Background
As CMOS process dimensions continue to shrink, Negative Bias Temperature Instability (NBTI) has become one of the major factors affecting the performance of p-MOSFET devices. The NBTI effect causes device parameter degradation, such as threshold voltage (Δ V)T) Linear and saturated drain currents, transconductance, and subthreshold slope, among others, thereby degrading performance of the circuit and system. Accurately describing and predicting the analytical model of NBTI degradation and recovery is a great problem to be perfected in the aspect of device reliability. The physical mechanism of NBTI has been studied extensively over the past decades and has led to different explanations. Generation of interface traps (Δ N) using the R-D theoryIT) Is believed to be the primary cause of NBTI degradation. On the other hand, the cavity is in the cavityProcess related gate insulator grown-in defects (Δ N)HT) The trapping/releasing (T/D) mechanism in (a) is also considered to be not negligible. Studies show thatHTComplete saturation or recovery can be achieved in a few seconds, and this process can be explained by a two-energy-well model. It can be seen that only Δ N is of interestITOr Δ NHTNone of the models of (a) provide a complete physical mechanism interpretation for NBTI. Except for delta NITAnd Δ NHTIn addition, studies have found defects (Δ N) in the gate insulator that occur during stressing when a higher gate voltage is appliedOT) Also has a significant impact on NBTI degradation. Therefore, many studies have attempted to convert Δ NIT,ΔNHTAnd Δ NOTA model is incorporated to give a better physical interpretation.
An important characteristic of NBTI is that damage to the device develops recovery immediately after the voltage applied to the gate of the p-MOSFET is removed. In general, NBTI recovery can be divided into three parts: 1) fast hole detachment from within the gate insulator layer defects originally present and created during stressing, 2) fast electron capture by interface defects, 3) slow recovery of remaining interface traps. Thus, long term NBTI recovery results only from slow repair of interface traps, which can be described by RD theory. Considering the slow recovery, H2Reacts with defects at the interface, making the defects less and less, so that over the recovery time, H2The probability of finding defects is constantly reduced, and this process can be represented by H2Diffusion coefficient D ofH2The following relationship over time is characterized:
wherein D isH20Finger H2Constant diffusion coefficient in the pressed phase, trecFinger device recovery time, tstrTo the device press time, BDFor description of DH2The degree of decay with time. In addition, due to H2The locking effect of, i.e. part of, the device degradation processH2Trapped defects are thus unable to participate in the recovery process and a portion of NBTI defects are unable to recover. During long-term recovery, the threshold voltage is degraded by Δ VTThe variation relation with respect to time t can be given by a numerical solution of the R-D model.
In order to describe and research NBTI long-term recovery characteristics more easily, it is necessary to propose a more simplified and effective analytical model. In consideration of DH2Decrease in sum H with time2On the basis of the locking effect, the invention provides an analytic model for describing NBTI long-time recovery. The model has physical significance and simple form, and is consistent with the numerical solution of the R-D model. For the explanation of the physical mechanism of NBTI, reference is made in particular to the following paper [1 ]](N.Goel and S.Mahapatra, Modeling of DC and ACNBTI degradation and recovery for SiON and HKMG MOSFETs, "in fundamental of Bias temporal instrumentation in MOS Transistors, S.Mahapatra, Ed.,1 st. NewDelhi, India: Springer,2016, pp.209-263.). For general analytical model derivation for R-D theory, reference is made in particular to the following paper [2 ]](Sanjay V.Kumar,Chris H.Kim,Sachin S.Sapatnekar,A Finite‐OxideThickness‐Based Analytical Model for Negative Bias Temperature Instability,IEEE Transactions on Device and Materials Reliability,vol.9,no.4,December2009,pp.537‐556.)。
Disclosure of Invention
The invention provides an analysis method for predicting NBTI long-time recovery based on a reaction-diffusion theory, which comprises the following steps:
the method comprises the following steps: acquiring device parameters of a p-MOSFET device;
step two: obtaining a general analytical model for describing NBTI long-time recovery based on a basic reaction-diffusion theory;
step three: fast recovery and H based on interface traps2Correcting the general analytical model;
step four: based on DH2The parameter ξ is introduced to modify the physical quantity changing along with time to obtain a complete analytical model for describing NBTI long-time recovery;
step five: and predicting NBTI long-time recovery of the p-MOSFET device according to the analytical model.
