JP2656054B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Summary] The present invention relates to a method for performing MeV-class high-energy ions for forming a buried diffusion layer such that an impurity concentration is higher in a substrate than in a semiconductor surface. Forming a mask layer having a desired pattern on the substrate, with the aim of reducing the extension of the high-concentration layer to the surface side in the step, and stopping energy for ions at least at an edge portion of the mask layer. Forming a film made of a material larger than the mask layer; and performing ion implantation using the mask layer and a film made of a material having a higher stopping power for ions than the mask layer as a mask.

[Industrial applications]

The present invention relates to a method for performing MeV-class high-energy ion implantation for forming a buried diffusion layer in which an impurity concentration is higher in a substrate than in a semiconductor surface.

By performing high-energy ion implantation of the MeV class, a deeper portion inside the substrate can be made to have a high impurity concentration. For example, the collector of a bipolar transistor can be set to, for example, 10 ²⁰ cm.
It is applied to the case of forming a buried diffusion layer having a high impurity concentration of about ^-3 . In this case, the high impurity concentration layer is necessary only inside the substrate, and the surface side must have a low impurity concentration.

[Conventional technology]

In manufacturing a semiconductor device as described above, generally,
As shown in FIG. 3, at the time of ion implantation, for example, a silicon oxide (SiO ₂ ) film 1 having a relatively large thickness is used as a mask material, and a high concentration of buried impurity is diffused inside the silicon (Si) substrate 2. The layer 3 is formed. In this case, ion implantation is 0.6M
At the energy of eV, the dose of phosphorus (P ⁺ ) to the substrate is 1E
13 cm ⁻² (1 × 10 ¹³ cm ⁻² ). As shown in FIG. 3, for example, the peak impurity concentration n = 2.69E17 cm ⁻³ (2.69 × 10 ¹⁷ cm ⁻² ).
^-3 ) The impurity diffusion layer 3 is formed.

At this time, the diffusion layer of the high-concentration impurity is generally formed in a portion having a certain depth from the surface of the silicon layer,
In principle, it is not formed in a shallower or deeper portion.

[Problems to be solved by the invention]

However, if the edge 1a of the silicon oxide film 1 used as the mask material has a gradient or the direction of the ions is not completely parallel to the mask edge, the ions implanted in the vicinity will first After reaching the edge 1a, it reaches the silicon substrate 2 below. As described above, the high concentration impurity layer is formed in a portion having a certain depth from the surface of the silicon layer. The diffusion layer 3 is formed. Since the silicon substrate 2 below the edge 1a of the silicon oxide film 1 has the sloped edge 1a thereon, the high concentration impurity diffusion layer 3 extends to the surface side of the substrate 2. Would. If the edge 1a shown in FIG. 3 has a gradient of 5 ° with respect to the normal of the wafer, the substrate 2
The maximum value of the concentration on the surface of the high-concentration impurity diffusion layer 3 extending to the surface reaches as high as n−1.58E16 cm ⁻³ . This is for a buried layer peak concentration of 2.69E17cm ^-3 Concentration.

Therefore, for example, when the collector of a bipolar transistor is formed of a high-concentration impurity buried diffusion layer, the high-concentration impurity diffusion layer penetrates into the base layer thereabove (substrate surface side), and normal characteristics can be obtained. There were no problems. This becomes an obstacle when applied to a semiconductor device using the surface side at a low concentration or a semiconductor device forming a diffusion layer of a reverse conductivity type.

An object of the present invention is, in particular, to provide a method of manufacturing a semiconductor device that reduces the extension of a high-concentration layer to the surface side under a mask edge in a substrate.

[Means for solving the problem]

In order to solve the above problems, in the present invention, there is provided a method of manufacturing a semiconductor device in which a high-concentration impurity buried layer is formed inside a substrate by ion implantation, comprising the steps of: forming a mask layer having a desired pattern on the substrate; A step of forming a film made of a material having a higher stopping power for ions than the mask layer at least at an edge portion of the mask layer; and forming the mask layer and a material having a higher stopping power for ions than the mask layer. Performing ion implantation using the film as a mask.

[Action]

In the present invention, ion implantation is performed after forming a film made of a material having a large stopping power against ions at the edge portion of the mask layer. This makes it difficult for ions entering from the edge portion to reach the substrate, so that a high-concentration impurity layer is not formed on the substrate surface below the edge portion, and a high-concentration impurity layer is formed only inside the substrate.

〔Example〕

FIG. 1 is a diagram showing a manufacturing process according to the present invention, and FIG. 2 is a graph showing an equal concentration distribution curve according to the present invention. Fig. 1 (A)
As shown in FIG. 1, a silicon oxide (SiO ₂ ) film 11 having a film thickness of 1. is used as a mask layer for ion implantation on the surface of a silicon (Si) substrate 10.
Formed at 5 μm. Hole (edge) 1 in silicon oxide film 11
1a is formed.

