JP5643618B2 - Height measuring method and charged particle beam drawing apparatus - Google Patents

Description

  The present invention relates to a height measurement method and a charged particle beam drawing apparatus.

  An electron beam drawing apparatus is used for the purpose of drawing a fine pattern on a sample such as a mask substrate or a semiconductor wafer. When a pattern is drawn on a sample using this apparatus, it is necessary to measure the exact height of the sample surface before drawing in order to avoid a shift in drawing position and a focus shift in an electron beam. Specifically, the height measurement unit of the electron beam drawing apparatus irradiates light near the irradiation region to detect reflected light and measures the height of the sample surface before drawing. Then, according to the measured height, for example, a lens that focuses the electron beam on the sample surface is adjusted. Thereby, the electron beam can be accurately focused on the surface of the sample.

  In the height measuring unit, the laser light emitted from the light source is converged on the surface of the sample by the light projecting lens. The converged light is reflected by the surface of the sample, enters the light receiving lens, and then converges again on the light receiving element. A PSD (Position Sensitive Detector) is used as the light receiving element. The PSD has a structure similar to that of a PIN type photodiode, and realizes measurement of the center of gravity of light by measuring a photocurrent by a photovoltaic effect.

When the spot light is incident on the PSD, an electric charge proportional to the light energy is generated at the incident position, passes through a resistance layer (P layer) having a uniform resistance value, and reaches an electrode installed on two end faces on the PSD. Flowing. The amount of current at this time is divided in inverse proportion to the distance to the electrode. If the output current from the electrode placed on one end face is I ₁ and the output current from the electrode placed on the other end face is I ₂ , the barycentric position X of the spot light from the PSD center is given by Is required. Here, L is the length of the light receiving surface. Further, the total photocurrent indicating the received light intensity of PSD is the sum of I ₁ and I ₂ .

  Incidentally, the reflectance of the sample surface with respect to the light emitted from the light source varies depending on the film thickness of the sample, the physical properties of the film, the wavelength of the light incident on the sample surface, and the polarization state. Ideally, the above equation will always show a constant value if the center of gravity of the light does not change even if the amount of received light changes. It does not affect.

  However, in practice, the offset voltage generated in the light receiving element and the analog signal processing circuit constituting the height measuring unit acts as a manufacturing error, so that it is not constant in the case of samples having different reflectivities. Therefore, when measuring the height between samples with different reflectivities, if the offset voltage is large, the error becomes larger than when measuring the height between samples with the same reflectivity, and the electron beam is applied to the surface of the sample. It becomes difficult to converge accurately.

  Such a problem becomes conspicuous, for example, in the manufacturing process of the phase shift mask. The phase shift mask is used as one of the techniques for improving the resolution of the transfer pattern in the field of photomasks. In the phase shift mask, a phase shift portion (shifter opening) is provided on one of the openings so that the phase of the transmitted light transmitted through the adjacent openings is reversed. As a result, when transmitted light interferes with each other, the light intensity at the boundary is weakened to improve the resolution and depth of focus of the transfer pattern.

  FIG. 8 is an example of a manufacturing process of a Levenson type phase shift mask.

First, as shown in FIG. 8A, a Cr film 302 is formed on a SiO ₂ substrate 301, and a first resist film 303 is further formed thereon. Next, after irradiating the first resist film 303 with an electron beam, development processing is performed to pattern the first resist film 303 into a predetermined pattern as shown in FIG. 8B. Next, the Cr film 302 exposed from the first resist film 303 is etched to obtain a structure shown in FIG. Thereafter, when the first resist film 303 is peeled off, the structure shown in FIG. 8D is obtained.

Next, a second resist film 304 is formed on the substrate of FIG. Thereby, the substrate shown in FIG. 8E is obtained. Next, after irradiating the second resist film 304 with an electron beam, development processing is performed to pattern the second resist film 304 into a predetermined pattern as shown in FIG. Next, the SiO ₂ substrate 301 exposed from the second resist film 304 is etched to obtain a structure shown in FIG. Thereafter, when the second resist film 304 is peeled off, the structure shown in FIG. 8H is obtained.

In FIG. 8E, the lower layer of the second resist film 304 is a patterned Cr film 302. That is, the lower layer of the second resist film 304 includes a Cr film 302 portion and a SiO ₂ substrate 301 portion. For this reason, when measuring the height of the surface of the second resist film 304 during electron beam drawing, the light measured by the PSD is different because the reflectance of the light emitted from the light source of the height measuring unit is different. The position of the center of gravity changes. Therefore, it becomes impossible to measure the exact height of the surface of the second resist film 304.

  FIG. 9 shows an example in which the surface height of a resist film similar to the resist film 304 is measured. In the Zmap shown in FIG. 9, the central portion is entirely recessed. This is because the reflectance is lowered due to the dense pattern provided in the lower layer of the resist film at the center, and the influence of the offset voltage is strongly exerted. Moreover, in Zmap of FIG. 9, the shape is convex at two points in the center. This is because the laser beam emitted from the light source at the height measurement unit has converged to the boundary of the pattern with different reflectivity, and the measurement error has increased due to the change in the barycentric position of the light measured by the PSD. It is.

  In order to solve such a problem, Patent Document 1 discloses an electron beam drawing apparatus including an adjusting unit that adjusts the intensity of light emitted from a light source according to the reflectance of a sample surface. However, in the method of Patent Document 1, the control circuit of the height measuring unit needs to be changed, and the intensity of the light emitted from the light source changes, which may cause a photoreaction on the sample surface or a temperature change. was there.

JP 2003-303758 A

  The present invention has been made in view of the above points. That is, an object of the present invention is to provide a height measurement method and a charged particle beam drawing apparatus capable of reducing the height measurement error caused by the pattern formed on the sample and improving the drawing accuracy. is there.

A first aspect of the present invention is a height measurement method for measuring the height of a sample by obliquely entering the sample and receiving the reflected light reflected by the surface of the sample with a PSD (Position Sensitive Detector). In
A step of determining a height reference range;
Obtaining an offset value on an analog signal processing circuit including PSD;
Obtaining the measurement data of the sample height using a value obtained by subtracting the offset value from the output value of the PSD;
A step of creating sample height data by performing fitting using the remaining values except for values not included in the reference range in the sample height measurement data It is.

The first aspect of the present invention includes a step of dividing a sample height measurement region by a predetermined grid,
When the height at the grid intersection is measured and the obtained value is within the reference range, the height at the next adjacent grid intersection is measured, but is not within the reference range. Preferably repeats the process of discarding the height at the intersection of the grid and measuring the height near the intersection.

The second aspect of the present invention is a height measurement method for measuring the height of a sample by obliquely entering the sample and receiving the reflected light reflected by the surface of the sample with a PSD (Position Sensitive Detector). In
Obtaining an offset value on an analog signal processing circuit including PSD;
Using the value obtained by subtracting the offset value from the output value of the PSD to obtain measurement data of the sample height;
A process of fitting using the measurement data of the height of the sample;
A step of re-fitting a sample obtained by removing erroneous measurement data from the sample height measurement data based on the result of the fitting, and creating the sample height data.

According to a third aspect of the present invention, there is provided a light source that emits light, a light projecting lens that focuses the light on the surface of the sample placed on the stage, and a light receiving lens that receives the reflected light reflected from the surface of the sample. A charged particle beam drawing apparatus comprising a PSD (Position Sensitive Detector) that receives reflected light converged by a light receiving lens and detects the position of the surface of the sample,
Means for storing an offset value on an analog signal processing circuit including a PSD;
The sample height obtained by subtracting the value not included in the pre-determined reference range from the sample height obtained by subtracting the offset value from the output value of the PSD, and performing fitting using the remaining value to obtain the sample height A means of creating data;
And a means for adjusting the charged particle beam based on the height data.

According to a fourth aspect of the present invention, there is provided a light source that emits light, a light projecting lens that focuses the light on the surface of the sample placed on the stage, and a light receiving lens that receives the reflected light reflected from the surface of the sample. A charged particle beam drawing apparatus comprising a PSD (Position Sensitive Detector) that receives reflected light converged by a light receiving lens and detects the position of the surface of the sample,
Means for storing an offset value on an analog signal processing circuit including a PSD;
Means for obtaining the height of the sample using a value obtained by subtracting the offset value from the output value of the PSD,
In the means for obtaining the sample height, fitting is performed using the sample height measurement data, and based on the obtained results, the sample height measurement data from which erroneous measurement data has been removed is fitted again. Create sample height data,
It has a means for adjusting a charged particle beam based on height data.

  ADVANTAGE OF THE INVENTION According to this invention, the height measurement method and charged particle beam drawing apparatus which can aim at the improvement of drawing precision by reducing the height measurement error resulting from the pattern formed in the sample are provided.

It is a conceptual diagram which shows the structure of the electron beam drawing apparatus in this Embodiment. It is an example of the electron beam drawing method by this Embodiment. It is explanatory drawing of the height measuring method by this Embodiment. It is a flowchart of the height data creation method by this Embodiment. It is a figure which shows the relationship between the light reception amount of a light receiving element, and the height of a mask surface. It is explanatory drawing of the height data creation method by this Embodiment. It is a flowchart of the height data creation method by this Embodiment. It is an example of the manufacturing process of a Levenson type phase shift mask. It is an example which measured the height of the resist film surface.

  FIG. 1 is a configuration diagram of an electron beam drawing apparatus according to the present embodiment.

  In FIG. 1, a stage 3 on which a mask substrate 2 as a sample is installed is provided in a sample chamber 1 of an electron beam drawing apparatus.

  In the present embodiment, a substrate having a pattern formed on the substrate is used as the mask substrate 2. For example, a substrate as shown in FIG. 8E, that is, a phase shift mask substrate in which a pattern is formed under the resist film can be obtained.

