JPS63252428A - Formation of x-ray mask - Google Patents

Abstract

PURPOSE:To solve the problem of a granular structure without having a columnar structure like a metallic film which is formed with a spatter vaporization technique by preparing heavy metal compounds with a plasma excitation CVD technique. CONSTITUTION:A substrate 2 is attached to a heater 3 and various gases are introduced from a lower electrode side to a reaction chamber, while the amount of outflowing gases which are supplied by gas cylinders 6-8 is being controlled by mask flow controllers 51-53. Further, the high frequency output having frequencies 13.56 MHz is supplied from a RF power source part 1 to a lower electrode and its electric field is impressed. Then, an X-rays absorber is held on the substrate 2, while its absorber is mainly composed of heavy metals which prevent transmission of the X-rays and is also patterned. This feature makes it possible to prepare an X-rays mask equipped with an X-rays transmission film having transmissivity to the X-rays as well as a housing to support its transmission film. Gases which are principally composed of hydrogen, boron, carbon, nitrogen, oxygen, silicon, and phosphorus and a gas containing tungsten or tantalum are used.

Description

[Detailed Description of the Invention] <Industrial Application Field> The present invention relates to lithography technology in semiconductor manufacturing technology;
In particular, the present invention relates to a method of forming an X-ray mask, which is a mask for X-ray phosphorography.

<Conventional technology> Over the past ten years, the degree of integration of ICs has been increasing at a rate of four times every three years. This increase in the degree of integration has been supported by the development of fine technology, and in particular the development of photolithography technology, which has made it possible to reduce the line width by 1/10 in 15 years. IMb DR with current 1.2μm rule
Production of AM has started, and 4 according to the 0.8 μm rule
Research presentations on Mb DRAM are being published one after another.

The mainstream of current lithography technology for LSI production is a reduction projection exposure apparatus, a so-called (photo)stepper. Current steppers use a 436 nm emission line (two lines) of mercury atoms using a mercury lamp as a light source. In the future, 365
Although it is expected that nm i-line will be used, the resolution limit of exposure equipment using ultraviolet light is approaching soon. Also,
The limit of the stepper is around the 0.5 μm rule, and the device is considered to have a degree of integration of 16 Mb DRAM class. Considering past trends in increasing integration density, it is expected that this limit will be reached in about 10 years and replaced by next-generation lithography technology.

Minimum line width 1/4μm, 64Mb DRA as a device
The X-ray phosphorography technology is considered to be the most promising lithography technology for mass production of M-class LSIs.

In particular, SOR lithography technology that uses synchrotron radiation (SOR) as an X-ray source, which has high brightness and little penumbra blur, is attracting attention. In X-ray lithography, a proximity type exposure apparatus is used because there is no X-ray lens. In the proximity method, since the mask pattern is projected onto the wafer at a ratio of 1:1, extremely 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. The membrane is a film with a thickness of around 2 μm made of light elements that do not easily absorb X-rays, and the materials include St, 5iNH, BNH,
Polyimide etc. are being used, and the diameter is already 10crI.
A mask of about t is formed.

<Problems to be Solved by the Invention> Since X-ray exposure is 1:1 projection exposure, it is necessary to strictly control the line width of the X-ray absorber on the mask.

X-ray exposure is performed on ultra-LSI devices with a minimum line width of 1/4 μm or less.
Since it is expected that the absorber pattern width will be applied to the absorber, the pattern width of the absorber needs to be controlled with high precision of 0.025 μm or more. Furthermore, in order to achieve a contrast ratio of 10 or more for X-rays with a wavelength of about 10A, a heavy metal pattern with a film thickness of 5000A or more is required. Furthermore, in order to prevent deformation of the mask around the pattern, an absorber with a low stress of 10 dyn/cn or less is required. Tungsten (W) can be patterned using a dry process as an X-ray absorber material
, mental (Ta), etc. are attracting attention. The above-mentioned metal film can be formed by sputtering deposition method or CVD method.
law is used. However, the metal film formed by sputtering vapor deposition generally has a columnar structure, and the crystal grain size is approximately 0.2 μm, and the line width is 0.25 μm.
It is difficult to stably control the line width below. Furthermore, when trying to control the internal stress of a metal film using a 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 grain 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, and oxygen.

