CN100538349C - Nano level high resolution stress measuring method - Google Patents

Abstract

Nano level high resolution stress measuring method relates to a kind of method for measuring stress, provides a kind of based on Auger electron spectrometer, as the excitaton source of measuring, can obtain the microcell method for measuring stress of the stress distribution value of high-space resolution with electronics.Its step is determined the chemical element composition and the ratio of sample with Auger spectroscopy, and is selected a zero stress point to search with 1 this prime element of sample and get its standard spectrum, as the stress Zero calibration for determining ultimate analysis and zero stress point; Utilization is searched the zero stress point standard spectrum of getting and is determined that fitting parameter must optimize the fitting theory auger spectrum; After setting up the stress calibration curve, the calibration curve that moves with stress according to the Auger of establishing gets the microcell stress value.Dirigibility is strong, can need to set up special model per sample and calculate, and also can set up the database of the STRESS VARIATION calibration curve of all compound elements.The spatial resolution that obtains is consistent with the Auger electron spectrometer of employing, can reach nanometer scale.

Description

Nano level high resolution stress measuring method

Technical field

The present invention relates to a kind of method for measuring stress, especially relate to a kind of high-resolution method for measuring stress in space of nanometer scale.

Background technology

Stress is the physical parameter on a basis, and corresponding force measurement also is exosyndrome material or device one a very important index.At present, the measuring method of microcell stress for solid material and photoelectric device commonly used, mainly contain Raman scattering spectrum (μ-Raman scattering spectroscopy), light fluorescence spectrum (Photoluminescence spectroscopy, PL) and x ray rocking curve methods such as (x-ray rocking curve).Wherein, Raman optical spectrum method mainly is to utilize visible light that sample excitation is produced Raman spectrum, and the moving of the Raman spectrum by measuring some special patterns, and is able to the distribution of measuring samples upper stress; The measuring method of PL spectrum also is similar to Raman optical spectrum method, is equally to measure spectral line to move the stress that obtains the sample microcell, and different is that it adopts exciting light; X ray rocking curve method is then utilized the diffraction effect of X ray, the strain that the deflection angle by the analytic sample crystal orientation comes measuring samples to cause under stress.Though, these traditional methods to a certain extent, the stress of reliable measurements sample comparatively, their spatial resolution can only reach micron dimension, also can only reach sub-micrometer scale under the best condition.The reason that causes their spatial resolutions to be difficult to improve comes from the character of the light beam of their employings.General wavelength of visible light scope is probably at 400-700nm, be about 360nm and arrived ultraviolet wavelength, after focusing on through optical focusing system, according to Rayleigh equation, the spot size that shines on the sample just can only be limited in sub-micrometer scale, and actual focusing system also can not reach good like this resolution, so be for micron dimension mostly; For X-ray, though it has very little wavelength, as the K of Cu _αThe line wavelength is 0.154nm, but very difficult to the focusing of X-ray, also can only obtain the hot spot of about 1 μ m diameter usually.Based on the limitation of such essential attribute, utilize the method for traditional stress measurement can not realize the high-resolution stress measurement needs in nanometer era space.

Electronics, at first it has very little wavelength, and under 100V accelerating potential situation, wavelength is 0.12nm only; Next utilizes, and electronic lens is very easy to carry out good focusing to it.So it on spatial discrimination, has overcome the limitation of light wave admirably, can reach the resolution of nanometer even Ya Nami.At present, based on the measuring technology of electronics,, all in the sign work of the material of minimum yardstick and structure, become very strong instrument as electron microscope (SEM), transmission electron microscope (TEM), Auger electron spectroscopy (AES) etc.

Summary of the invention

The objective of the invention is at the deficiency in the prior art, provide a kind of, as the excitaton source of measuring, can obtain the microcell method for measuring stress of the stress distribution value of high-space resolution with electronics based on Auger electron spectrometer.

