JP2876674B2 - Method for manufacturing MOS semiconductor device - Google Patents

Description

The present invention relates to a MOS semiconductor device, and more particularly to a method for forming a buried contact structure thereof.

[Conventional technology]

In a MOS semiconductor device, a buried contact is often used as a contact to an active region formed below a gate oxide film. The buried contact is formed by first forming a diffusion region for the buried contact, and then forming an active region by ion implantation so as to partially overlap the buried contact region.

FIG. 7 shows a part of the buried contact structure, in which the drawbacks which occur particularly with the conventional method can be seen.

Hereinafter, a method for forming the buried contact structure will be described with reference to the drawings. After selectively etching a part of the gate oxide film 33 (a portion where a contact is to be formed) to expose the P-type substrate 31, a polycrystalline silicon layer containing phosphorus is formed on the entire surface, and the polycrystalline silicon The phosphorus in the layer is diffused to form a buried contact region (N ⁺ type diffusion layer) 30. afterwards,
The polycrystalline silicon layer is selectively etched by an anisotropic etching method to form a polycrystalline silicon extraction electrode 37,
Next, ion implantation is performed by the self-alignment method using the extraction electrode 37 and the field oxide layer 32 as a mask to form an active region (N ⁺ diffusion layer).
39 had formed.

[Problems to be solved by the invention]

As described above, the buried contact region 30 is formed by thermal diffusion of phosphorus from the opening where the gate oxide film 33 is removed, while the active region 39 is formed by ion implantation using the extraction electrode 37 and the field oxide film 32 as a mask. Is done. In order to electrically connect the buried contact region 30 and the active region 39, one end of the polycrystalline silicon extraction electrode 37 can be extended above the gate oxide film 33 in consideration of manufacturing variations. First, one end of the extraction electrode 37 is formed in the opening of the gate oxide film 33 with a gap from the edge of the opening. Therefore, when the silicon extraction electrode 37 is formed, the gap portion of the substrate is also etched. At this time, this portion is damaged as shown in FIG. 7 and is also etched in the lateral direction. For this reason, there is a defect that a leakage current is generated and a resistance is generated between the electrode and the extraction electrode 37. This drawback becomes an increasingly serious problem with the miniaturization of the buried contact hole.

An object of the present invention is to provide a method of manufacturing a semiconductor device which has the above-mentioned disadvantages and has a highly reliable embedded contact structure.

[Means for solving the problem]

In the present invention, after the formation of the gate oxide film, a step of depositing aluminum on the gate oxide film, a step of forming a hole in the contact position of the photoresist applied to the aluminum film, and a step of forming the holed photoresist Etching the aluminum film by isotropic etching and the gate oxide film by anisotropic etching, using the mask as a mask, and removing the aluminum film deeper and outward from the end of the opening of the gate oxide film; Forming a buried contact region by ion-implanting using an aluminum film as a mask, and removing the entire aluminum film to extend the extraction electrode so that the leading end thereof extends over the gate oxide film. Forming, and using the extraction electrode as a mask, ion By forming an active region by incoming and forms a buried contact structure.

[Action]

An aluminum film opening and a gate oxide film opening are formed using the same photoresist, but the former is wider than the latter due to the difference in etching method. Therefore, when the buried contact region is formed by ion implantation from the aluminum film opening, this region is formed to extend from the end of the gate oxide film to a position inside the gate oxide film. Therefore,
In the next step, when the end portion of the extraction electrode is formed so as to be on the gate oxide film and then ion-implanted to form an active region, the active region is reliably internally connected to the buried contact region.

〔Example〕

An embodiment of the present invention will be described below with reference to the drawings. First, a cross-sectional view of a semiconductor device manufactured according to the present invention is shown in FIG. In the figure, 11 is a substrate (P type), 12
Is a field oxide film, 13 is a gate oxide film, 16 is a buried contact region (N ⁺ diffusion layer), 19 is an active region (N ⁺ diffusion layer), and 17 is an extraction electrode of polycrystalline silicon.

As shown in the figure, the buried contact region 16 extends far beyond the buried contact hole 16A,
3, and the tip of the extraction electrode 17 is on the gate oxide film 13 and has a buried contact region 16.
Is formed at a position inside of the end of the. The active region 19 is formed by ion implantation, and the buried contact region 16 is formed.
And where it overlaps.

Next, the manufacturing method will be described in the order of steps. First, in FIG. 2, a field oxide film 12, (8000 °) and an oxide film 13 are selectively oxidized on a P-type substrate 11 (1 × 10 ¹⁵ cm ⁻³ ).
(450mm), aluminum film 14 (1.0μm)
Is formed by a sputtering method. Thereafter, a photoresist 15 is applied, and the photoresist on the portion where the buried contact is to be formed is exposed, developed and removed.

Next, as shown in FIG. 3, the aluminum film 14 is isotropically etched with phosphoric acid using the photoresist 15 as a mask, and then the gate oxide film 13 is selected by anisotropic dry etching using the photoresist 15 as a mask. To form a buried contact hole 16A. Due to the difference between the two etching methods, the aluminum film 14 is patterned about 1.5 μm outside the buried contact hole 16A.

