JPS6177326A - Photo mask - Google Patents

Abstract

PURPOSE:To contrive to improve the yield of element formation by eliminating the remainings of unnecessary metallic film at the time of lift-off by a method wherein an alignment mark formed in the first dark field region of a mask pattern is connected to the second dark field region except the alignment mark at least at one point, and each dark field region is isolated by a bright field region. CONSTITUTION:After a photo mask having an alignment mark is positioned to the semiconductor substrate, a metallic pattern is formed on the substrate by the lift-off method. The lift-off method enables the metallic film patterns 13 formed on the substrate 12 to be two-divided by a slit 14 coincident with the third dark field region 11 of the mask pattern. Here, the efficiency of mask alignment in the patterning process improves because the photo mask has an alignment mark 8 smaller than an alignment mark 9 of the substrate 12. Besides, the dark field region of the mask pattern has no isolated island regions; therefore, isolated island regions do not generate in the unnecessary part of the metallic film deposited on the substrate after patterning.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a photomask, and more particularly to a photomask provided with alignment marks suitable for carrying out a lift-off method.

[Technical Background of the Invention] Patterning of a metal film for forming electrodes on a semiconductor device involves: (1) depositing a metal film on an insulating film, etc. on a semiconductor substrate, and then forming a resist pattern on the metal film; A so-called etching method is used in which a metal film pattern is formed by etching the metal film using the resist pattern as a mask. After that, a metal film is deposited on the resist pattern, and then the resist pattern and the metal film portion on the resist pattern are removed (leaving only the metal film portion that is not on the resist pattern). A so-called lift-off method is used to form a metal film pattern.

Among these, the lift-off method has the following advantages: (a) There is no need to etch the metal film, so there is no pattern conversion error caused by side etching, and (b) there is no risk of the substrate being corroded by the etching solution. Because of this, it is easily attacked by fine pattern processing and etching liquid.
-GaAsME is suitable for electrode wiring processing of semiconductor devices on group V crystal substrates, which requires a fine electrode structure and whose substrate is chemically more unstable than silicon.
It is used for forming electrodes of SFET.

When forming a metal pattern using the lift-off method, the lift-off property (that is, the unnecessary part of the metal film on the resist pattern can be easily and completely peeled off, making it possible to form a precise metal pattern) characteristics) is an important issue, and in order to achieve good lift-off properties, the pattern shape as well as the material of the metal film are important. In particular, if the pattern shape is inappropriate, the lift-off properties will be poor and a perfect<'C metal pattern will not be obtained.

Generally, when attempting to form a metal pattern by the lift-off method, the pattern must be designed so that isolated island-like regions do not occur in unnecessary metal film parts. In the lift-off method, when removing an unnecessary metal film part on the resist, an external mechanical force is applied to the unnecessary metal film part to peel it off, so if there is an isolated island-like area in the unnecessary metal film part, This is because the peeling force is not transmitted to the region or the peeling force transmitted to other unnecessary metal film portions connected to the region becomes small, resulting in unnecessary metal film portions being left behind. If unnecessary metal film parts are left behind in this way, the unnecessary metal film parts will remain on the semiconductor substrate in an unstable state where they are about to peel off. It will adhere to the parts and cause problems in device formation.

Therefore, when performing the lift-off method, patterning and pattern shape are important issues, and the mask pattern of the photomask and the shape of the alignment mark provided on the mask also have a large impact on the accuracy of the lift-off method. .

The conventional mask alignment method and alignment marks in the lift-off method will be explained below with reference to FIGS. 5 to 7.

Figure 5 shows the state in which the semiconductor substrate and photomask have been aligned using conventional alignment marks.
2 is the dark field region of the mask pattern, 2 is the alignment mark of the mask pattern, and 3 is the alignment mark formed on the semiconductor substrate. When forming a pattern using a positive resist, the dark field region 1 of the mask pattern is a region where the resist remains on the semiconductor substrate, and is a region where unnecessary metal film portions are removed.

FIG. 6 is a plan view of a state in which unnecessary portions of the metal film deposited on the resist pattern have been lifted off (peeled off) after forming the resist pattern.
This is the metal film left on the surface.

When aligning with the semiconductor substrate 5 using a photomask having alignment marks 2 as shown in FIG. 5, the entire unnecessary metal film portion (dark field region 1 in FIG. 5) that is lifted off after metal film deposition is It is a continuous area, and this pattern formation is a consideration to facilitate peeling off of unnecessary metal film portions, as described above.

FIG. 7 shows a conventional target pattern for automatic mask alignment. In the figure, 6 is a target mark of a mask pattern of a photomask, 1 is a dark field area of the mask pattern, and 7 is an alignment mark formed on a semiconductor substrate.

[Problems in the Background Art] In the conventional patterning and metal pattern formation method using composite marks shown in FIG. Although the lift-off property is good, the alignment mark 2 on the photomask is larger than the alignment mark 3 on the semiconductor substrate, which causes the following problem.

As shown in Figure 5, if the alignment mark 3 on the semiconductor substrate is smaller than the alignment mark 2 on the photomask, it has been empirically shown that the efficiency of mask alignment on the mass production line is lower than the reverse case. Therefore, it is difficult to achieve highly accurate alignment using the patterning method using alignment marks as described above. For this reason, it is known that misalignment occurs frequently in the manufacturing process of semiconductor devices that requires high alignment accuracy, and as a result, the productivity of semiconductor devices is significantly reduced due to redoing the photolithography work.

Therefore, in order to prevent misalignment from occurring frequently in the patterning process, it is necessary to adjust the pattern accuracy of semiconductor devices (for example, G
In an As MES FET, it is necessary to make the source-gate spacing or gate-drain spacing coarse, but in a GaAs MESFET, increasing the source-gate spacing in particular increases the source parasitic resistance. This is not preferable because it diminishes the excellent high frequency characteristics (for example, high gain at high frequencies and extremely low noise figure).

On the other hand, in the conventional target pattern for automatic mask alignment shown in FIG.
(This is the part that will be lifted off after the metal film is formed) is isolated without being connected to the surrounding ll11 viewing area 1, so as described above, unnecessary metal film parts with poor lift-off properties are formed. Therefore, it was not a photomask alignment mark suitable for the lift-off method.

[Object of the Invention] An object of the present invention is to provide a photomask equipped with alignment marks suitable for the lift-off method.It is also an object of the invention to provide a photomask equipped with alignment marks suitable for the lift-off method. It is an object of the present invention to provide a photomask having alignment marks free from such problems.

[Summary of the Invention] The photomask according to the present invention is characterized in that the alignment mark formed in the first dark-field area of the mask pattern forms a second dark-field area other than the alignment mark and a third dark-field area in at least one place. each dark field region is separated by a bright field region.

The metal film pattern at the alignment mark-H of the semiconductor substrate lifted off by the photomask of the present invention has a structure in which the metal film pattern surrounding the alignment mark is cut at at least one place corresponding to the third dark field region. However, if desired, the metal film pattern of this structure can be used as an alignment mark for the semiconductor substrate in the next culm.

[Embodiments of the Invention] The present invention will be described in detail below with reference to FIGS. 1 to 4.

FIG. 1 shows a state in which alignment marks 8 on a photomask according to a first embodiment of the present invention and alignment marks 9 formed on a semiconductor substrate have been aligned.

In the figure, 8 is an alignment mark of the mask pattern (1, that is, the first dark field region), 9 is an alignment mark formed on the semiconductor substrate, 10 is the second dark field region of the mask pattern,
11 is a third dark field region interconnecting the first and second dark field regions.

FIG. 2 shows a photomask having alignment marks as shown in FIG. 1 and a semiconductor substrate, which are aligned as shown in the same figure, and then a metal pattern is formed on the semiconductor substrate by a lift-off method. In FIG. 2, 12 is a semiconductor substrate, 13 is a metal film pattern formed on the semiconductor substrate 12, and 9a is a part of an alignment mark formed on the semiconductor substrate 12. As shown in FIG. 2, when a lift-off method is performed using a photomask having alignment marks as shown in FIG. It is divided into two parts by a slit 14 that matches.

