JPH0478151B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a beam size measuring device for a charged particle beam exposure device that draws and exposes a circuit pattern of an integrated circuit onto a semiconductor wafer, for example.

"Background of the Invention" One method of drawing and exposing a circuit pattern of a semiconductor integrated circuit (hereinafter referred to as IC) on a semiconductor wafer is to use a charged particle beam such as an electron beam or an ion beam. Charged particle beams can draw circuit patterns with relatively narrow line widths, making them suitable for drawing circuit patterns for highly integrated ICs.

When drawing an IC circuit pattern, the line width is an important element and its dimensions must be specified accurately. The line width is determined by changing the size of an aperture provided near the particle irradiation gun to limit the size of the charged particle beam.

The present invention provides a charged particle beam dimension measuring device that can accurately measure the dimensions of a charged particle beam.

"Prior Art" A conventional method for measuring the dimensions of a charged particle beam will be described with reference to FIGS. 4 and 5.

In FIG. 4, numeral 1 indicates a charged particle beam, and numeral 2 indicates a charged particle beam current detector that detects the amount of charged particles as a current by irradiation with the charged particle beam. For example, a Faraday tube is used as this beam current detector. A knife edge 3 is provided on the upper part of the beam current detector 2.
By masking the charged particle beam 3 and scanning the beam 1 in a direction perpendicular to the knife edge 3, the irradiation area on the beam current detector 2 can be changed.

The current detected by the beam current detector 2 is amplified by an amplifier 4 and further differentiated by a differentiating circuit 5.

When the charged particle beam 1 is scanned in the x direction while being masked by the knife edge 3, a scanning waveform signal IS as shown in FIG. 5A is obtained at the output side of the amplifier 4.

By firstly differentiating this scanning signal IS in the differentiating circuit 5, a rectangular differential waveform signal ΔIS as shown in FIG. 5B is obtained.

Conventionally, the half value between the peak value I _nax of this differential waveform signal △IS and the baseline value I _nio is taken as the slice level, and the width W between the intersections A and B of this slice level and the differential waveform signal △IS is charged. It is measured as the dimension of the particle beam 1 in the x-axis direction.

"Problem to be solved by the invention" Conventionally, the half value between the peak value of the differential waveform signal △IS and the baseline was taken as the slice level, and the beam width was determined from the intersection of this slice level and the differential waveform signal △IS. However, this method has the disadvantage that accurate dimensions cannot be measured.

The reason for this is that the differential waveform signal is
As shown in the figure, noise is superimposed on the rising portion, etc., and since the slice level is determined by considering this noise as the maximum value of the differential waveform, the value of the slice level will not be exactly half the value. As a result, there is a problem that the width W of the beam cannot be determined accurately.

"Means for solving the problem" The present invention includes a slice level determining means for determining the true half value of the waveform using the averaged values at both ends of the differential waveform and the averaged value near the center of the waveform;
It is composed of a position detecting means for detecting the position where the half value determined by the slice level determining means and the differential waveform intersect, and a means for determining the beam dimension from the two position information obtained by this position detecting means. be.

According to the configuration of the present invention, the half value of the waveform is obtained using the averaged values at both ends of the differential waveform and the averaged value near the center of the waveform, so this half value approximates the true half value. Highly reliable. Therefore, by determining the beam size from the position of the differential waveform that intersects this half value, a highly reliable beam size can be obtained.

Embodiment FIG. 1 shows an embodiment of a beam dimension measuring device according to the present invention. In the figure, parts corresponding to those in FIG. 3 are designated by the same reference numerals.

In Fig. 1, the scanning signal of beam 1 obtained from beam current detector 2 is amplified by amplifier 4 and AD
A converter 6 performs AD conversion and converts it into a digital signal.

The scanning waveform data AD-converted by the AD converter 6 is taken into the scanning waveform memory 7. The scanning waveform data taken into the scanning waveform memory 7 is transferred to the data bus 8.
The signal is taken into the controller 9 through the controller 9, where it is subjected to differential processing and converted into differential waveform data.

