JPH09145774A - Semiconductor device for evaluating device deterioration and device deterioration evaluation method using it - Google Patents

Abstract

PROBLEM TO BE SOLVED: To inexpensively and easily measure and evaluate the deterioration in the characteristics of a floating gate type MOSFET by forming an oscillation circuit and a floating gate type MOSFET for evaluation within a same semiconductor device. SOLUTION: A floating gate type MOSFET 30 for evaluation and a ring oscillator 11 for oscillation AC for AC stress being applied to the floating gate type MOSFET 30 are formed as a semiconductor device for evaluating device deterioration within a semiconductor device 10. In the ring oscillator 11, a device which is connected to a gate electrode 30G of the floating gate type MOSFET 30 for evaluation and a substrate electrode 30sub by wires is used, thus measuring and evaluating the deterioration in the characteristics of the floating gate type MOSFET.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor device for device deterioration evaluation and a device deterioration evaluation method using the same, and more particularly to a floating gate MOSFET.
The present invention relates to a semiconductor device for evaluating device deterioration for evaluating deterioration of characteristics of the device and a device deterioration evaluation method using the same.

[0002]

2. Description of the Related Art Electrical writing and erasing are performed in a MOSFET having a memory function, that is, a MOSFET having a floating gate. This writing or erasing is performed by applying a voltage between the electrodes to cause a tunnel current (leakage current) to flow through the gate oxide film and to accumulate or discharge electric charges in the floating electrode. Therefore, it is important to ensure the reliability of the writing / erasing operation of the transistor.

Therefore, in the present situation, as a reliability test,
A method using AC stress (pulse generator) is performed. The evaluation method based on AC stress will be briefly described below with reference to FIG. FIG. 3 is a circuit diagram schematically showing a conventional device evaluation semiconductor device and a power supply system for the semiconductor device.

In FIG. 3, reference numeral 40 denotes a semiconductor device, 30 denotes a floating gate type MOSFET for evaluation formed in the semiconductor device 40, and 310.
Is a floating gate. The semiconductor device 40 includes
Gate terminal 321, drain terminal 322, source terminal 3
23, a substrate terminal 324 and a pulse terminal 325 are formed, and a gate terminal 321 and a pulse terminal 32 are formed.
5 is connected to the gate electrode 30 _G of the floating gate MOSFET 30, the drain terminal 322 is connected to the drain electrode 30 _D , the source terminal 323 is connected to the source electrode 30 _S , and the substrate terminal 324 is the substrate. Electrode 30 _Sub
It is connected to the.

Reference numeral 70 denotes a control device (computer), which is connected to the pulse generator 50 and the DC power supply / measuring device 60 and controls them. Pulse generator
The output terminal 50 _P of the input terminal 50 is connected to the pulse terminal 325, the output terminal 60 _G of the DC power supply / measuring device 60 is connected to the gate terminal 321, and the output terminal 60 _D is connected to the drain terminal 322. 60 _S is a source terminal 323
, And the output terminal 60 _Sub is connected to the substrate terminal 324. The other output terminal 50 _{P ′} of the pulse generator 50 is the output terminal 60 of the DC power supply / measuring device 60.
_D , the output terminal 60 _S , and the output terminal 60 _Sub , respectively.

When applying AC stress, a DC power source
No DC voltage is applied to the gate terminal 321 from the measuring device 60, and the AC stress generated in the pulse generator 50 is gated through the output terminal 50 _P and the pulse terminal 325.
Applied to the electrode 30 _G. On the other hand, each of the drain terminal 322, the source terminal 323, and the substrate terminal 324 of the floating gate MOSFET 30 has a pulse having a phase opposite to the pulse given from the pulse generator 50 to the gate electrode 30 _G by the DC power supply / measuring device 60. Is given. In this state, the AC stress is applied to the floating gate type MOSFET 30 by the pulse generator 50 for an arbitrary time, and writing and erasing are continuously repeated. After that, the AC stress output from the output terminal 50 _P is turned off by a signal from the control device 70, and instead, the DC power source / measurement device 60 causes the gate to be controlled.
Terminal 321, drain terminal 322, and substrate terminal 324
An appropriate DC voltage is applied to each of them to perform writing or erasing, and the stress application is stopped in either the writing or erasing state. Then, the DC power supply / measuring device 60 measures various characteristics such as the threshold voltage V _th at this time. After that, the application of the AC stress and the measurement of the various characteristics are repeated over time, and the floating gate type MO
The characteristics of the SFET 30 are measured to evaluate the characteristic deterioration.

