JPH0817711A - Designing method of antireflection film - Google Patents

Abstract

PURPOSE:To restrain a halation and a staging-wave effect on materials layers by a method wherein change regions of the optical constant and the film thickness of an antireflection film which can suppress the standing-wave effect to a prescribed amount or lower are found regarding the respective material layers and the optical constant and the film thickness which are contained in common regions in the respective change regions are selected. CONSTITUTION:Change regions of optical constants [(n), (k)] and the film thickness (d) of an antireflection film which can suppress a standing-wave effect to a prescribed amount or lower are found regarding respective material layers. Then, the optical constants [(n), (k)] and the film thickness (d) which are contained in common regions of the respective change regions are selected so as to be optimized. As a means for optimization, the standing-wave effect is computed by a simulation. Then, the change regions which are converged to the prescribed amount or lower are narrowed down.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of designing an antireflection film used for improving the resolution of photolithography performed in a semiconductor device manufacturing process, and more particularly to a substrate having a plurality of material layers having different optical constants. A method of achieving good resolution on any material layer when coexisting on top.

[0002]

2. Description of the Related Art As the degree of integration of semiconductor devices progresses at an accelerating rate, the minimum processing size thereof is rapidly reduced. For example, one of the current generation that has been moved to a mass production line
The minimum processing size of 6MDRAM is about 0.5 μm,
The next-generation 64M DRAM is expected to be reduced to 0.35 μm or less, and the next-generation 256M DRAM is expected to be reduced to 0.25 μm or less.

This degree of miniaturization largely depends on the resolution of a photolithography process for forming a mask pattern. In the processing of 0.35 μm to 0.25 μm (deep submicron) class, a far-ultraviolet light source such as KrF excimer laser light (wavelength 248 nm) is required. However, in processes using monochromatic light such as excimer laser light, the contrast and resolution are significantly reduced due to halation and standing wave effects.

Halation is a phenomenon in which the light intensity of a specific region is increased by the reflected light from the stepped portion of the underlying material film, and the actual damage is the occurrence of constriction in the positive photoresist pattern. On the other hand, the standing wave effect is a phenomenon in which a light intensity distribution is generated in the film thickness direction of the photoresist film due to multiple reflection occurring in the photoresist film or between the underlayer film. Wavy deformation and variation in resist sensitivity in the substrate.

In order to reduce the halation and the standing wave effect, the reflected light from the underlying material film may be weakened. Therefore, it is expected that it will be essential to provide an antireflection film between the material layer having a high light reflectance and the photoresist film. In recent years, a SiO _x N _y (silicon oxynitride) material has been proposed as a constituent material of this antireflection film. The composition of the SiO _x N _y- based material can be finely adjusted by controlling the gas composition during film formation by CVD.
Along with this, the optical constant (n, k) (where n is the real number part of the complex refractive index and k is the imaginary number part coefficient) can be varied over a wide range, so that all exposure wavelengths,
It has an advantage that an antireflection film optimized for the resist material and the base material layer can be provided. In particular,
In the process of using a chemically amplified resist material in the far ultraviolet region such as the excimer laser wavelength region, there are very few films that show an effective antireflection effect, and in this sense, SiO _x N _y has great expectations. ing.

Optical constants (n, n) when the above SiO _x N _y type material is used as an antireflection film on a specific material layer
Regarding the optimization method of k), the applicant of the present invention first wrote about SPI.
E Volume 1927, Optical / Laser Microlithography VI (1
993), p. 263-272.
In this method, (1) first, under a given resist film thickness and a given film thickness d of the antireflection film, a change in the absorbed light amount of the resist film with respect to a change in the optical constant (n, k) of the antireflection film A locus is obtained (2) Next, loci are similarly obtained for other resist film thicknesses, and (3) optical constants (n, k) existing in a common region of these loci are obtained. When the processes (1) to (3) are sequentially performed for the other different thicknesses of the antireflection film, the optimum optical conditions (n, k, d) of the antireflection film are changed according to the thickness of the antireflection film. Can be asked.

[0007]

By the way, the above-mentioned method is to optimize the optical conditions (n, k, d) on a specific single kind of base material layer. However, during the actual semiconductor device manufacturing process, a plurality of material layers with different optical constants are exposed on the substrate, and a resist pattern may have to be formed on any of these material layers. is there. In such a case, even if the antireflection film optimized by the above-mentioned method is used, the halation and the standing wave effect may be suppressed only on a certain specific material layer. 1 and 10 by taking as an example a process of forming a contact hole pattern which addresses this problem both in the source / drain regions (Si substrate) and gate electrode (refractory metal silicide layer) of the MOS-FET.
Will be described with reference to.

