JP2012215636A - Method of manufacturing photomask - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method of manufacturing a photomask that deals with deterioration in positional accuracy due to generation of a drift where drawn pattern density changes largely when the photomask is drawn with an electron beam.SOLUTION: The drift is suppressed by the method of manufacturing the photomask including the steps of: predetermining a specified value of change in drawing density of a drawn pattern of the photomask; finding drawing density change of the drawn pattern; and dividing the drawn pattern into a plurality thereof so that change in drawing density is equal to or less than the specified value when the found drawing density change is larger than the predetermined specified value.

Description

  The present invention relates to a method for manufacturing a photomask used in the manufacture of a semiconductor device, and more particularly to a method for manufacturing a photomask that improves accuracy in an electron beam drawing process.

  The photomask corresponds to a negative (original) when a circuit is baked on a silicon wafer in a semiconductor device manufacturing process. A fine pattern is formed by reducing and exposing the pattern on the photomask onto the surface of the silicon wafer.

  In order to produce this photomask, a mask pattern is formed on the photomask substrate by laser light or electron beam drawing technology based on the circuit pattern data, and then completed through etching, resist stripping, cleaning, measurement, and inspection. Become.

  An electron beam drawing machine is used to create a photomask by the electron beam drawing technique. It is known that the position accuracy of the electron beam drawing machine drifts due to expansion / contraction of the device material due to temperature, humidity, atmospheric pressure, etc., the influence of a magnetic field, beam stability, and the like.

  The drift has a variation that occurs at the start of drawing called initial drift. There are also drifts that occur during drawing or depending on the drawing pattern. As drift factors during drawing, disturbance factors such as expansion / contraction of apparatus materials due to changes in temperature, humidity, atmospheric pressure, and changes in magnetic field are cited.

  Furthermore, if the electron beam column (electron optical system unit) of the electron beam lithography system is contaminated, the beam stability deteriorates due to the charge-up that accumulates charges, the irradiation position drifts, and the drawing position accuracy is increased. make worse.

  This charge-up can be improved by exchanging the electron optical system unit, but until then, the positional accuracy will be deteriorated according to the degree of contamination of the unit. Also, replacement of the electron optical system unit requires a high cost and a lot of time, and cannot be performed frequently.

  As conventional photomask manufacturing methods corresponding to these drifts, there are methods described in Patent Document 1 and Patent Document 2. The manufacturing method described in Patent Document 1 corrects drift in units of periods and disturbances. In period-by-period drift correction, the correction period is shortened during the initial drift when the change at the start of drawing is large, and the correction period is extended because the change is small during the stable period after the initial drift. In drift correction for disturbance units, drift correction was performed using changes in disturbance elements such as atmospheric pressure and temperature as triggers. In this way, it is possible to reduce the number of drift corrections while dealing with disturbances.

  The drawing method described in Patent Document 2 observes the drift of the irradiation position due to column contamination, and calculates a correction amount from a predetermined prediction function using the observed position error. Based on this correction amount, highly accurate irradiation is possible.

JP 2007-43083 A JP 2010-73909 A

  However, the technique described in Patent Document 1 has a disadvantage that it does not cope with drift due to a change in the drawing pattern density.

  In addition, the technique described in Patent Document 2 does not consider a drawing pattern, and thus has a disadvantage that it does not cope with a sudden deterioration in position accuracy at a place where a change in drawing pattern density is large.

  An object of the present invention is to provide a method for manufacturing a photomask corresponding to a drift in which the positional accuracy is deteriorated at a position where a change in the drawing pattern density is large.

  The present invention employs the following configuration in order to solve the above problems.

  The present invention relates to a photomask manufacturing method for manufacturing a photomask by electron beam drawing. Then, a step of predetermining a predetermined value of the drawing density change, a step of obtaining a drawing density change of the drawing pattern of the photomask, and if the obtained drawing density change is larger than the predetermined value of the drawing density change, the drawing density change And a step of dividing the drawing pattern into a plurality of values so as to be less than or equal to a predetermined value of the drawing density change.

  Further, a predetermined value of the drawing density change is set according to the degree of contamination of the optical system objective unit.