  The stage 3 is driven in the X direction and the Y direction by the stage driving unit 4. The stage driving unit 4 is controlled by the control computer 6 via the stage control unit 5. The position of the stage 3 is measured by the position circuit 7 using a laser interferometer or the like, and the measured data is sent from the position circuit 7 to the stage controller 5.

  An electron beam optical system 10 is installed above the sample chamber 1. The optical system 10 includes an electron gun 11, various lenses 12, 13, 14, 15, 16, a blanking deflector 17, a shaping deflector 18, a main deflector 19 for beam scanning, and a sub deflector for beam scanning. 20 and two beam shaping apertures 21, 22 and the like.

  FIG. 2 is an explanatory diagram of a drawing method using an electron beam. As shown in this figure, the pattern 51 drawn on the mask substrate 2 is divided into strip-shaped frame regions 52. Drawing with the electron beam 54 is performed for each frame region 52 while the stage 3 continuously moves in one direction (for example, the X direction). The frame area 52 is further divided into sub-deflection areas 53, and the electron beam 54 draws only necessary portions in the sub-deflection areas 53. The frame area 52 is a strip-shaped drawing area determined by the deflection width of the main deflector 19, and the sub deflection area 53 is a unit drawing area determined by the deflection width of the sub deflector 20.

  Positioning of the reference position of the sub deflection region is performed by the main deflector 19, and drawing in the sub deflection region 53 is controlled by the sub deflector 20. That is, the electron beam 54 is positioned in a predetermined sub-deflection area 53 by the main deflector 19, and the drawing position in the sub-deflection area 53 is determined by the sub-deflector 20. Further, the shape and size of the electron beam 54 are determined by the shaping deflector 18 and the beam shaping apertures 21 and 22. Then, the sub-deflection area 53 is drawn while continuously moving the stage 3 in one direction. When drawing of one sub-deflection area 53 is completed, the next sub-deflection area 53 is drawn. When drawing of all the sub-deflection areas 53 in the frame area 52 is completed, the stage 3 is stepped in a direction orthogonal to the direction in which the stage 3 is continuously moved (for example, the Y direction). Thereafter, the same processing is repeated, and the frame area 52 is sequentially drawn.

  In FIG. 1, drawing data of the mask substrate 2 is stored in a magnetic disk 8 that is a storage medium. The drawing data read from the magnetic disk 8 is temporarily stored in the pattern memory 25 for each frame area 52. The pattern data for each frame area 52 stored in the pattern memory 25, that is, the frame information composed of the drawing position, the drawing graphic data, etc. is sent to the pattern data decoder 26 and the drawing data decoder 27 which are data analysis units.

  Information from the pattern data decoder 26 is sent to a blanking circuit 28 and a beam shaper driver 29. Specifically, blanking data based on the data is created by the pattern data decoder 26 and sent to the blanking circuit 28. Desired beam size data is also created and sent to the beam shaper driver 29. Then, a predetermined deflection signal is applied from the beam shaper driver 29 to the shaping deflector 18 of the electron beam optical system 10 to control the size of the electron beam 54.

  The deflection control unit 30 in FIG. 1 is connected to a settling time determining unit 31, the settling time determining unit 31 is connected to a sub deflection region deflection amount calculating unit 32, and the sub deflection region deflection amount calculating unit 32 is a pattern data decoder. 26 is connected. The deflection control unit 30 is connected to the blanking circuit 28, the beam shaper driver 29, the main deflector driver 33, and the sub deflector driver 34.

  The output of the drawing data decoder 27 is sent to the main deflector driver 33 and the sub deflector driver 34. Then, a predetermined deflection signal is applied from the main deflector driver 33 to the main deflector 19 of the electron beam optical system 10, and the electron beam 54 is deflected and scanned to a predetermined main deflection position. Further, a predetermined sub deflection signal is applied from the sub deflector driver 34 to the sub deflector 20, and drawing in the sub deflection region 53 is performed.

  Next, drawing control by the control computer 6 will be described.

  The control computer 6 reads the mask drawing data recorded on the magnetic disk 8 as a storage medium. The read drawing data is temporarily stored in the pattern memory 25 for each frame area 52.

  Drawing data for each frame area 52 stored in the pattern memory 25, that is, frame information composed of drawing positions, drawing graphic data, and the like is transmitted via a pattern data decoder 26 and a drawing data decoder 27, which are data analysis units. It is sent to the sub deflection area deflection amount calculation unit 32, the blanking circuit 28, the beam shaper driver 29, the main deflector driver 33, and the sub deflector driver 34.

  The pattern data decoder 26 creates blanking data based on the drawing data and sends it to the blanking circuit 28. Further, desired beam shape data is created based on the drawing data and is sent to the sub deflection region deflection amount calculation unit 32 and the beam shaper driver 29.

  The sub deflection region deflection amount calculation unit 32 calculates the deflection amount (movement distance) of the electron beam for each shot in the sub deflection region 53 from the beam shape data created by the pattern data decoder 26. The calculated information is sent to the settling time determination unit 31, and the settling time corresponding to the moving distance by the sub deflection is determined.