In FIG. 1, a gate insulating film 2 made of SiO _x and a gate electrode 3 made of a W-polycide film are patterned on a Si substrate 1, and a thin antireflection film made of a SiO _x N _y type film is formed on the entire surface. 4 is covered with a conformal SiO _x interlayer insulating film 5, and a photoresist film 6 is planarized on the SiO _x interlayer insulating film 5. Now, let us consider a process of forming an opening by photolithography in the planned opening regions I and II of the photoresist film 6 following the contact hole pattern facing both the gate electrode 3 and the Si substrate 1. In the traditional way,
The optical constants (n, k) and the film thickness d of the antireflection film are optimized only on either the gate electrode 3 or the Si substrate 1. Therefore, for example, the gate electrode 3
The antireflection film 4 formed so as to have the optimum optical constant above does not always have the optimum optical constant on the Si substrate 1. As a result, for example, as shown in FIG. 10, even if the contact hole pattern 7 having a good shape can be formed in the photoresist film 6 in the area I to be opened on the gate electrode 3, the opening on the Si substrate 1 is to be planned. In the region II, the standing wave effect cannot be suppressed, and the contact hole pattern 8s having wavy deformation on the side wall surface is formed. If the optical constants are optimized on the Si substrate 1, the opposite will occur.

Therefore, even when photolithography is performed on material layers having different optical conditions, the optical constants (n, k) and the film thickness d are controlled so that halation and standing wave effects are suppressed on all material layers. There is a need for a method of designing an antireflection film that can set the value. An object of the present invention is to provide a method for designing such an antireflection film.

[0010]

A method for designing an antireflection film of the present invention is proposed to achieve the above-mentioned object, and is provided on a substrate where a plurality of material layers having different optical constants are exposed, When photolithography is performed using an antireflection film for patterning a transparent insulating film that covers these material films, the optical constants (n, k) of the antireflection film (where n is the real number of complex amplitude refractive index) are used. Part, k is also an imaginary part coefficient, and d is the film thickness respectively.) And the above-mentioned antireflection which can suppress the standing wave effect to a predetermined amount or less for each of the material layers when optimizing the film thickness d. Optical constant of film (n,
k) and the film thickness d are changed, and the optical constants (n, k) and the film thickness d included in the common part of these change regions are calculated.
The optimization is performed by selecting.

As a method for optimizing the optical constants (n, k) and the film thickness d, various numerical values are simultaneously substituted for n, k, and d, and the standing wave effect is calculated in a matrix by a computer.
It is also possible to use a method of calculating by simulation and narrowing down the change region where it finally converges to a predetermined amount or less.
Alternatively, by fixing any one of these three parameters, the number of parameters to be simulated can be reduced. In this case, it is theoretically possible to determine the optical constant (n, k) while keeping the film thickness d constant, but a simpler and more practical method is to determine the optical constant remaining under the condition that the optical constant n is fixed. k is a method of changing the film thickness d. It is empirically known that it is the atomic composition ratio of the antireflection film that essentially determines the optical constant (n, d), but n does not change as much as k even if the atomic composition ratio is changed. As such, this is possible.

The standing wave effect is represented by the value of the amplitude ratio. The amplitude ratio is a curve (swing curve) obtained by plotting the amount of light absorption in the photoresist film with respect to the film thickness of the photoresist film as shown in FIG. Amplitude Δ of the swing curve
It is defined as the ratio of A to the height A to the center line of the amplitude of the swing curve shown by the broken line in the figure (that is, the amount of light absorption when there is no standing wave effect).

According to the present invention, in order to achieve a practical photolithographic resolution, a change region capable of suppressing the amplitude ratio within 10% is obtained. The lower limit of the amplitude ratio is not particularly limited, but if it is set too small, the common part of the change region may not be found, so it is appropriately set according to the number and type of material layers having different optical constants. Just do it.

