JPS63209128A - Formation of resist pattern - Google Patents

Abstract

PURPOSE:To obtain a method having excellent reproducibility and dimensional accuracy by coating a wafer with positive type resist, giving a focus value larger than an optimum value, aligning a focal point under a resist layer to expose it, and forming an inversely tapered shape resist pattern. CONSTITUTION:A wafer 1 is coated with positive type resist, a focus value is increased larger than an optimum value to align a focus under the resist layer to be exposed, thereby forming an inversely tapered shape resist pattern 2. That is, the focus value is slightly increased for an optimum exposure time, i.e., the focus is slightly moved toward the lower part of the resist to be exposed. Accordingly, when a forming method for the pattern is used, an ideal metal pattern can be formed by a lifting OFF method in simple steps, and an ion-implanted region of concentration distribution can be formed in simple steps.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for forming a resist pattern in the manufacture of semiconductor devices, and more specifically, to optical lithography for forming a reverse tapered resist pattern.

2. Description of the Related Art As shown in FIG. 1(a), if a reverse tapered resist pattern 2 is formed on a wafer 1, the subsequent lift-off of the metal film can be simplified and ideally carried out. Here, the inverted tapered shape refers to a cross-sectional shape in which the upper ff13A of the side wall 3 of the resist pattern protrudes more than the lower ff13B, like the inverted trapezoidal cross-section of the pattern 2 shown in FIG. 1(a).

That is, such a reverse tapered resist pattern 2
When a metal film 4 is deposited on top and lifted off as shown in FIG. 1(b), a metal pattern 5 can be formed in an ideal shape as shown in FIG. 1(c).

Therefore, when using lift-off or the like, it is desirable to form a reverse tapered resist pattern. However, conventionally, a negative resist has been used to obtain a reverse tapered resist pattern. However, this negative resist requires severe process conditions, making it difficult to obtain a desired inverted tapered resist pattern with good reproducibility. Therefore, in the actual process, formation of a reverse tapered resist pattern using a negative resist is not utilized.

Generally, when patterning a positive resist, the second
As shown in the cross-sectional view of FIG. 7A, the resist pattern 6 has a trapezoidal cross-sectional shape, in which the lower edge 7A of the side wall 7 extends beyond the upper edge 7B, that is, a tapered shape. When a metal film 8 is formed on such a tapered resist pattern 6 and lifted off, a burr 10 is formed on the upper edge of the metal film pattern 9, as shown in FIG. 2(b).

On the metal film pattern 9 having such a bar,
As shown in FIGS. 2(C) and (d), the interlayer insulating film 11
When the upper layer metal wiring 12 and the like are formed, a protrusion corresponding to the burr 10 is formed on the interlayer edge film 11, so that a disconnection 13 occurs in the upper layer metal wiring 12 as shown in FIG. 2(C). , as shown in FIG. 2(d), the upper layer metal wiring 12
There is a problem that a short circuit 14 may occur between the metal pattern 9 and the underlying metal pattern 9.

In order to prevent wiring abnormalities caused by such burrs,
Buttering is performed using a multilayer resist (insulating film 15, insulating film 16, and resist 17) as shown in Figure (a),
A method has been proposed in which a metal film 18 is evaporated thereon, lifted off, and then flattened as shown in FIG. 3 to eliminate burrs. However, the use of multilayer resists and planarization processes complicate the process.

Therefore, in order to easily form an ideal metal pattern by lift-off, it is desired to form a reverse tapered resist pattern using a single layer resist.

Further, the inverted tapered resist pattern can be used not only for forming a metal pattern by lift-off, but also for forming a lightly ion-implanted region around an ion-implanted region, such as in ion implantation of an LDD structure. Conventionally, when forming such an LDD structure, as shown in FIG. 4, an insulating film 20 is formed on a resist pattern 19, and the resist pattern 19 is side-etched to form a thin layer.
A mask was formed in which the insulating film 20 protruded like an eave. When ions are implanted through such a mask, the range of the eaves length ΔX becomes a lightly doped region.

However, even in this case, as shown in FIG. 1(a), if an inverted tapered resist pattern in which the upper 1t3A of the side wall 3 of the pattern overhangs the lower edge 3B by a length ΔX can be formed using a single layer resist, the process It is possible to simplify the process and improve alignment accuracy.

Problems to be Solved by the Invention As explained above, the reverse tapered resist pattern, which brings various advantages in the semiconductor manufacturing process, can only be achieved by using a multilayer resist, which complicates the process, or a negative resist, which has poor reproducibility. could not be formed.

Therefore, the present invention aims to provide a method for forming an inverted tapered resist pattern with excellent reproducibility and dimensional accuracy using a single layer film of positive resist that is easy to handle.

According to the present invention, a positive resist is applied to the wafer, and the focus value is set to be larger than the optimum value and the focus is set below the resist layer for exposure. A resist pattern forming method is provided that is characterized by forming a shaped resist pattern.

The operation will be explained with reference to FIG. When a positive resist film is formed on the wafer 50 and patterned by exposure, the resist pattern 52 will not change as shown in FIG. , the resist pattern has a trapezoidal cross-sectional shape with a narrow top, that is, a tapered resist pattern.

And only for the optimal focus value and optimal exposure time,
As shown in the resist pattern 54 shown in FIG. 5(a), its side walls are vertical.

Here, the optimal focus value and optimal exposure time are determined as follows. For example, prepare a focusing reticle with test patterns such as L-shaped line and space (L/S) formed at various intervals,
A resist film uniformly coated on a Si wafer is exposed to light while changing the focus value little by little. At this time, the exposure time is kept constant, usually at the minimum exposure time.

Develop the exposed resist, observe the lines and spaces (L/S), and determine the focus value when exposing the area where the minimum distance lines and spaces are formed to the optimum focus. Decided to work 1st shift. In this case, it is unclear where on the resist the focal point is, but it is probably on the resist surface.

Next, the focus value was fixed at the optimal focus value obtained in this way, and the resist film uniformly coated on the Sl wafer was exposed using the same focusing reticle while changing the exposure time little by little. do. and,
After development, the line and space (L/S) is observed, and the exposure time when the portion where the side walls of the resist are vertically formed is determined to be the optimum exposure time.

However, if the focus value is slightly increased, i.e., the focus is moved slightly toward the bottom of the resist, and the exposure is performed at the optimum exposure time, an inverted tapered resist pattern can be formed as shown in FIG. 5(C). Discovered by the inventor of the present invention. The factors that lead to the formation of a resist pattern in an inversely tapered shape are probably related to various conditions such as the resist film thickness, the refractive index of the incident light, and the underlying material, but it cannot be clearly determined. . However, when a positive resist film is exposed using the method according to the present invention described above,
A reverse tapered resist pattern can be formed with good reproducibility.

EXAMPLE Hereinafter, an example of a method for forming a reverse tapered resist pattern according to the present invention will be described. However, the following example
This is merely a specific example of the method for forming an inverted tapered resist pattern according to the present invention, and the present invention is not limited to the following examples.

Preparation Example Sl A positive resist sold under the trade name Sumirecyst PF6200 was placed on a wafer to a thickness of approximately 1.5 μm.
It was applied uniformly to m. Then, using a 1/10 reduction exposure device, the overfocus value (the amount by which the focus is shifted farther than the optimal focus value) is approximately 1.0 μm, and the exposure time is 0.2
In seconds, a line and space pattern was exposed.

After that, 2 of the developer sold under the product name 5OPD.
It was immersed in a 4°C bath for 60 seconds and exposed to light.

As a result, as explained with reference to FIG. 1(a), it was possible to obtain a reverse tapered resist pattern 56 in which the upper edge 3A of the side wall 3 extended by 0.2 μm from the lower edge 3B.

Effects of the Invention As described above, according to the method according to the present invention, a reverse tapered resist pattern can be formed using a single-layer positive resist film.

Therefore, by using the method for forming a reverse tapered resist pattern according to the present invention, an ideal metal pattern can be formed by the lift-off method using a simple process, and an ion implantation region with a concentration distribution can be formed using a simple process. . Therefore, it can be widely used in semiconductor manufacturing processes.
The semiconductor manufacturing process can be simplified and the yield can be increased.

[Brief explanation of the drawing]

FIG. 1(a) is a cross-sectional view of the reverse tapered resist pattern, and FIG. 1(b) and FIG. 1(C) are cross-sectional views of the reverse tapered resist pattern shown in FIG. 1(a). Cross-sectional views illustrating the formation of a metal pattern by lift-off method, FIG. 2(a) and FIG. 2 et al. Cross-sectional views illustrating formation by the pattern lift-off method, FIGS. 2(C) and 2(d),
FIG. 2(b) is a cross-sectional view illustrating the state in which the upper wiring layer is formed on the metal pattern, and FIGS. 3(a) and 3(b) are the metal FIG. 4 is a cross-sectional view illustrating pattern formation by lift-off method; FIG. 4 is a cross-sectional view of an ion implantation mask conventionally proposed for forming an LDD structure; FIGS. 5(a) to 5(C) 2 is a diagram illustrating the cross-sectional shape of a pattern obtained when the focus value during exposure of a resist film is changed. FIG. [Main reference numbers] 1150...Wafer 2.6.52.54.56...Resist pattern 3...
Side walls 3A, 7B of resist pattern... Upper edges 3B, 7A of resist pattern side wall
・Lower edge of resist pattern side wall 4.8 ・Metal film 5.9 ・Metal pattern 10 ・Paris

Claims (1)

[Claims] A method for forming a resist pattern, comprising applying a positive resist onto a wafer, setting a focus value larger than an optimum value, and exposing with the focus set below the resist layer to form an inverted tapered resist pattern.