JPS5854495B2 - Alignment method and optical device - Google Patents

Description

[Detailed description of the invention] The present invention relates to i-photomask alignment technology.

In the manufacture of semiconductor devices, a technique for selectively removing an insulating film or metal thin film formed on a semiconductor wafer is essential.

As this method, a selective etching method has conventionally been used, and is performed through the following steps.

A film of photoresist, which is a photosensitive resin, is formed on a film to be etched formed on a semiconductor wafer.

A photomask with a desired pattern formed thereon is placed on the photoresist film, and the photoresist film is irradiated with ultraviolet rays through the photomask.

Thereafter, the photomask is removed, and the photoresist film is immersed in a developer to melt the areas that were irradiated with ultraviolet rays or the areas that were not irradiated with ultraviolet rays.

Next, using the selectively melted photoresist film as a mask, the film to be etched exposed through the mask is dissolved with an appropriate etching solution, and then the entire photoresist film is removed. .

In this way, the film to be etched is etched according to the desired pattern (the same pattern as the photomask), but accurate positioning is required to place the photomask on the photoresist film. .

For this purpose, this positioning is performed by irradiating the photomask surface with light and checking the photoresist film surface and the photomask surface with a microscope or the like.

Conventionally, mercury lamps have been used as the light for four reasons, including the fact that the light has a relatively high intensity and is the same as the light used in exposing the photoresist.

Moreover, since the light emitted from this mercury lamp contains ultraviolet rays, light other than ultraviolet rays is used by passing it through a color filter in order to prevent the photoresist film from being exposed.

As shown in Figure 1, the light from the mercury lamp is filtered out at different wavelengths, and only the non-ultraviolet portion (the portion surrounded by curve 1) is extracted using a color filter, and this light is passed through a photo mask. It is used for positioning.

However, the light extracted through the color filter is the first
As shown in the figure, since two bright lines with wavelengths of 546.1 mμ and 577.0 mμ are hidden, light interference occurs when the photomask is brought close to the semiconductor wafer surface, which can be confirmed using the microscope, etc. Several light and dark changes can be observed.

As shown in FIG. 2, this is because the light 2 of the mercury lamp irradiated through the color filter is reflected by the back surface 3a of the photomask 3 and the front surface 4a of the semiconductor wafer 4, resulting in a phase shift between the two. 5 of 2 mercury lights become parallel rays
When the wavelength of the 46.1 mμ emission line is shifted by half a wavelength, this emission line becomes dark.

This bright line also becomes dark when the wavelength of 577.0 mμ is shifted by half a wavelength.

In this case, the intensity of the two emission lines is very large, resulting in a large change in brightness as a whole.

This phase shift occurs between the photomask 3 and the semiconductor wafer.
This changes depending on the length of the gap t with respect to 4, which causes alternating light and darkness.

Therefore, when checking the mask positioning using a microscope, the above-mentioned brightness and darkness may cause misunderstandings.

This is true not only when an operator visually checks but also when using a photosensor.

The present invention eliminates these drawbacks and provides a photomask alignment technique that eliminates brightness and darkness caused by light interference when aligning a photomask on a semiconductor wafer.

This will be explained below using examples.

FIG. 3 is a simplified configuration diagram showing one embodiment of an apparatus used in the photomask alignment method according to the present invention.

In the same figure, there is Suigintou 11, and in front of this is Suigintou 1.
A convex lens 12 is arranged to convert the water emitted from the lens into parallel light beams.

Furthermore, in front of the convex lens 12, a FUMIN-1S device is installed for downwardly changing the direction of the parallel rays obtained by passing through the convex lens 12.

And below the above mirror 13 is a convex lens 14.
is arranged, the parallel light beams reflected by the mirror 13 are condensed by the convex mirror 14.

Further, a photomask 15 is fixed below the convex lens 14, and a semiconductor wafer 15 is fixed below this.
6 is arranged, and this semiconductor wafer 16 can be moved in the vertical direction, the X-axis, Y-axis directions, and the θ-axis direction by a mechanism not shown previously.

On the other hand, above the half mirror 13 is a reflecting mirror 1 for changing the direction of the light reflected from the photomask 15 and the semiconductor wafer 16 and passing through the half mirror 13.
A bandpass filter 18, which is the gist of the present invention, is arranged in the traveling direction of the light whose direction has been changed by the deflected reflecting mirror 17.

A convex lens 19 and a photo sensor 20 are arranged behind the band pass filter 18, and the light that has passed through the band pass filter 18 is condensed by the convex lens 19, and the condensed light is captured by the photo sensor 20. That's what I do.

Furthermore, this photosensor 20 is connected to a computer 21 and operates a mechanism (not shown) for moving the semiconductor wafer 16 in the X-axis, Y@ and θ-axis directions based on the signal from the photosensor 20. It has become.

Here, the bandpass filter 18, which is the gist of the present invention, is composed of a glass plate and a number of thin layers made of a material having a different refractive index from that of the glass. A plurality of bright lines are reflected, and only the light in the area surrounded by the curve 30 is allowed to pass through, as shown in the graph of FIG.

In this configuration, first, the semiconductor wafer 16 is placed below the fixed photomask 15, and the mercury lamp 11 is turned on.

The light from the mercury lamp 11 becomes parallel light by passing through the convex lens 12.Then, the direction is changed by the mirror 13, and the light is condensed by the convex mirror 14.The light is then transferred to the surface of the photomask 15 and the surface of the semiconductor wafer 160. irradiate.

Then, the semiconductor wafer 16 is slightly raised and brought into close contact with the photomask 15.

In this state, the light reflected from the surface of the photomask 15 and the surface 16 of the semiconductor wafer is transferred to the convex lens 1.
4,... - mirror 13, reflector 17, bandpass filter 18. The photo sensor 20 captures the signal through the convex lens 19, and the signal emitted from the photo sensor 20 is sent to the computer 21 for determination.

Thereafter, based on the signal emitted by the light received by the photosensor 20, the computer 21 lowers the semiconductor wafer .
Perform positioning by moving in the axial direction.

Next, the semiconductor wafer 16 is slightly raised to bring it into close contact with the photomask 15, and the photosensor 2 is
The computer 21 determines the alignment accuracy based on the light signal received by 0, and if it passes, the alignment is completed.

Conventionally, light other than ultraviolet rays was extracted from the light emitted from a mercury lamp, and this light was used to align the photomasked semiconductor wafer.

Therefore, this light has a wavelength of 546.1 mμ, 577
．． Since the two emission lines of 0 mμ were trenched, interference occurred especially at the stage of bringing the semiconductor knee into close contact with the photomask, resulting in repeated brightness and darkness.

If several of them are used as in this embodiment, the bandpass filter 18
Since the bright line can be removed, light having a constant intensity with no brightness or darkness is sent to the photosensor.

Therefore, since an accurate phase signal is sent from the photosensor to the computer 21, misidentification in positioning will not occur.

In this embodiment, a single pan-pass filter is used to extract light that is not ultraviolet light and has three bright lines, but as shown in Figure 5, only the conventional color filter and bright lines are removed. Alternatively, the object of the present invention can also be achieved by using a combination of a pass/docant filter (a filter that passes light below the curve 40 in the figure) that greatly reduces the transmittance of only the bright line.

Although this embodiment describes a case in which photosetting is automated using a computer, the present invention is not necessarily applicable to cases in which mask positioning is performed visually by an operator.

Furthermore, although the bandpass filter 18 is placed in front of the photosensor in this embodiment, it is of course possible to place it anywhere in the optical path of the light emitted from the mercury lamp, including in front of the mercury lamp.

As described above, according to the method of aligning a photomask according to the present invention, it is possible to eliminate brightness and darkness caused by interference in light removal for aligning a photomask on a semiconductor wafer.

[Brief explanation of drawings]

Figure 1 is a graph showing the bright line distribution of light from a mercury lamp, and is a graph explaining the case where the light is passed through a color filter. Figure 2 is a graph showing the interference effect of combined light when a photomask and semiconductor wafer are stacked. 3 is a simplified configuration diagram showing an embodiment of the apparatus used in the photomask alignment method according to the present invention, and FIGS. 4 and 5 are graphs showing the bright line distribution of light from a mercury lamp. It is a graph explaining the case where the light passes through a filter, which is the gist of the present invention. 3.15...Photomask, 4,16...
・A conductor Weber, 11...Mercury lamp, 12, 14
, 19...Convex lens, 13...Half mirror 17...Reflector, 18...Band pass filter, 20...Photo sensor, 2
1... Computer.

Claims (1)

[Scope of Claims] 1. A method for aligning a sample and a photomask by irradiating a sample with a light source having bright lines and receiving light reflected by the sample, the method comprising: An alignment method characterized in that the sample and the photomask are aligned using light other than ultraviolet light in which the emission lines are significantly reduced. 2. A light source having an emission line, an optical lens system, a means for fixing a photomask, a means for arranging a sample having a mechanism capable of moving the position of the sample with respect to the photomask, and receiving light reflected by the sample. and a light receiving means, wherein the light path section between the light source having the bright line and the sample placement means or the optical path section between the sample placement means and the light receiving means is provided with a light source other than ultraviolet rays. An optical device characterized by interposing a filter that allows light to pass through and significantly reduces the transmittance of bright lines.