CN1018953B - Trap Charge Relaxation Spectroscopy Method and Its Measurement System - Google Patents

Abstract

The invention belongs to the semiconductor measurement technology, and in particular relates to the detection technology of the insulating layer trap charge in the MOS system. The method of trap charge relaxation spectroscopy and its measurement system (TCRS) adopts a new differential sampling technique and a high-resolution common-mode input current compensation test circuit, which solves the direct measurement of insulating layer trap parameters and different types of traps for the first time separation detection problem. This spectral peak analysis technique is higher in measurement accuracy and sensitivity than existing detection methods and equipment, and is intuitive and convenient. It is of great significance to the research on the reliability and service life of VLSI circuits and devices.

Description

Trap Charge relaxation spectra method and its measuring system

Technical field is the semiconductor test technology under this patent, mainly relates to the detection method and the device of all kinds of trapped charges in the MOS system insulation layer.

About insulation course in the MOS system (mainly is SiO ₂) the existing detection technique of carrier traps electric charge:

(1) flat-band voltage bleach-out process: when to SiO ₂When injecting electronics, trap wherein can form the oxide layer volume charge by continuous trapped electron, causes the flat-band voltage (V of MOS structure _FB) change in time, can estimate trap density and capture cross-section in the oxide layer thus.

(2) high-field stress method: adopt constant voltage, or steady current, or High-Field strain method such as linear voltage, at SiO ₂In the body or interface produces a series of positive and negative trapped charges, modulation SiO ₂Cathode electric field makes Fowler-Nordheim tunnel current or tunnel voltage (V _FN) the time of origin associated change, utilize the method for computer fitting to determine the trapped charge parameter.

What the flat-band voltage drift method was measured is total charge trap insulation layer effect, can not discern dissimilar trapped charges and distribution thereof, and the method for definite capture cross-section is relatively more difficult, and degree of accuracy is very low.Also there is same problem in the high-field stress method, and is not directly perceived so the difficulty of computer fitting is very big because body internal trap kind is a lot, and can't isolate the centre of moment and two physical quantitys of surface density.

Existing detection technique about mobile ion trapped charge in the insulation course:

(1) temperature experimental technique (BT) partially: under constant temperature (423 ° of K-473 ° of K), the MOS structure is applied the bias voltage of opposed polarity respectively, mobile ion is driven to different near interfaces, make flat-band voltage (V _FB) change, by the C-V characteristic that obtains after inclined to one side processing of positive and negative twice temperature, can extrapolate the surface density of mobile ion.

(2) triangular voltage sweep method (TVS): under higher temperature (423 ° of K-473 ° of K), mos capacitance is added slow scanning voltage, drive mobile ion, the gas current that made on constant displacement current superposition, an electric capacity (electric current) peak on quasi static C-V curve, occurred, can calculate the mobile ion surface density from the area at peak.

(3) heat shock gas current method (TSIC): under certain electric field, temperature gradually raises, mobile ion is ejected from trap, form gas current, corresponding current peak occurs, utilize the area at peak and surface density, energy level depth and the jump frequency that the position can solve mobile ion.

(4) field helps heat shock gas current method (FA(T) SIC): both consider temperature activated mobile ion effect, also considered field effect (adopting Poole-Frenkel field effect trap model to describe).Be size, the position at movable ionic spectrum peak, not only relevant with temperature, and also relevant with an alive sweep speed.

The shortcoming of BT method be sensitivity low (can only measure～10 ¹⁰Cm ^-2Above mobile ion amount), is subjected to effect of the interface big, can not distinguishes the mobile ion kind, can not provide energy level depth.Though additive method sensitivity is very limited a little more than BT, and still there is variety of problems.Such as the TSIC technology, though provided the mobile ion surface density, three basic parameters of energy level depth and jump frequency are not considered field effect, and experimental temperature is higher, and can't handle the situation that jump frequency is the function of temperature.

Based on the deficiency of above-mentioned traditional measurement work, we have invented a kind of new check and analysis technology and test macro.Be called MOS charge trap insulation layer relaxation spectrum method (TCRS) and measuring system (TCRSS) thereof.

The TCRSS measuring system is mainly by the trap Charge relaxation spectra instrument, signal source, and digital-to-analogue, analog to digital converter, microcomputer (microcomputer comprises a computer-aided test, calculating and pattern analysis software package, abbreviates the TCRSS system software package as) is formed.Its hardware block diagram is seen Fig. 1.

