JP3299815B2 - Semiconductor integrated circuit - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor integrated circuit having a built-in protection circuit using a transistor whose characteristics may be degraded due to a hot carrier effect.

[0002]

2. Description of the Related Art When a transistor is miniaturized and its channel length becomes short, for example, shorter than 1.5 μm,
It is well known that hot carrier issues arise. As the miniaturization of transistors progresses, the internal electric field (electric field near the drain) increases, so that carriers in the channel (electricity flowing from the source to the drain) are accelerated by a strong electric field, and a large energy is obtained. It will be called a hot carrier. When the carrier gains a large energy in this way, impact ionization (impact
Ionization) to generate an electron-hole pair. These hot carriers are trapped in the gate oxide film of the transistor or create a surface state, which causes a change in the threshold voltage (threshold) of the transistor,
It causes a change in transconductance and changes the characteristics of the transistor. This problem of hot carriers is significant in NMOS transistors having a channel (gate) length of 1.5 μm or less.

As described above, when the channel length of a MOS transistor becomes shorter, the threshold voltage (Vt) is increased by the effect of hot carriers according to the conduction time.
h) varies from its initial value. Since the fluctuation of the threshold voltage gradually changes little by little, a semiconductor integrated circuit (hereinafter, referred to as an LSI) may suddenly stop working or become defective.

For this reason, in order to prevent transistor (device) deterioration (characteristic fluctuation) due to hot carriers,
The following various means are employed. When the transistor has an LDD structure, a DDD structure, or the like, an electric field inside the device (in the vicinity of the drain) is reduced, and the generation of hot carriers is suppressed. The generation of hot carriers is kept away from the Si—SiO ₂ interface by devising the impurity profiles of the source and drain of the transistor. A high quality gate oxide film, passivation film, etc. is used to suppress the generation of hot carriers in a process. The circuit is devised to reduce the duty ratio at which the substrate current occurs.

[0005] By the way, such characteristic fluctuations of MOS transistors due to hot carriers, that is, characteristic deterioration, are generally widely known, and methods for suppressing this characteristic deterioration are also well known, and various measures have been taken. I have.
However, although these measures can be taken to extend the life of the transistor, and thus the LSI, the hot carriers cannot be completely eliminated, and the deterioration of the transistor with time cannot be completely eliminated. Therefore, it has not been possible to solve such a problem as sudden stoppage of operation of an LSI using a transistor in which characteristics are likely to deteriorate due to hot carriers or the like. Nevertheless, such a change in transistor characteristics is detected,
There has been no circuit or device that informs the user of the life of the transistor, that is, the life of the LSI to the outside, that is, the user.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a semiconductor integrated circuit (LSI).
The same transistor as the transistor receiving the hot carrier effect among the transistors used in the above is used as a sensing transistor, and this sensing transistor is energized when the power is turned on, and the threshold value (Vth) due to the hot carrier is determined. An object of the present invention is to provide a semiconductor integrated circuit having a built-in hot carrier effect sensing circuit capable of outputting a signal to the outside and generating an alarm when a fluctuation larger than the value occurs.

[0007]

In order to achieve the above object, a first aspect of the present invention is a semiconductor integrated circuit having a transistor whose characteristics change with time due to hot carriers, wherein the same transistor as the transistor is used. used as the hot carrier sensing transistor, the semiconductor collection
When energizing the integrated circuit, the hot carrier sensing transistor is always turned on, and the hot carrier sensing transistor is turned on.
It is an object of the present invention to provide a semiconductor integrated circuit provided with a hot carrier effect sensing circuit for generating a lifetime signal when a characteristic variation of a transistor becomes equal to or more than an initial set value. Here, it is preferable that the hot carrier sensing circuit is a differential sense amplifier. In addition, the present invention
Transistors whose characteristics change over time due to carrier
A semiconductor integrated circuit having the same configuration as the transistor.
The same transistor as the hot carrier sensing transistor
The characteristics of this hot carrier sensing transistor
Life signal is generated when the variation of the property exceeds the initial set value.
Hot carrier effect with differential sense amplifier
Provide a semiconductor integrated circuit characterized by providing an intelligent circuit
Is what you do.

