CN1601385A - Method of determining range of exposure dose in tech of picture quality detection of aligner - Google Patents

Abstract

The invention provides a method for time-saving and effectively-defining FOCAL technigue exposure dose range, Based on basic principle of FOCAL technique a certain change law must be met between fine structure line width and out-or-focus amount under the optimum exposure dose. Said invention uses the change law of the fine structure line width and out-of-focus amount under the optimum exposure dose as limiting condition for defining exposure dose range, and utilizes the analysis of relationship curve between fine structure line width and out-of-focus amount under the different exposure doses to can remove the exposure dose correspondent to the curve which can not meet said limiting condition from FOCAL exposure dose range so as to implerment quick and effective definition of FOCAL exposure dose range. Said method is an analog process, can be implemented on computer by utilizing existent software.

Description

Definite method of exposure dose latitude in the litho machine picture element detection technique

Technical field

The present invention relates to the method for a kind of definite exposure dose latitude in the litho machine picture element testing process, particularly a kind of method of determining exposure dose latitude by computer simulation mode in the FOCAL technology.

Background technology

The image quality of litho machine directly influences Key Performance Indicators such as the CD homogeneity, alignment precision, depth of focus, exposure latitude of litho machine.Therefore the on-the-spot detection technique of image forming quality of photoetching machine is indispensable.

FOCAL (Focus calibration using alignment procedure) technology is a kind of picture element detection technique that is used for the high resolution litho machine, can be on-the-spot picture element parameters such as the best image planes of high Precision Detection, image planes inclination, the curvature of field, astigmatism (referring to technology 1 formerly, Peter Dirksen, Jan E.Van Der Werf. " Method ofrepetitively imaging a mask pattern on a substrate; and apparatus for performing themethod ", Application No.: 5,674,650).

Formerly discussed the ultimate principle of FOCAL technology in the technology 1 in detail.The FOCAL technology is under optimum exposure dosage, with a kind of special marker graphic---the FOCAL marker graphic is imaged on the silicon chip that is in different out of focus faces successively.Different with common litho machine alignment mark, a grating of FOCAL mark comprises a part of intensive lines in the cycle, and this part intensive lines is called the fine structure 1 of FOCAL mark, shown in Fig. 1 (a).Because the existence of grating fine structure, the space distribution of FOCAL mark reflective light intensity changes along with the variation of defocusing amount on the silicon chip, therefore, reflective light intensity reaches the pairing mark position of extreme value and is offset, and this side-play amount is called alignment offset amount (Alignment Offset).The alignment offset amount is relevant with the live width of FOCAL mark fine structure.Silicon chip on the photoresist has formation the FOCAL marker graphic of different live width fine structures, thereby produces different alignment offset amounts after exposure under the different defocusing amounts.At the FOCAL mark of best image planes place exposure, its alignment offset amount reaches maximal value.Aligned position deviation and defocusing amount with silicon chip mark connects thus, and the aligned position deviation by each the FOCAL mark that detects calculates the pairing best picture point axial location deviation of this mark.Axial location deviation according to a plurality of best picture points can calculate parameters such as best image planes, image planes inclination, the curvature of field, astigmatism, thereby realizes the detection of litho machine picture element parameter.

The FOCAL technology is under certain exposure dose, and the marker graphic on the FOCAL mask is imaged on the photoresist.Exposure dose is too small or cross incomplete exposure or the overexposure phenomenon that conference causes photoresist, and this all will cause the distortion of the back marker graphic that develops.Therefore before carrying out the FOCAL test, need to determine optimum exposure dosage.In certain exposure dose latitude, carry out the FOCAL test, determine the optimum exposure dosage that satisfies condition according to test result.If it is improper that exposure dose latitude is chosen, be not included in the exposure dose latitude as optimum exposure dosage, then can't find optimum exposure dosage.Therefore selecting suitable exposure dose latitude is to finish the necessary process of FOCAL test.