  Further, in a photomask manufacturing method for manufacturing a photomask by electron beam drawing, a step of predetermining a predetermined value of the drawing density, a step of obtaining a drawing density of a drawing pattern of the photomask, and the obtained drawing density being the drawing density And a step of dividing the drawing pattern into a plurality of parts so that the drawing density is equal to or lower than the predetermined value of the drawing density when larger than the predetermined value.

  A predetermined value of the drawing density is set according to the degree of contamination of the optical system objective unit.

  According to the present invention, since it has the above-described features, the following can be achieved.

  That is, in a photomask manufacturing method for manufacturing a photomask by electron beam drawing, a step of predetermining a predetermined value of a drawing density change, a step of obtaining a drawing density change of a drawing pattern of a photomask, A step of dividing the drawing pattern into a plurality of parts so that the drawing density change is less than or equal to the predetermined value of the drawing density change when the drawing density change is larger than the predetermined value. It becomes possible to cope with a drift in which the accuracy deteriorates.

  In addition, since a predetermined value of a change in drawing density is set according to the degree of contamination of the optical system objective unit, even if drawing becomes unstable due to contamination of the optical system objective unit, it is possible to perform drawing with sufficient quality.

  Further, in a photomask manufacturing method for manufacturing a photomask by electron beam drawing, a step of predetermining a predetermined value of the drawing density, a step of obtaining a drawing density of a drawing pattern of the photomask, and the obtained drawing density being the drawing density A step of dividing the drawing pattern into a plurality of parts so that the drawing density is equal to or less than the predetermined value of the drawing density when the value is larger than the predetermined value, and the drift that the position accuracy at a place where the change of the drawing pattern density is large is deteriorated It becomes possible to cope with.

  Since a predetermined value of the drawing density is set according to the degree of contamination of the optical system objective unit, even if the drawing becomes unstable due to contamination of the optical system objective unit, it is possible to perform drawing with sufficient quality.

Graph showing correlation between drawing time and drift by electron beam drawing system Graph showing the correlation between the change in the density of contamination of the electron optical system unit of the electron beam lithography system and the drift value The map which shows the density of the original drawing pattern which concerns on one Embodiment of this invention It is a figure explaining the manufacturing method of the photomask of one Embodiment, Comprising: The map which shows the density change of the original drawing pattern Map showing density of divided drawing patterns according to one embodiment Map showing density of divided drawing patterns according to one embodiment Map showing density of divided drawing patterns according to one embodiment Map showing density change of divided drawing pattern according to one embodiment The flowchart which shows the data processing which concerns on one Embodiment

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The present embodiment relates to a photomask manufacturing method using an electron beam drawing technique, and more particularly to a photomask manufacturing method capable of managing drift in an electron beam drawing process within a certain range.

  FIG. 1 is a graph for explaining what kind of drift occurs depending on the drawing time by the electron beam drawing apparatus. FIG. 2 is a graph showing the correlation between the degree of contamination of the electron optical system unit and the drift value due to density change. 3 to 8 show a drawing pattern and density or a map of density change. FIG. 9 is a flowchart showing how data is processed.

<Process to understand charge drift characteristics>
The change in drift will be described with reference to FIG. FIG. 1 is a graph showing the correlation between drawing time and drift. The initial drift is from the beginning of the drawing time to the point A, and the change in drift is large. After the initial drift, the drift from point A to point B is a stable period in which the change in drift is small. When the predetermined time elapses and the point B is reached, charge drift occurs thereafter, and the change in drift increases.

  FIG. 2 is a graph showing a relationship between a change in drawing density between adjacent sections and a drift value of charge drift depending on the degree of contamination of the electron optical system unit of the electron beam drawing apparatus. Obtained using the evaluation pattern of charge drift. As the time from column replacement elapses and the degree of contamination increases, the drift value that fluctuates increases. As shown in FIG. 2, if the contamination is large, the stability of the drawing is impaired, and if there is a density change with the adjacent section, a large drift value is obtained. If the contamination is small, the drawing is stable, and thus a large density The drift value that fluctuates even if there is a change is small.

  In FIG. 2, in order not to exceed the drift management value 1, the density change needs to be 25% or less in a high contamination state. Hereinafter, as a specific description of the photomask manufacturing method of the present embodiment, a case where the density change obtained from the drift management value 1 is within 25% will be described below.

