CN1821748A - Optical sensor for thin film detection - Google Patents

Abstract

This invention discloses an optical sensor composed of pump diode lasers, a chopper and a beam splitter prism, in which, the first pump diode laser and the second pump diode laser output two beams of laser of different frequencies and output a beam laser by regulation of the chopper to irradiate on a dual grid splitter to form a 2-D beam array to be reflected on a CCD focal plane and imaged by a film sample to display the light spot position distribution information and the light intensity variety information of each spot of the reflection beam array to get the growing rate of the film by computing the transformation information of said light intensity, evaluate the film stress by beam offset information and Stoney equation and evaluate components of the material based on the incident light vacuum wavelength lambda< 0 > put forward by Brunner and function of the Al component x.

Description

Optical sensor for thin film detection

Technical field

The invention belongs to optical technical field, relate to film and detect specifically a kind of optical sensor that detects film growth rate and stress.

Background technology

Known in the industry, make the product quality degradation owing to STRESS VARIATION in the thin film fabrication process may cause inefficacy of film interior bonds and layering, thereby the control film there is significance in the deformation degree of manufacture process.The modern semiconductors process all requires electronics and optoelectronic device will carry out accurate control to the deposition process of membraneous material, present most process need be measured parameters such as gas flow rate, settling chamber's internal pressure, growing environment temperature, so that the deposition process of control membraneous material.These parameters generally are in order to grow certain thickness, certain microstructure and to satisfy the film of certain electrical property and optical property and predefined empirical parameter, just film characteristics records after deposition often accurately.This control mode is called " half-closed loop control " on control theory.In the reality; can be by improvement so that the more stable operation of film production equipment to control system; but since status of equipment during with ambient conditions regular meeting different variations takes place; thereby; these change and often to cause rate of sedimentation in process of production or membrane structure that the variation that can not estimate takes place; need depositing system strictly to be safeguarded and calibration at every turn, will increase production cost like this, reduce production efficiency.

In order to be implemented in the deposition process membrane stress is directly measured, and adjust parameters such as gas flow rate, pressure, temperature on this basis, reach the purpose of control membrane stress in deposition process, just realize " control of full cut-off ring " of deposition process, optical sensor technology becomes the selection of nature.Because they are contactless, can be installed in the outside, settling chamber, and insensitive to the strong-electromagnetic field of film growth apparatus generation.In addition, most thin film depositions need high pressure and chemical reaction environment, and this makes optical sensor become on-the-spot unique selection that detects.At present, domestic membrane stress checkout equipment mostly is the off-line type checkout equipment greatly.Yang Yin hall for example, Fu Junxing, people such as Zhou Duan are published in Chinese journal of scientific instrument, have described the membrane stress proving installation with the light reflection principle development in " proving installation of the semiconductor chip upper film stress " literary composition on 1997 18 phases.People such as Zhang GuoBing, Hao Yilong, field Daewoo are published in the semiconductor journal, have described in " research of the polysilicon membrane stress characteristics " literary composition on 1999 20 phases with light polarization phase-shifting principle of interference and have measured polysilicon membrane stress.External M.Bicker, U.von H ü lsen, people such as U.Laudahn are published in Review of scientific instruments, proposed a kind of method of utilizing two-way light reflection in-site measurement membrane stress in " Optical deflection setupfor stress measurements in thin films " literary composition on 1998 69 phases, undertaken by the sensor device of forming by diode laser light source, spectroscope and some optical mirrors, two photoelectric position detectors etc.Because the beam detection resolution of its PSD is 100nm, thereby two-beam must focus on the PSD surface in strictness, to reach the maximization of resolution characteristic.There are two shortcomings in this on-the-spot membrane stress detection system: the one, because two bundle laser must strictly focus on, require too high to Design for optical system, installation, debugger routine and maintenance; The 2nd, because the inertia of PSD when the sample high speed rotating, can only detect the average of full sheet stress, and detect powerless to the stress and the growth rate of film regional area.

The content of invention

The objective of the invention is to overcome the deficiency of above-mentioned existing measured thin film sensor device, provide a kind of can online while MEASUREMENTS OF THIN stress and growth rate, and can make the optical sensor for thin film detection of accurate estimation to film refractive index and material component.

