Semiconductor device manufacturing: process – With measuring or testing – Electrical characteristic sensed
Reexamination Certificate
2001-06-05
2003-01-21
Chaudhuri, Olik (Department: 2813)
Semiconductor device manufacturing: process
With measuring or testing
Electrical characteristic sensed
C438S010000
Reexamination Certificate
active
06509202
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to semiconductor devices, and more particularly to a method and system for qualifying an ONO layer in a semiconductor device.
BACKGROUND OF THE INVENTION
FIG. 1
depicts a portion of a conventional semiconductor device
10
, such as a Flash memory device. The conventional semiconductor
10
utilizing an oxide-nitride-oxide (“ONO”) layer
13
formed on a semiconductor substrate
12
. The ONO layer
13
includes two oxide layers separated by a nitride layer
16
. The first oxide layer, which is closest to the substrate
12
is a tunnel oxide layer
14
. The upper oxide layer is a control oxide layer
18
. The thinned portion of the control oxide layer
18
corresponds to a bitline
20
that runs perpendicular to the plane of FIG.
1
. The nitride layer
14
acts as a charge storage layer, or a floating gate. Thus, charges can tunnel through the tunnel oxide layer
14
and be trapped on the nitride layer
14
. As a result, the threshold voltage of a device utilizing the ONO layer
13
is changed. In order to alter the threshold voltage, a voltage is typically applied to the control oxide layer
18
.
Typically, devices made using the ONO layer
13
are desired to be qualified, or investigated to determine that their properties meet certain specifications. In particular, it is desirable to ensure that when the ONO layer
13
is included in a device, such as a flash memory device, the ONO layer
13
will have a particular lifetime. It is, therefore, desirable to qualify the ONO layer
13
.
One property of the ONO layer
13
desired to be determined during qualification is the lifetime of the ONO layer
13
. Predicting the lifetime of the ONO layer
13
, particularly in structures such as the bitline
20
, is difficult. The ONO layer
13
is a multiplayer. As such, different layers within the ONO layer, such as the tunnel oxide
14
, the nitride
16
and the control oxide
18
, may have different properties. These layers
14
,
16
and
18
within the ONO layer
13
therefore have different lifetimes. As a result, the lifetime of the ONO layer
13
could vary. Consequently, reliably predicting the lifetime of the ONO layer
13
is difficult.
Accordingly, what is needed is a system and method for qualifying an ONO layer. The present invention addresses such a need.
SUMMARY OF THE INVENTION
A method and system for qualifying an oxide-nitride-oxide (ONO) layer including a first oxide layer, a nitride layer and a control oxide layer in a semiconductor device is disclosed. The method and system comprise determining a first plurality of lifetimes for the ONO layer. The first plurality of lifetimes is determined utilizing a first plurality of applied voltages at a first plurality of temperatures for each of a first plurality of ONO layers having a particular nitride layer thickness and a plurality of control oxide layer thicknesses. The method and system also comprise determining a second plurality of lifetimes for the ONO layer. The second plurality of lifetimes are determined utilizing a second plurality of applied voltages at a second plurality of temperatures for each of a second plurality of ONO layers having a particular control oxide layer thickness and a plurality of nitride layer thicknesses. The method and system also comprise determining a field acceleration factor for the ONO layer based on the first plurality of lifetimes, the second plurality of lifetimes, the first plurality of applied voltages and the second plurality of applied voltages. In addition, the method and system comprise determining an activation energy for the ONO layer based on the first plurality of lifetimes, the second plurality of lifetimes, the first plurality of temperatures and the second plurality of temperatures. The method and system also comprise determining a lifetime for the ONO layer based upon the field acceleration factor and the activation energy for the ONO layer.
According to the system and method disclosed herein, the present invention provides a method for qualifying an ONO layer, as well as selecting thicknesses of the control oxide and nitride layer that can improve performance of the ONO layer.
REFERENCES:
Japanese Abstract JP 10214966A Aug. 11, 1998. “Method for managing a process”.
Advanced Micro Devices , Inc.
Chaudhuri Olik
Sawyer Law Group LLP
Thompson Craig
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