  The settling time determined by the settling time determination unit 31 is sent to the deflection control unit 30, and then the blanking circuit 28, the beam shaper driver 29, It is appropriately sent to either the deflector driver 33 or the sub deflector driver 34.

  In the beam shaper driver 29, a predetermined deflection signal is applied to the shaping deflector 18 of the electron beam optical system 10, and the shape and size of the electron beam 54 are controlled.

  The drawing data decoder 27 creates positioning data for the sub deflection region 53 based on the drawing data, and sends this data to the main deflector driver 33. Next, a predetermined deflection signal is applied from the main deflector driver 33 to the main deflector 19, and the electron beam 54 is deflected and scanned to a predetermined position in the sub deflection region 53.

  The drawing data decoder 27 generates a control signal for scanning the sub deflector 20 based on the drawing data. After the control signal is sent to the sub deflector driver 34, a predetermined sub deflection signal is applied from the sub deflector driver 34 to the sub deflector 20. Drawing in the sub deflection region 53 is performed by repeatedly irradiating the electron beam 54 after the settling time has elapsed.

  Next, a drawing method by the electron beam drawing apparatus will be described.

  First, the mask substrate 2 is placed on the stage 3 in the sample chamber 1. Next, the position of the stage 3 is detected by the position circuit 7, and the stage 3 is moved to a position where drawing can be performed through the stage control unit 5 based on a signal from the control computer 6.

  Next, an electron beam 54 is emitted from the electron gun 11. The emitted electron beam 54 is collected by the illumination lens 12. Then, the blanking deflector 17 performs an operation of irradiating the mask substrate 2 with the electron beam 54.

  The electron beam 54 incident on the first aperture 21 passes through the opening of the first aperture 21 and is then deflected by the shaping deflector 18 controlled by the beam shaper driver 29. And it passes through the opening part provided in the 2nd aperture 22, and becomes a beam shape which has a desired shape and a dimension. This beam shape is a drawing unit of the electron beam 54 applied to the mask substrate 2.

  The electron beam 54 is shaped into a beam shape and then reduced by the reduction lens 15. The irradiation position of the electron beam 54 on the mask substrate 2 is controlled by the main deflector 19 controlled by the main deflector driver 33 and the sub deflector 20 controlled by the sub deflector driver 34. The main deflector 19 positions the electron beam 54 in the sub deflection region 53 on the mask substrate 2. The sub deflector 20 positions the drawing position in the sub deflection area 53.

  Drawing with the electron beam 54 on the mask substrate 2 is performed by scanning the electron beam 54 while moving the stage 3 in one direction. Specifically, the pattern is drawn in each sub deflection region 53 while moving the stage 3 in one direction. After all the sub-deflection areas 53 in one frame area 52 have been drawn, the stage 3 is moved to a new frame area 52 and drawn similarly.

  After drawing all the frame regions 52 of the mask substrate 2 as described above, the drawing is replaced with a new mask, and drawing by the same method as described above is repeated.

  By the way, when the mask substrate 2 is mounted on the stage 3, the mask substrate 2 is bent by its own weight. When the mask substrate 2 is supported on the lower surface by the stage 3, the thickness and parallelism inherent to the mask also affect the surface height of the mask substrate 2. For this reason, the irradiation position of the electron beam 54 is shifted or the focal point is defocused due to a change in height due to the combination of the surface shape, thickness, parallelism and deflection of the mask substrate 2, and a desired pattern is formed on the mask substrate 2. Cannot be formed. Therefore, it is necessary to accurately measure the height of the surface of the mask substrate 2.

  The height of the mask substrate 2 placed on the stage 3 is measured by the height measuring unit 40. The height measuring unit 40 includes a light source 41, a light projecting lens 42 that converges the light Li emitted from the light source 41 on the mask substrate 2, and a light receiving lens 43 that receives and converges the light Lr reflected on the mask substrate 2. And a light receiving element 44 that receives the light Lr converged by the light receiving lens 43 and detects the position of the light.

  When the light position is detected by the light receiving element 44, the height data is generated by the height data processing unit 70 through the signal processing unit 60. That is, the height data processing unit 70 receives the output signal from the light receiving element 44 and converts it into height data of the surface of the mask substrate 2 corresponding to the position of the light detected by the light receiving element 44.

  Next, a method for creating height data in the present embodiment will be described. In the present embodiment, first, a reference range of height data, that is, a range of probable height data is determined using a reference board. Here, the range of probable height data refers to the range of height data excluding the height measurement error caused by the pattern formed on the sample. Next, the height of the substrate to be drawn is measured, and values outside the reference range of the height data obtained previously from this measured value are removed. Fitting is performed using the remaining measurement values, and height data is created.

  The method for creating the height data will be described in more detail with reference to FIGS.

  First, a reference range of height data, that is, a range of probable height data is determined using a reference substrate.

