JPH03225825A - Cleaning - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a cleaning method, and particularly to a cleaning method suitable for removing organic matter from semiconductor wafers.

[Summary of the Invention] The present invention provides a cleaning method for removing organic substances remaining on a semiconductor wafer, for example, by using a cleaning agent composition 2 that can rapidly generate active species only when irradiated with light. This improves the ease of handling the agent composition and enables local cleaning by selective light irradiation.

(Prior Art) In the manufacturing process of semiconductor chambers, various processes such as a so-called 5C-1 cleaning process for removing organic substances, a so-called 5C-2 cleaning process for removing metals, and a light etch process are generally performed. By arbitrarily combining these, impurities and unnecessary parts are removed.

As the cleaning liquid used in the 5C-1 cleaning process, a mixture of hydrogen peroxide, ammonia, and water has been used, and is generally called 5C-1 cleaning liquid. Since hydrogen peroxide has the property of being extremely easily decomposed in the coexistence of basic substances such as ammonia, the above-mentioned 5C-1 cleaning solution is prepared at any time immediately before use. Also, when using it, 80
The cleaning solution is heated to about .degree. C., and organic matter is decomposed by active species generated in the cleaning solution.

[Problems to be Solved by the Invention] However, the above SC, 1 cleaning liquid has many practical problems. First, as is clear from the fact that hydrogen peroxide easily decomposes under basic conditions, it is impossible to store the 5c-1 cleaning solution for a long period of time. Needs to be replaced frequently. Second, when heating the S(,-1 cleaning solution, water with a high specific heat makes up a large part of the composition, it takes a certain amount of time to raise the temperature, and during this time hydrogen peroxide decomposes and ammonia evaporation is likely to occur6
In other words, the composition of the cleaning liquid during use is quite different from the initial composition, making it difficult to clean a large number of objects to be cleaned under the same conditions.

As a means to solve these problems, for example, in Japanese Patent Application Laid-open No. 59-46032, the concentration of hydrogen peroxide was measured by absorbance measurement at 300 nm, and the concentration of ammonia was measured by an ion electrode. A cleaning device is disclosed in which hydrogen peroxide or ammonia is replenished as appropriate. In the above cleaning device, the cleaning liquid collected from the cleaning tank is continuously supplied to the flow cell of the hydrogen peroxide concentration measuring section and the flow cell of the ammonia concentration measuring section, so the composition of the cleaning liquid can be monitored in-line. .

However, although the above-mentioned cleaning device enables cleaning solution management in place of traditional offline analysis that takes time such as titration analysis, there are problems with the device configuration. j! Contamination is unavoidable, and the life of the cleaning solution itself cannot be extended.

Furthermore, while conventional cleaning methods are mainly based on so-called batch processing, in which multiple objects to be cleaned are housed in a container or the like and immersed in a cleaning tank filled with cleaning liquid, the need for single-wafer processing will increase in the future. is expected. However, the above SC
It is difficult to spray or apply ~1 cleaning solution onto the surface of an object to be cleaned, such as a semiconductor wafer, while maintaining a temperature around 80'C, and therefore it is technically difficult to apply 5c-1 cleaning to single wafer processing. It is considered difficult to

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a cleaning method that solves the above-mentioned problems, uses a cleaning solution that can be stored for a long time, does not require a complicated cleaning device, and can also be used for single-wafer processing.

[Means to solve the problem]

As a result of intensive studies to achieve the above-mentioned object, the present inventor found that if hydrogen azide or water-soluble azide is used in place of ammonia contained in the conventional 5C-1 cleaning solution, the conventional problems can be solved. We have found that all of these problems can be solved, and have completed the present invention.

That is, the cleaning method according to the present invention involves cleaning the object while irradiating it with light while bringing the object to be cleaned into contact with a cleaning composition prepared by mixing hydrogen peroxide, hydrogen azide, or a water-soluble azide, and water. Poetics is about doing this.

