JPS6076736A - Reduction of reflected light from molybdenum layer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the manufacture of integrated circuits, and more particularly, the present invention relates to the manufacture of integrated circuits, and more particularly, the present invention relates to the manufacture of integrated circuits, and more particularly, to the manufacture of integrated circuits. Relating to reducing.

Near the final step of the integrated circuit manufacturing process, C typically has a metal layer (eg, a molybdenum layer) placed on its surface. At this stage of manufacturing, the surface of the wafer on which the integrated circuits are to be formed is generally not flat and often includes steep steps.

If the metal layer is patterned by photolithography, the exposure to the photoresist 1 will be irregular due to the high reflectivity of the metal layer and the presence of steps in the substrate. As a result, the line width of the pattern etched into the metal layer using the patterned iB l-resist is non-uniform in the vicinity of the steps. Additionally, standing waves of radiation without reflection result in non-uniform exposures of the photoresist, resulting in non-uniform line widths of patterns in the metal layer located on flat portions of the substrate.

One of the objects of the present invention is to provide a method for substantially uniformly covering the exposure of a layer of photosensitive material located on the highly reflective surface of a molybdenum layer in an integrated circuit wafer.

It is also an object of the present invention to provide a simple method compatible with current manufacturing processes that helps reduce the negative effects of molybdenum reflective surfaces during the fabrication of integrated circuits. .

The present invention relates to a method for pre-treating a molybdenum layer in order to optically transfer a pattern from a mask imprinted with the pattern to the molybdenum layer by use of a layer of photosensitive material. According to one embodiment of the implementation of such a method, the molybdenum layer is formed at a temperature Jj and at a time f'1 sufficient to produce a molybdenum nitride layer on the molybdenum layer for reducing reflected light from the molybdenum layer. is exposed to ammonia vapor, and then a layer of photosensitive material is deposited on the molybdenum nitride layer.

The novel features believed to be inherent in the invention are pointed out with particularity in the appended claims.

The structure and method of carrying out the invention, as well as other objects and advantages thereof, will, however, be best understood by considering the following description in conjunction with the accompanying drawings.

Turning first to FIG. 1, there is shown a series of graphs depicting the relative reflectance of molybdenum surfaces coated with molybdenum nitride layers of various grades relative to exposed aluminum surfaces as a function of wavelength. To draw graph 11, a molybdenum layer with a thickness of 3000 angstroms was formed on a silicon wafer by sputtering, and the reflected light obtained from the surface was measured at each wavelength within the range of 200 to 400 nm. The reflected light obtained from the aluminum reference surface and the corresponding wavelengths were compared. Similarly, graph 1
2, a molybdenum layer with a thickness of 3000 angstroms is formed on a silicon wafer by sputtering, and then annealed for 30 minutes at 100°C, and the reflected light obtained from the surface is 200 to 4.0 Or+11.
This is determined by measuring at each wavelength within the range of 1 and then comparing the reflected light obtained from the aluminum reference surface with the corresponding wavelength. Graph 13 was claimed using a material in which a molybdenum layer was formed on a silicon wafer by sputtering, and then a 400 angstrom thick molybdenum nitride (MO2N) layer was formed thereon. In order to produce a darkening molybdenum nitride layer, the substrate with the molybdenum layer on its surface is placed in a horizontal open tube furnace, into which a mixture of 10% (by volume) ammonia and the balance nitrogen is added. Gas was flowed at a rate of 2 liters per minute.

The substrate was moved to an area in the furnace set at a temperature of approximately 500°C where it was removed from the furnace for 10 minutes. As a result, a thickness of approximately 4 mm is obtained that adheres tightly above the unreacted portion of the molybdenum layer and completely covers the top surface of the molybdenum layer.
A layer of molybdenum nitride of 0.00 Å was produced. The above method for producing molybdenum nitride on a molybdenum layer was published in 1982 by the same assignee as the present invention.
No. 3,626, filed March 29, 2005, the contents of which are incorporated herein by reference.

