JPH0519975B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to lithography technology in semiconductor manufacturing technology, and particularly to a method for forming an X-ray mask that is a mask for X-ray lithography.

<Conventional technology> Over the past ten years, the degree of integration of ICs has increased at a rate of four times every three years. This increase in integration has been supported by the development of microtechnology, and in particular the development of photolithography technology, which has made it possible to reduce line width by 1/10 in 15 years. Currently 1.2μm
Production of the rule's 1Mb DRAM has begun,
Research publications on 4Mb DRAM based on the 0.8μm rule have been published one after another.

The mainstream of current lithography technology for LSI production is a reduction projection exposure system, a so-called (photo)stepper. Current steppers use a mercury lamp as a light source and use the emission line (g-line) of mercury atoms at 436 nm. In the future, it is expected that 365 nm i-line will be used, but the resolution limit of exposure equipment using ultraviolet light is approaching. Also, the limits of Stepsupa are
Around 0.5μm rule, 16Mb DRAM in device
It can be thought of as the degree of clustering of classes. Considering past trends in increasing density, this limit will be reached in about 10 years.
It is expected that this will change with the next generation of lithography technology.

Minimum line width 1/4 μm, as a device
X-ray lithography is considered the most promising lithography technology for mass production of 64Mb DRAM class LSIs. In particular, SOR lithography technology, which uses synchrotron radiation (SOR) as an X-ray source with high brightness and little penumbra blur, is attracting attention. In X-ray lithography, a proximity exposure system is used because there is no X-ray lens. In the proximity method, a mask pattern is projected onto a wafer at a ratio of 1:1, so very accurate patterning and alignment techniques are required. The mask consists of an X-ray absorber (heavy metal such as gold, tantalum, or tungsten) pattern that prevents the transmission of X-rays, and an X-ray transparent membrane that holds the pattern. Membrane is X
It is a film with a thickness of around 2 μm made of a light element that does not easily absorb radiation, and materials such as Si, SiNH, BNH, and polyimide are used, and masks with a diameter of about 10 cm have already been formed.

<Problems to be Solved by the Invention> Since X-ray exposure is 1:1 projection exposure, the line width of the X-ray absorber on the mask must be strictly controlled. X-ray exposure has a minimum line width of 1/4μm or less
Since it is expected to be applied to LSI, the pattern width of the absorber must be controlled with high precision of 0.025 μm or more. Also, for X-rays with a wavelength of about 10 Å
5000 to achieve a contrast ratio of 10 or more
A heavy metal pattern with a film thickness of Å or more is required. Furthermore, to prevent deformation of the mask around the pattern.
An absorber with low stress of 10 ⁹ dyn/cm ² or less is required.
The use of tungsten (W), tantalum (Ta), and the like, whose patterns can be formed through a dry process, as X-ray absorber materials is attracting attention. A sputtering vapor deposition method or a CVD method is used as a method for forming the metal film. However, the above metal films formed by sputtering vapor deposition generally have a columnar structure, and the crystal grain size is approximately 0.2 μm and the line width is large.
Stable line width control below 0.25 μm is difficult.
Furthermore, when trying to control the internal stress of a metal film using the sputtering method, it is possible to optimize the argon gas pressure during sputtering, but as shown in Figure 4, the stress changes rapidly with changes in gas pressure. It is extremely difficult to control stress with good reproducibility. Furthermore, under relatively high pressure conditions where the stress can be relatively weakened, the surface of the metal film may become rough. Furthermore, the CVD method requires a high-temperature process of 400°C or higher, and the particle size is also larger than that in the sputtering method, making it difficult to control the line width. Therefore, there is a need for a method that can form a low-stress heavy metal film that does not have a columnar structure.

The present invention was devised in view of the above points, and an object of the present invention is to provide a method for forming an X-ray mask equipped with a low-stress X-ray absorber that does not have a columnar structure.

<Means for Solving the Problems> In order to achieve the above object, the method for forming an X-ray mask of the present invention uses a patterned X-ray absorber whose main constituent element is a heavy metal that can prevent the transmission of X-rays. In the manufacturing process of the X-ray mask, which is equipped with an X-ray transmitting film that holds an a first gas containing tantalum, hydrogen, boron, carbon, nitrogen, oxygen,
It consists of a vapor phase growth method using a second gas containing silicon and phosphorus as the main constituent elements, and the above-mentioned first
At least one of the second gas and the second gas is partially excited and decomposed by gas discharge.