Effect j Hydrogen azide or water-soluble azide used in the present invention has lower basicity than ammonia contained in the conventional 5C-1 cleaning solution. Hydrogen azide behaves rather like an acidic substance in an aqueous solution. Therefore, under normal storage conditions, there is no risk of decomposition of these compounds even if they coexist with IP4 hydrogen oxide. is mixed with hydrogen peroxide and water, and can generate active species only when exposed to light.

The generation mechanism of this active species is roughly as follows.

First, hydrogen azide and water-soluble azide are decomposed by ultraviolet irradiation to produce nitrene and nitrogen gas as expressed by the following formula.

hν RN3 RN: +N! ↑ [However, in the formula, R represents a hydrogen atom or an organic group.] Since the above reaction proceeds in an aqueous solution, most of the generated nitrene immediately reacts with water and exists in the form of a hydroxylamino compound. For example, when R is a hydrogen atom, hydroxylamine (NH2OH) is produced. Alternatively, it is also possible that nitrogen radicals are generated in the reaction system.

On the other hand, hydrogen peroxide is decomposed by ultraviolet irradiation and generates hydroxyl radicals by cleavage of peroxide bonds as shown in the following formula.

hv HO-OH--→2HO0 Alternatively, hydroxyl radicals are also generated when the lone pair of electrons present on the nitrogen atom of the above-mentioned nitrene or hydroxylamino compound attacks hydrogen peroxide.

In the above reaction, chemical species that function as active species capable of decomposing organic matter include nitrogen radicals, hydroxyl radicals, nitrene, hydroxylamino compounds, and the like. These active species are generated extremely quickly by light irradiation. The reason for this is that each component of the cleaning composition is decomposed independently by UV irradiation to generate active species, while nitrogen-based active species generated from hydrogen azide or water-soluble azide decompose hydrogen peroxide. This is because the active species are produced through multiple routes due to the synergistic effect of each component, such as acting as a catalyst.

In addition, although not active species, nitrogen gas generated from the liquid phase by decomposition of hydrogen azide or water-soluble azide, or oxygen gas generated through other reaction routes activates the liquid circulation of the cleaning composition. It can also be expected to improve the cleaning effect.

By the way, in the manufacturing process of semiconductor devices, various organic substances are deposited on semiconductor wafers. The above-mentioned organic substances are mainly composed of polymers of low-molecular organic compounds derived from deposition gases used in the etching process, etching reaction products, or sputtered resist materials.

The active species generated in the cleaning composition can be removed by cutting the main chain of the organic substance and converting it into a lower molecular weight substance (solubilizing it). The above-mentioned cleavage of the main chain is carried out by a radical reaction or by a nucleophilic attack on carbonyl carbon by a lone pair of electrons present on the nitrogen atom of the active species.

The above cleaning process can be performed at room temperature and does not require heating as is the case when using the SC1 cleaning solution. Therefore, the cleaning composition can be easily sprayed or applied onto the surface of the object to be cleaned without causing a change in composition, and can also be applied to single-wafer processing.

In addition, in the present invention, by taking advantage of the characteristic that active species are generated only when light irradiation is performed, selective exposure is performed while the cleaning composition and the object to be cleaned are in contact with each other.
It also becomes possible to perform local cleaning in ultra-fine processes.

〔Example〕

Hereinafter, preferred embodiments of the present invention will be described.

This example is an example in which a single crystal silicon substrate in which a trench was formed was locally cleaned using a cleaning composition made of a mixture of hydrogen azide, hydrogen peroxide, and water. This will be explained with reference to FIG.

This figure shows a cleaning composition (4) on the surface of a single crystal silicon substrate (1) in which a trench (2) has been formed by etching.
) is applied, and cleaning is performed while irradiating ultraviolet rays through a mask (5) that opens facing the region where the trench (2) is to be formed.

Inside the trench (2), an organic substance (3) mainly composed of a carbon-based polymer derived from a deposition gas used as a component of the etching gas and a resist material is formed in the form of a sidewall protective film. There is.