[0008] A second aspect of the present invention is a hot carrier.
A main circuit in which a transistor whose characteristics vary with time due to the rear is incorporated; a peripheral circuit ;
The same transistor as the hot carrier sensing transistor
The characteristics of this hot carrier sensing transistor
Life signal is generated when the variation of the property exceeds the initial set value.
That the hot carrier effect sensing circuit is provided, there is provided a semiconductor integrated circuit, characterized by being configured to stop the peripheral circuit by generating for life signal of the hot carrier effect sensing circuit.

[0009]

The semiconductor integrated circuit according to the first aspect of the present invention has a hot carrier among transistors used in the semiconductor integrated circuit (LSI), such as MOS transistors, when the LSI is energized. The same transistor that is easily affected by
A hot carrier effect sensing circuit (hereinafter referred to as a sensing circuit) is constituted by using the sensing transistor, and a current always flows when current is applied. The variation is detected by a sensing circuit, a life signal is generated outside the sensing circuit and / or outside the semiconductor integrated circuit of the present invention, and deterioration of the characteristics of a transistor used is detected.

A semiconductor integrated circuit according to a second aspect of the present invention uses the life signal generated by the sensing circuit to perform LS
I. Peripheral circuits inside the I are stopped, the user is made aware of a defect (lifetime), and a main circuit inside the LSI, for example, a circuit for transmitting and receiving signals directly connected to the CPU is prevented from being stopped,
This is to prevent the function of the main circuit from being lost.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A semiconductor integrated circuit according to the present invention will be described in detail based on preferred embodiments shown in the accompanying drawings.

FIG. 1 is a circuit diagram showing an embodiment of a hot carrier effect sensing circuit (sensing circuit) used in a semiconductor integrated circuit according to the present invention. As shown in FIG. 1, a sensing circuit 10 used in the present invention includes a sense amplifier block 12.
And an input unit 14 and an output unit 16.

In the sense amplifier block 12, a resistor R₁
And NMOS transistor T₁And resistance R_TwoAnd NM
OS transistor T_TwoAre connected in series.
The resistance R₁And R_TwoAre connected to power
You. Transistor T₁And T _TwoSources connected to each other
The transistor T_FiveConnected to the drain of G
Lanista T_FiveAre grounded. Transistor T
₁Is a resistor R_TwoAnd transistor T_TwoContact with
Mode) A, transistor T_TwoIs a resistor R ₁And to
Lanista T₁Is connected to a contact (node) B. Ma
The transistor T_FiveAre connected to a power supply. This
Here, the NMOS transistor T₁Is the most characteristic of the present invention.
The hot carrier sensing transistor
18 and the transistor T₁The book
NMOS used in the body of the semiconductor integrated circuit of the invention
Most of the transistors are affected by hot carriers
The same NMOS transistor as the pan NMOS transistor
Is used.

The input section 14 has an input terminal 20 for inputting a monitor signal M, and an inverter 2 connected to the input terminal 20.
2, an NMOS transistor T ₄ whose gate receives the inverted monitor signal output (M bar) of the inverter 22,
Resistor R connected in series between the transistor T ₄ and the power source
_{And 4} . Here, the other electrode of the transistor T ₄ (source) is connected to the contact point A between the resistor R ₂ and the transistor T _2.

The output section 16 is connected to a contact point B between the resistor R ₁ and the hot carrier effect sensing transistor T _1, and has a gate connected to an input terminal 20 for inputting the monitor signal M.
The transistor T ₃ which is connected to this transistor T
₃ has a buffer amplifier 24 connected to the other electrode (source) and an output terminal 26 for outputting an inverted output of the buffer amplifier 24 as a lifetime signal S.

