JP5687227B2 - Photomask blank cleaning resistance evaluation method and photomask blank manufacturing method - Google Patents

Description

  The present invention relates to a method for evaluating the resistance to cleaning a photomask blank having an optical film, and a method for manufacturing a photomask blank in which dimensional variations in the pattern shape that occur during cleaning of the photomask are suppressed.

Photomasks that have optical films such as antireflection films, light-shielding films, and phase shift films on transparent substrates as photomasks used in a wide range of applications, including the manufacture of semiconductor integrated circuits such as ICs, LSIs, and VLSIs A mask blank in which a predetermined pattern is formed by lithography using ultraviolet rays, electron beams, or the like is used.
In recent years, along with market demands such as higher integration of semiconductor integrated circuits, pattern miniaturization has rapidly progressed, and the exposure wavelength has become shorter.

However, while shortening the exposure wavelength improves the resolution, it has the problem of reducing the depth of focus.
There is a phase shift method as an effective pattern transfer method for such a problem, and a phase shift mask is used as a mask for transferring a fine pattern.

  A halftone phase shift mask is widely used as a phase shift mask. This is a photomask composed of a translucent part and a translucent part. The phase difference between the light that has passed through the translucent part and the light that has passed through the translucent part has a transmittance with respect to the exposure wavelength of, for example, 3-20%. It is about 180 degrees. Examples of the halftone phase shift film that forms the semi-transparent portion of such a halftone phase shift mask include molybdenum silicide oxide (MoSiO), molybdenum silicide nitride (MoSiN), and molybdenum silicide oxynitride (MoSiON). It is used.

  As a halftone phase shift mask manufacturing method, a pattern is formed by lithography on a halftone phase shift mask blank in which an optical film made of a halftone phase shift film and a light-shielding film made of a chromium film are sequentially formed on a transparent substrate. Is used. This is done by applying a resist on the halftone phase shift mask blank, exposing a desired portion of the resist with an electron beam or ultraviolet light, developing the resist, forming a resist pattern, and then patterning the resist. Using the film as a mask, patterning of the light-shielding film made of a chromium film or the like is performed by etching, and after the patterning is performed by etching the phase shift film, the remaining resist film and at least the light-shielding film of the pattern forming portion are peeled off. That's it.

In general, when a photomask is used for pattern exposure of a wafer or the like, cleaning is performed after a certain period of use, and it is used repeatedly. However, the pattern size of the photomask changes due to the cleaning, which is a problem with miniaturization. It has become to.
From such a viewpoint, the problem of cleaning durability of functional thin films such as optical films and light-shielding films used for photomasks has become an important issue. In particular, when the halftone phase shift mask is cleaned by alkali cleaning, the transmittance and phase difference of the halftone phase shift film change, so that a sufficient transfer effect cannot be obtained. For this reason, development of a film having improved cleaning durability has been performed (Patent Documents 1 and 2).
Also, a photomask management method has been studied in order to improve the manufacturing yield in wafer transfer development (Patent Document 3).

  As a cleaning durability evaluation method for a photomask blank having an optical film, a test pattern is applied to the photomask blank for cleaning, and a method of directly measuring a change amount of a CD (Critical Dimension) value before and after cleaning by SEM. is there.

JP 2010-39300 A WO2010 / 092899A1 JP 2008-276002 A JP-A-7-140635

However, the method of forming a test pattern on a photomask blank and measuring the amount of change in CD before and after cleaning by SEM in the evaluation of cleaning durability of the photomask blank actually forms the pattern and changes the CD before and after cleaning. There is a problem that it takes time and labor to obtain the amount.
For this reason, in the film-forming process in the manufacture of the photomask blank, when evaluating the above-described cleaning resistance, the process must be paused for a long time until the evaluation result is obtained, or it can be performed as an evaluation after the manufacture. There is a problem that it takes time to provide feedback when it becomes.
In addition, the SEM measurement has a problem that the image is distorted by charging and the CD value may be inaccurate.

  From such a point, in the photomask blank cleaning resistance evaluation method, a method capable of simply and quickly evaluating the CD change amount before and after cleaning of the photomask obtained from the photomask blank is desired.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a method capable of simply and quickly evaluating the CD change amount before and after cleaning in the cleaning resistance evaluation of a photomask blank. .

