JPS641926B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an X-ray exposure mask used in an X-ray exposure method for transferring a fine pattern.

The X-ray exposure method is most effective when
This is in the process of transferring extremely fine patterns having a line width of around 1 μm or less. The X-ray exposure mask has high contrast against soft X-rays, low coefficient of thermal expansion, transparency against visible light, high flatness, high pitch accuracy, chemical resistance,
The following conditions are required.

Conventionally, as a practical X-ray exposure mask that generally satisfies the above conditions, a composite transparent film with a three-layer structure in which an SiO ₂ film is sandwiched between Si ₃ N ₄ films is supported by reinforcing support beams made of Si single crystals. A structure (hereinafter simply referred to as a three-layer structure) in which the composite transparent film is used as a support layer for a transferred pattern is known. However, this is not limited to the three-layer X-ray exposure mask mentioned above, but in general, for example, those with a B-doped Si P ⁺ diffusion layer as a pattern support layer, or those with a two-layer structure of Si ₃ N ₄ and SiO ₂ , etc. An X-ray exposure mask has a structure in which a patterned support layer with strong tensile stress is integrally laminated and fixed on the entire surface of a reinforcing support beam made of Si single crystal using a layered growth technique that does not use adhesives. There is a drawback that the entire transfer mask is warped due to the tension. This warpage has an adverse effect, such as increasing the amount of geometric positional deviation of the pattern to be transferred. Furthermore, when overlapping exposure is performed using multiple X-ray exposure masks, if the warpage of each X-ray exposure mask substrate is equal to each other, the positional deviation between the patterns transferred with each mask can be ignored. However, in reality, they usually warp in different ways, and misalignment between the patterns has a serious effect.

As a specific example of X-ray exposure conditions, consider a case where the distance between the X-ray source and the X-ray exposure mask is 300 mm, and the distance between the outermost pattern to be transferred to the wafer and the center of the wafer is 300 mm. The geometric positional deviation amount Δ of the pattern is Δ=d/10, where the distance between the X-ray exposure mask and the wafer is dμm. Therefore, in order to suppress the amount of positional deviation between transferred patterns to the minimum required ±0.1 μm or less for overlapping exposure of fine patterns with a minimum line width of 1 μm, the distance between the X-ray exposure mask and the wafer must be at least d. ±1μm
It must be realized with an accuracy of
It is necessary to suppress the warpage or local distortion of the line exposure mask substrate to ±1 μm or less even if the warpage of the wafer is ignored.

However, in the conventional X-ray exposure mask, Si
Since a transfer pattern support layer having a tensile stress of approximately 1×10 ⁹ dynes/cm ³ is formed on the entire surface of the reinforcing support beam made of a single crystal substrate, no matter how many cross-sections are taken, the The supporting layer side is warped so that it becomes a concave surface, for example, a diameter of 50 mm.
In the case of a transfer mask, the total thickness is approximately 20μm to 30μm.
This caused a warpage of m, and even if vacuum adsorption was performed on a mask holder with good flatness, it would be difficult to obtain the desired flatness.

On the other hand, X-ray exposure masks that use a thin film made of an organic material such as polyethylene terephthalate, polyimide, or Kapton as a transfer pattern support layer can achieve higher flatness than those with the conventional structure, but they all have moisture absorption and Due to large dimensional variations due to changes in ambient temperature, it is extremely difficult to achieve alignment accuracy of approximately ±0.1 μm.

The purpose of the present invention is to enable highly accurate alignment using visible light, have excellent flatness, and have small pattern deviations.
X has a coefficient of thermal expansion as low as that of Si and can realize high chip density, which eliminates various difficulties that the conventional technology could not solve, and which is easy to manufacture.
The purpose of the present invention is to provide a line exposure mask.

The X-ray exposure mask of the present invention is formed by integrally laminating and fixing a thin layer having tensile stress on the surface of a silicon single crystal substrate, and using this thin layer as a transfer pattern support layer, An X-ray exposure mask having a structure in which the single crystal substrate is removed and the removed area is used as a transfer pattern area, and the silicon single crystal substrate in the area left without being removed is used as a reinforcing support beam for the transfer pattern support layer, The present invention is characterized in that only a portion of the transfer pattern support layer that should exist on the reinforcing support beam near the inner periphery of the support beam remains.