The sense amplifier block 12 constitutes a differential sense amplifier. By adjusting the resistors R ₁ and R ₂ , the NMOS transistors T ₂ , T ₃ and T ₄ , which constitute this differential amplifier, This is to detect a change in the threshold value (threshold voltage V _th ) of the hot carrier effect sensing transistor 18 (T ₁ ), that is, a deterioration (decrease).

Here, the hot carrier effect sensing transistor 18 (T ₁ ) constituting the differential sense amplifier is the most transistor among semiconductor integrated circuits (LSI) incorporating the sensing circuit of the present invention. A transistor which is easily affected by the hot carrier effect is used. Such a transistor which is easily affected by hot carriers includes a transistor having a narrow channel width (channel length, gate length), for example, a MOS transistor having a width of 1.5 μm or less, particularly 1.0 μm or less. The NMOS transistor is more susceptible than the NMOS transistor. In addition, when the line width of the design rule is narrower, for example, the 0.8 μm design rule is more susceptible to hot carriers than the 1.0 μm design rule. Depends on structure and manufacturing method. Therefore, at the stage of designing and processing a semiconductor integrated circuit, it is possible to specify or select a transistor most susceptible to the effects of hot carriers, and to replace the same transistor with the hot carrier effect sensing transistor 18.
(T ₁ ).

Since the differential sense amplifier block 12 shown in FIG. 1 compares the currents flowing through the resistors R ₁ and R ₂ , the sensing transistor T ₁ and the transistor T ₂ have the same threshold. The value must be V _th ,
Threshold is gradually lowered in the sensing transistors T ₁ by a hot carrier effect, becomes more than a certain level difference between the threshold, the balance of the sense amplifier is inverted, from the output unit 16 to the inversion as an alarm signal Output to the outside. The deterioration (decrease) level of the threshold value (V _th ) of the hot carrier effect sensing transistor 18 (T ₁ ) detected by the sensing circuit 10 is determined by the resistance values of the resistors R ₁ and R ₂ , as described above. Although set by varying the current flowing through the hot carrier effect sensing Tonrajisuta T ₁ by adjusting the size of the transistor T _5,
The level is preferably such that a main circuit or a peripheral circuit that always accesses a semiconductor integrated circuit using the same transistor as the transistor 18, such as a CPU, malfunctions, stops functioning, or stops operating. More preferably,
It is better to set a level slightly higher than this level (just before stopping). Further, assuming the life of the LSI, for example, 10 years, the lowering level of the threshold value of the sensing transistor 18 (T ₁ ) may be sensed.

In the sensing circuit 10 shown in FIG.
The sensing NMOS transistor 18 (T₁) For
To form a block 1 comprising a differential sense amplifier.
Anti-R ₁, R_Two, NMOS transistor T_Two, T_FiveSuch as
The size is adjusted, and the sensing transistor 18 (T₁) Is
(OFF) and the transistor T_TwoTurns on
So that Therefore, at this time, each gate potential
The potentials of equal contacts A and B are
T₁And T_TwoThreshold (V_th) Lower potential and higher
Potential.

Here, during operation of the semiconductor integrated circuit of the present invention,
(When power is supplied), the input terminal 20
When the bell (LOW) monitor signal M is input, the
Jista T_ThreeLow level (L) signal as it is
Is input, and the Tonradista T _FourInverter at the gate
High level (HIGH) signal inverted at 22 is input
Is done. Therefore, the transistor T_ThreeOff, transi
Star T_FourTurns on. As a result, contact A is at high level
(H), the transitor T₁The gate is high level
(H), and the sensing transistor 18 (T₁) Is oh
On. At this time, the resistor R₁, Transistor T
₁, T_FiveThe current flows through to the ground. Meanwhile, for sensing
Transistor 18 (T₁) Turns on, the contact B
Becomes low level (L) and the transistor T_TwoHa
I will. At this time, the transistor T_ThreeIs off
, The change in the potential of the contact B is
, The life signal S is output from the output terminal 26.
Never.

