JP2004214415A - Pattern plotting method and device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve pattern transferring precision using a stepper by performing plotting added with the position deviation of a pattern formation face when the back face of a substrate is adhered to a predetermined standard face. <P>SOLUTION: This pattern plotting method for plotting a desired pattern on a substrate to be plotted held by a substrate holding part by an energy beam is provided to measure the distribution of the height position of a back face opposite to the face where the pattern of a substrate 11 is formed in a status that the substrate 11 is held by a substrate holding part 12, to calculate the position deviation value of the face where the pattern is formed generated in a status that the back face of the substrate 11 is corrected to a flat face based on the measured distribution of the height position, and to correct the pattern plotting position at the time of plotting the pattern based on the calculated position deviation value. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a pattern drawing method and a drawing apparatus for forming a semiconductor integrated circuit and other fine element patterns on a substrate such as a semiconductor wafer or a mask.
[0002]
[Prior art]
In recent years, in order to form an LSI pattern on a semiconductor wafer, a so-called stepper (transfer device) that uses an exposure mask in which a Cr pattern is formed on a glass substrate and sequentially transfers the pattern of the mask onto the wafer. Widely used. The reduction ratio of the stepper is about 1/5, and it has been said that the pattern of 1 μm or less cannot be resolved due to the limit of the wavelength of light. Micron patterns have been resolved. Furthermore, in order to form a pattern with a line width of 50 nanometers, development of an EUV (Extreme Ultra Violet) exposure technology using light having a shorter wavelength as a light source has been advanced.
[0003]
In a stepper, it is necessary to maintain an imaging relationship between the mask surface and the wafer surface. As the pattern becomes finer, the depth of focus of the lens becomes extremely shallow, about 1 μm, and it is necessary to maintain good flatness of the glass substrate constituting the mask. In EUV exposure, the exposure light is inclined at 7 degrees with respect to the substrate surface. Therefore, even with a flatness of 1 μm, the horizontal shift is 1 μm × 2 × tan7 ° = 250 nm, which causes a very large error. Become. Therefore, it is necessary to further improve the flatness of the substrate.
[0004]
The flatness of the substrate is finished by polishing, but at present there are irregularities of about 2 to 0.5 μm. Therefore, a method of improving the flatness of the substrate by adsorbing the substrate on a flat surface with a vacuum chuck or the like during pattern transfer has been adopted.
[0005]
On the other hand, a mask used for a stepper is formed by drawing a pattern on Cr deposited on a glass substrate by a pattern drawing apparatus using a focused electron or laser as a light source. In a pattern drawing apparatus using an electron beam or the like, in order to achieve high-precision pattern position accuracy,
(1) A method of eliminating deformation of a mask caused by holding force when the mask is mounted on an apparatus by supporting the mask at three points, and correcting a displacement due to its own weight in advance in terms of material dynamics (Patent Document 1) reference).
[0006]
(2) A method of acquiring height distribution data of a mask surface with respect to a reference surface in a state where the mask is mounted on a support point, obtaining a deformation amount when the mask is elastically deformed, and correcting the data (Patent Reference 2).
[0007]
Etc. have been proposed.
[0008]
However, the above method has the following problems. When transferring the pattern on the mask onto the wafer, the mask is held in a stepper, but as mentioned earlier, electrostatic forces and vacuum forces are used to keep the surface on which the pattern is formed at a high flatness. Utilizing the method, a method is employed in which the back surface is attracted to a chuck finished to high precision flatness.
[0009]
At this time, when the pattern is drawn by the method (1), a good pattern position accuracy can be obtained in a state where the correcting force does not act on the mask. This causes a pattern shift. Further, when the pattern is drawn by the method (2), good pattern position accuracy can be obtained in a state where the surface on which the pattern is formed is corrected to be flat. However, since the surface shape of the mask is determined independently for the front and the back, chucking the back surface of the mask does not make the surface on which the pattern is formed in a state where the back surface is corrected to be flat, and therefore the front surface and the back surface are flattened. A pattern position error occurs due to a difference in shape of the back surface.
[0010]
[Patent Document 1]
JP-A-8-250394
[Patent Document 2]
Japanese Patent Publication No. 3-52210
[Problems to be solved by the invention]
As described above, conventionally, when a mask on which a pattern is formed by a pattern drawing apparatus is mounted on a stepper and a pattern is transferred onto a wafer, there has been a problem that transfer accuracy is reduced due to a positional shift of a pattern forming surface of the mask.
