JPH01309322A - Method for inspecting x-ray mask - Google Patents

Abstract

PURPOSE:To detect defects not only on the surface layer of an absorber but also on the entire film by detecting the characteristic X rays which are emitted from the absorber when an electron beam is projected on a circuit pattern which is formed by using the heavy metal X-ray absorber. CONSTITUTION:A circuit pattern is formed on a mask supporting substrate 2 comprising a light element by using a heavy metal X-ray absorber 1. An X-ray mask formed in this way is mounted on a moving stage 12. An electron beam 6 is projected on the mask. Characteristic X rays 3 which are emitted from the absorber 1 are detected with a detector 4 through an X-ray filter 11. The intensity of the characteristic X rays 3 is changed in correspondence with the concentration of the heavy metal incorporated in the absorber 1. Therefore, when a specified treatment is performed in an X-ray signal processing circuit 9, the defects in the circuit pattern can be detected not only on the surface layer but also on the entire film.

Description

[Detailed Description of the Invention] [Summary of the Invention] An X-ray mask inspection method, particularly an X-ray exposure technique that is required as a means to transfer and form fine circuit patterns in the production of VLSI, Is it due to the X-ray absorber on the X-ray mask required for transfer? j1
Regarding the defect inspection method for 810 circuit patterns, we have developed a method for detecting defects in the X-ray absorber that could not be detected by conventional SEM inspection in the inspection of X-ray masks performed by irradiating the pattern with an electron beam. In the inspection of an X-ray mask having a mask support substrate composed of a heavy metal X-ray absorber and a light element supporting the X-ray absorber, The present invention includes an X-ray mask inspection method characterized in that defects in the circuit pattern are detected by irradiating the circuit pattern with an electron beam and detecting characteristic X-rays emitted from the X-ray absorber.

[Industrial application field]

The present invention relates to an X-ray mask inspection method, particularly an X-ray exposure technique that is required as a means to transfer and form fine circuit patterns in the manufacture of VLSIs, and in which X-rays are required to transfer circuit patterns. This invention relates to a method for inspecting defects in fine circuit patterns using an X-ray absorber on a mass flow.

As the degree of integration of VLSIs increases, the circuit patterns of monolithic ICs become finer, and a defect inspection method for fine circuit patterns on masks is required instead of optical means.

[Conventional technology]

In the conventional circuit pattern defect inspection method for transfer masks using optical means, the circuit pattern design rule is within the resolution limit of light, so the pattern of reflected or transmitted light applied to the mask surface is inspected. By doing so, we were able to perform defect inspection.

However, as the degree of integration of LSI increases, the design rules for circuit patterns are further refined, and eventually exceed the physical resolution limit of light (approximately 0.3 μm). Even if the wavelength of light is shortened to the extent that is currently possible, images will become blurred due to diffraction. Further, even if an electron beam is used as a probe, mere observation of reflected electrons and secondary electrons is insufficient in a system such as an X-ray mask where the thickness of the absorber film directly affects the contrast.

Figure 5 shows a conventional scanning electron microscope (ScanningEl).
This is a diagram showing the configuration of an electron microscope (SEM), in which 41 is an electron gun, 42 is a lens, and 4
3 is a deflection system, 44 is an electron beam (EB), 45 is a mask support substrate, 46 is an X-ray absorber, 47 is a secondary electron, 48
is a photomultiplier tube, 49 is an amplifier, and by using such a device to obtain the signal shown to the right of the amplifier in the same figure,
A signal 50 corresponding to the X-ray absorber 46 is obtained.

In the diagram on the right of the amplifier 49, the horizontal axis represents time;
The line axis measures signal strength.

[Problem to be solved by the invention]

Therefore, if the optical method is used, the circuit pattern cannot be identified due to lack of contrast due to diffraction blur.

In the electron beam scanning method, there is a problem that only information on the surface layer is known, and there is no pattern inspection method that includes X-ray mask contrast defects due to changes in absorber film thickness.

