JP2000205828A - Method for measuring step on transparent film and method for forming phase shift mask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To measure a step on a phase shifter fast nondestructively with high precision through easy operation without contacting when measuring a step on a transparent film. SOLUTION: In a process included in the measuring method, correlation between step quantities t1,..., tn of 1st grooves S1,..., Sn formed in part of a 1st transparent film 2 and the values of parameters indicating the polarization state of reflected lights from the 1st grooves S1,..., Sn is found and held in the form of a data base. Then 1st value of a parameter representing the polarized state of a reflected light of a 2nd groove 45 formed in part of a 2nd transparent film 424 is measured and a 1st step quantity of the 2nd groove 45 is found on the basis of the 1sts value and the correlation in the data base.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a level difference in a transparent film and a method for forming a phase shift mask, and more particularly, to a level difference in a transparent film used for a phase shift mask in a lithography process in the manufacture of a semiconductor device. And a method for producing a phase shift mask used as a projection original.

[0002]

2. Description of the Related Art In the manufacture of semiconductor devices, there is a step of patterning a film by a photolithography method. Photolithography is a method of applying a photoresist on a film, exposing and developing it, patterning it, and then patterning the film through a process of etching the film using the photoresist pattern as a mask. is there.

In exposing a photoresist, for example, a projection exposure apparatus is used. In projection exposure equipment,
By irradiating the resist with light transmitted through an exposure mask on which an original image pattern is drawn, the original image pattern is transferred to the resist to form a latent image. The resolving power indicating how fine a pattern can be transferred by a projection exposure apparatus is evaluated based on whether two adjacent patterns can be separated when a pattern on an exposure mask is transferred onto a wafer.

As one technique for improving the resolution, for example, a phase shift mask is known. The phase shift mask has a structure that gives a phase difference to exposure light transmitted through two adjacent transmission portions. In order to cause a phase difference in such exposure light, a structure in which the thickness of a transparent film constituting a mask substrate is partially different is described in, for example, JP-A-62-189468.

The thickness difference T of the transparent film for changing the phase by 180 ° is given by T = λ / 2 (n−1), where n is the refractive index of the transparent film and λ is the wavelength of the exposure light. . by the way,
As a method of measuring how the thickness difference in the transparent film actually appears, for example, an atomic force microscope (AM)
The thickness difference (step) of the transparent film has been measured using a film thickness measuring means such as F (atomic force microscope).

[0006]

However, the method of measuring the film thickness difference by AFM requires a complicated work such as scanning the surface of the sample with a needle, and the work load is large. Also, AF
According to the M method, after a step is formed in a transparent film using a resist, the step is measured with the resist once removed, so that when the value of the step is insufficient, the pattern of the resist is again measured. , And the size of the step is adjusted by repeating complicated steps such as making the step deeper.

Therefore, measuring the step of the phase shift mask using the AMF method complicates the manufacturing process of the phase shift mask, and lowers the throughput. A method for measuring the dimensions and cross-sectional shape of a structure formed on a substrate having a flat surface by using ellipsometry is described in, for example, Japanese Patent Application Laid-Open No. 9-237812. This measurement method obtains a correlation between a measurement value obtained by an optical method of ellipsometry and a width or a cross-sectional shape (taper angle) of a structure formed on a wafer, and an arbitrary structure is obtained from the correlation. It determines the width or cross-sectional shape of an object.

[0008] However, there is no proposal for measuring the depth of the groove. A conventional method for measuring the depth of a groove formed in a transparent film by ellipsometry generally requires that reflected light at the interface between the transparent substrate and the transparent film be very small. However, since the transparent substrate and the transparent film constituting the phase shift mask are made of materials having the same refractive index, it is actually difficult to measure the level difference of the phase shifter of the phase shift mask. Therefore, when using the ellipsometry, a high-reflectance silicon substrate is used, and the reflected light intensity at the interface between the substrate and the transparent film is increased.
Indirect measurements were taken.