As shown in FIG. 1, the photomask of this embodiment has alignment marks 8 that are smaller than alignment marks 9 on the semiconductor substrate 12, so the efficiency of the mask alignment work in the patterning process is improved, and the mask Since there is no isolated island-like region in the dark field region of the pattern, no isolated island-like region is generated in unnecessary parts of the metal film deposited on the semiconductor substrate after pattern nintering.

FIG. 3 shows an embodiment of a photomask for automatic mask alignment. In the figure, 6 is the target mark of the mask pattern of the photomask (i.e., the first dark field region), 1 is the dark field region of the mask pattern (i.e., the second dark field region), and 15 is the target mark 6 and the dark field region 1. An additional third dark field region provided to connect the , 7 is an alignment mark provided on the semiconductor substrate. In the photomask of this example, like the photomask shown in Fig. 1, all the dark field regions are continuous and there are no isolated parts, so there is no risk of unnecessary metal film parts being left behind during the lift-off process. .

FIG. 4 shows a metal film pattern 16 formed on a semiconductor substrate by a lift-off method after patterning using the photomask shown in FIG.

As shown in the figure, this metal film pattern 16 has a shape divided into two regions by slits 17 and 18 due to the ability to remove unnecessary metal leg portions, and the slit 18 is open at the outer edge of the metal film pattern 16.

[Effects of the Invention] As shown in the above examples, when the lift-off method is performed using the photomask of the present invention, good lift-off performance is achieved because unnecessary metal film portions in isolated island-like regions are not generated. Therefore, no unnecessary metal film portions are left behind during lift-off, and the yield in the element forming process can be improved.

Furthermore, as shown in the first embodiment, since the alignment mark on the mask is smaller than the alignment mark on the semiconductor substrate, the accuracy and efficiency of the mask alignment work is improved, and therefore, for example, Ga
It is possible to reduce the polyelectronic current 4iilWws of As MES FETs, and as a result, it is possible to suppress parasitic factors that deteriorate device characteristics such as source resistance and drain resistance, and to manufacture Ga As MES FETs with good high frequency characteristics at high yield. can.

In addition, the present invention realizes a photomask for automatic mask alignment suitable for carrying out the lift-off method, so automatic mask alignment can be adopted in the lift-off process, and automatic mask alignment can be widely introduced to mass production lines. It became.

Note that in the above embodiment, only the case where the metal film is lifted off using a resist is shown, but instead of the resist, other films (for example, S+02, 3 + 3 Na, etc.) may be used.
and composite membranes thereof, etc.) can also be used, and
A 5i02 film (vapor deposited) may be used instead of the metal film.
These changes and some modifications are included within the scope of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a partially enlarged plan view of a photomask according to the first embodiment of the present invention that is aligned with a semiconductor substrate, and FIG. 2 is a partially enlarged plan view of a photomask according to the first embodiment of the present invention, which is patterned on a semiconductor substrate using a lift-off method after patterning with the photomask shown in FIG. FIG. 3 is a partially enlarged plan view of the photomask for automatic mask alignment according to the present invention in a state where the mask is aligned with a semiconductor substrate, and FIG. 4 is a plan view showing the metal film pattern formed in FIG. A plan view showing a metal film pattern formed on a semiconductor substrate by the lift-off method after patterning, FIG. 5 is a partially enlarged plan view of a conventional photomask aligned with the semiconductor substrate, and FIG. Figure 7 is a plan view of a metal film pattern formed on a semiconductor substrate by the easy lift-off method after patterning with a photomask, and Figure 7 is a partially enlarged view of a conventional automatic mask alignment photomask that is aligned with the semiconductor substrate. FIG. 1.10.11.15... Dark field area (of mask pattern), 2.7.8... Alignment mark (of photomask), 3,7.9... Alignment (of semiconductor substrate): mark, 4...metal film, 5.12...1 semiconductor substrate, 6...target mark, 13.16...metal film pattern, 14.17.18...slit. Figure 1 Figure 3 Figure 4

Claims (1)

[Claims] 1. The alignment mark of the first dark field area of the mask pattern formed on the photomask is connected to the second dark field area other than the alignment mark at least in one place via the third dark field area, and each dark field area is A photomask whose regions are separated by bright field regions.