In the analytic method for predicting NBTI long-time recovery based on the reaction-diffusion theory, the device parameters of the p-MOSFET device comprise: the amount of threshold voltage degradation.
In the analysis method for predicting NBTI long-time recovery based on the reaction-diffusion theory, the general analysis model comprises the relation of the interface trap concentration at the initial moment of the recovery stage along with time, and the relation is expressed by the following formula (i):
wherein,
in the formula (i), Δ NIT(t) denotes the interface trap which is not restored at time t, Δ NIT(tstr) Represents the interface trap concentration, Δ N, at the initial moment of the recovery phaseIT(t) represents the concentration of interface traps repaired at time t, tstrIndicating the device stress time, ξ is used to describe H2Physical quantity of diffusion, Δ NH2 *(x is 0, t) represents time H2Concentration of diffusion front at interface, DH2Represents H2Diffusion coefficient of (d), trecDenotes the device recovery time, and t denotes the sum of the compression time and the recovery time.
In the analytical method for predicting NBTI long-time recovery based on the reaction-diffusion theory, after the rapid recovery amount of the interface trap is introduced, a corrected general analytical model is represented by the following formula (ii):
in the formula (ii), Δ VTRepresents the amount of threshold voltage degradation, Δ V, caused by interface traps that do not recover at time tIT0Representing the amount of threshold voltage degradation introduced by the interface trap at the initial moment of recovery, FFASTIndicating the specific gravity of the amount of rapid recovery of interface traps in the total interface defects, ξ is the function of trec/tstrParameter of variation, trecDenotes the device recovery time, and t denotes the sum of the compression time and the recovery time.
In the analytical method for predicting NBTI long-time recovery based on the reaction-diffusion theory, H is further introduced2After the lock-in effect, the modified general analytical model is represented by the following formula (iii):
in the formula (iii), Δ VT(t) represents the amount of threshold voltage degradation by interface traps that do not recover at time t, Δ VIT0Representing the amount of threshold voltage degradation introduced by the interface trap at the initial moment of recovery, FFASTIndicating the proportion of the amount of rapid recovery of interface traps in the total interface defects, α indicating defect-locked H2In a ratio of total, ξ is a function of trec/tstrThe parameter of variation, t, represents the total time.
In the analytical method for predicting NBTI long-term recovery based on the reaction-diffusion theory, the expression of the time-varying parameter xi introduced in the fourth step is shown as the following formula (iv):
in formula (iv), ξ represents H2Physical quantity of diffusion and with trec/tstrChange, tstrRepresents the device stress time, trecRepresenting the device recovery time, a, ξ0And η are fitting parameters.
In the analysis method for predicting NBTI long-term recovery based on the reaction-diffusion theory, an analysis model for describing the NBTI long-term recovery is shown as the following formula (v):
in the formula (V), Δ VIT0Representing the amount of threshold voltage degradation introduced by the interface trap at the initial moment of recovery, FFASTIndicating the proportion of the amount of rapid recovery of interface traps in the total interface defects, α indicating defect-locked H2In a ratio of total, ξ is a function of trec/tstrThe parameter of variation, t, represents the total time.
In the analysis method for predicting NBTI long-term recovery based on the reaction-diffusion theory, the analysis model for describing NBTI long-term recovery is further verified before the fifth step, and the method comprises the following steps:
performing numerical simulation on NBTI recovery based on an RD model to obtain the NBTI unrecoverable quantity and the change relation of the recoverable quantity along with time;
and substituting the data obtained by simulation into the analytical model to obtain analytical model parameters, and obtaining the coincidence condition of the analytical model and the RD numerical solution.