The technical scheme that realizes the object of the invention is: make up a kind of optical sensor that detects film growth rate and stress, utilize this optical sensor to detect film growth rate and stress.This optical sensor comprises: pump diode laser, chopper, Amici prism, the binary raster beam splitter, wherein, two bundle laser of first pump diode laser and second pump diode laser output different frequency, modulation output beam of laser by chopper, this a branch of laser shines by Amici prism and forms the two-dimentional light beam array on the binary raster beam splitter, this beam array is reflected in imaging on the CCD focal plane through film sample, demonstrate the light spot position distributed intelligence of folded light beam array and each some intensity variations information, by calculating the stress that information that this light spot position distributes and intensity variations information draw film, growth rate, refractive index and film chemical component.

Utilize the method for described optical sensor detection film growth rate and stress, by reflectivity of optical thin film curve calculation film growth rate under the match virtual interface; Utilize optical lever offset information and Stoney Equation for Calculating membrane stress; The model that proposes the function of incident light vacuum wavelength λ 0 and al composition x according to Brunner is estimated material component.

Described optical sensor, wherein chopper is controlled by external circuit, makes two bundle laser of first pump diode laser and second pump diode laser output different frequency, alternately sees through chopper, finally only exports beam of laser and enters Amici prism.

Above-mentioned optical sensor, wherein the binary raster beam splitter is made up of two-dimentional Dammann grating and Fresnel zone plate, in order to produce auto-convergence multiple beam array.

Above-mentioned optical sensor, wherein each spot intensity of the two-dimentional light beam array that forms on the binary raster beam splitter and the interval between the luminous point are identical, and beam separation is adjustable, regulate this beam separation can utilize the divergencing laser beam lighting time, the divergence point that changes light beam changes distance between the dot-matrix array luminous point to the distance of beam splitter.

The method of above-mentioned detection film, wherein, carry out according to the following procedure by reflectivity of optical thin film curve calculation film growth rate under the match virtual interface:

(1) survey the reflected light light intensity by the CCD device and change the reflectance curve that obtains film growth,

(2) reflectance curve is carried out parameter fitting, calculate growth for Thin Film rate and refractive index information.

The method of above-mentioned detection film is wherein utilized beam deviation information and Stoney Equation for Calculating membrane stress, carries out according to the following procedure:

(1) substrate curvature change amount is measured, promptly use two-dimentional convergent beam array irradiate sample surfaces, the CCD device is surveyed the folded light beam array information on its reflection direction, and record incoming laser beam array pitch d, incident angle α, the yaw displacement δ and the film thickness h of the relative distance L between sample and sensor array, L place light beam _fParameter;

(2) calculate membrane stress by the change amount of substrate curvature

$\mathrm{\&sigma;}=\frac{1}{6}\&CenterDot;[\frac{1}{r_{\mathrm{post}}}-\frac{1}{r_{\mathrm{pre}}}]\&CenterDot;\frac{E}{1-v}\&CenterDot;\frac{h_s^2}{h_f}$

Wherein: σ is post-depositional membrane stress;

r _PostBe the substrate curvature of curved surface after the deposition;

r _PreBe the substrate curvature of curved surface before the deposition;

E is a Young modulus; V is the Poisson coefficient;

h _sBe substrate thickness;

h _fBe film thickness.

The present invention is owing to adopted the structure of building the optical sensing applicator platform, thereby can be implemented in the thin film growth process real-time detection to membrane stress and growth rate, and on this basis, adjust parameters such as gas flow rate, pressure, temperature and control membrane stress, thickness and chemical composition, the science and the accuracy of MOCVD test have not only been strengthened, make high performance semiconductor material of manufacturing and device become possibility, and can improve the quality and the output of the growth of MOCVD disk, realize the industrial-scale production of MOCVD equipment and product.

Description of drawings

Fig. 1 is a structural drawing of the present invention

Fig. 2 is the curve of light distribution figure of beam splitting successor of the present invention delegation luminous point

Fig. 3 surveys the schematic diagram of membrane stress for the present invention

Fig. 4 for the present invention at locational reflectivity change curve in time

Fig. 5 is the laser spots bundle array image of the present invention on CCD

Fig. 6 is a Flame Image Process process flow diagram of the present invention

Embodiment

Followingly the present invention is described in further detail with reference to accompanying drawing.

