JP2594926B2 - Pattern formation method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a pattern forming method, and particularly to a method of forming a high aspect ratio resist pattern made of an organic material in a lithography step of a fine processing technique for a semiconductor or the like. About.

[Conventional technology]

Conventionally, in the field of microfabrication technology such as semiconductors, as a method of forming a resist pattern having a high aspect ratio,
There is a so-called three-layer resist method as described in JP-A-57-169245. Methods have been developed in which the upper layer resist contains a silicon element or the like to simplify the three layers into two layers (Japanese Patent Laid-Open No. 144369/1986), all of which have been developed by reactive ion etching of oxygen (hereinafter referred to as O ₂ -RIE). In this method, an upper layer or an intermediate layer of a predetermined pattern is transferred to a lower layer by utilizing the anisotropic etching ability (abbreviated).

[Problems to be solved by the invention]

The above prior art, the O ₂ -RIE process, tens mmTorr
Hereinafter, it is necessary to perform high-frequency discharge under a high vacuum of preferably several mmTorr or less. In order to maintain the high-frequency discharge under such a high vacuum, the apparatus is complicated and expensive. Further, in order to obtain a high aspect ratio, it is necessary to increase the degree of vacuum and increase the directionality of the reactive ions generated by the discharge. However, in such a case, the etching time becomes long, and the improvement of the so-called throughput increases at a high aspect ratio. Contrary to the realization of the ratio. Further, at this time, there is also a problem that ion bombardment, which can be a cause of element damage, cannot be avoided.

An object of the present invention is to realize a multilayer resist method for performing anisotropic etching in a simple process without using high vacuum or directional ion bombardment.

[Means for solving the problem]

The object is to form an organic layer on a substrate, and to form a predetermined pattern on the organic layer from a non-oxidizing material or a material that changes to a substantially non-volatile oxide by an oxidation reaction. And a step of irradiating the pattern with light in an oxidizing atmosphere, and removing the organic layer at the exposed portion by photo-oxidation etching (photo-ashing).

The material used for the lower organic layer is preferably a material that changes into a vaporizable substance such as CO ₂ or H ₂ O by oxidation and can be a coating film. As such a material, an organic polymer is preferable. It is preferable that the organic polymer does not contain a metal or a metalloid such as Si. This material may be a mixture of several substances.

Further, the light of the photo-oxidative etching is applied to the organic material layer by 1 μm of the layer.
It is desirable that the thickness is set to show an absorbance of 3 or more per m thickness. For example, mixing a dye with an organic polymer,
It is preferable to use a material whose mixing amount is adjusted so as to exhibit the above absorbance. Depending on the type of the dye, 0.1 wt% to several wt% of the dye may be mixed with the polymer. In addition, ordinary photoresists often contain about 5 to 30 wt% of a photoreactive substance mixed with an organic polymer, and most photoreactive substances are substances that absorb ultraviolet light. Therefore, any ordinary photoresist that does not substantially contain a metalloid such as Si or a metal can be used as a material for the organic layer. The amount of the dye or photoreactive substance added may be large. However, if the amount is too large, the amount of the polymer becomes small, so that the ability to form a coating film is reduced. Therefore, the addition amount may be large as long as a coating film can be formed.

Examples of such a material include a composition obtained by adding a dye such as sudan red, oil violet or Sudan R to an organic polymer such as polystyrene or polyvinyl phenol, or a polymer such as polyvinyl phenol or phenol resin to naphthoquinone-1,2-diazo. There is a photoresist to which -5-sulfonic acid ester or the like is added.

As a non-oxidizing material or a material which changes to a substantially non-volatile oxide by an oxidation reaction, a semi-metal such as silicon or a photoresist containing a metal is preferable. Since iodine also becomes a non-volatile oxide upon oxidation, a photoresist containing iodine can also be used.

As light for the photo-oxidizing etching, ultraviolet light and far-ultraviolet light are preferable in terms of resolution, but visible light can also be used.

A commercially available apparatus can be used as the apparatus for photooxidation etching. For example, the introduced gas is oxygen, the pressure is 1 atm, the UV illuminance is about 3 mW / cm ² (λ = 254 nm), and the substrate temperature is 120 ° C., and the organic layer having a thickness of 1 μm can be etched in about 400 minutes.

[Action]

Photo-oxidative etching of an organic material is performed by selectively oxidizing an exposed portion of the organic material placed in an oxidizing atmosphere such as oxygen and ozone, and generating volatile low-molecular compounds such as water and oxygen dioxide. Part is removed. At this time, if the partial surface of the exposed portion is a non-oxidizing coating or a coating that forms a nonvolatile oxide layer by oxidation, the organic material under the coating is not photo-oxidized. . In the present invention, since the exposure wavelength is selected to be a region where the organic material largely absorbs, the lower layer of the coating portion becomes substantially self-shielding, and even if the photooxidation etching of the exposed portion proceeds, the side etching substantially does not occur. Does not progress.

〔Example〕

Hereinafter, the present invention will be described in more detail with reference to the drawings.
FIG. 1 shows a photo-oxidation etching process according to the present invention.
Figure 2 shows a naphthoquinonediazide-based positive photoresist (Tokyo Ohka Kogyo Co., Ltd. OFPR-800) used for the organic material layer.
3 shows an absorption spectrum after baking at 20 ° C. for 20 minutes. At this time, the thickness of the coating film was about 0.1 μm.