At present ASML litho machine user is in device detection procedure, takes the method for repetition test to select the exposure dose latitude of FOCAL technology.If can not find optimum exposure dosage by the test of the FOCAL under the different exposure doses, then revise exposure dose latitude behind the analytical test result, carry out the FOCAL test under the different exposure doses again, till determining optimum exposure dosage.Generally speaking, choose bigger exposure dose latitude earlier, progressively reduce the scope, until finding the scope that comprises the optimum exposure dose value according to test result.Exposure dose latitude is subjected to the influence of lighting system, photoetching process bigger.After test condition changed, originally determined exposure dose latitude was just no longer suitable, need test to determine exposure dose latitude again.This process need repeated multiple times wastes time and energy.

Therefore, in order to save the test duration, to reduce testing cost, need seek a kind of new method of determining the FOCAL exposure dose latitude fast, reliably.

Summary of the invention

At the deficiency that above-mentioned prior art exists, the invention provides a kind of method that saves time, effectively determines FOCAL technology exposure dose latitude.This method is a simulation process, utilizes existing software to realize on computers, has fast, accurately advantage.

Based on the ultimate principle of FOCAL technology, need satisfy certain Changing Pattern between fine structure live width under the optimum exposure dosage and the defocusing amount.Owing to carry out the purpose of FOCAL test repeatedly in exposure dose latitude is to determine optimum exposure dosage, and therefore the Changing Pattern of fine structure live width under the available optimum exposure dosage and defocusing amount is as the qualifications of exposure dose latitude.By the fine structure live width under the more different exposure dose conditions of analysis and the curve of defocusing amount, the corresponding exposure dose that does not satisfy the curve of this Changing Pattern is got rid of outside the FOCAL exposure dose latitude, thereby realized determining of FOCAL exposure dose latitude.At present, there has been corresponding software can simulate the exposure process of FOCAL test on computers, such as the SOLID-C of SIGMA-C company and the PROLITH of KLA-Tencor company.Only need preestablish lighting condition and process conditions, mask graph and corresponding size, test parameterss such as defocusing amount and out of focus stepping amount just can be carried out numerical simulation in the exposure dose latitude of setting, obtain the intensive lines live width under the different exposure doses and the relation curve of defocusing amount.

The present invention determines that the method for FOCAL technology exposure dose latitude is a simulation process.Utilize lithography simulation software to carry out digital simulation on computers, can determine the FOCAL exposure dose latitude by the analysis mode result, as Fig. 2.Through the preproduction phase 10, the present invention determines that the flow process 100 of exposure dose latitude may further comprise the steps:

(a) determine lighting condition and the process conditions stage 11 that FOCAL tests;

(b) definite mask graph and corresponding size stage 12 that needs with the emulation of photoetching simulation software;

(c) determine the defocusing amount and the out of focus stepping amount stage 13 of simulation process;

(d) determine the minimum exposure dosage and the maximum exposure dosage stage 14 of simulation process;

(e) the lithography simulation software simulation stage 15, can obtain through exposure, back baking, develop afterwards different exposure doses, the pairing described marker graphic live width of different defocusing amount.

(f) determine minimum value stage 16 of FOCAL exposure dose latitude.The fine structure live width under the different exposure doses that analysis emulation obtains and the relation curve of defocusing amount.The minimum value that the pairing minimum exposure dose value of curve that satisfies the Changing Pattern that the fine structure live width reduces with the increase of defocusing amount is the FOCAL exposure dose latitude.

(g) determine maximal value stage 17 of FOCAL exposure dose latitude.The fine structure live width under the different exposure doses that analysis emulation obtains and the relation curve of defocusing amount.The maximal value that to have a certain amount of pairing maximum exposure dose value of curve that can be used for judging the non-zero number strong point of optimum exposure dosage be the FOCAL exposure dose latitude.Be good when having 5 non-zero number strong points on the curve at least.

Lighting condition in the above-mentioned steps (a) and process conditions are meant conditions such as coherence factor and numerical aperture size, photoresist type, photoresist thickness, back baking temperature, back baking time, development time.