Further, the stress after the film formation of the heavy metal or heavy metal compound for the X-ray absorber is preferably 1×10 ⁹ dyn/cm ² or less.

Further, it is desirable that the heavy metal or heavy metal compound for the X-ray absorber be in an amorphous state or a polycrystalline state consisting of crystal grains with an average size of 300 Å or less.

<Function> The method for producing an X-ray mask of the present invention is characterized by producing a heavy metal compound using plasma-enhanced CVD (PCVD), and examples of the metal film include tungsten nitride (WNx). ), tungsten silicide (WSix), etc. The above compound does not have a columnar structure like a metal film formed by sputter deposition, and can eliminate the grain structure. Furthermore, since the film quality can be easily controlled by changing the film forming conditions, it is possible to control the internal stress of the compound film.

<Example> An example of the present invention will be described in detail below with reference to the drawings.

FIG. 2 shows a schematic structural example of a PCVD apparatus for forming a tungsten nitride film. In Fig. 2, 1 is a PF power supply unit, 2 is a substrate, 3 is a heater, 4 is a vacuum exhaust unit, 51 to 53 are mass flow meters, 6 is a tungsten hexafluoride cylinder, 7 is an ammonia cylinder, and 8 is a hydrogen cylinder. The introduced gases were tungsten hexafluoride (WF ₆ ) gas and hydrogen (H ₂ ) diluted 50% ammonia (NH ₃ ) gas.
The flow rates are controlled by mask flow controllers 51 to 53, respectively, and they are introduced into the reaction chamber from the lower electrode side. Further, a high frequency output with a frequency of 13.56 MHz is supplied from the RF power supply section 1 to the lower electrode side via a matching box to apply an electric field. A heater 3 is built into the upper electrode to which the substrate 2 is attached, and heating up to 400°C is possible. Before film formation, the reaction chamber was heated 1x using an oil diffusion pump with a liquid nitrogen trap.
The reactor was evacuated to below 10 ^-6 Torr, and a reaction gas was introduced.
The reaction gas was exhausted through a conductance valve by a mechanical booster and a rotary pump. The pressure in the reaction chamber can be controlled in the range of 0.5 Torr to 2 Torr by a conductance valve.

Next, stress control of a tungsten nitride film according to the present invention will be described. In this example, the gas ratio is _WF6 :
NH ₃ :H ₂ =5:1:1, the gas pressure was fixed at 1.0 Torr, the substrate temperature was fixed at 300°C, and the RF power was varied from 100W to 350W. The results are shown in FIG. The film formation rate in this example was about 100 Å/min. As shown in FIG. 3, the formed tungsten nitride film exhibits tensile stress when the RF power is low, but changes to compressive stress as the RF power increases. When the RF power is 200W, the internal stress of the tungsten nitride film is
It became 0.5× ¹⁰⁸ dyn/ ^cm2 . This stress is a value suitable for use as an X-ray absorber. Furthermore, when the cross section of the tungsten nitride film was observed using a scanning electron microscope (SEM), it was found that there was no columnar structure and no grains could be observed. As a result, fine patterning of 0.25 μm or less becomes possible by using the grain-free tungsten nitride film with low internal stress produced by the above method as an X-ray absorber.

Although tungsten hexafluoride and hydrogen-diluted ammonia were used in the above embodiments, the present invention is not limited thereto, and various combinations of raw material gases are possible. Further, the film forming conditions are not limited to the values of the above embodiments.

Furthermore, in the above example, all the raw material gases were introduced into the reaction chamber at once to generate a gas discharge, but only the ammonia gas was decomposed by the gas discharge, and the tungsten hexafluoride was introduced near the substrate without being directly exposed to the discharge. It is also possible to react both raw material gases on the substrate.

Next, an example of a method for manufacturing an X-ray exposure mask using the X-ray absorber will be described with reference to manufacturing process diagrams shown in FIGS. 1a to 1f.