The light reflected from the surface of the molybdenum nitride layer having a thickness of about 400 angstroms was compared with the light reflected from the aluminum reference surface at each wavelength, and graphs 14, 15.
16 and 17 are 600.800.1400 respectively
and 22,007 J Angstroms of molybdenum surface coated with a layer of molybdenum nitride relative to an aluminum reference plane as a function of wavelength. Such thicknesses 600, 800, 1400 and 2200
An angstrom molybdenum nitride layer was produced on the molybdenum layer in 10 minutes according to the method described above using the respective furnace humidity. Various grades of molybdenum nitride (Mp2N) were produced on the sputter-formed molybdenum layer.
Generally speaking, compared to both the reflected light from the sputtered molybdenum layer and the reflected light from the annealed molybdenum layer shown in graph 11, However, as the thickness of the molybdenum nitride layer increases, the absorbed light increases and therefore the reflected light decreases.

The graph shown in Figure 1 relates to the relative reflectance of the layers of the display into the air. These graphs approximate one graph representing the relative reflectance from the display layer into the photoresist layer.

By using the graph in FIG. 1, it is possible to easily determine the thickness of the molybdenum nitride layer to be formed on the molybdenum layer in order to reduce reflected light during pattern formation. For example, assume that a layer of molybdenum nitride is illuminated with light at a wavelength of about 250 tv to expose a layer of photoresist, such as polymethyl methacrylate. Examining the graphs in FIG. 1, it can be seen that the 1400 angstrom thick molybdenum nitride layer produced on the sputter-formed molybdenum layer reflects approximately 35% of the light reflected from the aluminum reference surface, as represented by graph 16.
Therefore, it becomes clear that it is sufficient to use a molybdenum nitride layer having this thickness.

If desired, less than 40'O angstroms or 2
Graphs similar to graphs 13-17 can be obtained experimentally for molybdenum nitride layer thicknesses greater than 200 angstroms, as well as thicknesses intermediate to those shown in the graphs. Also, if desired, such a graph can be
It is also possible to extend wavelengths below 0 nm and above 400 nm.

The use of a molybdenum nitride layer not only has the desirable property of reducing light reflection from the surface of the sputter-formed molybdenum layer into the overlying photoresist layer;
It is also particularly advantageous in that it is compatible with subsequent processing operations of substrates with molybdenum patterns on their surfaces. That is, the molybdenum nitride layer formed on the molybdenum conductor is
Various chemicals (e.g. nitric acid and hydrogen peroxide) used in the manufacture of integrated circuits using molybdenum conductors, as well as reducing the passage of implanted and mobile ions.
It also reduces the corrosion of molybdenum and the formation of oxides. After patterning the resist layer, the molybdenum nitride and molybdenum layers are removed by use of a suitable dry etchant (eg, a mixture of carbon tetrachloride and oxygen). Note that when this mixed gas is used, the molybdenum layer is etched at a slightly slower rate than the molybdenum nitride layer.

If desired, a molybdenum nitride layer may remain on the molybdenum layer to achieve the above protection, or only the molybdenum nitride layer may be removed using a suitable etching agent, such as those described above. Additionally, the molybdenum nitride layer may be reconverted to molybdenum by exposing the molybdenum nitride layer to a reducing atmosphere of hydrogen under suitable temperature and time conditions; such methods are disclosed by the same assignee as in the present invention. 281, assigned April 1983, the contents of which are incorporated herein by reference.

Turning now to FIG. 2, there is shown a cross-sectional view of a structure 20 useful in illustrating a particular application of the method of the present invention.

First, it shows a resistivity of 10Ω・am and a crystal (100
A base plate 21 of P-type silicon semiconductor material 111 having a thickness of approximately 10 mils having a major surface 22 parallel to the ) plane is provided. After the cleaning treatment, the substrate was placed in dry oxygen for 100 min.
A silicon dioxide layer 23 having a thickness of 1000 angstroms is produced by 0''C'c oxidation. A layer 24 of molybdenum 24 having a thickness of 3000 angstroms is then formed on the silicon dioxide layer 23 by use of conventional sputtering equipment. Such a sputtering device is capable of converting carbon molybdenum into a silicon dioxide layer 23 by bombarding a molybdenum target with inert gas ions.
It is like being deposited on top. The substrate 21 with a molybdenum layer 24 on its surface is then placed in a horizontal open tube furnace into which a gas mixture of 10% (by volume) ammonia and the balance nitrogen is flowed at a rate of 2 liters per minute. It will be done. After moving the substrate to an area in the furnace set at a temperature of about 60° C. and exposing the substrate to a mixture of gases such as ammonia and nitrogen for 10 minutes, the substrate is removed from the furnace. As a result, a molybdenum nitride layer 25 having a thickness of approximately 140,071 Angstroms is produced which tightly adheres above the unreacted portions of the molybdenum layer 24 and completely covers the top surface of the molybdenum layer 24. It should be noted that the above method for producing a molybdenum nitride layer on a molybdenum layer is described in the aforementioned US Patent Application No. 3,62,682. As mentioned above, with this thickness of molybdenum nitride layer, 25
The light reflected from the molybdenum nitride layer at a wavelength of 0 nm is reduced to 35% of the light reflected from the aluminum reference surface. A suitable photoresist M26 is then placed on the molybdenum nitride layer. A suitable photoresist for such purpose is a photoresist such as PMMA (polymethyl metallurgical relay 1-) which is sensitive to light at a wavelength of 250 nm. A substrate 20 having various layers of materials on its surface is placed in a suitable device M (e.g., a photolithographic projection or printing device operating at a wavelength of about 250 nm) to form an image in the photoresist layer and then developed. will be held. By using a developed photoresist layer,
A pattern is etched into the molybdenum layer covered with the molybdenum nitride layer. Etching of such a pattern is accomplished using a suitable dry etchant such as a carbon tetrachloride and oxygen gas mixture as described above. The remaining photoresist layer is then removed. Thus 1! ? The resulting structure can be subjected to subsequent processing operations depending on the desired final structure of the integrated circuit.

One of the major advantages of using a molybdenum nitride layer as an anti-reflection coating on a molybdenum layer is that, as mentioned above, the molybdenum nitride layer can be utilized to preserve the molybdenum layer during subsequent processing operations. . If desired,
The molybdenum nitride layer can also be removed by a reactive ion etching process as described above. Furthermore, as described in the aforementioned U.S. Patent Application No. 489,613,
The molybdenum nitride layer can also be reconverted to molybdenum by exposing it to a reducing atmosphere (eg, hydrogen).

Although the invention has been described in connection with specific embodiments, it will be obvious to those skilled in the art that various modifications, such as those described above, may be made. It is therefore intended that the appended claims cover all such embodiments as do not depart from the spirit and scope of the invention.

[Brief explanation of drawings]

FIG. 1 shows the relative reflectance of various types of molybdenum nitride layers formed on a molybdenum layer to the exposed aluminum surface as a function of wavelength, and the relative reflectance of the sputtered molybdenum layer and the annealed molybdenum layer to the exposed aluminum surface. FIG. 2 is a cross-sectional view of a structure useful in explaining one embodiment of the invention. In the figure, 20 is a structure, 21 is a substrate, 22 is a main surface, 23 is a silicon dioxide layer, 24 is a molybdenum layer, 25 is a molybdenum nitride layer, and 26 is a photoresist layer. patent applicant

Claims (1)

[Claims] 1. In a method of pre-treating the molybdenum layer in order to optically transfer the pattern to the molybdenum layer from a mask with a pattern printed thereon by using an optical material layer, the molybdenum layer A method comprising: forming a molybdenum nitride layer on the molybdenum layer for reducing reflected light from the substrate; and then disposing the photosensitive material layer on the molybdenum nitride layer. 2. The molybdenum nitride layer is formed on the molybdenum layer by exposing the molybdenum layer to ammonia vapor under sufficient temperature and time conditions to form the molybdenum nitride layer. The method described in paragraph 1. 3. The molybdenum nitride layer has a composition of a2N
A method according to claim 1. 2. The method of claim 1, wherein the thickness is within about 2200 angstroms. 5. The method of claim 1, wherein the layer of photosensitive material is a photoresist layer sensitive to wavelengths within the range of about 200 to about 400 angstroms.