[0013]
The present invention has been made in consideration of the above circumstances, and an object thereof is to perform pattern drawing in consideration of a positional shift of a pattern forming surface when a back surface of a substrate to be drawn is brought into close contact with a predetermined reference surface. To provide a pattern drawing method and a drawing apparatus which can contribute to improvement of pattern transfer accuracy using a stepper or the like.
[0014]
[Means for Solving the Problems]
(Constitution)
In order to solve the above problems, the present invention employs the following configuration.
[0015]
That is, the present invention is a pattern drawing method for drawing a desired pattern by an energy beam on a substrate to be drawn held by a substrate holding unit, wherein the substrate is held by the substrate holding unit, Measure the distribution of the height position of the back surface opposite to the surface forming the pattern, based on the distribution of the measured height position, the back surface of the substrate occurs in a state corrected to an arbitrary curved surface or flat surface, The method is characterized in that a position shift amount of a surface on which a pattern is formed is calculated, and a pattern drawing position when drawing the pattern is corrected based on the calculated position shift amount.
[0016]
Further, the present invention is a pattern drawing method for drawing a desired pattern with an energy beam on a substrate to be drawn held by a substrate holding unit, wherein the substrate is held by the substrate holding unit before the substrate is held by the substrate holding unit. In a state where the back surface opposite to the surface on which the pattern of the substrate is formed is held so as to include the direction axis in which gravity acts, the unevenness distribution of the back surface is measured, and based on the measurement result, the substrate is mounted on the substrate holding unit. Calculate the distribution of the height position of the back surface in the state held in, based on the calculated distribution of the height position, the pattern generated in a state where the back surface of the substrate is corrected to an arbitrary curved surface or flat surface, the pattern The method is characterized in that a position shift amount of a surface to be formed is calculated, and a pattern drawing position when drawing the pattern is corrected based on the calculated position shift amount.
[0017]
The present invention also provides a pattern writing apparatus for performing the above method, wherein a means for writing a circuit pattern of a semiconductor device by irradiating a substrate to be drawn with an energy beam, a means for holding the substrate, and a pattern on the substrate. Means for measuring the distribution of the height position of the back surface facing the surface to be formed, based on the distribution of the measured height position, occurs in a state where the back surface of the substrate is corrected to any curved surface or flat surface, It is characterized by comprising means for calculating the amount of positional shift of the surface on which the pattern is formed, and means for correcting the pattern drawing position based on the calculated amount of positional shift.
[0018]
Here, preferred embodiments of the present invention include the following.
[0019]
(1) The energy beam must be an electron beam or a laser beam.
[0020]
(2) In order to measure the height position of the back surface of the substrate to be drawn, light is applied to the back surface of the substrate from an oblique direction, and the reflected light from the back surface of the substrate is detected by a position sensor such as a two-division detector.
[0021]
(3) The substrate holding unit holds the substrate to be drawn by three-point support.
[0022]
(4) To calculate the distribution of the height position on the back surface of the substrate, add the measurement result of the unevenness distribution on the back surface of the substrate and the calculation result of the deflection due to the weight of the substrate.
[0023]
(Action)
Consider the positional fluctuation of the substrate surface before and after the substrate is brought into close contact with a flat surface. As shown in FIG. 5A, when the substrate is curved convexly upward, compressive strain is generated on the surface of the substrate by bringing the back surface of the substrate into close contact with a flat surface. This results in pattern displacement. In addition, even when the substrate has no curvature, when the thickness of the substrate is not uniform and has irregularities on the back surface of the substrate, as shown in FIG. Irregularities are formed on the surface of the substrate reflecting the shape of the back surface of the substrate and the thickness distribution of the substrate, resulting in displacement of the surface of the substrate. When the back surface of the substrate is curved convexly downward, if the back surface of the substrate is brought into close contact with a flat surface, tensile strain is generated on the surface of the substrate. This results in pattern displacement.
[0024]
As described above, it is extremely difficult to form the rear surface of the substrate to be flat over the entire surface, and the distribution of the height position is generated on the rear surface of the substrate. Therefore, when the back surface of the substrate is brought into close contact with a flat surface, irregularities or distortions are generated on the surface of the substrate reflecting the shape of the back surface of the substrate, which causes a pattern position shift. The present invention takes this into consideration in advance and performs correction accompanying the above-mentioned positional deviation at the time of pattern drawing.
