JPS6248752B2 - - Google Patents

Description

[Detailed description of the invention]

[Background of the Invention] The present invention relates to a technique for forming a thin tungsten film on a substrate, and more specifically, for forming an adhesive tungsten film on a dielectric surface such as silicon dioxide or silicon nitride. Concerning the method. In the manufacture of semiconductor devices, it is often desirable to deposit thin metal layers or films on various dielectric surfaces to form components of integrated circuits. This process of depositing metal films is often called "metallization." Because the stresses associated with the layers obtained by metallization vary, and the degree of chemical bonding at the interface between such layers also varies, some metals may not adhere well to dielectrics. It turns out that this is true. One example is tungsten deposited on silicon dioxide by chemical vapor deposition (CVD). This means that the Journal of
The Electrochemical Society (Journal)
of the Electrochemical Society, Vol. 121, No. 2, pp. 298-303, CMMelliar-Smith et al., ``Chemical Vapor Deposited Tungsten for Semiconductor Metallization.'' However, it is still desirable to form an adherent tungsten film on the dielectric surface.
This is because tungsten exhibits high electrical conductivity and does not migrate (as does aluminum) even in areas of small film thickness and high current density. Such a migration phenomenon is often referred to as "electromigration," and it can cause parts of the metallization layer to separate. Furthermore, silicon can dissolve in aluminum, and if the two come into contact, the silicon will invade the aluminum surface, creating a void between the two surfaces. This phenomenon is often called "spiking." Because silicon does not dissolve in tungsten, and because tungsten has a high dielectric constant and resistance to electromigration, efforts have been made to fill contact and interconnect holes in integrated circuits with tungsten. An example is U.S. Patent Application No. 733,445, dated May 1985.
Examples include the method disclosed in the patent specification. In such methods, tungsten is deposited selectively on metal and semiconductor surfaces, and the adhesion is satisfactory. Note that with such methods, tungsten deposition on the dielectric surface is not desired. However, it would be advantageous if tungsten could be deposited in such a way that it would be possible to form the metallization layer simultaneously with the filling of the contact or connection holes. This would improve device performance by increasing manufacturing efficiency and reducing the number of contact interfaces. The problem of adhesion of metallized layers has commonly been solved by the use of adhesion-enhancing substances or "glue layers" between non-adhesive materials. However, it has been difficult to obtain adhesion enhancing materials suitable for tungsten films formed by chemical vapor deposition. Tungsten silicide is a known adhesion enhancing material for chemical vapor deposited tungsten. However, depositing layers of tungsten silicide ( <sub>WSi2</sub> ) is difficult. Special equipment is required to form such a layer by reaction of SiH <sub>4</sub> and WF <sub>6</sub> . On the other hand, forming a bonding adhesive layer by sputtering is quite simple and does not require complicated equipment. Sputter-deposited titanium and chromium have been proposed as adhesion enhancers for chemical vapor deposited tungsten. However, they have proven to be less than satisfactory. Proceedings of the International Conference on Chemical Vapor Deposition
the international conference on chemistry
In the report by JIFederer et al., ``Study on the adhesion of tungsten and molybdenum coatings,'' published on pages 591-599 of the 3rd edition of ``Vapor Deposition'', the reason for the poor adhesion is as follows:
It is stated that a displacement reaction occurs between chromium and chemical vapor deposition gas. Due to such a substitution reaction, the chromium layer is etched and removed. No. 4,404,234 discloses a method for depositing tungsten films on dielectric surfaces by sputtering. According to this method, the silicon dioxide dielectric surface is partially coated with chemical vapor deposited tungsten or chemical vapor deposited molybdenum to enhance the adhesion of the metallization layer formed by sputtering. The partially deposited tungsten or molybdenum forms small islands on the dielectric surface, thereby roughening the dielectric surface and enhancing adhesion. Unfortunately, this method is not suitable for manufacturing integrated circuits with high component densities and large aspect ratios, such as those required in very high density integrated circuits (VLSI) and ultra high density integrated circuits (USLI) applications. Appropriate. Metallized layers formed by sputtering do not exhibit the same uniformity as metalized layers formed by chemical vapor deposition, nor do they conform to the topography of the surface on which they are applied. This is explained by I.A. Bretzk and H.T. Vander Plass (J.Appl.Phys.), Vol. IABlech & H.A.Vander
Plas) in the article "Simulation and measurement of stepped coatings in a DC planar magnetron sputtering apparatus". More specifically, this paper discusses sputtering layer coatings (referred to in the paper as "graded coatings") on uneven soil areas. The reason for this lack of conformality in sputtering-formed layers is that sputtering is a line-of-site process with the metal source located far from the surface to be coated. , which makes uniform metal deposition difficult. In chemical vapor deposition, the metal source is a gas that contacts the surface of the substrate so that the metal can be evenly deposited anywhere on the surface. As such, it is non-flat with a large aspect ratio (having a height/width ratio greater than 1/2). It is difficult to fill the area by sputtering methods. The present invention is formed by chemical vapor deposition and