Step of the present invention is as follows:

1) ultimate analysis and zero stress point are determined.At first the sample surfaces of measuring is cleaned, remove surface contamination, with accuracy and the degree of accuracy that guarantees to measure.Determine the chemical element composition and the ratio of sample then with Auger spectroscopy, and, select a zero stress point to search and get its standard spectrum, as the stress Zero calibration with certain this prime element of sample.

2) theoretical Auger spectroscopy match.At first set up the compound structure model identical, adopt the analog computation of first principle simulated calculation, obtain the data of the density of electronic states of surface-element with sample.According to the CVV theory, auger spectrum is expressed as the function of valence electron density of states convolution, can get following theory spectrum computing formula through optimizing to revise

${\mathrm{\Γ}}_{\mathrm{CVV}}\left(E\right)=a_{\mathrm{pp}}{D}_p\left(E\right)\⊗D_p\left(E\right)+a_{\mathrm{sp}}{D}_s\left(E\right)\⊗D_p\left(E\right)+a_{\mathrm{ss}}{D}_s\left(E\right)\⊗D_s\left(E\right),---\left(1\right)$

Wherein,

With

Be the convolution integral value of density of electronic states, their linear combination has constituted auger spectrum, a _Pp, a _Sp, a _SsIt is the fitting coefficient of three correspondences.Utilize the standard spectrum of searching the zero stress point of getting in the step 1), determine three fitting parameters, can draw the theoretical auger spectrum of optimizing match.

3) set up the stress calibration curve.Calculate the model under the different stress, according to formula (1) and the definite optimization fitting parameter a in front _Pp, a _Sp, a _Ss, further calculate the theoretical auger spectrum under the different ess-strains.Analyze this a series of auger spectrum, and draw the relation (can be analytical form, also can be the numerical value form) between stress and the relative displacement of auger spectrum peak, i.e. stress calibration curve.

4) measurement of stress.Adopting accuracy of measurement to be the energy step-length of 0.1～0.5eV, chosen elements is carried out pointwise search spectrum.Simultaneously some stable elemental impurities (as carbon or argon) are carried out pointwise synchronously and search spectrum, be used for the demarcation of the possible electric charge accumulation in surface, to deduct the interference that charge shift is brought.The power spectrum of collecting is analyzed, and the power spectrum that the deduction charge shift causes moves, and the Auger physics that obtains being caused by microcell stress merely moves.According to step 2) in the Auger established move calibration curve with stress, draw the microcell stress value.

The cleaning of sample surfaces is that chemical cleaning and physics clean, and said chemical cleaning is cleaned sample surfaces for adopting acetone, ethanol and distilled water, and physics cleans to using Ar ⁺Clean carrying out etching near the measured zone.

Topmost key features of the present invention is the stress distribution that can obtain high-space resolution, it is based on the measurement that Auger electron spectrometer carries out simultaneously, and because combine the calculating of the first principle of mature and reliable, dirigibility is very strong, can need to set up special model per sample calculates, also can set up the database of the STRESS VARIATION calibration curve of all compound elements, in addition, also can carry out the analysis of the more deep character such as electronic structure relevant with stress.

Description of drawings

Fig. 1 is the sem photograph in GaN sample [11-20] the direction cross section of epitaxial lateral overgrowth.1 is Sapphire Substrate among the figure, and 2 is the GaN template, and 3 is the SiN masked areas, and 4 is the window area of mask, and 5 is unassembled strip cavity, and 6 is sample surfaces, (a) is the stress measurement zone.

Fig. 2 is that argon ion is to the Auger electron spectroscopy comparison diagram before and after the sample in cross section etching cleaning.Before (a) is argon ion etching among the figure, (b) be argon ion etching after, horizontal ordinate is kinetic energy (eV), ordinate is intensity (a.u.).

Fig. 3 is the s and the p partial wave density of electronic states figure of surperficial N element in the GaN model.Among the figure, horizontal ordinate is energy (eV), and ordinate is intensity (a.u.).