  The reference substrate can be a mask substrate on which a pattern is drawn, for example, the mask substrate 2. However, in order to determine the range of reference height data, an area where no pattern is drawn is set as a height measurement area (S101 in FIG. 4).

  In general, since the resist film thickness tends to be non-uniform in the peripheral portion of the substrate, this region is a drawing-prohibited region where drawing by an electron beam is not performed. An area inside the drawing prohibition area is an area where drawing is performed (drawable area). The drawing accuracy guaranteed area in which the predetermined drawing accuracy is guaranteed is an area further inside the drawable area. Since a pattern is not drawn in an area that can be drawn and is outside the drawing accuracy guarantee area, for example, this area can be used as a height measurement area on the reference substrate.

  Next, for the height measurement region of the reference substrate, the height measurement unit 40 in FIG. 3 performs height measurement (S102 in FIG. 4). For example, the height measurement region can be divided by an (8 × 8) grid, and the height of each intersection can be measured.

  Next, offset correction is performed on the measurement value obtained by the height measurement unit 40 (S103 in FIG. 4). Specifically, the offset correction is performed as follows.

  In the height measuring unit 40, the laser light emitted from the light source 41 is converged on the surface of the reference substrate by the light projecting lens 42. The converged light is reflected by the surface of the reference substrate, enters the light receiving lens 43, and then converges on the light receiving element 44.

  A position detection element (PSD: Position Sensitive Detector) is used as the light receiving element 44. The PSD has a structure similar to that of a PIN type photodiode, and realizes measurement of the center of gravity of light by measuring a photocurrent by a photovoltaic effect. When spot light is incident on the PSD, an electric charge proportional to the light energy is generated at the incident position and flows through a resistance layer (P layer) having a uniform resistance value to flow to an electrode installed on two end faces on the PSD. . The amount of current at this time is divided in inverse proportion to the distance to the electrode.

If the output current from the electrode placed on one end face of the PSD is I ₁ and the output current from the electrode placed on the other end face is I ₂ , the gravity center position X of the spot light from the PSD center is It can be obtained by the following formula. However, the length of the light receiving surface is L.
Here, the total photocurrent indicating the received light intensity of PSD can be obtained by the sum of I ₁ and I ₂ .

  The reflectance of the sample surface with respect to light emitted from the light source varies depending on the film thickness of the sample, the physical properties of the film, the wavelength of the light incident on the sample surface, and the polarization state. Ideally, the above equation will always show a constant value if the center of gravity of the light does not change even if the amount of received light changes. It does not affect. However, in practice, the offset voltage generated in the light receiving element and the analog signal processing circuit constituting the height measuring unit acts as a manufacturing error, so that it is not constant in the case of samples having different reflectivities. Therefore, when measuring the height between samples with different reflectivities, if the offset voltage is large, the error becomes larger than when measuring the height between samples with the same reflectivity, and the electron beam is applied to the surface of the sample. It becomes difficult to converge accurately.

The position of the center of gravity of the incident light can be obtained by measuring two weak current changes. For this reason, normally, an I / V conversion circuit is configured, and output current changes (I ₁ , I ₂ ) from the PSD are individually converted as output voltage changes (V ₁ , V ₂ ), and the barycentric position of the light Measure. At this time, since the dark current of the light receiving element, the leakage current on the circuit, and the offset current of the I / V conversion amplifier exist as manufacturing errors, the total sum of these current amounts is the offset voltage (V ₁₀ , V ₂₀ ) acts on the output voltage. That is, if the output voltage after voltage conversion is V ₁ and V ₂ , the measured height Z is expressed by equation (1). Here, α is a coefficient determined from the measurement range of the sample height and the range of movement of the center of gravity of the light on the PSD.

However, when the offset voltage is taken into account, the actually measured height Z ′ is expressed by equation (2). However, in the equation (2), V ₁₀ and V ₂₀ are offset voltages, respectively.

  Next, a method for obtaining the offset value of the light receiving element 44 will be described.

Since the actual measurement can be obtained by the equation (2) and theoretically shows a constant value (a) even if the light quantity changes,
It can be expressed as At this time, if the offset voltage sum (V ₁₀ + V ₂₀ ) is sufficiently small with respect to the amount of light, it is omitted.
It is. Therefore, if (V ₂₀ −V ₁₀ ) = b, (V ₁ −V ₂ ) can be expressed by the following equation.
Therefore, the coefficient a and the coefficient b are obtained by performing measurement with the light amount (V ₁ + V ₂ ) changed at least at two points.

On the other hand, when this coefficient is obtained at at least two points having different heights, when V ₁ = V ₂ = 0, the height is calculated using only the offset voltage and shows the same value. To do.
In this case, an error occurs due to omission of the sum of offset voltages, but V ₁₀ and V ₂₀ can be obtained by minimizing the error by repeatedly adding the obtained offset value.

  The offset value can be obtained by measuring at least two points. However, increasing the number of measurement points can reduce the influence of measurement errors and suppress fluctuations in the offset value.