[0007]

In the case of the conventional evaluation method using AC stress, the pulse generator 50 is provided outside the floating gate MOSFET 30.
However, there is a problem that a device for measuring and evaluating the deterioration of characteristics due to the application of AC stress becomes large.

The present invention has been made in view of the above problems, and AC stress is applied to a floating gate type MOSFE simply by applying a DC voltage from the outside without using a large-scale device such as a pulse generator as an AC generation source.
By applying to T, writing and erasing can be continuously performed,
An object of the present invention is to provide a semiconductor device for device deterioration evaluation capable of measuring and evaluating deterioration of characteristics and a device deterioration evaluation method using the same.

[0009]

In order to achieve the above object, in a semiconductor device for device deterioration evaluation according to the present invention, an oscillation circuit and a floating gate MOSFET for evaluation are formed in the same semiconductor device. The oscillation circuit is a floating gate type MOS for evaluation.
The FET is characterized in that it is connected to the gate electrode of the FET and the substrate electrode using wirings.

According to the above-mentioned semiconductor device for device deterioration evaluation, it is not necessary to dispose a large-scale device such as a pulse generator as an AC generation source outside the semiconductor device as in the conventional case, and the semiconductor device can be used from outside the semiconductor device. By simply applying a DC voltage for operating the oscillation circuit, AC stress can be applied to the evaluation floating gate type MOSFET to continuously perform writing and erasing. Therefore, by using the device evaluation semiconductor device, the floating gate M
Easy measurement of deterioration of OSFET characteristics at low cost
It can be evaluated, and it becomes possible to develop a highly reliable device in a short period of time.

A device deterioration evaluation method according to the present invention is a device deterioration evaluation method using the above-described semiconductor device for device deterioration evaluation, which is a floating gate type MO device.
A device deterioration evaluation method for evaluating deterioration of an SFET, comprising arranging metal wiring so that a signal from an oscillation circuit to a gate electrode and a signal from the oscillation circuit to a substrate electrode have opposite phases, The feature is that a power supply voltage is applied to the circuit from the outside.

According to the device deterioration evaluation method, the AC stress can be applied to the floating gate type MOSFET only by applying the DC voltage for operating the oscillation circuit from the outside of the semiconductor device. Therefore, by using the above method, the deterioration of the characteristics of the floating gate type MOSFET due to the AC stress can be easily measured and evaluated at low cost.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a semiconductor device for device deterioration evaluation and a device deterioration evaluation method using the same according to the present invention will be described below with reference to the drawings.

FIG. 1 is a circuit diagram schematically showing a semiconductor device according to an embodiment and a power supply system for the semiconductor device. In FIG. 1, reference numeral 10 denotes a semiconductor device, and 70 denotes a control device (computer) provided outside the semiconductor device 10.
And 20 indicates a DC power supply / measuring device.

Inside the semiconductor device 10, CMOS inverters are connected in a ring shape in which n stages (where n is an odd number having a value of 0 to several hundreds) from A _{1 to} A _n are connected in a ring shape. 11 and floating gate type MO for evaluation
The SFET 30 is formed. A floating gate 310 sandwiched between insulating films is formed below the gate electrode 30 _G of the floating gate MOSFET 30. The semiconductor device 10 has a gate terminal 321 and
Drain terminal 322, source terminal 323 and substrate terminal 3
24 terminals are formed, and the gate terminal 321 is the gate electrode 3 of the floating gate type MOSFET 30.
0 _G , the drain terminal 322 is the drain electrode 3
0 _D , and the source terminal 323 is connected to the source electrode 30 _S.
, And the substrate terminal 324 is connected to the substrate electrode 30 _Sub . Further, the semiconductor device 10 has a DC input terminal 1
11 and a GND terminal 112 are formed, the DC input terminal 111 is connected to the power supply terminal 11 _DC of the ring oscillator, and the GND terminal 112 is connected to the ground terminal 11 _GND of the ring oscillator 11. Further, the ring oscillator 11 is formed with two output terminals 11 _O1 and 11 _O2, and the output terminal 11 _O1 is a floating gate type M.
It is connected to the gate electrode 30 _G of the OSFET 30, and the other output terminal 11 _O2 is connected to the substrate electrode 30 _Sub . It should be noted that the output terminal 11 _O1 and the output terminal 11 _O2 are displaced by an odd number of CMOS inverter stages, so that the output from the output terminal 11 _O1 and the output from the output terminal 11 _O2 are in opposite phases to each other. It has become. The wiring and terminals (pads) in the semiconductor device 10 are made of a low-resistance metal such as Al.

The semiconductor device 1 is included in the DC power supply / measurement device 20.
The voltage supply terminals corresponding to the terminals formed on the
Has been established. That is, the terminal that supplies the ground voltage
20 _GND Is connected to the GND terminal 112 and the ring oscillator
-A terminal 20 for supplying DC power to the power supply 11._DCIs the DC input terminal
Floating gate type MOSF connected to the child 111
Terminal 20 for supplying gate voltage to ET30_G Is the gate edge
A terminal 20 connected to the child 321 and supplying a drain voltage
_D Is connected to the drain terminal 322 and supplies the source voltage
Terminal 20_S Is connected to the source terminal 323, and
Terminal 20 for supplying pressure_Sub Is connected to the board terminal 324
ing.

In the semiconductor device for evaluating device deterioration constructed as described above, the device A
C stress assessment is performed. <Applying AC stress> DC power supply / measurement device 20 to D
An appropriate DC power supply voltage (for example, 8 V) is applied to the power supply terminal 11 _DC of the ring oscillator 11 via the C input terminal 111. Further, an appropriate voltage (for example, 0V) is applied to the ground terminal 11 _GND via the GND terminal 112.

In one embodiment of the invention, the DC power supply voltage to the power supply terminal 11 _DC (8
V) is applied, the output signals from the output terminal 11 _O1 and the output terminal 11 _{O2 of} the ring oscillator 11 are opposite to each other in phase and CM
An AC having a frequency determined by the number of stages n of the OS inverters A _{1 to} A _n and the delay time per stage is output. That, CMOS inverter - the data A ₁ to A _n delay time T _HL (High Kararo - time required to switch to), T _LH - When (b time required for switching to-high), Ringuoshire - data 11 oscillation frequency f
_{The OSC} is f _OSC = 1 / (n × (T _HL + T _LH )).
The ACs having an oscillation frequency f _OSC and having opposite phases are floating gate type M as AC stress.
The gate electrode 30 _G and the substrate electrode 30 of the OSFET 30
applied to each _sub . As a result, the gate electrode 30 _G and the substrate electrode 30 _sub of the floating gate MOSFET 30 change in voltage at a constant cycle (for example, when the gate electrode 30 _G is 5 V, the substrate electrode 30 _sub is 0 V).
V, gate electrode 30 When the _G is 0 V, the substrate electrode 30
_sub is 5V), and writing and erasing are continuously performed. The application of the AC stress is maintained for an arbitrary time. At this time,
DC power supply / measurement device 20 terminal 20 _G and gate electrode 30
_{The G 2} and the terminal 20 _{sub of the} DC power supply / measuring device 20 and the board terminal 324 are not connected.

As described above, when stress is applied, an appropriate D is applied to the power supply 11 _DC and _GND 11 _GND of the ring oscillator 11.
Although the C voltage is applied, the voltage application to the power supply 11 _DC and _GND 11 _GND of the ring oscillator 11 is stopped when the characteristics are measured, and the characteristics of the floating gate MOSFET 30 for evaluation are measured in either the write or erase state. This stress application and measurement are repeated alternately to observe and evaluate the characteristic deterioration over time.

<Measurement of Characteristics> After the lapse of the arbitrary time, the DC power supply voltage (8 V) applied to the power supply terminal 11 _DC and the voltage applied to the ground terminal 11 _GND are turned off, and the ring oscillator 11 is turned off. The oscillation of the AC from the above is stopped, and the ring oscillator 11 and the floating gate type MOSFET 30 are electrically disconnected.
Then, the DC power supply / measurement device 20 automatically measures various characteristics of the floating gate MOSFET 30 as a single unit.

To evaluate the characteristic deterioration of the floating gate MOSFET 30 due to the application of AC stress, the <application of AC stress> and the <measurement of characteristic> are repeated alternately, and the deterioration of the characteristic in the measurement is observed with time. , By evaluating the observation results.

[0022]

EXAMPLES AND COMPARATIVE EXAMPLES Hereinafter, a semiconductor device for evaluating device deterioration and a device deterioration evaluation method using the same according to the embodiments will be described. In this example, the semiconductor device for device deterioration evaluation shown in FIG. 1 was used to measure and evaluate deterioration of characteristics by the method described in the above embodiment. The conditions are as follows.