It is a vapor phase growth method using a second gas containing silicon and phosphorus as the main constituent elements, and at least one of the first and second gases is partially excited and decomposed into two by gas discharge. It is configured as follows.

Further, the stress after the film formation of the heavy metal or heavy metal compound for the X-ray absorber is preferably I x 10 dyn/i or less.

In addition, the heavy metal or heavy metal compound for the X-ray absorber is in an amorphous state or the average size of crystal grains is 300 mm.
It is desirable that it be in a polycrystalline state consisting of crystal grains of A or less.

Function> The method for producing an X-ray mask of the present invention is a plasma-excited CVD method.
It is characterized by producing a heavy metal compound using a method (P CVD), and examples of the above metal film include:
Tungsten nitride (WNx).

Examples include tungsten silicide (WSix). The above compound does not have a columnar structure like a metal film formed by sputter deposition, and can eliminate 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 are tungsten hexafluoride (WF6) gas and hydrogen (Hz) diluted 50% ammonia (NH3) gas, and mask flow controllers 51 to 53 are used, respectively.
The flow rate is controlled by , and it is 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 the matching box to apply an electric field. The upper electrode to which the substrate 2 is attached has a built-in heater 3, which can heat up to 400°C. Before film formation, the reaction chamber was evacuated to below 1 x 1 O-6 Torr using an oil diffusion pump equipped with a liquid nitrogen trap.
Reactant gas was introduced. The reaction gas was exhausted through a conductance pulp by a mechanical booster and a rotary pump.

The pressure in the reaction chamber can be controlled by a conductance pulp in the range of 0.5 Torr to 2 Torr.

Next, stress control of a tungsten nitride film according to the present invention will be described. In this example, the gas ratio is WF6:NH3:H2
= 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 increased from 100W to 3
The power was varied up to 50W. The results are shown in FIG. The film formation rate in this example was about 10 OA/min.

As shown in FIG. 3, the formed tungsten nitride film has R
When the RF power is low, it shows tensile stress, but as the RF power increases, it changes to compressive stress.

When the RF power was 200 W, the internal stress of the tungsten nitride film was 0.5×10 dynA. This stress is a value suitable for use as an X-ray absorber.

In addition, the cross section of the tungsten nitride film was examined using a scanning electron microscope (S
As a result of observation using EM), 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 is shown in FIGS. 1(a) to (g). This will be explained according to the process diagram.

First, a silicon nitride film (S i
3N< )12, 12' is deposited (Fig. 1(a))
. The film thickness of this 5t3N4 film 12.12' is about tooX
It is. Next, hydrogenated silicon nitride (S i NxHy ), which will become the membrane 13, is deposited on the substrate surface by plasma CVD (FIG. 1(b)).
The thickness of the film 13 is approximately 3 pm, and the internal stress of the film is approximately 5×1.
The tensile stress is 0 dyn/i. Next, Figure 1 (c
) The process moves on to the step of removing the silicon substrate 11 in the membrane portion which becomes the mask area.

Single-crystal silicon dissolves approximately 10,000 times faster in sodium hydroxide solution than Si3N, so S
A part of the i3N4 film 12' can be removed and only the silicon (Si) in this part can be dissolved. Si3N,
The region of the film 12' corresponding to the back surface of the mask region is removed by photolithography, leaving the resist only outside the mask region, and using reactive ion etching. Next, approximately 6 hours were required to form the window portion 14 by heating the approximately 25% sodium hydroxide solution to 80° C. and etching the silicon.