Mask graph described in the above-mentioned steps (b) is 1: 1 intensive lines of dutycycle, shown in Fig. 2 (b).The live width of the intensive lines of getting is identical with the fine structure live width of the mask mark that affiliated FOCAL test process adopts.

Described lithography simulation software is meant the simulation software that can accurately simulate photoetching process and effect, as PROLITH, and lithography simulation softwares such as SOLID-C.

Defocusing amount described in the above-mentioned steps (c) is consistent with the defocusing amount of affiliated FOCAL test.Described out of focus stepping amount is consistent with the out of focus stepping amount of affiliated FOCAL test.

Minimum exposure dosage and maximum exposure dosage are meant in the analogue simulation process described in the above-mentioned steps (d), the minimum value of the exposure dose of being got and maximal value.Minimum exposure dosage is good when for institute the required lowest dose level value of photochemical reaction taking place with photoresist, and this value is determined by the technology condition that FOCAL tests.The maximum exposure dose value of being got should satisfy the exposure dose value of condition in described step (f) and the step (g) greater than all, this value can leave the setting in abundant leeway according to the grasp to art technology, is exactly an enough big value as 10 times minimum exposure dose values.

The definite exposure dose latitude minimizing agent value that is proposed in the above-mentioned steps (f) is fixed condition really, being the fine structure live width reduces with the increase of defocusing amount, with the definite exposure dose latitude maximum dose value that is proposed in the above-mentioned steps (g) fixed condition really, being to have five non-zero number strong points at least on the relation curve of fine structure live width and defocusing amount, is FOCAL exposure dose latitude proposed by the invention fixed condition really.This definite condition is to obtain on the basis of the Changing Pattern of intensive lines live width of FOCAL under the analysis optimum exposure dosage and defocusing amount.According to as follows:

The FOCAL technology is determined best image point position according to the alignment offset amount of FOCAL mark and the Changing Pattern of silicon chip defocusing amount, and the variation among a small circle of exposure dose can't cause the bigger change of Changing Pattern between alignment offset amount and the silicon chip defocusing amount, and therefore the alignment offset amount that obtains in the FOCAL exposure dose latitude should be consistent with the Changing Pattern of alignment offset amount under the optimum exposure dosage and defocusing amount with the Changing Pattern of silicon chip defocusing amount.

Under optimum exposure dosage, carry out the FOCAL test experiments, the alignment offset amount of record silicon chip when different out of focus faces expose.Can obtain the alignment offset amount under the optimum exposure dosage and the Changing Pattern of silicon chip defocusing amount by analyzing experimental result.Experimental result as shown in Figure 3, ordinate is the alignment offset amount of FOCAL mark, horizontal ordinate is the defocusing amount of silicon chip, sign is represented the direction of silicon chip out of focus.Asterism is represented the pairing alignment offset amount of different defocusing amounts, and data point is carried out getting curve 2 after the match.

By curve among Fig. 3 as can be seen, along with the increase of defocusing amount, the alignment offset amount reduces.The silicon chip out of focus position of correspondence was the best image planes of litho machine imaging system when the alignment offset amount was maximum value.The FOCAL technology is utilized this Changing Pattern of alignment offset amount and defocusing amount just, and the defocusing amount when being maximum value by calculating the alignment offset amount realizes the high-acruracy survey of best image planes.

Curve 2 can be expressed as polynomial function:

AO=a ₀+ a ₁Δ f+a ₂Δ f ²+ a ₃Δ f ³+ Λ+a _nΔ f ⁿ(A) Δ f is a defocusing amount in the formula, a ₀, a ₁, a ₂... a _nBe multinomial coefficient.

The variation of FOCAL mark fine structure live width will cause the variation of mark reflective light intensity space distribution, thereby produce the skew of aligned position.By analyzing the pairing spatial light intensity regularity of distribution of the different live widths of FOCAL mark, the aligned position side-play amount of FOCAL mark is:

In the formula $f=\frac{1}{T},$ T is the grating cycle.a _n, b _nRelevant with the fine structure live width, its expression formula is respectively:

$a_n=\frac{1}{\mathrm{n\π}}\{\exp \left(j2\mathrm{kd}\right)\sin \left(2\mathrm{\πnfa}\right)+2\exp \left({j2\mathrm{kd}}^{\′}\right)\underset{m=1}{\overset{M}{\mathrm{\Σ}}}\sin \frac{\mathrm{n\πfLwr}}{M(1+r)}\cos 2\mathrm{\πnf}(a+\frac{\mathrm{mLw}}{M}-\frac{\mathrm{Lwr}}{2M(1+r)})$

$+2\underset{m=1}{\overset{M}{\mathrm{\Σ}}}\sin \frac{\mathrm{n\πfLw}}{M(1+r)}\cos 2\mathrm{\πnf}(a+\frac{2m-1}{2M}\mathrm{Lw}-\frac{\mathrm{Lwr}}{2M(1+r)})+\sin \left(2\mathrm{\πnfc}\right)\}---\left(C\right)$

$b_n=\frac{1}{\mathrm{n\π}}\{\exp \left(j2\mathrm{kd}\right)(1-\cos \left(2\mathrm{\πnfa}\right))+2\exp \left({j2\mathrm{kd}}^{\′}\right)\underset{m=1}{\overset{M}{\mathrm{\Σ}}}\sin \frac{\mathrm{n\πfLwr}}{M(1+r)}\sin 2\mathrm{\πnf}(a+\frac{\mathrm{nLw}}{M}-\frac{\mathrm{Lwr}}{2M(1+r)})$

$+2\underset{m=1}{\overset{M}{\mathrm{\Σ}}}\sin \frac{\mathrm{n\πfLw}}{M(1+r)}\sin 2\mathrm{\πnf}(a+\frac{2m-1}{2M}\mathrm{Lw}-\frac{\mathrm{Lwr}}{2M(1+r)})+\cos \left(2\mathrm{\πnfc}\right)-1\}---\left(D\right)$

Wherein, d is key light grid groove depths, and d ' is the groove depth of fine structure, and a is the live width of key light grid, and Lw is the live width of fine structure, and c is that the seam of key light grid is wide, and r is the dutycycle of fine structure, and M is the periodicity of fine structure, and n is that the order of diffraction is inferior.

Can get the relation curve of alignment offset amount and fine structure live width by (B)～(D) formula, as shown in Figure 4.Become linear approximate relationship between alignment offset amount and the live width Lw, that is:

AO＝k.Lw (E)

Wherein k is a scale-up factor.

The alignment offset amount that obtains according to (E) formula and experiment and the Changing Pattern of defocusing amount can be determined the relation of fine structure live width and defocusing amount.By (A) formula and (E) Shi Kede:

CD＝a ₀′+a ₁′Δf+a ₂′Δf ₂+a ₃′Δf ₃+Λ+a _n′Δf ⁿ (F)

(F) Δ f represents defocusing amount in the formula, a ₀', a ₁', a ₂' ... a _n' be multinomial coefficient.

Fig. 5 is the relation curve of FOCAL test fine structure live width and defocusing amount.In exposure dose latitude, the fine structure live width reaches maximal value near center of curve, and along with the increase of defocusing amount, live width reduces gradually.When exposure dose was bigger, the fine structure live width under the different defocusing amounts all reduced, but the variation tendency of curve is constant.Condition can be determined the minimizing agent value of FOCAL exposure dose latitude thus.

Simultaneously, when in the FOCAL exposure dose latitude, choosing optimum exposure dosage, require to have at least 5 measurement points to drop on the AO～Δ f curve of optimum exposure dosage.Because AO becomes linear approximate relationship with the fine structure live width, therefore adopt the out of focus stepping amount of the out of focus stepping amount identical as analog simulation with test process, Lw～Δ f curve in the FOCAL exposure dose latitude should have five non-zero number strong points at least, and this standard is becoming a generally accepted criterion in the art.Exposure dose is big more, and the non-zero points on Lw～Δ f curve is few more.Condition can be determined the maximum dose value of FOCAL exposure dose latitude thus.

In resulting exposure dose latitude, carry out the FOCAL test, can determine the optimum exposure dose value.

Through workflow 100, can obtain exposure dose latitude, enter then and in exposure dose latitude, carry out FOCAL test phase 18, obtain optimum exposure dosage, enter again and under optimum exposure dosage, carry out FOCAL test phase 19, can obtain best image planes, image planes tilt, the curvature of field, picture element parameters such as astigmatism are finished test phase 20 thereby enter.

The present invention has the following advantages:

1, definite method of FOCAL technology exposure dose latitude of the present invention, by limiting fine structure live width and the required satisfied relation of defocusing amount, can once accurately determine exposure dose latitude, compare with the method for testing repeatedly, progressively approaching that ASML litho machine user is adopted, improved the accuracy of definite exposure dose latitude.

2, the present invention utilizes lithography simulation software to realize the fine structure live width under the different exposure doses and the accurate simulation of defocusing amount relation curve, compares with the test method that ASML litho machine user is adopted, and has quick, advantage reliably.And saved tests such as silicon chip, photoresist and used material, reduced testing cost.

3, definite method of FOCAL technology exposure dose latitude of the present invention does not influence the normal running of litho machine, has reached the purpose that off-line is accurately measured exposure dose latitude.

4, definite method of the exposure dose latitude that proposes of the present invention can be determined the exposure dose latitude under different illuminations, the process conditions quickly and easily by changing conditions such as illumination in the simulation process, technology.

Description of drawings:

Fig. 1: (a) the fine structure synoptic diagram in a grating cycle of FOCAL mark;

(b) the employed fine structure synoptic diagram of simulation process of the present invention;

Fig. 2: process flow diagram of the present invention;

Fig. 3: the alignment offset amount that the litho machine experiment obtains and the relation curve of defocusing amount;

Fig. 4: the relation curve of alignment offset amount and fine structure live width;

Fig. 5: the relation curve of fine structure live width and defocusing amount;

Fig. 6: the fine structure live width under the different exposure doses that PROLITH emulation obtains and the relation curve of defocusing amount.

Embodiment:

For a better understanding of the present invention, now provide a specific embodiment in conjunction with the accompanying drawings.

The FOCAL exposure dose latitude that Fig. 2 proposes for the present invention is determined the basic step of method.

The lighting condition of present embodiment FOCAL test is: traditional lighting, NA are 0.57, partial coherence factor is 0.7; Process conditions are: JSR AR165J photoresist, glue thick for 1000nm, back baking temperature be that 115 °, back baking time are that 60s, development time are 60s; It more than is stages 11 desired parameters.The pattern of institute's emulation mask is that dutycycle is 1: 1 intensive lines, and live width is 250nm, and this is stages 12 desired parameters.According to the correlation parameter of FOCAL test process, the out of focus scope of simulation process is-900nm～900nm, and out of focus stepping amount is 120nm, and this is stages 13 desired parameters.Be about 10mJ/cm2 by the required minimizing agent value of JSR AR165J photoresist developing, therefore, minimum exposure dosage is taken as 10mJ/cm2, and maximum exposure dosage is taken as 100mJ/cm2, and this is a required parameter of stage 14.The PROLITH lithography simulation software that present embodiment uses KLA-Tencor company to release.

After the analogue simulation stage 15, can obtain fine structure live width in the exposure dose latitude of getting and the relation curve of defocusing amount, as shown in Figure 6.Wherein horizontal ordinate is silicon chip defocusing amount Δ f, and ordinate is FOCAL mark fine structure live width Lw.Under 20 different exposure doses in 5mJ/cm2～100mJ/cm2 scope (see Fig. 6 right side, from top to bottom from top to bottom curve in the corresponding diagram) successively, obtain the relation curve of 20 fine structure live widths and defocusing amount.

