JPS59193028A - Projection type transfer device - Google Patents

Abstract

PURPOSE:To make the influence of particulate dust to the negligible degree even when the particulate dust is adhered when a photo mask is put on a semiconductor wafer applied with a sensitized film, and exposure is to be exerted on the sensitized film by projecting a beam having the prescribed wavelength by a method wherein exposure is performed covering the mask with a transparent glass layer having thickness the same or more with focal depth of the optical system of a transfer device. CONSTITUTION:A beam projected from a high-voltage mercury lamp 2 connected with an exposure control part 5 and an electronic control part 6 is irradiated to the surface of a semiconductor wafer 8 applied with a sensitized film through a photo mask 7 and an optical system 4. At this time, construction of the mask 7 is made as follows. Namely, a chrome metal film 14 having the prescribed pattern is formed on a transparent glass plate 13 made to have sufficient thickness for possession of mechanical strength, and a transparent glass layer 15 is adhered on the whole surface burying the gaps of the film 14. At this time, thickness of the glass layer 15 is selected to the same or more with focal depth of the optical system 4 of a transfer device 1, and even when dust is adhered, the influence thereof is made as not to affect on the sensitized film.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a projection-type transfer (printing) apparatus, and particularly to a projection-type transfer apparatus useful for manufacturing semiconductor devices, creating a working mask from a mask original, and the like.

In the manufacture of semiconductor devices including integrated circuits, there is a method currently used to transfer (print) fine patterns of circuits onto a photosensitive film such as a photoresist film coated on a semiconductor surface. They can be roughly divided into contact transfer methods and projection transfer methods. The projection transfer method, which does not bring the semiconductor wafer into close contact with the photomask, is superior to the contact transfer method in that the photomask can be used semi-permanently and the semiconductor wafer is not damaged, resulting in a higher manufacturing yield for semiconductor devices. Are better.

In this projection transfer method, a projection optical system is installed between a photomask on which a fine pattern is formed and a semiconductor unit coated with a photoresist film, and the photomask pattern is projected onto the photoresist film. This is an optical exposure method that forms an image. It can also be used when creating a working photomask from a photomask master →
This is the way to do it. The optical system used here is composed of lenses, reflectors, or a combination of these.
Various methods are currently being tried, such as 10:1 projection or 10:1 reduction projection.

Photomasks used for projection transfer typically have a thickness of about 2.
A pattern for forming a predetermined integrated circuit is formed on a transparent parallel glass substrate with a thickness of 3 mm using a chromium film or the like with a thickness of about 0.1 μm.

The projection transfer device and its surroundings, as well as the entire room, should be kept as clean as possible, but the transfer device and associated machinery, such as the automatic wafer transport device, may have a small diameter change during operation. Generates submicron or 1 to 2 micron dust. These dusts are thought to be carbon, metal fine particles, or fine particles of unknown composition. These fine particles sometimes adhere to the surface of the above-mentioned photomask, causing shadows outside the required mask pattern on the photosensitive film formed on the working mask or semiconductor wafer to be transferred, and manufacturing process. This can cause defects in working masks and semiconductor devices. Nowadays, the minimum width between patterns is on the order of 1 μm, so the influence of fine particles such as dust cannot be ignored.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a projection type transfer device in which, despite the generation of such dust, the influence thereof does not appear on the transfer medium or, even if it does, causes a negligible shift.

According to the present invention, the light-transmitting layer surface is separated from the substrate surface so that the image of dust generated for some reason and attached to the mask surface is less than the minimum width between patterns in the pattern image on the photosensitive film. The main point is that a mask was used.

Hereinafter, the present invention will be explained in detail based on examples and with reference to the accompanying drawings. FIG. 1 is a block diagram schematically showing the entire projection type mask transfer apparatus according to an embodiment of the present invention. The projection mask transfer device 1 includes a light source 2 , an electrical and/or mechanical operating section 3 , a projection optical system 4 , an exposure control section 5 and an electronic control section 6 . As the light source 2, a high-pressure mercury lamp that emits light of a predetermined wavelength is used. The operating unit 3 is an electrical and/or mechanical unit that places and aligns the photomask T and the semiconductor wafer 8, which is a transfer medium, in a predetermined position, and sequentially feeds and unfeeds the wafers as necessary. It has a specific device. The exposure control section 5 controls the exposure intensity, exposure time, etc. of the light source 2, and the electronic control section 6 electronically controls the positional relationship between the light source 2 and the operation section 3, especially the photomask 7 and the Ueno mask 8 therein. Control. The latter control includes both control 4I in the direction perpendicular to the optical axis (ie alignment with respect to the pattern) and control in the direction parallel to the optical axis (ie focusing). The operating section 3, the exposure control section 5, and the electronic control section 6 are well known to those skilled in the art, so further explanation will be omitted.

The projection optical system 4 can take various forms, - by way of example:
Figure 2 shows a combination of various reflecting mirrors. A first reflecting mirror 9, a main concave mirror 10, a convex border 11, and a second reflecting mirror 12 are placed between the photomask 7 and the wafer 8 coated with a photosensitive film, and a condenser (not shown) is placed as necessary. The light from the light source 2 that passes through the lens does not pass through the photomask 7, and the image of the photomask passes through the projection optical system 4 and is focused on the camera 8.

The advantages of such an optical system are that it can accurately perform projection transfer with a magnification of 1:10, that focusing is easy and accurate, and that it can be used as a second factor when sequentially exposing a large number of wafers. It is easy to scan in the direction of the middle arrow, and automatic mass production is possible. Since the first reflecting mirror 9 and the second reflecting mirror 12 can be made using 2,000 mutually perpendicular surfaces of a single optical glass, their optical precision is extremely high.

FIG. 3 shows an enlarged example of a photomask used in the present invention. The photomask 4 includes a transparent glass substrate 13 having a sufficient thickness as a mechanical support plate, a pattern portion (light-shielding layer) 14 made of a chromium metal coating on its surface, and a predetermined thickness deposited thereon. Transparent glass l1i with
It consists of J15. The transparent glass substrate 13 and the pattern portion 14 of the chromium metal coating were created by a conventional method. That is, after the surface of the transparent parallel glass substrate 13 with a thickness of about 2.3 nm is sufficiently cleaned by ultrasonic waves or the like, a metal coating of chromium is deposited to a thickness of about 0.1 μm by vapor deposition or sputtering. Thereafter, the metal film is etched using a photoetching method to form a pattern necessary for the circuit element.

A feature of the photomask shown in FIG. 6 used in the present invention is the transparent glass layer 15. It is important to select the thickness of this transparent glass layer 15 to be greater than or equal to the depth of focus of the optical system 4 of the transfer device 1. In other words, the surface of the substrate 13 and the glass layer 15
0 surface is selected so that the image of dust attached to the surface of the glass layer 150 on the photosensitive film is less than the minimum width between patterns in the pattern image. In the transfer device 1 according to the embodiment of the present invention, the depth of focus of the optical system was 2560 μm.

Therefore, good results were obtained by setting the thickness of the transparent glass layer 15 to 30.0 μm. In a glass layer having a thickness smaller than the depth of focus, for example, 20.0 μm, it was observed that the shadows of the microparticles attached to the outer surface of the glass were directly projected onto the Unino photosensitive film.

FIG. 4 shows a comparison of the patterns formed on the photosensitive film of a semiconductor wafer when dust adheres to the mask surface in a photomask used in the present invention and a conventional photomask. In FIG. 4, (a) is a plan view of the photomask, showing not only the mask pattern 14 but also dust 16 attached to the mask surface. (b) and (c
1 is (a) a cross-sectional view of the mask taken along the line rV-IV in the figure, (bH! is a mask according to the present invention with a transparent transparent glass layer 15, and (C) is a conventional mask without such a layer. (b') and (C') are masks.
) shows a pattern formed on a semiconductor wafer 8 using a mask shown in FIG.

When using the mask of the present invention, (b') 16 in the figure
As shown by ', the pattern formed by the dust 16 is very small and does not short-circuit the circuit pattern 14' and has no effect on the circuit pattern function. On the contrary,
When a conventional mask is used, the pattern formed by the dust 16 is almost the same size as the dust 16, as shown by 16 in the figure (c'), and the circuit pattern 14 is short-circuited. It's gone.

The depth of focus of the projection optical system used for projection transfer is usually from several μm to several tens of μm. If the depth of focus is too small, it will not be possible to absorb the warpage or unevenness of the semiconductor substrate, so it will be necessary to move the mounting table up and down, or if you want to form a circuit pattern with steps such as multi-stage metallization on the substrate. A problem arises. The greater the depth of focus, the more stringent requirements on semiconductor wafer position, flatness, etc. can be relaxed. The thickness of the photosensitive film varies depending on the purpose, but is usually 0.6 μm.
m to several μm.

