JP2786199B2 - Method for manufacturing thin film semiconductor device - Google Patents

Description

Description: FIELD OF THE INVENTION The present invention relates to a thin film semiconductor device and a method for manufacturing the same, and more particularly, to a method for manufacturing a high quality thin film semiconductor device having good step coverage.

[Prior art] Thin-film semiconductor devices are composed of a semiconductor film on an insulating substrate and a MOSFET.
Etc., so that the element isolation can be completely performed, the stray capacitance between the substrate and the element can be extremely reduced,
It has advantages such as no generation of parasitic elements, and enables high-speed operation and high integration.

Conventionally, elements are separated by separating a semiconductor layer such as silicon (Si) formed on the entire surface of an insulating substrate into a number of semiconductor islands by anisotropic etching. According to this anisotropic etching, the semiconductor layer between the elements is accurately removed in a direction perpendicular to the substrate, and a large number of semiconductor islands can be efficiently formed on a small-area substrate.

[Problems to be Solved by the Invention] However, due to the anisotropic etching described above, the edge of each semiconductor island becomes a substantially right-angled edge, and the gate insulating film and the electrode film formed by laminating on these islands have the edge In other words, the step coverage is deteriorated, which is thinned at the portion, and this may cause the deterioration of the insulation and the function of the element. Further, the threshold voltage of the transistor locally decreases at the substantially right-angled edge portion. That is, only the end of the semiconductor island is turned on at a low voltage, and as a result, there is a problem that the leakage current of the transistor increases.

SUMMARY OF THE INVENTION The present invention solves such a problem, and it is possible to prevent an increase in leakage current at an end of a semiconductor island portion, and to maintain a good quality without further reducing step coverage. It is an object of the present invention to provide a method for producing the same.

[Means for Solving the Problems] A method of manufacturing a thin film semiconductor device according to the present invention includes the steps of: depositing a surface semiconductor layer on an insulating substrate; and forming a first mask on a predetermined portion of the surface semiconductor layer. Etching the surface semiconductor layer through the first mask to separate the island into an island shape, and forming a plurality of semiconductor islands having side surfaces substantially perpendicular to the insulating substrate by the separation; By exposing the surface of the semiconductor island by removing the mask and then directly oxidizing the continuously exposed surface, the surface including the upper end surface of the semiconductor island is replaced with a dummy having a smooth curved upper surface. A step of coating with an insulating film; and a second step of forming an opening in a predetermined portion on the dummy insulating film.
Forming a mask, and exposing a portion of the dummy insulating film through the second mask, thereby exposing an upper surface of the semiconductor island and placing a surface of the dummy insulating film on an upper surface of the semiconductor island. Forming a continuous curved surface; and forming a film layer constituting a functional element on the exposed portion of the semiconductor island, and on the dummy insulating film including the smooth curved surface and the curved surface continuous with the upper surface of the semiconductor island. And a step.

[Operation] In the thin-film semiconductor device obtained by the above method, when the surface including the upper end face of the semiconductor island is covered with the dummy insulating film, the upper surface of the dummy insulating film is formed to have a smooth curved surface. Thereafter, when exposing the element formation surface of the semiconductor island, the surface of the dummy insulating film is formed into a curved surface that is continuous with the upper surface of the semiconductor island.

Thus, the element formation surface on the exposed upper surface of the semiconductor island, and the dummy insulating film having a smooth curved surface and a curved surface continuous with the upper surface of the semiconductor island have high step coverage and high quality. Furthermore, since the upper end surface of the semiconductor island is covered with the dummy insulating film,
The distance between the upper end surface of the semiconductor island and the wiring of the functional element formed thereon is longer than the distance between the wiring and the upper surface of the semiconductor island. For this reason, it is possible to suppress an increase in leakage current at the upper end face of the semiconductor island.

Further, in the present invention, after the first mask is removed to expose the surface of the semiconductor island, the exposed surface is directly oxidized to cover the surface of the semiconductor island with the dummy insulating film. Therefore, the surface including the upper end surface of the semiconductor island can be covered with the dummy insulating film in a small number of steps, particularly in a step without an extra Si deposition step.

