JPS62140425A - Etching method - Google Patents

Abstract

PURPOSE:To reduce damage to a substrate by electron beams, X-rays and ion beams, and to detect a positioning mark by applying a resin layer, a glass layer and an electron-beam resist in succession starting at an lower-most layer and conducting transfer and removal by specific operation. CONSTITUTION:A resin layer 8 containing a heavy element as a lowermost layer, a coatable glass film 9 in approximately 0.1mum thickness as an intermediate film and an electron-beam resist 10 as an uppermost layer are applied, a pattern formed by electron beams is transferred to lower layers in succession through dry etching, and an unnecessary section in a substance to be processed 2 is removed. The passage of incident electron beams 12 to a pattern forming region is prevented by the resin layer 8 containing the heavy element as the lowermost layer, thus reducing damage to a substrate 1. Since a projecting structure mark 11 is used as a positioning mark, the thickness of the resin layer 2 containing the heavy element is thinned extremely in the mark section, thus sufficiently detecting a signal from stepped structure by electron beams 13 for detecting the mark.

Description

[Detailed description of the invention] [Field of application of the invention] The present invention relates to an etching method, particularly an electron beam etching method.

The present invention relates to an etching method that is effective in reducing damage caused by radiation when forming patterns using X-ray or ion beam irradiation.

[Background of the invention]

With the miniaturization of semiconductor devices, lithography methods have changed from the conventional transfer method using light to electron beam lithography and X-ray exposure methods, which are capable of forming even finer patterns.

There is a shift to writing methods using focused ion beams. However, these pattern forming methods have a problem in that the characteristics of the semiconductor element change due to the influence of radiation, which is so-called damage.

Various studies have been conducted on this damage, but research on solutions to it is not necessarily sufficient.One possible solution is, for example, Proceedings of the 29th Applied Physics Association Lectures, Spring 1980. 669 Shimaya et al. "Reduction of EB damage by three-layer resist". In this method, as shown in FIG.
It is applied in layers. The pattern formed by electron beam lithography is sequentially transferred to the lower layer by dry etching, and the workpiece 2 is processed.

Most of the incident electron beams are reflected by the heavy metal layer 4 and only a small amount reaches the substrate, making it difficult to detect the marks provided thereon. The shape of the alignment mark is the shape of a step 6 provided on the substrate as shown in FIG. 3 or the shape of a heavy metal 7 as shown in FIG. However, in either case of FIG. 3 or FIG. 4, passage of the electron beam is blocked by the heavy metal interlayer film 4, so that the signal from the mark cannot be detected. For the purpose of accurately transferring the electron beam resist pattern, heavy metal intermediate llA4 is used.
It is desirable that it be thin (0.1 μm or less). However, in order to sufficiently block the electron beam, the thickness of the heavy metal intermediate film 4 is required to be 0.2 to 0.3 μm when a platinum film is used against the electron beam accelerated to 20 kV, for example. Therefore, problems remain in forming fine patterns of semiconductor elements or the like with high precision using electron beam or X-ray irradiation.

[Purpose of the invention]

The purpose of the present invention is to eliminate the drawbacks of the above-mentioned prior art, and to
It is an object of the present invention to provide an etching method that can reduce damage to a substrate caused by X-rays and ion beams and can detect alignment marks provided on the substrate.

[Summary of the invention]

In order to achieve the above object, in the etching method of the present invention, a resin layer containing a heavy element with an atomic number of 3°5 or more is formed as the bottom layer on the workpiece, and a resin layer 8. A coatable glass film 9 with a thickness of 0.1 μm is used as the intermediate film, and an electron beam resist 10 is applied as the top layer, and the pattern formed by the electron beam is sequentially transferred to the lower layer by dry etching to form the workpiece 2. Remove unnecessary parts. Since the incident electron beam 12 in the pattern forming region is blocked from passing by the resin film 8 containing a heavy element in the lowermost layer, damage caused to the substrate 1 can be reduced. On the other hand, by using a convex structure mark 11 as an alignment mark as shown in FIG. It becomes possible to sufficiently detect signals from the

Another advantage of the present invention is that by using a silicon-containing resist film as the top layer, the workpiece can be etched using a two-layer resist method. The two-layer resist method not only simplifies the process, but also has the advantage of improving dimensional accuracy because the number of pattern transfers is small.However, in this case, the effect of electron beams on the substrate material can be reduced by using a resin layer containing heavy metals. It is possible to reduce this by

Further, according to the experiments of the present inventor, when bromine or iodine is used as a heavy element contained in the resin layer, processing by reactive ion etching using oxygen gas plasma is easy and the blocking ability against electron beams and XIJ& is large. It was confirmed that this method is extremely suitable for implementation.

[Embodiments of the invention]

An embodiment of the present invention will be described below with reference to FIG.

FIG. 5 shows the present invention applied to an aluminum wiring process for an MO8 type transistor. In the MO5 type transistor, a polysilicon gate electrode 17 is formed on a silicon substrate 14 with a gate insulating film 16 interposed therebetween, as shown in FIG. 2(a). This transistor is electrically isolated from other transistors by a thick thermal oxide film 15. The wiring aluminum 20 is deposited via an interlayer insulating film 19, and is brought into contact with the substrate 14 through a contact hole 18. In this example, iodinated polystyrene was used as the resin layer 21 containing heavy metals. Iodinated polystyrene has the chemical structure shown below and is a material that can be easily applied by spin coating using lychlorobenzene as a solvent.