To explain this in more detail, according to conventional SEH,
Information can only be obtained from the surface of the X-ray absorber to a depth of several to several dozen people. FIG. 6 is a schematic cross-sectional view of the X-ray absorber 46 for explaining the inspection using SEM.
EB4 scanned by the line absorber 46 as shown by the broken line in the figure.
4 is incident, secondary electrons 47 are generated near the surface or deep (backscattering). Secondary electrons 47 formed close to the surface jump out of the X-ray absorber 46 and are detected by the photomultiplier tube 48, but secondary electrons 47 formed deep inside jump out of the X-ray absorber 46. It cannot be detected by the photomultiplier tube 48.

The mask support substrate 45 is made of X such as BL SiL Sxc.
It is made of a light element with a low density that allows the radiation to pass through, and on top of that, Ta
, a heavy metal film such as W is formed and patterned to form the X-ray absorber 46. There are two problems in the formation of such an X-ray absorber. One is that during the formation of the X-ray absorber film, for some reason some parts of the film have a lower density or are thicker than other parts. Another problem is that heavy metals are not completely removed during film patterning (during processing) and remain in areas where they should be removed completely.

Referring to the plan view of FIG. 7, the figure (al) shows a case where the pattern is not completely removed during patterning of the X-ray absorber 46 and a defect 51 remains. Detection of such a defect is performed by S
Since it can be detected by EM, there is no particular problem in its inspection.

As shown in FIG. 4B, if a portion 52 with low density or thin film thickness is formed during film formation of the X-ray absorber, this portion 52 cannot be detected by SEl'l.

Furthermore, as shown in FIG. 2C, if m-metal 43 remains as shown by the sandy area in the figure when it should be removed during processing, it will not be detected by the SEM if it is a minute amount.

By the way, in X-ray exposure, since the X-rays have a wavelength that is approximately the size of an atom, the X-rays may or may not be transmitted depending on the presence or absence of atoms. Therefore, as shown in Figure 7 (bl), there is a possibility that X-rays will pass through the thin film or the part with low density, and as shown in Figure 7 (C1), even a trace amount of heavy metal 53 may remain. However, it is not transparent to X-rays, and although in both cases a defect in the X-ray absorber exists, it has not been possible to detect it in the past.

SUMMARY OF THE INVENTION Therefore, the present invention provides a method for detecting defects in an X-ray absorber that could not be detected by conventional SEM inspections in an X-ray mask inspection performed by irradiating a pattern with an electron beam. purpose.

[Means to solve problems]

The above problem was solved when inspecting an X-ray mask that has a mask support substrate made of a heavy metal X-ray absorber and a light element that supports the X-ray absorber. This problem is solved by an X-ray mask inspection method characterized by detecting defects in circuit patterns by irradiating an electron beam onto the X-ray absorber and detecting characteristic X-rays emitted from the X-ray absorber.

FIG. 1 is a diagram explaining the principle of the present invention. In the figure, 1 is an X-ray absorber, which is made of a heavy metal material approximately 1 μm thick. 2
is a mask support substrate and is made of a light element. 3 is a characteristic X-ray generated by irradiation with the electron beam 6, and 4 is its detector. 5 is an electron beam optical system, and 6 is an electron beam. 7 is an electron beam deflection system, 8 is an electron beam deflection system drive circuit that drives the electric signal applied to the deflection system, and 9 is an X-ray signal processing circuit that processes signals from the detector, and is used for beam deflection (scanning). The signal is processed in synchronization with 8 by a synchronous processing circuit 10 that drives the accompanying signal processing.

[Effect]

In the present invention, as shown in FIG. When the absorber material is irradiated with X-rays, characteristic X-rays are emitted from the absorber material, and the intensity thereof depends on the thickness of the absorber, so it is detected.

〔Example〕

Hereinafter, the present invention will be specifically explained with reference to an illustrated embodiment.

FIG. 2 is a block diagram of one embodiment of the present invention, and in the figure, the same parts as shown in FIG. 1 are indicated by the same symbols.

The X-ray absorber 1 is an alloy of heavy metals such as Ta, W, and Mo and other metals, and the mask support substrate 2 is made of BN and SiN.
, composed of light element compounds such as SiC. The electron beam 6 can be focused to an arbitrary beam diameter by the electron beam optical system 5, but the diameter is set to about 0.01 μm in order to accommodate fine circuit patterns (assuming a minimum of 0.05 μm). The accelerating voltage is set to 50 KeV or more, taking into account that the thickness of the heavy metal layer and the X-ray absorber 1 is 1 μm. In the figure, 11 is an X-ray filter, a crystal spectrometer, or something similar that has been newly added to FIG. 1, and is used for the purpose of detecting only characteristic X-rays of a specific wavelength. 12 is X
This is a stage for moving the X-ray mask.It is provided because the deflection distance of the electron beam is short, 0 to 300 degrees, so it is necessary to move the X-ray mask.

