JPH04233719A - Manufacture of semiconductor integrated circuit - Google Patents

Abstract

PURPOSE: To provide an integrated circuit process using a highly adhesive and chemically inert antireflective film consistent to other process. CONSTITUTION: An antireflective film 21 used in an integrated circuit is an X-silicon nitride thin film; where X is a metal selected among Ti, Va, Cr, Zr, Nb, Mo, Hf, Ta and W. This thin film is pref. formed by the sputtering in an N-contg. atmosphere.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to thin coating technology, and more particularly to a method for manufacturing semiconductor integrated circuits using antireflection coatings.

0002

2. Description of the Related Art One step in the manufacture of semiconductor integrated circuits is the formation of a conductor pattern on a semiconductor substrate by masking and etching using photolithography. This step typically requires a continuous expanse of metal film insulated from the substrate by a dielectric layer. The photoresist coating on the metal layer is selectively exposed to actinic radiation through a mask that defines the desired pattern. The photoresist coating is developed so that it now constitutes a mask with openings defining the desired conductor pattern. In modern integrated circuit technology,
Reactive ion etching is often used to selectively etch exposed metal down to the dielectric layer. The remaining photoresist is then removed, leaving the desired conductor pattern on the dielectric layer.

The trend toward increased circuit density requires greater control of photolithographic processes to meet more stringent requirements for conductor patterning. Protrusion reflections of actinic radiation from the metal film tend to blur the edges of the pattern being created. Dye photoresists can be used to reduce the effects of such reflections, but such compounds are thickness, shelf life, and chemical formula dependent and, as a result, do not give reliable uniform results. Therefore, it has been recognized that a separate antireflective coating should often be wrapped between a metal layer and a photoresist film in integrated circuits that are fabricated with a high degree of precision.

0004

Various compounds that have been proposed for use as photolithographic antireflective coatings include titanium nitride, titanium-tungsten, silicon nitride, and amorphous silicon. We have found that these various known antireflective coatings have distinct disadvantages, particularly for use in gallium arsenide integrated circuits using aluminum conductors. For example, titanium nitride produces very high stresses when applied over aluminum, which causes adhesion and other problems. Silicon coatings tend to react with aluminum and also have non-reflective properties that are highly dependent on thickness. Therefore, it is necessary for the industry to fully recognize the antireflection coatings described below. That is, anti-reflective coatings are robust in the sense that extreme care is not required to control their properties and are resistant to the use of metals such as aluminum and subsequent device processing steps such as reactive ion etching. It must be chemically stable, capable of adhering well to materials such as aluminum, and its use must be consistent with other process requirements in the fabrication of integrated circuits, particularly gallium arsenide integrated circuits.

[0005]

[Means for Solving the Problems] According to the present invention, metal-
Many advantages and benefits can be obtained by using silicon-nitride compounds as antireflective coatings. The film is preferably formed by sputtering from a metal silicide target in a nitrogen-containing atmosphere. This metal is preferably
One of the materials selected from titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten. Metal silicide targets or separate metal and silicon targets are used for sputtering.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In FIG. 1(a), a semiconductor substrate 11 is shown schematically (not to scale). This semiconductor substrate 11
is typically gallium arsenide, upon which it is desired to form integrated circuits using known photolithographic processes. Overlying the semiconductor substrate is a layer 12 of dielectric material, such as silicon oxynitride. Overlying the dielectric layer 12 is formed a layer 13 of a metal, such as aluminum, in which it is desired to form a conductive pattern. Overlying the metal layer 13 is formed a layer 15, typically an organometallic material known as a photoresist, which is sensitive to actinic radiation. A pattern in photoresist layer 15 is formed by selectively exposing the photoresist layer through a patterned photomask 16 having openings 17 to actinic radiation as indicated by arrows.

