Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having insulated gate
Reexamination Certificate
2002-10-11
2004-08-24
Nelms, David (Department: 2818)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having insulated gate
C438S218000, C438S400000
Reexamination Certificate
active
06780701
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the technique for forming a high-breakdown voltage transistor and a low-breakdown voltage transistor on the same substrate.
2. Description of the Related Art
Driver devices for driving photo devices, liquid crystal displays (LCDs), print heads, and the like are provided with a drive section and a logic section for controlling the drive section. Ordinarily, the drive section includes a high-breakdown voltage transistor with relatively high drain-source breakdown voltage (also called “drain breakdown voltage”), and the logic section contains a low-breakdown voltage transistor with relatively low drain breakdown voltage. The high-breakdown voltage transistor, for example, operates at a supply voltage of about 10 volts or higher, whereas the low-breakdown voltage transistor operates at a supply voltage of about 5 volts or lower.
It is desirable that the high-breakdown voltage transistor and the low-breakdown voltage transistor for the above-described driver device are formed on a single substrate. Conventionally, in order to efficiently form transistors with different breakdown voltages on the same substrate, part of the process for manufacturing each transistor is common to both, but in many cases the characteristics of at least one of the transistors are damaged accordingly.
SUMMARY OF THE INVENTION
The object of the present invention is thus to solve the drawbacks of the prior art discussed above and to provide a technique for efficiently forming a high-breakdown voltage transistor and a low-breakdown voltage transistor on the same substrate while reducing the deterioration of each transistor's characteristics.
At least part of the above and the other related objects is attained by a method for manufacturing a semiconductor device of the present invention. In the semiconductor device, a high-breakdown voltage transistor and a low-breakdown voltage transistor of insulated-gate type, having different drain-source breakdown voltages, are present on the same semiconductor substrate, each transistor being formed in one of element formation regions of the substrate, each element formation region including a source formation region and a drain formation region. The manufacturing method comprises the steps of: (a) forming an insulating film containing portions to be used as gate insulating films within each of the element formation regions, the insulating film portions formed on the drain and source formation regions for the high-breakdown voltage transistor being thicker than those for the low-breakdown voltage transistor; (b) forming gates on the insulating films of the transistors; (c) forming sidewalls on the sides of the gate of at least the low-breakdown voltage transistor, and making apertures in the insulating film portions over the drain and source formation regions for the transistors by etching, wherein when the apertures are made in relatively thick insulating film portions on the drain and source formation regions for the high-breakdown voltage transistor, the etching is performed without narrowing widths of sidewalls formed on the sides of the gate of the low-breakdown voltage transistor; and (d) introducing impure elements into the drain and source formation regions for the transistors through the apertures made in the insulating film so as to form drain and source regions of the transistors.
In this method, when the apertures are made in the relatively thick insulating film portions on the drain and source forming regions for the high-breakdown voltage transistor, etching is performed not to narrow the widths of the sidewalls formed on the sides of the low-breakdown voltage transistor gate. This enables the drain-source distance on the low-breakdown voltage transistor to be kept relatively precise, which makes it possible to reduce the lowering of drain-source breakdown voltage (that is, drain breakdown voltage). In other words, using this method makes it possible to efficiently form the high-breakdown voltage transistor and the low-breakdown voltage transistor on the same substrate, and to reduce the deterioration of each transistor's characteristics.
In one preferable application, the step (c) may include: (c1) forming, on the element formation region for at least the low-breakdown voltage transistor, a material film composed of insulating material different from the insulating film; (c2) performing selective etching for etching the material film without etching the insulating film, so as to form the sidewalls on the sides of the gate of at least the low-breakdown voltage transistor; and (c3) performing selective etching for etching the insulating film without etching the material film, so as to make the apertures in the insulating film portions present above the drain and source formation regions for the transistors.
This arrangement makes it possible to selectively etch the material film and the insulating film, which in turn makes it possible to etch the insulating film portions on the drain and source formation regions for the high-breakdown voltage transistor in a way that does not cause the sidewalls formed on the sides of the low-breakdown voltage transistor gate to narrow.
In the above method, the semiconductor substrate may be a silicon substrate; the insulating film may be a silicon oxide film; and the material film may be a silicon nitride film.
In the above method, it is preferable that the step (b) includes forming the gates of the transistors of polysilicon; the step (c) includes forming a silicon oxide film on the sides of the gates formed of polysilicon prior to the formation of the sidewalls; and the step (d) includes introducing impure elements into the gates.
In this way, it is possible to form the transistor gate from polysilicon into which impure elements have been introduced rather than from metallic materials. Also, by using the above method, a silicon oxide film is formed between the gate composed of polysilicon and the sidewalls composed of silicon nitride. The interposition of the silicon oxide film makes it possible to relax the stress that arises due to the formation of the silicon nitride film, which in turn makes it possible to reduce the occurrence of pealing and cracking.
In another preferable application, the step (c) may include: (c1) forming, on the element formation region for at least the low-breakdown voltage transistor, a material film composed of the same material as the insulating film; (c2) etching the material film so as to form the sidewalls on the sides of the gate of at least the low-breakdown voltage transistor; and continuing the etching so as to make the apertures on the relatively thin insulating film portions present over the drain and source formation regions for the low-breakdown voltage transistor; (c3) forming a resist for protecting the element formation region for the low-breakdown voltage transistor; and (c4) further etching the insulating film so as to make the apertures on the relatively thick insulating film portions remaining over the drain and source formation regions for the high-breakdown voltage transistor.
In this arrangement, when the apertures are made in the relatively thick insulating film portions that remains above the drain and source formation regions for the high-breakdown voltage transistor, the sidewalls formed on the sides of the low-breakdown voltage transistor gate will not be etched. This makes it possible to etch the insulating film portions on the drain and source formation regions for the high-breakdown voltage transistor without narrowing the width of the sidewalls.
In the above method, the semiconductor substrate may be a silicon substrate; and the insulating film and the material film may be silicon oxide films.
In the above method, it is preferable that the semiconductor substrate is a silicon substrate; the insulating film is a silicon oxide film; the step (b) includes forming the gates of the transistors of polysilicon; and the step (d) includes introducing impure elements into the gates.
I
Haga Yasushi
Kanda Atsushi
Nelms David
Nguyen Thinh T
Oliff & Berridg,e PLC
Seiko Epson Corporation
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