The transparent glass layer 15 of the photomask according to the present invention is desirably provided so as to be in close contact with the pattern portion 14 of the metal coating. The thickness of the transparent glass layer 15 is 150. C1μm
By selecting a value not exceeding f, it is possible to maintain good adhesion between the glass substrate 13 and the metal pattern 14.

Although the material of the layer 15 of the photomask in FIG. 3 has been described as transparent glass, it may also be 5102, and the important point is that it is translucent. Formation of @15 can be performed by sputtering of glass or SiO2, CvD, or vacuum evaporation. Further, as the material A of the layer 15, a plastic material suitable for optical use such as methyl methacrylate, cyclohex'//l/ methacrylate, styrene, allyl diglycol carbonate, etc. can also be used. The same applies to the substrate 13 of the photomask. An adhesive, glass material, or other viscous liquid may be filled between the surface of the transparent substrate on which no pattern is formed and the transparent layer. Suitable adhesives include optical adhesives such as varnum and epoxy resins.

The trick is that a transparent plate or layer having a thickness equal to or greater than the depth of focus of the optical system 4 is present on both sides of the pattern section 14, respectively.

Incidentally, the light-transmitting lie provided on the surface of the substrate is the pattern part 14.
Although it has been illustrated and described as covering the pattern portion 14, it is only necessary to cover at least the gap in the pattern portion 14, that is, the light-transmitting portion of the pattern.

The present invention) is based on a projection type transfer device.

For photomasks used in fixing type transfer devices different from this,
In order to prevent the metal pattern film from peeling off during close contact,
It is known that a thin protective glass film is damaged and adhered to a metal pattern film, but this is extremely thin at 2000A, and even if it is used in a projection type transfer device such as the present invention, Since the thickness of the protective film is smaller than the depth of focus of the optical system, the effects of the present invention cannot be obtained. It goes without saying that increasing the thickness of the protective film as seen in the contact type transfer device (τ) is inconsistent with the principle of contact type transfer, and the intended purpose cannot be achieved.

Although the above embodiment describes the case where a photomask pattern is transferred onto a semiconductor wafer', the present invention is not limited to this, and it goes without saying that it can be similarly applied to the case where a working photomask is created from a photomask original plate. . Furthermore, although the optical system has been described for a one-size projection type with a specific configuration, it is clear that the principles of the present invention can be similarly applied to other configurations or a reduced projection type such as 10:1. It is.

According to the present invention, only the desired mask pattern is focused on the photosensitive film, and the undesired particles 1 are not focused or only a negligible small image is formed. The generation of semiconductor devices can be reduced.

[Brief explanation of the drawing]

FIG. 1 is a schematic block diagram showing an entire projection type mask transfer apparatus according to an embodiment of the present invention, FIG. 2 is a configuration diagram showing an example of an optical system used in the apparatus shown in FIG. 1, and FIG. FIG. 4 is an enlarged cross-sectional view of an example of a photomask used in the present invention, and shows the formation of dust on the photosensitive film of a semiconductor wafer when dust adheres to the mask surface in the photomask used in the present invention and a conventional photomask. FIG. 3 is an explanatory diagram for comparing patterns. 2... Light source, 4... Projection optical system, 7... Mask,
8... Transfer medium (semiconductor wafer), 13... Transparent substrate (transparent galanium substrate), 14... Light shielding layer (chrome metal coating), 15... Light transmitting layer (transparent glass layer). Agent Akira Asamura Figure 1 Figure 3 Figure 4 (a) (b) (C) (C')

Claims (2)

[Claims] (1) A light source that irradiates light of a predetermined wavelength, a mask in which a transparent part is defined by a transparent layer with a predetermined pattern formed on the surface of a transparent substrate, and light that passes through the transparent part of the mask. In a projection type transfer device equipped with a projection optical system that projects an image of a predetermined pattern onto a photosensitive film on a transfer medium, a light-transmitting layer covering at least a light-transmitting part is provided on the surface of the substrate, and the light-transmitting layer and the surface of the substrate are provided. 1. A projection type transfer device characterized in that the distance from the surface of the light-transmitting layer is selected so that the image of dust attached to the surface of the light-transmitting layer on the photosensitive film is less than the minimum width between patterns in the pattern image. (2) The distance between the substrate surface and the transparent layer surface is selected to exceed a depth of focus determined by a predetermined wavelength of light and a minimum width between patterns in the pattern image. The projection type transfer device according to scope 1.