning liquids having an H value of more than 7, and usually contains an inorganic or organic alkali as a main component, and preferably contains hydrogen peroxide and water. Ammonia is mentioned as the inorganic alkali, and it is usually used as a 1 to 30% by weight aqueous solution. Further, in the case where washing with water is sufficiently performed in the subsequent step, a hydroxide of an alkali metal or an alkaline earth metal can be used as the inorganic alkali, and sodium hydroxide, potassium hydroxide, calcium hydroxide or the like can be used. 1 to 10% by weight aqueous solution is exemplified. Examples of the organic alkali include quaternary ammonium salts such as quaternary ammonium hydroxide, and other amines, which are usually used as 1 to 30% by weight aqueous solution. Typical examples of the quaternary ammonium hydroxide include, but are not limited to, tetramethylammonium hydroxide (TMAH) and trimethyl-2-hydroxyethylammonium hydroxide (choline). . Known other amines are used, for example, tertiary amines such as trimethylamine and triethanolamine, diamines such as ethylenediamine, guanidine and toluidine. These inorganic or organic alkalis are 2
There is no problem even if more than one kind is added, and the total concentration in the total solution of the cleaning composition is usually 0.01 to 30% by weight, preferably 0.1 to 20% by weight.

The alkali component of the alkaline cleaning composition of the present invention has a vapor pressure of 1 atm (= 1.013 × 10 6) at the operating temperature, especially when it is heated before being used for cleaning.
^It is preferable to use one lower than ⁵ Pa). That is, it is preferable to use a vapor pressure lower than 1 atm at 40 ° C., which is commonly used, and a vapor pressure lower than 1 atm at 80 ° C. used in many cleaning processes. More preferable. In other words, the temperature of the alkaline cleaning composition in the present invention is usually set to an appropriate temperature, but it is preferable to perform cleaning at a temperature at which the vapor pressure is lower than 1 atm. If the vapor pressure and temperature are too high, the volatilization of the alkali component is rapid, and as a result, the pH of the liquid is biased toward the acidic side due to the influence of fluoride ions, and the ability to remove fine particles is unfavorable.

When hydrogen peroxide is mixed with the alkaline cleaning composition of the present invention, it is usually used as an aqueous solution of 20 to 40% by weight, and the concentration of hydrogen peroxide in the total cleaning composition solution is usually 0.01. It is used so as to be in a concentration range of ˜30 wt%, but even if it is out of the range, it does not particularly affect the cleaning effect.

The fluoride ion in the present invention may be added in any form, but is usually added as hydrofluoric acid or fluoride. When hydrofluoric acid is added, it is usually used as an aqueous solution of 1 to 80% by weight. When it is added as a fluoride, it is usually added as an organic alkali fluoride or ammonium fluoride. Fluoride ion concentration in the entire cleaning composition solution is 0.15 mol
/ L or more, preferably 0.20 mol / l or more, and the upper limit is usually 2.0 mol / l. If it is less than the above-mentioned addition amount, the Al adhesion preventing effect and the removing effect are not sufficient, and if it is too much, no further effect can be obtained, and the addition amount of alkali for pH adjustment is meaninglessly increased. It must be unfavorable.

When the semiconductor substrate is cleaned, the inorganic or organic alkali, hydrofluoric acid, or fluoride is of high purity with sufficient removal of foreign substances and metal contamination. Specifically, it is preferable that the content of each metal element other than the alkali metal is 100 ppb or less.

Since the cleaning method in the present invention is wet cleaning with a cleaning liquid, a method of directly contacting the liquid with the substrate is used. Examples of such cleaning methods include dip-type cleaning in which a cleaning tank is filled with a cleaning solution and immersing the substrate, spray-type cleaning in which the solution is sprayed onto the substrate for cleaning, and spin-type cleaning in which the cleaning solution is dropped onto the substrate and rotated at high speed. Etc. In the present invention, an appropriate one of the above-mentioned cleaning methods is used, but dip-type cleaning in which a cleaning bath is filled with a cleaning liquid to immerse the substrate is preferably used.

Regarding the washing time, the washing is carried out for an appropriate time, preferably 3 to 20 minutes, more preferably 5 to 1
5 minutes. If the time is shorter than the above time, the cleaning effect is not sufficient, and if it is too long, the throughput is deteriorated, and the cleaning effect is not improved and is meaningless. Further, in the case of washing, a washing method using physical force may be used together. Examples of the cleaning method using such a physical force include ultrasonic cleaning and mechanical cleaning using a cleaning brush.