It was developed in response to the industry's need for a simple method to obtain an adherent tungsten metallization layer suitable for VLSI and ULSI applications. SUMMARY OF THE INVENTION Generally speaking, the present invention provides a method for forming an adherent tungsten film on a dielectric surface by chemical vapor deposition. To achieve this purpose, molybdenum is used as an adhesion enhancer or bonding adhesive layer. Such a molybdenum adhesion layer is not attacked by reactive gases for chemical vapor deposition of tungsten and is not only effective in flat areas but also in uneven areas with high aspect ratios (especially height/width ratios greater than 1). Provides excellent adhesion of tungsten to silicon dioxide. More particularly, the present invention relates to a method for forming a continuous, conformable tungsten film on a dielectric surface comprised of silicon dioxide or silicon nitride. The method is characterized by the steps of depositing molybdenum on the dielectric surface by sputtering to form a continuous molybdenum layer, and then depositing tungsten on the molybdenum layer by chemical vapor deposition. . The primary object of the present invention is to improve the adhesion of chemical vapor deposited tungsten films to silicon dioxide;
Thereby the object is to provide a method for forming a continuous conformable metallization layer suitable for integrated circuit applications. Other purposes will become apparent upon reading the detailed description below. DESCRIPTION OF THE PREFERRED EMBODIMENTS Dielectric surfaces that may be treated in accordance with the present invention include silicon dioxide and silicon nitride surfaces. Such dielectrics are most commonly found in transistors and integrated circuits utilized in the electronics industry. These dielectrics can be deposited by sputtering onto a substrate, such as a semiconductor surface of a silicon wafer or chip, to form an insulating layer. The silicon dioxide layer can also be formed by oxidizing the semiconductor surface of a silicon substrate. Furthermore, the silicon dioxide layer contains silane congeners (i.e., SiH <sub>4</sub> and SiCl <sub>2</sub> H <sub>2</sub> ) and oxygen sources (i.e., O <sub>2</sub> and
It can also be deposited on the substrate by chemical vapor deposition methods based on reaction with N <sub>2</sub> O) or by plasma enhanced chemical vapor deposition methods. Furthermore, plasma-enhanced chemical vapor deposition method is
This method uses a high frequency generator to generate plasma, thereby increasing the activity of the gas and enabling chemical vapor deposition at lower temperatures. The dielectric surface as described above may be a continuous, planar surface, or alternatively may be a patterned, uneven surface. Examples of the latter include surfaces of silicon wafers that include contact or connection holes that have been patterned to expose the underlying substrate (silicon layer or layer of tungsten, aluminum or molybdenum). Such patterned dielectric surfaces can be obtained by methods known in the art. Examples of such methods include:
Photolithographic techniques include treating the surface of a dielectric with photoresist and then exposing it to radiant energy through a mask. When the patterned dielectric surface is obtained by photolithography, the contact hole depth is preferably in the range of about 10 angstroms to 3 microns, and preferably in the range of about 500 angstroms to 1 micron. Most preferably, it is within the range of . Molybdenum is deposited by sputtering on such dielectric surfaces as an adhesion enhancer or bonding adhesive layer. "Sputtering" as used herein refers to a method of depositing a metal film by bombarding an electrode made of a metal material with ions of an inert gas (for example, argon) to knock out metal atoms from the electrode. Argon ions in this case are generated by irradiating argon with high frequency waves. To attract argon ions,
A direct current is passed through the electrodes. The argon ions bombarding the electrode knock out the metal atoms on the electrode, resulting in an increase in the vapor pressure of the metal atoms.
Once the system is saturated with metal atoms, they condense on cold surfaces, including substrate surfaces. Such plasma generation continues until the metal atoms condensing on the substrate form a layer of desired thickness. Almost any sputtering method known in the art can be used to form a molybdenum adhesive layer as described above. Examples include glow discharge sputtering, cylindrical magnetron sputtering, planar magnetron sputtering, S-gun magnetron sputtering, and ion beam evaporation. Note that these sputtering methods are based on Vossen & Kern.
Author: Thin Film Processes
(Academic Press, 1978)
(2013), pp. 12-204.
Also, almost any equipment can be used to form such a molybdenum adhesive layer by sputtering. Such devices are described in more detail in Botsen and Kahn, supra. Note that these devices can take various forms depending on the shape of the magnetron used (for example, circular, planar, cylindrical, etc.). As a result of the formation of the molybdenum adhesion layer, the dielectric surface is not exposed to aggressive reactant gases as found in chemical vapor deposition processes. Since no displacement of the dielectric surface material occurs in the presence of plasma and molybdenum vapor, the dielectric surface remains intact. Since sputtering depends on the geometry of the line of sight, this sputtering process ensures that areas with large aspect ratios, such as contact holes and connection holes, are filled uniformly. There isn't. However, sputtering forms a continuous molybdenum adhesive layer on the dielectric surface. A "continuous" layer here refers to at least the upper surfaces of the dielectric (i.e. contact holes,
It means a coating that completely covers a flat surface (excluding the inner surface of areas with a large aspect ratio such as connection holes). Also, "high aspect ratio uneven areas" are defined as areas where a portion of the high surface is removed, for example by photolithography, and thereby generally has a height/width ratio greater than about 1/2. Refers to the area where the hole has been formed. In short, the side walls and bottom walls of the contact holes do not need to be coated with a molybdenum adhesive layer. As long as the molybdenum adhesive layer coats the upper surface surrounding the contact hole, this hole will be filled with tungsten in a subsequent step and a satisfactory result will be achieved. Although it is not necessary for the molybdenum adhesive layer formed by sputtering to cover the internal surfaces of contact holes, connection holes, etc., it is beyond the scope of the present invention even if such a molybdenum adhesive layer covers those surfaces. Not that I will. In fact, if possible, it is preferred to form a uniform molybdenum layer that conforms to the topography of the entire surface of the dielectric, including areas that are not planar. The thickness of the molybdenum adhesion layer is selected to minimize stress in the layer while maintaining its continuity on the dielectric surface. In practice, a molybdenum adhesive layer having a thickness of about 250 to 1000 angstroms is preferred;