  In order to achieve the above object, the present invention provides a method for evaluating the cleaning resistance of a photomask blank having an optical film on a transparent substrate. The amount of the measured optical characteristic value and the change amount of the CD are calculated, and when evaluating the cleaning resistance, a photomask blank having an optical film formed on the transparent substrate to be evaluated is measured. The amount of change in the optical characteristic value before and after cleaning of the optical film is measured, and the measured value is converted into the amount of change in CD before and after cleaning using the previously obtained relational expression, and the converted CD is a predetermined value. Provided is a photomask blank cleaning resistance evaluation method characterized in that the following is a non-defective product.

  As described above, according to the evaluation method of the present invention, the change amount of CD can be easily determined in a short time by measuring the change amount of the optical characteristic value before and after the cleaning. For this reason, the period until an evaluation result comes out can be shortened, and the productivity of a photomask blank can be improved.

At this time, it is preferable that the optical characteristic value to be measured is at least one of transmittance, reflectance, and phase difference.
With such an optical characteristic value, since the correlation with the CD is clear, a highly accurate evaluation can be performed.

At this time, the optical film can be a phase shift film.
In the present invention, a photomask blank having such a phase shift film can be evaluated.

  The present invention is also a method for manufacturing a photomask blank having a film forming step of continuously forming an optical film on a transparent substrate, wherein the photomask blank on which the optical film is formed is formed in the film forming step. The photomask blank cleaning resistance evaluation method of the present invention is evaluated for each predetermined number of sheets, and the photomask blank formed between the photomask blanks determined to be non-defective by the evaluation is defined as non-defective. A method for manufacturing a photomask blank is provided.

  With such a photomask blank manufacturing method, the optical film can be continuously formed while evaluating the photomask blank easily and accurately in a short time, so the evaluation feedback time can be shortened and the productivity can be reduced. Can be improved.

As described above, according to the cleaning resistance evaluation method of the present invention, an optical film such as an antireflection film, a light shielding film, or a phase shift film on a transparent substrate is cleaned, and the CD is measured by measuring the amount of change in the optical characteristic value. The amount of change can be calculated easily and in a short time.
Therefore, in evaluating the amount of change in CD due to cleaning in the film forming process in the production of a photomask blank, the period until the evaluation result is shortened. Even if it is performed as an evaluation after manufacturing, the time for feedback to manufacturing conditions and the like can be shortened, the productivity of the photomask blank can be improved, and the yield and quality can be improved.

It is a flowchart which shows the method of producing the test | inspection board | substrate which has a halftone phase shift film pattern in the washing | cleaning tolerance evaluation method of the photomask blank of this invention. It is the schematic which shows the fluctuation | variation of the phase shift film pattern by washing | cleaning. It is a graph which shows the relationship between the variation | change_quantity of the transmittance | permeability of the phase shift film before and behind washing | cleaning by the washing | cleaning tolerance evaluation method of this invention, and the variation | change_quantity of CD of the photomask before and behind washing | cleaning. It is a graph which shows the relationship between the variation | change_quantity of the phase difference of the halftone phase shift film before and behind washing | cleaning by the washing | cleaning tolerance evaluation method of this invention, and the variation | change_quantity of CD of the photomask before and behind washing | cleaning. It is a graph which shows the relationship between the variation | change_quantity of the reflectance of the halftone phase shift film before and behind washing | cleaning by the washing | cleaning tolerance evaluation method of this invention, and the variation | change_quantity of CD of the photomask before and behind washing | cleaning. It is a flowchart of the test | inspection in the film-forming process of the halftone phase shift film of the manufacturing method of the photomask blank of this invention.

  As a result of studying a method capable of simply evaluating the CD change amount of the optical film in a photomask blank having at least one optical film such as an antireflection film, a light shielding film, or a phase shift film on a transparent substrate. The present inventors have found that there is a correlation between the amount of change in CD of the optical film and the amount of change in optical characteristics in the cleaning, and completed the present invention as follows.

Hereinafter, the present invention will be described in detail as an example of an embodiment with reference to the drawings, but the present invention is not limited thereto.
Hereinafter, the method of the present invention when a halftone phase shift film is formed on a transparent substrate as an optical film will be described.

