The present invention relates to a positive resist compo› sition suitable for use in nanolithography processes for manufacturing VLSI and high-capacity microchips, or other photo-fabrication processes. More specifically, the invention is concerned with a positive resist composition capable of forming finer-resolution patterns by using electron beams, X-rays or EUV rays. In particular, the invention relates to a positive resist composition highly suitable for use in super minute patterning for semiconductor devices by utilizing high-energy beams, such as electron beams. 

In manufacturing processes of semiconductor devices, such as ICs and LSI circuits, fine patterning by photolithog› raphy using resist compositions has hitherto been carried out. In recent years, demand for superfine patterning in a submicron region or a quarter-micron region has grown as integrated circuits have increased in packing density. In order to meet such a demand, exposure light sources used in photolithography have been changed to those of shorter wavelengths, specifically from g-ray to i-ray, further to KrF excimer laser light. In addition to photolithography using excimer laser light, developments of lithography processes using either electron beams, or X-rays, or EUV light are proceeding now, too. 

As resists suitable for the lithography processes using electron beams, X-rays and EUV light, respectively, chemi- cal amplification resists utilizing acid-catalyzed reaction are mainly used from the viewpoint of increases in sensitivity. With respect to positive resists, chemically amplified resist compositions whose main components are polymers having properties of being insoluble or slightly soluble in alkaline aqueous solutions and becoming soluble therein under the action of acids (hereinafter referred to as acid-decomposable resins, too) and acid generators are used effectively. 

Transfer of resist techniques for KrF excimer laser to positive resists for electron-beam lithography or X-ray lithography have been mainly tried so far, and feasibility thereof has been contemplated. For instance, Patent Docu› ment 1 (JP-A-2-19847) discloses the resist composition containing poly(p-hydroxystyrene) whose phenolic hydroxyl groups are totally or partially protected by tetrahy- dropyranyl groups. 

Patent Document 2 (JP-A-4-219757) discloses the resist composition containing a polymer obtained by replacing 20 to 70% of the phenolic hydroxyl groups in poly(p-hydroxy› styrene) with acetal groups. 

50 Patent Document 3 (JP-A-2002-49156) discloses the positive photoresist composition containing a polymer obtained by replacing phenolic hydroxyl groups of poly(p› hydroxystyrene) with acetal groups of two different kinds and thereby giving excellent performances in terms of $_{55 }$ resolution, development defect, linearity and dry-etching resistance. 

Patent Document 4 (JP-A-2002-323768) discloses the resist composition ensuring improved line-width stability in patterns formed under a condition that the resist coating is left standing in vacuo after exposure. 

However, the present state is that high resolution, slight line edge roughness and in-vacuo PED (Post Exposure Delay) characteristic requirements cannot be satisfied con› currently even by the foregoing art. 

The term "line edge roughness" refers to a condition that, owing to characteristics of a resist composition used, the edges of the interface between each resist line pattern and a 

# POSITIVE RESIST COMPOSITION 

## FIELD OF THE INVENTION 

## BACKGROUND OF THE INVENTION 

substrate have such a shape as to fluctuate in a direction perpendicular to the line direction. When this line pattern is observed from the position right above, the edges look rough (to an extent of– dozens nm). This roughness is transferred to the substrate through an etching process, and too rough edges cause impairment of electric characteristics and reduce yield. Thus, the desire to improve line edge rough› ness is growing as the pattern size is reduced to a quarter micron or below. 

Further, the line-width stability of patterns formed under a condition that the resist coating is left standing in vacuo after exposure (in-vacuo PED) is a very important property because exposure is carried out in vacuo when electron beams or X-rays are used as exposure source. Inferiority of in-vacuo PED characteristic causes great variations in resist properties between the beginning and the end of drawing with electron beams or X-rays; as a result, line widths of the drawn patterns seriously lack in-plane uniformity and a considerable reduction in yield occurs. 

In addition, there is a problem that the line edge roughness also becomes worse by leaving the resist coating standing in vacuo. 

On the other hand, the use of EUV as light source causes a problem that the contrast is lowered by concerted photo› chemical reaction, such as positive-to-negative conversion, ascribable to EUV light, because the wavelengths of the light source are included in the extreme ultraviolet region and the EUV light has high energy. 

It is difficult for the combinations of hitherto known arts to ensure both very acceptable line edge roughness and favorable in-vacuo PED characteristic (variations in line width and line edge roughness) under irradiation with elec› tron beams or X-rays, so it has been desired to attain compatibility between those two performances. Addition› ally, it has also been desired to achieve both sufficiently high sensitivity and contrast even under EUV irradiation. 

[Patent Document 1] JP-A-2-19847 

[Patent Document 2] JP-A-4-219757 

[Patent Document 3] JP-A-2002-49156 

[Patent Document 4] JP-A-2002-323768 

An object of the invention is to solve problems of per› formance-enhancement techniques in fine patterning for semiconductor devices by use of high-energy beams, espe› cially electron beams, X-rays or EUV light. More specifi- cally, an object of the invention is to provide a positive resist composition capable of satisfying both requirements for in-vacuo PED characteristic and line edge roughness when electron beams are used as an irradiation source and having excellent sensitivity and dissolution contrast when EUV light is used as an irradiation source. 

The following positive resist compositions responsive to electron beams, X-rays or EUV are embodiments of the invention. 

(1) A positive resist composition for electron-beam, X-ray or EUV, comprising: 

(a) a polymer capable of increasing its solubility in an alkali developer under action of an acid, 

wherein the polymer has repeating units represented by formula (I), repeating units represented by formula (II) and repeating units represented by formula (III), 

(b) a compound capable of generating an acid upon irradiation with an actinic ray or radiation, and 

## SUMMARY OF THE INVENTION 