The antireflection film may be provided above or below the insulating film. In the present invention, it is particularly preferable that the antireflection film is composed of a SiO _x N _y based film. The SiO _x N _y based film can be formed using a parallel plate plasma CVD device or an ECR plasma CVD device. As a typical source gas for this plasma CVD, SiH ₄ / O ₂ / N ₂ mixed gas or SiH
_{There is a 4} / N ₂ O mixed gas. In addition, the S that is actually formed
iO _x N for the _y-based film contains a small amount of hydrogen, in order to demonstrate this, SiO _x is in the following specification
The notation of N _y : H film is used.

The atomic composition ratio of the SiO _x N _y : H film can be changed based on the flow rate ratio of the raw material gas, and the optical constant (n, k) can be changed based on this. Note that the preferable change range of the optical constants (n, k) and the film thickness d differs depending on the type of the underlying material layer. That is, when the base is a Si-based material layer, n =
1.8-2.6, k = 0.1-0.8, d = 20-15
0 nm; n = 1.78 to 2.38, k when the base is a pure metal layer of Al or Cu, a silicide layer or an alloy layer
= 0.55 to 1.15, d = 20 to 40 nm; n = 1.8 to 3.0, k = 0.5 to 0.0 when the base is a refractory metal layer or a refractory metal silicide layer. 9, d = 15
~ 35 nm.

By the way, a state in which a plurality of material layers having different optical constants are exposed on the surface of the substrate may appear at various stages of a normal semiconductor device manufacturing process. Typically, a layer made of Si and a layer made of a wiring material may appear, as when the gate electrode of the MOS-FET is formed on the Si substrate. However, the number of different material layers is not limited to two and may be three or more.

[0017]

According to the method of designing an antireflection film of the present invention, even if a plurality of material layers having different optical constants are exposed, the standing wave effect is less than a predetermined amount, preferably 10 or less, for each of these material layers. %, The optical constants (n, k) and the film thickness d of the antireflection film that can be suppressed to not more than 10% are selected, so that the antireflection film can exert a practically sufficient antireflection effect on any material layer. it can.

The selection of the above-mentioned optical conditions can be performed very simply and in a short time by fixing the optical constant n which does not change so much in practice and reducing the number of parameters. SiO _x as the antireflection film
When the N _y -based film is used, the antireflection film satisfying the optical constant (n, k) selected as described above can be formed by changing the flow rate ratio of the film forming gas in plasma CVD.

Therefore, for example, on a substrate where a layer made of Si and a layer made of a wiring material are exposed, these layers are coated with the SiO _x N _y antireflection film designed as described above, Photolithography for patterning the transparent insulating film can form a photoresist pattern having a good shape on both layers.

[0020]

EXAMPLES Specific examples of the present invention will be described below. Example 1 In this example, reflection is obtained when the present invention performs resist patterning for forming a gate contact and a source / drain contact of a MOS-FET by KrF excimer laser lithography (exposure wavelength 248 nm). This is an example in which the optical conditions of the SiO _x N _y : H film used as the prevention film are optimized. This embodiment will be described with reference to FIGS.
This will be described with reference to FIGS. 4 and 5.

First, the state of the substrate when performing photolithography in this embodiment is as shown in FIG. That is, the gate insulating film 2 made of SiO _x and the gate electrode 3 made of a W-polycide film are patterned on the Si substrate 1, and the entire surface thereof is thin SiO _x N _y :
An antireflection film 4 made of an H film was coated, and a conformal SiO _x interlayer insulating film 5 was coated on the antireflection film 4, and a photoresist film 6 was used to planarize the coating.

Here, on the Si substrate 1, an impurity diffusion layer serving as a source / drain region is already formed by ion implantation. The surface of the gate electrode 3 is WSi
_x (tungsten silicide) film. The photoresist film 6 is made of a chemically amplified positive photoresist material WKR-PT1 (trade name; manufactured by Wako Pure Chemical Industries, Ltd.).
The SiO _x interlayer insulating film 5 is conformally formed, and the film thickness D ₁ on the gate electrode and the film thickness D ₂ on the Si substrate are both 500 nm.

Areas I and II to be opened for contact holes
Are on the gate electrode and on the Si substrate, respectively. Anti-the above
Determine optical constants (n, k) and film thickness d of anti-reflection film
System to be considered in simulation for
In the planned opening area I is WSi _x/ SiO_xN_y: H /
SiO_x/ Photoresist laminated system, in the planned opening area II
Si / SiO_xN_y: H / SiO_x/ Photoresist product
It becomes a layer system.