Example 1. On a silicon substrate, a naphthoquinonediazide-based positive photoresist OFPR-800 was applied by spin coating at 200 ° C.
A resist film of an organic layer is formed by baking for 20 minutes. At this time, the thickness of the coating film was 1.1 μm. After the above resist film is formed, a silicon-containing positive photoresist (Hitachi Chemical Reycast RG-8500P) is applied thereon by a spin coating method, and the thickness is baked at 80 ° C. for 20 minutes.
A 0.5 μm resist film is formed. After exposing a predetermined test pattern using a reduction projection exposure machine (RA-101 manufactured by Hitachi, Ltd.), an organic alkali developing solution (Tokyo Oka Industrial Developer NMD-3, 2.38%) is used, and a conventional method is used. Accordingly, development was performed to form an upper resist pattern.

This substrate was subjected to photo-oxidation etching for 40 minutes using a photoresist stripper equipped with a 120 W low-pressure mercury lamp (UV DRYSTRIPPER UV-1 manufactured by Samco International Laboratories Inc.). At this time, the oxygen flow rate was 500 ml / min. The photo-oxidation etching step will be described with reference to FIG. FIG. 1 is a silicon substrate, 2 is a resist film of the organic layer described above, and 3 is a silicon-containing upper layer pattern formed in a predetermined pattern. Reference numeral 4 denotes an oxidizing gas atmosphere, which is an oxygen gas containing ozone generated by a built-in ozonizer in the above apparatus. Reference numeral 5 denotes a photo-oxidation exposure light beam. In the above-mentioned apparatus, a 253.7 nm bright line of a low-pressure mercury lamp is mainly used. The upper layer pattern 3 contains silicon,
A non-volatile silicon dioxide film is formed by the photo-oxidation, and the etching does not proceed any further. On the other hand, the surface of 2 not covered by 3 efficiently absorbs the exposure light, and the photo-oxidative etching proceeds sequentially until it reaches the silicon substrate. As shown in FIG. 2, the lower layer resist has an absorbance of about 0.3 at a thickness of 0.1 μm at 253.7 nm, and thus has an absorbance of about 3 at a thickness of 1 μm. Therefore, in the upper layer pattern coating portion, the exposure light hardly reaches the lower layer, and even if the photooxidation etching of the exposed portion proceeds, side etching does not substantially occur. Observation of the substrate after the completion of the photo-oxidation etching with a scanning electron microscope revealed that a lower resist pattern having a high aspect ratio to which the upper resist pattern was faithfully transferred was formed.

Example 2. As an organic material layer resist, a material used for forming an upper layer resist pattern, which is a material that effectively absorbs g ^- rays
Example 1 except that RG-3900B (Hitachi Chemical) was used.
In the same manner as in the above, an organic layer resist pattern having a high aspect ratio was formed.

Example 3. Organic layer resist rake cast RG- on a silicon substrate
After forming a coating film of 3900B, spin-coating a coating type glass (Tokyo Ohka Kogyo OCD-P59310) as an intermediate layer,
After baking at 30 ° C. for 30 minutes, a glass layer of 0.1 μm was obtained. The substrate was further coated with a positive photoresist OFPR-800 by a spin coating method and baked at 90 ° C. for 20 minutes to form a 0.5 μm-thick patterning layer. After exposure of the test pattern with a reduction projection exposure machine RA-101, an organic alkali developer NMD-3,
Developed at 2.38% (Tokyo Ohka Kogyo) to obtain a test pattern. The test pattern was transferred to the intermediate layer by exposing the substrate to fluorine-based plasma, and then the upper layer patterning resist was stripped with an organic solvent. The obtained substrate has a shape in which a glassy upper layer of a predetermined pattern is coated on the organic material layer. This was subjected to photooxidative etching in the same manner as in Example 1, and then observed with a scanning electron microscope. As a result, good pattern transfer similar to that of Example 1 was confirmed.

Example 4. Using a positive-type electron beam resist, Rakecast RE-5000P (Hitachi Chemical Co., Ltd.) as an upper layer patterning resist, and performing a predetermined test pattern drawing using an electron beam exposure apparatus HL-600, a dedicated alkaline developer. (RE-5000P developer, Hitachi Chemical Co., Ltd.) A high aspect ratio organic layer resist pattern was obtained in the same manner as in Example 3 except that the upper layer pattern was formed.

〔The invention's effect〕

According to the present invention, since a pattern can be transferred to an organic layer resist film in a multilayer resist method under a voltage (atmospheric pressure), it is easy to form a continuous process. Conventional O ₂
In the multi-layer resist method using -RIE, O ₂ -RIE used for pattern transfer to the lower resist film requires complicated and expensive equipment that enables high-frequency discharge under high vacuum, and keeps high vacuum Therefore, a batch process has to be performed, which is a problem in forming a continuous process. In the present invention, this difficulty was avoided, and ion bombardment that could cause damage to the semiconductor device could be eliminated, thereby contributing to improvement in device reliability.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a substrate to which a pattern is transferred by photo-oxidation etching of the present invention, and FIG. 2 is a view showing an absorption spectrum of an organic layer resist used in one embodiment. 1 ... substrate, 2 ... organic layer, 3 ... upper pattern, 4 ...
... oxidizing atmosphere, 5 ... photo-oxidizing light beam.

Claims (3)

(57) [Claims] 1. A step of forming an organic layer on a substrate, and a step of forming an upper layer on the organic layer containing a non-oxidizable material or a material that changes to a substantially non-volatile oxide by an oxidation reaction. Processing the upper layer into a predetermined pattern shape to expose the organic material layer, and irradiating the organic material layer with light in an oxidizing atmosphere using the upper layer of the predetermined pattern shape as a mask to photo-oxidize the organic material layer. Having a step of etching,
And the irradiation light is 3 μm per 1 μm thickness of the organic material layer.
A pattern formation method using light having a wavelength showing the above absorbance. 2. The pattern forming method according to claim 1, wherein said oxidizing atmosphere contains oxygen gas or ozone. 3. The pattern forming method according to claim 1, wherein said upper layer is made of a material containing a silicon element.