In the present invention, a relational expression between the amount of change in the CD of the phase shift film pattern before and after cleaning and the amount of change in the optical characteristic value of the halftone phase shift film is obtained in advance.
FIG. 1 shows how to determine the correlation between the change amount of the optical characteristic value of the halftone phase shift film and the change amount of CD of the phase shift film pattern before and after cleaning in the photomask blank cleaning resistance evaluation method of the present invention. FIG. 5 is a flowchart showing an example of a method for producing an inspection substrate on which a halftone phase shift film pattern is formed.

As cleaning used here, SC1 cleaning using a cleaning liquid in which ammonia water (NH ₄ OH), hydrogen peroxide water (H ₂ O ₂ ) and pure water (H ₂ O) are mixed, hydrochloric acid (HCl) and peroxide are used. SC2 cleaning using a cleaning liquid in which hydrogen water (H ₂ O ₂ ) and pure water (H ₂ O) are mixed, sulfuric acid (H ₂ SO ₄ ), hydrogen peroxide (H ₂ O ₂ ), and pure water (H ₂ O) It is preferable to use SPM cleaning using a cleaning liquid mixed with the above or two or more cleaning liquids. Of these, SC1 cleaning and SC2 cleaning with a high cleaning effect are more preferable, and SC1 cleaning is most preferable.

As shown in FIG. 1A, a phase shift film 21 is formed on a transparent substrate 20 to produce a photomask blank 30, and an electron beam resist 22 is applied on the phase shift film 21.
Next, as shown in FIG. 1B, a test pattern is drawn on the electron beam resist 22 on the photomask blank 30 by an electron beam drawing machine and then developed to form a resist pattern.
Subsequently, the halftone phase shift film 21 is etched using the resist pattern as a mask (FIG. 1C), and then the resist 22 is removed to form an inspection substrate (test photo) on which the halftone phase shift film pattern is formed. A mask) is prepared (FIG. 1D).

Thereafter, the optical characteristic value of the formed phase shift film 21 before cleaning is measured. Examples of the optical characteristic value include transmittance, phase difference, and reflectance, and at least one of them can be measured. The wavelength used for measuring the optical characteristics is not particularly limited, but for example, the exposure wavelength may be used. These optical characteristic values can be measured with a general optical measuring instrument.
In addition, the CD before washing is measured. The CD measurement may be a line width or a space width. CD can be measured by CD-SEM.

  After the measurement is completed, the inspection substrate is cleaned under the photomask cleaning conditions, and the measurement of the optical characteristic value and the measurement of the CD are repeated as before the cleaning. Thus, the change amount of the optical characteristic value (change amount from the optical property value before cleaning) and the change amount of CD (change amount from the CD before cleaning) are obtained.

Such cleaning changes the CD and the optical characteristics as shown in FIG. Then, by the measurement as described above, a relational expression between the change amount of each optical characteristic value before and after the cleaning and the change amount of CD as shown in FIGS. 3, 4, and 5, for example, can be obtained.
The relational expression may be an exponential function or a second-order or higher-order polynomial, but is preferable because the first-order expression is simpler. The amount of change in CD and the amount of change in optical characteristic value before and after cleaning are proportional to each other as shown in FIGS. 3, 4, and 5, and can be expressed by the following equation. Each time, and by measuring the optical characteristics and CD, a highly accurate relational expression can be obtained.

  Then, when evaluating the cleaning resistance, the change amount of the optical property value before and after cleaning of the optical film of the photomask blank in which the optical film was formed on the transparent substrate to be evaluated was measured, and the measured value was obtained in advance. Using a relational expression, the amount of change in CD before and after cleaning is converted, and a product whose converted CD is equal to or less than a predetermined value is regarded as a non-defective product.

In the evaluation in the present invention, it is not always necessary to form a test pattern on the optical film in order to measure the value of the optical characteristic. For example, the transmittance of the halftone phase shift film on which the pattern is not formed is measured. What is necessary is just to measure with a measuring device, and to convert the amount of change of this transmittance before and after cleaning into the amount of change before and after cleaning of CD.
It is also possible to measure the reflectance of the halftone phase shift film on which no pattern is formed with a reflectance measuring device, and to convert the amount of change in reflectance into the amount of change in CD.

