JP2003522827A - Diffusion barrier material with improved step coverage - Google Patents

Abstract

  (57) [Summary] A chemical vapor deposition method is provided for forming conformal layers including metal nitrides. A film consisting primarily of titanium nitride is deposited on a surface heated to about 350 ° C. from a vapor mixture consisting of tetrakis (diethylamido) titanium, ammonium and trimethylamine. This method can be used to form a diffusion barrier layer between metal and silicon in a computer microcircuit.

Description

Detailed Description of the Invention

[0001] Background of the Invention 1. FIELD OF THE INVENTION The present invention relates to a chemical vapor deposition (CVD) method of metal nitride films with improved step coverage or conformability. The main application of this method is to form semiconductor microcircuits, where the metal nitride acts as a barrier to prevent diffusion of metals such as aluminum and copper into silicon transistors.

2. 2. Description of Related Art In computer processors and memory chips, metal circuits connect to transistors and capacitors formed near the surface of silicon. Aluminum, copper and tungsten are the metals commonly used in these circuits. To provide a functional and durable computer, this metal must be separated from the silicon by a barrier layer. In the absence of such a barrier layer, aluminum alloys with silicon to form etch pits that can short circuit electrical circuits; copper diffuses into silicon, causing harmful recombination of electrons and holes; tungsten. Are believed to be separated from the silicon dioxide insulating layer.

Titanium nitride is a material commonly used as a barrier layer. Titanium nitride is usually produced by reactive sputtering of a titanium target in nitrogen gas at low pressure. Sputtering materials are perfect for making computer chips with feature sizes down to about a quarter of a micron.
The size of this feature is decreasing as the industry strives to produce circuits that are fast-acting and store more information. The feature size is less than about one-quarter of a micron, so sputtering can provide adequate coverage for the sides and bottom of trenches and narrow holes that are etched to a depth of 1 micron in the substrate. Can not.

The sidewalls and bottom coating of the etched features are as large as the outer surface (orde
The film thickness of r) is desirable. This relationship is described as step coverage. "Step coverage" is defined as the ratio of the thickness of the film deposited on the bottom of the holes to the thickness of the film on top of the silicon dioxide layer. It is desirable that the step coverage be close to 1 in the electrical features. Therefore, the need for a barrier layer deposited by a method that has better step coverage than sputtering is recognized.

Chemical vapor deposition (CVD) is a widely used method in forming solid materials, such as coatings, from reactants in the vapor phase. Since the CVD method is limited to line-of-sight coverage, it often produces better step coverage than sputtering. For a comprehensive review of CVD methods, see “CVD of Nonmetals”, WS Leeds (WS
Rees), Jr., VCH Publisher, Weinheim, Germany, 1996, “CVD of composite semiconductors (CV
D of Compound Semiconductors ", AC Jones and P.
P. O'Brien, VCH, 1996, and "The Chemistr of Metal Chemistry (The Chemistr
y of Metal CVD ”, T. Kodas and M. Hampton Smith (M.
Hampden-Smith), VCH, 1994.

Thermal CVD of tetrakis (dimethylamido) titanium or tetrakis (diethylamido) titanium alone, ie ammonia-free, has been found to provide good step coverage (Eizenberg et al., J Vac Sci. Technol. A. , 13: 590
(1995)). It is believed that the good step coverage is due to the low adhesion coefficient of the titanium amide compound and the low adhesion coefficient of any reaction intermediate. Molecules with a low sticking coefficient can remain without being deposited there, even though they collide with the sidewalls of the feature in large numbers. The molecule thus has the potential to eventually deposit further into the feature trenches, giving good step coverage. A good step coverage appears, but unfortunately many films have carbon incorporation, high electrical resistance, and high porosity (low density).

Better quality titanium nitride films were obtained by CVD of tetrakis (diethylamido) titanium and ammonia vapors as disclosed by US Pat. No. 5,139,825 (1990) to Gordon et al. . This method is carried out at a substrate temperature of 400 ° C. or lower, which is low enough to be used in a semiconductor microcircuit. The step coverage obtained by this method is about the size of the feature.
Sufficient to form a barrier layer on currently manufactured microcircuits with quarter micron and aspect ratios up to 4: 1. However, it is considered that the step coverage obtained by this method is not high enough for the size of the smaller feature of the microcircuit planned to be manufactured in the future.