[0025]
That is, if the distribution of the height position of the back surface of the substrate in a state where the substrate to be drawn is held by the substrate holding unit is determined in advance, it is determined how much distortion is applied to the surface of the substrate when the back surface of the substrate is in close contact with a flat surface. And the horizontal displacement of the substrate surface can be calculated. If correction is made during pattern writing by the amount of this positional deviation, the original pattern is formed on the substrate surface in a state where the back surface of the substrate is in close contact with a flat surface.
[0026]
Therefore, when a mask is used as a substrate to be drawn, when a pattern is drawn on the mask, the pattern can be corrected so as to have no displacement when the mask is mounted on a stepper and used. This makes it possible to realize a mask that can contribute to the improvement of pattern transfer accuracy by the stepper.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described in detail with reference to the illustrated embodiments.
[0028]
(1st Embodiment)
FIG. 1 is a schematic configuration diagram showing an electron beam writing apparatus according to the first embodiment of the present invention.
[0029]
An electron optical barrel 20 having an electron gun, various deflection systems, various lenses, and the like is installed on a drawing chamber 10 held in vacuum. The electron optical column 20 is controlled by a drawing control circuit 21 and irradiates an electron beam onto a surface of a substrate 11 to be described later to draw a desired pattern. In the drawing chamber 10, a stage 12 for holding a substrate 11 to be drawn, which serves as an exposure mask, is housed. The holding of the substrate 11 by the stage 12 is performed by a spring mechanism 13 that supports the substrate 11 from below and a guide 14 that contacts the surface of the substrate 11 and defines the height position of the substrate surface. The holding of the substrate 11 is, for example, three-point support as shown in FIG.
[0030]
The stage 12 can be moved in the horizontal direction (X, Y directions) by the motor 15 under the control of the drawing control circuit 21. Further, a height measuring device for measuring a height position (irregularity) on the back surface of the substrate 11 is provided. This measuring device is composed of an irradiation system 17 for irradiating the back surface of the substrate 11 with light obliquely, and a detection system 18 for detecting the reflected light from the back surface of the substrate 11 with a two-part detector or the like. Is processed by the signal processing, so that the height position on the back surface of the substrate can be measured. Then, the height distribution of the entire back surface of the substrate 11 can be measured by sequentially moving the stage 12 in the X direction and the Y direction by the motor 15.
[0031]
The height distribution h (x, y) (x and y are measurement coordinates) obtained by the measuring device is supplied to the arithmetic circuit 22. The calculation result of the calculation circuit 22 is supplied to the drawing control circuit 21 so that the pattern drawing position by the electron optical barrel 20 is corrected.
[0032]
Next, a pattern drawing method using the above apparatus will be described.
[0033]
First, the substrate to be drawn 11 is held on the stage 12. This holding is three-point support using the spring mechanism 13 and the guide 14 as described above. The substrate 11 finally becomes a mask for exposure. For example, a Cr film is formed on the entire surface of a glass substrate, and a resist is applied thereon. Further, the thickness distribution of the substrate 11 is given as substrate data and is assumed to be known in advance. If the thickness distribution of the substrate 11 is not known, measure the distance between the front surface and the back surface using a contact-type measuring instrument such as a micrometer or a non-contact displacement meter based on the optical principle or the like as a pre-process of drawing. With this, the thickness distribution of the substrate 11 is measured.
[0034]
Next, the height position of the back surface of the substrate 11 is measured by a measuring device, and the height distribution of the back surface is measured by moving the stage 12 in the X and Y directions. The correction amount is calculated by the arithmetic circuit 22 based on the measured height distribution and the thickness distribution of the substrate 11. That is, based on the height distribution and the thickness distribution of the substrate 11, when the back surface of the substrate 11 is chucked flat from the state where the substrate 11 is held on the stage 12 of the pattern drawing apparatus, the pattern of the substrate 11 is The amount of displacement of the drawing surface in the horizontal direction is calculated, and the amount of correction of the pattern drawing position is calculated based on the amount of displacement. Then, the drawing control circuit 21 corrects the pattern drawing position and performs pattern drawing.
[0035]
After the LSI pattern is drawn on the resist by this pattern drawing, the resist is developed to form a resist pattern, and the Cr film is selectively etched using the resist pattern as a mask to form an LSI pattern on the Cr film. Will be. Then, the exposure mask thus formed is mounted on a stepper, and the mask pattern is transferred while the back surface is attracted to a flat surface by a vacuum chuck or the like. The transfer method of the mask pattern in the stepper may be a reflection type or a transmission type. If a chuck member or the like is present on the back side of the mask and these may be shadowed, the reflection type is preferable.
[0036]
As described above, according to this embodiment, the height distribution of the back surface of the substrate 11 is measured for the substrate 11 held on the stage 12, and the height distribution of the substrate 11 when mounted on a stepper and the back surface is held flat is measured. The displacement of the substrate surface is calculated, and drawing is performed based on the calculation result so that the substrate 11 is mounted on the stepper so as to have an optimal pattern. Therefore, when the back surface of the substrate 11 is held flat by the stepper, it is possible to realize high-precision pattern position accuracy, and it is possible to improve pattern transfer accuracy.
[0037]
(Second embodiment)
FIG. 3 is a schematic configuration diagram showing an electron beam writing apparatus according to the second embodiment of the present invention. The same parts as those in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted.
[0038]
In this apparatus, a height measuring device is omitted from the apparatus shown in FIG. 1, and instead of measuring the height distribution on the back surface of the substrate, the height distribution is obtained by calculation. In the present embodiment, before mounting the substrate to be drawn 11 serving as an exposure mask on the stage 12, the correction amount at the time of drawing is calculated in advance.
[0039]
First, as shown in FIG. 4, the substrate 11 is placed (vertically) so that the pattern drawing surface and the back surface facing the pattern drawing surface include the direction of the gravity axis. The back surface of the substrate 11 is arranged close to an optical flat (a glass plate finished with high precision flatness and parallelism: plane parallel) 41 and illuminated via a half mirror 43 by an illumination light source 42 whose wavefront is controlled. Is done. Since the substrate 11 and the plane parallel 41 are placed close to each other, the observation optical system 44 observes interference fringes according to the flatness of the substrate 11. By performing image processing on the shape of the stripe with the signal processing circuit 45, the unevenness (flatness) on the back surface of the mask can be accurately measured. Then, from this measurement result, the displacement amount of the mask surface (pattern drawing surface) when the mask back surface is chucked to a flat surface can be calculated.
[0040]
Next, the same substrate 11 is placed on the stage 12 accommodated in the drawing chamber 10. At this time, since the substrate 11 is supported at three points, the substrate 11 is deformed by its own weight. However, since the amount of deformation is uniquely determined by the material of the substrate, the position of the supporting point, the size of the substrate, and the like based on the material dynamics, the amount of deformation due to its own weight can be obtained in advance. Then, the amount of displacement of the pattern drawing surface due to the deflection of the mask under its own weight can be calculated based on the amount of deformation.
[0041]
Therefore, the correction amount of the pattern drawing position can be calculated by inputting the displacement amount due to its own weight deflection and the displacement amount based on the measurement result of the mask back surface to the arithmetic circuit 22 at the time of drawing. Then, based on this correction amount, the pattern drawing position is corrected by the electron optical barrel 20 to perform the pattern drawing, so that when the back surface of the substrate 11 is held flat by the pattern transfer device, the pattern position accuracy is high. Can be realized.
[0042]
The calculation of the correction amount of the pattern drawing position can also be performed as follows. Since the deflection of the substrate 11 due to its own weight can be calculated in advance, the amount of deformation of the back surface of the substrate due to its own weight can also be calculated. Therefore, the height distribution of the back surface of the substrate 11 in a state where the substrate 11 is mounted on the stage 12 can be calculated by adding the previously measured unevenness of the back surface of the substrate and the amount of deformation of the back surface of the substrate due to its own weight deflection. . If the height distribution of the back surface of the substrate is known, the amount of displacement of the pattern drawing surface of the substrate 11 in the horizontal direction when the back surface of the substrate 11 is chucked flat is calculated as in the first embodiment. The correction amount of the pattern drawing position can be calculated based on the displacement amount.
[0043]
As described above, in the present embodiment, similarly to the first embodiment, it is possible to draw the LSI pattern so that the pattern position accuracy becomes high when the back surface of the substrate 11 is held flat. Thus, the accuracy of pattern transfer by the stepper can be improved. In this case, this can be realized only by providing the arithmetic circuit 22 for the correction calculation, and there is no need to provide a height measuring device in the drawing apparatus. Therefore, there is an advantage that the conventional apparatus can be used as a drawing apparatus as it is.
[0044]
(Modification)
Note that the present invention is not limited to the above embodiments. In the embodiment, an electron beam is used to draw a pattern, but an ion beam, a laser beam, or the like may be used instead of the electron beam.
[0045]
The substrate to be drawn is not necessarily limited to an exposure mask, but may be a semiconductor wafer. A plurality of patterns are transferred to a semiconductor wafer. In order to achieve both accuracy and throughput, there is a method of drawing a fine pattern with an electron beam and transferring other patterns with a stepper. As described above, the present invention can be effectively applied to the case where an LSI pattern is formed on a semiconductor wafer by combining pattern drawing by an electron beam drawing apparatus and pattern transfer by a stepper.
[0046]
Further, in the embodiment, when the substrate to be drawn is mounted on the stepper, the description has been made on the assumption that the back surface of the substrate is brought into close contact with a flat surface. The present invention is similarly applicable to the present invention. The means for measuring the height of the back surface of the substrate is not limited to oblique incidence illumination, and a laser interferometer that irradiates laser light from the vertical direction to the back surface of the substrate and measures the distance to the back surface of the substrate is used. be able to. Further, any measuring instrument that can measure without contacting the back surface of the substrate can be used.
[0047]
In addition, various modifications can be made without departing from the scope of the present invention.
[0048]
【The invention's effect】
As described in detail above, according to the present invention, it is possible to perform pattern drawing in consideration of the positional deviation of the pattern forming surface when the back surface of the substrate to be drawn is brought into close contact with a predetermined reference surface, using a stepper or the like. This can contribute to improvement in pattern transfer accuracy.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram showing an electron beam writing apparatus according to a first embodiment.
FIG. 2 is a diagram showing a state in which a mask is supported at three points on a stage in the first embodiment.
FIG. 3 is a schematic configuration diagram showing an electron beam writing apparatus according to a second embodiment.
FIG. 4 is a diagram showing a state of measuring flatness of a back surface of a mask in the second embodiment.
FIG. 5 is a diagram illustrating a state of a positional shift of a mask surface that occurs when the back surface of the mask is brought into close contact with a flat surface.
[Explanation of symbols]
Reference Signs List 10 drawing room 11 drawing substrate 12 stage 13 spring mechanism 14 guide 15 motor 17 irradiation system 18 detection system 20 electron optical column 21 drawing control circuit 22 arithmetic circuit 41 optical flat 42 ... Illumination light source 43 ... Half mirror 44 ... Observation optical system 45 ... Signal processing circuit

Claims (3)

A pattern drawing method for drawing a desired pattern by an energy beam on a substrate to be drawn held by a substrate holding unit,
In a state where the substrate is held by the substrate holding unit, a distribution of height positions on a back surface facing a surface on which a pattern is formed on the substrate is measured, and based on the measured distribution of height positions, Calculate the positional shift amount of the surface forming the pattern, which occurs when the back surface is corrected to an arbitrary curved surface or flat surface, and correct the pattern drawing position when drawing the pattern based on the calculated positional shift amount. A pattern drawing method characterized by the above-mentioned. A pattern drawing method for drawing a desired pattern by an energy beam on a substrate to be drawn held by a substrate holding unit,
Before holding the substrate in the substrate holding unit, in a state where the substrate is held so that the back surface opposite to the surface on which the pattern of the substrate is formed includes the direction axis in which gravity acts, the unevenness distribution of the back surface is measured. In advance, based on the measurement result, the distribution of the height position of the back surface in a state where the substrate is held by the substrate holding unit is calculated, and based on the calculated distribution of the height position, the back surface of the substrate is Calculating a positional shift amount of a surface on which the pattern is formed, which is generated in a state corrected to an arbitrary curved surface or a flat surface, and correcting a pattern drawing position when drawing the pattern based on the calculated positional shift amount. Characteristic pattern drawing method. Means for drawing a circuit pattern of a semiconductor device by irradiating an energy beam on a substrate to be drawn, means for holding the substrate, and means for measuring the distribution of height positions on the back surface facing the surface on which the pattern of the substrate is formed Based on the distribution of the measured height position, the back surface of the substrate occurs in a state corrected to an arbitrary curved surface or flat surface, means for calculating the amount of positional deviation of the surface forming the pattern, Means for correcting a pattern writing position based on the calculated positional deviation amount.

Images