JP3169024B2 - Cleaning liquid for silicon wafers and semiconductor devices - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hydrogen peroxide cleaning solution used for cleaning silicon wafers and semiconductor devices. More specifically, the present invention relates to hydrogen peroxide which has a low surface tension, a small contact angle with the silicon wafer surface, excellent wettability, and can be suitably used for cleaning highly integrated semiconductor elements having a fine pattern and for cleaning silicon wafers. Related to system cleaning liquid.

[0002]

2. Description of the Related Art The degree of integration of semiconductor devices has been improving year by year, and it is now possible to manufacture 4MDRAM. Along with this, the patterns have become finer and the line widths have become smaller than 1 μm. In order to effectively perform such cleaning or etching of a fine pattern, a processing liquid having a low surface tension, which easily penetrates into a gap between the fine patterns, a small contact angle, and excellent wettability is required.

In general, a surfactant is effective for improving the wettability. For example, a method of treating a semiconductor element with an aqueous solution of a surfactant in advance or using a treatment liquid to which a surfactant is added is used. Have been. For example, in the case of buffered hydrofluoric acid (a mixed solution of hydrofluoric acid and ammonium fluoride) used for etching a silicon oxide film, use of a fluorinated carboxylic acid as an effective surfactant is disclosed in
9176), use of fluoroalkyl sulfonate (JP-A
60-249332), the use of aliphatic carboxylic acids or salts, aliphatic amines and aliphatic alcohols (JP-A-63-283028).

On the other hand, a hydrogen peroxide-based cleaning solution is widely used for cleaning silicon wafers and semiconductor elements because it is effective for cleaning dust and metal impurities, and is used in combination with acids such as hydrochloric acid, formic acid, sulfuric acid and hydrofluoric acid. An acidic cleaning solution and an alkaline cleaning solution combined with an alkali such as ammonia water, choline (hydroxyltrimethylammonium hydroxide), and TMAH (tetramethylammonium hydroxide) are used. Similarly, when a semiconductor element is cleaned using a hydrogen peroxide-based cleaning liquid, a cleaning liquid having improved wettability is demanded. In cleaning silicon wafers, a hydrogen peroxide-based cleaning liquid which has excellent wettability and can efficiently remove dust on the surface of the silicon wafer is desired. Furthermore, when cleaning a silicon wafer with an alkaline hydrogen peroxide-based cleaning solution, fine irregularities are likely to be formed on the surface of the silicon wafer. The generation of these fine irregularities is a problem in recent high integration and accompanying thinning of an oxide film. It has become to. From this point, there is a strong demand for the development of a hydrogen peroxide-based cleaning solution that can exhibit a leveling effect and improve the surface smoothness.

[0005] In general, a surfactant is used to improve the wettability. However, a surfactant that is truly suitable for a hydrogen peroxide-based cleaning solution has not yet been found. Furthermore, surfactants such as alkylbenzene sulfonic acid conventionally used in combination with hydrogen peroxide have not been satisfactory according to the study of the present inventors.

[0006]

Under the above background, the present inventors have searched for a surfactant suitable for a hydrogen peroxide-based cleaning solution used for cleaning silicon wafers and semiconductor elements, and furthermore, As a result of detailed examination of the conditions, it has been clarified that the surfactant that can be used in the present invention must satisfy the following conditions. Since the addition of a surfactant causes foaming of the cleaning solution and hinders the cleaning operation, it is necessary to show an effect with a small addition amount of 500 ppm or less at which foaming can be ignored. In order for the addition of a surfactant to exhibit a practical effect, the surface tension under the use conditions must be 30 dyne / cm or less, and the contact angle with the hydrophobic silicon surface must be 5 degrees or less. The cleaning is often performed at a relatively high temperature of around 85 ° C., and the effect must not be lost at the high temperature. Since the surfactant is particularly deteriorated in the ammonia water / hydrogen peroxide mixture, the surfactant must be stable in the ammonia water / hydrogen peroxide mixture. After preparation, the washing liquid is subjected to dust removal by circulating filtration, but should not be removed and lose its effect in this process.

An object of the present invention is to satisfy the above conditions,
Low surface tension, small contact angle with silicon surface, easy to get into fine pattern gaps, effective cleaning of highly integrated semiconductor elements, excellent wettability, high dust removal and cleaning effect An object of the present invention is to provide a hydrogen peroxide-based cleaning solution that can be suitably used for cleaning a silicon wafer.

[0008]

DISCLOSURE OF THE INVENTION The present inventors have searched for a surfactant satisfying the above conditions and found that a certain type of ethylene oxide-added nonionic surfactant is specifically effective. And completed the present invention.
That is, the present invention provides an acidic or alkaline hydrogen peroxide-based cleaning solution containing 1 wt% or more of hydrogen peroxide with an ethylene oxide-added nonionic surfactant having an ethylene oxide addition mole number of 3 to 10 in an amount of from 5 to 5. 500pp
The present invention relates to a silicon wafer and semiconductor element cleaning liquid characterized by adding m.

Representative examples of the ethylene oxide-added nonionic surfactant used in the present invention include three kinds of polyoxyethylene alkyl ether, polyoxyethylene alkyl phenyl ether and polyoxyethylene fatty acid ester. Here, the number of carbon atoms of the alkyl group and the fatty acid is not particularly limited as long as it exhibits an effect as a lipophilic group of the surfactant.
To 22 are preferred.