Fig. 4 is the fitted figure of N element standard K VV auger spectrum and theoretical spectrum.Dotted line is the component of three different convolution items among the figure.Among the figure, horizontal ordinate is energy (eV), and ordinate is intensity (a.u.).

Fig. 5 is the N element KVV auger spectrum displacement of theory and the calibration curve of dependent variable.Among the figure, horizontal ordinate is dependent variable (%), and ordinate is the NCVV Auger peak shift amount of moving (eV).

Fig. 6 is a different film micro area N KVV auger spectrums peak position distribution plan.Among the figure, horizontal ordinate is the distance (μ m) to mask, and ordinate is kinetic energy (eV).

Fig. 7 is the ess-strain distribution plan of the different film micro areas measured.Among the figure, horizontal ordinate is the distance (μ m) to mask, and ordinate is dependent variable (%).

Embodiment

Choose the sample of intending carrying out stress-strain test, sample should satisfy the requirement of Auger electron spectroscopy test, as good electric conductivity, non-volatile, anti-oxidant etc.In addition, for carrying out stress measurement accurately and reliably, sample also should have high chemical purity, and low-doped character is good.Be example with GaN semiconductor samples (its sectional view as shown in Figure 1) below, the present invention is elaborated.

＜1〉sample is at first tentatively cleaned.Ultrasonic cleaning 5min in acetone soln; Take out sample repeatedly, place ethanolic solution ultrasonic cleaning 5min again with the ethanolic solution rinsing; Take out sample rinsing in distilled water and place distilled water ultrasonic cleaning 5min at last for several times.

＜2〉cleaning finishes, and puts sample and dries in baking box.Afterwards, sample is fixed on the sample stage with the conduction double faced adhesive tape, and sends into the Sample Room of Auger electron spectroscopy.Treat that Sample Room vacuum tightness is evacuated to 10 ^-5Pa sends into sample in the vacuum chamber.

＜3〉treat ER equipment ready, utilize the electron microscopic observation of energy spectrometer and determine the zone of desiring to measure.Before measurement, open Ar ⁺Rifle, low angle (＜30 °) cleans carrying out etching near the measured zone, and to remove contaminated sample surfaces layer, etching time is unsuitable long, is advisable to 15s with 5s.This is in order to allow the surface go up remaining a small amount of simple substance C element so that make the usefulness of the demarcation of charge shift, to look concrete condition, also can making electric charge with the Ar element and demarcate.Fig. 2 has provided the auger spectrum that sample surfaces is carried out the argon ion etching front and back, and C element peak obviously reduces after the etching, illustrates that the C element is present in sample surfaces with the pollutant of simple substance form, can make the usefulness of the demarcation of charge shift.In addition, element spectral peaks such as Ga, N, O are stable, illustrate that the chemical stability of GaN sample is good, and the O element does not influence the accuracy of measurement result for mixing on a small quantity unintentionally.

＜4〉at sample surfaces (label 6 places among Fig. 1) the N element is searched the integral spectrum of getting the KVV spectral line, as standard spectrum, in order to the match of theory spectrum, and as the reference point of stress.When searching spectrum, (0.1～0.5eV), the stacking fold of searching spectrum also should be more than 100 times for the very crucial high energy step-length that should adopt.

＜5〉first principle simulated calculation.The Fotran program that compiles on the basis of local density functional's theory is carried out first principle and is calculated.And the mould conservation pseudo potential of the Ga that utilized this program structure and N atom is in order to calculate the GaN system, the expansion first-harmonic function that calculates adopts the mixing basic vector of plane wave and Bloch ripple, so just can obtain the valence electron character of surface atom very accurately, simulate the requirement of match work with the theoretical auger spectrum of being satisfied with.