Next, as shown in FIG. 1(d), the tungsten nitride 15, which will become 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 6
000! It is. Further, an electron beam resist film is applied to pattern the tungsten nitride film 15, and a pattern is drawn and developed using an electron beam lithography device, with a line width of 0.2.
A resist pattern 16 with a 5 μm rule is formed (first
Figure (f)) Next, using the resist pattern as a mask, the tungsten film 15 is etched with sulfur hexafluoride (
Etching is performed using a reactive ion etching method using SF6). At this time, since the tungsten nitride film 15 has low stress and has 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 (first
Figure (b))).

<Effects of the Invention> As described above, according to the present invention, it is easy to produce a low stress WNx film that does not have a columnar structure, and by using this WNx film as an absorber of an X-ray mask, it is possible to achieve low distortion and line width control. This makes it possible to manufacture highly functional X-ray masks. Therefore, the present invention is indispensable in the development and production of X-ray masks, and
The practical application of line lithography has a large ripple effect on society and is of great industrial value.

[Brief explanation of the drawing]

FIGS. 1(a) to (g) 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. 2 is a diagram showing the plasma used in carrying out the present invention. A schematic diagram showing the structure of the excitation CVD equipment. Figure 3 is a diagram showing the change in stress for RF power when a tungsten nitride film is formed by the equipment shown in Figure 2. Figure 4 is a diagram showing the change in stress for RF power when a tungsten nitride film is formed using the equipment shown in Figure 2. FIG. 3 is a diagram showing changes in stress due to pressure when a film is formed. 11... Silicon substrate serving as frame material, 12... Silicon substrate etching gask, 13... Membrane, 14
...Window part, 15...Tungsten nitride absorber/cutan. Agent Patent Attorney Takeshi Sugiyama (and 1 other person) Figure 1 Drawing of Joko No. 1 Figure 82 Figure 100 200 300 4
00 ty) RFII "Ku'1.3 Figure""
”'(x/(7'7?zrr)1force*4 figure Procedural amendment (method) May 1988, Yuφ day 2, Title of invention: Method of forming an X-ray mask 3, Person making amendment and case Relationship Patent applicant address 1122-2 Nagaike, Abeno-ku, Osaka 8545
25 ;- Name (504) Sharp Corporation Representative Haruo Tsuji 4, Agent April 26, 1988 6, Subject of amendment 7, Contents of amendment (1) “On page 10, line 13 of the specification” Figure 1(a)-(g
)” has been corrected to “Figure 1 (mu) to (f).” (2) The description of "Figure 1 (f)" on page 12, line 6 of the specification will be corrected to "Figure 1 (e)." (3) The description of "Figure 1 (g)" on page 12, line 14 of the specification will be corrected to "Figure 1 (f)." (41aA specification, page 3, line 5 IN diagram (a) to sulfur)
” has been corrected to “Figure 1 (a) to (f).” (5) In the figures, "Figure 1 (f)" and "Figure 1 (g)" are replaced with "Figure 1 (e)" and "Figure 1 (
f)”. that's all

Claims (1)

[Claims] 1. An X-ray transmitting film that holds a patterned X-ray absorber whose main constituent element is a heavy metal that can prevent the transmission of X-rays and has a high transmittance to X-rays; In the process of manufacturing an X-ray mask equipped with a support frame that holds a membrane, the process of manufacturing the X-ray absorber comprises using a first gas containing tungsten or tantalum, and hydrogen, boron, carbon, nitrogen, oxygen, or silicon. , a vapor phase growth method using a second gas containing phosphorus as a main constituent element, and at least one of the first and second gases is partially excited and decomposed by gas discharge. A method for forming an X-ray mask, characterized in that: 2. Formation of the X-ray mask according to claim 1, characterized in 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^2 or less Method. 3. Claim 1, wherein the heavy metal or heavy metal compound for the X-ray absorber is in an amorphous state or a polycrystalline state consisting of crystal grains with an average size of 300 Å or less. A method for forming an X-ray mask as described in .