JPH0350411B2 - - Google Patents

Description

[Detailed Description of the Invention] The present invention relates to the manufacture of semiconductors, ICs, LSIs, etc., and uses silicon wafers as the main raw material.
Regarding impurity diffusion technology in IC and LSI manufacturing.

In the manufacture of ICs and LSIs, the technique of selectively diffusing impurity elements such as _As , B, P, and _Sb into silicon wafers is one of the very important techniques for manufacturing circuits.

Conventionally, the following process has been used to selectively diffuse impurities into silicon wafers.

First, thermal oxidation or
A _{SiO 2} film is formed by CVD or the like, and a photoresist is applied on the _{SiO 2} film. After exposing the photoresist film in a pattern and performing a prescribed development, holes are selectively formed in the _{SiO 2} film by etching, and the resist is peeled off. For each impurity element, the impurity is selectively diffused into a portion of the silicon wafer where there is no _{SiO 2} film by thermal diffusion using a gas source, liquid source, solid source impurity, or ion implantation method.

With the above techniques, it is difficult to process the S _i O ₂ film to the designed device dimensions due to the problem of adhesion between the photoresist and the S _i O ₂ film, and the problem of N _a ⁺ contamination when using an organic photoresist. There were some problems.

The present invention relates to a process for manufacturing semiconductor integrated circuits such as ICs and LSIs that improves the above-mentioned drawbacks.As a result of research into a new method for selectively diffusing impurity elements into silicon wafers, it has been found that impurity elements in the IC manufacturing process have been improved. When an organic photoresist is used in the photoetching process of _{the SiO2} film in the selective diffusion process, as mentioned above, contamination such as Na ₊ caused by ^the organic resist process and changes in element dimensions during etching of _{the SiO2} film may occur. However, photolithography using organic photoresists as described above and
If the S _i O ₂ film etching process is replaced with a process that uses an electron beam-sensitive inorganic resist thin film made of a mixture of silicon and silicon oxide as ^{an impurity diffusion mask, the effects of contamination such as Na +} _will be eliminated.
Furthermore, we have discovered that it is possible to diffuse impurity elements with extremely high precision for the designed element dimensions, and based on this knowledge, we have completed the present invention.

That is, the gist of the present invention is to provide an electron beam-sensitive inorganic resist layer made of a mixture of silicon and silicon oxide on a silicon wafer, draw a pattern on the inorganic resist layer with an electron beam, and develop the area not irradiated with the electron beam. This is a selective diffusion method characterized by removing an inorganic resist layer and using the remaining inorganic resist as a diffusion mask for impurity elements to diffuse impurities into a silicon wafer.

As an electron beam sensitive inorganic resist, amorphous
Se-Ge-based chalcogenide compound thin films and iron oxide thin films are known. But in either case,
It is unsuitable as an impurity element diffusion mask on a silicon wafer. That is, if these metals are used as an impurity diffusion mask, the metals will diffuse into the silicon wafer, and the diffusion mask itself will become a source of contamination.

The required performance as a mask material for impurity diffusion is that the diffusion coefficient for impurity elements such as As, B, and Sb is sufficiently smaller than that of a silicon wafer, and the SiO ₂ film satisfies this condition.

An inorganic resist made of a mixture of silicon and silicon oxide has a sufficient diffusion masking effect against impurities, although it is not as strong as SiO ₂ . but,
The higher the SiO ₂ /Si ratio, the better the diffusion mask effect. Practically speaking, if the SiO ₂ /Si ratio is around 3, it can be used as a diffusion mask for impurity elements.

Next, the present invention will be explained in detail with reference to the drawings.

FIGS. 1A to 1D show the steps of the selective diffusion method according to the present invention.

First, as shown in FIG. 1A, an electron beam-sensitive inorganic resist layer 2 made of a mixture of silicon and silicon oxide is provided on a silicon wafer 1.