After photographic exposure, the photoresist layer 15 is
The final photoresist layer 15 defined by the photoresist layer 15 with openings 19 is developed, typically by etching the exposed portions to actinic radiation and removing it, as shown in FIG. 1(b). Leaves a pattern. In order to accurately perform the photolithography process, it is necessary to
) is required to match the opening 17 in the photomask 16 of FIG. 1(a) as closely as possible. Metal layer 13 in FIG. 1(a)
is typically fairly highly reflective so that light is reflected from its surface to provide a bump exposure to a portion of photoresist layer 15. This has the effect of obscuring the edges of opening 19 in FIG. 1(b), thus resulting in etching parts of the photoresist mask that do not coincide with the openings in the photomask at all. To overcome this problem,
In the prior art, as shown in FIG. 1(a),
An antireflection film 2 is provided between the metal layer 13 and the photoresist layer 15.
It is known to contain 1. Such a film is made of a material that has low reflectance and adheres well to the metal layer 13,
It is usually important to have properties that are suitably non-reactive and invariant to the processing steps to which it is subjected.

In FIG. 1(c), photoresist layer 1
5, the antireflection layer 21 is provided only in the portion that coincides with the opening 19.
and is commonly used as an etch mask to allow etching of the metal layer 13. For example, known reactive ion etching techniques may be used to selectively etch aluminum without etching any of the silicon oxynitride dielectric layer 12. After the conductor pattern is defined in this way, the photoresist film 1
5 is normally etched, resulting in the structure shown in FIG. 1(d). Although it is customary in the prior art to also remove the anti-reflective coating 21, as will be explained later, according to the invention it is convenient to leave the patterned anti-reflective coating in place.

In the present invention, antireflection coating 21 is a thin layer of metal-silicon-nitride. wherein the metal is a metal selected from titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, tungsten. It is deposited by sputtering using a device. FIG. 5 schematically shows a sputtering reactor 23 with a cathode 24 and an anode 25. FIG. The substrate 26 to be coated is supported by a support 27 which is kept at an anodic potential. The reactor is evacuated with a vacuum pump 28 and a controlled amount of argon from a source 29 is introduced into the reactor in a controlled manner. The cathode is energized by a direct current (DC) power source 31 that generates a plasma between the anode and cathode electrodes. As is known, radio frequency (RF) power sources can be used instead. Target 32 faces substrate 26 and consists of the material desired to be deposited at cathodic potential. Using low pressure argon, e.g. 25.0 μmHg argon, positive argon ions are bombarded with target 32 by appropriate DC power, thereby causing substrate 2
Sprinkle the target material to be coated onto 6. A more complete description of modern sputtering techniques is provided by A. J
．． Aronson, "Fundamentals of Sputtering" in Microelectronics Manufacturing and Testing, January 1987, pages 22 and 23, and R. L. Maniscallo et al., Hybrid Circuit Technology, September 1984 issue, pp. 19-23.
This is described in the paper ``Metallization for Hybrid Devices''. "Sputtering"
is well understood in the art to mean the volume from the plasma due to the collision of molecules onto the target, and is used interchangeably.

In one embodiment of the invention, target 32 is made from tungsten silicide. Nitrogen from source 33 is mixed with argon and injected into the reactor to create a nitrogen and argon plasma. As a result, an anti-reflective coating is formed on the tungsten-silicon-nitride (WSiN) substrate 26.

The actual machine used to form the anti-reflective coating of the present invention is a machine known as the MRC943 sputtering machine, available from Materials Research, Inc. of Orangeburg, New York. A valve, shown schematically as 34 in Figure 5, was used to control the introduction of argon and nitrogen. Table 1 shows the parameters for the deposition of various films of WSi0.45 and WSiN.
Shown below.