As described above, the structure is such that the sensing transistor (T ₁ ) is always turned on when the semiconductor integrated circuit of the present invention is energized. Thus, over time the sensing transistor T ₁ of the threshold (Suresshihorudo voltage) is lowered by influence of hot carriers. At this time,
Periodically or as needed, the monitor signal M is changed from a low level (L) to a high level (H) to monitor the state of the sensing transistor 18 (T ₁ ).

When the life is monitored, the monitor signal M is set to the high level.
(H), the transistor T_ThreeGate is H
The transistor T_ThreeTurns on, while Tonradis
T_FourGate becomes L of the inverted monitor signal (M bar)
So the transistor T_FourIs turned off and the resistance R_FourCut
Will be separated. As a result, the change in the potential of the contact B is
Can be output from output terminal 26 as life signal S
Becomes Where the resistance R _TwoThe resistance value of R₁Resistance value
Greater (R_Two> R₁) And the sensing transistor T₁
And transistor T_TwoEqual to (V_th(T₁)
= V_th(T_Two)) Or the resistance R₁And R_Twoof
Transistor T_TwoSensing the threshold of
Transistor T₁Greater than the threshold of (V
_th(T_Two)> V_th(T₁)) If you keep it, it will be used for sensing
Jista T₁If the life of the
(If it has not deteriorated below the set value),
As in the case of the sensing transistor T₁Is on, Transis
T_TwoIs turned off, the potential of the contact A is high level
(H), and the potential of the contact B becomes the low level (L).
You. As a result, the potential of the contact B becomes_Three,
Is transmitted to the output terminal 26 through the
Then, the life signal S becomes low level (L). Therefore, longevity
Transistor T for sensing at the time of life monitoring₁Fluctuation of threshold
If (deterioration) is smaller than a preset value, output
L level life signal S is output from output terminal 26 of section 16
Is done.

On the other hand, when the life is monitored, that is,
When the monitor signal M is set to the H level, the hot carrier effect sensing transistor T
_When the variation (deterioration) of the threshold value of ₁ becomes larger than a preset value, and the threshold voltage V _th (T ₁ ) increases, that is, when the life of the sensing transistor T ₁ becomes longer, the sensing voltage becomes lower. transistor T ₁ is turned off, so that the transistor T ₂ is turned on. Therefore, the potential of the contact B changes from the L level before the end of the life to the H level, passes through the transistor T ₃ , is shaped by the buffer amplifier 24, and the life signal S output from the output pad 26 has the initial value of L. From the level, it becomes H level which is a life alarm signal, and it is detected that the characteristic of the sensing transistor fluctuates beyond the set value and the life has come. In this way, before the semiconductor integrated circuit stops or its components or their functions stop, it is possible to detect in advance the fluctuations in the characteristics of the transistors that make up these components.

In the example shown in FIG. 1, the sensing transistor 1
When the characteristic (threshold) deterioration of 8 (T ₁ ) does not reach the predetermined level, the sensing circuit 10 outputs an L level signal as the life signal S, and when the characteristic deterioration exceeds the predetermined level, the H level life Although an alarm signal is configured to be output, the present invention is not limited to this. Conversely, the life alarm signal may be set to L level, and the life signal when the characteristic deterioration has not reached the predetermined level may be set to H level. Good. In the illustrated example, an N-channel transistor, that is, an NMOS transistor is used, but the present invention is not limited to this.
It goes without saying that a P-channel transistor, that is, a PMOS transistor or a bipolar transistor may be used. Further, in the example shown in FIG. 1, as the load of the transistors T _1, T _2, T _4, although each with resistors R _1, R _2, R _4, the invention is not limited to this, the resistance R ₁ , R ₂ and R ₄ may be replaced by load transistors T _P1 , T _P2 and T _P3 , respectively, as shown in FIG. Here, load transistors T _P1 , T _P2 , T
Each gate of _P3 is grounded.