Therefore, it was considered that a reaction with ammonia was necessary in order to manufacture a TiN film having a small amount of carbon and a low resistance. Reaction of the dialkylamidotitanium complex with ammonia results in transamination to form the corresponding free dialkylamine. Weiller regulates the reaction rate of metal-amide compounds and is used in the Journal of the Electrochemical Society.
), 144: L40-L43 (1997) and to the CVD reactive gases tetrakis (dimethylamido) titanium vapor and ammonia gas as disclosed by U.S. Pat. We have tried to improve the quality of step coverage by adding amine. Although the addition of dialkylamine succeeded in extending the reaction time, there was no conclusive evidence that the addition of dimethylamine actually increased the step coverage of the titanium nitride film.

Therefore, until now, the prior art could not provide a method of depositing a metal nitride film having both good film quality and a large step coverage.

What is particularly needed is a method for increasing the step coverage without adversely affecting the carbon content, electrical resistance or density of the titanium nitride film.
No. 5,763,007 to Iller) does not provide such a method.

[0011] The main SUMMARY OF THE INVENTION An object of the invention is to provide a method for depositing a metal nitride layer step coverage is improved.

Another object of the present invention is to provide a method for forming a metal nitride film containing a transition metal nitride and having high purity, high electrical conductivity and effective diffusion barrier performance. .

Another object of the present invention is to provide a method of chemical vapor depositing a conformal metal nitride film from the vapor of a stable and homogeneous solution.

A particular object of the invention is to provide a method for depositing a titanium nitride coating with good step coverage, low electrical resistance, and low carbon content.

Another particular object of the invention is to successfully prevent the diffusion of substances through the membrane,
A method of depositing a conformal metal nitride film is provided.

A related object is to deposit conformal layers containing several metal nitrides by chemical vapor deposition.

Another particular object of the invention is to provide a method of depositing a conformal nitride film that adheres strongly to silicon and silicon dioxide.

A more specific object of the present invention is to provide a titanium nitride film conforming to the shape in which the tungsten film has a strong bond.

Another particular object of the invention is to successfully prevent the diffusion of substances through the membrane,
A method of depositing a conformal, electrically conductive niobium nitride film.

Other objects of the invention will be apparent to those of ordinary skill in the art upon reading the invention.

The above objectives have been substantially achieved using a chemical vapor deposition method, which method comprises:
A gaseous mixture of a vapor of a metal alkylamide, ammonia and a tertiary amine is provided by contacting with a heated surface on which a film of conformal metal nitride is deposited. For example, tetrakis (diethylamido) titanium vapor, ammonia gas, and trimethylamine gas are sprayed onto a patterned substrate kept at 350 ° C to evenly cover the holes and grooves of the substrate to form titanium nitride. Deposit a film of material.

The metal dialkylamide used in the method of the present invention is of the general formula M (NR ¹ R ² ) _n , where R ¹ and R ² are alkyl groups or substituted containing heteroatoms such as nitrogen. It may be an alkyl group, and n is an integer representing the oxidation state of the metal. The most preferred composition of the metal dialkylamide comprises a ligand derived from diethylamine such as tetrakis (diethylamido) titanium or tetrakis (diethylamido) niobium.

The tertiary amine is preferably triethylamine with the same or different alkyl groups. The alkyl group preferably contains less than or equal to 6 carbons, more preferably less than or equal to 3 carbons. In the process of the present invention, trimethylamine may be replaced with liquid triethylamine or other tertiary alkylamines such as pyridine vapor.

Another preferred embodiment of the present invention is the chemical vapor deposition of metal nitrides using a reactive vapor generated by the instantaneous vaporization of a liquid mixture of one or more metal dialkylamides and a liquid tertiary amine. Provide a way to do. These mixed vapors are
Next, ammonia gas and optionally an inert carrier gas such as nitrogen are mixed in the gas phase and subsequently fed in contact with the heated substrate. This method can be used to form films containing, but not limited to, titanium and niobium nitride.

