JPS5831730B2 - Manufacturing method of semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a semiconductor device in which a plurality of island regions are insulated and isolated from each other.

In recent years, as the density of integrated circuits has increased, there has been a major trend toward shorter delay times and lower power consumption per gate.

In particular, in order to achieve the latter, techniques for forming active parts in isolated island regions with low stray capacitance and low leakage current (e.g. 5ilcon on 5apphir
e technology, etc.) are attracting attention, and as one such technology, an insulation isolation method using porous silicon has been proposed, for example, in Japanese Patent Application No. 51133371.

The present invention provides a manufacturing method for manufacturing an insulation isolation structure using porous silicon, which realizes a structure with high carrier mobility and extremely good insulation properties.

FIGS. 1A to 1E show an example of process diagrams for seizing integrated circuit boards using the conventional insulation separation method.

First, a P-type layer 2 and an N-type layer 3 are epitaxially grown in sequence on an n-type silicon substrate 1 (FIGS. 1A and 1B).

Next, a silicon oxide film 4 is formed on the surface of the N-type layer 3 by thermal oxidation, and a diffusion window 5 is opened by ordinary photolithography (FIG. 3C).

Thereafter, a P-type impurity such as boron is diffused from the diffusion window 5 by thermal diffusion or ion implantation, and a P-type impurity region 6 is formed so as to cross the N-type epitaxial layer 3 and reach the P-type epitaxial layer 2.

As a result, an n-type island region 7 whose side and bottom surfaces are surrounded by the P-type regions 2 and 6 is formed (D in the same figure).

Next, the above-mentioned substrate is immersed in an electrolytic solution such as a hydrofluoric acid aqueous solution and anodized, thereby converting only the P-type regions 2 and 6 into porous silicon 8 and 9 (FIG. 3E).

Further, when the above-mentioned substrate is heat-treated in an oxidizing atmosphere, the porous silicon 8, 9 easily becomes an oxide film 10, 11 on the bottom surface.
An integrated circuit substrate is constructed having a plurality of n-type island regions 7 whose side surfaces are insulated and separated by oxide films 10 and 11 (FIG. F).
.

Various types of semiconductor devices, such as J-FET, I2L, MOS, etc., can be formed in the N-type island region 7 obtained in this way, and if necessary for forming these semiconductor devices, It is also possible to form N-type and P-type regions in advance within the N-type island region.

An integrated circuit consisting of a collection of isolated islands formed by such a method has low leakage current and small stray capacitance, and is therefore characterized by high speed and low power consumption.

However, according to the conventional method described above, the P-type region 2,
The porosity of 6 occurs non-uniformly, and as a result, when the porous silicon regions 8 and 9 are oxidized, the thickness of the oxide film 10 becomes non-uniform, which in turn may cause distortion to the N-type island region 7. confirmed experimentally.

When a semiconductor device is formed in this island region, such distortion causes a decrease in carrier mobility μ and an increase in leakage current due to crystal defects, which significantly deteriorates characteristics such as high speed and low power consumption of the device. It was the cause.

The present invention has been made in view of such problems.

The phenomenon in which the porous silicon region becomes non-uniform will be explained using FIGS. 2A and 2B.

FIG. 2A schematically shows a transitional state from the first diagram to E.

The formation of porosity is usually carried out by immersing it in a hydrofluoric acid-based aqueous solution and anodizing it, and in many cases irradiating it with light 13 to speed up the reaction.

A silicon nitride film or the like 14 is selectively deposited on the surface of the portion 7 to become the N-type island region to prevent the surface from becoming rough during anodization (FIG. 2A).

In this case, silicon becomes porous starting from the P-type region of the opening 5 of the nitride film 14, progressing in the depth direction, and progressing laterally when reaching the bottom surface of the P-type region 2.

At this time, most of the current that contributes to porosity is a photocurrent generated in the depletion layer of the PN junction composed of the P-type region 2 and the N-type substrate 1, and most of it is shown by arrow 12. It flows along a similar path.