A molybdenum adhesive layer with a thickness of Angstroms is most preferred. However, it may be desirable if a thinner, continuous layer can be formed uniformly. In the method of the present invention, there is no upper limit to the thickness of the molybdenum adhesive layer formed by sputtering. However, if the molybdenum adhesive layer is too thick,
It may block the contact hole or connection hole. Following the deposition of the successive molybdenum adhesion layer, a tungsten metallization layer is deposited by chemical vapor deposition. The tungsten metallization layer is continuous and conformable. By "conformable" we mean a layer that covers the entire substrate surface, including high flat areas and uneven areas with high aspect ratios. Areas with a high aspect ratio (height/width ratio) will be filled with tungsten because chemical vapor deposition produces a film at the surface by reacting components in the gas phase. Chemical vapor deposition does not rely on line-of-sight geometry, ie, all locations on the surface that are in contact with the gas constitute a film formation site. Using the present invention, tungsten metallization layers having a thickness of up to 3 microns can be formed; thicker tungsten metallization layers are believed to be too stressed and unsuitable. , the preferred thickness range is about 500 angstroms to 2 microns. Virtually any tungsten chemical vapor deposition method can be used in the present invention. The most common tungsten chemical vapor deposition methods are WF <sub>6</sub> or WCl <sub>6</sub>
The idea is to reduce the Among other things, WF <sub>6</sub>
A tungsten chemical vapor deposition method based on the reaction +3H <sub>2</sub> →W↓+6HF↑ is suitable for the present invention. A more detailed explanation of chemical vapor deposition methods can be found in the Encyclopedia of Chemical Technology (3rd edition), edited by Kirk-Othmer, volume 13, page 636, and above. ``Thin Film Processes'' by Botsen and Kahn.
(1978), pages 257-319. A suitable chemical vapor deposition method involves (1) supplying reactant and diluent gases (with controlled flow rates and timing);
(2) providing the necessary heat for reaction of the reactant gas and diffusion of the reactant gas to the surface; and (3) It consists of various processes for transporting by-product gases desorbed from the surface. Examples of suitable chemical vapor deposition methods include low temperature CVS, high temperature
Examples include CVD method, low pressure CVD method, plasma enhanced CVD method and normal pressure CVD method. Note that a low-pressure CVD method is preferred. Almost any equipment suitable for performing chemical vapor deposition of tungsten can be used in the present invention. Such devices include horizontal, pedestal, barrel or pancake shaped hot wall reactors and cold wall reactors such as those described in Thin Film Processes by Botsen and Kahn. . Suitable conditions for carrying out chemical vapor deposition include a temperature in the range of about 300 to 700°C and a temperature of about 0.1°C.
Pressures in the range of Torr to about 1 atmosphere are used. The preferred temperature range is about 400 to 500°C, and the preferred pressure range is about 1 to 2 torr. The ratio of hydrogen to tungsten hexafluoride may range from about 3:1 to 1000:1. Note that the preferred ratio range is 5:1 to 20:1,
Also, a ratio around 20:1 is most preferred. The product obtained after carrying out such a chemical vapor deposition process can be subjected to subsequent treatments. When tungsten is deposited on a substrate by the method described herein, the resulting metallized layer exhibits excellent adhesion, the contact holes and connection holes are well covered, and the substrate dielectric Little or no deterioration of body materials occurs. Examples are shown below to explain the present invention in more detail. Note that these Examples should not be construed as limiting the scope of the present invention. Examples 1-18 In these examples, a Materials Research company was used to form an adhesive layer on a silicon wafer by sputtering.
A cold wall reactor manufactured by J.D. Research Corp. was used. 3 consisting of molybdenum, titanium and chromium
A variety of metal adhesive layers were tested. Furthermore, adhesion to polysilicon layers obtained by chemical vapor deposition was also tested. Note that the metal adhesive layer described above was formed to a thickness of 500 angstroms, and the polysilicon layer was formed to a thickness of about 1000 angstroms. Tungsten metallization layers of various thicknesses were formed on the metal adhesion layer and polysilicon layer. The thickness range was approximately 0.5 to 2.5 microns. Chemical vapor deposition of tungsten was performed in a cold wall reactor operating at about 450° C. using hydrogen and tungsten hexafluoride in a ratio of about 10:1 to 20:1. Such chemical vapor deposition is approximately 10
It lasted for 25 minutes. The adhesion of the laminate thus obtained was tested according to the method described in "Test Procedures" below. The thickness of the tungsten layer, the type of adhesive layer, and the rating of adhesive strength in each example are shown in Table 1 below. Example 1 illustrates the level of adhesion of tungsten to a semiconductor surface (rather than a dielectric surface), and Example 2 illustrates the level of adhesion of tungsten to a dielectric surface comprised of silicon dioxide. . Examples 1 and 2 are not included within the scope of the present invention. These are presented to provide a measure of the adhesion level of the resulting product according to the invention.