[Embodiment] FIGS. 1 to 3 show a thin film MO according to an embodiment of the present invention.
FIG. 3 is a plan view of the SFET, and FIGS. 1 and 2 are sectional views taken along lines II and II-II in FIG. 3, respectively.

In the figure, an insulating substrate 1 is formed by forming a SiO2 field insulating film 12 on one surface of a Si single crystal plate 11 by dry oxidation, and a large number (one of which is shown) of polycrystalline Si is formed on the insulating substrate 1. A semiconductor island 2 is formed.

The semiconductor islands 2 forms a rectangle with the thickness of about 8000 Å, generally by impurity diffusion P ^- the upper surface of the element formation plane 2a with are regions respectively drain 21 and N ⁺ region is formed at two points Source 22 has become.

A relatively thick (about 4000 °) SiO2 dummy insulating film 3 is formed on the periphery of the semiconductor island 2 excluding the functional element forming surface 2a and on the insulating substrate 1, and the upper surface of the insulating film 3 exhibits a smooth curved surface. And is continuous on the functional element forming surface 2a.

A gate insulating film 4 of SiO2 is formed on the dummy insulating film 3 in contact with the functional element forming surface 2a, and a gate film 5 of polycrystalline Si is formed on the gate insulating film 4 at a position between the drain 21 and the source 22. Is formed. BPSG covering these
An interlayer insulating film 6 made of a film is formed, and a drain electrode film 7, a source electrode film 8, and a gate electrode film 9 penetrate through the interlayer insulating film 6 and are connected to the drain 21, source 22, and gate film 5, respectively. It is.

Since the gate insulating film 4 is formed on the dummy insulating film 3 having a smooth curved surface, the gate insulating film 4 has a uniform film thickness without being locally thin, thereby improving the step coverage.

The main part of the method for manufacturing the thin film MOSFET is described below in the fourth section.
Description will be made with reference to the drawings.

On the insulating substrate 1 on which the surface of the Si single crystal plate 11 is dry-oxidized to form the field insulating film 12, a polycrystalline Si film 10 as a surface semiconductor layer is formed to a thickness of approximately 10,000 ° (FIG. 4 (1)). ). A resist R1 serving as a first mask is formed and masked only at a portion where a semiconductor island is to be formed (FIG. 4 (2)). After patterning by anisotropic etching such as dry etching, the resist R1 is removed (fourth). Figure (3)).

Since the anisotropic etching is performed perpendicular to the surface of the insulating substrate 1, a large number of isolated semiconductor islands 2 can be efficiently formed on the substrate 1 having a small area. As shown in section B, a right-angled corner is formed at the edge. Therefore, when a gate insulating film or the like is formed directly on such an island 2, the film thickness becomes thin at the corner portion, and the insulating property is reduced.

According to the present invention, the entire surface of the substrate 1 on which the semiconductor island 2 is formed is subjected to dry oxidation at about 1200 ° C. for about 6 hours to make the upper end surface smooth and curved, and the surface of the semiconductor island 2 is made of SiO _2. Dummy insulating film 3
(FIG. 4 (4)). The insulating film 3 has a thickness of 4000
The upper surface is a smooth curved surface without bending at right angles. During the dry oxidation, the thickness of the semiconductor island 2 is reduced by about 2000 mm.

Thereafter, a resist R2 as a second mask is formed on the dummy insulating film 3 (FIG. 4 (5)), and the resist R2 extends over the functional element forming surface 2a on the upper surface of the semiconductor island 2 with a dimension l. Leave it as a sagging hole. The dimension 1 is set to be smaller than the diameter of the island 2 by several μm in consideration of a positional shift at the time of masking.

While masking with the resist R2, isotropic etching is performed with a hydrofluoric acid-based etchant. The element formation surface 2a of the semiconductor island 2 is formed by this isotropic etching.
Is exposed, and the dummy insulating film 3 is removed in a mortar shape through a process indicated by lines K, L, and M in FIG. 4 (6), forming a curved surface continuous with the exposed element formation surface 2a. .

