JPS6081828A - Fine pattern forming process - Google Patents

Abstract

PURPOSE:To enable to form finely thin patterns by a method wherein the first grade thin pattern is formed within a recess formed by etching process and then the second grade thin pattern is formed. CONSTITUTION:Resist pattern 43 to form ohmic metal pattern are formed on the surface of an active layer 42 formed on a semi-insulating GaAs substrate 41. At this time, before coating the active layer 42 with an ohmic metal, the active layer 42 is etched utilizing the resist pattern 43 as mask making the etching depth similar to the metal thickness. Later the surface of GaAs substrate may be flattened by means of coating it with ohmic metal 44 and lifting off the same. The surface is heat-treated to come into ohmic contact with the active layer 42. Next a Schottky gate metallic pattern is formed in a region 45 between the ohmic metals on the surface of the active layer 42. An opening 47 to form a minute gate may be formed with excellent precision since resist 46 to form patterns may be coated with even thickness due to flattened surface of GaAs.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field] The present invention relates to a method of forming a fine thin film pattern on a semiconductor substrate.

[Background technology]

As is well known, in the manufacture of semiconductor devices and the like, with the demand for higher integration, techniques for forming fine patterns of 1 μm or less are required. Fine pattern formation methods can be roughly divided into
■Lift-off method and ■Etching method.

In the lift-off method, as shown in FIG. 1(, ), a photoresist pattern 12 is first formed on a semiconductor substrate 11, and a desired thin film 18 is deposited thereon by a vapor deposition method or the like.
Thereafter, unnecessary parts of the thin film formed on the resist film are removed together with the resist, and a thin film 28 is deposited on the surface of the thin plate 21 on the semiconductor substrate 11 as shown in FIG. 1(b). , forming a sea resist pattern 22' thereon,
Next, as shown in FIG. 1 Φ), the thin film 8 is selectively etched using the resist pattern as a mask, and the resist is further removed to obtain a desired thin film pattern 23'.

The resist pattern in the above-mentioned lift-off method and etching method is usually formed by a contact exposure method. This is a method in which a resist coated on the entire surface of a semiconductor substrate is selectively exposed and developed through a mask pattern to form a resist pattern. In order to form a fine pattern, the uniformity of the resist film thickness and the adhesion between the photomask and the resist surface are important issues.

Let us consider the case where a second thin film pattern is formed in a region 31' between 34 on the surface of the semiconductor substrate 81 where the thin film pattern 84 is formed. The surface of the resist 82 coated on the entire surface is not flat, and due to the step difference at the end of the first thin film 84, a low step d' occurs above the region 81'. d
The size of ' becomes smaller as the distance between the regions 34 becomes smaller, but the resist thickness d on the region 31' becomes thicker than on other parts, and the uniformity of the resist thickness is lost. The sizes of d' and d affect the accuracy of the opening 32'' of the formed resist pattern 82' as shown in FIG. 8(b). It is considered that the resist thicknesses of the thin film 34 are approximately equal. At this time, d' is approximately equal to the thickness of 34. At this time, the photomask is
It does not come into close contact with the resist surface on 1', but is separated by a distance d'. Therefore, the dimensional accuracy deteriorates, and the opening width l differs from the dimension on the photomask.

When L is small, d' is small and the mask adhesion is good, but the resist thickness d becomes large and the exposure and development conditions are different between the resist openings 32'' and 32'' above 34. Become. Therefore, it is difficult to control the dimensional accuracy of the minute opening 82'' with good reproducibility.

That is, when the first type thin film pattern has already been formed on the surface of the semiconductor substrate and there is a step on the surface, uniformity of the resist film thickness and adhesion between the photomask and the resist surface are not compatible.

[Disclosure of the invention]

The present invention eliminates such inconveniences and provides a method for forming fine thin film patterns.

The present invention will be described in detail below using the manufacturing process of a GaAs Schottky barrier field effect transistor as an example.

