JP2988884B2 - Beam adjustment method in charged beam writing apparatus - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a pattern writing technique using a charged beam, and more particularly to a beam adjusting method for adjusting a shaped beam with high precision in a variable shaped beam type charged beam writing apparatus.

[0002]

2. Description of the Related Art In a variable shaped beam type electron beam drawing apparatus, a pattern is drawn by connecting basic unit figures such as rectangles on a sample surface. At this time, in order to draw a high-precision pattern, the dimensions of the forming beam are determined with high accuracy,
It is necessary to connect shots (basic figures) of the formed electron beam with high precision.

In a variable shaped beam type electron beam writing apparatus, in order to obtain a desired beam size, adjustment of a forming sensitivity and a forming offset for determining an electron beam size are performed. However, beam drift where the position and current of the electron beam change with time, measurement errors of the stage position,
Due to various error factors such as disturbance noise and processing accuracy of an aperture for forming a beam, even if a forming sensitivity adjustment or a forming offset adjustment is performed, a high adjustment accuracy cannot be obtained, and a beam dimensional error always occurs. This beam dimensional error is a major factor that lowers the accuracy of electron beam shot connection and lowers writing accuracy.

Here, if the dimensional error of the beam can be obtained with high accuracy, the dimensional error can be greatly reduced by feeding back the error to the drawing apparatus. However, with an optical microscope or a scanning electron microscope conventionally used as a means for evaluating a shaped beam, it has been difficult to perform beam evaluation at the nanometer level required for shot connection.

[0005]

As described above, in the conventional electron beam writing apparatus of the variable shaped beam type, the dimension of the shaped beam cannot be measured with high accuracy at the nanometer level. It has been difficult to perform accurate drawing. Further, the above problem is not limited to the electron beam writing apparatus, but can be similarly applied to the ion beam writing apparatus.

The present invention has been made in consideration of the above circumstances, and an object of the present invention is to evaluate a beam size at a nanometer level, and to feed back the result to obtain a beam size at a nanometer level. An object of the present invention is to provide a beam adjusting method in a charged beam writing apparatus capable of improving writing accuracy.

[0007]

[Means for Solving the Problems]

(Structure) In order to solve the above problem, the present invention employs the following structure. That is, the present invention provides a charged beam forming means having at least a forming offset adjusting function and a forming sensitivity adjusting function for obtaining a desired charged beam shot shape and size on a sample surface, and a charged beam formed by this means is used as a sample. A deflecting means for deflecting to a desired position on the surface, a charged beam drawing apparatus for drawing a desired pattern on the sample surface by connecting shots of the charged beam,
When adjusting the size and shot shape of the forming beam,
After performing molding offset adjustment and molding sensitivity adjustment in advance,
Perform drawing on the resist applied on the substrate with a plurality of beam size setting values and a plurality of molding sensitivity setting values, respectively, and develop the drawn resist in a time shorter than the optimal developing time, thereby forming a joint between shots. The resist is scanned by a scanning probe microscope to measure the height of the resist, and a molding sensitivity error and a molding offset error are obtained based on the measured resist height and the beam dimension setting value and the molding sensitivity setting value. The feedback is provided to the charged beam adjusting means and the deflecting means.

Here, preferred embodiments of the present invention include the following. (1) The resist must be a positive resist. (2) The charged beam must be an electron beam. (3) The scanning probe microscope is an atomic force microscope (AFM) or a scanning tunneling microscope (STM) that scans the resist with the probe kept at a fixed distance from the resist surface.

(Operation) If a resist on which a pattern is drawn by connecting shots of a charged beam is developed in a time shorter than an appropriate developing time, a resist residue corresponding to the developing time is generated in a pattern portion. This resist residue (resist height)
When there is no beam dimensional error, the same applies to the joints of shots and other portions. However, if there is a beam dimensional error, the resist height at the joint of shots differs from that at the other portions. And even if there is a slight beam size error at the nanometer level, the above difference in height is in a range that can be sufficiently detected by the scanning probe microscope.

Therefore, according to the present invention, a resist in which a pattern is drawn by connecting shots of a charged beam is developed in a time shorter than an appropriate developing time, and then the resist height at a connecting portion of the shots is measured by a scanning probe microscope. Thereby, the beam size error can be measured at the nanometer level. Furthermore, by performing writing with a plurality of beam size setting values and molding sensitivity setting values, and measuring the resist height in the same manner, it is possible to obtain a molding sensitivity error and a molding offset error with high accuracy. Then, by feeding them back to the charged beam shaping means and the deflecting means, it becomes possible to perform high-precision drawing at the nanometer level.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The details of the present invention will be described below with reference to the illustrated embodiments. FIG. 1 is a schematic configuration diagram showing an electron beam writing apparatus used in the embodiment. Electron gun 1
The cross-over image of the electron beam emitted from is formed five times by the first illumination lens 2, the second illumination lens 3, the first projection lens 4, the second projection lens 5, and the reduction lens 6, and
Finally, an image is formed on the main surface of the objective lens 7. The image of the first shaping aperture 12 is formed on the second shaping aperture 13, and a shaping image is formed on the sample surface 15 by the reduction lens 6 and the objective lens 7. Further, a shaping deflector 9 is provided between the first shaping aperture 12 and the second shaping aperture 13, and the rotation is adjusted based on a previously calculated value and incorporated into the electron optical column. .

In the figure, reference numeral 8 denotes a blanking deflector, 1
0 indicates an objective deflector, and 11 indicates a blanking aperture. A method of generating a variable shaped beam using the above-described electron beam drawing apparatus will be described with reference to FIG. The first shaping aperture 12 having the rectangular opening shown in FIG. 2A is illuminated by the illumination systems 1, 2 and 3 of FIG. 1, and the image of the first shaping aperture 12 is projected by the projection lenses 4 and 5 in FIG.
It is projected on the second shaping aperture 13 having an arrow-shaped opening shown in FIG. At this time, by changing the position of the first shaping aperture image on the second shaping aperture by the shaping deflector 9, it is possible to generate a rectangular or right isosceles triangular beam as shown in FIG. it can.
By changing the voltage applied to the shaping deflector 9, FIG.
As shown in (d), the size of the beam of each shape can also be changed.

The electron beam formed by the first and second shaping apertures is reduced at a predetermined reduction ratio by the reduction lens 6 and the objective lens 7 and is imaged on the sample surface 15.
At this time, a desired position is selected as an image forming position by the objective deflector 10, and a desired position on the sample surface 15 is irradiated with an electron beam. The voltage applied to the shaping deflector 9 is determined by the beam size setting value, the shaping sensitivity setting value, the shaping offset setting value, and the like.

There is an upper limit to the size of the electron beam generated by the above method on the sample surface. To draw a large-scale pattern such as a circuit pattern of an integrated circuit, a basic unit pattern of the generated electron beam is required. (Hereinafter called a shot) must be connected and drawn on the sample surface. An error generated at this time is an electron beam connection error.

FIG. 3 shows the cause of the connection error. FIGS. 3A and 3B are schematic diagrams in the case of drawing by connecting rectangular basic unit figures. FIG. 3A shows a case where there is no connection error, and FIG. 3B shows a case where there is a connection error. The connection error in FIG. 3B is due to a dimensional error of the shot. Since the shots overlap each other, the irradiation amount in this portion increases, which causes pattern shape deterioration and pattern dimensional errors. The same applies to the case where the shot size is small and separation occurs.

FIGS. 3 (c) and 3 (d) show schematic diagrams of oblique lines connecting triangular shots. FIG. 3 (c)
(D) shows a case where drawing is performed using the triangle shots of TYPE2 and TYPE4 in FIG. 2 and TYPE3 and TYPE.
This is a case where drawing is performed using the triangle shot No. 5. FIG. 3C shows a case where there is no connection error, and FIG. 3D shows a case where there is a connection error. In FIG. 3D, a connection error occurs due to an error in the beam size, and an overlap occurs at the shot joint. Due to such connection errors, the pattern shape and the pattern dimensional accuracy deteriorate as in the case of the rectangular shape.

Conventionally, an optical microscope or a scanning electron microscope has been used to evaluate the connection accuracy. At this time, the existence of a connection error was observed as color unevenness due to a difference in interference caused by a difference in the amount of resist film reduction when developed due to a difference in resist exposure amount due to shot separation or overlap. However, in this method, the evaluation accuracy is limited to a level of several tens of nanometers or more, a feedback error to a writing apparatus is large, and a considerable amount of time is spent for adjustment for high-accuracy writing.

In the present embodiment, in order to solve such a problem, the height of the resist after electron beam writing and development is measured by a scanning probe microscope to obtain a height distribution caused by a shot connection error. Enables accurate evaluation and adjustment. This will be described below.

First, a conceptual diagram of a scanning probe microscope used in the present embodiment is shown in FIG. The scanning probe microscope used in this embodiment is an atomic force microscope (AFM)
Then, the interatomic force acting between the sample and the probe is detected, and the surface of the sample is scanned so that the force becomes constant.

This method can be roughly classified into three methods: a method in which a probe is pressed against a sample to detect a repulsive force between the probe and the sample, a method in which the probe is separated by about 50 nm from the sample to detect an attractive force, a method in which the sample is separated from the probe and the probe In some cases, the probe is vibrated to such an extent that the probe hits the sample, and the change in amplitude at that time is detected. Although the measurement can be performed by either method, the most suitable one may be selected according to the surface condition of the sample. Further, a scanning microscope of a type that is most easily measured according to the characteristics of the sample, such as another scanning tunnel microscope (when the sample is conductive), may be used as appropriate.

First, FIG. 4 shows the relationship between the beam size setting value s and the actual beam size S. 4A is an ideal case, and the actual beam size S can be expressed as S = A _J × s using the ideal forming sensitivity A _J. Originally, A _J = 1 because the actual beam size S matches the beam size setting value s. However, in the actual case, S = A × s + β where A = A _J + α, and includes the molding sensitivity error α (the difference between the molding sensitivity adjustment value and the ideal molding sensitivity A _J ) and the molding offset error β. .
For this reason, the beam size setting value and the actual beam size are shown in FIG.
(B).

Next, a description will be given of the drawing and the scanning probe microscope measurement in which the beam size setting value and the molding sensitivity setting value are changed. FIG. 5 shows shot connection when the molding sensitivity is A _J and the molding offset error is zero. a represents a unit beam size setting value, and as an example, a beam size setting value a, 1.5
FIGS. 5 (a), 5 (b) and 5 (c) show the cases a and 2a, respectively. The beam intensity distribution is a trapezoidal distribution for simplicity. Further, (a), (b), (c) 'in FIG. 5 are (a), (b), (c), respectively.
Of the beam intensity distributions, and corresponds to the resist height.

When the molding offset error is zero at the molding sensitivity A _J , the irradiation amount at the shot joint portion coincides with the peripheral irradiation amount, so that the resist film reduction amount is also constant. The resist height h is also constant. Since the molding sensitivity error and molding offset error are zero,
As shown in FIG. 6, even if the beam size setting value is changed, the beam size error ΔS becomes zero.

However, in the actual case, since the molding sensitivity error α and the molding offset error β exist, as shown in FIG. 7A, the resist height h is not constant at the shot joint. Also, when the beam size setting value is changed due to molding sensitivity error, the resist height h at the shot joint changes.
In FIGS. 7 (2) (3) and 8 (4) (5), the molding sensitivity was deliberately shifted by -ΔA, ΔA, 2ΔA, 3ΔA, respectively, and the semi-developed resist was measured with a scanning probe microscope. The resist height h at the shot joint is shown.

The greater the amount of shift in molding sensitivity, the greater the overlap between shots, so that the height h of the resist at the joint between shots decreases. FIG. 9 shows a graph in which these h are plotted. The molding sensitivity shift amount at which the resist height becomes zero with respect to each beam size setting value was ΔA ₀ . This is because the adjustment value A (= A _J +
It means that when the beam size is shifted by ΔA _{0 with} respect to α), the beam size becomes an ideal value. Assuming that the difference from the ideal beam size value is a beam size error ΔS, it is represented by ΔS = ΔA ₀ × s. FIG. 10 shows ΔS obtained with respect to each beam size set value and plotted. Since the beam size error ΔS is generated by the molding sensitivity error α and the molding offset error β, it is expressed by ΔS = α × s + β. By approximating FIG. 10 with this equation,
The inclination can be obtained as a molding deflection sensitivity error α, and the intercept can be obtained as a molding deflection offset error β. Since the measurement reproducibility of the resist height h of the scanning probe microscope is not more than nm, α and β can also be obtained with an error at the nm level. Therefore, when α is obtained, this is fed back to the molding sensitivity adjustment value A, and A-α is used as the sensitivity value,
High-precision drawing at the sensitivity error nm level becomes possible. Also,
Similarly, with respect to the molding offset error, by feeding back β, a high-precision drawing at an offset error nm level becomes possible.

The present invention is not limited to the above embodiment. In the embodiment, the beam intensity distribution is described as a trapezoidal shape. However, the beam intensity distribution may be implemented as a Gaussian distribution or another distribution. Further, the change rates of the beam size setting values are set to 1, 1.5, and 2, but are not limited thereto as long as they can be set.

Also, the explanation has been given using a rectangular beam as an example.
In the case of using a triangular beam, drawing is performed by changing the molding sensitivity setting value and the beam dimension setting value in the same manner, and the shot joint portion is evaluated with a scanning probe microscope to obtain a nm.
Needless to say, it is possible to obtain a level forming sensitivity error and a forming offset error, and to feed back these errors to the drawing apparatus to perform high-precision drawing.

Although the embodiment has been described by taking an electron beam lithography apparatus as an example, the invention is not limited to this and can be applied to an ion beam lithography apparatus. In addition, various modifications can be made without departing from the scope of the present invention.

[0029]

As described above in detail, according to the present invention, in a charged beam drawing apparatus of a variable shaped beam system, a resist in which a pattern is drawn by connecting shots of a charged beam is developed in a shorter time than an appropriate developing time. Thereafter, the beam height error can be measured at the nanometer level by measuring the resist height at the joint of the shots with a scanning probe microscope. Then, by feeding back the evaluation result to the drawing apparatus, the drawing accuracy can be improved at the nomometer level.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an electron beam writing apparatus used in an embodiment of the present invention.

FIG. 2 is a diagram showing an aperture shape and a variable shaped beam generation principle in the apparatus of FIG. 1;

FIG. 3 is a diagram for explaining a cause of a beam connection error of a variable shaped beam.

FIG. 4 is a diagram showing a relationship between a set beam size s of a variable shaped beam and an actual size S.

FIG. 5 is a diagram showing a beam intensity distribution and a resist height when there is no molding sensitivity error and molding offset error.

FIG. 6 is a diagram showing a beam size error with respect to a beam size set value when there is no molding sensitivity error and molding offset error.

FIG. 7 is a diagram showing a beam intensity distribution and a resist height when there is a molding sensitivity error and a molding offset error.

FIG. 8 is a diagram showing a beam intensity distribution and a resist height when there is a molding sensitivity error and a molding offset error.

FIG. 9 is a diagram showing a relationship between a molding sensitivity shift amount and a resist height at a shot joint portion.

FIG. 10 is a diagram for explaining a method of obtaining a molding sensitivity error and a molding offset error from a relationship between a beam size setting value and a beam size error.

FIG. 11 is a schematic configuration diagram showing a scanning probe microscope used in an embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Electron gun 2,3 ... Illumination lens 4,5 ... Projection lens 6 ... Reduction lens 7 ... Objective lens 8 ... Blanking deflector 9 ... Shaping deflector 10 ... Objective deflector 11 ... Blanking aperture 12 ... First shaping Aperture 13: second forming aperture 15: sample surface

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-9-82603 (JP, A) JP-A-9-63933 (JP, A) JP-A-9-186070 (JP, A) 251939 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 21/027 G03F 7/20

Claims (1)

(57) [Claims] 1. A charged beam forming means having at least a forming offset adjusting function and a forming sensitivity adjusting function for obtaining a desired charged beam shot shape and size on a sample surface,
A deflecting means for deflecting the charged beam formed by this means to a desired position on the sample surface, and a charged beam drawing apparatus for drawing a desired pattern on the sample surface by connecting shots of the charged beam; After performing molding offset adjustment and molding sensitivity adjustment,
Perform drawing on the resist applied on the substrate with a plurality of beam size setting values and a plurality of molding sensitivity setting values, respectively, and develop the drawn resist in a time shorter than the optimal developing time, thereby forming a joint between shots. The resist is scanned by a scanning probe microscope to measure the height of the resist, and a molding sensitivity error and a molding offset error are obtained based on the measured resist height and the beam dimension setting value and the molding sensitivity setting value. A beam adjusting method in a charged beam drawing apparatus, wherein feedback is performed to a charged beam adjusting unit and a deflecting unit.