With reference to Fig. 1, optical sensor of the present invention is by first laser instrument 1, second laser instrument 2, controlled chopper 3, Amici prism 4, and binary beam splitter 5 is formed.This chopper (3) makes two bundle laser of the different frequency of first pump diode laser (1) and second pump diode laser (2) output by external circuit control, alternately sees through chopper, finally only exports beam of laser and enters Amici prism (4).This binary raster beam splitter (5) is made up of two-dimentional Dammann grating and Fresnel zone plate, in order to produce auto-convergence multiple beam array.The present invention adopts the structure of bi-coloured light incident and controllable optical chopper, can obtain the reflection of light rate change curve under two different wave lengths of same film deposition process shown in Figure 4, to improve measuring accuracy.Light path principle of the present invention is: the laser of first laser instrument 1 and second laser instrument, 2 output different frequencies, this two-beam is by being subjected to the modulation of the programme controlled chopper 3 of PC, make chopper 3 alternately block the light path of first laser instrument 1 and second laser instrument 2, only allow beam of laser wherein to enter Amici prism 4 at any time, the laser that sends when first laser instrument 1 during by chopper 3 through Amici prism 4 most of transmissives to binary beam splitter 5, at this moment the laser that sends of second laser instrument 2 is blocked by chopper 3; The laser that sends when second laser instrument 2 shines on the binary beam splitter 5 in that total reflection takes place on the Amici prism 4 during by chopper 3, and at this moment the laser that sends of first laser instrument 1 is blocked by chopper 3.Laser forms the beam array of a two dimension by binary beam splitter 5 backs, as shown in Figure 5, each spot intensity and the interval between the luminous point on this array are all identical, as shown in Figure 2, change this two-dimentional light beam array divergence point and can change distance between the dot-matrix array luminous point, realize that beam separation is adjustable to the distance of beam splitter.These luminous points on the beam array see through optical filter imaging on the focal plane 7 of CCD after film sample 6 reflections, demonstrate light spot position distributed intelligence and each some intensity variations information of folded light beam array, as shown in Figure 5.Light beam spot spacing data in this imaging has reflected the film surface curved transition in the deposition and the variation of membrane stress; Light beam spot intensity variations data in the imaging have reflected the variation and the change of refractive of film internal reflection rate.Beam array shown in Figure 5 reflects from stressless substrate surface, and promptly the dotted line dot matrix if there is heterogeneous being applied to of power to make its curature variation on the silicon chip, will cause the variation that reflexes to luminous point image space on the sensor, i.e. the solid line dot matrix.These information shown in Figure 5 are carried out analog to digital conversion by dsp processor system 8 to be become to send into PC after the numerical information and carry out running software, test out the stress of film with the light spot position distributed intelligence on the image, photoelectricity half-tone information with image tests out film growth rate and refractive index, and obtains film chemical component and refractive index.

Utilize the method for above-mentioned optical sensor on-line testing film to be: by reflectivity of optical thin film curve calculation film growth rate and refractive index under the match virtual interface; By the Stoney equation beam deviation information shown in Figure 5 is calculated, drawn membrane stress; The refractive index that utilization calculates is by incident light vacuum wavelength λ ₀Estimate the component of membraneous material with the function model of al composition x, realize the on-line measurement in the thin film growth process, detailed process is as follows:

(1) surveys the reflected light light intensity by the CCD device and change the reflectance curve that obtains film growth, as Fig. 4, this reflectance curve can be similar to thinks a decay oscillation curve, wherein curve oscillation frequency, oscillation amplitude center and decay factor have comprised us and have wanted the growth rate that obtains and the information of film refractive index, obviously, any one section information that has all comprised above-mentioned curve oscillation frequency, oscillation amplitude center and decay factor of intercepting curve;

(2) by MATLAB software programming algorithm, reflectance curve shown in Figure 4 is carried out parameter fitting, promptly draw curvilinear equation and need the parameters relationship of match to be approximately from theoretical analysis

$R\left(t\right)=R_{\&infin;}-2\sqrt{R_{\&infin;}{R}_i}(1-R_{\&infin;})e^{-\mathrm{rt}}\cos (\mathrm{wt}-\mathrm{\&theta;})$