In another aspect of the invention, the mixed metal nitride is formed by evaporating two or more metal dialkylamides, the vapors of which are ammonia gas and tertiary amine vapors and optionally Mixed with an inert carrier gas.
The mixture of vapors is provided in contact with a substrate heated to a temperature sufficient to deposit a material containing two or more metal nitrides. This method includes, but is not limited to, titanium, zirconium, hafnium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, aluminum,
It may be used to form multi-metal nitride films such as gallium, indium and tin.

The present invention will be described with reference to the drawings, which are shown by way of illustration only and not in a manner intended to limit the invention.

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a metal nitride film with excellent step coverage, low carbon content, and low resistance. The method of the present invention comprises a chemical vapor deposition process in which a gaseous mixture containing a vapor of a metal alkylamide, ammonia and a tertiary amine is provided in contact with a heated surface to deposit a conformal film of metal nitride. Including. For example, tetrakis (
Diethylamide) titanium vapor, ammonia gas, and trimethylamine gas,
A titanium nitride film is deposited by spraying on a patterned substrate kept at 350 ° C. to uniformly cover the holes and trenches in the substrate. This method has a diameter of 0.
It appears that it can be used to provide good step coverage for features with aspect ratios (depth: diameter) of 4: 1 or greater with dimensions below 25 microns. Step coverage greater than 70% and approaching 95-100% for these outer surface morphologies can be obtained by the method of the present invention.

Certain embodiments of the invention require the use of one or more metal dialkylamides and a tertiary amine.

The metal dialkylamides used in the method of the present invention have the general formula M (NR ¹ R ² ) _n , where R ¹ and R ² are alkyl groups or heteroatoms such as nitrogen. May be a substituted alkyl group containing and n is an integer indicating the oxidation state of the metal. Other ligands such as alkyl or alkylimide groups may also be attached to the metal atom. In preferred embodiments, the alkyl group contains less than or equal to 6 carbons, more preferably less than or equal to 3 carbons. The most preferred composition of the metal dialkylamide comprises a ligand derived from diethylamine such as tetrakis (diethylamido) titanium or tetrakis (diethylamido) niobium.

The tertiary amine is preferably triethylamine in which the alkyl groups are the same or different. The alkyl group preferably contains less than or equal to 6 carbons, more preferably less than or equal to 3 carbons. In the process of the present invention, trimethylamine may be replaced with liquid triethylamine or other tertiary alkylamines such as pyridine vapor. In another preferred embodiment, the tertiary amine is trimethylamine or triethylamine. In another preferred embodiment, the tertiary amine is believed to be pyridine.

A variety of tertiary amines can be utilized in practicing the present invention. The preferred tertiary amines are all commercially available from many suppliers. Trimethylamine is a gas at standard temperature and atmospheric pressure, and is usually supplied in a liquefied state in a compression cylinder. Triethylamine and pyridine are liquid at the temperature and pressure of the state. These tertiary amines do not have a hydrogen atom directly attached to the nitrogen atom and therefore they do not undergo the transamination reaction characteristic of the secondary amines used in US Pat. No. 5,763,007.

The metal dialkylamides of the present invention can be formed by reacting a suitable dialkylamide salt of an alkali metal with a metal halide. For example,
Lithium diethylamide can be reacted with titanium tetrachloride to synthesize tetrakis (diethylamido) titanium. Commercial sources of tetrakis (diethylamido) titanium include Schumacher (Carls
bad, CA) and Advanced Technology Materials
Materials) (Danbury, CT). Commercial sources of tetrakis (diethylamido) niobium include Chemat (Northridge, CA) and Advanced Technology Materials.