The core circuit of trap Charge relaxation spectra instrument adopts a kind of common mode input current offset-type circuit (see figure 2), utilizes multipole switch, and this circuit can be changed into difference-mode input circuit (see figure 3).

The TCRSS system software package is an ingredient of VLSI/ULSI MOS structure trap Charge relaxation spectra instrument, application menu drives the interactive program method for designing and develops, it can comparatively accurately analyze Trap Characteristics under the MOS structure oxide layer high-field stress condition, and test, control, analysis, graphing capability and the good user interface of providing convenience for the user.As shown in Figure 4, the TCRSS system software package mainly is made up of main program module, control and test procedure module, DAP module, pattern analysis program module and five parts such as result's storage and written-out program module.To make brief description respectively to the functional structure and the design concept of this several sections below.

(1) main program module

Main program module is total guiding of system and administration module, the guiding and the System self-test that comprise operating system, the foundation of the required language environment of TCRSS system software package, the introducing of the required form watch of graphics package, register system user's name and service time, the function that the self-starting guiding enters several aspects such as TCRSS system software package main management menu.

(2) control and test procedure module

Control and test procedure module are made up of several sections such as normal signal test, random signal test and periodic signal test and corresponding test condition remote control procedure.

The TCRSS system software package provides following ten control function:

1. interface initialization function;

2. normal running and demarcation mode are selected;

3. inquiry mode is selected;

4. unitary sampling time and Validity Test figure place are selected;

5. test job model selection (DC current and voltage tester, alternating current and voltage tester etc. are equipped with suitable probe, also applicable to physical parameters such as probe temperatures);

6. test data transmission mode control;

7. measurement range selection (automatic/hand);

8. select from triggering continuous real-time testing mode;

9. float the time and the drift calibration;

10. the output error state is selected.

Considering the similarity of testing software main structure body, is example with normal signal test procedure process flow diagram (see figure 5) here, and the structural principle of test procedure is described.

(3) DAP module

The DAP module can be divided into the insulation course PITFALL ANALYSIS by its function, several sections such as mobile ion analysis.The core of trap Charge relaxation spectra method is a finite-difference algorithm, obtain the good finite difference open score of precision, and key is the interpolation algorithm of fixing a point.Interpolation algorithm commonly used has 3 Lagrangian methods of monobasic and Etta's gold stepwise method, and the former fast operation can reflect the variation tendency of spectral line, but precision is relatively poor, big rise and fall, and the latter then computing is very slow, but precision is very high.In order to obtain comparatively accurate result in the short period of time, the native system software package has adopted a kind of compromise algorithm, promptly takes out the algorithm that interested section (generally being less than 10 numbers) carry out secondary analysis based on monobasic three point interpolation result and solves this problem.

(4) pattern analysis program mould is fast

The pattern analysis program module comprises pattern analysis program and two parts of figure way of output control program.The pattern analysis program is based on the basic development environment of microcomputer and physical mathematics analysis the requirement of graphics software is designed voluntarily, provides to have the character that prompting and cursor indicate under the graphics mode and dose functions such as function, graphical window size set-up function, graphic display mode selection.The user can be as required the part whole or interested of analyzed pattern easily.This subprogram comprise physical quantity the time become relation curve drafting and several program modules such as routine analyzer, two relevant physical quantity function relation curve programs and semilog diagram conformal analysis program.Figure way of output control program mainly is to be used for the figure output control function of providing convenience to the user, comprises two parts of printer and plotting apparatus control program, makes the user can control factors such as the size of figure output and shape.

(5) result's storage and written-out program module

This subprogram designs for the user can be managed easily with the analytical test result.By using this part software, the user can store or read data of interest and manage and analyze to the file or the position of appointment.Simultaneously, consider the versatility of data and pattern analysis software package, also can use result that this subprogram obtains according to advanced test macros such as HP4145B and set up corresponding data file and analyze, these advanced test macro functions are further expanded and only need few spending.

The characteristics of TCRSS: 1. AC and DC parameter detecting compatibility; 2. have the high resolving power mode of operation, highly sensitive, be easy to detect little variable small-signal; 3. has the bi-directional tracking compensate function; 4. the common mode input characteristics has improved the antijamming capability of instrument.