The reflectivity of R (t) for detecting at film surface

R _∞Reflectivity for the infinite thick film of top layer of equivalent layer structure

R _iBe layer internal reflection rate

R is the e damped expoential of curve

W is the angular frequency of curve

θ is the initial phase of curve

This formula can represent to become an expression formula that contains Wucan numbers such as α, β, r, w, θ, promptly

y＝α+βe ^-rtcos(wt-θ)

Here α represents is R in the curvilinear equation _∞

What β represented is in the curvilinear equation

By obtaining n discrete data (y on the curve ₁, t ₁), (y ₂, t ₂) ... (y _n, t _n), the initial value of given damped expoential r utilizes sinusoidal curve fitting algorithm IEEE 1057 international standards can provide the estimated value of other four parameter, utilizes the value of other four parameter that r is carried out the minimum variance match again, and both repeatable operation obtain all parameters R _∞, R _i, r, w and θ estimated value, reach till our permissible accuracy.The inner constant refractive index of film is defined as N=n-ik,

N is the real part of refractive index

K is the imaginary part of refractive index

The equation that obtains by theoretical analysis:

$(1+\frac{r^2}{{\mathrm{\&theta;}}^2})(R_{\&infin;}-1)n^2+2(R_{\&infin;}+1)n+R_{\&infin;}-1=0$ Just can solve the real part n of refractive index expression formula according to the value of known parameters, again the equation that obtains by theoretical analysis:

$k=\frac{r}{\mathrm{\&theta;}}n$

$G=\frac{\mathrm{r\&lambda;}}{4\mathrm{\&pi;k}}$

G is a film growth rate

λ is an incident wavelength

π is the mathematics constant coefficient

Thereby obtain the imaginary part k of growth for Thin Film rate G and refractive index expression formula.

(3) MEASUREMENTS OF THIN substrate curvature change amount, when film just deposits on substrate, membrane stress just begins to cause that substrate curvature changes, so can calculate membrane stress by the change amount of substrate curvature, promptly use the surface of two-dimentional convergent beam array irradiate sample 6, on the reflection direction of this film sample, survey the folded light beam array information by the CCD device, according to schematic diagram shown in Figure 3, record incoming laser beam array pitch d respectively, incident angle α, the yaw displacement δ and the film thickness h of the relative distance L between sample and sensor array, L place light beam _fParameter;

(4) calculate membrane stress by the change amount of substrate curvature shown in Figure 4, promptly calculate membrane stress σ by following Stoney relation equation

$\mathrm{\&sigma;}=\frac{1}{6}\&CenterDot;[\frac{1}{r_{\mathrm{post}}}-\frac{1}{r_{\mathrm{pre}}}]\&CenterDot;\frac{E}{1-v}\&CenterDot;\frac{h_s^2}{h_f}$

Wherein: σ is post-depositional membrane stress; r _PostBe the substrate curvature of curved surface after the deposition, r _PreBe the substrate curvature of curved surface before the deposition, E is a Young modulus, and v is the Poisson coefficient, h _sBe substrate thickness, h _fBe film thickness;

(5) utilize the Brunner model to estimate membraneous material al composition x., utilize promptly that Brunner proposes with Al _xGa _1-xThe refractive index of N film accurately is expressed as incident light vacuum wavelength λ ₀Function model with al composition x:

$n^2(\mathrm{\&lambda;},x)=C\left(x\right)+A\left(x\right)\left(\frac{2-\sqrt{1+y}-\sqrt{1-y}}{y^2}\right)$

A in the formula (x) and C (x) are two functions about x, and (x, λ T) are the function of x, wavelength and temperature to y, measuring under the known condition of temperature and incident wavelength, by separating above-mentioned equation, obtain the al composition x of membraneous material.

Described " virtual interface " is identical with " effectively interface " with " the equivalent layer structure " of continuing to use a lot of years in the optical filter design, is meant the interface of artificial given calculating film growth, and virtual interface is following to be virtual substrate.