The invention has the beneficial effects that: the analytical model provided by the invention is incorporated into H2The diffusion coefficient of (2) decays along with the recovery time and the locking effect are two factors, and the effectiveness of the invention is verified by comparing with the numerical solution of the R-D model. The model is based on RD theory, and H is considered in the invention for the first time2The diffusion coefficient of (1) decays with recovery time andon the basis of the latch-in effect, an analytical relationship that threshold voltage degradation caused by NBTI is recovered along with time in a device recovery phase is proposed. The prediction result of the model can describe the NBTI long-time recovery condition of the device more accurately and conveniently. The analytical model has the advantages of less required parameters and wide applicability, and provides simple and accurate prediction for the reliability of devices.
Detailed Description
The present invention will be described in further detail with reference to the following specific examples and the accompanying drawings. The procedures, conditions, experimental methods and the like for carrying out the present invention are general knowledge and common general knowledge in the art except for the contents specifically mentioned below, and the present invention is not particularly limited.
The analysis method provided by the invention introduces an innovative NBTI analysis model, is based on the traditional RD theory and considers H2The long-term recovery of NBTI degradation is accurately calculated by the diffusion coefficient of (A) fading along with the recovery time and the locking effect. The analysis method of the invention comprises the following steps:
the method comprises the following steps: and acquiring device parameters of the p-MOSFET device. The device parameters of the p-MOSFET device include: the amount of threshold voltage degradation.
Step two: based on the basic RD theory, a general analytic model for describing NBTI long-time recovery is obtained
In the recovery phase, a portion of H is generated by the reaction near the original interface2Continue to diffuse into poly-Si with a portion of H near the interface2And reacting with an interface trap to repair the defect and realize the recovery of NBTI. H2The diffusion profile in poly-Si can be approximated as a triangle, as shown in fig. 2. Let Δ NIT(tstr) The interface trap concentration at the initial time of the recovery phase can be expressed by the area of the triangle below the solid line in fig. 2. Delta NIT *(t) represents the concentration of interface traps repaired at time t, and can be represented by the area of the shaded portion in FIG. 2. Thus, at time t, an interface trap that is not restored may be expressed as
According to FIG. 2, the interface trap repaired at time t can be expressed as
Where parameter ξ is a time-varying physical quantity the area of the triangle under the solid line in fig. 2 is equal to the area under the dashed line, and therefore the interface trap concentration deltan at the initial moment of the recovery phaseIT(tstr) Can be expressed as
It should be noted that one H2Corresponding to two defects, the area of the triangle representing the defect concentration is therefore calculated without being multiplied by 1/2. From the expressions (1) to (3), the relationship of the interface trap concentration with time in the recovery stage is as follows
In the above formulas 1 to 4,. DELTA.NIT(t) denotes the interface trap which is not restored at time t, Δ NIT(tstr) Represents the interface trap concentration, Δ N, at the initial moment of the recovery phaseIT *(t) represents the concentration of interface traps repaired at time t, tstrIndicating the device stress time, ξ is used to describe H2Physical quantity of diffusion, Δ NH2 *(x is 0, t) represents time H2Concentration of diffusion front at interface, DH2Represents H2Diffusion coefficient of (d), trecDenotes the device recovery time, t denotes the total time equal to (═ t)rec+tstr)。
Equation (4) above is consistent with conventional RD theory and can be used to blur the description of the slow recovery of NBTI. However, equation (4) ignores a part of the interface traps recovered due to the fast capture of electrons. Combined formulae (4) and Δ VIT=q*(ΔNIT)/CoxThe amount of threshold voltage degradation caused by NBTI during the recovery phase varies with respect to time as follows (4'):
wherein, is Δ VIT0Indicating NBTI degradation caused by the original interface traps. Equation (4') can briefly describe NBTI recovery behavior, but theoretically has serious limitations: 1) fast recovery is not considered; 2) do not consider H2The amount of irrecoverability due to lock-in effects; 3) is not taking into account H2Based on the time decay of the diffusion coefficient of (c), the time dependence of the parameter ξ is obtained.
Step three: consider the fast recovery of a portion of interface traps and a portion of H2The locking effect of (2), the model is corrected.