On the other hand, the length of the polyoxyethylene chain, that is, the number of moles of ethylene oxide added is one of the important requirements for the surfactant used in the present invention. Must be in range.
If the number of moles of ethylene oxide added is less than 3, sufficient surface tension and the effect of reducing the contact angle cannot be obtained. Conversely, if the number of added moles is more than 10, although the effect is exhibited at the initial stage, the deterioration is large particularly under the cleaning condition of heating to 85 ° C. with an ammonia / hydrogen peroxide-based cleaning solution, and the effect can be maintained. No, it is practically difficult to use. In the present invention, the addition amount of the surfactant is also important, and in the present invention used for cleaning silicon wafers and semiconductor elements, the addition amount of at least 500 ppm or less, preferably 100 ppm or less from the above-mentioned cleaning operation. Need to be suppressed. If the content is less than 5 ppm, the intended object of the present invention cannot be achieved.

The hydrogen peroxide-based cleaning solution to which the surfactant of the present invention is added must have a hydrogen peroxide concentration of 1 wt% or more, but generally a concentration of 3 to 30 wt% is suitably used. In addition, an acid or alkali needs to be added in order for the hydrogen peroxide-based cleaning solution to exhibit a cleaning effect, such as hydrochloric acid, formic acid, and hydrofluoric acid for removing metal impurities, and sulfuric acid for removing organic impurities. Ammonia water for dust removal purpose
An alkali such as choline or TMAH is mainly added. The addition amount of these acids or alkalis is appropriately determined depending on the purpose, and is not particularly limited.
It is added at the above concentration. The surfactant may be added by a usual addition method, and may be added in advance to hydrogen peroxide, an acid, an alkali, or diluting water, or may be added last after preparing a cleaning solution. Next, the present invention will be described specifically with reference to examples.

[0012]

Example 1 31% hydrogen peroxide, 28% aqueous ammonia,
Ultrapure water was mixed at a ratio of 4: 1: 20 (by volume), and 100 ppm of each of the surfactants shown in Table 1 was added thereto to prepare a washing solution. The surface tension and contact angle of this cleaning solution were measured at 30 ° C. and 85 ° C. Further, regarding the surface tension, the liquid measured at 85 ° C. was cooled and then measured again at 30 ° C.
The degree of deterioration due to heating was determined. The surface tension was measured using an automatic surface tensiometer CBVP-A3 (Wilhelmy type) manufactured by Kyowa Interface Science Co., Ltd. For measuring the contact angle, a contact angle meter CA-D type (droplet method) manufactured by Kyowa Interface Science Co., Ltd.
Using a silicon wafer from which the surface oxide film was removed by dilute hydrofluoric acid treatment, the contact angle with the hydrophobic silicon surface was measured. At this time, the measurement at 30 ° C.
The measurement was performed in 80 seconds, and the measurement at 85 ° C. was 1
Performed after 0 seconds.

[0013]

[Table 1]

[00114]

Example 2 The cleaning solution of Example 1 was replaced with 31% hydrogen peroxide,
The same experiment was performed in place of the mixed liquid in which 6% hydrochloric acid and ultrapure water were mixed at a ratio of 1: 1: 6 (volume ratio), and the effect of the surfactant was examined. This is shown in Table 2. (Below)

Table 2 Measurement results of surface tension and contact angle Surfactant Surface tension (dyne / cm) Contact angle (degree) Remarks 30 ° C 85 ° C 30 ° C (re) 30 ° C 85 ° C ───────── Polyethylene glycol 27 27 28 <5 <5 Ethylene oxide Lauryl-ter Addition moles 6 (Product name Emulken 106) (100 ppm added) None 71 62 70 60 58 It was recognized that the surfactant of the present invention was effective also in an acidic hydrogen peroxide-based detergent.

[0016]

Example 3 The effect of filtration with a 0.2 μm Teflon filter on the cleaning solution to which 100 ppm of Emulgen 106 was added in Example 1 was examined. Table 3 shows the results.

Table 3 Surface tension (dyne / cm) Contact angle (degree) 30 ° C 85 ° C 30 ° C 85 ° C ─────────────────────────前 Before filtration 27 26 <5 <5 After filtration 28 26 <5 <5 It was confirmed that the surfactant of the present invention did not lose its effect even by filtration.

[0018]

Example 3 A silicon wafer having a 3-inch silicon wafer from which a natural oxide film was removed by dilute hydrofluoric acid treatment was immersed in an aqueous solution in which 0.5 μm polystyrene latex particles were dispersed, and the particles were attached to the wafer. The particles were immersed in the cleaning solution of Example 1 at 85 ° C. for 5 minutes to examine the effect of removing particles. As a comparison, a similar experiment was performed with respect to the cleaning liquid of Example 1 to which no surfactant was added.
The number of particles attached to the wafer was measured by observation with a scanning electron microscope.

Table 4 Number of adhered particles on wafer (particles / cm ² ) Removal rate (%) Before / after cleaning of surfactant Addition after cleaning Yes 221 2 99 No 206 19 91

[0020]

As described above, the hydrogen peroxide-based cleaning solution to which the surfactant of the present invention has been added has a low surface tension and a small contact angle with the silicon surface, so that it is easy to enter the gaps of the fine pattern, and the semiconductor is highly integrated. The element can be effectively cleaned. Further, it is excellent in wettability, has a high dust cleaning effect, and can be suitably used for cleaning silicon wafers.

(56) References JP-A-63-274149 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/304 647

Claims (1)

(57) [Claims] 1. An acidic or alkaline hydrogen peroxide-based cleaning solution containing 1% by weight or more of hydrogen peroxide is mixed with 5 to 10 ethylene oxide-added nonionic surfactants having an ethylene oxide addition mole number of 5 to 10. A cleaning liquid for silicon wafers and semiconductor elements, which is added at 500 ppm.