In FIG. 4(a), semi-insulating GaAs substrates 4, 1
A resist pattern 418 for forming an ohmic metal pattern is formed on the surface of the active layer 42 formed above. Conventionally, ohmic metals were deposited using this resist pattern as a mask and then lifted off. Therefore, as described above, a step equal to the thickness of the ohmic metal (for example, approximately 200X) is generated on the surface 1 of the GaAs substrate. In the present invention, the resist pattern 48 is used as a mask before the ohmic metal is deposited on the active layer 42, as shown in FIG.
Add an etching process.

This etching depth is comparable to the ohmic metal thickness.

Thereafter, an ohmic metal 44 is deposited and lifted off, so that the surface of the GaAs substrate becomes flat.

In order to obtain ohmic contact with the active layer, the substrate is heat-treated at 400° C. for 4 minutes in N2 gas. Next, a Schottky gate metal pattern is formed in the regions 4 and 5 between the ohmic metals on the surface of the active layer 5. Resist for Schottky metal Bakoon formation) 4.6. Since the GaAs surface is flat compared to the conventional method, it can be coated with a uniform thickness, and therefore the openings 4 and 7 for forming fine gates (for example, gate length 0.5 μm) can be formed with high precision. (Same figure (C))
. By lift-off forming the gate metal 48 using the resist patterns 4 and 6, a Schottky barrier field effect transistor can be formed as shown in FIG. 4(d).

The gate length g of the Schottky barrier field effect transistor formed according to the present invention corresponds precisely to the dimensions of the photomask pattern, and a fine gate can be obtained with better reproducibility than in the conventional method.

Reducing the gate length Lg is an indispensable task for increasing the frequency of transistors, and the present invention can achieve this relatively easily.

As can be seen from the above description, the present invention merely adds an etching step to the conventional process, and in some cases does not require changing the photomask.

6- Therefore, it is clear that the present invention is highly effective in forming fine patterns without adding complicated steps.

As another example, in FIG. 4(C), before depositing and forming the gate metal, regions 4 and 5 are etched using photoresists 4 and 6 as masks, and then a gate metal pattern is formed by lift-off. It is also possible.

The cross-sectional shape of the Schottky barrier field effect transistor in this case is schematically shown in FIG. The active layer thickness a' directly under the Schottky gate 58 is one parameter that determines the characteristics of a field effect transistor, and this value is

[Brief explanation of drawings]

Figure 1 (,) (b) is a diagram showing a thin film pattern forming method using a conventional lift-off method, Figures 2 (,) and (b) are diagrams showing a thin film pattern forming method using a conventional etching method, and Figure 3 is a diagram showing a thin film pattern forming method using a conventional etching method.
Figures (,) and (b) are diagrams showing problems in the conventional pattern forming method, Figure 4 (a), (b), (C) and (d)
5 is a diagram showing an embodiment of the present invention, and FIG. 5 is a diagram showing a modification of the embodiment of the present invention. 11.2331.41.51...Semiconductor substrate 12.2
2', 82', 4 3.4 (6... Photoresist patterns 13', 28', 84... 1st thin film pattern 4.2
52... Active layer 4+4'', 54... Ohmic metal 48.58... Gate metal (0), 2+, 21 Figure 2 (O) ~ 41 (d)

Claims (2)

[Claims] (1) A first type thin film pattern is formed on the surface of the semiconductor substrate, and the distance between the peripheral parts of the thin film pattern is several μm or less, in a region narrowed between the first type thin films on the semiconductor surface, In the process of newly forming a second type of thin film pattern, the surface of the semiconductor substrate is etched using the photoresist pattern for forming the first type of thin film pattern as a mask, and then the first type of thin film pattern is etched into the recesses formed by the etching. A fine pattern forming method characterized by forming a thin film pattern, and then forming a second type thin film pattern. (2) The method for forming a fine pattern according to claim 1, wherein the first type thin film is an ohmic metal, and the second type thin film is a gate metal.