When a thin gate insulating film 4 constituting a part of the functional element is formed on the dummy insulating film 3 (FIG. 4 (7)), the gate insulating film 4 is formed on a smooth curved surface of the dummy insulating film 3. As a result, it is formed almost uniformly without producing a partial thin portion. Of course, the gate film 5 formed on the gate insulating film 4 is also uniform (FIG. 4 (8)).

Thus, a decrease in the insulating property or the function of the element is effectively prevented.

Note that the dummy insulating film 3 does not necessarily need to be formed on the entire surface of the insulating substrate, and may be formed only on the peripheral portion of the semiconductor island. Of course, if formed over the entire surface of the substrate, better insulating properties can be obtained.

Further, the dummy insulating film 3 may be formed by sputtering or CVD other than dry oxidation, and the material is not limited to SiO2, and a nitride film or the like may be used.

The present invention is not limited to the MOSFET as in the present embodiment, but can be applied to other thin film semiconductor devices.

[Effects of the Invention] As described above, according to the method of the present invention, by oxidizing the surface of a semiconductor island having a substantially right-angled edge, the upper end surface is formed into a smooth curved surface, and the dummy insulation covering the surface is further formed. When the film is etched to expose the element formation surface on the upper surface of the semiconductor island, the upper end surface of the dummy insulating film has a smooth curved surface, so that step coverage is improved. Further, since the periphery of the semiconductor island is covered with the dummy insulating film, an increase in leakage current at the upper end surface of the semiconductor island can be suppressed, and a high-quality semiconductor element can be obtained.

[Brief description of the drawings]

FIGS. 1 to 4 show an embodiment of the present invention. FIGS. 1 and 2 are cross-sectional views of a thin-film MOSFET, taken along lines II and II-II in FIG. 3, respectively. FIG. 3 is a plan view excluding an interlayer insulating film, and FIG. 4 is a cross-sectional view showing a manufacturing process. DESCRIPTION OF SYMBOLS 1 ... Insulating substrate 2 ... Semiconductor island 2a ... Functional element formation surface 3 ... Dummy insulating film 4 ... Gate insulating film (film layer) 10 ... Semiconductor film

Continued on the front page (72) Inventor ▲ Sakaki ▼ Nobuyoshi Hara 14 Iwatani, Shimowakakucho, Nishio City, Aichi Prefecture Inside the Japan Automobile Parts Research Institute (72) Inventor Seiji Fujino 14 Iwatani, Shimowakakucho, Nishio City, Aichi Prefecture Japan Corporation Inside the Automotive Parts Research Laboratory (72) Inventor Tadashi Hattori 14 Iwatani, Shimowasumi-cho, Nishio-shi, Aichi Prefecture Inside the Japan Automotive Components Research Institute (72) Inventor Masami Yamaoka 1-1-1 Showa-cho, Kariya-shi, Aichi Japan Nippon Denso Co., Ltd. (56) References JP-A-62-219961 (JP, A) JP-A-59-130465 (JP, A) JP-A-59-155167 (JP, A)

Claims (1)

(57) [Claims] A step of depositing a surface semiconductor layer on an insulating substrate; a step of forming a first mask on a predetermined portion of the surface semiconductor layer; and etching the surface semiconductor layer through the first mask. Forming a plurality of semiconductor islands having side surfaces substantially perpendicular to the insulating substrate by this separation; removing the first mask to expose the surface of the semiconductor island; Then, the surface including the upper end surface of the semiconductor island is covered with a dummy insulating film having a smooth curved surface by directly oxidizing the continuously exposed surface, and a predetermined surface is formed on the dummy insulating film. Forming a second mask having an opening in a portion thereof, and etching a portion of the dummy insulating film through the second mask, thereby forming the semiconductor. Exposing the upper surface of the island, and making the surface of the dummy insulating film a curved surface that is continuous with the upper surface of the semiconductor island; and exposing the exposed portion of the semiconductor island, and the smooth curved surface and the upper surface of the semiconductor island. Forming a film layer constituting a functional element on a dummy insulating film including a continuous curved surface.