0012

[Table 1]

This Table 1 shows the parameters of two WSiN materials, one deposited at high DC power and called WSiN-G, and the other deposited at lower power and called WSiN-HR. It is called. Table 1
"Target constituents" refers to the ratio of tungsten to silicon in the tungsten-based target. μmH
"Pressure", expressed in g, indicates the total gas pressure in the reactor. "% Nitrogen" refers to the percentage of nitrogen in the total input gas. With MRC943 sputtering machine,
The substrate is moved laterally relative to the gas plasma during deposition. That is, "rate" indicates the thickness, in angstroms, of material deposited per traverse or "pass" of the substrate in the plasma. "Sample velocity" refers to the speed in centimeters per minute of the substrate passing through the plasma.

FIG. 6 is a graph of relative reflectance versus wavelength in nanometers for different films made with the deposition parameters of Table 1. Relative reflectance is the reflectance scaled with respect to the reflectance of aluminum. In other words, the reflectance of aluminum is 100, as depicted by curve 35.
% taken. Curve 36 shows the relative reflectance of WSi0.45 prepared using the deposition parameters of Table 1 and coated to a thickness of 250 Angstroms. It can be seen that the reflectance of this film is between 50 and 70 percent that of aluminum and therefore provides an effective anti-reflection effect. Curve 37 represents W with a thickness of 300 angstroms.
The relative reflectance of SiN-G is shown. It can be seen that this provides an effective anti-reflection effect over curve 36. Curve 38 shows the relative reflectance of 300 angstrom thick WSiN-HR. It has a reflectance of only about 6% of that of aluminum over its useful wavelength range.

FIG. 7 shows the change in relative reflectance at a wavelength of 436 nanometers versus film thickness (in Angstroms) for three antireflective coatings. Curve 40 is WSi
0.45, curve 41 is WSiN-H
The curve 42 depicts the change in reflectance for WSiN-G. Generally, the thickness of the anti-reflective coating for optimal anti-reflective effectiveness is between 125 and 75 mm.
It can be seen that it is between 0 angstroms. This indicates that the anti-reflection coating produced by the anti-invention is not significantly dependent on thickness.

FIGS. 6 and 7 show that although the WSi0.45 antireflection coating provides a useful effect, a much greater effect in terms of low relative reflectance can be obtained from WSiN. Figure 7 is effective, meaning that it does not require extreme care to be deposited to the appropriate thickness. The WSi0.45 embodiment has the advantage of not requiring nitrogen input, and the antireflection effect obtained therefrom is acceptable, depending on the process requirements.

[0017] The film called WSiN-G is
μm) is higher and is fabricated using the method used to fabricate WSi gate electrodes for field effect transistor components of integrated circuits in gallium arsenide integrated circuit fabrication, except that the process uses nitrogen, which is not used in the gate process. . The good antireflection results of the present invention, as shown by curve 37 in FIG. 6 and curve 42 in FIG. parameters can be used for anti-reflective coating fabrication, thereby eliminating the need for separate coating equipment for anti-reflective coating fabrication. Although the parameters of WSiN-HR are very different from those of WSiN-G, the anti-reflection properties are also very effective. This shows that careful control of the spalling process parameters is not critical to obtaining good antireflection effects. All of the above considerations point to the fact that the anti-reflective coating process is a "robust" process step in integrated circuit fabrication. All coatings were tested and exhibit good stress properties at the aluminum contact surface indicating good long-term adhesion to the aluminum. The films are tantalum-silicon-nitride (TaSiN) and titanium-silicon-nitride (TiSiN) deposits, but using different equipment than that shown in FIG. The equipment used here was
MRC sputtering equipment (Material Research)
ch Corporation). Metal targets are operated in DC magnetron mode and silicon targets in RF magnetron mode. The sample is rotated under two targets and deposited in very thin layers. Deposition parameters are given in Table 2.

[0018]

[Table 2]

The moving speed of the sample is given by the rotational speed. Separate targets are used and metal/silicon ratios are given in place of target component ratios. For comparison, a pure amorphous silicon anti-reflection coating was also used and the parameters of that coating are given as well.

