Semiconductor device manufacturing: process – Making field effect device having pair of active regions... – Having schottky gate
Reexamination Certificate
1999-01-27
2001-04-10
Chaudhuri, Olik (Department: 2823)
Semiconductor device manufacturing: process
Making field effect device having pair of active regions...
Having schottky gate
C438S217000, C438S278000, C438S290000
Reexamination Certificate
active
06214654
ABSTRACT:
TECHNICAL FIELD
The present invention relates generally to semiconductor fabrication, and more particularly to methods for fabricating improved ultra-large scale integration (ULSI) semiconductor devices such as ULSI metal oxide silicon field effect transistors (MOSFETs).
BACKGROUND OF THE INVENTION
Semiconductor chips or wafers are used in many applications, including as processor chips for computers, and as integrated circuits and as flash memory for hand held computing devices, wireless telephones, and digital cameras. Regardless of the application, it is desirable that a semiconductor chip hold as many circuits or memory cells as possible per unit area. In this way, the size, weight, and energy consumption of devices that use semiconductor chips advantageously is minimized, while nevertheless improving the memory capacity and computing power of the devices.
A common circuit component of semiconductor chips is the transistor. In ULSI semiconductor chips, a transistor is established by forming a polysilicon gate on a silicon substrate, and then forming a source region and a drain region in the substrate beneath the gate by implanting appropriate dopant materials into the areas of the substrate that are to become the source and drain regions. The gate is insulated from the substrate by a thin gate oxide layer, with small portions of the source and drain regions, referred to as “extensions”, extending toward and virtually under the gate.
Between the source and drain regions and under the gate oxide layer is a channel region, a portion of which is doped. The doped portion of the channel region typically is doped early in the fabrication process, with the channel dopant usually being implanted during the steps of forming the gate and source and drain regions. This generally-described structure cooperates to function as a transistor.
To suppress deleterious “short channel” effects such as threshold voltage roll-off (i.e., transistor operation at below intended voltages), it is important that the dopant profile of the channel be steep. Stated differently, it is important that virtually all of the dopant in the channel region be concentrated within a relatively small area that is to function as the doped portion of the channel, with little or no dopant being located outside this relatively small doped region between the small doped region and the source and drain regions. With this in mind, it is desirable that the dopant profile of the channel region be a so-called “super-steep retrograded channel” (SSRC) profile.
As recognized by the present invention, semiconductor fabrication entails considerable heating during processing. Accordingly, structures such as doped channel regions that are established relatively early in the process are exposed to more heat than are structures formed relatively late in the process. As further recognized herein, however, exposing a channel region that has been doped relatively early in the manufacturing process to subsequent heating steps can cause the dopant in the channel to thermally diffuse and, hence, can cause the dopant profile of the channel undesirably to spread. Fortunately, the present invention addresses this problem.
BRIEF SUMMARY OF THE INVENTION
A method for establishing a transistor on a semiconductor device includes providing a semiconductor substrate, and forming a source region and a drain region in the substrate. Also, a sacrificial gate is formed above the source and drain regions, without forming a doped channel region between the source and drain regions. Then, the sacrificial gate is removed and a neutral ion species is implanted in the substrate between the source and drain regions to define an amorphous region. A dopant is implanted in the amorphous region, and the amorphous region is then heated to activate the dopant and thereby establish a doped channel region. Following channel activation, a gate stack is established above the doped channel region.
In a preferred embodiment, the heating step is accomplished by heating the amorphous region to no more than nine hundred fifty degrees Celsius (950° C.), and more preferably to no more than nine hundred degrees Celsius (900° C.), by laser annealing. Specifically, the amorphous region is irradiated with a laser for no more than ten nanoseconds, and more preferably for no more than five nanoseconds, such that the temperature of the amorphous region does not exceed nine hundred fifty degrees Celsius (950° C.). A semiconductor device made according to the present method, and a digital processing apparatus incorporating the device, are also disclosed.
In another aspect, a method is disclosed for making an ultra-large scale integration (ULSI) semiconductor device. The method includes forming source and drain regions in a semiconductor substrate using a first activation temperature, and then forming a doped channel region between the source and drain regions using a second activation temperature less than the first activation temperature.
In still another aspect, a semiconductor device includes a semiconductor substrate, a transistor gate on the substrate, and source and drain regions in the substrate below the gate. A channel region is between the source region and the drain region. Also, an activated dopant implant is in the channel region, as is a neutral ion species implant.
Other features of the present invention are disclosed or apparent in the section entitled “DETAILED DESCRIPTION OF THE INVENTION”.
REFERENCES:
patent: 5899732 (1999-05-01), Gardner et al.
patent: 5917219 (1999-06-01), Nandakumar et al.
patent: 5960270 (1999-09-01), Misra et al.
patent: 6017781 (2000-01-01), Shimizu et al.
patent: 6054355 (2000-04-01), Inumiya et al.
patent: 6124188 (1999-09-01), Gardner et al.
patent: 6150693 (2000-11-01), Wollesen
Advanced Micro Devices , Inc.
Chaudhuri Olik
Coleman William David
LaRiviere Grubman & Payne, LLP
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