Trap Charge relaxation spectra (TCRS) measuring technique:

At first utilize the TCRSS measuring system.Sample (MOS structure) is applied certain range of excitation voltage, measure the electric current of MOS structure.For example,, apply constant plus or minus voltage, measure FN tunnel current I(t) measuring insulation course carrier traps electric charge; And, then apply linear ramp to measuring insulation course mobile ion trap parameters, measure the displacement current and the gas current I(V of mos capacitance).At last electric current is carried out difference Sampling, ask its relaxation spectrum.

Be that example illustrates above-mentioned measuring technique to measure carrier traps electric charge parameter below.

Control image data by the TCRSS system software package, and raw data is done suitable formal argument: F=∫ ^τ _oJ(t) dt/q,

=ln(J(t)/J _o).J(t wherein) be t current density constantly, q is an electronic charge, and F is an electronic flow density, J _oBe initial current density,

Be logarithm normallized current density.Then, get suitable electronic flow density at interval, obtain an electric current difference

(KF)-

(F) as the change curve of the function of electronic flow density (F).We are referred to as the trap Charge relaxation spectra line, and wherein K is called the difference Sampling factor.

Because the generation time constant or the capture cross-section of the various traps of primary trap and high field excitation are different in the insulation course, then will show different peaks in the relaxation spectral line, the position at peak and highly represent corresponding trap parameter.Capture cross section of traps＜σ has been embodied in position (Fm) such as the peak 〉, the height at peak has implied trap density (N) and two parameters of the distribution lotus heart (X).

In the trap Charge relaxation spectra line, electronic flow density is taken as F at interval ₂=KF ₁, K is the difference Sampling factor, its span is about 1.2～1.0001, be determined on a case-by-case basis, when the K value get suitable the time, the inverse of relaxation spectral line peak position (Fm) has promptly been represented the numerical values recited of capture cross-section.

The schematic diagram of trap Charge relaxation spectra technology is Fig. 6.

The advantage of TCRS measuring method is:

(1) can distinguish different types of trapped charge effect.Because different trapped charges has the specific relaxation behavior that is different from other traps, thereby shows different spectrum peaks in relaxation spectrum.

(2) can directly provide three basic parameters of trap, particularly can provide the dynamic parameter-capture cross-section＜σ of trap intuitively 〉.

(3) degree of accuracy and highly sensitive.Owing to adopted the difference Sampling technology in the relaxation spectrum, initial current, saturation current influence that background current in the measuring process and other trapped charges are caused reduce to minimum, distinct spectrum peak character, make slight change more eye-catching.

Embodiment one: detect trapped charge parameter in the MOS insulation course

Here we are example with the relaxation under the constant voltage stress, illustrate to utilize the TCRS method to detect primary trap parameters in the insulation course.

Use TCRSS measuring system (Fig. 1), tested MOS sample is placed shielding specimen platform, sample stage is under the constant room temperature, applies the constant voltage stress effect with signal source, measures MOS insulation course (SiO by the trap Charge relaxation spectra instrument ₂) time correlation FN tunnel current.Its theoretical formula is:

J（t）＝AEc ²exp（-B/Ec） （3）

Here, be t current density constantly J(t), Ec is the insulation course (SiO that is applied ₂) cathode electric field, A, B are two constants relevant with material.If SiO ₂In have primary trap, these traps are captured negative charge in the tunneling electron organizator, the cathode electric field variable quantity of Chan Shenging is therefrom:

△Ec＝-qXNot（1-exp（-<σ>F））/∈iTox （4）

Wherein Not is primary trap density, and X is apart from Si/SiO ₂The lotus heart at interface,＜σ〉be average capture cross-section, ∈ i is SiO ₂Specific inductive capacity, Tox is SiO ₂Thickness, F are electronic flow density,＜σ〉and F can be expressed as:

<σ>＝（∫ ^τ _oσJdt）/F·q （5）

F＝∫ ^τ _oJ（t）dt/q （6）

Initial cathode electric field is Eo, and the cathode electric field variable quantity that primary trap causes is △ E, then

Ec（F）＝Eo+△E（F） （7）

Substitution (3) can obtain the approximate formula of tunnel current:

ln（J/Jo）≌（2+ (B)/(Eo) ） (△E)/(Eo)

＝-（2+ (B)/(Eo) ） (q)/(Eo∈iTox) XNot〔1-exp

（-<σ>F）〕 （8）

Here Jo is an initial current density, in case after the decision of effect voltage, preceding two of following formula is a constant, makes H=(2+ (B)/(Eo)) (q)/(Eo ∈ iTox), then have,

ln＝ln（J（F）/Jo）＝-HXNOt〔1-exp（-<σ>F）〕 （9）

Do difference Sampling, make F ₂=KF ₁, obtain

S（F）＝HXNot〔exp（-K<σ>F）-exp（-<σ>F）〕 （10）

Following formula is the theoretical expression of primary trap relaxation spectral line, makes (dS)/(dF) | _Fm=0 can release the position and the height at spectrum peak.