The transfer pattern support layer on the reinforcing support beam attracts the reinforcing support beam and promotes warping of the mask. Therefore, by removing the transferred pattern support layer other than the minimum fixed area necessary for spreading to the reinforcing support beam, the warpage of the entire mask can be significantly reduced.
Moreover, this area is quite wide, and most of the area in and around the reinforcing support beam corresponds to the frame of the window frame. Therefore, it is only necessary to remove a sufficient area to achieve the object of the present invention, and it is not necessarily necessary to remove the entire area.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained below by specifically explaining an example of its embodiment with reference to the drawings.

Each of the figures from FIG. 1 to FIG. 6 is a schematic sectional view conceptually showing the structure of a part of an X-ray exposure mask according to an embodiment of the present invention in each manufacturing process.

First, as shown in FIG. 1, a thermal oxidation method is applied to the surface of a single Si substrate 1 having a thickness of several hundred μm to 1 mm and having a mirror-finished {100} surface on at least one surface. Thickness from several thousand Å to 1 μm
SiO ₂ films 2 and 2' are formed, and a Si ₃ N ₄ film 3 having a thickness of 1000 Å to several thousand Å is formed on the surface of one of the SiO ₂ films by CVD. This surface does not necessarily have to be a mirror surface.

Next, a resist pattern formed by patterning using a normal optical exposure method etc. is used as a protective film.
A part of the Si ₃ N ₄ film 3 is etched away by plasma etching or the like to form 3', and then all of the SiO ₂ film 2' and 2' are removed by chemical etching using buffered hydrofluoric acid or the like. After forming an opening 4 for later etching away a portion of the Si single crystal substrate, the resist pattern is removed to obtain the state shown in FIG. 2.

Thereafter, as shown in FIG. 3, a Si ₃ N ₄ film 5 with a thickness of several thousand angstroms is deposited on the mirror surface of the Si single crystal substrate 1, which has been exposed by removing the SiO ₂ film 2'. The SiO ₂ film 6 with a thickness of Å to 1.5 μm and the Si ₃ N ₄ film 7 with a thickness of several thousand Å are formed by, for example, CVD method,
Formed sequentially using RF sputtering method and CVD method.

Next, as shown in FIG. 4, a resist film 8 is formed on the surface of the Si ₃ N ₄ film 7 by, for example, a normal optical exposure method so as to correspond to the area of the opening 4 formed previously. . In this case, the alignment between the window 4 and the resist film 8 is such that both the exposure mask used to form the opening 4 and the exposure mask used to form the resist film 8 are placed on the Si single crystal substrate. This is conveniently carried out by means of marks provided in such a way as to be able to be aligned with two facets indicating the <110> direction provided in advance in 1.

Next, after covering the other surface of the Si single crystal substrate 1 with a resist film 9, the Si ₃ N ₄ film 7 is etched using a plasma etching method or the like using the resist film 8 as a protective film.
A part of the SiO 2 film 6 is etched away to form 7', and then a part of the SiO ₂ film 6 is etched away using buffered hydrofluoric acid to form 6', and then the Si A portion of _{the 3N4 film} 5 is removed to form 5', and the unnecessary resist is peeled off to form the state shown in FIG.

Next, as shown in FIG. 6, a desired transfer pattern 10 is formed on the surface of the Si ₃ N ₄ film 7' using Au, Pt, etc. with a thickness of several thousand Å by a selective plating method, a lift-off method, or the like. do. Finally, while protecting the heavy metal pattern with an arbitrary jig using an O-ring or the like, a predetermined area of the Si single crystal substrate 1 is etched using an anisotropic etchant such as a KOH aqueous solution through the opening 4. The transfer pattern area 11 as shown in FIG. 6 is formed by etching and removing the desired X.
The line exposure mask is completed.

