Pattern forming material and pattern forming method

Details Pattern forming material and pattern forming method Pattern forming material and pattern forming method

2001-04-17

2002-04-23

Hamilton, Cynthia (Department: 1752)

Radiation imagery chemistry: process, composition, or product th

Imaging affecting physical property of radiation sensitive...

Making electrical device

C430S326000, C430S328000

Reexamination Certificate

active

06376154

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a fine-line pattern forming method for use in a manufacturing process for a semiconductor IC device and the like, and a material for forming a pattern used in the pattern forming method.
In the manufacture of ICs, LSIs and the like, a pattern is conventionally formed through photolithography using UV, in which a light source with a shorter wavelength has become mainly used in accordance with refinement of a semiconductor a device. Recently, a surface imaging process using dry development has been developed in order to increase the depth of focus and improve practical resolution in using a light source with a shorter wavelength.
As an example of the surface imaging process, U.S. Pat. No. 5,278,029 discloses a method in which, after selectively forming a polysiloxane film on the surface of a resist film of a resist material which can generate an acid through exposure, the resist film is dry etched by using the polysiloxane film as a mask, so as to form a resist pattern.
Now, this conventional method of forming the resist pattern will be described with reference to FIGS.
5
(
a
) through
5
(
d
).
In this method, a copolymer of 1,2,3,4-tetrahydronaphthyridinenimino-p-styrene sulfonate (NISS) and methyl methacrylate (MMA) is used as the resist material for generating an acid through exposure.
First, as is shown in FIG.
5
(
a
), a resist film
401
, which generates an acid through exposure, coated on a semiconductor substrate
400
is irradiated with a KrF excimer laser
404
by using a mask
403
, and thus, the acid is generated in an exposed area
401
a
of the resist film
401
. Owing to this acid, the exposed area
401
a
is changed to be hydrophilic, so that water in air can be easily adsorbed by the exposed area
401
a
. As a result, a thin water absorbing layer
405
is formed in the vicinity of the surface of the exposed area
401
a
as is shown in FIG.
5
(
b
).
Next, when an alkoxysilane gas
406
is introduced onto the surface of the resist film
401
, the acid generated on the surface of the exposed area
401
a
works as a catalyst, so that alkoxysilane is hydrolyzed and dehydrated. As a result, an oxide film
407
is formed on the surface of the exposed area
401
a
as is shown in FIG.
5
(
c
). Subsequently, when the resist film
401
is dry etched by RIE using O
2
plasma
408
by using the oxide film
407
as a mask, a fine-line resist pattern
409
is formed as is shown in FIG.
5
(
d
).
This pattern forming method thus adopts a negative type lithography process for forming a resist pattern in an exposed area, in which the acid generated in the exposed area of the resist film is used as the catalyst for selectively forming the oxide film in the exposed area and the oxide film is used as a mask in the dry etching for forming the resist pattern.
The negative type lithography process has the following problems in, for example, forming a contact hole for connecting multilayered interconnections of an IC:
First, usage of a mask generally adopted in pattern exposure can cause the following problem: In the lithography for forming a contact hole, the aperture ratio of the mask is very high when the negative lithography process is used. Specifically, while a light shielding film against exposing light is formed merely in a portion corresponding to the contact hole on the mask, the light shielding film is removed and quartz of the mask substrate is bare in the other portion excluding the contact hole in order to transmit the exposing light. Since the area occupied by all the contact holes in the entire area of a semiconductor chip is generally very small, the proportion of the area occupied by the bare quartz to the area of the light shielding film on the mask becomes high, namely, the aperture ratio of the mask becomes high.
When the aperture ratio of the mask is high, the effect of ambient dusts is increased. Specifically, dusts adhered to the light shielding film on the mask scarcely affect the process, but those adhered to the transparent portion of the mask change this portion into a light shielding portion. When the exposure is effected by using the mask to which dusts are thus adhered, a pattern defect is caused in the portion to which the dusts are adhered. In this manner, since the aperture ratio of the mask is high in the negative type lithography process, the process can be easily affected by dusts, resulting in easily decreasing the yield.
Secondly, in the lithography process for forming a contact hole, a half-tone type mask can be used for the purpose of increasing the depth of focus. However, the effect of increasing the depth of focus can be attained merely in a positive type lithography but cannot be attained in the negative type lithography. Accordingly, in the formation of a contact hole, the depth of focus is smaller in the negative type process than in the positive type process.
The occurrence of these first and second problems are not limited to the formation of a contact hole, but can be caused in the cases where a mask having a larger area of the transparent portion is used and where the depth of focus is desired to be increased.
SUMMARY OF THE INVENTION
In view of the aforementioned conventional problems, the object of the invention is realizing a positive type surface imaging process replaceable with the negative type surface imaging process.
In order to achieve this object, a resist film including an acidic or a basic group is selectively irradiated with an energy beam in this invention, so that a basic or an acidic group having the reverse property to that of the group included in the resist film can be generated in an exposed area. Alternatively, after generating an acidic or a basic group in an exposed area by selectively irradiating a resist film with an energy beam, the entire surface of the resist film is irradiated with another energy beam, so that a basic or an acidic group having the reverse property to that of the group generated in the exposed area can be generated on the entire surface of the resist film. Thus, neutralization is effected in the exposed area of the resist film, and in an unexposed area of the resist film, the acidic or the basic group works as a catalyst for forming an oxide film. In this manner, a positive type surface imaging process, which cannot be attained by the conventional method, can be realized by this invention.
The first pattern forming material of this invention comprises a copolymer including a first group for generating a base through irradiation with an energy beam and a second group having an acidic property.
When the resist film formed out of the first pattern forming material is selectively irradiated with the energy beam, the first group is dissolved into the base in the exposed area on the resist film, so that the generated base is neutralized with the second group having the acidic property, while the unexposed area on the resist film remains to be acidic. Accordingly, since merely the unexposed area on the resist film can selectively retain its acidic property, the positive type surface imaging process can be realized.
The second group in the first pattern forming material is preferably a group including a sulfonic acid group. In this case, owing to the strong acidic property of sulfonic acid, sulfonic acid can exhibit its strong catalytic function in the formation of the metal oxide film in the unexposed area on the resist film. Therefore, the strong acidic property can be selectively retained merely in the unexposed area on the resist film.
The copolymer in the first pattern forming material is preferably a binary copolymer represented by the following general formula or a ternary or higher copolymer obtained by further polymerizing the binary copolymer with another group:
Chemical Formula 1:
wherein R
1
indicates a hydrogen atom or an alkyl group; R
2
and R
3
independently indicate a hydrogen atom, an alkyl group, a phenyl group or an alkenyl group, or together indicate a cyclic alkyl group, a cyclic alkenyl group, a cyclic alkyl g

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