FIG. 8 shows a relative reflectance versus wavelength curve 44 for a tantalum-silicon-nitride film and a relative reflectance versus wavelength curve 45 for a titanium-silicon-nitride film. Absorption becomes very high in the wavelength range of 400-500 nm. FIG. 9 shows the relationship between relative reflectance versus film thickness at a wavelength of 436 nm. Curve 47 is for a pure silicon film, and curve 48 is for a tantalum-silicon film.
This is the case for nitride films. Tantalum-silicon-nitride films and titanium-silicon-nitride films have much lower reflectivities than that of amorphous silicon films. Particularly low at thicknesses of 200-350 angstroms.

Titanium, tantalum, and tungsten are known as refractory metals. Titanium belongs to group IV of the periodic table, tantalum belongs to group V, and tungsten belongs to group V.
Belongs to group I. In this sample, the refractory metal reacts with silicon and nitrogen to form a metal-silicon-nitride that functions well as an anti-reflective coating and has many of the properties described above. Thus, the present invention provides an X-silicon-nitride (where X is titanium, vanadium, chromium,
Zirconium, niobium, molybdenum, hafnium,
including the use of tantalum, tungsten).

[0022] Aluminum is known to react well with various semiconductor materials, including silicon, and is susceptible to the formation of an aggravation known as electromigration. With respect to FIG. 1(d), we have found that the antireflection coating 21 formed according to the present invention also serves as a very good protective layer for the aluminum conductor 13. The coating adheres well, prevents electromigration, and maintains its properties under conditions of successive integrated circuit processing. and it is,
It also serves as a protective layer during long-term use of the device as an integrated circuit. As another advantage, the etching equipment for the aluminum layer 13 in general can also be easily used to etch the anti-reflective coating formed according to the present invention. Another advantage is that, like dielectric materials, antireflective coatings formed according to the present invention can be etched in a CF4 plasma. It is advantageous to remove the antireflection coating along with the dielectric in a common plasma to ensure good electrical contact to the underlying aluminum layer. For the sake of brevity, we will not restate those dependent processing steps in which antireflective coatings find benefit.

The present invention was made during the development of a gallium arsenide integrated circuit process using aluminum conductors, and the effects of the present invention have been explained above. The present invention is used with metals such as gold, tantalum and tungsten used in integrated circuit processing, and also as an anti-reflective coating for bare silicon. The present invention includes silicon,
It is also applicable to processes for making integrated circuits from other semiconductor materials such as indium-phosphide. Various AR
C films can also be made by alternating sputtering from separate refractory metal targets and silicon targets. If each layer is small enough (e.g. less than 50 angstroms), complete reaction of the contacting layers will occur and the metal-
Form silicon-nitride.

Visible light constitutes only one band of the electromagnetic spectrum. Electromagnetic radiation other than visible light is used to selectively expose photoresist or other radiation sensitive materials. Various modifications of the present invention can be devised by those skilled in the art, but all of them are included within the technical scope of the present invention.

[Brief explanation of the drawing]

FIG. 1 shows successive steps of a photolithography process in which an embodiment of the invention is used.

FIG. 2 is a schematic diagram illustrating a sputtering apparatus for depositing an antireflection coating according to an embodiment of the invention.

FIG. 3 is a graph showing the relationship between relative reflectance and wavelength of various antireflection coatings formed according to the present invention.

FIG. 4 is a graph showing the relationship between relative reflectance at a wavelength of 436 nanometers and film thickness for various antireflection coatings formed according to the present invention.

FIG. 5 is a graph showing the relationship between relative reflectance and wavelength of various antireflection coatings formed according to the present invention.

FIG. 6 is a graph showing the relationship between relative reflectance and thickness of various antireflection coatings.