Next, the photoresist 15 is removed, and as shown in FIG.
Using the aluminum film 14 as a mask, phosphorus is implanted by ion implantation at an energy of 70 keV and a dose of 1 × 10 ¹⁵ cm ⁻² to form a buried contact region (N ⁺ diffusion layer) 16. Thereafter, the aluminum film 14 is entirely removed with phosphoric acid.

Next, an N-type doped polycrystalline silicon layer (40
00Å) is formed by the CVD method, the photoresist 18 is patterned by the photoetching method as shown in FIG. 5, and then the polycrystalline silicon layer is selectively anisotropically etched to form the extraction electrode 17. . One end of the extraction electrode 17
The gate oxide film 13 is formed so as to overlap with the gate oxide film 13 by about 0.6 μm. Therefore, the substrate 11 is not directly exposed to the etching in the subsequent steps.

Next, the photoresist 18 is removed, and ions are implanted by self-alignment using the extraction electrode 17 and the field oxide film 12 as a mask (As. Energy: 70 keV, dose: 5 × 10 ¹⁵ cm ⁻² ) _.
By forming the active region 19 of the diffusion layer, the structure as shown in FIG. 1 is obtained. At this time, as shown in FIG. 4, the buried contact region 16 formed using the aluminum film 14 as a mask is formed.
Is formed deeper than 1.5 μm from the end of the gate oxide film 13, and the end of the extraction electrode 17 is 0.1 mm from the end of the gate oxide film 13.
Since it is at 6 μm, the buried contact region 16 and the active region 19 overlap with each other by about 1.0 μm and are surely electrically connected. In addition, in FIG.
When the is formed by anisotropic etching, the substrate 11 is not directly exposed, so that the conventional example is not damaged. Therefore, there is no damage at the connection between the buried contact region 16 and the active region 19, and it is possible to prevent generation of leakage current or increase in electrode resistance.

Incidentally, in the above embodiment, the gate distortion and the like of the oxide film 13 selectively when removed by anisotropic etching, as shown in FIG. 6, N ₊ diffusion layer by thermal diffusion of phosphorus from the extraction electrode 17 It can be reduced by adding the step of forming 20.

〔The invention's effect〕

As described above, the present invention selectively etches a gate oxide film and forms a buried contact hole before forming the buried contact hole.
An aluminum film is deposited, and the gate oxide film and the aluminum film are etched with the same mask. However, by changing the etching method between anisotropic etching and isotropic etching, the aluminum opening is larger than the buried contact hole. A large pattern is formed, and a buried contact region is formed by ion implantation using the aluminum film as a mask. Therefore, since the end of the buried contact region is formed below the gate oxide film, the end of the extraction electrode is formed on the gate oxide film so as to overlap the buried contact region, and the extraction electrode is used as a mask. When the active region is formed by ion implantation, the active region and the buried contact region are electrically connected internally. When forming the extraction electrode, the substrate is covered with a gate oxide film and is not directly exposed to etching, so that the substrate is not damaged and a highly reliable contact is obtained. The above process also has the effect of being performed by the self-alignment method without increasing the number of photoresists.

[Brief description of the drawings]

FIG. 1 is a longitudinal sectional view of a buried contact structure formed according to one embodiment of the present invention, FIGS. 2 to 5 are longitudinal sectional views showing the embodiment in the order of steps, and FIG. 6 is another embodiment. FIG. 7 is a longitudinal sectional view of a buried contact structure formed by an example, and FIG. 7 is a longitudinal sectional view of a buried contact structure formed by a conventional example. 11 ... (P type) substrate, 12 ... field oxide film, 13 ... gate oxide film, 14 ... aluminum film, 15, 18 ... photoresist, 1
6: buried contact region (N ⁺ type diffusion layer), 17 ... extraction electrode (phosphorus-doped polycrystalline silicon layer), 19 ... active region (N ⁺ type diffusion layer).

Claims (1)

(57) [Claims] In a method of manufacturing a MOS device having a buried contact region in a substrate in an active region formed under a gate oxide film as a MOS semiconductor device, a gate oxide film is formed after forming the gate oxide film. A step of applying aluminum thereon, a step of making a hole at a contact expected position of the photoresist applied to the aluminum film, and using the holed photoresist as a mask, an aluminum film by isotropic etching, Each gate oxide film is etched by anisotropic etching,
A step of removing the aluminum film deeper from the end of the opening of the gate oxide film, a step of removing the photoresist, ion-implanting the aluminum film as a mask to form a buried contact region, and removing the entire aluminum film Then, a step of forming the extraction electrode so that the tip portion extends to above the gate oxide film, but in the buried contact region position, and a step of forming an active region by ion implantation using the extraction electrode as a mask A method for manufacturing a MOS semiconductor device, comprising forming a buried contact structure.