The vapor of the liquid precursor may be produced in a thin film evaporator, or about 150
It may be produced by spraying on a carrier gas preheated to ℃. The spraying can be carried out pneumatically or ultrasonically. Liquid metal dialkylamides are generally fully miscible with organic solvents and include hydrocarbons such as dodecane, tetradecane, xylene, and mesitylene. In some cases, these solutions are usually less viscous than pure liquids because it is easier to spray and evaporate the solution rather than the pure liquid. Thin film evaporators are manufactured by Artisan Industries (Waltham, Massachusetts). Commercial equipment (DLI) for direct liquid evaporation is available from MKS Instruments.
nts) (Andover, Massachusetts), ATMI (Danbury, Connecticut), Novels (No
vellus) (San Jose, California) and COVA Technologies
) (Tiburton, California). Ultrasonic nebulizers are manufactured by Sonotek Corporation (Milton, New York) and Cetac Technologies (Omaha, Nebraska).

A desired portion of the system gas by introducing a gaseous reactant, such as ammonia or trimethylamine, into the vapor through a mass flow regulator with or without an inert carrier gas. Pressure can be provided.

The method of the present invention can be carried out on standard equipment well known in the chemical vapor deposition (CVD) art. The CVD apparatus contacts the vapor of the reactant with a heated substrate on which the material is deposited. The CVD method can be performed at various pressures, especially at normal atmospheric pressure and lower pressures. Commercial atmospheric CVD reactors are available at the Watkins-Johnson Company (Scotts Valley, California), BTU International (North Billerica, Massachusetts), and Sierra Therm (Watsonville, California). Manufactured in the United States by. Low-pressure CVD equipment is based on Applied Materials (San
ta Clara, California), Spire Corporation (Bedfo
rd, Massachusetts), Materials Research Corporation
Reseach Corporation) (Gilbert, Arizona), Novellus (San Jose,
California), Emcore Corporation (Somersetm
NJ) and NZ Applied Technologies (Wobuen, Mas
manufactured by Sachusetts).

Typical deposition temperatures are in the range of about 200 ° C to 400 ° C. Also, the deposition reaction appears to be promoted by light, as well as by heat, or by the electrical energy of the plasma discharge. Normal deposition pressures range from moderate atmospheric pressure to a few millitorr.

Example 1 A titanium nitride film was formed on a Watkins-Johnson Medel model.
) Atmospheric pressure chemical vapor deposition in a 965 belt furnace. Tetrakis (diethylamido) titanium (purity 99 from Schumacher)
.995%) was vaporized at 140 ° C. by an MKS model LDS 100 liquid feed and vaporization system and placed in a water and oxygen purified nitrogen carrier gas by an Oxiclear purifier. Ammonia (NH ₃ , purity 99.995%) and trimethylamine gas (NMe ₃ , purity 99.5%) obtained from Matheson Gas Company were passed through a Nanochem purifier designed for ammonia, followed by Further purification was carried out on water and oxygen contamination by preheating to 160 ° C. The tetrakis (diethylamido) titanium vapor was mixed with ammonia and trimethylamine gas in the deposition zone, the molar concentration of the gas phase being 0.01% Of tetrakis (diethylamido) titanium, 1.0% ammonia, and 0.68% trimethylamine with a nitrogen carrier gas in balance.

The substrate is a silicon wafer pre-coated with a 2.4 micron thick layer of silicon dioxide into which 0.7 micron diameter and 2.4 micron deep holes (aspect ratio about 3.5: 1) were etched. ing. Preheat this substrate to 370 ° C, then 2 cm
It was moved through the deposition zone at a belt speed of / min. In a control experiment using a wafer with a thin thermocouple wire bonded to its surface, the temperature of the substrate plunged to about 320 ° C during its passage through the deposition zone, with its top surface at about 160 ° C. It was shown to be kept at temperature.

After completion of the deposition, the wafer was broken and the cracked edges were examined using a scanning electron microscope. The step coverage is shown in FIG. 1 for the film thickness at the surface of the film portion 100 of the film as shown in FIG. 1A and the bottom portion of the groove 102 as shown in FIG. 1B. It is determined by measuring the thickness of the film. Considering the experimental accuracy of the thickness measurement, the step coverage was found to be between 95% and 100%.