[Explanation of symbols]

11 Semiconductor substrate 12 Dielectric layer 13 Metal layer 15 Photoresist layer 16 Photomask 21 Anti-reflection film

Claims (18)

[Claims] 1. Covering a reflective surface of a substrate with an anti-reflective coating; covering the anti-reflective coating with a radiation-sensitive material; and passing electromagnetic radiation through a patterned mask to form a pattern. selectively exposing a sensitive material to electromagnetic radiation; selectively removing the radiation-sensitive material according to the pattern to form a patterned mask; - A method for manufacturing a semiconductor integrated circuit, which is a compound containing nitride, and the material X is a material selected from titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, and tungsten. 2. The method according to claim 1, wherein the antireflection coating is formed by sputtering. 3. The method of claim 2 further characterized in that the reflective surface of the substrate has a coating of aluminum. 4. A method according to claim 3, characterized in that the mask is used as a pattern for selectively etching the aluminum and the antireflection coating. 5. The method of claim 4, wherein the sputtering is performed in an atmosphere containing nitrogen, and the antireflective coating is a compound containing tungsten, silicon, and nitrogen. 6. The method of claim 1, wherein the antireflection coating is a tungsten-silicon-nitride compound. 7. The method of claim 1, wherein the antireflection coating is a titanium-silicon-nitride compound. [Claim 8] The antireflection film is made of tantalum-silicon.
2. The method according to claim 1, wherein the compound is a nitride-containing compound. 9. The method of claim 2, wherein the sputtering step uses a single target comprising tungsten and silicon and the antireflective coating has a thickness of 125-750 angstroms. 10. The sputtering step uses two targets, one target containing silicon and the other target containing titanium, vanadium, chromium,
Zirconium, niobium, molybdenum, hafnium,
3. The method of claim 2, further comprising a material selected from the group consisting of tantalum and tungsten. 11. Forming a dielectric layer on the semiconductor layer, forming a metal layer on the dielectric layer, and forming an X-silicon-nitride antireflection film on the metal layer. wherein material X is a material selected from titanium, vanadium, chromium, zirconium, niobium, molybdenum, hafnium, tantalum, tungsten; selectively exposing the photoresist material to light by directing the light through the patterned mask onto selected areas of the photoresist material to form a patterned mask with the remaining photoresist material; selectively removing the photoresist material according to the pattern to form a conductive pattern of the metal layer on the dielectric layer; using a patterned mask to etch the integrated circuit. 12. The antireflection coating is formed by first placing a metal layer in a sputtering reactor having a target of material X and a silicon target, and including nitrogen between the metal layer and the target. establishing a low pressure atmosphere and transferring molecules from the target onto the metal layer by the plasma to generate a plasma between the metal layer and the target to produce an X-silicon-nitride coating on the metal layer; ionizing the atmosphere with sufficient energy to be sputtered;
12. A method according to claim 11, characterized in that the method comprises: 13. A method according to claim 12, characterized in that the metal layer consists of aluminum. 14. The method of claim 13, wherein the antireflective coating has a thickness of 125 to 750 angstroms. 15. X-silicon-nitride has the chemical formula T
15. The method of claim 14, comprising iSiN. 16. X-silicon-nitride has the chemical formula T
15. The method of claim 14, comprising aSiN. 17. Forming a dielectric layer on the semiconductor layer, forming a metal layer on the dielectric layer, and forming a tungsten-silicon-nitride anti-reflection film on the metal layer. selectively coating the photoresist material by directing light through a patterned mask onto selected areas of the photoresist material to form a pattern; exposing the remaining photoresist material to form a patterned mask, selectively removing the photoresist material according to the pattern, and forming a conductor pattern of the metal layer on the dielectric layer. , using a patterned mask to selectively etch exposed areas of the anti-reflective coating and the metal layer. 18. The anti-reflection layer is formed by first placing a metal layer in a sputtering reactor with tungsten and silicon targets and applying a low pressure atmosphere containing nitrogen between the metal layer and the target. Establishing a tungsten-silicon layer on the metal layer.
ionizing the atmosphere with sufficient energy to cause molecules to be sputtered from the target onto the metal layer by the plasma to create a plasma between the metal layer and the target to produce a nitride coating; 18. The method of claim 17, comprising: