JPS5950518A - Project printing method - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for projection printing masks onto workpieces, particularly wafers for use in integrated circuit fabrication.

To make integrated circuits, it is necessary to print a mask with a predetermined pattern on a wafer coated with a photosensitive layer. If the Ueno already contains circuit elements, it is necessary to project the pattern of the mask within a strictly defined area.
The mask and substrate must be aligned with each other before the printing process. During this alignment process, an alignment pattern (alignment pattern) is provided to the mask.

The alignment pattern t has the shape of a transparent window, for example,
Alignment mask on wafer
is provided. The alignment mask is, for example, a linear miso layer that falls on the 5i02 layer of the wafer. Corresponding alignment masks and alignment patterns are projected by alignment light reflected from the workpiece to obtain alignment fiducials.

Visibility - Most of the manual alignment methods use multi-colored alignment lights.3 Since the light source of the stand is an incandescent bulb or xenon lamp, the spectrum of the alignment light is Alignment methods using polychromatic light span from about 50 nm to the infrared region, however, there are many drawbacks. The alignment signal must be characterized not only by high intensity but also by high contrast. Therefore, the alignment light must be properly tuned by the alignment marks on the wafer. The layer structure of the wafer differs from region t. When using multicolor alignment light, the alignment light reflected from the wafer includes areas with poor adjustment or low adjustment, resulting in poor contrast.

For the reasons mentioned above and the high projection efficiency of the lens used for alignment, most automatic alignment methods employing indigo light use alignment light with a relatively narrow spectrum (on the order of several nanometers). are using.

One of these prior art systems is an exposure light source (generally a mercury lamp) for the alignment process? use. Jutte, 547
Id captured in a narrow spectral region near nm, 457 n
A spectral region around m is used as alignment light.

There are further problems with this. For reasons explained later, the spectral region near 547 nm N is not appropriate;
If the alignment process is performed by 436 nm alignment light, its intensity should be very low.

This is because the photosensitive layer on the wafer has high absorption and high sensitivity at wavelengths below 450 nm. 3. However, the photosensitive layer cannot be pre-exposed with the alignment light described above. Moreover, since the refractive index of the photosensitive layer is increased, a significant portion of the alignment light at the air/photosensitive layer interface is reflected or absorbed by the photosensitive layer. This causes a decrease in alignment (M), and in particular, a decrease in the noise ratio of No. 48.

Furthermore, it is known to use another alignment light source with a narrow spectrum for the alignment process.

As already mentioned, the alignment signal must be characterized by high intensity and high contrast in order to have a high value. Both values are determined in part by the order of the layers on the wafer, which is adjusted during manufacturing. The features on the wafer are comparable to those in the optical layer.

Even though the layer thickness is a multiple of the alignment wavelength, the coherent length of the alignment light is large, resulting in interference interference and artifacts.
That is, the evening light 1j reflected from the sea urchins is often significantly attenuated. This adversely affects the intensity as well as the contrast of the alignment light.

Therefore, an object of the present invention is to improve the method of projection printing (printing) of a mask on a wafer.
The improvement is that a high intensity, deep contrast alignment signal is provided for relative alignment of the mask and wafer, largely independent of the order of the layers on the wafer.

This, according to the invention, provides aligned light consisting of at least two narrow wavelength ranges whose wavelengths are at a predetermined distance from each other and to which the photosensitive layer of said workpiece (wafer) is insensitive or has low sensitivity. , is achieved by measuring the intensity of the alignment light reflected from the workpiece and generating an alignment signal from the wavelength region of the alignment light of high intensity.

This ensures an alignment signal that is always optimal in terms of intensity and contrast, almost irrespective of the order of the layers on the wafer or the combination of layer thicknesses.

The present invention will be described in detail below with reference to the accompanying drawings.
1 shows an apparatus for projection printing (baking) of a mask onto a wafer consisting of a lens 6 and a wafer 4; Before projecting the pattern of mask 2 onto the photosensitive layer of wafer 4, the mask and wafer must be mutually aligned. 1st a
As shown in the figure.

The mask 2 is arranged outside the circuit pattern 11.

It has an alignment pattern that is a rectangular transparent window. According to FIG. 1b, corresponding linear alignment marks 12 are arranged on the wafer 4 within the projection area of the projection lens 30. As shown in FIG. The alignment pattern 5 and the alignment mark 12 are also the circuit pattern 11
It is clear that the molecule can be arranged within the area provided by the molecule.