Next, as shown in FIG. 1B, a pattern is drawn on the electron beam sensitive inorganic resist layer 2 using an electron beam 3.
Next, development is performed to remove the electron beam-sensitive inorganic resist layer in the areas that have not been irradiated with the electron beam, thereby forming an inorganic resist pattern 4, as shown in FIG. Next, impurities are diffused into the silicon wafer 1 using the inorganic resist pattern 4 as a diffusion mask for impurity elements. FIG. 1D shows a state in which impurities are selectively diffused into a silicon wafer, with reference numeral 5 indicating a diffused impurity portion and 6 an oxide film formed during thermal diffusion. Therefore, in the present invention, the silicon wafer is of n-type and p-type.
Either type or i type is fine.

Next, the electron beam sensitive inorganic resist layer 2 is 0.1 to 1μ
The thickness of approximately m is formed by a normal thin film forming method such as a vacuum evaporation method or a sputtering method. When forming a thin film, it is necessary to form the thin film in a trace amount of oxygen atmosphere in order to control the mixing ratio of silicon and silicon oxide, and to control the atmospheric pressure etc. in order to control the sensitivity to electron beams. It is necessary.

There are two methods for developing electron beam-sensitive inorganic resists: wet etching using a fluoride-based aqueous solution and dry etching using silicon-reactive plasma gas. Dissolve or remove by reaction,
Preferably, the irradiated portion is not removed at all or hardly removed.

In the wet etching method, a common etching solution for silicon wafers can be used. That is, two types of chemical solutions can be used, broadly classified into acidic aqueous solutions containing fluorine ions and basic solutions. As the acidic solution containing fluorine ions, for example, an aqueous solution of hydrofluoric acid or a water-soluble fluoride such as ammonium fluoride, antimony fluoride, or tin fluoride, or a heavy fluoride or borofluoride such as potassium hydrogen fluoride is used. can.

Further, as the basic solution, potassium hydroxide aqueous solution, ethylenediamine pyrocatechol aqueous solution, etc. can be used.

The dry etching method uses CF ₄ , CCl ₂ F ₂ , CClF ₂
−Freon gas such as CCl ₂ F and Freon gas and O ₂
Dry etching processes such as plasma etching using a gas mixture, reactive ion etching, etc. can be used.

Compared to the wet etching method, the dry etching method has the advantage that there is no contamination such as Na ⁺ and the characteristics of the semiconductor device are stabilized.

The characteristics of the residual film thickness after development of the inorganic resist thin film for electron beam writing are as shown in the second diagram, and by changing the electron beam irradiation amount, it is possible to form an inorganic resist thin film pattern of silicon and silicon oxide with any residual film thickness. .

Although the pattern formation mechanism using inorganic resist is not clear, the present inventors have found that the degree of crystallinity of silicon and silicon oxide in the irradiated area changes depending on the electron beam energy, and that it is soluble in chemicals or reacts to reactive plasma gas. There is a difference in
We believe that it will be possible to form a pattern as a so-called negative resist in which the unirradiated areas are removed and the irradiated areas remain. Therefore, pattern formation is not necessarily limited to electron beam energy, as long as it has sufficient energy to change the degree of crystallinity of silicon and silicon oxide, and pattern formation using other high-energy beams such as radiation or laser beams is also possible. be.

As an electron beam irradiation device, the electron beam diameter is 0.1 to 1 μm.
There are devices that use a computer to scan a pattern using a focused electron beam, and devices that create an enlarged pattern using a metal thin film, reduce it with ^{an electron} lens, and transfer it ^all at once. ^However , the inorganic resist thin film according to the present invention is sensitive to electron beam irradiation of 10 ^-6 coulombs/cm ² or more, although it varies slightly depending on the conditions at the time of forming the thin film or the heat treatment of the thin film. , both devices can be used.

According to experiments conducted by the present inventors, the electron beam sensitivity of a silicon-based inorganic resist changes depending on the mixing ratio of silicon and silicon oxide. ESCA (Eletron
Spectroscopy for Chemical Analysis). As a result, silicon oxide vs.
The relative intensity ratio of the ESCA spectrum was approximately 3:1. Since the ESCA spectrum relative intensity ratio is approximately proportional to the component ratio of the object to be measured, in this case the mixing ratio of silicon oxide and silicon is approximately 3.
The ratio is 1 to 1.

Impurity diffusion methods include thermal diffusion using a gas source, liquid source, or solid source, and ion implantation.

In general impurity diffusion, the SiO ₂ film is used as a diffusion mask for As, B, P, and Sb.
The diffusion coefficient of impurity elements such as _Si
This is because it is so small that it can be ignored compared to the inside.

ESCA analysis of silicon inorganic resist has revealed that the mixing ratio of silicon and silicon oxide can be controlled arbitrarily by controlling the oxygen atmosphere during thin film formation. Therefore, it seems that the diffusion masking effect of the impurity element by the silicon inorganic resist is due to the silicon oxide. Selective diffusion occurs when the mixing ratio of silicon oxide and silicon in the inorganic resist is 3.
A sufficient diffusion mask effect was obtained if both were used.

As described in detail above, according to the method of the present invention, it is possible to diffuse impurity elements with extremely high precision for the designed device dimensions without contaminating the silicon wafer with Na ⁺ etc. .

Example 1 A 4000 Å thick inorganic resist thin film made of a mixture of silicon oxide and silicon (spectral relative intensity ratio by ESCA: 3:1) was deposited on a phosphorus-doped n-type silicon wafer with a specific resistance of 5 Ω by electron beam evaporation. It was set up. The degree of vacuum during electron beam evaporation was 1 x 10 ^-4 mmHg, the distance between the evaporation source and the substrate was 50 cm, and the evaporation rate was 1000 Å/hr.

Next, using an electron beam irradiation device manufactured by Elionix Co., Ltd., the inorganic resist thin film was pattern irradiated with an acceleration voltage of 20 KV, an irradiation amount of 1×10 ^-4 coulombs/cm ² , and an electron beam diameter of 0.25 μm, followed by 1 g of ammonium fluoride in concentrated nitric acid. 70
It was immersed for 30 seconds in a chemical solution consisting of 5 ml of 1% hydrofluoric acid and 100 ml of deionized water to obtain a mask pattern for impurity diffusion with a minimum line width of 1 μm. Using a thermal diffusion furnace using this wafer BBr ₃ as a diffusion source, the carrier gas was N ₂ gas 1/min and O ₂ gas 10 c.c./min.
Deposition diffusion was performed at 1200°C for 5 minutes, and the carrier gas was _N2 gas at 1/min for 30 minutes.
Perform drive-in diffusion for 5 minutes to create a PN junction depth of 5 μm.
A surface resistance of 200Ω/mouth was obtained.

Example 2 On the same n-type silicon wafer as in Example 1, a 4000 Å inorganic resist thin film made of a mixture of silicon oxide and silicon (spectral relative intensity ratio by ESCA of 4:1) was formed by high-frequency sputtering.
The thickness was set at . The sputtering gas used was a mixed gas of argon and carbon gas, the gas pressure during sputtering was 6 x 10 ^-2 mmHg, and the distance between the substrate and the target was 7 cm.

The inorganic resist thin film layer was subjected to electron beam irradiation and development in the same manner as in Example 1 using an electron beam irradiation device to obtain an impurity diffusion mask pattern.

Impurity diffusion was also carried out in the same manner as in Example 1, and exactly the same results were obtained.

[Brief explanation of drawings]

FIGS. 1A to 2D are cross-sectional views showing the process of the method of the present invention, and FIG. 2 is a graph of the electron beam irradiation amount versus the remaining film ratio. 1... Silicon wafer, 2... Inorganic resist thin film layer, 3... Electron beam, 4... Inorganic resist pattern, 5
... Diffusion impurity part, 6... Oxide film generated during thermal diffusion.

Claims (1)

[Claims] 1. An electron beam-sensitive inorganic resist layer made of a mixture of silicon and silicon oxide is provided on a silicon wafer by a thin film forming method such as a vacuum evaporation method or a sputtering method, and this inorganic resist layer is irradiated with an irradiation charge of 10 ^-3 coulombs/ A pattern is drawn with an electron beam of cm ² or less to change the degree of crystallinity in the electron beam irradiated area, and then the inorganic resist layer in the area not irradiated with the electron beam is removed by development, and the inorganic resist layer remaining on the silicon wafer is A selective diffusion method characterized in that an impurity element is selectively diffused into a silicon wafer using a layer as a diffusion mask for the impurity element.