Next, as shown in FIG. 1 (B), for example, a tungsten (W) film 12 having a higher stopping power for ions than the mask layer (silicon oxide film 11) is formed on the surface of the substrate 10 and the silicon oxide film 11 by holes 11a. It is formed with a film thickness of 2000 mm, including the thickness. Tungsten (TiW), tantalum (Ta), or the like may be used instead of tungsten. If the stopping power is 1, silicon is 1.5 for tantalum, 2 for titanium / tungsten, and 2.5 for tungsten.

Next, as shown in FIG. 1C, the surface of the silicon oxide film 11 and the surface of the substrate 1 excluding the edge 11a of the silicon oxide film 11 by anisotropic etching using, for example, sulfur hexafluoride (SF ₆ ) gas. The tungsten film 12 is removed. Thus, the tungsten film 12a is formed only on the edge 11a of the silicon oxide film 11.

Next, in this state, ion implantation is performed under the same conditions as in the conventional example. At this time, since the tungsten film 12a is formed on the edge 11a of the silicon oxide film 11, ions do not easily enter this portion, and the substrate 10 does not easily reach. Therefore, the second
As shown in the figure, in the portion of the substrate 10 below the tungsten film 12a, the high-concentration impurity diffusion layer 13 (particularly, a concentration region of the order of 10 ¹⁶ cm ⁻³ ) does not extend to the surface side, but fits inside the substrate 10, and The concentration in the lower part of 12a is n = 2.64E
It is 15cm ^-3 . This is because the buried layer peak concentration is 2.69E17c
For m ^-3 And the surface density under the edge is lower than that of the conventional example.

When the ion implantation is completed, the tungsten film 12a is removed by dry etching using, for example, sulfur hexafluoride (SF ₆ ) gas. Thereafter, the silicon oxide film 11 is used as a field oxide film.

It should be noted that instead of using the silicon oxide film 11 as in the above embodiment as a mask material during ion implantation, it is conceivable to use a mask material in which the entire mask material is formed of a tungsten film. When a silicon oxide film is used as the film, the silicon oxide film must be formed after the tungsten film is removed, which not only increases the number of steps after ion implantation but also reduces the contamination of the field oxide film with metal. It is not preferable because the possibility increases.

Also, the steps shown in FIG. 1 (C) are omitted, and FIG.
The ion implantation may be performed in the state shown in FIG. In this case, since the edge 11a has a gradient, it is equivalent to a large film thickness from the viewpoint of ion implantation, and ions passing through the tungsten film 12 in this portion hardly reach the substrate 10, while
The ions that have passed through the flat portion of the tungsten film 12 easily reach the inside of the substrate 10, and substantially the same results as shown in FIG. 2 can be obtained. However, in this case, the depth of the high-concentration buried diffusion layer becomes slightly shallow because the flat portion also has the tungsten film 12 interposed therebetween.

〔The invention's effect〕

As described above, according to the present invention, since a film having a large stopping power for ions is formed at the edge portion of the mask layer before ion implantation, high-concentration impurities are present on the substrate surface under the edge portion. In the case where the collector of the bipolar transistor is formed of a high-concentration impurity buried diffusion layer, for example, the high-concentration impurity diffusion layer does not penetrate into the base layer thereabove as in the conventional example. Properties can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a manufacturing process according to the present invention, FIG. 2 is an iso-density distribution curve according to the present invention, and FIG. 3 is an iso-density distribution curve and density characteristic diagram according to a conventional example. In the figure, 10 is a silicon substrate, 11 is a silicon oxide film (mask layer), 11a is a hole (edge), 12 is a tungsten film, 12a is a tungsten film at an edge portion, and 13 is a high concentration impurity diffusion layer.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁶ Identification number Agency reference number FI Technical indication H01L 29/73 (72) Inventor Takashi Igarashi 1015 Uedanaka, Nakahara-ku, Kawasaki-shi, Kanagawa Fujitsu Limited (72) Inventor Hiromichi Hiromichi 1015 Uedanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture Inside Fujitsu Limited (72) Inventor Kazushi Nakajima 2-1844-2 Kozoji-cho, Kasugai-shi, Aichi Prefecture Inside Fujitsu VSI Co., Ltd. (56) Reference Document JP-A-58-190029 (JP, A)

Claims (1)

(57) [Claims] 1. A method of manufacturing a semiconductor device in which a high-concentration impurity-implanted layer is formed in a substrate by ion implantation, a step of forming a mask layer having a desired pattern on the substrate, and at least an edge portion of the mask layer. Forming a film made of a material having a higher stopping power for ions than the mask layer; and ion-implanting the mask layer and a film made of a material having a higher stopping power for ions than the mask layer as a mask. A method of manufacturing a semiconductor device, comprising: