JP2680923B2 - Method for manufacturing semiconductor device - Google Patents

Description

The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for forming a trench.

[Conventional technology]

A conventional method of forming a trench in a semiconductor substrate will be described with reference to FIG.

First, as shown in FIG. 2 (e), a channel stopper 5 is formed in the element isolation region on the semiconductor substrate 1 by ion implantation, and then a thick element isolation oxide film 4 and a thin oxide film 3 are formed in the element formation region. To do. Next, a photoresist film is formed on the entire surface and then patterned to form a mask 2 having an opening in contact with the element isolation oxide film 4. Next, a thin oxide film 3 on the semiconductor substrate 1 is wet-processed.
Are etched using the mask 2. Then, the semiconductor substrate 1 is etched by the dry etching method using the mask 2 to form the trench 6. At this time, the opening diameter L ₁ of the mask 2 and the opening diameter L ₃ above the trench 6 become substantially equal.

Next, as shown in FIG. 2B, boron is ion-implanted into the side wall and the bottom of the trench 6 at an angle θ with respect to the semiconductor substrate 1 to secure the capacitance by using the mask 2 to form a boron diffusion layer. Form 7. Thereafter, an electrode made of an insulating film and polysilicon is formed on the surface of the trench to complete the capacitor section 4.

[Problems to be solved by the invention]

The conventional trench forming method described above has the following problems.

Since the opening diameter of the thin oxide film 3 immediately below the photoresist on the semiconductor substrate and the diameter of the trench are almost the same,
When boron ions are implanted into the side wall and bottom of the trench into the semiconductor substrate from the oblique direction by ion implantation, the boron ions are also implanted into the diffusion layer of the channel stopper 5. Therefore, a portion of the boron diffusion layer on the side wall of the trench overlaps a portion of the channel stubber 5 at the portion A, and the boron concentration increases, so that a leak path from the side wall of the trench occurs and the amount of accumulated charge in the capacitor portion is increased. As a result, the yield of semiconductor devices deteriorates.

[Means for solving the problem]

A method of manufacturing a semiconductor device according to the present invention comprises a step of forming a thin oxide film on an element formation region on a semiconductor substrate and a thick element isolation oxide film on a device isolation region via a channel stopper, and a photoresist film on the entire surface. And then patterning to form a first mask having a first opening in contact with the element isolation oxide film on the element formation region, and using the first mask to wet etch the thin oxide film. A step of etching the film to form a second mask having a second opening having an opening diameter smaller than that of the first opening; and etching the semiconductor substrate by a dry etching method using the second mask Forming a trench having an opening diameter larger than that of the mask, and using the first and second masks, ion-implanting boron into the trench surface from obliquely above. Configured to include a step.

〔Example〕

 Next, the present invention will be described with reference to the drawings.

1 (a) and 1 (b) are sectional views of a semiconductor chip for explaining one embodiment of the present invention.

First, as shown in FIG. 1 (a), impurities are ion-implanted into the semiconductor substrate 1 to form a channel stopper 5 by the same operation as in the prior art, and then a thin oxide film 3 is formed in the element formation region by a selective oxidation method. An element isolation oxide film 4 is formed in the element isolation region. Next, a photoresist film is formed on the entire surface and then patterned to form a mask 2A having an opening diameter L ₁ in contact with the element isolation oxide film 4.

Next, the thin oxide film 3 on the semiconductor substrate is etched by wet etching using this mask 2A, and L ₁
An opening having a smaller opening diameter L ₂ is formed. Next,
Using the oxide film having the opening diameter L ₂ as a mask, the semiconductor substrate 1 is patterned by the dry etching method to form the opening diameter L ₂
Forming a trench having a larger opening diameter. At this time, the opening diameter L ₁ of the mask 2A and the oxide film 3 can be adjusted by appropriately selecting the wet processing time and the processing solution of buffered hydrofluoric acid.
The difference in the opening diameter L ₂ is about 0.4 μm.

Next, as shown in FIG. 1B, boron ions are ion-implanted from obliquely above the semiconductor substrate 1 at an angle θ.
(10 to 20 degrees) drive into the sidewall and bottom of the trench 6,
A boron diffusion layer 7 is formed on the side wall and bottom of the trench 6. At this time, the opening diameter of the opening formed in the thin oxide film 3
Since L ₂ is smaller than the opening diameter L _{1 of the} mask 2A made of photoresist, the boron diffusion layer 7 on the side wall of the formed trench 6 and the diffusion layer of the channel stopper 5 do not overlap each other. Therefore, unlike the conventional case, the generation of leak paths is eliminated, and the yield of semiconductor devices is improved.

That is, as shown in FIG. 3, the yield was 30 to 40% when the difference in opening diameter (L ₁ −L ₂ ) between the photoresist film and the thin oxide film was almost the same, whereas the yield of the present embodiment was 30%. In this case, a yield of about 90% was obtained.

〔The invention's effect〕

As described above, according to the present invention, since the diffusion layer of boron on the side wall of the trench and the diffusion layer of the channel stopper do not overlap each other, a leak path from the side wall of the trench to the channel stopper can be avoided, and the yield of the semiconductor device is improved. There is an effect of doing.

[Brief description of the drawings]

1 (a) and 1 (b) are sectional views of a semiconductor chip for explaining an embodiment of the present invention, and FIGS. 2 (a) and 2 (b) are sectional views of a semiconductor chip for explaining a conventional example. FIG. 3 and FIG. 3 are views showing the relationship between the difference in aperture diameter and the yield. 1 ... Semiconductor substrate, 2, 2A ... Mask, 3 ... Thin oxide film, 4 ... Element isolation oxide film, 5 ... Channel stopper, 6 ... Trench, 7 ... Boron diffusion layer.

Claims (1)

(57) [Claims] 1. A step of forming a thin oxide film on an element formation region on a semiconductor substrate and a thick element isolation oxide film on a device isolation region through a channel stopper, and a patterning after forming a photoresist film on the entire surface. Forming a first mask having a first opening in contact with the element isolation oxide film on the formed element formation region, and etching the thin oxide film by wet etching using the first mask. Forming a second mask having a second opening having a smaller opening diameter than the first opening; and etching the semiconductor substrate by a dry etching method using the second mask to form an opening having a diameter larger than that of the second mask. And forming a large trench, and ion-implanting boron into the trench surface obliquely from above using the first and second masks. The method of manufacturing a semiconductor device according to claim.