JPS6236508A - Method of matching position of mask with position of wafer - Google Patents

Abstract

PURPOSE:To accurately measure a distance between a mask and a wafer at all times, by using the half-width of a bright line spectrum of a luminescent line for matching the position of the mask with that of the wafer. CONSTITUTION:A mask 1 where prescribed linear Fresnel zone targets are formed and a wafer whereon diffraction gratings are formed are disposed opposite to each other, and then parallel beams 5 of light are projected from above the surface of the mask. The beams of light diffracted by the linear Fresnel zone targets, which are converged on the wafer 2, are reflected by the diffraction gratings 4 on the wafer 2, and a spectrum of light is displayed. While the displayed spectrum of light is varied in luminance and half-width according to a distance between the wafer 2 and the mask 1, the half-width can be detected irrespective of an absolute level, and therefore it can be used not only for matching the position of the mask 1 with that of the wafer 2, but also for measuring an arbitrary distance between the two.

Description

Detailed Description of the Invention [Summary] The present invention projects parallel light rays onto a mask on which a linear Fresnel zone target is formed, and the projected light is After the light is focused on the wafer surface on which the diffraction grating is formed, the distance between the mask and the wafer can be accurately determined by using the optical spectrum of the reflected light displayed by the diffraction grating and finding the half-width of the optical spectrum. The wafer and mask are set at a predetermined distance by measurement.

[Industrial Field of Application] The present invention relates to accurate alignment between a mask and a wafer in an exposure process of semiconductor devices, such as X-ray exposure.

In recent years, as semiconductor devices have become more highly integrated, extremely precise, minute, and dense patterns are required. For this reason, it is extremely important to accurately set the distance between the mask and the wafer when performing proximity exposure. is important.

In these exposure methods, in order to eliminate pattern shift and defocus, a Fresnel Zone Plate (Fresnel Zone Plate, hereinafter referred to as F
There is a method of forming a ZP (abbreviated as ZP), projecting parallel light onto it, focusing the transmitted light on a diffraction grating section on the wafer surface, and comparing the brightness of the reflected spectral light to determine the interval.

This FZP mark consists of a group of multiple lines arranged according to a certain rule, and when parallel light is projected onto this, the transmitted light will form a focal point at an accurate distance due to the phenomenon of diffraction. By detecting the imaging position,
The distance between the mask and the wafer is detected and alignment is performed through automatic control.

However, in the conventional method, the condensed light beam transmitted through a mask with the FZP mark observes the reflected spectrum light displayed by a diffraction grating on the wafer surface, and the position of the highest brightness is set as the optimum position. Since there is a difference in the brightness level between the two, and the brightness level is not an absolute brightness level, there is a disadvantage that an error often occurs in detecting the optimum distance between the wafer and the mask.

In addition, in the exposure process, in addition to finding the optimal distance between the wafer and mask, it is also necessary to constantly detect the mutual distance in order to align the wafer and mask, so the distance between the wafer and mask is always accurately measured. There is a need for a method to do so.

[Prior Art] FIG. 3 is a sectional view of a main part showing the relationship between a mask having an FZP mark and a wafer on which a diffraction grating is formed, and FIG. 4 is a perspective view thereof.

The mask 1 and the wafer 2 are arranged at intervals, and the mask 1 is formed with an FZP mark 3 having a focal length of %IF, and the wafer 2 is formed with a diffraction grating 4.

When a parallel light ray 5 is projected onto the surface of the mask 1 as shown by the arrow, the transmitted light 6 that has passed through the FZP mark on the mask will be at a distance of D from the mask surface as shown by the one-dot line if F=D. The light is focused on a diffraction grating portion of a certain wafer 3 as a focal spot.

FIG. 5 is a spectrum diagram showing the relationship between the light intensity and the shift X between the position of the diffraction grating on the wafer surface and the focal point of the transmitted light, which is observed using a condensed spectrum on the wafer.

When the wafer is near the focal point of the FZP mark, the deviation X between the focal point position and the diffraction grating results in a spectrum with a brightness intensity distribution as shown in a.If the distance is larger than the focal point, b, and if it is smaller than the focal point, the spectrum will be The spectrum will look like C.

FIG. 6 is a cross-sectional view showing how transmitted light is diffracted by the diffraction grating 4 on the wafer 2 and becomes reflected light. The spectrum of reflected light is observed in the θ direction.

Therefore, by observing the optical spectrum of the transmitted light focused by the FZP mark and comparing the magnitude of the brightness, it is possible to approximately detect the appropriate distance between the wafer and the mask, but in reality, the absolute value of the brightness is Since the level is not constant and the appropriate spacing and position are set based on the compared relative brightness, the error increases and accuracy is lost. It is necessary to quantitatively understand the spacing between masks, but this cannot be achieved using conventional methods that only detect the maximum bright line.

[Problems to be solved by the invention] In the conventional alignment of a mask and a wafer using the FZP method, it is not possible to accurately detect the spacing and positional relationship between the wafer and the mask, and it is difficult to quantify the distance in the vicinity of the optimal position or spacing. The problem is that it is difficult to understand the situation in detail.

[Means for Solving the Problems] The present invention proposes a method for aligning a mask and a wafer in order to solve the above-mentioned problems. After placing the formed mask and the wafer on which the diffraction grating has been formed facing each other, by projecting a parallel beam of light from above the mask surface, the light beam diffracted by the linear Fresnel zone target is focused onto the wafer. is reflected by a diffraction grating on the wafer, and the spectrum of the light is displayed.

The spectrum of this light displays a spectrum with different brightness and half-width depending on the distance between the wafer and the mask, but since the half-width can be detected regardless of the absolute level, it is not only necessary to align the mask and wafer. This makes it possible to measure any distance between the mask and the wafer.

[Function] In the conventional alignment of a mask and a wafer using the FZP method, the distance and positional relationship between the wafer and the mask cannot be set accurately just by detecting the maximum bright line, and the distance and positional relationship between the wafer and the mask cannot be set accurately by simply detecting the maximum bright line. Since it is difficult to quantitatively grasp the distance between change in conjunction,
Moreover, since it was confirmed that the half-value width fluctuates at a constant rate regardless of the absolute level, automatic position detection was performed by using this value for signal processing.

[Example] FIG. 1 is a waveform diagram showing the intensity distribution of bright lines when the distance between a mask having an FZP mark and a wafer is changed.

If the focal length of the mask with the FZP mark is F, then
When the distance between the mask and the wafer is changed and D=F, the bright line spectrum of the diffracted light is like Sl, and the bright line peak p1
is large, and the half width d1 is small.

When the distance between the mask and the wafer is changed so that D>F, the bright line spectrum becomes as shown in S2, the peak p2 of the bright line becomes slightly smaller, and the half width d2 becomes larger instead.

As the distance increases, the emission line spectrum becomes S3
, S4, the peaks p8 and p4 of the emission line become smaller and smaller, and the half widths da and d4 become larger.

Generally, detecting the peak value of the brightness spectrum is
Since the peak value of the brightness spectrum cannot be compared with the absolute level, there is a great risk that the peak value of the brightness spectrum will fluctuate, leading to inaccurate detection. However, the waveform shape of the half-width changes very clearly as shown in the figure, so comparative detection is possible. It is easy to do.

FIG. 2 shows a block diagram of a half-width detection device.

The diffracted light from the wafer is detected by the photodetecting element 11, for example, pi.
After being input to the n diode, the signal is input to the waveform memory circuit I3 via the amplifier 12.

The waveform memory circuit outputs the signal to the display device 14, and a functional circuit 15 that performs a curve fitting function and digital differentiation has a circuit configuration that allows distance to be detected from the half width.

The waveform memory circuit contains the relative coordinates X, Y of the mask and wafer.
Signals based on coordinates, angles of projected light and diffracted reflected light, etc. are inputted by a counter 16 and synchronized.

Since the distance between the wafer and the mask determined by the half-width in this way is extremely accurate, the distance can be determined at any position in the alignment of the wafer and the mask, making alignment extremely easy. .

[Effects of the Invention] As explained in detail above, by using the half width of the brightness spectrum of the bright line in the alignment of the mask and wafer of the present invention, accurate measurement can be made at any position on the mask and wafer. This has a great effect in that it can be used for high-precision exposure of semiconductor devices.

[Brief explanation of the drawing]

Figure 1 is a waveform diagram showing the intensity distribution of the bright line when the distance between the mask with the FZP mark and the wafer is changed, Figure 2 is a block diagram of the half-width detection device, and Figure 3 is the FZP mark.
FIG. 4 is a cross-sectional view of a main part showing the relationship between a mask having a ZP mark and a wafer on which a diffraction grating is formed, FIG. 4 is a perspective view thereof, and FIG. A spectrum diagram showing the relationship between the light intensity and X when the deviation X is observed using a condensed spectrum on the wafer. Figure 6 is a cross section showing how transmitted light is diffracted by a diffraction grating on the wafer and becomes reflected light. In the figures, 11 is a photodetection element, 12 is an amplifier, 13 is a waveform memory circuit, 14 is a display device, 15 is a curve fission and digital differentiation circuit, and 16 is a counter. ! Sufutori? ,j Togo, *df, 扉-Kumuhiro branchsha? , main goo j-shaped country a51 figure throat 29 toe f146a IL ~ murderous p - ear - 7" o 17c 2nd flash

Claims (1)

[Claims] A mask on which a linear Fresnel zone target is formed and a wafer on which a diffraction grating is formed are placed facing each other, and by projecting parallel light rays onto the mask surface, light is focused onto the wafer. A mask characterized in that the distance (D) between the mask and the wafer is detected by detecting the half-width (d) of the spectrum (S) of light formed when the light beam is reflected by the diffraction grating. How to align the wafer.