Next, FIG. 3 shows a semiconductor integrated circuit according to a second embodiment of the present invention incorporating the above-described hot carrier effect sensing circuit. The semiconductor integrated circuit (IC or L
SI) 30 as its internal circuit (system) as shown in FIG.
And a timer 32 for generating a monitor signal M to be sent to the hot carrier effect sensing circuit 10 shown in FIG.
And a main circuit 34 that performs the main functions of the semiconductor integrated circuit 30, a peripheral circuit 36 provided around the main circuit 36, and a life signal S output from the sensing circuit 10 as a control signal. A three-state gate 38 to which an inverted signal of the output of the peripheral circuit 36 is input.

Here, the timer 32 is connected to the hot carrier sensing transistor 1 of the hot carrier effect sensing circuit 10.
8 characteristic degradation (decrease in threshold) of (T ₁₎ for generating a monitor signal M which determines the monitor timing detected. The main circuit 34 is, for example, a circuit which processes a signal directly connected to the CPU and exerts a main function. The main circuit 34 uses the same transistor as the sensing transistor 18 (T ₁ ) of the sensing circuit 10 under the influence of the hot carrier. This is a circuit that is used as a transistor that is easily affected. The peripheral circuit 36
For example, it is a circuit that performs a part of the function of the system such as turning on a lamp.

In the illustrated semiconductor integrated circuit 30, when the monitor signal M output from the timer 32 and input to the sensing circuit 10 is at the H level, the life of the sensing transistor 18 (T ₁ ) must be longer. For example, the life signal S output from the sensing circuit 10 is at L level,
Since an L level signal is input to the control terminal of the state gate 38, an output signal from the peripheral circuit 36 input to the input terminal of the three-state gate 38 is output from the three-state gate 38 as it is. Therefore, the function of the peripheral circuit 36 is not stopped. When the monitor signal is at the L level (when the LSI is operating), the life signal S is not output from the sensing circuit 10 as in the initial state, so the control terminal of the three-state gate 38 is L level, and the output of the peripheral circuit 36 has three states.
The signal is output from the gate 38 as it is, and the function of the peripheral circuit 36 is not hindered.

On the other hand, when the characteristic (threshold value V _th ) of the sensing transistor 18 (T ₁ ) of the sensing circuit 10 deteriorates beyond a predetermined level, the life signal S output from the sensing circuit 10 becomes H level. , The output from the 3-state gate 38 is in a high-impedance state regardless of whether the output of the peripheral circuit 36 is an H-level signal or an L-level signal. Stop. As described above, when the output signal S from the sensing circuit 10 is a lifetime alarm signal, the output of the peripheral circuit 36 is cut off and fixed to a high impedance state in the illustrated example by using the lifetime alarm signal. By arranging such that some of the functions of the main circuit 30 are stopped, the main circuit 34 constantly accessing the CPU, for example, does not stop functioning or malfunction. Therefore, the entire semiconductor integrated circuit 30, that is, the entire system does not stop or malfunction due to deterioration of the transistor which is most susceptible to the hot carrier effect.

[0029] In the example described above, the life signal output from the sensing circuit 10 has a life alarm signal when an H level signal, it may be used L-level signal as a life alarm signal course is there. Further, in the illustrated example, a three-state gate 38 using the life signal S as a control signal is used, and the output of the peripheral circuit 36 is controlled by the life signal S. When the life signal S is an H-level life alarm signal, the three-state gate 38 is used. The output of the gate is set to a high impedance state and cut off, and the function of the peripheral circuit 36 is stopped. However, the present invention is not limited to this. The L level may be forcibly set. In the illustrated example,
Although a three-state gate is used as a means for stopping the function of the peripheral circuit 36 by the life alarm signal, the present invention is not limited to this. When the life signal S is the life alarm signal (H / L), Any circuit can be used as long as the function of the circuit can be stopped, and an AND circuit, an OR circuit, or another logic circuit may be used.