<Step of dividing drawing pattern>
Taking the actual drawing pattern as an example, the process of dividing the drawing pattern by the drawing density will be described. Here, the unit of pattern analysis is preferably an arbitrary mesh unit, but may be a pattern unit as necessary. FIG. 3 shows a drawing density map 2 of a drawing pattern, and FIG. 4 shows a drawing density change map 3.

  FIG. 3 is a drawing density map 2 showing an example of a drawing pattern, and is composed of a central section 4 and a U-shaped portion surrounding it. As for the drawing density of each part, the drawing density of the central section 4 is 40%, and the upper and lower sections 5 located above and below the central section 4 in the U-shaped portion are the drawing density of 30%. The vertical section 6 on the right side of the portion 5 has a drawing density of 10%, and the section 7 at the left end of the upper and lower portions has a drawing density of 5%.

  FIG. 4 is a drawing density change map 3, and shows a difference (density change) in drawing density between each section and an adjacent portion. That is, the drawing density difference between the adjacent portions in the contour portions of the respective sections is shown. In the outline portion 4a of the central section 4, the adjacent portion is not provided with a pattern and is a portion having a drawing density of 0%, so the density change is 40%. Further, the density change between the contour portion 5a of the upper and lower sections 5 and the portion where the pattern is not provided is 30%, and the density change between the adjacent sections is a portion overlapping the contour section 6a of the vertical section 6 Is 20 percent, and the portion overlapping the contour portion 7 a of the end section 7 is 25 percent.

  The number of pattern divisions is determined from the drawing density change map 3 shown in FIG. 4 and a predetermined value of density change. Since the density change in the central section is a maximum of 40%, the pattern density needs to be reduced to 25% or less in order to make the drift management value or less, and the number of divisions is 2 or more. The density change in the upper and lower sections 5 is 30%, and it is necessary to reduce the pattern density to 25% or less, and this part also needs to be divided into two or more.

  The drawing density map 2 shown in FIGS. 5 and 6 shows an example in which the drawing pattern shown in FIG. 3 is divided into two drawing patterns. A drawing density change map 3 corresponding to the drawing density map 2 shown in FIG. 5 is shown in FIG. 7, and a drawing density change map 3 corresponding to the drawing density map 2 shown in FIG. 6 is shown in FIG. As shown in the drawing density change map 3 in FIGS. 7 and 8, the density change in the drawing density map 2 shown in FIGS. 5 and 6 is both less than 25 percent of the drift management value 1.

  By forming the drawing pattern in this way, a stable photomask can be manufactured even in a state where the contamination of the optical system objective unit is high and drawing is unstable and drift is likely to occur.

  Further, as described above, there are various types of drift, such as initial drift, in addition to contamination of the optical system objective unit. However, since drawing is stable, it is possible to cope with such drift. If stable drawing can be maintained, the drawing speed can be increased as necessary.

  The flowchart shown in FIG. 9 summarizes the data processing method in this embodiment. First, the left part of the flowchart will be described. This portion corresponds to “a step of grasping charge drift characteristics”.

  First, drift data is acquired (step S1). For example, the drift data is a graph showing the relationship between the drawing density change between adjacent sections and the drift value depending on the degree of contamination of the electron optical system unit of the electron beam drawing apparatus shown in FIG. This drift management value 1 is determined from this drift data (step S2). From the drift management value 1, the upper limit value of the density change with the adjacent portion is obtained, and the drift density upper limit value is determined (step S3).

  Next, the right part of the flowchart will be described. This portion corresponds to “the step of dividing the drawing pattern”.

  A drawing density map 2 of the drawing pattern is created from the drawing pattern (step S4). A drawing density change map 3 corresponding to the drawing density map 2 is created using the drawing density map 2, a density change with an adjacent portion is obtained, and a drawing pattern density analysis is performed (step S5).

  The density change of the drawing density change map 3 obtained in step S5 is compared with the upper limit value of the density change obtained in step S3 so that the density change of the drawn drawing pattern after the division does not exceed the upper limit value. The number is determined (step S6).