【table】

Table The above table shows that molybdenum provides an excellent adhesion layer for chemical vapor deposited tungsten layers of all thicknesses. Only the combination of a 500 angstrom titanium adhesion layer and a 2.1 micron tungsten layer provided adhesion ratings comparable to those obtained with all combinations of molybdenum and tungsten. In the case of chromium, adhesion was always poor and sometimes no tungsten adhesion occurred. Test Procedure To evaluate the adhesion of the adhesive layer to chemical vapor deposited tungsten, a stepwise adhesion test was conducted as shown in Table 2 below. If a "tape" was used, the tape was 3/4 inch wide cellophane tape No. 6100 commercially available from LePages, Inc., Pittsburgh, Pennsylvania, USA. In the case of "etching," the tungsten was coated with black wax in an array of dots on the surface. The uncoated portions of the tungsten layer were removed by exposing the coated surface to an etching solution. This etching solution weighs 30g.
of _K3Fe (CN) ₆ , 10g NaOH and 100ml _H2O
It consisted of After removing wax,
The adhesion of the remaining tungsten layer was tested. For "scribbling", 6-8 lines were scored into the tungsten layer using a diamond pen. Then, the adhesion force at the position of the scribe line was examined.

[Table] Eru.

[Table]
The thickness of the molybdenum adhesion layer and the chemical vapor deposited tungsten layer can vary over a wide range. Based on the above description, it will be obvious to those skilled in the art that various other implementations are possible without departing from the scope of the invention.

Claims (1)

[Claims] 1. A method for forming a continuous, conformable tungsten film on a dielectric surface made of silicon dioxide or silicon nitride, comprising: (a) depositing molybdenum by sputtering to deposit molybdenum on the dielectric surface; Form a continuous molybdenum layer on the surface, then
(b) forming a continuous conformable tungsten layer on the molybdenum layer having a thickness of about 3 microns or less by chemical vapor deposition. 2. The method of claim 1, wherein the dielectric surface includes high aspect ratio uneven regions having a height/width ratio greater than 1/2. 3. The dielectric surface is patterned by photolithography, and in the uneven areas an underlying layer of material selected from silicon, tungsten, aluminum and molybdenum is exposed. The method described in Scope No. 2. 4. The method of claim 3, wherein the patterned dielectric surface is part of an integrated circuit and the high aspect ratio uneven areas are contact holes and connection holes. 5. Claim 1, wherein the molybdenum layer is formed to a thickness of about 250 to 1000 Angstroms.
The method described in section. 6. The method of claim 1, wherein the tungsten layer is formed to a thickness of about 500 Angstroms to 2 microns. 7. The method of claim 1, wherein said chemical vapor deposition step to form said tungsten layer is accomplished by reaction of a gaseous mixture of _WF6 and _H2 . 8 The molybdenum layer is formed to a thickness of about 500 angstroms, and the tungsten layer is formed to a thickness of about 500 angstroms.
The chemical vapor deposition process for forming the tungsten layer is performed at a temperature of about 400 to 500° C., a pressure of about 1 to 2 Torr, and a pressure of about 10:1 to 25:1.
2. A method according to claim 1, which is carried out under conditions of _H2 / _WF6 ratio.