However, since the porous state progresses at a slow rate between the porous region 8 and the substrate 1, the interface of the N-type substrate 1 also becomes porous, and the lower part of the N-type island region 7 becomes porous. At the time when the layers 8 are connected, the difference between the thickness of the porous silicon directly under the center of the N-type island region 7 and the thickness of the opening 5 becomes a non-negligible value (FIG. 2A).

When oxidation is performed, the thickness of the oxide film 10 becomes non-uniform, resulting in convex distortion in the N-type island region 7 (see Fig. 2B).
).

Furthermore, as can be seen from the perspective of the path of photocurrent, the P-type region 15 directly below the center of the N-type island region 7 is not completely made porous and remains at the time when the porous regions that have progressed from the left and right have not formed. Since the oxide film becomes thinner in that portion, this also causes a decrease in the withstand voltage of the N-type island region 7 and the N-type substrate 1.

The present invention is intended to solve the above problems.

The present invention will be explained using FIGS. 3A and 3B. In the present invention, the N-type substrate 3 is in contact with the P-type regions 32 and 33 to be made porous.
An N5 type region 30 having an impurity concentration lower than that of 1 is provided, and the surface of the P type region 32 adjacent to 30 is made of, for example, a silicon nitride film that is resistant to hydrofluoric acid, which is an electrolytic solution used in anodizing. It is characterized by covering 14 (
Figure 3A).

When anodizing is performed in this way, most of the photocurrent 34 that contributes to the formation of porous oxides is generated by the P-type regions 32 and 33 with large depletion layers and the N-type region 30.
This is from an N-junction, and the porosity immediately below the N-type island region 7 progresses quickly in the lateral direction.

By appropriately selecting the impurity concentration of the N-type substrate 31 and the N-type region 30 to 5, it is possible to minimize the formation of porosity in the N-type substrate 31, and therefore, the formation of porosity in the lower part of the N-type island region 7 can be minimized. Since this is done much more uniformly than in the conventional example, the two problems mentioned above are solved.

Of course, since the porous fluoride on the N-type substrate 31 is not completely removed, some unevenness usually remains on the surface after oxidation, as shown in the second diagram.

However, since the N-type island region 7 rests on one slope of the unevenness, almost no stress is applied to the island region 7.

Therefore, the integrated circuit formed in the island region 7 as shown in FIG. 5 has the characteristics of high speed and low power consumption based on the characteristics such as low leakage current and low capacitance due to insulation separation.

Further, the effects of the present invention can also be obtained when the impurity concentration of the N-type region 30 is higher than the concentration of the N-type substrate 31.

However, in this case, since the rate at which the N-type substrate 31 becomes porous is relatively high, the above-mentioned surface irregularities tend to become large.

An embodiment of the manufacturing process for an isolated N-type island region according to the present invention is shown in FIGS. 4A to 4H.

First, a P-type layer 51 is placed on an N-type silicon substrate 50. N-type layer 52
is provided by epitaxial growth (A and B in the same figure).

In this case, other methods such as ion implantation may be used instead of epitaxial method.

Next, an oxide film is formed on the surface of the N-type layer 52 by thermal oxidation, and a silicon nitride film is further formed on the surface by CVD or the like to form a two-layer structure film 53 of a nitride film and an oxide film.

A diffusion window 54 is opened in this by photoetching (C
) A P-type impurity such as boron is diffused from this diffusion window 54 by a method such as thermal diffusion or ion implantation so that it traverses the N-type epitaxial layer 52 and reaches the P-type epitaxial layer 51 (D in the same figure).

Next, the N-type island region 58, the surrounding P-wall region, and the opening 54' that will become the opening when making the porous structure in the future are selectively covered with a photoresist 56, and an N-type impurity such as phosphorus is coated with the photoresist 56. After ion implantation and removal of the photoresist, annealing is performed to form an N-type region 57 having a lower impurity concentration than the substrate 50 (FIG. 5E).