In scanning, referring to FIG. 3, the synchronization processing circuit 1
0 outputs the signal shown in FIG. 3 (al).

In the same figure (al to fdl, time is plotted on the horizontal axis; in figure fa), (C1, (d), the vertical axis is the signal strength, and in figure BL, voltage is plotted on the vertical axis. (In response to the synchronization signal of al, the electron beam deflection system drive circuit 8 generates the voltage shown in FIG. (V
It is determined by pc(L, where L is the deflection distance). Furthermore, in response to the signal shown in FIG. 3(a), the X-ray signal processing circuit 9
When the trigger signal shown in Figure 3 (C) is issued, the signal shown in Figure 3 (D) is input from the detector to the input section of the signal processing system, and this signal It corresponds to the type and amount. In addition, in FIG. 3 (di), 13 is a defect signal corresponding to the heavy metal 53 in FIG. 7 (C1).

Regarding the magnitude of the density of the X-ray absorber, referring to FIG. Although no change is observed, when the low-density portions 14 are averaged as schematically shown in the figure, the X-rays do not pass through them on average, so this is not a defect. However, if a low density portion 15 is formed in the depth direction of the X-ray absorber 1 as shown in FIG. A signal appears, and the presence of a low-density part that is a defect is detected.The reason why characteristic X-rays generated from deep parts of the X-ray absorber as shown in Figure 6 are detected is because Since is a particle, the secondary electrons formed in the deep part disappear before reaching the surface of the absorber, whereas the characteristic X-ray is a single wave, so as shown schematically in the figure. It is understood that it can go out of the X-ray absorber.

〔Effect of the invention〕

As described above, according to the present invention, unlike the conventional electron beam scanning method, the type and amount of elements can be detected.
This greatly contributes to the inspection of circuit pattern defects on masks, including contrast defects due to changes in absorber thickness.

[Brief explanation of the drawing]

Fig. 1 is an explanatory diagram of the principle of the present invention, Fig. 2 is a configuration diagram of an embodiment of the present invention, Fig. 3 ta) to (d) are diagrams of an embodiment of the method of the present invention, and Fig. 4 is a diagram of the embodiment of the present invention. Figures illustrating method implementation examples, in which (a) and (bl are cross-sectional views, (C) are signal waveform diagrams, Figure 5 is a configuration diagram of a conventional SEM, Figure 6 is a diagram showing secondary electrons, and Figure 7 is a diagram showing secondary electrons. (C1 is a plan view of an X-ray absorber pattern. In the figure, 1 is an X-ray absorber, 2 is an X-ray mask support substrate, 3 is a characteristic X-ray, 4 is an X-ray detector, and 5 is a Electron beam optical system, 6 is an electron beam, 7 is an electron beam deflection system, 8 is an electron beam deflection system drive circuit, 9 is an X-ray signal processing circuit, 10 is a synchronization processing circuit, 11 is an X-ray filter, 12 is an X-ray Mask moving stage, 13 is a defect signal, 14 and 15 are low density parts. Patent applicant: Fujitsu Ltd. Representative Patent Attorney Akimoto Kuki Yoshiyuki Osuga Signal 1. Mipu precept pH 16)
? Shelf [cop 3. Low altitude part 14 〆7th generation Σlt part departure 15 Bu word number 5! Keimoto Inventor: A dog's country! τ4 (4, @To-shape 41) Conventional SEM elliptical 5th figure T-section 6th figure showing the double layer

Claims (1)

[Claims] In the inspection of an X-ray mask having a heavy metal X-ray absorber (1) and a mask support substrate (2) made of a light element that supports the X-ray absorber, the X-ray absorber ( Defects in the circuit pattern are detected by irradiating the circuit pattern formed using 1) with an electron beam (6) and detecting characteristic X-rays (3) emitted from the X-ray absorber (1). An X-ray mask inspection method characterized by: