JPS62271424A - Exposure to charged particle beam - Google Patents

Abstract

PURPOSE:To form a coupled pattern of high precision by a method wherein two light patterns which are positioned on the opposite sides of the boundary of two adjacent exposure fields of a charged beam exposure apparatus and parallel to the boundary are exposed in the fields respectively. CONSTITUTION:An electron beam 105 is deflected by a deflector 106, and thereby a part 202 of a pattern for evaluating the precision of an exposure field coupling is exposed in the end portion of an exposure field 201 so that it is parallel to the boundary of the exposure field 201. Then, a quartz substrate 101 is taken out of an electron particle beam exposure apparatus 103, a CMS resist 102 of the substrate 101 is developed, and thereafter baking is applied in an N2 atmosphere at a temperature of 100 deg.C for 30 minutes. Next, the substrate 101 is set on a sample stage 108 of a low accelerated electron beam length measuring instrument 107 which can generate an electron beam 109 of an acceleration voltage of several kilovolts or below, and thereafter the pattern for evaluating the field coupling located on the quartz substrate 101 is measured.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a highly accurate exposure method in electron beam exposure or focused ion beam exposure.

[Conventional technology]

In electron beam exposure equipment or focused beam exposure equipment,
Because it is necessary to reduce the beam deflection size for higher resolution, exposure is performed within an exposure field smaller than the LSI chimp size. Therefore, exposure is performed by moving the stage within the same chip. The stage movement method is a step-and-movement method that alternates exposure and stage movement.
There are two methods: a repeat type and a continuous movement type in which the stage is exposed while continuously moving. However, in either case, there is a connecting portion of the exposure field within the same number. Therefore, it is necessary to measure the connection accuracy of exposure fields and use the measurement results to input correction parameters to the exposure apparatus. Conventionally, the following two methods have been used for correction.

The first method is the vernier method. A substrate coated with resist is loaded onto a sample stage of an electron beam or focused ion beam exposure device. Two adjacent exposure fields are exposed with a main scale pattern and a vernier pattern, respectively, so as to face each other across the exposure field boundary. The exposed substrate is removed from the material stage and developed. The developed substrate is mounted on a sample stage of an optical microscope, the scales of the main and vernier patterns are enlarged, and the amount of pattern deviation is visually measured. Since the value of the amount of deviation between the main and vernier patterns immediately corresponds to the connection accuracy of the exposure fields, correction parameters are input to the exposure apparatus from this value.

The second method is to optically measure the pitch of a line pattern that has been exposed and developed.

A substrate coated with resist is loaded onto a sample stage of an electron beam exposure device or a focused ion beam exposure device.

Two adjacent exposure fields are exposed with line patterns parallel to each other across the boundaries of the exposure fields. The exposed substrate is taken out from the sample stage and developed. The pitch of the line pattern formed after development is measured using an optical method as described below. That is, a line pattern is projected onto a monitor television using an optical microscope, a cursor placed on a CRT is placed over the pitch position of the line pattern, and the distance between the cursors is determined. Alternatively, computer processing is applied to the video signal to automatically detect edges and determine the pitch distance of the line pattern.

Another optical method is to scan a narrowly focused laser beam over a line pattern, detect the scattered light generated at the edge of the line pattern with a detector, and calculate the pitch distance of the line pattern from the laser scanning distance. demand. Since the pitch distance of the line pattern measured by the above-mentioned optical method is related to the connection accuracy of the exposure fields, a correction parameter is input to the exposure apparatus from this value.

[Problem that the invention seeks to solve]

On the other hand, when exposing submicron patterns using an electron beam exposure device or a focused ion beam exposure device,
The dimensional accuracy of the exposure pattern is required to be one order of magnitude lower than the minimum line width, that is, 0.1 μm or less. Correspondingly, a similar value is required for the connection accuracy of exposure fields.

Therefore, as a method for measuring the joint accuracy, a measurement range that is one digit below the allowable joint accuracy of 0.1 μm, that is, up to the 0.01 μm level is required. Furthermore, in order to improve measurement reproducibility, automation during measurement is also required.

In the vernier method described as the first method in the prior art section, the measurement limit is 0.1 .mu.m, and since it is a visual inspection method, there are large variations in measurement depending on the measurer. Also, it is not suitable for automation. The second method, the pinch measurement method between line patterns, uses an optical method as a measurement means, so it is limited by the limit of resolution due to the use of light.The limit value is 0. It is thought that the resolution is about .5 μm, which is insufficient resolution.

