JPH0574696A - Lithographic method using high energy beam - Google Patents

Abstract

PURPOSE:To realize sufficiently high adhesion even when a PMMA resist is used by successively applying an HMDS layer, first PMMA layer having a relatively high crosslinking density, and second PMMA layer having a relatively low density and performing a development process by selectively irradiating the laminated resin layers with an energy beam. CONSTITUTION:After hexamethyldisilazene 2 is applied to the surface of a substrate as an adhesion strengthening agent, a thin high-crosslinking-density PMMA layer 3 having an excellent adhesive property is formed by application. Then a low-crosslinking-density PMMA layer 4 is formed on the layer 3 as a main resist pattern forming layer. Since the adhesion between the PMMA layers 3 and 4 is good, the adhesion of the layer 4 to the substrate 1 becomes good as a whole. Therefore, since the PMMA layer 4 having an inferior adhesive property can be firmly stuck to the substrate, no resist stripping occurs even under a more severe processing condition when the PMMA layer 4 which is excellent in resolution is utilized as an electron-beam resist.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam lithography technique, and particularly improves adhesion to a substrate when using polymethyl methacrylate (hereinafter referred to as PMMA) suitable for forming a fine pattern as an electron beam resist. It is related to processing.

PMMA is widely used as a high-resolution photosensitive resist. However, in order to adjust the chemical structure of the PMMA to adjust the photosensitivity and the adhesion to the substrate as desired, it is necessary to satisfy all the various requirements. Is almost impossible,
It is a normal usage pattern to seek the best for the main characteristics and to supplement the dissatisfaction with respect to the other characteristics with the usage technology.

Dry processing such as dry etching is often used in a lithography process for forming a fine pattern of an integrated circuit having a high degree of integration. Dry etching is used to realize an overhang structure by using side etching. Is almost impossible, and we have no choice but to rely on wet etching.

When wet etching is performed by using the resist as a mask for selective etching, if the adhesion between the resist and the substrate is weak, the resist peels off from the substrate as the etching progresses, making it impossible to form a fine pattern. .. P
If an MMA-based resist is selected on the basis of resolution, the adhesion will be insufficient. Therefore, when wet etching is performed, an adhesion enhancer is interposed between the substrate and the resist to enhance the etching resistance. ing.

[0005]

2. Description of the Related Art When using a PMMA electron beam resist, hexamethyldisilazane (HMDS) is coated on the surface of a substrate as a means for improving its adhesion, and PM is then applied.
A MA-based resist layer is formed by coating. Since HMDS is an adhesion enhancer, it does not need to be formed thick, and may be thick enough to be removed together with the development processing of the resist layer.

[0006]

This method was effective for PMMA type resists which have been widely used in the past, but PMMA whose crosslink density is lowered in order to improve resolution.
When a resist such as OEBR-1000 (trade name, manufactured by Tokyo Ohka Co., Ltd.) is used, the effect of enhancing the adhesion of HMDS is weakened, and it becomes impossible to provide sufficient resistance to wet etching.

An object of the present invention is to provide a processing method which realizes sufficient adhesion even when using a high resolution PMMA type resist such as OEBR-1000.

[0008]

In order to achieve the above object, in the high energy beam lithography of the present invention, the HMDS, the layer and the first PM having a relatively high crosslink density are formed on the surface of the substrate.
The MA layer and the second PMMA layer having a relatively low cross-linking density are sequentially applied, the laminated resin layers are selectively irradiated with energy rays, and a developing process is performed to perform a lithographic process.

In addition, a second PMMA having a relatively low crosslink density
To obtain an overhang pattern suitable for forming a specific structure of a semiconductor device by combining a layer with a PMMA-based resist having a relatively high sensitivity to an electron beam and a PMMA-based resist having a relatively low sensitivity to an electron beam. Is also done.

[0010]

The PMMA-based resin generally has a higher resolution as the crosslinking density is lower, but on the other hand, the adhesion to other objects is lower. A substance having a strong acting force, such as an etching solution, may penetrate into an interface having insufficient adhesiveness to cause undesired etching, resulting in a cross-sectional shape unfavorable for device formation.

This tendency also appears in the case of bonding through a substance having a relatively large adhesive force such as HMDS,
The effect of HMDS as an adhesion enhancer will not be fully exhibited. However, such a situation is not possible with PMMA having a high crosslink density, and the adhesion to the substrate via HMDS is sufficiently high.

On the other hand, the low resolution, which is a drawback of the high crosslink density PMMA, is that the thickness of the high crosslink density PMMA layer is small,
This is supplemented by laminating a low cross-linking density PMMA layer on this and using it as the main body for resist pattern formation.

In other words, by using two resist layers, one layer realizes high adhesion and the other one layer realizes high resolution.

[0014]

1 (a) to 1 (e) are schematic sectional views showing steps of the most basic embodiment of the present invention. Hereinafter, this embodiment will be described with reference to FIG.

The semiconductor substrate 1 is, for example, a Si wafer, but the surface of the substrate is made of Si, SiO _2, or the like, and an impurity introduction region may be formed in the substrate in some cases. HMDS, which is an adhesion enhancer, is applied onto this substrate by spin coating (FIG. 2 (a)). Since the HMDS layer 2 functions as an adhesive, so to speak, it suffices if the entire surface of the substrate is reliably covered, and it is generally desirable that its thickness is small.

On top of that, ZCM which is a high cross-link density PMMA
R-100 (trade name, manufactured by Nippon Zeon Co., Ltd.) is applied to a thickness of 0.1 μm or less ((b) in the same figure). This high cross-link density PMMA layer 3
Since it only improves the adhesiveness of the low cross-linking density PMMA layer which is the main constituent of the pattern formation, it is not preferable that the thickness thereof exceeds the above-mentioned 0.1 μm.

OEBR, which is a low crosslink density PMMA
Apply -1000 (trade name, manufactured by Tokyo Ohka Co., Ltd.) to the required thickness ((c) in the same figure). The thickness of the resist layer in the lithographic process is almost always determined by the minimum size of the pattern to be formed. In forming a submicron pattern, it is difficult to increase the aspect ratio, which is the ratio of the depth of the aperture to the diameter of the aperture, and the pattern is usually formed by setting it to 5 or less. When forming,
The low crosslink density PMMA layer 4 has a thickness of about 2 μm.

After that, the same process as in the ordinary electron beam lithography is performed, and if the electron beam is selectively irradiated and developed as shown in FIG. 3D, a resist pattern is formed as shown in FIG. It The development treatment of PMMA is usually performed using methyl isobutyl ketone (MIBK) and isopropyl alcohol (IPA).

The above embodiment relates to the basic usage of the present invention, and the following description is to obtain a special effect by combining two kinds of resists having different photosensitivity. First, an embodiment corresponding to claim 2 will be described with reference to FIG.

In FIG. 1A, the high crosslink density PMMA layer 3 is provided on the surface of the semiconductor substrate 1 as in the above-mentioned embodiment. Specifically, this is the same as in the above-mentioned embodiment.
-100 layers. Although omitted in the figure, the substrate and ZC
An HMDS layer is present between the MR-100 layers, and both are firmly fixed.

Further, a PMMA layer 4a having a low crosslinking density and a low sensitivity and a PMMA layer 4b having a low crosslinking density and a high sensitivity are formed on the high crosslinking density PMMA layer 3. PM with low crosslinking and low sensitivity
MA is, for example, OEBR-1000 described above, and PMMA with low cross-linking and high sensitivity is, for example, EBR-9 (trade name, manufactured by Toray).
Is.

This is selectively irradiated with an electron beam, but the dose amount is set to be large in the portion where the low-sensitivity PMMA layer is opened. Since the high-sensitivity PMMA layer 4b is exposed to an electron beam with a small dose to be exposed, a relatively large opening is formed by developing it, whereas the low-sensitivity PMMA layer 4a has a large dose of electrons. It is exposed only to radiation and a small opening is formed by the development process. This state is shown in FIG.

After forming the resist pattern in this way, an Al layer 5 is vapor-deposited as shown in FIG.
The l layer is in contact with the substrate only at the fine openings provided in the low sensitivity PMMA layer. If this is subjected to a lift-off process by removing the resist layer, only the Al layer 5a remains. By applying the processing of this embodiment to the formation of the gate electrode of the MESFET, it becomes possible to form a fine electrode having a gate length of 0.2 μm.

Next, the process of the third embodiment corresponding to claim 3 will be described with reference to FIG. FIG. 1A shows a high crosslink density PMMA layer 3 on a semiconductor substrate 1, a low crosslink density and high sensitivity PMMA layer 4b, and a low crosslink density and low sensitivity PMM.
The A layer 4a is laminated in this order. Again, an HMDS layer is present as an adhesion enhancer between the semiconductor substrate 1 and the high crosslink density PMMA layer 3, but it is omitted in the figure.

When this is selectively irradiated with an electron beam and subjected to a developing treatment, the low-sensitivity PMMA layer 4a removes only the irradiated region even if the irradiation condition and the developing condition are common. The high-sensitivity PMMA layer 4b is opened more widely because the weakly exposed region around it is removed. This situation is shown in FIG. 2B, and it is easily understood that the process of this embodiment is suitable for forming a mask pattern having an overhang for lift-off.

[0026]

As described above, according to the present invention, a low cross-linking density PMMA layer having poor adhesion can be firmly fixed to a substrate. Therefore, a low cross-linking density PMMA layer having excellent resolution can be obtained. When used as an electron beam resist, electron beam lithography with higher resolution becomes possible without peeling of the resist even under more severe processing conditions.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a treatment process of an example.

FIG. 2 is a diagram schematically showing the process of the second embodiment.

FIG. 3 is a diagram schematically showing a process of a third embodiment.

[Explanation of Codes] 1 semiconductor substrate, 2 HMDS layer 3 high crosslink density PMMA layer 4 low crosslink density PMMA layer 4a low sensitivity PMMA layer 4b high sensitivity PMMA layer 5,5a Al layer

Claims (7)

[Claims] 1. A hexamethyldisilazane (HMDS) layer, a first polymethylmethacrylate (PMMA) layer, and a second PMMA layer having a crosslink density lower than that of the first PMMA are sequentially coated on the surface of the substrate, and the layers are laminated. A high energy beam lithography method comprising the step of selectively irradiating the resin layer with an energy beam to remove the energy beam irradiation region or the non-irradiation region of the laminated resin layer. 2. The lithographic method according to claim 1, wherein a third PMMA layer having a photosensitivity to the energy rays higher than that of the PMMA is applied onto the second PMMA layer. Energy ray lithography method. 3. The lithography method according to claim 1, wherein a third PMMA layer having a photosensitivity to the energy rays lower than that of the PMMA is applied onto the second PMMA layer. Energy ray lithography method. 4. The high energy beam lithography method according to claim 1, wherein the outermost surface layer of the substrate is a semiconductor layer. 5. The high energy beam lithography method according to claim 1, wherein the outermost surface layer of the substrate is an insulator layer. 6. The high-energy-ray lithography method according to claim 1, wherein the energy beam is a charged particle beam. 7. The lithography method according to claim 1, wherein the energy ray is an electromagnetic wave having an energy higher than 300 nm.