In the structure shown in FIG. 6, the Si ₃ N ₄ film 5',
The transfer pattern support layer, which is composed of a composite film of the SiO ₂ film 6' and the Si ₃ N ₄ film 7', is tensed due to its own tensile stress, so it prevents warping not only in the transfer pattern area but also in the entire mask. Since this occurs hardly, it is possible to obtain an X-ray exposure mask with extremely good flatness.

In the example shown in FIG. 6, as can be seen from the fact that only the central portion is taken out and shown, the transfer pattern support layer is removed from almost all of the reinforcing support beams, so that the transfer pattern can be placed most reliably. period effect is achieved. However, even if the reinforcing support beam, which is located in the center of the mask and corresponds to the window frame shown in the figure, is not forcibly removed, the warping can be sufficiently minimized by removing the surrounding window frame. There are cases where it is possible. Furthermore, although it is convenient to remove the entire periphery of the window frame in an annular manner, it may be sufficient to remove the entire periphery in some cases.

FIGS. 7 and 8 are a plan view and a sectional view, respectively, conceptually showing the outline of a second embodiment of the present invention. In the figure, 12 is a Si single crystal substrate with {100} plane as the surface, 13 is a facet showing <110> orientation, and 14 is Si ₃ N ₄ film sandwiching SiO ₂ 3.
Transfer pattern support layer consisting of a composite film with a layered structure, 1
5 is a transfer pattern composed of heavy metals, 17 is a
Transfer pattern area formed by removing a part of the Si single crystal substrate with an anisotropic etching solution using a protective film 16 formed of a Si ₃ N ₄ film or a composite film of an Si ₃ N ₄ film and a SiO ₂ film. It is. This example is obtained by a manufacturing process completely similar to that of the first example. The feature of this embodiment is that reinforcement support is provided at a portion corresponding to the frame of the lattice-shaped window formed of Si single crystal, which was provided to reinforce and support the transferred pattern support layer in the first embodiment. The beams are removed, and the transferred pattern support layer is supported only by reinforcing support beams at the portion corresponding to the frame of the window frame made of Si single crystal at the outermost periphery of the X-ray exposure mask. The main cause of warpage in conventional X-ray exposure masks using Si substrates is stress at the interface between the transfer pattern support layer, which has tensile stress, and the Si substrate that supports it. In this embodiment, the interface between the transfer pattern support layer and the Si single crystal substrate is further reduced than in the first embodiment, and as a result, the flatness is further improved.

9 and 10 respectively show the third embodiment of the present invention.
FIG. 2 is a plan view and a cross-sectional view conceptually showing an outline of an embodiment of the present invention. In the figure, 18 is a reinforcing support beam made of Si single crystal, and 19 is a Si ₃ N ₄ film made of SiO ₂
A transfer pattern support layer consisting of a three-layer composite film sandwiching the film, 20 a transfer pattern made of heavy metal, 22 a Si ₃ N ₄ film or a composite film of an Si ₃ N ₄ film and a SiO ₂ film. This is a transfer pattern area formed by removing a part of the Si single crystal substrate using an anisotropic etchant using a protective film 21. In this embodiment, the outer periphery of the Si single crystal substrate 12 was left in the wafer shape in the second embodiment, but this was shaped.
It is shaped like a rectangular window frame consisting of eight sides parallel to the <110> direction, and can further improve the flatness of the X-ray exposure mask of the second embodiment.

In the second and third embodiments of the present invention, since the lattice-shaped beams that reinforce and support the transfer pattern support layer are removed, it is possible to form a desired transfer pattern with high density. What you can do is also one of the big effects. In addition, in the actual MOS semiconductor device process, the wafer also undergoes various heat treatment steps, thin film formation steps, etc., resulting in large warpage, and this warpage varies in each process, so generally This is a serious problem in the X-ray exposure process, which requires strict control of the distance between the X-ray exposure mask and the wafer.・According to the and-repeat method, it is possible to adjust the spacing and alignment between the wafer and the X-ray mask for each small exposure area. Even if there is warpage, it can be controlled with high precision, so the alignment accuracy and processing accuracy of the transferred pattern can be maintained at an extremely high level. In the step-and-repeat method described above, the number of exposures per wafer increases, but since the distance between the X-ray source and the X-ray exposure mask can be brought closer, the exposure time per small area can be shortened. As a result, the exposure time per wafer does not increase significantly. As X-ray exposure masks used in the step-and-repeat method having these advantages, those shown in the second and third embodiments of the present invention show extremely good results.