Differential waveform data obtained by differential processing by the controller 9 is written into a differential waveform memory 11. This writing is performed by a write signal outputted through the write signal line 12.

FIG. 2 shows an example of a differential waveform written in the differential waveform memory 11 as an analog waveform.

The controller 9 determines the base level V _B at both ends of the differential waveform from the waveform data written in the differential waveform memory 11 . This base level V _B is calculated by calculating the average of each data in the address areas AR ₁ and AR ₂ that are separated by a certain amount from both ends of the differential waveform, and the average value is determined as the base level V _B.

The controller 9 searches the waveform data stored in the differential waveform memory 11 and extracts data corresponding to the maximum value V _P therein.

The controller 9 calculates the half value of the base level V _B and the maximum value V _P to obtain a temporary slice level V _S. This temporary slice level V _S is data bus 8.
The signal is outputted to the position detecting means 10 which detects the intersection signal between the differential waveform and the slice level. This position detection means 10 is a slice level register 13
, a differential waveform register 14 , a digital comparator 15 , a position counter 16 , a register file 18 , and an address counter 17 .

The temporary slice level V _S is stored in the slice level register 13. At the same time, the differential waveform data stored in the differential waveform memory 11 is stored in the differential waveform register 14 one by one. When writing differential waveform data to the differential waveform register 14, the write signal is given to the position counter 16 to count the number of writes.

The output of the slice level register 13 and the differential waveform register 14 are applied to input terminals B and A of a digital comparator 15, respectively. Digital comparator 15 outputs a pulse from output terminal C every time the values at input terminals B and A match.

The pulse output from digital comparator 15 is applied to address counter 17 and register file 18. When the register file 18 receives a pulse from the digital comparator 15, it takes in the count value of the position counter 16. That is, each time the differential waveform data matches the temporary slice level, the write number (corresponding to the address of each part of the differential waveform data) at that time is written to the register file 18.

On the other hand, when a match pulse is output from the digital comparator 15, the address counter 17 increments the address by one, and the address in the register file 18 increments by one. Therefore, when the differential waveform data intersects the temporary slice level again, the intersection position information A _e1
A _e2 (see FIG. 2) is written from the position counter 16 to the register file 18.

In this way, the position information where the differential waveform data and the temporary slice level intersect is stored in the register file 18.
A _e1 and A _e2 are obtained.

The controller 9 takes in the position information A _e1 and A _e2 stored in the register file 18 through the data bus 8, and determines the center position A _C of the differential waveform from this position information A _e1 and A _e2 . This center position is A _c = (A _e1 +
It can be determined by A _e2 )/2.

The differential waveform data is averaged in a range of ±ΔB with the center position A _c as the boundary, and the value is taken as the true peak value V _PT .

V _PT =1/2△B+1 _Ac+ △ _B 〓 D(i) ^i=Ac- △ ^B D _i represents differential waveform data.

The true slice level _VST is determined from the true peak value _VPT and the base level _VB . The true slice level V _ST is determined by V _ST =V _PT +V _B /2.

When the true slice level V _ST is determined, the controller 9 stores the true slice level V _ST in the slice level register 13 of the position detecting means 10 again, and in the position detecting means 10 it is stored by the digital comparator 15 in the same manner as described above. The true slice level V _ST and the differential waveform data are compared, and the position information where the differential waveform data crosses the true slice level V _ST is taken into the register file 18 .

The position information A _eT1 and A _eT2 obtained in this way can be regarded as position information corresponding to the true half value of the differential waveform.

The width W of the charged particle beam 1 can be determined accurately using the position information A _eT1 and A _eT2 .

W=A _eT2 −A _eT1 The width of charged particle beam 1 is the width W when beam 1 is scanned in the x direction and the width H when it is scanned in the Y direction.
Both are measured.