Iodinated polystyrene was applied to a thickness of 2 μm to form the bottom layer, and a coatable glass film was applied as the intermediate film 22 to a thickness of 0.1 μm.
RD5000P is deposited as the electron beam resist film 23.
(Product name: Hitachi Chemical positive resist) was deposited to a thickness of 0.6 μm. The interlayer alignment mark was formed by a convex oxide film 26 formed on a base formed of an oxide film 24 and polysilicon 25. The acceleration voltage of electron beam lithography equipment is 3
A 0 kV variable rectangular beam type was used for mark detection with an electron beam size of 27 (current value 50 nA) having an aperture of 1 μm. The mark signal at this time was comparable to that when a lower layer film containing no heavy elements was used and an alignment mark with a concave structure was used. The irradiation amount of the pattern part is 4μ
It was carried out using a C/cd electron beam 28. Further, only the mark area was irradiated with an electron beam 27 at a dose of 300 μC/d, and the resist was used as a negative resist to protect the mark. Next, the electron beam resist film 23 was developed with an aqueous solution of tetramethylammonium hydroxide to form a pattern 29 as shown in FIG. 5(b). Next, the exposed portion of the glass film 22 was etched using gas plasma containing carbon tetrafluoride to form a glass film pattern 30 (FIG. 4(C)). Next, the exposed portion of the iodinated polystyrene film 21 was etched by reactive ion etching using oxygen plasma to form a pattern 31 of iodinated polystyrene as shown in FIG. 5(d). Although the etching time required at this time was about 1.5 times that of polystyrene containing no iodine, it was possible to form a pattern with high precision.

After removing the coated glass film pattern 30 with diluted hydrofluoric acid, the exposed portion of the aluminum film 20 was etched using gas plasma containing carbon tetrachloride to form an electrode 32.

In this example, iodinated polystyrene was used as the resin layer containing heavy elements, but other materials suitable for the purpose of the present invention include, for example, 2 having the chemical structure below.
,4. ．． Many materials can be used, such as 6-triiodium phenol. 2,4.6-Triiodium phenol is usually used as a positive photoresist (for example, 0FFR800, manufactured by Tokyo Ohka)
It is possible to use it as a lower layer film of a three-layer structure resist by mixing it with.

(2) Generally speaking, iodinated novolak resins, iodinated phenolic resins, iodinated polyvinylphenols, etc. are suitable for the purpose of the present invention. In addition, like iodine, bromine can be easily made into an organic compound, has excellent coating properties, and can be subjected to reactive ion etching with oxygen. There is.

In the present invention, various elements having an atomic number of 35 or more can be appropriately selected and used as the heavy element contained in the bottom layer film. However, from a practical standpoint, such as reactivity with organic compounds and removability during etching, iodine and bromine are most preferred. The amount of these elements added depends on the thickness of the bottom layer, the intensity of the electron beam or X-ray irradiated, the type of semiconductor device to be formed, the type of element added, etc.
Selected appropriately.

Further, in the above example, etching was performed after forming three layers, a bottom layer film, an intermediate layer film, and an upper layer film (resist film), on the workpiece film.

However, if a silicon-containing electron beam resist or Since it is resistant, it is also possible to omit the use of an interlayer film. This method simplifies the process and is therefore advantageous in practice. Also in this case, very favorable results can be obtained by incorporating the heavy element into the lower layer film.

Note that since the above-mentioned intermediate film is used as a mask when etching the exposed portion of the bottom layer film, it must have sufficient resistance to the etching used at this time (for example, reactive sputter etching). is necessary. Such a material can be appropriately selected from many materials such as silicon oxide, phosphosilicate glass, titanium dioxide, and spin-on glass (trade name).

〔Effect of the invention〕

As explained above, according to the present invention, radiation exposure such as electron beam drawing, This method is extremely useful for realizing highly reliable large-scale integrated circuits (LSIs) because it is possible to form fine patterns with high precision while reducing damage caused by damage.

[Brief explanation of drawings]

FIG. 1 is a sectional view for explaining the present invention in detail. 2 to 4 are process diagrams showing a conventional etching method, and FIG. 5 is a process diagram showing an embodiment of the present invention. 1... Silicon substrate, 2... Workpiece film, 3...
Resin layer, 4... Heavy metal layer, 5... Electron beam resist,
6... Step mark for alignment, 7... Heavy metal mark for alignment, 8... Resin layer containing heavy elements, 9...
Coatable glass film, 10... Electron beam resist, 11...
- Convex structure mark for alignment, 12... Electron beam for drawing, 13... Electron beam for mark detection, 14...
- Silicon substrate, 15... Oxide film for isolation between elements, 16... Gate insulating film, 17... Polysilicon gate electrode, 18... Contact hole, 19... Interlayer insulating film, 20 ... aluminum electrode, 21 ... iodinated polystyrene, 22 ... coatable glass film, 23.
...Electron beam resist, 24... Oxide film for element isolation in mark area, 25... Polysilicon in mark area, 2
6... Convex oxide film for mark, 27... Electron beam for mark detection, 28... Electron beam for pattern drawing, 29...
Pattern of electron beam resist, 30... Pattern of intermediate coating glass, 31... Pattern of iodized polyethylene, 32... Aluminum electrode.
,-1,t ゛,

Claims (1)

[Claims] 1. A step of forming an organic film containing an element with an atomic number of 35 or more on a workpiece, and a mask pattern having greater dry etching resistance than the organic film and having a desired shape. on the organic film by a process including irradiation with electron beams, X-rays, or ion beams; removing the exposed portion of the organic film; and removing the exposed portion of the workpiece. An etching method that includes a step of removing. 2. The etching method according to claim 1, wherein the element is iodine or bromine.