Data processing: generic control systems or specific application – Specific application – apparatus or process – Product assembly or manufacturing
Reexamination Certificate
2002-07-09
2004-02-24
Gandhi, Jayprakash N. (Department: 2125)
Data processing: generic control systems or specific application
Specific application, apparatus or process
Product assembly or manufacturing
C700S028000, C700S044000, C700S090000, C438S800000, C438S005000
Reexamination Certificate
active
06697697
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to semiconductor devices, more particularly to a method and system for controlling and maintaining an effective channel length in a semiconductor device by adjusting ion implant conditions derived from a fed-forward measurement of the gate electrode.
2. Description of Related Art
Over the years, in order to keep up with modem technology, it has been indispensably necessary to reduce semiconductor device size as well as enhance performance thereof. Semiconductors which have been decreased in size over the years have included, but are not limited to, field effect transistors (FETs), metal oxide semiconductor FETs (MOSFETs), complementary metal oxide silicon FETs (CMOS FETs), and the like. However, in decreasing feature sizes of the modern semiconductors, the bearable error of feature size control tolerances have also been reduced. As feature size control tolerances decrease, the ability to produce FETs with smaller specifications becomes increasing difficult, and as such, the normal random variances produced by such FETs provides undesirable semiconductor circuits.
In a conventional semiconductor, such as a FET, current flows along a semiconductor path called a channel.
FIG. 1A
illustrates a typical example of a CMOS device
20
comprising an NFET
1
and a PFET
2
, while
FIG. 1B
illustrates the left half NFET
1
and the right half PFET
2
superimposed. As further illustrated, the conventional CMOS FET
20
has a gate electrode
3
having a gate width
21
. The gate electrode may be offset by a variety of spacers, such as, spacers
4
,
5
, and
6
, whereby the spacer
4
may define an ion implantation mask for creating a lightly doped drain (LDD) region
11
, or an extension of the NFET
1
, while spacer
5
may define an ion implantation mask for creating a LDD region
12
of the PFET
2
. Spacer
6
may define an ion implant mask of both FETs for creating a source region
13
and drain region
14
of the substrate for both FETs. The gate electrode
3
lies over a thin gate insulator film
8
, wherein the gate is positioned above and between shallow trench isolation regions
9
(“STI”). Therebetween the shallow trench isolation regions
9
lies LDD regions
11
and
12
, whereby the region of substrate located between LDD regions
11
and
12
, under the gate electrode
3
, constitutes the channel. As will be recognized, when the gate electrode
3
is turned “on,” a depletion zone
17
forms in the channel whereby the region of substrate surface under the gate electrode
3
, between edges of the depletion zone
17
, is called an effective channel length
18
of the FET.
In a FET, any variation between a desired gate electrode width and the actual formed gate electrode width has a first-order effect on the effective channel length, while the effective channel length has a first-order effect on the drive current of the FET. Likewise, the drive current of the FET has a first-order effect on the speed of the resultant circuit having an effect on the maximum clocking frequency. As will be recognized, a circuit's value, performance, and consumer desirability are typically determined by the maximum clocking frequency of the resultant circuit. Thus, the effective channel length of a FET affects the resultant circuit's overall performance, value, and desirability. Therefore, as feature sizes of the modern semiconductors continue to decrease, and therewith the control of the tolerable feature error, any variation between a desired gate electrode width and the actual, as-formed gate electrode affects the underlying effective channel length, thus affecting the clocking frequency to provide a circuit having decreased value and desirability.
Therefore, a need exists in the art to control the effective channel length to provide a manufacturing process that provides FETs, and thus circuits, to meet desired specifications. Prior art is aimed at controlling the effective channel length using Rapid Thermal Anneal (RTA) or drive-in process steps, whereby any variation of the actual gate electrode from the ideal gate electrode may be corrected by adjusting RTA time or temperature using a downstream process. However, adjusting RTA time or temperature using downstream processes can be problematic with other device parameters including overlap capacitance, increasing the thermal budget, and affecting both NFET and PFET as well as all dopant simultaneously, for example. As a result of modem semiconductors having smaller effective channel lengths, and thus being at an increased sensitivity to overlap capacitance due to the associated reduced tolerable feature error and thermal cycle budget, adjusting RTA time or temperature using downstream processes is not ideal for controlling a smaller effective channel length in modern semiconductors.
Prior art is also directed to controlling the effective channel length by correcting for variations in the gate electrode using techniques such as photolithography, polysilicon reactive ion etching (“RIE”), and the possible use of hardmasks for gate definition. For example, prior art is directed to techniques of controlling gate width variations by photolithography to reactive ion etching “RIE” whereby a measurement of the photoresist mask width determines an adjustment to the RIE etch-bias to control the gate width. However, as gate width dimensions continue to shrink to sub-quarter micron in modern semiconductors all available etch-bias may be used in achieving such sub-lithographic dimensions, thereby leaving no available etch-bias for later adjustments to control the smaller effective channel lengths in modem semiconductors.
Thus, as the gate electrodes of modem semiconductors continue to shrink to sub-quarter micron, typically less than 0.25 &mgr;m, it is becoming more difficult to effectively and efficiently control the associated smaller effective channel lengths, and thus more difficult to provide fast, reliable, and desirable semiconductors. Therefore, a need continues to exist in the art to provide improved systems and methods of forming, controlling and maintaining smaller effective channel lengths in modern semiconductors.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide an improved system and method of forming and controlling an effective channel length in a semiconductor.
Another object of the present invention is to provide an improved system and method for compensating for gate electrode width deviation from target.
It is another object of the present invention to provide a system and method for controlling channel length or other device parameter by compensating for gate electrode width deviation from target.
Yet another object of the present invention is to provide an improved semiconductor, such as a FET, having a gate width less than about 0.25 &mgr;m which exhibits improved yield and performance.
It is another object of the present invention to provide a more reliable, efficient, effective, and desirable FET.
Still another object of the present invention is to provide a manufacturing process that decreases variance of one or more device parameters while simultaneously increasing product yield thus decreasing scrap.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
SUMMARY OF THE INVENTION
The above and other objects and advantages, which will be apparent to one of skill in the art, are achieved in the present invention which is directed to, in a first aspect, a method and system of forming a semiconductor device, such as a FET, MOSFET, and CMOS, whereby a gate electrode is provided over a substrate and subsequently a dimension of the gate electrode is determined. The determined dimension of the gate electrode is then fed forwarded to a feed-forward controller wherein an ion implant recipe, including ion implant recipe comprising n-type and p-type impurities, is determined based on the
Conchieri Brian P.
Ellis-Monaghan John J.
Ruegsegger Steven M.
Delio & Peterson LLC
Gandhi Jayprakash N.
Reynolds Kelly M.
Sabo William D.
LandOfFree
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