JPH07114181B2 - Etching method - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to an etching method, and is particularly effective for reducing damage due to radiation when pattern formation is performed using irradiation with electron beams, X-rays or ion beams. The present invention relates to various etching methods.

[Background of the Invention]

Along with the miniaturization of semiconductor devices, the lithographic method is shifting from the conventional transfer method using light to an electron beam drawing method capable of forming finer patterns, an X-ray exposure method, and a drawing method using a focused ion beam. . However, these pattern forming methods have a problem in that the characteristics of the semiconductor element are changed by the influence of radiation, that is, so-called damage is caused.

There have been various studies on this damage, but research on the solution is not always sufficient. One solution is described, for example, in the proceedings of the 29th Joint Lecture on Applied Physics, Spring 1982 p.669 Shimaya et al. “Reduction of EB damage by three-layer resist”. In this method, as shown in FIG. 2, a resin layer 3, a heavy metal film 4 and an electron beam resist 5 are overlaid and deposited on a workpiece 2 on a silicon substrate 1. The pattern formed by the electron beam drawing method is sequentially transferred to the lower layer by dry etching to process the workpiece 2. Most of the incident electron beams at this time are reflected by the heavy metal layer 4 and few reach the substrate side, and therefore damage due to the electron beams can be reduced. One problem with this method is that it is difficult to detect the marks provided for interlayer alignment. The shape of the alignment mark is the stepped shape 6 provided on the substrate as shown in FIG. 3 or the shape of the heavy metal 7 as shown in FIG. However, in either case of FIG. 3 or FIG. 4, the electron beam passage is blocked by the heavy metal intermediate film 4, so that there is a drawback that the signal from the mark cannot be detected. For the purpose of accurately transferring the electron beam resist pattern, it is desirable that the heavy metal intermediate film 4 be thin (0.1 μm or less). However, in order to sufficiently block the electron beam, this heavy metal intermediate film 4
When the platinum film is used for the electron beam accelerated to 20 kV, for example, the thickness of 0.2 is required to be 0.2 to 0.3 μm. Therefore, there remains a problem in forming a fine pattern of a semiconductor device or the like with high precision by using irradiation of electron beams or X-rays.

[Object of the Invention]

The object of the present invention is to solve the above-mentioned drawbacks of the prior art, and
It is an object of the present invention to provide an etching method capable of reducing damage to a substrate due to an ion beam or an ion beam and detecting an alignment mark provided on the substrate.

[Outline of 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 35 or more is formed as the lowermost layer on the workpiece, and the workpiece is processed by the multilayer resist method. Is. That is, as in the example shown in FIG. 1, the lowermost layer is a resin layer 8 containing a heavy element, the intermediate film is a coatable glass film 9 having a thickness of 0.1 μm, and the electron beam resist 10 is applied to the uppermost layer to form an electron beam. The pattern formed by the above is sequentially transferred to the lower layer by dry etching, and the unnecessary portion of the workpiece 2 is removed. Incident electron beam in pattern formation area
Since 12 is blocked from passing by the resin film 8 containing the heavy element in the lowermost layer, it is possible to reduce damage given to the substrate 1. On the other hand, by using the convex structure mark 11 as the alignment mark as shown in FIG. 1, the thickness of the resin layer 2 containing a heavy element becomes extremely thin in the mark portion,
The signal from the step structure can be sufficiently detected by the mark detecting electron beam 13.

Another advantage of the present invention is that by using a silicon-containing resist film as the uppermost layer, etching of a workpiece can be performed by a two-layer resist method. The two-layer resist method not only simplifies the process but also has the advantage of improving the dimensional accuracy because the number of times of pattern transfer is small. However, even in this case, the influence of the electron beam on the substrate material is reduced by the resin layer containing a heavy metal. Therefore, it becomes possible to reduce.

Further, according to the experiments of the present inventor, when bromine or iodine is used as the heavy element contained in the resin layer, processing by reactive ion etching of oxygen gas plasma is easy,
It was also confirmed that the dimensional shift due to side etching is small and the electron beam and X-ray blocking ability is large, which is extremely suitable for carrying out the present invention.

Example of 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 a MOS transistor. In the MOS transistor, a polysilicon gate electrode 17 is formed on a silicon substrate 14 via a gate insulating film 16 as shown in FIG. This transistor is electrically isolated from other transistors by a thick thermal oxide film 15. The wiring aluminum 20 is deposited via the interlayer insulating film 19 and is in contact with the substrate 14 through the contact hole 18. In this embodiment, iodinated polystyrene is used as the resin layer 21 containing a heavy metal. Iodinated polystyrene has the chemical structure shown below and is a material that can be easily deposited by spin coating using chlorobenzene as a solvent.

