JP3248353B2 - Anti-reflection coating design method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art As high integration of semiconductor devices progresses at an accelerated pace, their minimum processing dimensions are rapidly reduced. For example, the current generation 1
The minimum processing size of 6MDRAM is about 0.5 μm,
It is expected that the size will be reduced to 0.35 μm or less in the next-generation 64 MDRAM, and to 0.25 μm or less in the next-generation 256 MDRAM.

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

[0004] Halation is a phenomenon in which the light intensity in a specific region increases due to reflected light from a stepped portion of a base material film, and the actual harm is the occurrence of constriction in a positive photoresist pattern. On the other hand, the standing wave effect is a phenomenon in which light intensity distribution occurs in the thickness direction of the photoresist film due to multiple reflections occurring in the photoresist film or between the photoresist film and the underlying film. And variations in resist sensitivity within the substrate.

In order to reduce such halation and standing wave effects, the reflected light from the underlying material film may be weakened. For this reason, it is expected that an antireflection film will be indispensable in the future between the material layer having high light reflectance and the photoresist film. In recent years, a SiO _x N _y (silicon oxynitride) -based material has been proposed as a constituent material of the 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,
As a result, the optical constants (n, k) (where n is the real part of the complex refractive index and k also represents the imaginary part coefficient) can be changed over a wide range.
There is an advantage that an antireflection film optimized for a resist material and a base material layer can be provided. In particular,
In a process using a chemically amplified resist material in the deep ultraviolet region such as the excimer laser wavelength region, very few films exhibit an effective antireflection effect, and in this sense, SiO _x N _y has great expectations. ing.

When the SiO _x N _y -based material is used as an antireflection film on a specific material layer, the optical constant (n,
Regarding the optimization method of k), the applicant of the present invention has first made SPI
E Vol. 1927, Optical / Laser Microlithography VI (1
993), p. 263-272.
In this method, (1) First, a change in the amount of light absorbed by the resist film with respect to a change in the optical constant (n, k) of the antireflection film under an arbitrary resist film thickness and an arbitrary antireflection film thickness d. A locus is determined, (2) Next, a locus is similarly determined for other plural resist film thicknesses, and (3) an optical constant (n, k) existing in a common area of each of these loci is determined. When the above-described processes (1) to (3) are sequentially performed for other different thicknesses d of the antireflection film, the optimum optical conditions (n, k, d) of the antireflection film according to the thickness of the antireflection film are obtained. Can be requested.

[0007]

The above-mentioned method optimizes the optical conditions (n, k, d) on a specific single type of underlayer. However, during the actual semiconductor device manufacturing process, there are cases where multiple material layers with different optical constants are exposed on the substrate, and a resist pattern must be formed on any of these material layers. is there. In such a case, even if the antireflection film optimized by the above method is used, there is a possibility that the halation and the standing wave effect can be suppressed only on a specific material layer. FIGS. 1 and 10 show an example of a process for forming a contact hole pattern facing both a source / drain region (Si substrate) and a gate electrode (refractory metal silicide layer) of a MOS-FET.
This will be described with reference to FIG.

FIG. 1 shows that 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 the entire surface thereof is a thin anti-reflection film made of a SiO _x N _y -based film. 4 shows a state in which this is covered with a conformal SiO _x interlayer insulating film 5, and is further planarized with a photoresist film 6. Now, consider a process of forming an opening by photolithography in the planned opening regions I and II of the photoresist film 6 according to a 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 thickness d of the antireflection film are optimized only on one of the gate electrode 3 and the Si substrate 1. Therefore, for example, the gate electrode 3
The antireflection film 4 formed so as to have the optimal optical constant above does not always have the optimal optical constant on the Si substrate 1. As a result, for example, as shown in FIG. 10, even if a contact hole pattern 7 having a good shape can be formed in the photoresist film 6 in the opening region I on the gate electrode 3, In the region II, the standing wave effect cannot be suppressed, and the contact hole pattern 8s having a wavy deformation on the side wall surface is formed. If the optical constants are optimized on the Si substrate 1, the opposite occurs.

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

[0010]

The method for designing an anti-reflection film according to the present invention is proposed to achieve the above-mentioned object, and is provided on a substrate on which a plurality of material layers having different optical constants are exposed. When performing photolithography using an antireflection film to pattern a transparent insulating film covering these material films, the optical constant (n, k) of the antireflection film (where n is a real number of complex amplitude refractive index) Part, k is an imaginary part coefficient, and d is a film thickness, respectively). When optimizing the film thickness d, the antireflection which can suppress the standing wave effect to a predetermined amount or less for each of the material layers. The optical constants of the film (n,
k) and the change region of the film thickness d are obtained, and the optical constant (n, k) and the film thickness d included in the common part of these change regions are obtained.
The above 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 into n, k, and d to obtain a standing wave effect in a matrix by a computer.
It is also possible to use a method of calculating by simulation and finally narrowing down a change region where this converges to a predetermined amount or less.
Alternatively, if any one of these three parameters is fixed, the number of parameters to be simulated can be reduced. In this case, it is theoretically possible to determine the optical constants (n, k) while keeping the film thickness d constant. However, a simpler and more practical method is to determine the optical constants remaining under the condition where the optical constant n is fixed. k is a method of changing the film thickness d. What essentially determines the optical constants (n, k) is the atomic composition ratio of the antireflection film. It has been empirically known that n does not change as much as k even if this atomic composition ratio is changed. This makes this possible.

The standing wave effect is represented by a value of an amplitude ratio. As shown in FIG. 3, the amplitude ratio is a curve (swing curve) obtained by plotting the amount of light absorption in the photoresist film with respect to the thickness of the photoresist film. 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 drawing (that is, the amount of light absorption when there is no standing wave effect).

In the present invention, in order to achieve a practical photolithography resolution, a change region in which the amplitude ratio can be suppressed within 10% is obtained. The lower limit of the amplitude ratio is not particularly limited, but if it is set too small, a common portion of the change region may not be found. Therefore, the lower limit is appropriately set according to the number and type of the material layers having different optical constants. Just do it.

The anti-reflection film may be provided on any of the upper and lower sides of the insulating film. In the present invention, it is particularly preferable that the antireflection film is formed of a SiO _x N _y -based film. The SiO _x N _y -based film can be formed using a parallel plate type plasma CVD apparatus or an ECR plasma CVD apparatus. A typical source gas for the plasma CVD is a mixed gas of SiH ₄ / O ₂ / N ₂ or SiH ₄ / O ₂ / N _2.
There are ₄ / N ₂ O mixture gas. In addition, S which is actually deposited
Since the iO _x N _y -based film contains a small amount of hydrogen, in the following description, SiO _x
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 source gas, and the optical constant (n, k) can be changed based on this. 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 underlayer 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 underlying layer is a pure metal layer, silicide layer or alloy layer of Al or Cu
= 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
３５35 nm.

Incidentally, 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, as when a gate electrode of a MOS-FET is formed on a Si substrate, a layer made of Si and a layer made of a wiring material may appear. However, the number of different material layers is not limited to two, and may be three or more.

[0017]

In the method for designing an anti-reflection film according to the present invention, the standing wave effect of each of these material layers is not more than a predetermined amount, preferably not more than 10 even on a substrate on which a plurality of material layers having different optical constants are exposed. % In order to select the optical constant (n, k) and the thickness d of the antireflection film that can be suppressed to not more than%, the antireflection film can exhibit 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 vary much in practice and reducing the number of parameters. SiO _x as the antireflection film
When an _Ny- based film is used, an antireflection film that satisfies the optical constants (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 on which 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 -based anti-reflection film designed as described above. By performing photolithography for patterning the transparent insulating film, a photoresist pattern having a good shape can be formed on both layers.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, specific embodiments of the present invention will be described. Embodiment 1 In this embodiment, when the present invention is applied to a case where resist patterning for forming a gate contact and a source / drain contact of a MOS-FET is performed by KrF excimer laser lithography (exposure wavelength: 248 nm), reflection occurs. 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 is shown in FIGS.
This will be described with reference to FIGS.

First, the state of the substrate when performing photolithography in the present embodiment is as shown in FIG. 1 described above. That is, the gate insulating film 2 made of SiO _x and the gate electrode 3 made of the W-polycide film are patterned on the Si substrate 1, and the entire surface thereof is thin SiO _x N _y :
The film was covered with an antireflection film 4 made of an H film, the upper surface was covered with a conformal SiO _x interlayer insulating film 5, and the upper surface was planarized with a photoresist film 6.

Here, an impurity diffusion layer serving as a source / drain region is already formed on the Si substrate 1 by ion implantation. The surface of the gate electrode 3 is made of 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 formed conformally, and the thickness D ₁ on the gate electrode and the thickness D ₂ on the Si substrate are both 500 nm.

Contact hole opening regions I and II
Are on the gate electrode and on the Si substrate, respectively. Above
Determine the optical constants (n, k) and thickness d of the anti-irradiation film
Systems to be considered in simulation for simulation
Indicates that WSi _x/ SiO_xN_y: H /
SiO_x/ Photoresist lamination system, 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, SiO _x n _y: H film n of (antireflection film 4) 2.
FIG. 4 shows the result of calculating the standing wave effect in the expected opening region I when k is fixed to 10 and k and d are changed.

Similarly, when the n of the SiO _x N _y : H film (the antireflection film 4) is fixed at 2.10 and the k and d are changed, the standing wave effect in the expected opening area II is calculated. Is shown in FIG. In FIGS. 4 and 5, regions in which the amplitude ratios serving as the judgment index of the standing wave effect have the same value are connected like contour lines, and each line is displayed in increments of 1%.

In the figures, two hatched portions indicate a common region in which the amplitude ratio is 2% or less in both figures. From the coordinates (k, d) about the center of these common regions, the preferred 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 and d = 87 nm. The former optical condition (n, k) = (2.10, 0.56) is SiO _{0.67
Depending on} the composition of N _0.22 : H, the optical conditions (n,
k) = (2.10,0.27) is SiO _0.75 N _{0. 25:} H
Can be achieved by the compositions of However, as long as the same effect of suppressing the standing wave effect can be obtained, the thickness d does not exceed a small value.
The former optical condition, which requires only 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 from a previous experiment conducted by the present applicant. be able to. An example of the film forming conditions is described below. Apparatus Parallel-plate 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. Distance between electrodes 1 cm (400) When the photoresist film 6 was patterned by KrF excimer laser lithography using the anti-reflection film 4, as shown in FIG. 2, contact holes were formed in both the planned opening regions I and II. -The openings 7, 8 following the pattern could be formed with a good shape.

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

First, the state of the substrate when performing photolithography in the present embodiment is as shown in FIG. That is, a gate insulating film 12 made of SiO _x and a gate electrode 1 made of a W-polycide film are formed on a Si substrate 11.
3 and a thin SiO _x N _y :
Coated with an anti-reflection film 14 made of H film,
_The film was once flattened by the _x interlayer insulating film 15, and a photoresist film 6 was further formed thereon.

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

In the figures, two hatched portions indicate a common area in which the amplitude ratio is 4% or less in both figures. From the coordinates (k, d) about the center of these common regions, the preferred 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 and d = 82 nm. The former optical condition (n, k) = (2.10, 0.60) is SiO _{0.67
Depending on} the composition of N _0.22 : H, the optical conditions (n,
k) = (2.10,0.27) is SiO _0.75 N _{0. 25:} H
Can be achieved by the compositions of 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.

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 according to the contact hole pattern were excellently formed in both of the opening regions I and II. It could be formed with a shape. As described above, the present invention has been described based on the two embodiments, but the present invention is not limited to these embodiments.

For example, in the above 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 value not exceeding 10%, The selection range of the atomic composition ratio of the SiO _x N _y : H film can be widened. In addition, the exposure wavelength, the type of the photoresist material, and the configuration of the substrate can be appropriately selected.

[0034]

As is apparent from the above description, by applying the method for designing an antireflection film of the present invention, the standing wave effect can be suppressed to a constant level even on material layers having different optical constants. In addition, the resolution of the photoresist film can be stabilized. In the present invention, while it becomes necessary to employ an antireflection film along with shortening of the exposure wavelength of photolithography,
This improves the practical performance of the antireflection film, and greatly contributes to miniaturization, high integration, and high performance of semiconductor devices.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view showing a state of a substrate before performing 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 according to a contact hole pattern.

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

[4] _{WSi x / SiO x N y:} H / SiO x (D 1
FIG. 4 is a diagram illustrating a simulation result of a standing wave effect in a photoresist laminated system.

FIG. 5: Si / SiO _x N _y : H / SiO _x (D ₂ = 5)
FIG. 12 is a diagram illustrating a simulation result of a standing wave effect in a (00 nm) / photoresist laminated system.

FIG. 6 is a schematic cross-sectional view showing a state of a substrate before performing photolithography in another process for forming a gate contact and a source / drain contact of a 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 according to a contact hole pattern.

[8] _{WSi x / SiO x N y:} H / SiO x (D 1
FIG. 4 is a diagram illustrating a simulation result of a standing wave effect in a photoresist laminated system.

[9] _{WSi x / SiO x N y:} H / SiO x (D 2
FIG. 7 is a diagram illustrating a simulation result of a standing wave effect in a photoresist laminated system.

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

[Explanation of symbols]

1, 11 Si substrate 3,13 gate electrode 4 and 14 anti-reflection film 5,15 SiO _x interlayer insulating film 6 and 16 photoresist film 7, 17 (in the opening region where I) the opening 8 and 18 (opening scheduled region 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

──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-6-69122 (JP, A) JP-A-5-299338 (JP, A) JP-A-4-234109 (JP, A) 290920 (JP, A) JP-A-4-96231 (JP, A) JP-A-7-201990 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01L 21/027 G03F 7 / 11 503

Claims (5)

(57) [Claims] When performing photolithography using an antireflection film to pattern a transparent insulating film covering these material layers on a substrate on which a plurality of material layers having different optical constants are exposed, the antireflection is prevented. The optical constants of the film (n,
k) (where n represents the real part of the complex amplitude refractive index, and k also represents the imaginary part coefficient) and a method of designing an antireflection film for optimizing the film thickness d. For each of the material layers, a change 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 optical region included in the common part of these change regions is determined. A method for designing an antireflection film, wherein the method is performed by selecting a constant (n, k) and a film thickness d. 2. The method according to claim 1, wherein the optimization is performed by obtaining a change region of an optical constant k and a film thickness d capable of suppressing a standing wave effect to a predetermined amount or less under a condition that an optical constant n is constant. The method for designing an antireflection film according to claim 1. 3. The variable region in which the standing wave effect can be suppressed to a predetermined amount or less as a variable region in which the amplitude ratio can be suppressed to within 10%. The method for designing an anti-reflection film described in the above. 4. The method for designing an anti-reflection film according to claim 1, wherein the anti-reflection film is formed of a SiO _x N _y -based film. 5. The plurality of material layers having different optical constants,
The method for designing an antireflection film according to any one of claims 1 to 4, wherein the layer is made of a layer made of Si and a layer made of a wiring material.