HK1063079A - Fused silica pellicle - Google Patents

Description

Fused silica film

Background

Photomasks, also known as masks, are used in the semiconductor industry to transfer micro-scale images defining semiconductor circuits onto silicon or gallium arsenide wafers. Generally, a photomask is formed of a transparent substrate having a patterned layer of masking material adhered thereto. The pattern of masking material is a function of the size ratio of the image desired to be formed on the semiconductor wafer.

The photomask image is transferred to a semiconductor wafer by a process commonly referred to as photolithography. More specifically, using a wafer exposure system, a photomask is inserted between a semiconductor wafer coated with a layer of photosensitive material and an optical energy source. Energy from the wafer exposure system is prevented from passing through the areas of the photomask having masking material. However, the energy generated by the wafer exposure system may pass through portions of the photomask wafer not covered by the masking material and cause reactions in the photosensitive material of the semiconductor wafer. The image produced on the photosensitive material is transferred to the semiconductor wafer by a subsequent processing procedure.

Because the mask image on the photomask is directly related to the image produced on the semiconductor wafer, any foreign matter or contamination on the photomask surface during the photolithography process will cause unwanted images belonging to these artifacts to be printed on the semiconductor wafer. To reduce or eliminate photomask surface contamination, a thin and transparent film, commonly referred to as a pellicle, is extended over an anodized aluminum frame mounted on the photomask prior to the start of the photolithography process.

FIGS. 1A and 1B show top and side views of a typical photomask designed for use in a photolithographic process. As shown, photomask 2 (typically six inches by six inches in size and one-quarter inch thick) is comprised of a transparent substrate 4 (e.g., fused silica) and a patterned layer of masking material 6 (e.g., chrome) that defines the desired image to be fabricated on a semiconductor wafer. The film frame 8 extends around the patterned masking material 6 and is adhered to the substrate 4 by vapor deposition methods well known in the art. The film 10 extends over and adheres to the upper surface of the film frame 8. As shown, the surface of the pellicle 10 is generally parallel to the surface of the photomask and covers the entire patterned area in the masking material 6. Thus, any contaminants will fall on the pellicle 10, out of the focal plane of the wafer exposure system, instead of falling on the photomask.

Films known in the art are made of organic materials such as nitrocellulose or other fluorocarbon based polymers. Film-induced inconsistencies in transmission and birefringence cause pattern fidelity errors that become more prevalent when patterning features on semiconductor wafers to a range of sizes below the wavelength, which ultimately can lead to reduced device performance or failure.

The prior art films are susceptible to scratching and tearing, and any damage to the film requires the entire film to be removed and replaced. Of course, photomasks cannot be used in semiconductor manufacturing during the removal and replacement of thin films. Also, the extensive rework procedures required to remove and replace the damaged film sometimes result in the entire photomask eventually being scrapped. In addition, as described above, pellicle film 10 is used to prevent contaminants from reaching the photomask surface and must therefore be cleaned from time to time. The film is typically cleaned using a nitrogen gun. However, due to their fragile nature, prior art films have a tendency to break or become easily damaged during cleaning procedures that require their removal and replacement. Furthermore, defects that cannot be removed with a nitrogen gun cannot be mechanically removed due to fear of scratching or tearing the film. Here, during the film homing procedure, the photomask cannot be used for semiconductor manufacturing and there is a risk that the entire photomask is scrapped.

Disclosure of Invention

It is therefore an object of the present invention to provide a pellicle for use on a photomask that overcomes the disadvantages of the prior art, wherein the pellicle has improved consistency of transmission and birefringence, thereby increasing pattern fidelity.

It is another object of the present invention to provide a film that is not easily damaged and therefore is easily cleaned.

It is another object of the present invention to provide a reusable pellicle that can be easily removed, cleaned, and remounted on a photomask.

Drawings

FIG. 1A is a cross-sectional view of a prior art photomask designed for use in a photolithographic process.

FIG. 1B is a top view of a prior art photomask designed for use in a photolithographic process.

Figure 2 is a cross-sectional view of a photomask designed in accordance with the present invention for use in a photolithographic process.

Figure 3 is a cross-sectional view of a photomask having a movable frame assembly according to the present invention.

Those skilled in the art will appreciate that fig. 1A-3 are for illustrative purposes only and are not drawn to scale.