＜6〉utilize＜5〉the middle program of being compiled, carry out the first principle analog computation of GaN, obtain the partial wave density of states of the valence electron of surperficial N atom.Because the GaN sample is the structure of wurtzite, i.e. HCP structure, so constructed the super primitive unit cell of GaN in the analog computation, this super primitive unit cell with [000-1] direction N atom as the surface.Result of calculation has obtained the valence electron s of superficial layer N element and the partial wave density of states of p attitude, as shown in Figure 3.

＜7〉s of N and p attitude density of electronic states are intersected convolution.Utilize convolution integral

$D_V\left(E\right)\⊗D_V.\left(E\right)=\mathrm{d\ω}{D}_V\left(\mathrm{\ω}\right)D_{V\′}(E-\mathrm{\ω})---\left(2\right)$

Here, D _V(E) the partial wave density of states of expression valence electron.Utilize this expression formula, be programmed into line number value integration, obtain

With

Convolution results.

＜8 〉, obtain theoretical N KVV auger spectrum by match standard N auger spectrum.According to the result of research, the Auger spectroscopy of KVV form in theory is the linear combination of convolution item of the density of states of valence electron, so theoretical KVV auger spectrum can use formula (1) to represent:

${\mathrm{\Γ}}_{N,\mathrm{KVV}}\left(E\right)=a_{\mathrm{pp}}{D}_p\left(E\right)\⊗D_p\left(E\right)+a_{\mathrm{sp}}{D}_s\left(E\right)\⊗D_p\left(E\right)+a_{\mathrm{ss}}{D}_s\left(E\right)\⊗D_s\left(E\right),---\left(1\right)$

A wherein _pP, a _Sp, a _SsBe the coefficient of three convolution items, the match that can compose is by experiment determined.With the match of standard N KVV auger spectrum, determine optimized fitting coefficient a _Pp, a _Sp, a _SsBe respectively 0.35,0.18 and 0.47, the theoretical auger spectrum that obtains like this can coincide finely with experimental spectrum, as shown in Figure 4.

＜9〉the GaN model under the differently strained environment of analog computation, and obtain the partial wave density of electronic states of N atom and their convolution, the optimization coefficient a that determines above utilizing _Pp, a _Sp, a _Ss, further obtain the KVV auger spectrum of the N under the different ess-strains.Relatively these auger spectrums calculate relatively moving of their spectrum peaks, in conjunction with corresponding strain value, can set up strain and move calibration curve with the spectrum peak.As shown in Figure 5, the displacement at N element KVV Auger peak and the calibration curve of strain among the GaN.Certainly, different material systems, the relation between them may be different, but can establish the calibration curve of Auger peak shift and strain by this computation model.Utilize this theoretical calibration curve, just can obtain the stress distribution of sample by measuring the mode of Auger peak shift.

＜10〉choose the microcell that will carry out stress measurement,, adopt and a little search spectrum as (a) zone that vertical line is marked among Fig. 1.Mainly two kinds of elements of N, C are carried out specific aim and search and get integral spectrum, should take little energy step-length when searching spectrum equally, and do repeatedly circulation stack, to guarantee the reliability of microcell spectrum.(a) location is at the intersection of the SiN of GaN sample mask and window, and the STRESS VARIATION situation is more special, and the meaning of be worth investigating is arranged, and the change profile of main is this regional stress is comparatively trickle, needs high-resolution stress measurement to understand its physical property.

＜11 〉, get rid of the spectrum peak drift that the surface charge accumulation causes to the N auger spectrum of top gained.At first the drift of the C auger spectrum of each point is demarcated.The C auger spectrum do not have charge shift the time standard kinetic energy be 268.5eV, each point C peak is the charge shift amount at auger spectrum peak, each point place with respect to the drift of this standard kinetic energy.Come again, the kinetic energy position at N Auger peak is detained go its charge shift amount, just got rid of the influence of charge displacement, obtain not having the N auger spectrum peak of charge displacement.

＜12〉the kinetic energy position at measuring N KVV peak.Measure the N element KVV spectrum peak kinetic energy values of each point on (a) perpendicular line, the result as shown in Figure 6.

＜13〉draw the ess-strain value in measured zone.With＜4〉in determined zero stress point N auger spectrum be benchmark, can try to achieve the spectrum peak with respect to the relative shift of reference value from the spectrum peak kinetic energy values of Fig. 6 gained.With this displacement, utilize the calibration curve among Fig. 5, just can converse the Strain Distribution situation of each microcell on (a) line, the result is as shown in Figure 7.From this STRESS VARIATION situation, we begin to have the stress release region of a key from mask " 3 " as can be seen, and this zone is until about 3.0 μ m places, mask top, here the position of the joint of the cavity shown in label among Fig. 1 " 5 " just.So the stress measurement of this high-space resolution can be explained the stress evolution of sample microcell well, thereby understands the growth of material and the character of physics.

Claims (4)

1. nano level high resolution stress measuring method is characterized in that the steps include:

1) determines ultimate analysis and zero stress point, at first the sample surfaces of measuring is cleaned, determine the chemical element composition and the ratio of sample then with Auger spectroscopy, and with 1 this prime element of sample, select a zero stress point to search and get its standard spectrum, as the stress Zero calibration;

2) fitting theory Auger spectroscopy, at first set up the compound structure model identical with sample, adopt the analog computation of first principle simulated calculation, obtain the data of the density of electronic states of surface-element, be expressed as the function of valence electron density of states convolution, the theory spectrum computing formula of revising followingly according to the theoretical auger spectrum of CVV

${\mathrm{\Γ}}_{\mathrm{CVV}}\left(E\right)=a_{\mathrm{pp}}{D}_p\left(E\right)\⊗D_p\left(E\right)+a_{\mathrm{sp}}{D}_s\left(E\right)\⊗D_p\left(E\right)+a_{\mathrm{ss}}{D}_s\left(E\right)\⊗D_s\left(E\right),---\left(1\right)$

Wherein,

With

Be the convolution value of density of electronic states, their linear combination has constituted auger spectrum, a _Pp, a _Sp, a _SsBe the fitting coefficient of three correspondences, utilize the standard spectrum of searching the zero stress point of getting in the step 1), determine three fitting parameters, draw the theoretical auger spectrum of optimizing match;

3) set up the stress calibration curve, calculate the model under the different stress, according to formula (1) and the definite optimization fitting parameter a in front _Pp, a _Sp, a _Ss, calculate the theoretical auger spectrum under the different ess-strains, draw the relation between stress and the relative displacement of auger spectrum peak, i.e. the stress calibration curve;

4) measure stress, adopt accuracy of measurement to be the energy step-length of 0.1～0.5eV, chosen elements is carried out pointwise search spectrum, carry out pointwise synchronously and search spectrum stablizing elemental impurities simultaneously, be used for the demarcation of the electric charge accumulation on surface, to deduct the interference that charge shift is brought, the power spectrum of collecting is analyzed, the power spectrum that the deduction charge shift causes moves, the Auger physics that obtains being caused by microcell stress merely moves, move calibration curve with stress according to the Auger of establishing in the step 3), draw the microcell stress value.

2. nano level high resolution stress measuring method as claimed in claim 1, the cleaning that it is characterized in that sample surfaces is that chemical cleaning and physics clean, said chemical cleaning is cleaned sample surfaces for adopting acetone, ethanol and distilled water, and physics cleans to using Ar ⁺Clean carrying out etching near the measured zone.

3. nano level high resolution stress measuring method as claimed in claim 1 is characterized in that the pass between stress and the relative displacement of auger spectrum peak is analytical form or numerical value form.

4. nano level high resolution stress measuring method as claimed in claim 1 is characterized in that said stable elemental impurities is carbon or argon.

Images