It is an object of the present invention to provide a method of measuring a step of a transparent film and a method of preparing a phase shift mask including a step of measuring a step of a phase shifter with high speed and high accuracy by a non-contact, non-destructive and simple operation. To provide.

[0010]

Means for Solving the Problems (1) The above-mentioned problems are:
As illustrated in FIGS. 1, 2, 6, and 7, the first transparent
A plurality of first grooves S formed in a part of the bright film 1₁, ..., S
_nStep t₁,…. t _nAnd the first groove S₁, ..., S_n
Between the value of the parameter indicating the polarization state of the reflected light from the surface
Relation f₁After creating a database for
Polarization of light reflected from second groove 45 formed in part of film 42
Measuring a first value of the parameter indicating the state;
The second value based on the value and the correlation in the database.
Wherein the first step amount of the groove 45 is determined.
The problem is solved by a method of measuring the step of the film.

[0011] In the method for measuring a step of a transparent film, the parameter is measured by an ellipsometry. In the above-described method for measuring a step of a transparent film, the parameters are a complex amplitude reflectance ratio Ψ and a phase difference Δ of the polarization state. In the method of the step of the transparent film mentioned above, the first groove S _1, ..., the step amount t ₁ of S _n, ..., t _n is characterized by being measured by atomic force microscopy.

In the above-described method for measuring the level difference of the transparent film, when the patterns 43 and 44 are formed on the second transparent film 42, the film thickness of the patterns 43 and 44 is measured in advance. The first step amount of the second groove is obtained by subtracting the film thickness of the patterns 43 and 44 from the correlation of the database.

In the method for measuring the level difference of the transparent film described above,
The patterns 43 and 44 are made of a light shielding material.
It is characterized by that. (2) Examples of the above-mentioned problems are shown in FIGS. 1, 2, 6, and 7.
As shown in FIG.
First groove S₁, ..., S_nStep t₁, ..., t _nAnd said
First groove S₁, ..., S_nIndicates the polarization state of light reflected from
Parameter value Δ ₁, ..., Δ_nAnd Ψ₁,…, Ψ_nWith
Correlation f₁To create a database for
A resist pattern 44 on the transparent film 42 for masking
And a step of measuring the thickness of the resist pattern 44.
Before the portion not covered by the resist pattern 44
The mask transparent film 42 is etched to form a second groove 45.
Forming step and the polarization state of the reflected light of the second groove 45
The first values Δ and の of the parameters indicating
And the correlation f in the database₁Based on
From the step amount obtained before the resist pattern 44
By subtracting the film thickness, the first groove 45
A step of determining the step amount; and the step amount reaches the target value.
Judging whether or not the first step amount is equal to the target value.
When the reference value is not reached, the reflected light of the second groove 45 is
Parameters indicating the polarization state and the phase of the database
Relation f₁Of the second groove 45 determined based on
The second groove 45 until the step amount of No. 2 reaches the target value.
While the etching of the second groove 45 is repeated.
If the first or second step amount has reached the target value,
Stop etching of the mask transparent film and remove the resist.
Stripping step.
It is solved by the method of creating a disc.

In the preparation of the phase shift mask described above, a light shielding pattern 43 is formed on the mask transparent film 42.
Is formed, and the first and second step amounts of the second groove 45 are values obtained by further subtracting the film thickness of the light shielding pattern 43 from a value obtained from the correlation in the database. And It should be noted that the above-mentioned figure numbers and reference numerals are cited in order to facilitate understanding of the present invention, and the present invention is not limited thereto.

Next, the operation of the present invention will be described. According to the present invention, while measuring the step amounts of the plurality of grooves of the transparent film by means such as the AFM method, the parameters Δ and Ψ of the grooves are measured by an optical method of ellipsometry, and based on the results. After making the correlation between the step amount and the parameters Δ and て into a database, the parameters Δ and Ψ of the groove to be detected are measured by the ellipsometry, and the parameters Δ and 、 are measured.
Ψ is applied to the database to calculate the level difference.