Detailed Description

Figure 2 illustrates a photomask designed according to this invention. As shown, photomask 20 comprises a substantially transparent substrate 22 having a patterned layer of masking material 24 adhered (affix) thereto. This patterned layer of masking material 24 represents a scaled image of the pattern that is desired to be created on the semiconductor wafer. As described above, the wafer may be composed of fused silica and the masking material may be composed of chromium. Those skilled in the art will appreciate that other materials may be used to fabricate the photomask and the present invention is not limited to use with photomasks comprising fused silica substrates and chrome masking materials. In addition, those skilled in the art will appreciate that the thin films of the present invention may be used in conjunction with all types of photomasks, including, but not limited to, binary masks (described above) and Phase Shift Masks (PSM).

Referring again to fig. 2, photomask 20 also includes a film frame or ring 26 that extends around patterned masking material 24. In the preferred embodiment, the frame 26 is made of anodized aluminum, however, other materials may be used. Although shown as a continuous loop, this is not a requirement of the present invention and the frame 26 may contain various indentations or vents to ensure that the pressure is balanced at the end user. The frame 26 is adhered to the substrate 22 using an adhesive 27, which is of a type well known to those skilled in the art.

The film 28 is formed of a flat, polished, low birefringence fused silica sheet having dimensions generally corresponding to the dimensions of the frame 26. The sides or corners 30 of the fused silica film or films 28 may be beveled or rounded for safety reasons. The total thickness of fused silica film 28 may vary, the only limitation being that the total thickness of photomask holder 26, adhesive 27, and film 28 may allow the entire assembly to be mounted on a wafer exposure system. Typically, this may require the total thickness of the assembly to be less than or equal to 7 mm. Generally, the thicker the fused silica film, the more durable it is.

The fused silica film 28 may be adhered to the upper surface of the frame 26 using adhesives well known to those skilled in the art, including, for example, SAG, acrylic, and SEB. Alternatively, to enhance removability, the fused silica film may be adhered to the upper surface of the frame 26 using a reusable adhesive, examples of which are well known to those skilled in the art. Alternatively, the film 28 may be secured to the upper surface of the frame 26 by way of an electrostatic charge.

In another embodiment, the pellicle may be secured to the frame using a movable frame assembly so that the pellicle may be easily removed and cleaned. For example, as shown in the cross-sectional view of FIG. 3, a frame 42 made of anodized aluminum is adhered to the substrate 22 by an adhesive, wherein applicable adhesives are well known to those skilled in the art. Those skilled in the art will appreciate that the frame 42 may be made of a material other than anodized aluminum. In a preferred embodiment, the frame 42 extends around the entire patterned masking material, however, the frame 42 need not be continuous and may include one or more notches. The frame 42 includes a first receiving area 44 that forms a shelf parallel to the surface of the substrate 22 to receive the lower surface of the outer edge of the film 28. The frame 42 also includes a second receiving area or detent 46 that can receive a lower projection 52 of a flexible positioning ring 50, wherein the positioning ring can be made of a variety of materials, including plastic and teflon. The upper ledge 54 of the retaining ring 50 extends beyond the first receiving area 44 of the frame 42 and beyond the upper surface of the outer edge of the membrane 28, thereby securely retaining the membrane 28 therein. Thus, in the present embodiment, there is no need to use an adhesive to adhere the film to the frame. To assist in the installation and removal of the flexible positioning ring 50, the corners of the positioning ring 50 may include flexible protrusions (tabs) 56. When an upward force is applied to the flexible projections 56, the lower projections 52 disengage from the second receiving areas 46 of the frame 42. With the lower projection 52 disengaged from the frame 42, the retaining ring 50 can be removed, thereby also removing the membrane 28.

In this embodiment, no vents are required in the frame 42 because pressure can be relieved through the gaps between the frame 42, the membrane 28 and the retaining ring 50. Moreover, because no adhesive is used to secure the membrane to the frame, the membrane may be easily removed, cleaned, and/or replaced.

Various additional modifications and improvements will readily occur to those skilled in the art. For example, films made from F-doped fused silica for 157nm applications, or Si for EPL and NGL applications₃N₄The prepared material is characterized by being prepared into a finished product,

rather than fused silica. Therefore, the spirit and scope of the present invention should be construed broadly and limited only by the appended claims and not by the foregoing patent specification.

Claims (36)

1. A premask for semiconductor fabrication, the photomask comprising:

(a) a substantially transparent substrate having a first surface and a second surface,

(b) a patterned region of masking material adhered to the substrate,

(c) a frame adhered to the substrate, a patterned region substantially surrounding all of the masking material, and

(d) a silicon dioxide film adhered to the frame.

2. The photomask of claim 1, wherein the film is a fused silica film.

3. The photomask of claim 1, wherein the thin film is made of F-doped fused silica.

4. The photomask of claim 1, wherein the thin film is formed from Si₃N₄And (4) preparing.

5. The photomask of claim 1, wherein the silicon dioxide film is adhered to the frame with an adhesive.

6. The photomask of claim 1, wherein the silicon dioxide film is adhered to the frame with a reusable adhesive.

7. A photomask for printing an image on a semiconductor wafer, the photomask comprising:

(a) a substantially transparent substrate having a first surface and a second surface,

(b) a patterned region of masking material adhered to the substrate,

(c) a frame having an upper surface and a lower surface, substantially surrounding all of the patterned region of masking material, the lower surface being adhered to the substrate and the upper surface of the frame extending above the patterned region of masking material, and

(d) a silicon dioxide film secured to the upper surface of the frame.

8. The photomask of claim 7, wherein the film is a fused silica film.

9. The photomask of claim 7, wherein the thin film is made of F-doped fused silica.

10. The photomask of claim 7, whereinThe film is made of Si₃N₄And (4) preparing.

11. The photomask of claim 7, wherein the silicon dioxide film is secured to the frame with an adhesive.

12. The photomask of claim 7, wherein the silicon dioxide film is secured to the frame with a reusable adhesive.

13. The photomask of claim 7, wherein the silicon dioxide film is secured to the frame using an electrostatic charge.

14. The photomask of claim 7, wherein the silicon dioxide film is secured to the frame with a flexible retaining ring.

15. The photomask of claim 7, wherein the flexible retaining ring comprises a first protrusion for attaching the flexible retaining ring to the first receiving area of the frame and a second protrusion extending beyond an outer edge of the membrane.

16. The photomask of claim 15, wherein the flexible retaining ring comprises at least one flexible projection.

17. A photomask for producing an image on a semiconductor wafer, the photomask comprising:

(a) a substantially transparent substrate having a first surface and a second surface,

(b) a patterned region of masking material adhered to the substrate,

(c) a frame adhered to the substrate, surrounding substantially all of the patterned region of masking material,

(d) a fused silica film, and

(e) means for securing the fused silica membrane to the frame.

18. The photomask of claim 17, wherein the film is a fused silica film.

19. The photomask of claim 17, wherein the thin film is made of F-doped fused silica.

20. The photomask of claim 17, wherein the thin film is formed from Si₃N₄And (4) preparing.

22. The photomask of claim 17, wherein the silicon dioxide film is secured to the frame with an adhesive.

23. The photomask of claim 17, wherein the silicon dioxide film is secured to the frame with a reusable adhesive.

24. The photomask of claim 17, wherein the silicon dioxide film is secured to the frame using an electrostatic charge.

25. The photomask of claim 17, wherein the fused silica pellicle is secured to the frame with a flexible retaining ring.

26. The photomask of claim 25, wherein the flexible retaining ring comprises a first projection for attaching the flexible retaining ring to the first receiving area of the frame and a second projection extending beyond an outer edge of the membrane.

27. The photomask of claim 26, wherein the flexible retaining ring comprises at least one flexible projection.

28. A photomask for semiconductor manufacturing, the photomask comprising:

a) a substantially planar substrate having an upper surface and a lower surface,

b) a patterned region of masking material adhered to the upper surface of the substrate, the masking material having a maximum height h above the substrate₁，

c) A frame adhered to the upper surface of the substrate and surrounding substantially all of the patterned region of masking material,

d) a silicon dioxide film having an upper surface and a lower surface fixed to the frame and a patterned region covering substantially all of the masking material, wherein the frame comprises a height h substantially parallel to the upper surface of the substrate₂To receive a lower surface of an outer edge of the film, wherein a height h of the receiving area₂Greater than the height h of the masking material₁And are and

e) means for securing the membrane to the frame.

29. The photomask of claim 28, wherein the silicon dioxide film is secured to the receiving area of the frame with an adhesive.

30. The photomask of claim 28, wherein the silicon dioxide film is secured to the receiving area of the frame with a reusable adhesive.

31. The photomask of claim 28, wherein the silicon dioxide film is secured to the receiving area of the frame using an electrostatic charge.

32. The photomask of claim 28, wherein the silicon dioxide film is secured to the receiving area of the frame with a flexible retaining ring.

33. The photomask of claim 32, wherein the flexible retaining ring comprises a first projection for coupling with a detent in the frame and a second projection extending beyond the outer upper surface of the pellicle.

34. The photomask of claim 33, wherein the flexible retaining ring comprises at least one flexible projection.

35. The photomask of claim 28, wherein the film is a fused silica film.

36. The photomask of claim 28, wherein the thin film is made of F-doped fused silica.

37. The photomask of claim 28, wherein said thin film is formed from Si₃N₄And (4) preparing.