<σ>Fm＝ (ln K)/(K-1) （11a）

${\mathrm{S\; (F\; m)\; =\; HXN}}_{\mathrm{otK}}{}^{\frac{K}{\mathrm{1-K}}}\mathrm{·\; (1-K)\; (11b)}$

The position and the capture cross section of traps of being composed the peak by (11a) formula as can be seen have definite corresponding relation, when difference sampling factor K selects when suitable＜σ〉be approximately equal to the inverse (K generally gets between 1.2 to 1.0001) of peak position (Fm):

$\mathrm{＜\sigma \; ＞\; =\; lnK\; /(K\; -\; 1)Fm}$

When adopting different voltage effect polarity chron (substrate injects and grid inject), then obtain two relational expressions about peak height:

Separate this Simultaneous Equations and can obtain X and two parameters of Not.

This shows three basic parameters very intuitive and convenient obtaining trapped charge with this trap Charge relaxation spectra technology.Fig. 7 is an experimental patterns of trap Charge relaxation spectra method.

Embodiment two: about the measuring technique of mobile ion trap parameters in the MOS insulation course

Utilize the TCRSS measuring system not only can do routine measurement and detect the insulation course mobile ion, measure, easily and accurately distinguish and detect two or more mobile ions but also can do high resolving power.

When having two or more mobile ion in the insulation course (as Na ⁺, K ⁺Deng), because the part of different ions current peak overlaps, measure (as FA(T) SIC method with conventional method), will influence Measurement Resolution and degree of accuracy as a result greatly.

The concrete grammar that the present invention detects the mobile ion electric charge is:

Utilize the TCRSS measuring system, under hot conditions (350 ° of K-500 ° of K), tested MOS sample is applied linear ramp, sweep velocity is 0.5 volt/second to 0.01 volt/second, utilize the dynamic tracking compensate function of TCRSS, the constant displacement current compensation is fallen, obtain the higher mobile ion current spectrum of resolution (Fig. 8 (a)), wherein J ₁, J ₂It is respectively the peak value of two kinds of mobile ions.The tie-in equation of its peak point and ion trap parameter is:

$\mathrm{E\; =\; kTln\; (}\frac{\mathrm{2kTS}}{{\alpha }_V\beta }{\mathrm{<figure-callout\; id="1"\; label="V\; m"\; filenames="90104535\_DRIMG2.png,90104535\_DRIMG5.png"\; state="\{\{state\}\}">V</figure-callout>}}_m{}^{\mathrm{1\; /\; 2}}\mathrm{)\; +\; <figure-callout\; id="1"\; label="\beta \; V\; m"\; filenames="90104535\_DRIMG2.png,90104535\_DRIMG5.png"\; state="\{\{state\}\}">\beta \; V\; m</figure-callout>}{}^{\mathrm{1\; /\; 2}}\mathrm{(15)}$

Here E is a trap depth, and S is the effusion frequency of ion, and Vm is a crest voltage, and T is a heat-shock temperature, α _VBe linear sweep rate, k is the Baltzmann constant,

$\mathrm{\beta \; =\; (}\frac{{\mathrm{<figure-callout\; id="3"\; label="q"\; filenames="90104535\_DRIMG5.png"\; state="\{\{state\}\}">q</figure-callout>}}^3}{\mathrm{\pi \; \in \; iTox}}{)}^{\mathrm{1\; /\; 2}}$

Here Tox is a thickness of insulating layer, and ∈ i is SiO ₂Permittivity, q is an electric weight.