Furthermore, a film 59 such as a silicon nitride film that serves as a mask during anodization is used to cover the N-type region 57 and a portion of the surrounding P-wall region 60 and N-type island region 58, and while irradiating light 61, the anodization is performed. Processing is performed (FIG. F).

Porous formation begins from the opening 54', as shown in FIGS. 3A and B above.
As described above, a substantially uniform porous region 62 is obtained (G in the same figure).

Furthermore, if heat treatment is performed in an oxidizing atmosphere, the porous region 62
becomes an oxide film 63 in a very short time, and the isolated N
A mold island region 58 is obtained (H in the figure).

As mentioned earlier, the N-type island region 58 formed through such a process has less distortion in the crystal compared to a similar structure formed by a conventional manufacturing method, so that the carrier It has high mobility and is suitable for high-speed production.

■ The same side of the island region is completely porous and becomes an insulating film, so the withstand voltage with the silicon substrate is high and the leakage current is low.

■ Microfabrication is possible because the silicon substrate surface is relatively flat.

It has such characteristics.

Since this N-type region (for example, 57 in Fig. 3), which is formed as a source of photocurrent, reaches the N-type substrate, a P-wall region is formed in this region, and a protective diode and a diffused resistor are formed. Therefore, the silicon substrate can be used effectively.

FIG. 5 shows an isolated junction FET formed using the manufacturing method according to the present invention.

A P wall region 102 is formed in an N type region 101 formed as a photocurrent source when the P shadow region is made porous, and is connected to the gate to serve as a protection diode.

In the N-type island region 107 surrounded by the porous oxide film 103,
An N-type source 106 and drain 104 and a P-type gate 105 are formed to constitute a junction FET.

The element having this structure formed by the method of the present invention has a small crystal strain, so the mobility μ of current carriers is high, and the parasitic capacitance is small, so it has excellent high-frequency wave characteristics.

As described above, by using the method of the present invention, an integrated circuit consisting of high-performance isolated elements can be produced relatively easily and at low cost.

In this text, we have described the case where porous silicon is oxidized to transform it into an insulator, but it can also be transformed into a nitride film by heat treatment at a high temperature (1000 to 1100° C.) in an ammonia gas atmosphere.

[Brief explanation of drawings]

FIGS. 1A to 1F are diagrams for explaining a conventional silicon insulation isolation method using porous formation, and FIG. B is an explanatory diagram of the principle of the conventional method, FIGS. 3A and B are detailed explanatory diagrams of the present invention, FIGS. FIG. 2 is a cross-sectional view of an isolated semiconductor device formed using the method of the invention. 50...N-type substrate, 53.59...Hydrofluoride acid-resistant thin film (for example, silicon nitride film, etc.)
, 57... N-type region serving as a charging current supply source during porous formation, 58... N-type island region, 60...
...P wall region to become a porous layer, 63...Silicon oxide film.

Claims (1)

[Claims] 1. A step of forming an N-type island region in a P-type trench type semiconductor layer formed on an N-type conductivity type semiconductor substrate, and a step of forming an N-type island region in at least a part of the P-type trench type semiconductor layer. a step of forming an N-type conductivity type region reaching an N-type conductivity type semiconductor substrate; and a surface of the P-type groove conductivity type semiconductor layer sandwiched between the N-type conductivity type region and the N-type conductivity type island region. a step of forming a hydrofluoric acid-resistant film on a region containing the film, and making the P-type trench type semiconductor layer porous from the side where the film is not formed toward the side where the film is formed. A method for manufacturing a semiconductor device, comprising: a step of changing the porous region into an insulator. 2. In the method for manufacturing a semiconductor device according to claim 1, the N-type impurity concentration of the N-type conductivity type region reaching the N-type conductivity type semiconductor substrate is lowered than the concentration of the N-type conductivity type semiconductor substrate; A method for manufacturing a semiconductor device, comprising making it porous by irradiating it with light.