Due to these shortcomings of the conventional technology, the optimum value cannot be obtained for the input value of the correction parameter related to the connection of the exposure field to the electron beam exposure device or the focused ion beam exposure device, and as a result, the actual exposure This was one of the reasons why the joining accuracy in the exposure field of the pattern obtained by the method could not be improved to 0.1 μm or less.

The purpose of the present invention is to provide an exposure method that solves this problem and forms a pattern having highly accurate exposure field connections by electron beam exposure or focused ion beam exposure.

[Means for solving problems]

In the charged beam exposure method of the present invention, two lines parallel to and sandwiching the field boundary are formed in each of two adjacent exposure fields of a charged beam exposure device on a resist material coated on a substrate (on the reverse side). A step of exposing a pattern for measuring field joint accuracy by exposing the pattern, a step of developing the exposed substrate to form a resist pattern for measuring field joint accuracy, and a step of forming a resist pattern for measuring field joint accuracy on the substrate. The secondary electron current waveform obtained by detecting the secondary electrons emitted from each irradiation point by operating a focused electron beam with an accelerating voltage of several kilovolts or less and a diameter of several tens to hundreds of beams. The process of processing the field in the processing unit and measuring the field connection accuracy, and from the obtained field connection accuracy, create a correspondence table between the field connection accuracy and the exposure field correction variation prepared in advance in the processing unit. For a low-acceleration electron beam with an accelerating voltage of several kilovolts or less, it is possible to focus the beam diameter from several tens to several hundreds using an electron optical system, so it is possible to obtain the same resolution as this beam diameter. Therefore, it is expected that the resolution will be improved by more than an order of magnitude compared to conventional optical methods.On the other hand, the secondary electron emission rate of the material, that is, the secondary electron emission rate corresponding to the amount of current of the primary electron beam incident on the material, The ratio of electron emission current varies depending on the material, but generally the acceleration voltage for primary electrons exceeds 1 in the range of several hundred volts to several kilovolts, so if the acceleration voltage for -secondary electrons is set within this range, It is possible to measure even insulating samples without charging them.Therefore, there is no need to cover the sample with conductive material such as Au, so measurement accuracy does not deteriorate.Furthermore, it is possible to measure the measurement accuracy without charging the sample. By computer processing the secondary electron signal waveform obtained by measuring the accuracy evaluation pattern, it becomes possible to automatically measure a large number of evaluation patterns on the board.Based on the measurement results obtained in this way, If the accuracy correction parameters are fed back to the deflector of a charged particle beam exposure apparatus, it is expected that an exposure pattern with highly accurate field connections can be obtained.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS A charged particle beam exposure method according to the present invention will be described below with reference to illustrated embodiments.

FIG. 1 is a conceptual diagram showing an electron beam exposure method according to the present invention. A negative resist for electron beam 102, such as chloromethylated polystyrene (
CMS) was applied to a thickness of about 5,000 layers, and then beta-coated at 100° C. for 930 minutes in a N2 atmosphere.

This substrate 101 is loaded onto a sample stage 104 of an electron beam exposure apparatus 103. The electron beam exposure device 103 generates a variable rectangular electron beam 105 with an acceleration voltage of 20 kV, and the electron beam 105 is deflected by a deflector 106 to expose the substrate 101. Since the electron beam exposure device 103 can only expose within the exposure field limited by the deflection width of the deflector 106, it is not possible to perform a so-called step-and-exposure method in which the sample stage 104 is moved by the deflection width and then exposed.
It uses a repeat exposure method.

Using this electron beam exposure device 103, the resist 10
2, a pattern for evaluating the connection accuracy of the exposure fields is exposed. The details of the method of exposing the evaluation pattern are shown in FIG. In FIG. 2 (al), the electron beam 105 is
6 to expose a part 202 of the exposure field connection accuracy evaluation pattern to the edge of the exposure field 201 in parallel to the boundary line of the exposure field 201. Next, as shown in FIG. 2 (bl), the sample is moved by the length of one side of the exposure field, and another part 204 of the exposure field connection accuracy evaluation pattern is placed at the end of the exposure field 203. Exposure is performed parallel to the pattern 202 across the boundary 'a205 between the exposure field 201 and the exposure field 203.

As described above, the pattern for evaluating the connection accuracy of exposure fields is formed from two line patterns 202 and 204 that are parallel to each other and face each other across the boundaries of exposure fields 201 and 203.

The size of each line pattern is 5 μm in width.