Iodinated polystyrene is applied to a thickness of 2 μm to form the lowermost layer film, a coatable glass film is applied as an intermediate film 22 to a thickness of 0.1 μm, and an electron beam resist film 23 is RD5000P (trade name: Hitachi Chemical positive resist ) Was deposited to 0.6 μm. The interlayer alignment mark was formed by the convex oxide film 26 formed on the base made of the oxide film 24 and the polysilicon 25. KoTsuta the electron beam lithography system at an acceleration voltage of variable rectangular beam type electron beam size of 1 [mu] m ^□ the mark detection using those of 30 kV 27 (current value 50 nA). The mark signal at this time was comparable to that when the lower layer film containing no heavy element was used and the alignment mark having the concave structure was used. The pattern area was irradiated with an electron beam 28 of 4 μC / cm ² . Further, only the mark area was irradiated with an electron beam 27 with an irradiation dose of 300 μC / cm ² , and the resist was used as a negative type 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 shown in FIG. 5 (b). Next, the exposed portion of the glass film 22 was etched with a gas plasma containing carbon tetrafluoride to form a glass film pattern 30 (FIG. 5C).
Next, the exposed portion of the iodinated polystyrene film 21 is etched by reactive ion etching with oxygen plasma to form a pattern of iodinated polystyrene as shown in FIG. 5 (d).
31 formed. The etching time at this time was about 1.5 times that of polystyrene containing no iodine, but accurate pattern formation was possible. Coating glass film pattern
After removing 30 with diluted hydrofluoric acid, the exposed portion of the aluminum film 20 was etched by gas plasma containing carbon tetrachloride to form an electrode 32.

In this embodiment, iodide polystyrene was adopted as the resin layer containing a heavy element, but other materials suitable for the purpose of the present invention have, for example, the following chemical structure:
Many materials can be used, such as 4,6-triiodophenol. 2,4,6-Triiodophenol can be usually used as an underlayer film of a three-layer structure resist by mixing with a positive photoresist (for example, OFPR800, manufactured by Tokyo Ohka).

Generally speaking, iodinated novolac resins, iodinated phenol resins, iodinated polyvinyl phenols, etc. are suitable for the purposes of the present invention. In addition, bromine, like iodine, can be easily used as an organic compound, has excellent coating properties, and is capable of reactive ion etching with oxygen, and is therefore suitable for the material of the present invention. Specifically, brominated novolac resin, brominated phenol resin, brominated polyvinyl phenol and the like are suitable for the purpose of the present invention.

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

Further, in the above embodiment, etching is performed by forming three layers of the lowermost layer film, the intermediate layer film and the upper layer film (resist film) on the film to be processed.

However, if, for example, an electron beam resist film or an X-ray resist film containing silicon is used as the upper layer film, these films are sufficiently resistant to the reactive sputtering when removing the exposed portion of the lowermost layer film. Since it has excellent resistance, it is possible to omit the use of the intermediate film. By doing so, the process is simplified, which is practically advantageous. Also in this case, by including a heavy element in the lower layer film, extremely preferable results can be obtained.

Since the intermediate film is used as a mask when etching the exposed portion of the lowermost layer film, it has sufficient resistance to etching (eg, reactive sputtering etching) used in this case. It is necessary. Examples of such materials include silicon oxide, phosphosilicate glass, titanium dioxide, spin-on
It can be appropriately selected and used from many things such as glasses (trade name).

〔The invention's effect〕

As described above, according to the present invention, radiation such as electron beam drawing, X-ray exposure, and ion beam drawing can be performed without affecting mark detection for alignment between layers, which is essential for manufacturing various devices such as semiconductor devices. Since it is possible to form a fine pattern with high accuracy while reducing damage due to, it is extremely useful for realizing a highly reliable large scale integrated circuit (LSI).

[Brief description of drawings]

FIG. 1 is a sectional view for explaining the constitution of the present invention, FIGS. 2 to 4 are process drawings showing a conventional etching method, and FIG.
The drawings are process drawings showing an embodiment of the present invention. 1 ... Silicon substrate, 2 ... Work film, 3 ... Resin layer, 4 ... Heavy metal layer, 5 ... Electron beam resist, 6 ... Positioning step mark, 7 ... Positioning heavy metal mark ,
8: resin layer containing heavy element, 9: coatable glass film,
10: electron beam resist, 11: convex mark for alignment, 12: electron beam for writing, 13: electron beam for mark detection, 14: silicon substrate, 15: element separation Oxide film, 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 the mark area, 25: polysilicon in the mark area, 26: convex oxide film for the mark, 27 ...
… Mark detection electron beam, 28 …… Pattern drawing electron beam,
29 …… electron beam resist pattern, 30 …… intermediate coating glass pattern, 31 …… iodinated polyethylene pattern,
32 …… Aluminum electrode.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Osamu Suga 1-280 Higashi Koigakubo, Kokubunji City, Tokyo Inside Central Research Laboratory, Hitachi, Ltd. (56) Reference JP-A-59-107348 (JP, A) JP-A-58 -151022 (JP, A)

Claims (5)

[Claims] 1. A step of forming a first film made of an organic material containing bromine or iodine on a substrate having an alignment mark having a convex structure and a workpiece, and a dry etching resistance higher than that of the first film. The second film, which has a desired shape and is made of a material having high properties, is formed into an electron beam, an X-ray, or an ion.
A step of forming on the first film by a process including irradiation of a beam, a step of removing an exposed portion of the first film, and a step of removing an exposed portion of the workpiece. Etching method characterized by. 2. The first film is an iodinated novolac resin,
The etching method according to claim 1, comprising an iodinated phenol resin or an iodinated polyvinyl phenol resin. 3. The first film is a brominated novolac resin,
The etching method according to claim 1, comprising a brominated phenol resin or a brominated polyvinylphenol resin. 4. The first to third aspects of the present invention, wherein the second film is a silicon-containing resist film.
The etching method according to the item. 5. The etching method according to any one of claims 1 to 3, wherein the second film is made of silicon oxide, phosphosilicate glass, titanium dioxide or spin-on glass.