  In addition, when measuring the phase difference, in order to create a portion where the film for measuring the phase difference is not formed, a masking tape is applied to the substrate, a phase shift film is formed, and then the masking tape is peeled off. May be measured by a phase difference measuring device. As another method, in order to create a portion where the film for measuring the phase difference is not formed, a magic is applied to the substrate, a phase shift film is formed, and then the phase shift is applied to the portion where the magic is applied with alcohol or the like. The phase difference may be measured by removing the film. The amount of change in the phase difference before and after cleaning can be converted into the amount of change in the CD value before and after cleaning.

  The measurement of transmittance, reflectance, and phase difference as described above can be similarly performed when obtaining the relational expression. For example, a substrate in which a pattern for measuring CD is partially formed on a halftone phase shift film. You can also find the relational expression with

  In this way, if the amount of change in the optical characteristic value before and after cleaning is obtained and converted into the amount of change in CD using the relational expression obtained in advance, it is possible to quickly evaluate the cleaning resistance against the amount of change in CD.

  For example, the photomask blank can be manufactured while evaluating using the cleaning resistance evaluation method of the present invention as described above.

When the allowable value of the CD change amount of the phase shift film pattern of the photomask is S, the change amount of the optical characteristic value corresponding to the allowable value S of the CD change amount converted from the change amount of the optical characteristic value is the allowable value. Assuming T, in order to evaluate the change amount of the CD in the cleaning, the test substrate for evaluation is cleaned by a predetermined number of times of cleaning, and the film forming conditions and the like are set so that the change amount of the optical characteristic value does not exceed the predetermined value T. May be managed. That is, in the present invention, if the amount of change in the optical characteristic value measured at the time of evaluation before and after cleaning is equal to or less than the predetermined value T, it can be determined as a non-defective product.
For example, if the photomask blank to be manufactured is for manufacturing a 45 nm-capable photomask, the allowable value S of the amount of change due to CD cleaning of the halftone phase shift film pattern is 10 nm, and the photomask blank to be manufactured is 22 nm. The thickness may be 5 nm if it is for the production of a photomask.

In order to manage the manufacturing process so as not to exceed the predetermined value T, there are the following methods.
A halftone phase shift film is continuously formed on a transparent substrate (FIG. 6A), and an inspection substrate is loaded every time a predetermined number of optical films are formed (FIG. 6B). An optical film is formed, or a substrate on which the optical film is formed every predetermined number is extracted for inspection. The film-formed inspection substrate is washed a predetermined number of times, and the manufacturing can proceed while confirming that the measured change amount of the optical characteristic value does not exceed the predetermined value T (FIG. 6C). This is possible (FIG. 6D). In addition, a photomask blank formed between inspection substrates on which optical films that have not exceeded the predetermined value T (determined as non-defective) are formed can be made non-defective.

On the other hand, if the amount of change in the measured optical characteristic value exceeds the predetermined value T, the film formation is stopped and the conditions are adjusted, or it is determined that the substrate is determined to be non-defective this time from the substrate determined to be non-defective in the previous evaluation. The photomask blank formed between the substrates is discarded (FIG. 6E). Since the evaluation method of the present invention has a short feedback time, such a manufacturing loss can be reduced.
Further, as shown in FIG. 6, a threshold value t smaller than the predetermined value T is set (FIG. 6F), the amount of change in the optical characteristic value obtained from the inspection board is equal to or less than the predetermined value T, and the threshold value t is set to If it exceeds, the film formation conditions are adjusted (FIG. 6G), and the halftone phase shift film can be manufactured continuously and stably by lowering the value to a value equal to or less than the threshold value t.

  The threshold t may be determined in consideration of the measurement interval and the rate of change, such as a change amount of the optical characteristic value corresponding to 70% of the allowable value S.

  When measuring the optical characteristic value of the optical film, there is no particular restriction on the position of the measurement, but if an in-plane distribution occurs in the film quality of the optical film by the film forming apparatus or film forming method, take this into account A plurality of measurement positions may be provided.