[0016] Thus, the accurate groove depth is automatically extracted from the database only by measuring the parameter of the step generated in the transparent film by the ellipsometry. Therefore, when such a method of measuring the step amount of the transparent film is applied to the phase management and the phase adjustment of the phase shifter portion of the phase shift mask, the measurement of the depth of the groove of the phase shifter portion is compared with the AFM method. Easier.

Moreover, even if the resist remains on the transparent film on which the groove is formed, if the resist film thickness is measured only once by the AFM method or the like, the resist can be obtained from the step amount calculated from the database. When the film thickness is subtracted, the step amount of the groove is determined, so that a complicated operation of removing the resist and measuring the step of the groove every time the groove is etched as in the measurement method using only the ellipsometry becomes unnecessary.

Further, it is not necessary to form the substrate constituting the phase shift mask from a highly reflective material, and the range of choice of the substrate material and the material of the transparent film on the substrate is widened.

[0019]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention. FIG. 1 is a flowchart for obtaining data relating to a step required for a method of manufacturing a phase shift mask according to an embodiment of the present invention, and FIG. 2 is a cross-sectional view showing a film thickness measurement process for obtaining the data. FIG. FIG. 3 is a configuration diagram of an apparatus for measuring the film thickness by the AMF method, and FIG. 4 is a configuration diagram of an apparatus for measuring the film thickness by the ellipsometry.

First, as shown in FIGS. 1A and 1A, a transparent film 2 is formed on a transparent substrate 1 made of a material that transmits light used for exposure, for example, glass. The transparent film 2 transmits light used for exposure and
Higher etching rate than (for example, 10 times or more)
It is made of a selectable material, for example, SOG (spin on glass).

Next, as shown in FIGS. 1 (2) and 2 (b),
Grooves S with different depths₁, S_Two, ..., S _nFormed on the transparent film 2
I do. The groove S₁, ..., S_nMeans multiple resist masks
Can be made separately by using
Adjusting the spacing adjusts the depth. The groove
S₁, ..., S_nDepth t₁, T_Two, ..., t_nIs a transparent film
Groove S from the top of 2₁, ..., S_nIndicates the distance to the bottom of the
Hereinafter, it is also referred to as a step or a film thickness difference.

Subsequently, as shown in FIGS. 1 (3) and 2 (c), each groove S ₁ ,...
Depth for each S _n t _1, ..., to measure the t _n. AFM device 1
0 depth measured by is t _1, ..., t _n are each groove S _1, ..., associated to S _n is output to the data processing unit 20. Next, by using an ellipsometry (ellipsometry) device 30 as exemplified in FIG.
(4) As shown in FIG. 2 (d), the phase difference Δ ₁ ~Δ _n indicating the change in the polarization state in each their groove S ₁ to S _n by performing a polarization analysis of each groove S ₁ to S _n And complex amplitude reflectance ratios Ψ _{1 to} Ψ _n .

In the polarization analyzer 30, a transparent substrate 1 having a transparent film 2 in which a plurality of grooves S ₁ ,..., _Sn are formed is placed on a stage 31, and a He-Ne (helium-neon) laser A light beam having a wavelength of 32 to 6328 ° is applied to each groove S
Individually irradiated in ₁ to S _n. The output light of the He-Ne laser 32, a predetermined polarization angle by the first polarizer 33, for example, is changed to linearly polarized light having a polarization angle of 45 ° C., the predetermined angle of incidence for each groove S ₁ to S _n, e.g. Irradiation at an incident angle of 70 °.

[0024] Then, further groove S ₁ passes through the groove S ₁ to S _n, ..., the light beam reflected by S _n has an elliptical polarization state. Then, the light beam in the elliptically polarized state enters the light receiving element 35 after being converted into linearly polarized light by the rotation analyzer 34. At that time, the detection of the incident light by the light receiving element 35 is executed while rotating the rotary analyzer 34. A quarter-wave plate 36 for adjusting the phase of the reflected light beam is arranged before or after the rotary analyzer 34.