  A drawing density map 2 and a drawing density change map 3 are created for each drawing pattern divided by the result of step S6, and the upper limit value of the density change of the drawing density change map 3 is obtained in step S3. After confirming that the upper limit value of the density change is not exceeded, the drawing pattern density analysis is performed (step S7).

  By processing the data as described above and using the drawing pattern created by dividing based on the determination, a photomask can be stably manufactured even in a state where drawing is unstable and fluctuation is likely to occur.

  In the above-described embodiment, the drawing pattern is divided so that the density change is not more than the upper limit value corresponding to the management value 1 while paying attention to the density change, but the upper limit value is determined by paying attention to the drawing density of the drawing pattern. May be divided. This is because if the maximum value of the drawing density is lowered, the density change does not occur beyond the lower value of the drawn density, and therefore the density change between adjacent portions is also reduced. If the division is performed according to the drawing density, the step of obtaining the density change can be omitted, which is simpler.

  In addition, if the number of divisions of the drawing pattern is too large, the stage moves more and as a result, the drawing time is lengthened. Further, the pattern division range may be the entire surface, or may be for each arbitrary area.

  Moreover, the method of dividing | segmenting will not be ask | required if a density is divided. For example, a commercially available pattern dividing software for multiple exposure may be used, or the pattern may be divided by software or the like corresponding thereto.

  The drift management value 1 can be variously set according to the performance of the electron beam drawing machine used. In this example, it was found that the pattern density should be 16% or less using the charge drift evaluation pattern.

  Further, a drawing density map 2 and a drawing density change map 3 of the drawing pattern were created, and it was analyzed that the maximum value of the density change was 42%.

  In order to make the charge drift less than or equal to the control value, the drawing pattern of 16% or more was divided into three, and each was divided so as to be 16% or less.

A 6-inch Qz (quartz glass) substrate with a Cr light-shielding film was prepared, and this substrate was coated with a positive resist for electron beam: FEP171 (manufactured by Fujifilm) with a thickness of 300 nm and divided into three by an electron beam drawing apparatus. Draw a pattern. At this time, the drawing condition was a dose of 10 μC / cm ² .

  Next, post-exposure heat treatment (PEB: Post Exposure Bake) was performed, and then development processing was performed with a tetramethylammonium hydroxide (TMAH) 2.38% developer. The development time was 90 seconds.

Next, the Cr film as a light shielding film was etched using an ICP (Inductively Coupled Plasma) dry etching apparatus. The Cr etching conditions were Cl ₂ flow rate 40 sccm, O ₂ flow rate 10 sccm, He flow rate 80 sccm, pressure 15 mTorr, ICP power 300 W, and RIE (Reactive Ion Etching) power 30 W.

Finally, the resist was peeled off by O ₂ plasma ashing (conditions: O ₂ flow rate 500 sccm, pressure 30 Pa, RF power 1000 W).
As described above, a photomask with reduced charge drift was manufactured.

  In the photomask of this example, it was possible to reduce deterioration in positional accuracy due to charge drift compared to the conventional case.

1 Drift Management Value 2 Drawing Density Map 3 Drawing Density Change Map 4 Center Division 5 Top and Bottom Division 6 Vertical Division 7 Edge Division

Claims (4)

In a photomask manufacturing method for manufacturing a photomask by electron beam drawing,
A step of predetermining a predetermined value of a change in drawing density;
Obtaining a drawing density change of a drawing pattern of the photomask;
When the obtained drawing density change is larger than a predetermined value of the drawing density change, dividing the drawing pattern into a plurality of patterns so that the drawing density change is not more than a predetermined value of the drawing density change;
A method for manufacturing a photomask, comprising: 2. The method for producing a photomask according to claim 1, wherein a predetermined value of the drawing density change is set according to a degree of contamination of the optical system objective unit. In a photomask manufacturing method for manufacturing a photomask by electron beam drawing,
A step of presetting a predetermined value of the drawing density;
Obtaining a drawing density of a drawing pattern of the photomask;
When the obtained drawing density is larger than a predetermined value of the drawing density, a step of dividing the drawing pattern into a plurality so that the drawing density is not more than the predetermined value of the drawing density;
A method for manufacturing a photomask, comprising: 4. The method for producing a photomask according to claim 3, wherein the predetermined value of the drawing density is set according to the degree of contamination of the optical system objective unit.

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