Step 3a: introduction parameter FFAST. If using Δ VIT0Representing NBTI degradation due to the original interface trap, then Δ VIT1=ΔVIT0*FFASTThe amount of rapid recovery that can be used to represent NBTI degradation. It should be noted that after some of the interface traps are neutralized by electrons, they can still react with H2The defect is reacted and repaired, but the Si-H bond recovery at this time does not contribute to the overall NBTI recovery.
According to the formula (4), based on H2The amount of interfacial repair can be expressed as Δ NIT0*(ξ*trec/t)1/2But wherein the ratio is FFASTHas been neutralized by electrons and no Δ V can be recalculatedTSo that the total recovery is Δ NIT0*FFAST+ΔNIT0*(1-FFAST)*(ξ*trec/t)1/2. Bound Δ VIT=q*(ΔNIT)/CoxNBTI long term recovery can be expressed as
And step 3 b: during the device compression phase, a portion H2Locked in traps, causing a portion of NBTI degeneration to fail recovery, so a parameter α needs to be introduced to describe the amount of unrecoverable H of FIG. 22Does not contain locked H in the distribution2Accordingly, the combination of formula (4) is based on H2Should correct the amount of interfacial repair to Δ NIT0*(1-α)*(ξ*trec/t)1/2. The total recovery amount can be expressed as Δ N in view of electron captureIT0*FFAST+ΔNIT0*(1-FFAST)*(1-α)*(ξ*trec/t)1/2. Equation (5) can be modified to
In formulae (5) and (6), Δ VT(t) denotes the boundary that did not recover at time tAmount of threshold voltage degradation, Δ V, due to surface trapsIT0Representing the amount of threshold voltage degradation introduced by the interface trap at the initial moment of recovery, FFASTIndicating the proportion of the amount of rapid recovery of interface traps in the total interface defects, α indicating defect-locked H2In the proportion of the total amount, tstrRepresents the device stress time, trecDenotes the device recovery time, t denotes the sum of the compression time and the recovery time, ξ is description H2Physical amount of diffusion.
Step four: consider DH2Is a time-varying physical quantity, and introduces a time-varying expression of the parameter ξ
With restoration of interface traps, H2The time required to find a defect is longer and longer, so D can be equivalently regarded asH2Decays over time. The above formula (4') is deduced to be H2The diffusion coefficient is uniformly constant in the compression phase and the recovery phase, but theoretically, in the recovery phase DH2Is a physical quantity that changes with time.
H in poly-Si during device recovery2There are two possibilities of diffusion when diffusing: (1) diffusing to the interface and repairing the defect; (2) continue to diffuse into the poly-Si. If it is symmetric diffusion (symmetric diffusion means H in the system)2The same degree of diffusion into the interface or into the poly-Si), ξ should be equal to 0.5, but at the beginning of recovery, near the interface H2Higher concentration of H near the interior of poly-Si2Low concentration and H in the system2The concentration is constantly changing, therefore H2Not likely to be symmetric diffusion, ξ is a time-varying parameter if H2Are all flared, ξ equals 1 if H2All extending toward the interface, ξ should be equal to 0. during the initial phase of recovery, H is near the interface2Is consumed rapidly to cause H diffusion to the vicinity of the interface2The concentration gradient is much greater than the diffusion of H to the deep poly2A concentration gradient. Thus, H2Diffusion rate near the interface is much higher than ambient, making ξ less than 0.5 with H2Consumption of H2The concentration gradient decreases continuously, but close to the interfaceThe rate of decrease of the nearby concentration gradient must be faster than the rate of decrease at the poly depth, so ξ increases with time, and as recovery progresses, the interfacial defects gradually decrease, H2The longer and longer the time required to find the interface defect, the H will be caused finally2Build-up at the interface, thereby reducing the diffusion of H to the interface2Concentration gradient such that ξ increases with time, known paper [2 ]]The general RD model numerical solution and analytic model are used to obtain the relationship of the parameter ξ with continuously increasing time, but no specific relationship of ξ with time is determined.
