JPH02241023A - Pattern forming method - Google Patents

Abstract

PURPOSE:To form a pattern of extremely narrow width of high alignment precision for an alignment pattern by a method wherein an alignment pattern formed on a substrate is irradiated with charged particle beam in a material gas atmosphere, and generated secondary electron or reflected electron is detected, thereby performing alignment. CONSTITUTION:In a material gas atmosphere, an alignment pattern 2 formed on a substrate 1 is irradiated with charged particle beam 3. Secondary electron generated by the irradiation or reflected electron is detected, thereby performing alignment. For example, a semiconductor substrate 1 is arranged in a sample chamber of an electron beam irradiation apparatus; resist material gas like alkylnaphthalene is introduced; the pressure of the gas is kept about 10<-7>-10<-5>Torr. By the electron beam 3, the pattern 2 is scanned in the direction parallel with the upper side 2a; the semiconductor substrate 1 is moved in the arrow direction; the position of the upper side 2a of the pattern 2 is detected by the intensity of secondary electron emission. In this state, the substrate is canned along the upper side 2a by the electron beam 3. Hence a resist pattern 4 composed of amorphous hydrogencarbon is formed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a pattern forming method, and is particularly suitable for forming a pattern by irradiating a charged particle beam in a source gas atmosphere. It is.

[Summary of the invention]

In a pattern forming method, the present invention irradiates an alignment pattern formed on a substrate with a charged particle beam in a source gas atmosphere, and detects secondary electrons or reflected electrons generated by this irradiation. I'm trying to make adjustments. Thereby, it is possible to form a pattern with a very fine width with high alignment accuracy with respect to the alignment pattern.

[Conventional technology]

In recent years, the integration and density of LSIs have been increasing, and at the same time, research and development of quantum effect devices has also been actively conducted. In manufacturing these LSIs and quantum effect devices, it is important to form resist patterns with minute dimensions.

Electron beam lithography, X-ray lithography, and the like are known as techniques for forming resist patterns with such minute dimensions. In these electron beam lithography and X-ray lithography, a resist is first applied onto a semiconductor substrate, the resist is exposed to electron beams or X-rays, and then the resist is developed to form a resist pattern. do. In this case, especially when forming a resist pattern on a large-area semiconductor substrate or a semiconductor substrate that already has a structure after going through a process, it is necessary to determine the irradiation position of the electron beam or X-ray with high precision. occurs.

By the way, in conventional electron beam lithography and X-ray lithography, exposure is usually performed using a stepper type exposure device that does not have a mechanism for monitoring the beam irradiation position.

On the other hand, in direct exposure with an electron beam, in order to form a pattern with high overlay accuracy on the underlying pattern, the following exposure methods are known (molecular beam epitaxy technology, industrial research (1984), pp. 380-381), according to this method, alignment marks called fiducial (FD) marks are formed in advance at three points on the semiconductor substrate before exposure. At the start of exposure, the positions of these FD marks are detected using reflected electron signals to measure the deviation of the electron beam irradiation position, and the electron beam irradiation position is corrected based on this measurement result, and then exposure is performed.

In addition, when performing vector scanning electron beam exposure, alignment marks are formed in some corners of the field of view, and when the electron beam scans over these alignment marks, the reflected electrons (rearward A method is known in which the position of the alignment mark is detected by changes in the number of scattered electrons) and secondary electrons, and alignment is performed based on this (VLSI TECHNOLOGY, 5).
econd Bdition (1988).

McGraw-)fill Book Company
, p. 166).

[Problem to be solved by the invention]

In the conventional pattern forming method described above, the positioning accuracy of the beam irradiation position is determined by the mechanical accuracy of the movement of the stage on which the semiconductor substrate is placed, and is at best 0.1.
It is about μm. For this reason, it is difficult to determine the irradiation position with high accuracy for several hundred to several dozen people, and therefore it is difficult to form a pattern with high alignment accuracy.

An object of the present invention is to provide a pattern forming method that can form a pattern with a very fine width with high alignment accuracy with respect to an alignment pattern.

[Means to solve the problem]

In order to achieve the above object, the pattern forming method of the present invention includes an alignment pattern (2) formed on a substrate (1).
, 5) is irradiated with a charged particle beam (3) in a source gas atmosphere, and positioning is performed by detecting secondary electrons or reflected electrons generated by this irradiation.

Here, as the charged particle beam (3), in addition to an electron beam, a positron beam, a mini-on beam, etc. can be used. When using an electron beam, it is preferable to use a field emission electron gun that can generate an electron beam with good coherence.

[Effect]

When the substrate (1) is irradiated with the charged particle beam (3) in a source gas atmosphere, the source molecules adsorbed on the surface of the substrate (1) decompose, forming a pattern (4) consisting of the resulting substances.
) is formed in substantially the same shape as the irradiation pattern of this charged particle beam (3). In this case, the charged particle beam (3)
Since the beam diameter of can be made extremely small,
A pattern (4) with an extremely fine width can be formed.

Incidentally, the intensity of secondary electrons or reflected electrons generated by irradiation with the charged particle beam (3) differs depending on the type of material. Therefore, when the charged particle beam (3) is irradiated to the alignment pattern (2) formed in advance on the substrate (1) so as to cross this alignment pattern (2), this alignment pattern ( 2) and the intensity of the secondary electrons or reflected electrons generated from the substrate (1) that forms the background, it is possible to determine the type of material that makes up this alignment pattern (2) and the material that makes up the substrate (1). Accordingly, the intensity decreases or increases in the alignment pattern (2) portion. Therefore, the position of the alignment pattern (2) can be detected from this intensity pattern. This position detection can be performed with high accuracy comparable to the resolution of the charged particle beam (3), for example, with an accuracy of several tens of people.

As described above, the position of the alignment pattern (2) can be detected with high precision, so when forming the pattern (4) by irradiating the charged particle beam (3), the alignment with respect to the alignment pattern (2) can be performed. can be performed with high precision.

〔Example〕

Embodiments of the present invention will be described below with reference to the drawings. In all the figures of the embodiment, parts having the same function are given the same reference numerals, and repeated explanations will be omitted as appropriate.

Emperor's Five Earths 1A and 1B show Embodiment I of the present invention.

In this Example I, a scanning electron microscope (SEM)
An electron beam irradiation device having a similar configuration is used. As shown in FIG. 1A, first, for example, a semiconductor substrate 1 is placed on a stage in a sample chamber of this electron beam irradiation apparatus that is evacuated to a high vacuum (for example, about 3.times.10-' Torr). Specifically, this semiconductor substrate 1 is, for example, a gallium arsenide (GaAs) substrate. It is assumed that, for example, a rectangular pattern 2 has already been formed on this semiconductor substrate 1. This pattern 2 is used as an alignment pattern. Here, this pattern 2 may be a pattern that is actually used, or may be a dummy pattern that is used only for alignment. Next, a resist source gas such as alkylnaphthalene is introduced into the sample chamber. The pressure of this source gas in the sample chamber is, for example, about 10-' to 10-' Torr.

Now, consider the case where a linear resist pattern is formed in contact with the upper side 2a of the pattern 2 in FIG. 1A. In this case, since the position of this upper side 2a is not known in advance, the position of this upper side 2a is first detected as follows. In other words, while observing pattern 2 with SEM,
First, an electron beam 3 whose beam diameter has been narrowed to, for example, several tens of beams is scanned linearly in a direction parallel to the upper side 2a of the pattern 2 as shown by the dotted line. The scanning locus of this electron beam 3 is indicated by Sl in FIG.

By scanning the electron beam 3, secondary electrons are emitted from the pattern 2 and the semiconductor substrate 1. Then, these secondary electrons are detected by a detector such as a photomultiplier tube.

The secondary electron emission intensity pattern detected in this way is shown by the bottom curve in FIG. now,
The pattern 2 is a resist made of amorphous hydrocarbons (Electron Beam I
The resist made of amorphous hydrocarbon has a lower secondary electron emission ability than a semiconductor, and therefore, as mentioned above, in FIG. When the electron beam 3 is scanned as shown in FIG. 3, the secondary electron emission intensity drops in the pattern 2, as shown by the bottom curve in FIG. Next, while monitoring the secondary electron emission intensity in the same manner, the semiconductor substrate 1 is moved by the stage in the direction indicated by the arrow in FIG. 1A. This movement is performed until the electron beam 3 separates from the pattern 2. St and Ss in FIG. 3 is the locus when the electron beam 3 scans, and S3 is the locus when the electron beam 3 scans the semiconductor substrate 1 at a certain distance from the pattern 2.

The secondary electron emission intensity pattern when the electron beam 3 is scanned as shown by these Sz and Ss is as shown by the upper two curves in FIG.

From FIG. 3, it can be seen that the drop in the secondary electron emission intensity in the pattern 2 becomes smaller as the semiconductor substrate 1 is moved in the direction indicated by the arrow in FIG.
It can be seen that when the distance from pattern 2 increases, the secondary electron emission intensity becomes uniform. When the secondary electron emission intensity changes to a uniform state, the irradiation position of the electron beam 3 becomes pattern 2.
This is when it is located on the upper side 2a of . From this, it can be seen that the position of the upper side 2a of the pattern 2 can be detected by changing the secondary electron emission intensity pattern as shown by the top curve in FIG.

After detecting the upper side 2a of pattern 2 as described above,
In this state, the electron beam 3 is scanned along this upper side 2a. By scanning the electron beam 3, the raw resist molecules adsorbed on the surface of the semiconductor substrate 10 are decomposed, and as a result, as shown in FIG. It is formed in contact with the upper side 2a.

The resist pattern 4 thus formed is used, for example, as a mask when patterning the semiconductor substrate 1 into a very fine width by etching. By using the ultrafine semiconductor lines formed in this way, it is possible to manufacture, for example, a quasi-dimensional channel field effect transistor (FET).

As described above, according to this embodiment (2), the position of the upper side 2a of the pattern 2 is detected by detecting the secondary electron emission intensity when the pattern 2 is scanned by the electron beam 3, and the upper side 2a of the pattern 2 is detected. Since the resist pattern 4 is formed by scanning the electron beam 3 along the electron beam 3, the resist pattern 4 can be formed with an extremely fine width with an extremely high alignment accuracy comparable to the resolution of the electron beam 3 (~several tens of people). can be formed. Moreover, according to this method, by using a pattern already formed in the vicinity of the resist pattern 4 to be formed as the alignment pattern, alignment accuracy is high over the entire surface even when the semiconductor substrate 1 has a large area. resist pattern 4
can be formed.

Note that the irradiation of the electron beam 3 for the above-mentioned alignment is performed in the resist raw material gas atmosphere, but since the irradiation time of the electron beam 3 for this alignment can be sufficiently shortened, this alignment It can be considered that almost no resist growth occurs during this process.

Real m FIGS. 4A to 4C show Embodiment 2 of the present invention.

This Example (2) is an example in which the present invention is applied to the manufacture of a Schottky gate FET.

As shown in FIG. 4A, in this embodiment (2), a source electrode 5 and a drain electrode 6 are first formed on a semiconductor substrate 1, and then a metal film 7 for forming a gate electrode is formed on the entire surface by, for example, sputtering. do.

Specifically, this metal film 7 is, for example, a tungsten (W) film.

Next, which metal film 7 is patterned to form a Schottky gate electrode. Consider forming the source electrodes close to each other.For this purpose, it is necessary to form a resist pattern close to this source electrode 5, which will serve as a mask when patterning the metal film 7 by etching. In the same manner as above, the metal film 7 is scanned with the electron beam 3 while monitoring the secondary electron emission intensity.In this case, a step is created in the metal film 7 at a portion corresponding to the end of the source electrode 5. , the secondary electron emission intensity is smaller in this step part than in other parts. Therefore, from this secondary electron emission intensity pattern, it is possible to detect the end of the source electrode 5 in the same manner as in Example I. can.

After detecting the end of the source electrode 5 in this manner, the electron beam 3 is scanned linearly along the end at a position a short distance away from the end. As a result, as shown in FIG. 4B, a resist pattern 4 having an extremely fine width can be formed on the metal film 7 in the vicinity of the end of the source electrode 5.

Then, using this resist pattern 4 as a mask, the metal film 7 is anisotropically etched by, for example, reactive ion etching (RIB). By this, Figure 4C
As shown in FIG. 2, a Schottky gate electrode 8 having an extremely fine width is formed close to the source electrode 5, and the intended Schottky gate FET is completed.

As described above, according to this embodiment (2), the position of the end of the source electrode 5 is detected by monitoring the secondary electron emission intensity when the electron beam 3 scans the metal film 7. The resist pattern 4 can be formed with high alignment accuracy with respect to the source electrode 5, and thereby the Schottky gate electrode 8 can be formed close to the source electrode 5. Specifically, for example, when the distance between the source electrode 5 and the drain electrode 6 is about 1 μm, the Schottky gate electrode 8 and the source electrode 5
It is extremely easy to change the distance between, for example, 500 people. Since the Schottky gate electrode 8 can be formed close to the source electrode 5 in this way,
The series resistance between the source and gate can be made extremely small.

Moreover, since it is easy to make the width of the Schottky gate electrode 8, that is, the gate length, to a very fine width of, for example, several hundred to 1,000 lines, extremely high transconductance can be obtained.

From the above, it can be seen that according to this embodiment (2), an extremely high performance Schottky FET can be easily realized.

Although the embodiments of the present invention have been specifically described above, the present invention is not limited to the above-described embodiments, and various modifications can be made based on the technical idea of the present invention.

For example, in the above-mentioned embodiment I, (2), the electron beam 3
Alignment with respect to the pattern 2 and the source electrode 5 is performed by detecting secondary electrons generated by irradiation, but alignment can also be performed in the same way by detecting reflected electrons instead of secondary electrons. I can do it. Also,
The alignment pattern 2 in the above-mentioned embodiment (2) can also be made of metal, for example. However, −
In general, the secondary electron emission power of metals is higher than that of semiconductors, so in this case, when the pattern 2 made of this metal is scanned with the electron beam 3, the secondary electron emission intensity is equal to that of the pattern 2. Some parts are more expensive than others.

〔Effect of the invention〕

Since the present invention is configured as described above, it is possible to form a pattern with a very fine width with respect to the alignment pattern with high alignment accuracy.

[Brief explanation of drawings]

FIG. 1A and FIG. 1B are perspective views for explaining Embodiment I of the present invention in the order of steps, and FIG. 2 is a perspective view for explaining electron beam scanning for aligning the electron beam irradiation position. Figures 3 and 3 are diagrams showing secondary electron emission intensity patterns when an alignment pattern formed on a semiconductor substrate is scanned with an electron beam, and Figures 4A to 4C are diagrams showing the implementation of the present invention. FIG. 3 is a perspective view for explaining example (2) in the order of steps. gate electrode.

Claims (1)

[Claims] It is characterized by irradiating the alignment pattern formed on the substrate with a charged particle beam in a source gas atmosphere, and performing alignment by detecting secondary electrons or reflected electrons generated by this irradiation. A pattern forming method.