Specifically, the height measurement unit 40 performs height measurement by changing the height of the reference substrate surface and the amount of light emitted from the light source 41. For the obtained voltage values V ₁ and V ₂ , a graph is drawn with the value of (V ₁ + V ₂ ) on the horizontal axis and the value of (V ₁ −V ₂ ) on the vertical axis. The relationship between (V ₁ + V ₂ ) and (V ₁ −V ₂ ) is approximated by a straight line, and the slope (a) and intercept (b) of this straight line (y = ax + b) are obtained. And
By using the relationship, offset values V ₁₀ and V ₂₀ are obtained. The obtained offset values V ₁₀ and V ₂₀ are stored in the offset value memory unit 80. This measurement is repeated, and the value obtained when the obtained offset value is within the allowable value or no longer changes is set as the final registered value.

  FIG. 5 is a diagram showing the relationship between the amount of light received by the light receiving element and the value obtained by measuring the height of the mask surface. In this figure, a dotted line is a line obtained by connecting values obtained without performing processing in the height data processing unit to an output value from the light receiving element, and a solid line is processing in the height data processing unit. This is a line connecting values obtained by performing. That is, the former corresponds to the height data obtained without performing the offset correction, and the latter corresponds to the height data obtained after the offset correction. As can be seen from this result, when the processing in the height data processing unit is not performed, the variation of the measured value increases in a region where the light receiving amount of the light receiving element is small. This is because the influence of the offset value cannot be ignored in a region where the light receiving amount of the light receiving element is small because the measurement value includes the offset value. On the other hand, when the processing by the height data processing unit is performed, since the offset value is removed from the measurement value, the height data is substantially constant regardless of the amount of light received by the light receiving element.

In the height measuring unit 40, two signals (I ₁ , I ₂ ) are output from the light receiving element 44 as described above. These signals are converted from current values to voltage values by the I / V conversion amplifier 45, and then input to the signal processing unit 60. In the signal processing unit 60, the signals V ₁ and V ₂ are amplified to an appropriate voltage level by the non-inverting amplifier 61 and then converted into digital data by the A / D conversion unit 62. The converted data is sent to the height data processing unit 70, and processing for removing the offset voltage value is performed. Here, the height data processing unit 70 is a means for obtaining the height of the sample using a value obtained by subtracting the offset value from the output value of the light receiving element. The offset value memory unit 80 corresponds to a means for storing the offset value of the light receiving element, and the stage 3, the stage driving unit 4 and the stage control unit 5 use the height of the sample to obtain a desired sample. A means for adjusting the position is configured.

The offset voltage value removing unit 71 of the height data processing unit 70, while the measured value from the signal processing unit 60 _(V 1, V ₂₎ is inputted, the offset value from the offset value memory unit 80 _(V 10, V ₂₀ ) is input. This value corresponds to the offset voltage of the light receiving element 44. In the present embodiment, the height data of the reference substrate surface is created using a value obtained by subtracting the offset values (V ₁₀ , V ₂₀ ) from the measured values (V ₁ , V ₂ ).

The offset voltage value removing unit 71 uses the values (V ₁ ′, V ₂ ′) obtained by subtracting the offset values (V ₁₀ , V ₂₀ ) from the measured values (V ₁ , V ₂ ), and (V ₁ ′ −V ₂ ′) / (V ₁ ′ + V ₂ ′) is calculated (normalization process). This value is a predetermined time interval (e.g., 20 milliseconds or less) is updated with, on average the obtained value time (averaging process), obtain height data Z ₁ of the surface of the mask substrate 2. The averaging process can be performed on values excluding the maximum value and the minimum value of the sampling data.

Then, at the level correcting unit 72, after the same averaging process and the relative height data Z _1, it performs linearization correction. This linearization correction process is a process for calibrating the linearity of the height change of the sample surface. Specifically, a polynomial calculation process is performed using a unique correction coefficient that outputs a change in the sample surface accurately when the normalized data obtained by the light receiving element 44 is multiplied by a specific resolution (um / bit). I do. Calculation of the correction coefficient for the polynomial calculation is based on the result of measuring the height of the sample 2 as the reference material for the height reference. This is done by calculating from the square method. Here, the original device is a sample having a stepped shape and having a plurality of steps, and the dimensions of the steps are accurately measured in advance. Although the height data is created in this way, the height of the reference substrate surface needs to be measured as a relative height with respect to the height reference plane of the electron beam drawing apparatus. Therefore, taking the difference of the height data of the height data and the reference substrate surface height reference plane, obtain height data Z ₂ of the reference substrate surface.

Then, bending of the substrate, device stability height measuring unit, taking into account the individual differences of the substrate, defined within a certain range the height data Z _2. This is the reference range of height data, that is, the range of reliable height data (S104 in FIG. 4).

  Next, the height measurement unit 40 in FIG. 3 measures the height of the mask substrate 2 to be drawn (S105 in FIG. 4). For example, the height measurement region can be divided by an (8 × 8) grid, and the height of each intersection can be measured.