Do difference Sampling by the TCRS software package to measuring the ion-conductance flow pattern, get normalized characteristic =β V ^1/2/ kT obtains new gas current relaxation spectrum, J(K

)-J(

) (Fig. 8 (b)), the difference factor K generally gets 1.2 to 1.0001, and its spectrum peak equation is:

$\mathrm{2(}\frac{\mathrm{kT}}{\beta }{)}^2\frac{S}{a_v}\mathrm{exp\; (-}\frac{\mathrm{E\; i}}{\mathrm{kT}})$

Utilize two Simultaneous Equations under the close temperature can obtain the S and the Ei parameter of different ions trap.S among Fig. 8 (b) ⁺ ₁And S ^- ₂Be respectively the spectrum peak of reflection two class mobile ion character.

The superior part of TCRS technology is: owing between the different kinds of ions electric current interaction is arranged, such as first current peak among Fig. 8 (a) is not only first kind of gas current, also superposition second kind of gas current of a part, so FA(T) the ion trap parameter determined with peak value of SIC has been subjected to very big influence.From Fig. 8 (b) as can be seen, the TCRS technology is actually the rising edge of using first current peak and determines first kind mobile ion parameter, determine the second class mobile ion with the trailing edge of second current peak, influencing each other of such two class gas currents just is reduced to bottom line.Measurement Resolution and experimental precision have then been improved greatly.

Figure of description

Fig. 1 trap Charge relaxation spectra instrument measuring system (TCRSS) block diagram

Fig. 2 common mode input current offset-type circuit theory diagrams

The G operational amplifier

R ₁Feedback resistance

Z ₂Detected element

Z ₄Balanced compensated element

R ₃Balance resistance

Fig. 3 difference-mode input test circuit schematic diagram

The G operational amplifier

R ₁Feedback resistance

Z ₂Detected element

The structural principle block diagram of Fig. 4 trap Charge relaxation spectra instrument measuring system (TCRSS) software package

Fig. 5 normal signal test flow chart

Fig. 6 single-electron trap relaxation spectrum schematic diagram

A is normalized (F) relaxation spectral line

B HXNot=1, the TCRS relaxation spectral line during K=1.1

TCRS experimental patterns when injection of Fig. 7 grid and substrate inject

(a) substrate injects

(b) grid inject

Fig. 8 high resolving power mobile ion trap relaxation spectrum

(a) compensation mobile ion current spectrum J(V)

(b) TCRS relaxation spectrum

Claims (4)

1. A method for measuring MOS insulating layer trap charges by applying an excitation voltage to the sample to be tested, characterized in that it also includes: (1) Utilize the common-mode input current compensation circuit or the differential-mode input circuit to detect the current of the sample under test; (2) The relaxation spectrum of the trap charge is obtained by sampling the difference of the current of the measured sample. The relaxation spectrum is a function curve of the finite difference value of the current amplitude relative to the electron flux density, which has a peak characteristic. Peaks and peak positions are directly related to trap parameters. 2. According to claim 1, the MOS insulating layer trap charge measurement method is characterized in that the measured sample is placed at a constant room temperature, a constant excitation voltage is applied to the measured sample, and the current of the measured sample is differentially measured according to the following method: Take a sample for its relaxation spectrum: (1) Find the electron flux density F=∫ ^τ _o J(t)dt/q; (2) Calculate the logarithmically normalized current density

With respect to the finite difference of the electron flux density F

(K·F)-

(F), K takes 1.2 to 1.0001. 3. The method for measuring trap charges in the MOS insulating layer according to claim 1, characterized in that the sample to be tested is placed under high temperature conditions (350°K-500°K), and a scan rate of 0.5 volts/second to 0.01 V/s linear voltage sweep, the current of the sample under test is differentially sampled according to the following method to obtain its relaxation spectrum: (1) Find the normalized dimensionless quantity =βV ^1/2 /kT; (2) Finding the current density of mobile ions excited by field-assisted heating

For normalized dimensionless quantities

The finite difference J(K ·

)-J(

), K takes 1.2 to 1.0001. 4. A MOS insulating layer trap charge measurement system consisting of a trap charge relaxation spectrometer, a signal source, a digital-to-analog, an analog-to-digital converter, and a microcomputer system, characterized in that the trap charge relaxation spectrometer includes a common-mode input current Compensation circuit or differential mode input circuit, the microcomputer system contains a computer-aided test, calculation and graphic analysis software package, the software package includes: (1) Main program module; (2) Control and test program modules; (3) Data analysis program module; (4) Graph analysis program module; (5) Result storage and output program module.

Images