A cleaning composition is applied to the negative side of the substrate. The cleaning composition is a mixture of hydrogen azide, hydrogen peroxide, and water.

The mixing ratio of each of these components is not particularly limited as it can be changed as appropriate depending on the cleaning speed and degree of cleaning. It may be considered that the content ratio of hydrogen azide and hydrogen peroxide is stoichiometrically equimolar to each other, but the photolysis product of hydrogen azide is used as a decomposition catalyst for hydrogen peroxide and for organic matter. Considering that hydrogen azide can be used both as a decomposition active species, hydrogen azide may be used in a slightly excess amount than hydrogen peroxide. Even if hydrogen azide coexists with hydrogen peroxide, it will not be decomposed unless exposed to ultraviolet irradiation, so storage and concentration control of this cleaning composition is extremely easy. moreover,
Since the above-mentioned cleaning composition can be applied at room temperature, it is easy to apply or spray onto the object to be cleaned, and there is no possibility that the composition will change due to heating during use.

Here, although hydrogen azide is used in the above-mentioned cleaning composition, a water-soluble azide can also be used instead of the hydrogen azide. As the water-soluble azide, general formula R
When expressed as NHs, compounds containing a hydrophilic organic group as R are preferred.

Examples of such organic groups include saturated hydrocarbon groups, unsaturated hydrocarbon groups, alkoxy groups, etc. each having about 1 to 4 carbon atoms, and those in which hydrophilic groups such as hydroxyl and carboxyl groups are bonded to these groups. It may be. Since there are water-soluble compounds among metal azides, the metal azide can be appropriately selected and used depending on the object to be cleaned. However, especially when the purpose is to clean semiconductor wafers as in this embodiment, metal azide is not preferable because it causes unnecessary metal contamination.

With the cleaning composition coated on the substrate in this way, a mask (
5) UV irradiation was performed. As the light source at this time, an ultraviolet light source having a line spectrum or continuous spectrum in the wavelength range of 200 to 400 nm can be used, such as a low pressure mercury lamp, a medium pressure mercury lamp,
High-pressure mercury lamps, deuterium lamps, metal halide lamps, etc. are suitable. Due to such ultraviolet irradiation, active species such as nitrogen radicals, hydroxyl radicals, nitrene, and hydroxylamino compounds were rapidly generated in the exposed areas due to photodecomposition reactions of the cleaning composition, and nitrogen gas and oxygen gas were also generated. The organic substance (3) was effectively decomposed and removed by the decomposition action of these active species and the stirring action of the gas generated from the liquid phase. On the other hand, no chemical change occurred in the cleaning composition in the area covered by the mask, and therefore no change occurred in the substrate. This selective exposure made it possible to selectively clean extremely fine areas.

In addition, in the above example, the mask (5) is used as a selective exposure means.
However, by scanning with an ultraviolet laser such as a nitrogen gas laser, local cleaning can be performed without using the mask (5). Of course, neither the mask (5) nor the ultraviolet laser need be used if local cleaning is not the purpose and therefore there is no need to limit the area to be cleaned.

[Effects of the Invention] As is clear from the above explanation, if the present invention is applied, the cleaning composition can be easily stored and managed, and stable cleaning is always possible even in single wafer processing. The cleaning method of the present invention can be widely used as a so-called pre-cleaning method in the field of manufacturing semiconductor devices, such as cleaning before film formation or before diffusion processing. Furthermore, since there is no need to heat the cleaning composition during use, it can also be used for single-wafer processing. Furthermore, by combining the present invention with selective exposure, a new type of cleaning method, local cleaning in ultra-fine processes, is provided.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an example in which the cleaning method of the present invention is applied to cleaning a single crystal silicon substrate in which a trench is formed. Single crystal silicon substrate trench organic cleaning agent composition mask

Claims (1)

[Claims] A cleaning method characterized by carrying out cleaning while applying light irradiation in a state where an object to be cleaned is in contact with a cleaning composition formed by mixing hydrogen peroxide, hydrogen azide or a water-soluble azide, and water. .