Described " integrated binary grating " refers to the element that Fresnel zone plate and Dammann grating are combined into, and it has beam splitting and focusing function simultaneously.Should " Dammann grating " be a kind of Nitride Binary-Phase grating of two dimension, 0 of this grating generation, ± 1, ± 2, the amplitude of ± N order diffraction light equates, can obtain the equal strength diffraction light that (2N+1) bundle is propagated along different directions with a branch of coherent light irradiation one dimension Dammann grating, for two-dimentional Dammann grating (2N+1) * (2N+1) bundle equal strength diffraction light can be arranged then.

With reference to Fig. 6, image processing process of the present invention is: the beam array that test sample reflects is by the front end camera lens and the processing back imaging on the area array CCD focal plane that filters, this image is handled, promptly the light signal that has comprised light spot position information and intensity signal is changed into electric signal, be transformed into the numerical information that is used for data processing through analog to digital converter again, carry out data operation by PC at last, draw membrane stress σ, refractive index n-ik, growth rate G and the thin film aluminum component x that finally will test.

Claims (7)

1. optical sensor that detects film growth rate and stress, comprise pump diode laser, chopper, Amici prism, it is characterized in that, two bundle laser of first pump diode laser (1) and second pump diode laser (2) output different frequency, modulation output beam of laser by chopper (3), this a branch of laser shines binary raster beam splitter (5) by Amici prism (4) and goes up formation two-dimentional light beam array, this beam array is reflected in CCD focal plane (7) through film sample (6) and goes up imaging, demonstrate the light spot position distributed intelligence of folded light beam array and each some intensity variations information, by calculating the stress that information that this light spot position distributes and intensity variations information draw film, growth rate, refractive index and film chemical component.

2. optical sensor according to claim 1, it is characterized in that chopper (3) controlled by external circuit, make two bundle laser of first pump diode laser (1) and second pump diode laser (2) output different frequency, alternately see through chopper, finally only export beam of laser and enter Amici prism (4).

3. optical sensor according to claim 1 is characterized in that binary raster beam splitter (5) is made up of two-dimentional Dammann grating and Fresnel zone plate, in order to produce auto-convergence multiple beam array.

4. optical sensor according to claim 1, each spot intensity and the interval between the luminous point that it is characterized in that the two-dimentional light beam array that binary raster beam splitter (5) upward forms are identical, and the divergence point that can pass through to change light beam realizes that to the distance between the distance change dot-matrix array luminous point of beam splitter beam separation is adjustable.

5. method of utilizing claim 1 to detect film growth rate and stress is by reflectivity of optical thin film curve calculation film growth rate and refractive index under the match virtual interface; By the Stoney equation beam deviation information is calculated, drawn membrane stress; The refractive index that calculates is passed through incident light vacuum wavelength λ ₀Estimate the component of membraneous material with the function model of al composition x, realize the on-line measurement in the thin film growth process.

6. method according to claim 5, wherein, carry out according to the following procedure by reflectivity of optical thin film curve calculation film growth rate under the match virtual interface:

(1) survey the reflected light light intensity by the CCD device and change the reflectance curve that obtains film growth,

(2) reflectance curve is carried out parameter fitting, obtain growth for Thin Film rate and refractive index information.

7. method according to claim 5 is wherein utilized beam deviation information and Stoney Equation for Calculating membrane stress, carries out according to the following procedure:

(1) film-substrate curature variation amount is measured, promptly use two-dimentional convergent beam array irradiate sample surfaces, the CCD device is surveyed the folded light beam array information on its reflection direction, and record incoming laser beam array pitch d, incident angle α, the yaw displacement δ and the film thickness h of the relative distance L between sample and sensor array, L place light beam _fParameter;

(2) calculate membrane stress by the change amount of substrate curvature

$\mathrm{\&sigma;}=\frac{1}{6}\&CenterDot;[\frac{1}{r_{\mathrm{post}}}-\frac{1}{r_{\mathrm{pre}}}]\&CenterDot;\frac{E}{1-v}\&CenterDot;\frac{h_s^2}{h_f}$

Wherein: σ is post-depositional membrane stress;

r _PostBe the substrate curvature of curved surface after the deposition;

r _PreBe the substrate curvature of curved surface before the deposition;

E is a Young modulus; V is the Poisson coefficient;

h _sBe substrate thickness;

h _fBe film thickness.

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