The light receiving element 35 sends a signal corresponding to the intensity of the incident light to the amplifier 37, and the signal amplified by the amplifier 37 is sent to the polarization processor 39 in the form of a digital signal via an A / D converter 38. Sent. The polarization processing device 39 calculates the phase difference Δ and the complex amplitude reflectance ratio 基 づ い based on the light beam incident on the light receiving element 35 based on the supplied digital signal, and converts these parameters Δ and Ψ into the data processing device 20.
Output to In the data processing device 20, the polarization processing device 3
9 retardation Δ and complex amplitude reflectance ratio Ψ output from is a database in association with each of a plurality of grooves S ₁ to S _n.

The data processing device 20 includes a plurality of grooves S _{1 to} S
phase difference delta ₁ every _{n, Δ 2, ..., Δ} n and the complex amplitude reflectance ratio _{Ψ 1, Ψ 2, ...,} Ψ n correspondence, further the parameters _{Δ 1, Δ 2, ...,} Δ n, Ψ ₁ , Ψ ₂ ,…, Ψ _n
Calculating a multiple regression analysis by the prediction step on each groove S ₁ to S _n (depth) t of. The predicted step t is t = f
(Δ, Ψ) (where Δ = Δ ₁ ,..., Δ _n , Ψ = Ψ ₁ ,
..., Ψ _n ). Further, the data processing device 20
, Each groove S _1, ..., prediction step t and AFM depth t ₁ was measured by method ~t determined by multiple regression analysis for S _n
in association with _n obtaining a correlation function f _1. When the correlation function f ₁ is represented in a diagram, for example, a calibration curve of the step amount and the parameters Δ and Ψ as shown in FIG. 5 is obtained.

The correlation function f ₁ is calculated each time the material of the transparent film 2 changes and stored in the data processing device 20. Incidentally, the groove S ₁ described above, ..., the depth of the S _n AFM
Instead of measuring by law, groove S ₁ by tracer method, other methods, ..., it may be actually measured the depth of the S _n. Or groove S ₁ by, ..., obtaining work data relating to the depth of the S _n (step) is completed.

Next, a step of forming a step for giving a phase difference to the exposure light transmitted through the Levenson-type phase shift mask will be described with reference to FIGS. First, in FIG.
As shown in (1) and FIG. 7 (a), a transparent substrate 41 such as glass is used.
After forming a transparent film 42 such as silicon oxide on the
A light-shielding film made of chromium is formed on the transparent film 42, and the light-shielding film is patterned by photolithography to form a light-shielding pattern 43. Followed by measuring the film thickness t _c of the light shielding pattern 43 in at least once by AFM method.

Subsequently, as shown in FIG. 6B, a resist is applied on the transparent film 32 and the light-shielding film 43, and is exposed and developed to form a resist pattern 44. Thickness t _r of the resist pattern 44 is determined by AFM method. Thickness t _r of the resist pattern 44 is detected in at least one in a short time in an arbitrary area is almost constant.

Next, as shown in FIGS. 6 (3) and 7 (b), the transparent film 42 exposed from the resist pattern 44 is etched to form a groove 45 in the phase shifter to a depth smaller than the target value t _0. Form. The target value t ₀ of the depth of the groove 45 formed in the transparent film 42 is a phase difference of light obtained by the transparent film 42 having a thickness equal to the height of the top surface of the transparent film 2 and the height of the bottom of the groove 45. Assuming that the phase difference is 180 °, t ₀ = λ / 2 (n
-1). Here, λ is the wavelength of light used at the time of exposure, and n is the refractive index of the transparent film 42.