[0025]

The reason why the cleaning composition of the present invention exerts a particularly good effect on the prevention and removal of Al is not yet clear, but the conventional complexing agents have a low equilibrium constant for complex formation with Al. , OH ^- for towards the complexation ability was much stronger with respect to the sufficient adhesion prevention and removal effect is not obtained, the addition of fluoride ion 0.15 mol / l or more, to sufficiently complex formed even under alkaline atmosphere, stably present in an aqueous solution complex of Al and F, and at the same time OH ^- for complexation is inhibited with, an excellent effect on adhesion prevention and removal It is presumed to do.

[0026]

EXAMPLES Specific examples of the present invention will be described below with reference to examples, but the present invention is not limited to the following examples without departing from the scope of the invention. Examples-1 to 4 and Comparative Examples-1 to 4 Ammonia water (30% by weight) and hydrofluoric acid were added in appropriate amounts to a liquid obtained by mixing hydrogen peroxide solution (31% by weight) and water in a ratio of 1: 5. Adjust the pH value shown in -1 and the fluoride ion concentration (the addition ratio of ammonia water is also shown), and
After heating to the temperature shown in, Al was added at 10 ppb as chloride.

A clean 2-inch p-type, crystal orientation (100) silicon wafer was immersed in the cleaning liquid thus prepared for 10 minutes, rinsed with ultrapure water for 10 minutes, and then the amount of Al adhering to the wafer surface was quantified. did. In addition, the cleaning liquid not added with fluoride ion, fluoride ion 0.1mo
Cleaning solution added at a concentration of less than 1 / l, and
The same experiment was conducted on the cleaning liquid containing the complexing agent described in Japanese Patent No. 275405. The Al adhering to the silicon wafer was recovered with an aqueous solution containing 0.1% by weight of hydrofluoric acid and 1% by weight of hydrogen peroxide, and the amount of the metal was measured by the flameless atomic absorption method and converted into the surface concentration. .

Table 2 shows the experimental results. Example-2
When an experiment was performed to remove fine particles with the cleaning liquids of Nos. 4 and 4, a cleaning power equivalent to that of [ammonia + hydrogen peroxide + water] cleaning without addition of fluoride ions was exhibited.

[0029]

[Table 1]

[0030]

[Table 2]

Examples 5 to 6 Organic alkalis and hydrofluoric acid shown in Table 3 were added to a liquid obtained by mixing 1: 5 hydrogen peroxide solution (31% by weight) and water, and shown in Table 3. After adjusting the alkali concentration and the fluoride ion concentration and heating to 80 ° C., Al was added at 10 ppb as chloride.

A clean 2-inch p-type, crystal orientation (100) silicon wafer was immersed in the cleaning liquid thus prepared for 10 minutes, rinsed with ultrapure water for 10 minutes, and the amount of Al adhering to the wafer surface was quantified. did. The Al adhering to the silicon wafer was recovered with an aqueous solution containing 0.1% by weight of hydrofluoric acid and 1% by weight of hydrogen peroxide, and the amount of the metal was measured by the flameless atomic absorption method and converted into the surface concentration. .

Further, in order to know the volatilization of the alkaline component in the cleaning liquid, p before and after the silicon wafer is immersed for 10 minutes.
The H value was measured. The experimental results are shown in Table-4.

[0034]

[Table 3]

[0035]

[Table 4]

[0036]

The alkaline cleaning composition of the present invention is
Since the adherence is prevented and the removal ability is excellent, the electrical characteristics of the semiconductor or the like are not deteriorated. Moreover, since the SC-2 cleaning which has been conventionally used can be omitted by using the present cleaning composition in the final step of the cleaning sequence, the cleaning cost and the cost of the clean room such as the exhaust facility can be significantly reduced, and thus the high integration can be achieved. It is a great advantage for the industrial production of circuits.

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Claims (5)

[Claims] 1. An alkaline cleaning composition containing 0.15 mol / l or more of fluoride ions. 2. Fluoride ions in an amount of 0.20 to 2.0 mo
An alkaline cleaning composition containing 1 / l. 3. An alkaline cleaning composition containing ammonia, an organic amine or an organic quaternary ammonium ion, and hydrogen peroxide, and 0.15 mol / l or more of fluoride ion. 4. The alkaline cleaning composition according to claim 1, wherein the content of the metal element other than the alkali metal is 100 ppb or less. 5. The alkaline cleaning composition according to any one of claims 1 to 4, wherein the cleaning composition has a vapor pressure of 1 or less.
A method of cleaning a substrate, comprising cleaning at a temperature lower than atmospheric pressure.