First, silicon nitride films (Si ₃ N ₄ ) 12, 12' are deposited by LPCVD on both sides of a silicon (Si) substrate 11 that will serve as a support frame for the membrane 13 (FIG. 1a). The thickness of the Si ₃ N ₄ films 12, 12' is approximately 1000 Å.
It is. Hydrogenated silicon nitride (SiNxHy), which will become the membrane 13, is then deposited on the substrate surface by plasma CVD (FIG. 1b). This SiNxHy film 13
The film thickness is about 3μm, and the film internal stress is about 5×10 ⁸
It is the tensile stress in dyn/cm ² . Next, the process moves to the step of removing the silicon substrate 11 in the membrane portion which will become the mask area shown in FIG. 1c.

Since single crystal silicon dissolves in sodium hydroxide solution about 10,000 times faster than Si ₃ N ₄ , a portion of the Si ₃ N ₄ film 12' on the back side of the mask area is removed and only the silicon (Si) in this area is removed. Can be dissolved. The area corresponding to the back surface of the mask area of the Si ₃ N ₄ film 12' is removed by photolithography, leaving the resist only outside the mask area, and using reactive ion etching. Next, about 25%
The silicon substrate 11 is etched by heating the sodium hydroxide solution to 80°C. The etching speed is
The etching rate was approximately 1.5 μm/min, and it took approximately 6 hours to form the window portion 14 by etching the 0.5 μm thick silicon substrate 11.

Next, as shown in FIG. 1d, the tungsten nitride 15, which will serve as an X-ray absorber, is deposited on the membrane 13 by the method described above. The thickness of the tungsten nitride film 15 is approximately 6000 Å. Further, in order to pattern the tungsten nitride film 15, an electron beam resist film is applied, and a pattern is drawn and developed using an electron beam lithography device to form a resist pattern 16 with a line width of 0.25 μm (FIG. 1e). Next, using the resist pattern as a mask, the tungsten film 15 is etched by a reactive ion etching method using sulfur hexafluoride (SF ₆ ) as an etching gas. At this time, the tungsten nitride film 1
Since No. 5 has low stress and no grain structure, an X-ray absorber pattern without pattern distortion and with stable line width can be obtained. After etching, the resist film 16 is removed to complete the X-ray mask (FIG. 1f).

<Effects of the Invention> As described above, according to the present invention, it is easy to fabricate a low stress WNx film that does not have a columnar structure.
By using a WNx film as an absorber in an X-ray mask, it becomes possible to manufacture an X-ray mask with low distortion and high line width controllability. Therefore, the present invention is indispensable in the development and production of X-ray masks, has a large ripple effect on society through the practical application of X-ray lithography, and is of great industrial value.

[Brief explanation of the drawing]

FIGS. 1a to 1f are process diagrams for explaining the manufacturing process of one embodiment of the method for forming an X-ray mask of the present invention, and FIG. A schematic diagram showing the structure, Figure 3 is a diagram showing the change in stress due to RF power when a tungsten nitride film was deposited using the apparatus shown in Figure 2, and Figure 4 is a diagram showing the change in stress due to RF power when a tungsten film was deposited using the sputtering deposition method. FIG. 11... Silicon substrate serving as a frame material, 12... Silicon substrate etching mask, 13... Membrane, 14... Window portion, 15... Tungsten nitride absorber pattern.

Claims (1)

[Claims] 1. Tungsten that blocks the transmission of X-rays, or
It holds a patterned X-ray absorber whose main constituent element is tantalum, a heavy metal, and includes an X-ray transparent film made of a light element with high transmittance to X-rays, and a support frame that holds the transparent film. In the method for forming an X-ray mask, in the step of manufacturing the X-ray absorber, at least one of a first gas containing tungsten or tantalum, and a second gas containing hydrogen, nitrogen, and silicon as main constituent elements. A method for forming an X-ray mask, characterized by using a vapor phase growth method in which one of the gases is excited or decomposed by gas discharge. 2. In the manufacturing process of the X-ray absorber according to claim 1, it is required that the stress after the film formation of the heavy metal or heavy metal compound for the X-ray absorber is 1×10 ⁹ dyn/cm ³ or less. Characteristic method for forming an X-ray mask.