Thereafter, as shown in FIGS. 6 (4) and 7 (c), the parameter Δ
_0, to measure the Ψ _0. Then, as shown in FIG. 6 (5), the parameters Δ ₀ and Ψ ₀ are input to the data processing device 20 and the actual step amount (depth) t _x of the groove 45 is calculated based on the correlation function f _1. I do. In this case, when applying the parameter delta ₀ was measured by ellipsometer 30, the [psi ₀ correlated f _1, as shown in FIG. 8, the light-shielding film thickness t _r of the resist pattern 44 from the correlation f ₁ pattern 43
The value obtained by adding the thickness t _c of drawn. Therefore, a value obtained by subtracting t _r and t _c from the value t _t is calculated from the correlation f _1, namely _t t - a (t _r + t _c) of the actual grooves 45 step amount t _x. Well, if the light shielding pattern 43 is not present in its thickness t _c is zero, the resist pattern 4
The film thickness t _r is zero in the case of 4 does not exist.

The step amount t _{x in} the measurement of the groove 45 is equal to the target depth t.
If it does not reach ₀ , as shown in FIG.
Is performed to further deepen the step of the groove 45. Thereafter, the parameter delta, measured [psi, determine the depth t _x of the groove 45 on the basis of this, the step amount t _x is the target value t ₀
If it does not match, the process of performing additional etching of the transparent film 2 is repeated. The additional etching time is adjusted while observing the difference between t _x and t ₀ .

The measurement of the depth t _x of the groove 45 and the subsequent additional etching as described above are performed as shown in FIGS. 6 (6) and (7), where t _x = t ₀ = λ / 2 (n−1). ). The etching process ends when t _x = t ₀ . Then, as shown in FIG. 7E, the resist pattern 44 is peeled off to complete the phase shift mask.

As described above, when forming the groove 45 in the transparent film 42 constituting the exposure mask, the resist pattern 44 is formed.
Since the depth of the groove 45 can be measured with high accuracy while leaving the pattern, the trouble of peeling off the resist pattern 44 can be omitted, and the throughput can be improved. In addition, the measurement of the depth of the groove 45 is performed in a short time by a simple operation without contact, non-destruction.

[0035]

As described above, according to the present invention, AF
While the steps of the plurality of grooves of the transparent film are measured by a method such as the M method, the parameters Δ and の of the grooves are measured by an optical method of ellipsometry, and the step amounts and the parameters Δ After creating a database of correlations with Ψ,
Since the parameters Δ and Ψ of the groove to be detected are measured by the ellipsometry and the parameters Δ and 当 て are applied to the database to calculate the amount of step, the phase management of the phase shifter part of the phase shift mask, When the method is applied to the phase adjustment, the measurement of the depth of the groove in the phase shifter becomes easier as compared with the AFM method.

In addition, even if the resist remains on the transparent film on which the groove is formed, if the resist film thickness is measured only once by the AFM method or the like, the resist can be obtained from the step amount calculated from the database. Since the step amount of the groove is determined by subtracting the film thickness, a complicated operation of removing the resist and measuring the step of the groove every time the groove is etched can be omitted.

Moreover, it is not necessary to form the substrate constituting the phase shift mask from a highly reflective material, and the range of choice of the substrate material and the material of the transparent film on the substrate can be widened.

[Brief description of the drawings]

FIG. 1 is a flowchart for obtaining a correlation between a groove depth and parameters Δ and に お け る in a phase shift mask forming method according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating processing of a transparent film, film thickness measurement, and parameters Δ and Ψ for obtaining a correlation between a groove depth and parameters Δ and に お け る in a phase shift mask forming method according to an embodiment of the present invention. It is sectional drawing which shows the process of a measurement.

FIG. 3 is a diagram showing a connection relationship between an apparatus for measuring the depth of a groove and a data processing apparatus in the method for producing a phase shift mask according to one embodiment of the present invention.

FIG. 4 is a configuration diagram of an ellipsometer for measuring groove parameters Δ and に お け る in the phase shift mask forming method according to one embodiment of the present invention.