It has a length of 20 μm and is exposed 5 μm inward from the boundary of the exposure field. Therefore, the pitch length between two lines in an ideally connected exposure field is 15 μm.

Substrate 1 patterned by the above exposure method
01, as shown in FIG.
After developing the CMS resist 102 on the quartz substrate 101, the CMS resist 102 was taken out from the quartz substrate 101, and then subjected to beta testing at 100° C. for 30 minutes in an N2 atmosphere. Next, the substrate 101 is loaded onto the sample stage 108 of a low-acceleration electron beam length measuring machine 107 capable of generating an electron beam 109 with an accelerating voltage of several kV or less, and then a field connection evaluation pattern on the quartz substrate 101 is measured.

The details of the measurement method are shown in Figure 3. In FIG. 3(a), an electron beam 109 with an acceleration voltage of 0.9 kV, a beam current of 5 pA, and a beam diameter of 150 people is scanned by a deflector 110 over field connection evaluation patterns 202 and 204, and the electron beam is emitted at each irradiation point. The secondary electron 301 is detected by the detector 1
11. Figure 3 (bl is the electron beam 10
This is a secondary electron signal waveform when the horizontal axis represents the input to the deflector 110 corresponding to the scanning position No. 9, and the vertical axis represents the secondary electron detection current from the detector 111. A waveform having a peak value at a position corresponding to the edge of the field connection evaluation patterns 202 and 204 is obtained. The pitch of the two parallel ins 202 and 204 in the evaluation pattern is
It is calculated by the average (A+B)/2 of the distances A and B between the peak positions in the secondary electron signal waveform. These processes are performed in the signal processing section 112 in FIG.

For example, if the exposure field is exposed larger by 0.19 μm on one side, 14.62 μm is obtained as the measured value of the field connection accuracy evaluation pattern.

The field splicing accuracy measurement value calculated in the above manner is determined by referring to the correspondence table between the field splice accuracy measurement value and the exposure field correction parameter prepared in advance in the signal processing unit 112 to determine the optimum correction parameter. This correction parameter is applied to the electron beam exposure apparatus 103.
input to the deflector 106. As a result, the deflection distance of the electron beam is corrected, and it becomes possible to improve the field connection accuracy in the pattern obtained by exposure to 0.05 μm or less.

〔Effect of the invention〕

As described above, it can be seen that the pattern exposed by the charged beam exposure method according to the present invention has significantly improved field joining accuracy compared to the pattern exposed by the conventional method. Moreover, it is possible to automatically measure a large number of evaluation patterns on the substrate and input correction parameters online from those measured values to the charged particle beam exposure system, which is expected to speed up the process and improve the stability of the exposure system. .

[Brief explanation of drawings]

FIG. 1 is an overall configuration diagram for explaining one embodiment of the present invention. FIG. 2 is a diagram showing an exposure method of a pattern for evaluating exposure field connection accuracy using an electron beam exposure device. FIG. 3 1 is a diagram showing a method for evaluating the accuracy of exposure field connections using a low-acceleration electron beam length measuring machine. 101...Quartz substrate 102...Negative resist 103 for electron beam exposure
...Variable rectangular electron beam exposure device 104...Sample stage 105...Variable rectangular electron beam 106...Deflector 107...Low acceleration electron beam length measuring device 108...Sample stage 109...Low Accelerated electron beam 110...Deflector 111...Secondary electron detector 112...Signal processing unit 201...Exposure field 202.204...Part of exposure field connection accuracy evaluation pattern 203...・Exposure field 205...Field boundary 301...Secondary electron electron beam lighting! Figure 1 (a) Figure 2

Claims (1)

[Claims] (1) On the resist material coated on the substrate, in each of two adjacent exposure fields of the charged beam exposure device,
A step of exposing a pattern for measuring field connection accuracy by exposing two line patterns parallel to the field boundary, and a step of developing the exposed substrate to form a resist pattern for measuring field connection accuracy. , a secondary beam emitted from each irradiation point is scanned with an electron beam focused at an accelerating voltage of several kilovolts or less and a diameter of several tens of angstroms to several hundred angstroms on a resist pattern for measuring field connection accuracy on a substrate. The process involves detecting electrons, processing the obtained secondary electron current waveform in the processing unit, and measuring the field connection accuracy.From the obtained field connection accuracy, the field connection accuracy prepared in advance in the processing unit is calculated. Charged beam exposure characterized by including the step of determining optimal correction parameters by referring to a correspondence table with exposure field correction parameters, inputting the correction parameters to a deflector of a charged beam exposure device, and performing exposure. Method.