The optical constants (n, k) of each material used in the above simulation are shown below. Si (Si substrate 1): n = 1.57, k = 3.58 WSi _x (gate electrode 3): n = 1.93, k = 2.73 SiO _x (SiO _x interlayer insulating film 5): n = 1.52, k = 0 photoresist (photoresist film 6): n = 1.80, k = 0.01 First, n of the SiO _x N _y : H film (antireflection film 4) is 2.
FIG. 4 shows the result of calculation of the standing wave effect in the planned opening region I when k and d were changed while fixing to 10.

Similarly, as a result of calculating the standing wave effect in the planned aperture region II when n of the SiO _x N _y : H film (antireflection film 4) is fixed to 2.10 and k and d are changed. Is shown in FIG. 4 and 5 are obtained by connecting regions having the same value of the amplitude ratio, which is an index for determining the standing wave effect, like contour lines, and each line is displayed in 1% increments.

In the figures, the two shaded areas indicate the common areas in which the amplitude ratios in both figures are both below 2%. From the coordinates (k, d) of the approximate center of these common regions, suitable optical conditions for the SiO _x N _y : H film are n = 2.
10, k = 0.56, d = 30 nm, or n = 2.
10, k = 0.27, d = 87 nm. The former optical condition (n, k) = (2.10, 0.56) is SiO _0.67.
N _0.22 : Depending on the composition of H, the latter optical condition (n,
k) = (2.10,0.27) is SiO _0.75 N _{0. 25:} H
Can be achieved by the respective compositions. However, as long as the same effect of suppressing the standing wave effect can be obtained, the film thickness d is never too small.
The former optical condition of m was selected, and the composition of the antireflection film 4 to be formed was determined to be SiO _0.67 N _0.22 : H.

The antireflection film 4 having such a composition is formed by performing plasma CVD at a flow rate ratio of SiH ₄ / N ₂ O of 1.2 to 1.3 according to a previous experiment conducted by the applicant of the present application. be able to. An example of film forming conditions will be described below. Apparatus Parallel plate type plasma CVD apparatus SiH ₄ flow rate 50 SCCM N ₂ O flow rate 40 SCCM Gas pressure 333 Pa (2.5 Torr) RF power 190 W (13.56 MHz) Film formation temperature 360 ° C. Electrode distance 1 cm (400 When the photoresist film 6 was patterned by KrF excimer laser lithography using this antireflection film 4, as shown in FIG. 2, contact holes were formed in both the planned opening regions I and II. The openings 7 and 8 following the pattern could be formed with a good shape.

Embodiment 2 In this embodiment, the resist patterning for forming the gate contact and the source / drain contact of the MOS-FET is performed by KrF excimer laser.
In the example performed by lithography, the substrate was once flattened with a SiO _x interlayer insulating film. This embodiment will be described with reference to FIGS. 6 to 9.

First, the state of the substrate when performing photolithography in this embodiment is as shown in FIG. That is, the gate insulating film 12 made of SiO _x and the gate electrode 1 made of a W-polycide film are formed on the Si substrate 11.
3 and 3 are patterned, and the entire surface thereof is thin SiO _x N _y :
It is covered with an antireflection film 14 made of an H film and SiO
_{The x} interlayer insulating film 15 was once flattened, and then a photoresist film 6 was formed thereon.

The thickness D ₁ of the SiO _x interlayer insulating film 5 in the planned opening region I is 500 nm, and the film thickness D ₂ in the planned opening region II is 700 nm. Here, using the optical constants of the respective material layers described in Example 1, the calculation result of the standing wave effect in the planned aperture region I when n is fixed at 2.10 and k and d are changed is shown. 8 、 Similarly planned opening area
The calculation results for II are shown in FIG.

In the figure, the two shaded areas indicate a common area in which both the amplitude ratios are 4% or less. From the coordinates (k, d) of the approximate center of these common regions, suitable optical conditions for the SiO _x N _y : H film are n = 2.
10, k = 0.60, d = 25 nm, or n = 2.
10, k = 0.27, d = 82 nm. The former optical condition (n, k) = (2.10,0.60) is SiO _0.67.
N _0.22 : Depending on the composition of H, the latter optical condition (n,
k) = (2.10,0.27) is SiO _0.75 N _{0. 25:} H
Can be achieved by the respective compositions. It selects the former optical conditions thickness d requires only 25 nm, the composition of the anti-reflection film 4 is to be deposited SiO _0.67 N _{0. 22:} was determined with H.

By using the antireflection film 4 having such a composition, KrF
When the photoresist film 16 was patterned by excimer laser lithography, as shown in FIG. 9, the openings 17 and 18 following the contact hole pattern were excellently formed in both the planned opening regions I and II. It could be formed with a shape. The present invention has been described above based on the two examples, but the present invention is not limited to these examples.

For example, in the above-described embodiment, the range of the amplitude ratio for determining the common area is set to 2% or less and 4% or less, but if this value is set to a larger value within the range of not more than 10%, The selection range of the atomic composition ratio of the SiO _x N _y : H film can be expanded. In addition, the exposure wavelength, the type of photoresist material, and the structure of the substrate can be appropriately selected.

[0034]

As is apparent from the above description, by applying the antireflection film designing method of the present invention, the standing wave effect can be suppressed to a constant level even on material layers having different optical constants. The resolution of the photoresist film can be stabilized. The present invention, in which the adoption of an antireflection film is essential with the shortening of the exposure wavelength of photolithography,
It improves the practical performance of this antireflection film, and thus contributes greatly to miniaturization, high integration, and high performance of semiconductor devices.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view showing a state of a substrate before photolithography in a process of forming a gate contact and a source / drain contact of a MOS-FET.

FIG. 2 is a schematic cross-sectional view showing a state in which an opening is formed in the photoresist film of FIG. 1 following a contact hole pattern.

FIG. 3 is a swing curve for explaining the definition of the amplitude ratio.

FIG. 4 shows WSi _x / SiO _x N _y : H / SiO _x (D ₁
= 500 nm) / photoresist stacking system. FIG.

FIG. 5: Si / SiO _x N _y : H / SiO _x (D ₂ = 5)
(00 nm) / photoresist stacking system. FIG.

FIG. 6 is a schematic cross-sectional view showing a state of the substrate before photolithography in another process of forming the gate contact and the source / drain contact of the MOS-FET.

FIG. 7 is a schematic cross-sectional view showing a state in which an opening is formed in the photoresist film of FIG. 6 following a contact hole pattern.

FIG. 8: WSi _x / SiO _x N _y : H / SiO _x (D ₁
= 500 nm) / photoresist stacking system. FIG.

FIG. 9: WSi _x / SiO _x N _y : H / SiO _x (D ₂
= 700 nm) / photoresist stacking system. FIG.

10 is a schematic cross-sectional view showing a state in which the substrate shown in FIG. 1 is subjected to photolithography using a conventional antireflection film, and an opening having a cross-sectional shape deteriorated by a standing wave effect is formed.

[Explanation of symbols]

1, 11 Si substrate 3, 13 Gate electrode 4, 14 Antireflection film 5, 15 SiO _x Interlayer insulating film 6, 16 Photoresist film 7, 17 Opening portion (in opening opening area I) 8, 18 (Opening opening area II) of) the opening d antireflection film in a thickness D ₁ (thickness of the film thickness D ₂ (in the open plan area II) SiO _x interlayer insulating film opening scheduled in region I) SiO _x interlayer insulating film

Claims (5)

[Claims] 1. When photolithography is performed on a substrate where a plurality of material layers having different optical constants are exposed by using an antireflection film for patterning a transparent insulating film covering these material layers, the antireflection film is used. Optical constant of film (n,
k) (where n is the real number part of the complex amplitude refractive index and k is the imaginary number part coefficient respectively) and the method of designing the antireflection film for optimizing the film thickness d. For each of the material layers, a variation region of the optical constant (n, k) and the film thickness d of the antireflection film capable of suppressing the standing wave effect to a predetermined amount or less is obtained, and the optics included in the common portion of these variation regions is obtained. A method for designing an antireflection film, which is performed by selecting a constant (n, k) and a film thickness d. 2. The optimization is performed by obtaining a change region of an optical constant k and a film thickness d capable of suppressing the standing wave effect to be a predetermined amount or less under a condition where the optical constant n is constant. The method for designing an antireflection film according to claim 1. 3. The change region capable of suppressing the standing wave effect below a predetermined amount is defined as a change region capable of suppressing an amplitude ratio within 10%. A method for designing the antireflection film described. 4. The method for designing an antireflection film according to claim 1, wherein the antireflection film is composed of a SiO _x N _y based film. 5. The plurality of material layers having different optical constants,
The antireflection film design method according to claim 1, wherein the antireflection film is a layer made of Si and a layer made of a wiring material.