The above explanation has been made using a three-layer structure that achieves the best results in terms of other strongly required properties in addition to warpage ^.
A composite film consisting of either a B-doped p ⁺ layer or a Si ₃ N ₄ layer and a thin film of a polymeric material such as polyimide or Kapton, or even a Si ₃ N ₄ layer and a SiO ₂ layer. It is widely applicable and sufficient for X-ray exposure masks of the type formed by integrally laminating and fixing a thin layer having tensile stress on the surface of a silicon single crystal substrate, such as a two-layer film, etc., as a transfer pattern support layer. It has a great effect.

[Brief explanation of drawings]

6 from FIG. 1 to FIG. 6 are X according to the present invention.
This is a schematic cross-section showing the manufacturing process of the first example of the line exposure mask, with the center portion thereof being taken out and shown. FIG. 6, which is used to explain the final process, shows a schematic cross-sectional view of an embodiment of the X-ray exposure mask according to the present invention in a completed state. FIG. 7 and FIG. 8 respectively show the second embodiment of the present invention.
FIG. 2 is a plan view and a sectional view conceptually showing an outline of an embodiment of the present invention. Further, FIGS. 9 and 10 are a plan view and a sectional view, respectively, conceptually showing the outline of a third embodiment of the present invention. In the figure, each symbol indicates the following. 1...Silicon single crystal substrate, 1'...Reinforcement support beam corresponding to a window frame, 2...SiO ₂ film, 2'...
SiO ₂ film, 3... Si ₃ N ₄ film, 2''... Etching protective film composed of a part of SiO ₂ film 2, 3'... Si ₃ N ₄
An etching protection film formed from a part of film 3, 4...
An opening 5 in which a portion of the Si ₃ N ₄ film 3 and the SiO ₂ film 2 are removed to expose a portion of the surface of the silicon single crystal substrate 1;
...Si ₃ N ₄ film, 6... SiO ₂ film, 7... Si ₃ N ₄ film,
5'...Transfer pattern support layer composed of a part of the Si ₃ N ₄ film 5, 6'...Transfer pattern support layer composed of a part of the SiO ₂ film 6, 7'...Si ₃ N ₄ film 7 A transfer pattern support layer composed of a part of 8...resist film, 9...resist film, 10...transfer pattern composed of a metal thin film, 11...a part of the silicon single crystal substrate 1 is removed. The formed transfer pattern area, 12...Silicon single crystal substrate, 13...Facet, 14...3-layer structure transfer pattern support layer in which the SiO ₂ film is narrowed by the Si ₃ N ₄ film, 15... formed of heavy metal. transfer pattern, 16... Si ₃ N ₄ film or
Etching protection film formed of a composite film of Si ₃ N ₄ film and SiO ₂ film, 17... Transfer pattern area formed by etching away a part of silicon single crystal substrate, 18...
... Reinforcement support beam corresponding to a window frame made of silicon single crystal, 19 ... Transfer pattern support layer with a three-layer structure in which the SiO ₂ film is narrowed by a Si ₃ N ₄ film, 20 ... Transfer pattern formed of heavy metal, 21... Etching protective film,
22...Transfer pattern area formed by removing a portion of the silicon single crystal substrate.

Claims (1)

[Claims] 1. A thin layer of silicon, a compound thereof, or a polymer material having tensile stress is integrally formed on the surface of a silicon single crystal substrate so as to be laminated and fixed, and this thin layer is used as a transfer pattern support layer, and the In an X-ray exposure mask having a structure in which the silicon single crystal substrate is removed and the removed area is used as a transfer pattern area, and the silicon single crystal substrate in the area left without being removed is used as a reinforcing support beam for the transfer pattern support layer. . An X-ray exposure mask characterized in that only a portion of the transfer pattern support layer that should exist on the reinforcing support beam near the inner periphery of the support beam is left.