As is clear from the above description, the controller 9 constitutes various means described below.

(a) Differential calculation means for obtaining differential waveform data from scanning waveform data (b) Means for calculating the base level V _B (c) Means for searching for the maximum value from the differential waveform data (d) Means for calculating the base level V _B and the maximum value Means to determine the temporary slice level V _S based on the value (e) Take the positions A _e1 and A _e2 where the temporary slice level V _S intersects with the differential waveform data and calculate the center position.
Means for calculating A _c (F) Means for finding the average value in the range of ±△B with the center position A _C as the border, and calculating the average value as the true maximum value V _PT (G) Means for calculating the true maximum value V _PT Means for determining the true slice level V _ST from the base level V _B and _{the base} level V _B
In addition to the various means described above, the controller 9 also constitutes various control means for capturing scanning waveform data, controlling readout, inputting and outputting data to and from the position detecting means 10, etc. There is. This can be configured by a microcomputer, and executes the operations as the various means described above by executing programs in a predetermined order. Figure 3 shows an overview of the program as a flowchart.

In the embodiment shown in FIG.
Although an example in which AD conversion output is provided has been described, the AD conversion output can be directly taken in by the controller 9, and written into the differential waveform memory 11 while being converted into differential waveform data. Therefore, it is possible to omit the scanning waveform memory 7.

Further, in the above embodiment, the position counter 16 counts the number of writes of the differential waveform data transferred to the differential waveform register 14, and the counted value is used as position information, but the position counter 16 is used as a register, and the differential waveform register It is also possible to write the read address of the differential waveform data sent to 14 into this register and use this address information as position information.

Further, the differential waveform register 14 is not necessarily required, and the differential waveform register 14 is not necessarily required;
It can also be configured to directly supply differential waveform data to 5.

"Effects of the Invention" As described above, according to the present invention, the average value near the center of the differential waveform is obtained, the true maximum value V _PT of the differential waveform is obtained from this average value, and this true maximum value V _PT and the base True slice level by level V _B
Since V _ST has been obtained, it can be seen that the intersection position of this slice level V _ST and the differential waveform data intersects at the true half-value position of the differential waveform. Therefore, the accurate dimensions of the charged particle beam can be measured, and the advantage is that, for example, the line width of a drawing line of a semiconductor integrated circuit can be accurately defined.

[Brief explanation of the drawing]

Fig. 1 is a block diagram for explaining one embodiment of this invention, Fig. 2 is a waveform diagram for explaining the operation of this invention, and Fig. 3 is for operating the controller which is the main part of this invention. FIG. 4 is a flowchart for explaining the outline of the program, FIG. 4 is a block diagram for explaining the conventional method for measuring dimensions of a charged particle beam, and FIG. 5 is a waveform diagram for explaining the conventional measuring method. 1: Charged particle beam, 2: Beam current detector,
3: knife edge, 4: amplifier, 6: AD converter, 7: scanning waveform memory, 8: data bus, 9:
Controller, 10: Position detection means, 11: Differential waveform memory, 13: Slice level register, 14: Differential waveform register, 15: Digital comparator, 1
6: Position counter, 17: Address counter, 1
8: Register file, V _B : Base level,
V _S : temporary slice level, V _ST : true slice level, V _P : maximum value, V _PT : true maximum value, A _c : center of differential waveform.

Claims (1)

[Claims] 1. A charged particle beam current detector having a knife edge, B. Differentiating means for differentiating a scanning waveform signal obtained from this beam current detector, and C. A differential waveform signal obtained from this differentiating means. a differential waveform storage means for storing; D a slice level determining means for determining the half value of the waveform using the averaged values at both ends of the differential waveform and the averaged value near the center of the waveform; and E the half value determining means. A charged particle beam dimension measuring device comprising: a position detecting means for detecting a position where the half value determined by F intersects with the differential waveform; and a means for determining the beam dimension from two pieces of position information obtained by the position detecting means. .