  For example, in the following process, a half-tone phase shift film that has become a non-defective product is formed by a sputtering method using a chromium-based light-shielding film as the main component. A functional film such as a mask film may be stacked.

  The optical film having an optical function such as an antireflection film, a light shielding film, or a phase shift film laminated on the transparent substrate used in the evaluation method of the present invention may be a single layer, a multilayer, or a material layer having an inclined composition. There is something to be. Materials used include silicon, which may contain transition metals such as Mo, Zr, Ti, Ta, W, and Nb, containing light elements such as oxygen and nitrogen (for example, see Patent Document 4). In addition, as a partial layer, a transition metal such as Cr or a layer containing a light element such as oxygen or nitrogen in the transition metal is used.

  When a silicon material that may contain a transition metal is used as the halftone phase shift film material or the light shielding film material, specifically, an alloy of a transition metal and silicon, a transition metal, silicon, and oxygen And a transition metal silicon compound containing at least one selected from nitrogen and carbon, preferably a transition metal silicon compound containing a transition metal, silicon, and oxygen and / or nitrogen. More specifically, as the transition metal silicon compound, transition metal silicon oxide, transition metal silicon nitride, transition metal silicon oxynitride, transition metal silicon oxycarbide, transition metal silicon oxynitride, transition metal silicon oxynitride carbide, etc. Can be mentioned. Further, as the transition metal, at least one selected from titanium, vanadium, cobalt, nickel, zirconium, niobium, molybdenum, hafnium, tantalum and tungsten is a suitable material. In particular, molybdenum from the viewpoint of dry etching processability. It is preferable that

The halftone phase shift film has a transmittance of 3% or more and 20% or less with respect to the exposure wavelength, and the phase difference between the light passing through the semi-transmissive portion and the light passing through the transmissive portion is about 180 ± 3 degrees. Is.
As the light shielding film, when the photomask blank is composed of a halftone phase shift film, a light shielding film, and an antireflection film, the total optical density is 2.5, more preferably 3.0. Is. Furthermore, the present invention can be used when there is no halftone phase shift film (such as a photomask blank for a binary mask in which a photomask pattern is composed of a light-shielding portion and a light-transmitting portion). In this case, the total optical density is 2.5, more preferably 3.0. Further, when it is composed of a halftone phase shift film, an etching stopper film, a light shielding film, and an antireflection film, or when it is composed of an etching stopper film, a light shielding film, and an antireflection film, the total optical density is 2. 5, more preferably 3.0.

  As described above, according to the cleaning evaluation method and the manufacturing method of the present invention, a photomask blank capable of manufacturing a photomask having high cleaning resistance can be stably manufactured.

EXAMPLES Hereinafter, although an Example and a comparative example are shown and this invention is demonstrated more concretely, this invention is not limited to these.
(Example)
[Method for obtaining correlation between optical characteristic value variation and CD variation in cleaning resistance evaluation, and test pattern creation method therefor]
On the synthetic quartz substrate, a phase shift film made of molybdenum silicide oxynitride having a phase difference of 180 ° and a transmittance of 6% with respect to an exposure wavelength of 193 nm was formed.

Next, a resist was applied (FIG. 1A), and a test pattern was drawn on the resist with an electron beam drawing machine (FIG. 1B). Next, the phase shift film was processed by fluorine-based dry etching (FIG. 1C).
Next, the resist was peeled off to produce a substrate in which a test pattern was applied to the phase shift film (FIG. 1 (d)).

The initial optical characteristic values (transmittance, phase difference, reflectance) of this substrate were measured by MPM193 manufactured by Lasertec, and CD was measured by CD-SEM (E3610 manufactured by Advantest). Thereafter, washing is performed four times under predetermined washing conditions (APM solution (NH ₄ OH: H ₂ O ₂ : H ₂ O = 1: 1: 100), washing for 30 minutes), and the optical characteristic value after washing each time. CD was measured. 3, 4, and 5 are graphs plotting transmittance, phase difference, and reflectance and CD variation, which are optical characteristic values in each cleaning, respectively.
3, 4, and 5 are proportional to each other, and the correlation coefficient is 1.00 for the transmittance of FIG. 3, 0.99 for the phase difference of FIG. 4, and the reflectance. In this case, it was 0.99.