According to the invention, an alignment light source 10 is provided for the alignment process. The alignment light source 10 emits alignment light in at least two narrow wavelength regions spaced apart from each other, in which the photosensitive layer on the wafer 4 is non-absorbing. Since the currently commonly used layer contains a diazo compound and is therefore highly absorbent and photosensitive in the wavelength region below 450 nm, wavelengths above 450 nm are suitable for alignment illumination.

Therefore, as the alignment light source 10, at least two spectral lines λ1=m488 nm and λ2=514.5 nm
An argon ion laser is used that emits .

The selection of the desired spectral lines is very simple, for example by adjusting the corresponding resonance conditions. In the apparatus of FIG. 1 showing a pair of joint marking optical paths, 2
The two alignment beams λl and 2 illuminate different regions of the window-shaped alignment pattern 5 on the mask 2 by means of a mirror 14, and are directed to the wafers with alignment marks 12 inside by means of an auxiliary lens system and a projection lens 6. The auxiliary lens system 6 is composed of two mirrors 19.19', two semi-transparent mirrors 18.18' and one interference filter 8. The filter 8 separates the alignment light from the wafer 4 into an alignment beam of wavelength λl and wavelength λ2. The alignment beams λl and λ2 are transmitted through semi-transparent mirrors 18 and 18', and image L7 the alignment mark 12 and alignment pattern 5 onto separate photoelectric scanning devices 7, 7', respectively.

The scanning device 7d in turn indicates the distance of the alignment mark 12 to the edge of the window-shaped alignment pattern 5, which is proportional to the position of the alignment pattern 5 with respect to the alignment mark 12 in the usual manner. Issue an alignment signal.

The selection switch 9 is a high-strength, high-contrast alignment signal S.
x, so that the mask 2 and substrate 4 are relatively aligned Fl+
It's helpful to point out.

FIG. 2 shows the multilayer structure of the crucible 4 in the area of the alignment mark 12. The wafer 4 consists of a silicon substrate 17 and an Sj,02 layer 15 arranged on the surface of the substrate 17.

The linear alignment mark 12 is formed by the edge of the EliO2 layer 15. The wafer 4 is completely covered by a photosensitive layer 16 into which the circuit pattern of the mask is to be transferred. Since the optical features of the photosensitive layer 16 and the S i 02 layer 15 are similar, the wafer 4 has a thickness d
defined as a reflector 17 covered by a partially reflective layer of t.

High-intensity, high-contrast alignment signals are generated using alignment mask 1.
The reflectivity of the combined layer of thickness d arranged on the wafer 4 adjacent to 2 is obtained only if the order of magnitude 9,1, ie constructive interference is satisfied.

The thickness d under this condition is d=j.-1. where u j is a natural number, λ is the vacuum wavelength of the alignment light, and n is the refractive index of the layer. In other words, the intensity of the alignment light reflected from the wafer is sufficient only when the layer thickness d is an even multiple of the alignment light wavelength A.

The intensity of the alignment light reflected from the wafer is reduced when the layer thickness 2d is in the region characterized by: d, = (2:i + 1) · − n alignment light reflected from the wafer It is clear that the interference condition for the attenuation of λ recurs periodically (period −λ/2n) with the thickness of the layer. The attenuation of the alignment light reflected from the wafer also causes a deleterious reduction in contrast.To eliminate this negative effect, the present invention uses at least two narrow wavelength ranges kept at a predetermined distance from each other. We use alignment light with . As shown in FIG. 3, the two narrow wavelengths λ1 and λ2 are arrayed on the wafer when one wavelength range is attenuated and the reflectivity of the combined layer is reduced to a second wavelength range '2'.
K pairs (7 can be maxed out.

Since relatively large variations in the thickness of the combined layers on the wafer e'5 also result in a minimum or maximum superposition of both wavelengths λl and λ2 when the spacing is large, the present invention also uses a third wavelength range. Plotting the wavelength region of highest intensity provides an optimum value, especially for the contrast of alignment no. 18, and thus for the precision of the alignment. This is particularly important if the alignment process has to be carried out not only in the plane of the wafer 4 or mask 2 but also in the direction of the optical axis of the projection lens 6.

Exclusive alignment in the direction of the optical axis, ie focusing of the image of the mask onto the wafer, is essential in the first step of integrated circuit manufacturing, for example since the wafer is not yet provided with circuit patterns and alignment marks.

In order to generate the alignment signal 2 in one direction, ie for focusing, the image of the window-shaped alignment pattern 5 on the wafer is scanned. When the image reaches its /I high contrast,
That is, the system will be in focus when the intensity change in the region of the edge of the window is maximum.

FIG. 2 shows an image of the linear alignment phase mark 12 and the transparent window-shaped alignment pattern 5 on the photoelectric scanning device 7 and, for example, by scanning the image perpendicular to the #I-shaped alignment mark 12. The resulting in-plane trap of the wafer shows an alignment signal for a certain coordinate X. Figure 2c shows the intensity flow of the image. As already mentioned, optical axis alignment 18 can be determined from the image by plotting contrast or intensity changes.
You can also get the number.

According to FIG. 4, it is preferable to use an argon ion laser as the alignment light source 10, and the alignment light has at least spectral lines λ, (=4Sanm)7λ, (=
514.5nrr+). It is clear that a high contrast alignment signal can be obtained with layer thicknesses in the range of 1 to 2.5 μm. As already mentioned, in order to obtain the aligned signal, the intensities of both 7 vectors are removed by 70, so t is not 1.

It is essential to plot only high intensity spectral lines. .

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an apparatus for projecting and gliding a mask onto a wafer according to the present invention; FIG.
Figure b is a cross-sectional view of the wafer, Figure 2a is a cross-sectional view of the wafer in the area of the alignment marks, and Figure 2b shows the alignment marks on the wafer and the alignment pattern on the mask projected onto each other; Figure 2C shows the intensity of the alignment light reflected from the wafer in the direction perpendicular to the linear alignment marks; Figure 3 shows the alignment reflected from the wafer as a function of the layer thickness adjusted by the manufacturing process. Figure 4 shows the intensity of the light reflected off the wafer, 7t, aligned to provide two spectral lines, preferably spaced apart from each other, 3 (numbered in the figure) 2... e-mask 3...projection 1/lens 4...
- Wafer 5... Alignment pattern 7... Scanning device 1o... Alignment light source 12... Alignment mark 16... Photosensitive layer agent Patent attorney (8107)
Kiyotaka Sasaki (and 5 others) Engraving of the drawings (no changes to the contents) 1 已 = Sote = = Ko-4 Procedural amendment November 1982 Special Application No. 150825 2, Invention name projection printing method 3, person making the amendment Relationship with the case: Patent applicant 8, contents of the amendment as shown in the attached sheet

Claims (1)

[Claims:] In a method for projection printing of a mask onto a workpiece, particularly a wafer for manufacturing integrated circuits, in which the pattern of the mask is projected onto a coated photosensitive layer of the workpiece by means of exposure light directed through a projection lens. , before the projection printing, the photosensitive layer of the workpiece is reflected from the workpiece in at least two narrow wavelength ranges spaced apart from each other, the wavelength range being non-photosensitive or having low light sensitivity. With the aligned light,
Aligning the mask and the already marked workpiece relative to each other by means of mutually corresponding alignment marks on the mask and alignment marks on the workpiece, which correspond to each other; A method for projection printing of a mask onto a workpiece, characterized in that the intensity of the reflected alignment light is measured; and an alignment signal is generated from a wavelength region of the alignment light having a maximum intensity t-1f. 2) The projection printing method according to claim 1, wherein the alignment light consists of three or more narrow wavelength regions spaced apart from each other at a constant interval. 3) The projection printing method according to claim 1 or 2, wherein the wavelength range of the alignment light is greater than 450 nm. 4) Argon-ion laser has a wavelength of 488 nm
2. A method as claimed in claim 1, characterized in that said alignment light is emitted consisting of at least two spectral lines of , % and 514.5 nm. 5) A method of projection printing a mask onto a workpiece, especially a wafer for manufacturing integrated circuits, in which the pattern of the mask is projected onto a coated photosensitive layer of the workpiece by means of exposure light directed through a projection lens. Prior to printing, the photosensitive layer of the workpiece is provided with an array of reflections from the workpiece consisting of at least two narrow wavelength ranges spaced apart from each other in wavelength ranges to which the photosensitive layer is non-photosensitive or photosensitive. Focusing the image of the mask on the workpiece by projecting alignment marks of the mask onto the workpiece in the evening light and scanning the image; alignment marks reflected from the workpiece; A method for projection printing of a mask onto a workpiece, characterized in that the intensity of the light is measured; and an alignment signal is generated from the wavelength region of the alignment light having the highest intensity.