When exposure dose during greater than 25mJ/cm2, the corresponding fine structure live width and the relation curve of defocusing amount satisfy the Changing Pattern that Lw reduces with the increase of Δ f.When exposure dose during less than 65mJ/cm2, satisfying on the corresponding curve has at least five non-zero number strong points.Can determine that thus under this lighting condition and process conditions, the FOCAL exposure dose latitude is 25～55mJ/cm2.

Claims (9)

1. method (100) of in litho machine FOCAL picture element testing process, determining exposure dose latitude,

It is characterized in that, adopt following steps:

(a) determine lighting condition and the process conditions stage (11) that FOCAL tests;

(b) definite mask graph and corresponding size stage (12) that needs with the emulation of photoetching simulation software;

(c) determine the defocusing amount and the out of focus stepping amount stage (13) of simulation process;

(d) determine the minimum exposure dosage and the maximum exposure dosage stage (14) of simulation process;

(e) the lithography simulation software simulation stage (15); The determined parameter of input step (a) to (d) obtains through exposure, back baking, the live width of different exposure doses, the pairing described marker graphic of different defocusing amounts afterwards of developing;

(f) determine minimum value stage (16) of FOCAL exposure dose latitude; The fine structure live width under the different exposure doses that analysis emulation obtains and the relation curve of defocusing amount; The minimum value that the pairing minimum exposure dose value of curve that satisfies the Changing Pattern that the fine structure live width reduces with the increase of defocusing amount is the FOCAL exposure dose latitude;

(g) determine maximal value stage (17) of FOCAL exposure dose latitude; The fine structure live width under the different exposure doses that analysis emulation obtains and the relation curve of defocusing amount; The maximal value that to have 5 pairing maximum exposure dose values of curve that can be used for judging the non-zero number strong point of optimum exposure dosage be the FOCAL exposure dose latitude.

2. the method for in litho machine FOCAL picture element testing process, determining exposure dose latitude as claimed in claim 1, it is characterized in that described lighting condition and described process conditions are meant coherence factor that the FOCAL test process is adopted and numerical aperture size, photoresist type, photoresist thickness, back baking temperature, back baking time, development time; Described lighting condition is identical with lighting condition and the process conditions that the FOCAL test process is adopted respectively with described process conditions.

3. the method for determining exposure dose latitude in litho machine FOCAL picture element testing process as claimed in claim 2 is characterized in that described mask graph is 1: 1 intensive lines of dutycycle.

4. the method for determining exposure dose latitude in litho machine FOCAL picture element testing process as claimed in claim 3 is characterized in that, the live width of fine structure that the live width of the intensive lines of getting and FOCAL test the mask mark that is adopted is identical.

5. the method for determining exposure dose latitude in litho machine FOCAL picture element testing process as claimed in claim 4 is characterized in that described lithography simulation software is meant the simulation software that can accurately simulate photoetching process and effect, as PROLITH, and SOLID-C.

6. the method for determining exposure dose latitude in litho machine FOCAL picture element testing process as claimed in claim 5 is characterized in that described defocusing amount is consistent with the defocusing amount of FOCAL test.

7. the method for determining exposure dose latitude in litho machine FOCAL picture element testing process as claimed in claim 6 is characterized in that described out of focus stepping amount is consistent with the out of focus stepping amount of FOCAL test.

8. the method for determining exposure dose latitude in litho machine FOCAL picture element testing process as claimed in claim 7 is characterized in that the minimum exposure dosage described in the step (d) is the exposure dose minimum value of being got in the analogue simulation process; Described minimum exposure dosage for the required lowest dose level value of photochemical reaction takes place with photoresist.

9. the method for determining exposure dose latitude in litho machine FOCAL picture element testing process as claimed in claim 8 is characterized in that the maximum exposure dosage described in the step (d) is the exposure dose maximal value of being got in the analogue simulation process; Described maximum exposure dosage is 10 times minimum exposure dose value.

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