[Method for producing inspection substrate and method for evaluating washing resistance]
Next, a line having a width of 1 mm and a length of 2 cm was marked with a magic at the center of the substrate in order to attach a portion where an optical film for phase difference measurement was not formed on the quartz substrate. A phase shift film was formed on this substrate in the same manner as described above, and the magic part was wiped off with methanol to obtain an inspection substrate.
The value of the transmittance before cleaning of the inspection substrate was measured by MPM193 manufactured by Lasertec. Next, the inspection substrate was washed three times continuously under the same cleaning conditions as described above, and then the transmittance value of the inspection substrate was measured. At this time, the amount of change in the transmittance value before and after cleaning was 0.42%.

  From FIG. 3 showing the relationship between the change amount of transmittance of the halftone phase shift film before and after cleaning and the change amount of CD of the photomask before and after cleaning, when the change amount of transmittance is converted into the change amount of CD, it is about It was found to be 5.2 nm.

[Determination method of predetermined value and threshold value of phase shift film]
Since the photomask blank to be manufactured is used for manufacturing a photomask for 45 nm, assuming that the predetermined value of the CD change amount is 10 nm, the corresponding transmittance change amount (predetermined value) is about 0.81%. Further, when the change amount of CD corresponding to 70% of the predetermined value is set as a threshold value, this threshold value is 7 nm, and the transmittance change amount at this time is 0.57% when converted from FIG.

[Method for producing phase shift film]
By the method for producing the inspection substrate, the first substrate manufactured was used as the inspection substrate. After measuring the transmittance of this test substrate, it was washed three times continuously under the washing resistance evaluation washing conditions. After cleaning, the transmittance of the test substrate was measured again, and the transmittance change amount was found to be 0.44%. When converted to the CD change amount, it was about 5.4 nm.
Next, the 50th substrate manufactured was used as an inspection substrate. After measuring this transmittance, it was washed three times continuously under the washing conditions for washing resistance evaluation. After cleaning, the transmittance of the test substrate was measured again, and the amount of change in transmittance was obtained. As a result, it was 0.43%, which was below the threshold value.
Therefore, the halftone phase shift films formed on the first and 50th films were not more than a predetermined value and were judged as non-defective products. Therefore, it can be determined that the photomask blank formed between the first sheet and the 50th sheet is a good product.

  The present invention is not limited to the above embodiment. The above-described embodiment is an exemplification, and the present invention has substantially the same configuration as the technical idea described in the claims of the present invention, and any device that exhibits the same function and effect is the present invention. It is included in the technical scope of the invention.

20 ... Transparent substrate, 21 ... Halftone phase shift film, 22 ... Resist,
30 ... Photomask blank.

Claims (4)

In a method for evaluating the cleaning resistance of a photomask blank having an optical film on a transparent substrate,
Advance, obtains the amount of change in the CD before and after washing of the optical film variation and before and after washing of the optical characteristic value of the optical film is measured, the measured amount of change in the optical characteristic value and the CD variation relationship ,
In the evaluation of the cleaning resistance, a change amount of the optical property value before and after cleaning of the optical film of the photomask blank in which the optical film is formed on the transparent substrate to be evaluated is measured, and the measured value is obtained in advance. It was converted to the amount of change in cleaning before and after CD optical film of a photomask blank in which the evaluated using a relational expression, and characterized in that the variation of CD was the converted to the good ones is less than a predetermined value To evaluate the cleaning resistance of a photomask blank.   2. The photomask blank cleaning resistance evaluation method according to claim 1, wherein the optical characteristic value to be measured is at least one of transmittance, reflectance, and phase difference.   The photomask blank cleaning resistance evaluation method according to claim 1, wherein the optical film is a halftone phase shift film. A method for producing a photomask blank having a film forming step of continuously forming an optical film on a transparent substrate,
In the film formation step, the photomask blank on which the optical film is formed is evaluated for each predetermined number of sheets by the photomask blank cleaning resistance evaluation method according to any one of claims 1 to 3, A photomask blank manufacturing method characterized in that a photomask blank formed between photomask blanks determined to be non-defective by evaluation is non-defective.

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