FIG. 5 is a diagram illustrating an example of a correlation between groove parameters Δ and に お け る and a groove step amount (depth) by an AFM method in the phase shift mask forming method according to one embodiment of the present invention; .

FIG. 6 is a flowchart showing a step of forming a groove in an exposure mask using the correlation between the groove depth and the parameters Δ and 求 め obtained in FIG. 1;

FIG. 7 is a cross-sectional view showing a step of forming a groove in an exposure mask using a correlation between the depth of the groove obtained in FIG. 1 and parameters Δ and Ψ.

FIG. 8 is a diagram illustrating a correlation between groove parameters Δ and に お け る and a groove step amount (depth) according to an AFM method in a method of manufacturing a phase shift mask according to an embodiment of the present invention. It is a figure showing a changing state.

[Explanation of symbols]

1: transparent substrate, 2: transparent film, 3: needle, S ₁ ,..., S _n :
Groove, 10: AFM device, 20: Data processing device, 30:
Ellipsometer, 41: transparent substrate, 42: transparent film, 43:
Light shielding pattern, 44: resist pattern, 45: groove.

Continued on front page F term (reference) 2F063 AA14 AA15 AA16 BA30 BB10 BC05 BD06 CA11 DA01 DA23 DA30 DD08 EA16 JA04 LA01 LA18 LA19 LA22 LA23 LA25 LA29 LA30 2F065 AA25 AA30 BB02 BB18 BB22 CC18 CC31 CC32 DD06 FF44H05 FF50 GG50 JJ01 JJ08 LL33 LL34 PP12 PP24 QQ00 QQ03 QQ18 QQ23 QQ25 QQ26 QQ27 QQ41 UU05 2H095 BB03 BD02 BD18 BD19 BD28

Claims (8)

[Claims] 1. A correlation between a step amount of a plurality of first grooves formed in a part of a first transparent film and a value of a parameter indicating a polarization state of light reflected from the first grooves is determined. After making the database, the first value of the parameter indicating the polarization state of the reflected light of the second groove formed in a part of the second transparent film is measured, and the first value is measured.
And measuring the first step amount of the second groove based on the correlation between the first step and the database. 2. The method according to claim 1, wherein the parameter is measured by ellipsometry. 3. The method according to claim 1, wherein the parameters are a complex amplitude reflectance ratio の and a phase difference Δ of the polarization state. 4. The method according to claim 1, wherein the step amount of the first groove is measured by an atomic force microscope. 5. When a pattern is formed on the second transparent film, the film thickness of the pattern is subtracted from the correlation in the database after measuring the film thickness of the pattern in advance. The method for measuring a step of a transparent film according to claim 1, wherein the first step amount of the second groove is obtained by: 6. The method according to claim 5, wherein the pattern is made of a light shielding material. 7. A correlation between a step amount of a plurality of first grooves formed in a part of the sample transparent film and a value of a parameter indicating a polarization state of light reflected from the first grooves is determined. Creating a database, forming a resist pattern on the mask transparent film, measuring the thickness of the resist pattern, etching the mask transparent film in a portion not covered by the resist pattern. Forming a second groove by measuring a first value of a parameter indicating a polarization state of reflected light of the second groove, and based on the first value and the correlation of the database. Calculating a first step amount of the second groove by subtracting the film thickness of the resist pattern from the obtained step amount; and determining whether the first step amount has reached a target value. Performing the first step difference amount before If the target value is not reached, the second step amount of the second groove determined based on the parameter indicating the polarization state of the reflected light of the second groove and the correlation of the database is the target value. While the etching of the second groove is repeated until reaching the above, when the first or second step amount of the second groove reaches a target value, the etching of the mask transparent film is stopped to stop the etching. Removing the resist. 8. A light-shielding pattern is formed on the mask transparent film, and the first and second step amounts of the second groove are determined based on a value obtained from the correlation in the database. 8. The method according to claim 7, wherein the value is a value obtained by further subtracting the film thickness of the pattern.