(1) AC stress test Frequency: 50 MHz, applied voltage _MAX : 8 V, applied voltage
_MIN : 0 V, application time: 10 ⁶ sec, number of repetitions:
5 × 10 ¹³ times, (2) Measurement condition of threshold shift amount ΔV _{th Applied} voltage Drain electrode 30 _D : 0.1 V, Source electrode 30 _S : 0
V, Substrate electrode 30 _sub : OV (3) Floating gate type MOSFET 30 Wiring material: Al, Material of gate electrode and floating gate: polySi, Gate oxide film: SiO ₂ film thickness Between substrate and floating gate: 6 nm Floating gate and control gate Space: 6 nm Channel width: 25 μm, channel length: 0.6 μm In addition, the conventional apparatus shown in FIG. 3 was used as a semiconductor device for device deterioration evaluation according to the comparative example, and an AC stress test was performed under the same conditions as those of the example. It was

FIG. 2A shows a floating gate type MOSFET measured by the AC stress applying method according to the embodiment.
The change in the threshold voltage (V _th ) with time of writing and erasing of 30 is shown. As a comparative example to this, FIG.
Shows the change with time of the threshold voltage measured by the AC stress applying method according to the comparative example. In FIG. 2, the horizontal axis represents the application time (sec) of AC stress, and the vertical axis represents the A
C threshold voltage shift amount with respect to C stress application time Δ
th (mV) is shown.

As can be seen by comparing the graph shown in FIG. 2A with the graph shown in FIG. 2B, even when the ring oscillator 11 is used, the pulse generator 50 is externally provided. The change with time of the deterioration can be measured and evaluated with the same accuracy as in the case of preparing for measurement.

As described above, in the device deterioration evaluation semiconductor device according to the embodiment, the evaluation floating gate type MOSFET 30 and the AC applied to the floating gate type MOSFET 30 in the semiconductor device 10.
A ring oscillator 11 for oscillating AC for stress is formed, and the ring oscillator 11 is a gate electrode 30 of a floating gate MOSFET 30 for evaluation.
_{The G} and the substrate electrode 30 _sub are connected to each other using wiring. Therefore, it is not necessary to prepare a large-scale device such as a pulse generator as an AC generation source as in the conventional case, and the DC power supply / measurement device 20 to the semiconductor device 1 can be used.
By simply applying an appropriate DC voltage to each terminal of 0, AC stress can be applied to the floating gate MOSFET 30 for evaluation under conditions close to the operating conditions of the actual device, and writing and erasing can be performed. Therefore, if the semiconductor device for device deterioration evaluation according to the embodiment is used, the deterioration of the characteristics of the floating gate MOSFET 30 due to the AC stress can be easily measured and evaluated at low cost.

The oscillating frequency of the ring oscillator 11 is the same as that of the CMOS inverter which constitutes the ring oscillator 11.
It can be easily changed by changing the number of steps A _{1 to} A _n .

[Brief description of the drawings]

FIG. 1 is a circuit diagram schematically showing a semiconductor device for device deterioration evaluation according to an embodiment of the present invention and a power supply system for the semiconductor device.

FIG. 2 is a graph showing a relationship between an AC stress application time and a threshold voltage shift amount (Δth), and FIG. 2A is a graph showing a result measured by an AC stress application method according to an example. , (B) are graphs showing the results measured by the AC stress applying method according to the comparative example.

FIG. 3 is a circuit diagram schematically showing a conventional device deterioration evaluation semiconductor device and a power supply system for the semiconductor device.

[Explanation of symbols]

10 Semiconductor Device 20, 60 DC Power Supply / Measuring Device 11 Ring Oscillator (Oscillation Circuit) 30 Floating Gate MOSFET 310 Floating Gate 30 _G Gate Electrode 30 _D Drain Electrode 30 _S Source Electrode 30 _Sub Substrate Electrode 70 Control Device (Computer)

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical indication H01L 27/04 H01L 27/04 T 21/822 27/10 434 27/115

Claims (2)

[Claims] 1. An oscillation circuit and a floating gate MOSFET for evaluation are formed in the same semiconductor device, and the oscillation circuit has wirings for the gate electrode and the substrate electrode of the floating gate MOSFET for evaluation. A semiconductor device for device deterioration evaluation, characterized in that it is connected by using the semiconductor device. 2. A device deterioration evaluation method for evaluating deterioration of a floating gate MOSFET, wherein a signal from an oscillation circuit to a gate electrode and a signal from the oscillation circuit to a substrate electrode have opposite phases. 2. The device deterioration evaluation method using the semiconductor device for device deterioration evaluation according to claim 1, wherein wiring is arranged and a power supply voltage is applied to the oscillation circuit from the outside.