Further, in the above-described example, the differential type sense amplifier is used for sensing (detecting) deterioration of the characteristics of the transistor which is most susceptible to the hot carrier effect, for example, the threshold value (V _th ). The present invention is not limited to this, and any circuit may be used as long as deterioration of the characteristics (for example, threshold value) of the transistor can be reliably detected.

[0031]

As described in detail above, according to the present invention,
In a semiconductor integrated circuit (LSI), when a transistor, for example, a MOS transistor, whose characteristics may change over time due to the influence of hot carriers or the like, the characteristics of which may deteriorate, the transistor is continuously operated when the LSI is energized, and the characteristics change. A transistor (MOS transistor) that constitutes an LSI that is miniaturized year by year by incorporating a hot carrier effect sensing circuit that outputs a life alarm signal ("H / L") when the value of the signal becomes equal to or more than an initially set value. Due to the characteristic fluctuation over time, which is a drawback of the above, it is possible to monitor the life of each LSI in which the LSI suddenly malfunctions or stops operating at the time of use, and issues a life alarm signal to the user before these problems occur. It is possible to prompt the exchange of the LSI. Therefore, at present, in important systems (for example, airplanes), a plurality of computers are operated to perform backup, but by applying the present invention, a significant system is provided by having only important LSIs as backups. Costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a configuration circuit diagram of an embodiment of a hot carrier effect sensing circuit built in a semiconductor integrated circuit according to the present invention.

FIG. 2 is a configuration circuit diagram of another embodiment of a hot carrier effect sensing circuit built in a semiconductor integrated circuit according to the present invention.

FIG. 3 is a block diagram of one embodiment of a semiconductor integrated circuit according to the present invention.

DESCRIPTION OF SYMBOLS 10 Hot carrier effect sensing circuit 12 Sense amplifier block 14 Input unit 16 Output unit 18 Hot carrier effect sensing transistor 20 Input terminal 22 Inverter 24 Buffer amplifier 26 Output terminal 30 Semiconductor integrated circuit 32 Timer 34 Main circuit 36 Peripheral circuit 38 three-state gates R _1, R _2, R ₄ resistance _{T 1, T 2, T 3} , T 4, T 5 NMOS transistor T _P1, T _P2, T _P3 load transistor

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-291475 (JP, A) JP-A-3-228360 (JP, A) JP-A-62-32641 (JP, A) 500785 (JP, A) (58) Field surveyed (Int. Cl. ⁷ , DB name) H01L 21/822 G01R 31/26 H01L 27/04 H03F 3/45

Claims (4)

(57) [Claims] 1. A semiconductor integrated circuit having a transistor whose characteristics vary with time due to hot carriers, wherein the same transistor as the transistor is used as a hot carrier sensing transistor, and power is supplied to the semiconductor integrated circuit.
Sometimes this hot carrier sensing transistor is always off.
And a hot carrier effect sensing circuit for generating a lifetime signal when a characteristic variation of the hot carrier sensing transistor becomes equal to or greater than an initial set value. 2. The semiconductor integrated circuit according to claim 1, wherein said hot carrier effect sensing circuit is a differential sense amplifier. 3. A characteristic variation with time due to hot carriers.
A semiconductor integrated circuit having a transistor,
Hot carrier sensing for the same transistor as the transistor
For hot carrier sensing
When the transistor characteristic fluctuation exceeds the initial set value
A hot sensor consisting of a differential sense amplifier that generates a life signal
Semiconductor with a carrier effect sensing circuit
Body integrated circuit. 4. A characteristic variation with time due to hot carriers.
The main circuit in which the transistor is incorporated, the peripheral circuit and the same transistor as the hot transistor
This hot carrier is used as a rear sensing transistor.
A If the characteristic fluctuation of the sensing transistor
Hot carrier effect detection circuit that generates a life signal when
The road is provided, a semiconductor integrated circuit, characterized in that configured to stop the peripheral circuit by generating for life signal of the hot carrier effect sensing circuit.