  Next, offset correction is performed on the measurement value obtained by the height measurement unit 40 in the same manner as described above (S106 in FIG. 4).

  Next, in the height correction unit 72, a value outside the reference range of the height data obtained in S104 using the reference substrate is excluded from the measured value after offset correction (S107 in FIG. 4).

  For example, when the height measurement area is divided by an (8 × 8) grid, as shown in an enlarged view of a part of FIG. 6, one intersection of the grid is A, and an intersection adjacent to the intersection A is B. Further, the above grid is further divided into a, b,... In order from a position close to the intersection A.

  As shown in FIG. 7, first, the height at the intersection A of the grid is measured (S201), and it is determined whether or not the obtained value is within the reference range (S202). If it is within the reference range, the height is measured in the same manner for the intersection B of the next adjacent grid (S203). On the other hand, if it is not within the reference range, the measurement data at the intersection A is discarded, and the position a close to the intersection A is selected as the next measurement point (S204). Then, after returning to S201 and measuring the height at the position a, it is determined in S202 whether or not the measured value is within the reference range. If it is within the reference range, the process proceeds to S203 to move to the measurement of the intersection B. If it is not within the reference range, the measurement data at the position a is discarded, and the position b is selected as the next measurement point at S204. . Next, the height at the position b is measured in S201. The above processing is repeated to remove values that are outside the reference range of height data.

  In the height correction unit 72, fitting is performed using the measurement values remaining after the processing in S107, and height data is created (S108 in FIG. 4). The obtained height data is obtained by reducing the height measurement error caused by the pattern formed on the mask substrate 2. That is, according to the above method, accurate height measurement data can be obtained, and the electron beam can be accurately focused on the surface of the mask 2 by adjusting the lens according to the height.

  Next, another example of the height data creation method in the present embodiment will be described.

  In this example, the number of measurements on the mask substrate 2 is increased instead of using the reference substrate. For example, the height measurement region is divided by a grid such as (20 × 20) or (100 × 100), and the height of each intersection is measured. The height measurement is performed by the height measuring unit 40 in FIG. Next, offset correction is performed in the offset voltage value removing unit 71 on the measurement value obtained by the height measuring unit 40. Offset correction can be performed in the same manner as described above. Next, fitting is performed in the height correction unit 72 using the value after offset correction. If the number of measurement data with large errors due to the pattern is smaller than the number of normal measurement data, the former should be a point away from the fitting curve or an unnaturally changing shape of the fitting curve. is there. That is, when there is a shape change different from the bending due to the weight of the mask substrate 2, it is considered that this change is caused by the pattern, and the corresponding measurement data (false measurement data) is discarded. Then, by performing the fitting again, it is possible to obtain height data in which the height measurement error due to the pattern formed on the mask substrate 2 is reduced.

  In the present embodiment, the above two height measurement data creation methods may be combined. Below, the example in the case of a combination is demonstrated.

  First, a reference range of height data, that is, a range of probable height data is determined using a reference substrate. Next, the height of the mask substrate 2 to be drawn is measured. For example, the height measurement area is divided by an (8 × 8) grid, and the height of each intersection is measured.

  Next, offset correction is performed on the obtained measurement value. Next, a value outside the reference range of the height data is excluded from the measured value after offset correction. Then, fitting is performed using the remaining measurement values.

  Here, with the above reference range alone, the point with a large measurement error due to the pattern cannot be sufficiently removed, and there may be a point with a large measurement error on the fitting curve. The height of the mask substrate 2 is measured again by increasing the number of measurement points. For example, the height measurement region is divided by a grid such as (20 × 20) or (100 × 100), and the height of each intersection is measured. Then, fitting is performed using the value after offset correction. If the number of measurement data with large errors due to the pattern is smaller than the number of normal measurement data, the former should be a point away from the fitting curve or an unnaturally changing shape of the fitting curve. is there. Therefore, the measurement data corresponding to such a point is discarded and the fitting is performed again. Thereby, height data in which the height measurement error due to the pattern formed on the mask substrate 2 is reduced can be obtained.

When drawing with an electron beam, first, the position of the stage 3 is adjusted via the stage drive unit 4. Thereby, the height of the surface of the mask substrate 2 is adjusted. After completion of this adjustment process, the adjustment of the electron beam optical system 10 is performed based on the height data Z ₂ obtained by the height data processing unit 70. For example, after the height data Z ₂ is sent from the height data processing unit 70 to the deflection control unit 30 via the control computer 6, a predetermined deflection signal is applied from the main deflector driver 33 to the main deflector 19 and the main data is transmitted. The deflector 19 is adjusted. Accordingly, the main deflector is optimally adjusted in height reference surface is adjusted according to the height data Z _2, it is possible to draw in the desired position and size of the sample. Incidentally, being adjusted according to the height data Z ₂ is not limited to the main deflector 19, the electrostatic lens 16 and the sub-deflector 20 may be adjusted. Even if these are adjusted, the same effect as described above can be obtained.

  As described above, according to the present embodiment, accurate height measurement data can be obtained. By adjusting the lens according to this height, the electron beam can be accurately focused on the surface of the sample. Can do.

  The present invention is not limited to the above-described embodiment, and various modifications can be made without departing from the spirit of the present invention. For example, although the electron beam is used in the above embodiment, the present invention is not limited to this, and the present invention can also be applied to the case where another charged particle beam such as an ion beam is used.

DESCRIPTION OF SYMBOLS 1 Sample chamber 2 Mask substrate 3 Stage 4 Stage drive part 5 Stage control part 6 Control computer 7 Position circuit 8 Magnetic disk 10 Electron beam optical system 11 Electron gun 12, 13, 14, 15, 16 Lens 17 Blanking deflector 18 Shaping deflector 19 Main deflector 20 Sub deflector 21 1st aperture 22 2nd aperture 25 Pattern memory 26 Pattern data decoder 27 Drawing data decoder 28 Blanking circuit 29 Beam shaper driver 30 Deflection control unit 31 Settling time determination unit 32 Sub-deflection area deflection amount calculation unit 33 Main deflector driver 34 Sub-deflector driver 40 Height measurement unit 41 Light source 42 Projection lens 43 Light reception lens 44 Light reception element 45 I / V conversion amplifier 51 Pattern to be drawn 52 Frame area 53 Sub deflection region 54 Beam 60 signal processing unit 61 a non-inverting amplifier 62 A / D converter 70 height data processor 71 offset voltage value removing unit 72 height correction section 80 offset value memory unit

Claims (4)

In a height measurement method for measuring the height of the sample by receiving light obliquely on the sample and receiving the reflected light reflected by the surface of the sample with a PSD (Position Sensitive Detector),
Determining a reference range of the height;
Obtaining an offset value on an analog signal processing circuit including the PSD;
The height measurement area of the sample is divided by a predetermined grid, the height at the intersection of the grid is measured, and the height of the sample is measured using a value obtained by subtracting the offset value from the output value of the PSD. A process for obtaining data;
In the measurement data of the height of the sample, when the obtained value is within the reference range, the height at the intersection of the next adjacent grid is measured. If not, discard the height at the intersection of the grid, repeat the step of measuring the height in order from the position closer to the intersection obtained by further dividing the grid, values not included in the reference range And a step of performing fitting using the remaining value and creating the height data of the sample. A light source that emits light, a light projecting lens that converges the light onto the surface of the sample placed on the stage, a light receiving lens that receives reflected light reflected from the surface of the sample, and a light receiving lens that converges the light. A charged particle beam drawing apparatus comprising a PSD (Position Sensitive Detector) that receives the reflected light and detects the position of the surface of the sample,
Means for storing an offset value on an analog signal processing circuit including the PSD;
The height of the sample obtained by dividing the height measurement region of the sample by a predetermined grid, measuring the height at the intersection of the grid, and subtracting the offset value from the output value of the PSD If the obtained value is within the reference range, the height at the intersection of the next adjacent grids is measured. If the obtained value is not within the reference range, Discard the height at the intersection, repeat the process of measuring the height in order from the position closer to the intersection that further divided the grid further, except for the value not included in the pre-determined reference range, using the remaining value Means for fitting and creating height data of the sample;
A charged particle beam drawing apparatus comprising means for adjusting the charged particle beam based on the height data. In a height measurement method for measuring the height of the sample by receiving light obliquely on the sample and receiving the reflected light reflected by the surface of the sample with a PSD (Position Sensitive Detector),
Obtaining an offset value on an analog signal processing circuit including the PSD;
The height measurement region of the sample is divided by a predetermined grid, the height at the intersection of the grids is measured, and the value obtained by subtracting the offset value from the output value of the PSD is used. A process for obtaining measurement data;
Performing the fitting using the measurement data of the height of the sample;
Based on the result of the fitting, the erroneous measurement data is removed from the measurement data of the sample height, the height of the erroneous measurement data near the intersection is measured, and the fitting is repeated, And a step of creating height data. A light source that emits light, a light projecting lens that converges the light onto the surface of the sample placed on the stage, a light receiving lens that receives reflected light reflected from the surface of the sample, and a light receiving lens that converges the light. A charged particle beam drawing apparatus comprising a PSD (Position Sensitive Detector) that receives the reflected light and detects the position of the surface of the sample,
Means for storing an offset value on an analog signal processing circuit including the PSD;
The height measurement area of the sample is divided by a predetermined grid, the height at the intersection of the grid is measured, and the height of the sample is obtained using a value obtained by subtracting the offset value from the output value of the PSD. Means,
The means for obtaining the height of the sample performs fitting using the measurement data of the sample height, and removes erroneous measurement data from the measurement data of the sample height based on the obtained result. Measure the height of the position near the intersection of the measurement data, repeat the fitting again, create the height data of the sample,
A charged particle beam drawing apparatus comprising means for adjusting the charged particle beam based on the height data.