Thus, the present invention introduces an expression of the time-varying parameter ξ for characterizing H2The effect of diffusion coefficient decay over time on NBTI recovery. In consideration of DH2Decay with time and H2On the basis of the locking effect, the change relation of the parameter ξ with respect to time is obtained by using an RD model numerical solution and an analytic model, and the details are as follows:
determining parameter F using RD modelFASTAnd α, combining the numerical solution of RD model and the formula (6), calculating ξ value and obtaining ξ about trec/tstrAs indicated by the symbol in fig. 3, it can be seen that ξ relates to trec/tstrExhibits an approximately logarithmic relationship, but ξ is related to log (t)rec/tstr) Is not perfectly proportional, so the correction term (t) continues to be introducedrec/tstr)ηξ are obtained for trec/tstrIs expressed as follows
Wherein a, ξ0And η are fitting parameters.
From analytical formula (7), the solid line in FIG. 3 is obtained, and it can be seen that formula (7) can accurately express ξ with respect to trec/tstrThe analytical relationship of (1).
In the above formula (7), ξ is the description H2Diffused articleRational and with trec/tstrChange, tstrRepresents the device stress time, trecRepresenting the device recovery time, a, ξ0And η are fitting parameters.
And after the fourth step, further verifying the analytical model. The specific verification steps are as follows:
step 4 a: and performing numerical simulation on the NBTI recovery based on the RD model to obtain the change relation of the NBTI recoverable quantity and the unrecoverable quantity along with time.
And 4 b: and substituting the data into the analytical model to obtain analytical model parameters, and obtaining the coincidence condition of the analytical model and the RD numerical solution.
NBTI Long term recovery is shown as (6), equivalent to Δ VIT2Is recovered and can be rewritten as
Due to the locking effect of H2, a part of the interface is broken (N)IT0α) is unrecoverable, but a portion thereof is neutralized by electrons, so the total unrecoverable amount should be
PTG=ΔVIT0(1-FFAST)α (9)
From (8) and (9), Δ VIT2Can be divided into unrecoverable amount and recoverable amount, the latter can be expressed as
Fig. 4 shows that the proposed analytical model can be well matched with the numerical solution of the RD model, thereby verifying the validity of the analytical model.
In the above formulae 8-10,. DELTA.VIT2(t) represents the amount of unrecovered threshold voltage degradation introduced by the interfacial defect at time t, Δ VIT2,SDRepresenting the amount of threshold voltage degradation, P, that can be recovered at time t but has not yet been recoveredTGDenotes the amount of unrecoverability,. DELTA.VIT0Representing the amount of threshold voltage degradation introduced by the interface trap at the initial moment of recovery, FFASTIndicating the proportion of the amount of rapid recovery of interface traps in the total interface defects, α indicating defect-locked H2In the proportion of the total amount, tstrRepresents the device stress time, trecIndicating device recovery time, ξ is description H2Physical amount of diffusion.
Step five: and predicting NBTI long-time recovery of the p-MOSFET device according to a complete analytical model. The method comprises the following specific steps:
step 5a, placing the p-MOSFETs device under an NBTI stressed condition, and testing the relation of the change of the threshold voltage of the device along with time;
step 5b, after the device is stressed for a long time, removing the grid voltage to enable the device to enter a recovery state, and continuously testing the time-varying relation of the threshold voltage of the device;
and 5c, obtaining the threshold voltage degradation quantity delta V caused by the interface trap of the device at the initial recovery moment according to the RD model by using the dataIT0Fitting to obtain related parameters in an analytical model by combining the change data of the threshold voltage degradation quantity of the device in the recovery stage with respect to time;
and 5d, predicting NBTI long-time recovery by the analytical model by using the parameters obtained by fitting.
The model considers H for the first time according to RD theory2On the basis of the diffusion coefficient attenuation along with the recovery time and the locking effect, the analytical relation that the threshold voltage degradation caused by NBTI is recovered along with the time in the device recovery phase is provided. The model can predict the NBTI long-time recovery condition of the device more accurately.
The protection of the present invention is not limited to the above embodiments. Variations and advantages that may occur to those skilled in the art may be incorporated into the invention without departing from the spirit and scope of the inventive concept, and the scope of the appended claims is intended to be protected.