The composition of the film was examined by helium ion sputtering experiments to be titanium nitride with some incorporation of hydrogen and oxygen. No carbon was detected in the film above the detection level of 3 atomic percent.

Comparative Example 2 Example 1 was repeated using a degraded trimethylamine flow. This step coverage is shown in FIG. 2, where the film thickness at the surface of the film portion 200 of the film as shown in FIG. 2A and the bottom portion of the groove 202 as shown in FIG. 2B. It is determined by measuring the film thickness at. The step coverage was found to be 70%, which is significantly lower than that obtained in Example 1. The chemical composition, resistance, and density of this film are
In all other respects they were identical to those of Example 1.

Example 3 Example 1 was repeated with a preheat temperature of 390 ° C. This step coverage was determined to be 45%.

Comparative Example 4 Example 3 was repeated using a degraded trimethylamine flow. This step coverage was found to be 35%, which is significantly lower than that obtained in Example 3. The chemical composition, resistance, and density of this film were identical to those of Example 3 in all other respects.

Example 5 Tetrakis (diethylamido) titanium was mixed with 20 volumes of liquid triethylamine and the liquid solution was vaporized by a MKS Model LDS 100 liquid supply system at 140 ° C. into a purified nitrogen carrier gas. This vapor mixture was reacted with ammonia in an experiment similar to that of Example 1 except that trimethylamine was not used. Similar results were obtained.

Example 6 Example 1 was replaced by tetrakis (diethylamido) titanium instead of tetrakis (
Diethylamido) niobium was repeated. Niobium nitride films with excellent step coverage were obtained.

The liquids and solutions described in all of these examples were found to be non-pyrophoric by the method published by the US Department of Transportation. In one test,
It requires placing about 5 milliliters of a liquid or solution in a non-pyrophoric porous solid and observing that spontaneous ignition does not occur. Another test involves dropping 0.5 milliliters of a liquid or solution onto Whatman No. 3 filter paper and observing that the filter paper does not ignite or burn.

The precursors typically react with the humidity or oxygen in the ambient air and should therefore be stored under a dry atmosphere such as nitrogen.

Those skilled in the art will recognize, or be able to ascertain, without undue experimentation, many equivalents to the specific embodiments of the invention specifically described herein. It seems possible. Such equivalents are intended to be within the scope of the claims.

[Brief description of drawings]

FIG. 1 is a photomicrograph of (A) upper portion, (B) lower portion, and (C) full field of view of a feature coated as described in Example 1.

FIG. 2 is a photomicrograph of (A) upper portion, (B) lower portion, and (C) full field of view of a feature coated as described in Comparative Example 2.

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Claims (16)

[Claims] 1. A method of making a material comprising one or more metal nitrides, comprising the steps of: providing a vapor comprising one or more metal alkylamides, ammonia, and a tertiary amine. And in a deposition step for depositing a material containing one or more metal nitrides,
Contacting the vapor mixture with a heated surface. 2. The method of claim 1, wherein the one or more metals are selected from the group consisting of titanium, vanadium, niobium, and molybdenum. 3. The method according to claim 2, wherein the metal is titanium. 4. The method of claim 2, wherein the metal is niobium. 5. The method according to claim 1, wherein the tertiary amine is an alkylamine. 6. The method of claim 5, wherein the alkyl groups are the same or different. 7. The method of claim 6, wherein the alkyl group contains a number of carbons less than or equal to 6. 8. The method of claim 6, wherein the alkyl group contains a number of carbons less than or equal to three. 9. The method of claim 1, wherein the tertiary amine is trimethylamine. 10. The method of claim 1, wherein the tertiary amine is triethylamine. 11. The method of claim 1, wherein the tertiary amine is pyridine. 12. The method of claim 1, wherein the metal alkylamide comprises an alkyl group having less than or equal to 6 carbons. 13. The method of claim 1, wherein the metal alkylamide comprises an alkyl group having less than or equal to 3 carbons. 14. The surface is heated to a temperature in the range of about 200-400 ° C.
The method described. 15. The method according to claim 1, wherein the step coverage is 75% or more. 16. The method according to claim 1, wherein the step coverage is 95 to 100%.