JP7569252B2 - Method for storing etching solution composition - Google Patents

Description

The present disclosure relates to a method for storing an etching solution composition and an etching solution package.

The components contained in the polishing and etching compositions used in the manufacturing process of semiconductor devices may be altered when stored or transported for long periods of time. Therefore, excellent storage stability even under such conditions is considered to be one of the important properties.

For example, Patent Documents 1 and 2 focus on the fact that a polishing liquid composition containing alumina and a preservative discolors a resin container when stored in the container for a long period of time, and propose a polishing liquid composition that does not discolor the container even when stored for a long period of time and has excellent storage stability.
In Patent Document 3, an etching solution containing nitric acid, phosphoric acid, and acetic acid is proposed as an etching solution for etching metals.

JP 2006-206698 A JP 2006-176733 A JP 2013-237873 A

In general, etching solution compositions contain nitric acid, and when such etching solution compositions are stored in a resin container, the resin container may be discolored by the nitric acid. In order to reduce costs, there is a demand for a method of storing an etching solution composition that has excellent storage stability and does not discolor the container, even when an inexpensive resin container such as polyethylene resin or polypropylene resin is used.

Therefore, in one aspect, the present disclosure provides a method for storing an etching solution composition that can suppress discoloration of the container even when stored for a long period of time and has excellent storage stability.

In one aspect, the present disclosure relates to a method for storing an etching solution composition for etching a layer to be etched that contains at least one metal, the etching solution composition containing a nitrogen-containing compound, an acid containing at least nitric acid, and water, and the method for storing the etching solution composition includes filling the etching solution composition in a container made of polyethylene resin or polypropylene resin and storing the etching solution composition at a temperature of -10°C or higher and 40°C or lower.

In one aspect, the present disclosure relates to an etching solution package in which an etching solution composition is filled in a container, the etching solution composition containing a nitrogen-containing compound, an acid containing at least nitric acid, and water, the container being a container made of a polyethylene resin or a polypropylene resin, and the etching solution composition being an etching solution composition for etching a layer to be etched that contains at least one type of metal.

According to one aspect of the present disclosure, a method for storing an etching solution composition that can suppress discoloration of the container even when stored for a long period of time and has excellent storage stability can be provided.

In one aspect, the present disclosure is based on the finding that adding a nitrogen-containing compound to an etching solution containing nitric acid and water can suppress discoloration of a container made of polyethylene resin or polypropylene resin even when the etching solution is filled in the container, and can improve storage stability.

In one aspect, the present disclosure relates to a method for storing an etching solution composition for etching a layer to be etched that contains at least one metal, the etching solution composition containing a nitrogen-containing compound, an acid containing at least nitric acid, and water, and the method for storing an etching solution composition (hereinafter also referred to as the "storage method of the etching solution composition of the present disclosure") includes filling the etching solution composition in a container made of polyethylene resin or polypropylene resin (hereinafter also simply referred to as the "resin container in the present disclosure") and storing the etching solution composition at a temperature of -10°C or higher and 40°C or lower. The etching solution composition filled in the resin container in the present disclosure is hereinafter also referred to as the "etching solution composition of the present disclosure".

According to the present disclosure, a method for storing an etching solution composition can be provided that can suppress discoloration of the container even when stored for a long period of time, and has excellent storage stability. In addition, because discoloration of the container can be suppressed even when the container is made of inexpensive polyethylene resin or polypropylene resin, semiconductor substrates can be manufactured at low cost.

Although the details of the mechanism by which the effects of the present disclosure are manifested are not clear, it is presumed as follows.
When an etching solution composition containing nitric acid is filled into a container made of polyethylene resin or polypropylene resin, the resin constituting the container may be oxidized by the acid, causing the container to discolor.
In the present disclosure, it is believed that the nitrogen-containing compound protects the surface of the container and inhibits the resin constituting the container from being oxidized by nitric acid, thereby inhibiting discoloration of the container.
In addition, the decrease in the amount of nitric acid consumed for discoloration of the container is suppressed, which is believed to improve storage stability.
However, the present disclosure need not be construed as being limited to these mechanisms.

In this disclosure, "discoloration of a container" refers to a change in at least one of the hue, saturation, and brightness of a container before use.

[Storage method]
A method for storing the etching solution composition of the present disclosure includes filling the etching solution composition of the present disclosure into a container made of polyethylene resin or polypropylene resin and storing the composition at a temperature of −10° C. or higher and 40° C. or lower. In the present disclosure, “storage” includes, for example, storage during transportation, storage in a warehouse, etc.

In the storage method of the etching solution composition disclosed herein, the storage temperature is -10°C or higher, preferably -5°C or higher, more preferably 0°C or higher, and 40°C or lower, preferably 35°C or lower, more preferably 30°C or lower, from the viewpoint of suppressing discoloration of the container and improving storage stability. From the same viewpoint, the storage temperature is -10°C or higher and 40°C or lower, preferably -5°C or higher and 35°C or lower, more preferably 0°C or higher and 30°C or lower.

The storage period in the storage method of the etching solution composition disclosed herein is preferably 2 years or less, more preferably 1 year or less, and even more preferably 0.5 years or less, from the viewpoint of reducing costs associated with semiconductor substrate manufacturing.

[Polyethylene resin or polypropylene resin container]
The etching solution composition of the present disclosure is filled in a container (resin container) made of polyethylene resin or polypropylene resin. Therefore, in one aspect, the present disclosure relates to an etching solution composition for etching a layer to be etched that contains at least one metal, the etching solution composition containing a nitrogen-containing compound, an acid containing nitric acid, and water, and filled in a container made of polyethylene resin or polypropylene resin. Examples of the polyethylene resin include low-density polyethylene, medium-density polyethylene, high-density polyethylene, and mixtures thereof.

In the present disclosure, the term "polyethylene resin or polypropylene resin container" refers to a container in which at least the portion of the container that comes into contact with the etching solution composition is made of polyethylene resin or polypropylene resin. As the resin container in the present disclosure, for example, a container in which a layer of polyethylene resin or polypropylene resin is provided as the inner layer that comes into contact with the etching solution composition and a resin of another material or the like is laminated on the outside thereof may be used.
Incidentally, although commercially available containers made of polyethylene resin or polypropylene resin generally contain an antistatic agent such as a surfactant or a metal oxide, the etching solution composition of the present disclosure preferably does not contain an antistatic agent.
In addition, since the etching solution composition of the present disclosure contains nitric acid as an essential component, in order to prevent decomposition due to sunlight, etc., it is preferable that the exterior of the container be colored gray, blue, or the like or light-shielding, rather than a translucent or white container.

Examples of the resin container form in this disclosure include a resin container with a capacity of 0.1 to 30 L, a composite container that combines a resin inner container with a capacity of 0.1 to 30 L with cardboard, a composite container that combines a resin inner container with a capacity of 1 to 30 L with a metal can, a resin drum container with a capacity of 20 to 300 L, a composite container that combines a resin inner container with a capacity of 20 to 300 L with a metal drum, and a composite container that combines a resin inner container with a capacity of 500 to 1200 L with a metal container.

The resin container in this disclosure may be any container that can be used for the purpose of storing or transporting the etching solution composition, and may be manufactured, for example, by injection molding, extrusion molding, or rotational molding.

The method of filling the resin container with the etching solution composition in this disclosure is not particularly limited, and filling can be performed by a conventional method depending on the shape of the container, etc.

[Etching solution composition]
The etchant composition of the present disclosure comprises a nitrogen-containing compound, an acid comprising at least nitric acid, and water.

(Nitrogen-containing compounds)
The nitrogen-containing compound contained in the etching liquid composition of the present disclosure is not particularly limited, and examples thereof include at least one selected from polyalkyleneimines, alkylamines, compounds having an amino group and an ethylenically unsaturated double bond, polymers having a structural unit derived from a compound having an amino group and an ethylenically unsaturated double bond, alkanolamines, alicyclic amines, and polyalkylenepolyamines.
The polyalkyleneimine may, for example, be polyethyleneimine.
The alkylamines include pentaethylenehexamine and the like.
Examples of the compound having an amino group and an ethylenically unsaturated double bond include allylamine and diallylamine.
Examples of the polymer containing a structural unit derived from a compound having an amino group and an ethylenically unsaturated double bond include an allylamine polymer, a diallylamine polymer, a diallylamine/sulfur dioxide copolymer, a diallyldimethylammonium chloride polymer, and a diallyldimethylammonium chloride/sulfur dioxide copolymer.
The alkanolamines include, for example, 2-(2-aminoethylamino)ethanol.
The alicyclic amine may, for example, be N-(2-hydroxyethyl)piperazine.
The polyalkylene polyamine may, for example, be pentaethylenehexamine.
Among these, from the viewpoints of inhibiting discoloration of the container and improving storage stability, the nitrogen-containing compound is preferably at least one selected from polyalkyleneimine, alkylamine, allylamine polymer, and diallylamine/sulfur dioxide copolymer, more preferably at least one selected from polyalkyleneimine and alkylamine, even more preferably polyalkyleneimine, and even more preferably polyethyleneimine.
The nitrogen-containing compound may be used alone or in combination of two or more kinds.

When the nitrogen-containing compound is a polyalkyleneimine, the number average molecular weight is preferably 300 or more, more preferably 600 or more, and even more preferably 1,200 or more from the viewpoint of suppressing discoloration of the container and improving storage stability, and is preferably 100,000 or less, more preferably 5,000 or less, and even more preferably 3,000 or less from the viewpoint of viscosity. More specifically, the number average molecular weight of the nitrogen-containing compound is preferably 300 or more and 100,000 or less, more preferably 600 or more and 5,000 or less, and even more preferably 1,200 or more and 3,000 or less.
When the nitrogen-containing compound is a (co)polymer other than polyalkyleneimine, from the viewpoint of suppressing discoloration of the container and improving storage stability, the weight-average molecular weight is preferably 2,000 or more, more preferably 3,000 or more, even more preferably 4,000 or more, and preferably 50,000 or less, more preferably 25,000 or less, and even more preferably 10,000 or less. More specifically, the weight-average molecular weight of the nitrogen-containing compound is preferably 2,000 or more and 50,000 or less, more preferably 3,000 or more and 25,000 or less, and even more preferably 4,000 or more and 10,000 or less.

In the present disclosure, the average molecular weight can be measured by gel permeation chromatography (GPC) under the following conditions.
<GPC Conditions (Polyalkyleneimine)>
Sample solution: adjusted to a concentration of 0.1 wt%. Apparatus/detector: HLC-8320GPC (integrated GPC) manufactured by Tosoh Corporation. Column: α-M + α-M (manufactured by Tosoh Corporation).
Eluent: 0.15 mol/L _{Na2SO4 ,} 1% _CH3COOH /water Column temperature: 40°C
Flow rate: 1.0mL/min
Sample solution injection volume: 100 μL
Standard polymer: pullulan with known molecular weight (Shodex P-5, P-50, P-200, P-800)
<GPC Conditions ((Co)polymers other than polyalkyleneimines)>
Sample solution: adjusted to a concentration of 0.1 wt% Detector: HLC-8320GPC (integrated GPC) manufactured by Tosoh Corporation Column: α-M + α-M (manufactured by Tosoh Corporation)
Eluent: 0.15 mol/L _{Na2SO4 ,} 1% _CH3COOH /water Column temperature: 40°C
Flow rate: 1.0mL/min
Sample solution injection volume: 100 μL
Standard polymer: pullulan with known molecular weight (Shodex P-5, P-50, P-200, P-800)

The content of the nitrogen-containing compound in the etching solution composition of the present disclosure is preferably 0.1% by mass or more, more preferably 1% by mass or more, even more preferably 3% by mass or more, and even more preferably 5% by mass or more, from the viewpoint of suppressing discoloration of the container and improving storage stability, and is preferably 20% by mass or less, and more preferably 15% by mass or less, from the viewpoint of viscosity. From the same viewpoint, the content of the nitrogen-containing compound in the etching solution composition of the present disclosure is preferably 0.1% by mass or more and 20% by mass or less, more preferably 1% by mass or more and 15% by mass or less, even more preferably 3% by mass or more and 15% by mass or less, and even more preferably 5% by mass or more and 15% by mass or less. When the nitrogen-containing compound is a combination of two or more types, the content of the nitrogen-containing compound is the total content thereof.

(acid)
The acid contained in the etching solution composition of the present disclosure is an acid containing at least nitric acid. The acid may be used alone (only nitric acid) or in combination of two or more kinds.

In one or more embodiments, the acid in the present disclosure may further include an acid other than nitric acid. From the viewpoint of suppressing discoloration of the container and improving storage stability, the acid other than nitric acid is preferably at least one selected from inorganic acids such as sulfuric acid, hydrochloric acid, and phosphoric acid; and organic acids such as citric acid, formic acid, tartaric acid, oxalic acid, sulfamic acid, acetic acid, and malonic acid. From the viewpoint of suppressing discoloration of the container and improving storage stability, the acid in the present disclosure is preferably a combination of an inorganic acid and an organic acid, and among these, a mixed acid consisting of phosphoric acid, acetic acid, and nitric acid is more preferable.

From the viewpoint of suppressing discoloration of the container and improving storage stability, the content of the acid in the etching solution composition of the present disclosure is preferably 60% by mass or more, more preferably 65% by mass or more, and from the same viewpoint, it is preferably 95% by mass or less, more preferably 93% by mass or less, and even more preferably 90% by mass or less. From the same viewpoint, the content of the acid in the etching solution composition of the present disclosure is preferably 60% by mass or more and 95% by mass or less, more preferably 60% by mass or more and 93% by mass or less, and even more preferably 65% by mass or more and 90% by mass or less. When two or more types of acid are used in combination, the content of the acid is the total content thereof.

From the viewpoint of suppressing discoloration of the container and improving storage stability, the content of nitric acid in the etching solution composition of the present disclosure is preferably 0.1% by mass or more and 10% by mass or less, more preferably 0.5% by mass or more and 7.5% by mass or less, and even more preferably 1% by mass or more and 5% by mass or less.

When a mixed acid consisting of phosphoric acid, acetic acid and nitric acid is used as the acid in the present disclosure, the content of phosphoric acid in the mixed acid is preferably 50% by mass or more and 95% by mass or less, more preferably 60% by mass or more and 93% by mass or less, and even more preferably 65% by mass or more and 90% by mass or less, from the viewpoint of suppressing discoloration of the container and improving storage stability. From the same viewpoint, the content of acetic acid in the mixed acid is preferably 2% by mass or more and 30% by mass or less, more preferably 3% by mass or more and 20% by mass or less, and even more preferably 5% by mass or more and 15% by mass or less. From the same viewpoint, the content of nitric acid in the mixed acid is preferably 0.5% by mass or more and 20% by mass or less, more preferably 1% by mass or more and 10% by mass or less, and even more preferably 1.5% by mass or more and 5% by mass or less. The mass ratio of phosphoric acid, acetic acid and nitric acid (phosphoric acid/acetic acid/nitric acid) can be appropriately set, for example, to 76/7/3.

The ratio of the nitrogen-containing compound content to the nitric acid content in the etching solution composition of the present disclosure (nitrogen-containing compound content/nitric acid content) is preferably 0.5 or more, more preferably 1.5 or more, and even more preferably 2.5 or more, from the viewpoint of suppressing discoloration of the container and improving storage stability, and is preferably 10 or less, more preferably 7.5 or less, and even more preferably 5 or less, from the viewpoint of viscosity. From the same viewpoint, the ratio of the nitrogen-containing compound content to the nitric acid content (nitrogen-containing compound content/nitric acid content) is preferably 0.5 or more and 10 or less, more preferably 1.5 or more and 7.5 or less, and even more preferably 2.5 or more and 5 or less.

(water)
Examples of the water contained in the etching solution of the present disclosure include distilled water, ion-exchanged water, pure water, and ultrapure water.

From the viewpoint of suppressing discoloration of the container and improving storage stability, the water content in the etching solution composition of the present disclosure is preferably 1% by mass or more, more preferably 1.5% by mass or more, and even more preferably 2% by mass or more, and from the same viewpoint, it is preferably 30% by mass or less, more preferably 20% by mass or less, and even more preferably 10% by mass or less. From the same viewpoint, the water content in the etching solution composition of the present disclosure is preferably 1% by mass or more and 30% by mass or less, more preferably 1.5% by mass or more and 20% by mass or less, and even more preferably 2% by mass or more and 10% by mass or less.

(Other ingredients)
The etching solution composition of the present disclosure may further contain other components within the scope of the present disclosure, such as a chelating agent, a surfactant, a solubilizing agent, a preservative, a rust inhibitor, a bactericide, an antibacterial agent, and an antioxidant.

In one or more embodiments, the etching solution composition of the present disclosure preferably does not contain hydrogen peroxide.

[Method of producing etching solution composition]
In one or more embodiments, the etching solution composition of the present disclosure is obtained by blending a nitrogen-containing compound, an acid containing nitric acid, water, and the above-mentioned optional components by a known method. Therefore, in one aspect, the present disclosure relates to a method for producing an etching solution composition (hereinafter also referred to as the "etching solution production method of the present disclosure") including a step of blending at least a nitrogen-containing compound, an acid containing nitric acid, and water. In the present disclosure, "blending at least a nitrogen-containing compound, an acid containing nitric acid, and water" includes, in one or more embodiments, simultaneously or sequentially mixing a nitrogen-containing compound, an acid containing nitric acid, water, and the above-mentioned optional components as necessary. The order of mixing may not be particularly limited. The blending can be performed using a mixer such as a homomixer, a homogenizer, an ultrasonic disperser, and a wet ball mill. The preferred blending amount of each component in the etching solution production method of the present disclosure can be the same as the preferred content of each component of the etching solution composition of the present disclosure described above.

In this disclosure, "the content of each component in the etching solution composition" refers, in one or more embodiments, to the content of each component of the etching solution composition used in the etching process, i.e., at the time of starting use in the etching process (at the time of use).

Embodiments of the etching solution composition disclosed herein may be so-called one-component types, in which all components are premixed and supplied to the market, or so-called two-component types, in which components are mixed at the time of use.

From the viewpoint of suppressing discoloration of the container and improving storage stability, the pH of the etching solution composition of the present disclosure is preferably 2 or less, more preferably 1 or less, even more preferably 0 or less, even more preferably less than 0, and even more preferably about -1. In the present disclosure, the pH of the etching solution composition is a value at 25°C and can be measured using a pH meter, specifically, by the method described in the examples.

The etching solution composition of the present disclosure may be stored and supplied in a concentrated state to the extent that its stability is not impaired. In this case, it is preferable in that production and transportation costs can be reduced. This concentrated solution can be appropriately diluted with water or an aqueous acid solution as necessary and used in the etching process. The dilution ratio can be, for example, 5 to 100 times.

[Layer to be etched]
The etching solution composition of the present disclosure is for etching a layer to be etched that contains at least one metal. The metal contained in the layer to be etched is preferably at least one metal selected from tungsten, tantalum, zirconium, hafnium, molybdenum, niobium, ruthenium, osmium, rhenium, rhodium, copper, nickel, cobalt, titanium, titanium nitride, alumina, aluminum, and iridium. In one or more embodiments, the etching solution composition of the present disclosure is preferably used for etching a tungsten film, a niobium film, a tantalum film, a zirconium film, and a molybdenum film.

[Etching solution package]
In one aspect, the present disclosure relates to an etching solution package (hereinafter also referred to as the "etching solution package of the present disclosure") in which an etching solution composition is filled in a container, the etching solution composition containing a nitrogen-containing compound, an acid containing at least nitric acid, and water, the container being a container made of polyethylene resin or polypropylene resin, and the etching solution composition being an etching solution composition for etching a layer to be etched containing at least one metal. In one or more embodiments, the etching solution package of the present disclosure is a combination of an etching solution composition and a container. The etching solution composition and the container in the etching solution package of the present disclosure may be those described above.

The present disclosure will be explained in detail below with reference to examples, but the present disclosure is not limited to these examples.

1. Preparation of Etching Solution Compositions (Examples 1 to 15 and Comparative Examples 1 and 2)
Etching solution compositions (pH: -1) of Examples 1 to 15 and Comparative Examples 1 and 2 were prepared by mixing the nitrogen-containing compound, mixed acid (phosphoric acid/acetic acid/nitric acid), and water shown in Table 1. The mixing amount (mass %, active content) of each component in the prepared etching solution composition is shown in Table 1.

The following nitrogen-containing compound, acid and water were used in preparing the etching solution composition.
(Nitrogen-containing compounds)
Polyethyleneimine [number average molecular weight 1800, "Epomin SP-018" manufactured by Nippon Shokubai Co., Ltd.]
Pentaethylenehexamine [molecular weight 232, manufactured by Tosoh Corporation]
Allylamine polymer [weight average molecular weight 5000, "PAA-05" manufactured by Nittobo Medical Co., Ltd.]
Diallylamine/sulfur dioxide copolymer [weight average molecular weight 5000, "PAS-92A" manufactured by Nittobo Medical Co., Ltd.]
(Mixed acid)
Phosphoric acid [Rinkagaku Kogyo Co., Ltd.]
Acetic acid [FUJIFILM Wako Pure Chemical Corporation]
Nitric acid [FUJIFILM Wako Pure Chemical Corporation]
(water)
Water [ultrapure water produced using a continuous pure water production system (Pure Conti PC-2000VRL type) and subsystem (Macace KC-05H type) manufactured by Kurita Water Industries Ltd.]

2. Measurement method of each parameter [pH of etching solution composition]
The pH value of the etching solution composition at 25° C. was measured using a pH meter (manufactured by DKK-Toa Corporation), and was the value measured one minute after the electrode of the pH meter was immersed in the etching solution.

3. Container The following container was used for filling the etching solution composition.
Polyethylene resin container: Hyper Pure Bottle, KM-331-2, blue, manufactured by Kodama Resin Industry Co., Ltd. Polypropylene resin container: JP Bottle Light Shielding, JP-1000A, brown, manufactured by Nikko Hansen Co., Ltd.

4. Evaluation [Evaluation of container discoloration]
9 L or 0.9 L of the etching solution composition (Examples 1 to 15 and Comparative Examples 1 and 2) shown in Table 1 was filled into various resin containers having a capacity of 10 L or 1 L, and the containers were stored at room temperature (25° C.) for two weeks with the lids closed. After storage, the contents were removed, the inside of the container was washed with water, and the appearance of the container was observed by visual comparison with an unused container, and the presence or absence and the degree of discoloration of the container were evaluated according to the following evaluation criteria.
<Evaluation criteria>
A: No discoloration of the container is observed. B: Very slight discoloration of the container is observed. C: Discoloration is observed in most of the container.

As shown in Table 1, it was found that Examples 1 to 15, in which the etching solution composition contains a nitrogen-containing compound, can suppress discoloration of the container even when stored for a long period of time, compared to Comparative Examples 1 and 2, in which the etching solution composition does not contain a nitrogen-containing compound.

The etching solution composition disclosed herein is useful in a method for manufacturing semiconductor substrates.

Claims (7)

A method for storing an etching solution composition for etching a layer to be etched that contains at least one metal, comprising the steps of:
The etching solution composition comprises a nitrogen-containing compound, an acid including at least nitric acid and phosphoric acid , and water;
A method for storing an etching solution composition, comprising filling the etching solution composition in a container made of polyethylene resin or polypropylene resin and storing the composition at a temperature of -10°C or higher and 40°C or lower. 2. The method for storing an etching solution composition according to claim 1, wherein a ratio of a content (mass%) of the nitrogen-containing compound to a content (mass%) of nitric acid in the etching solution composition (content of the nitrogen-containing compound/content of nitric acid) is 0.5 or more and 10 or less. The method for storing an etching solution composition according to claim 1 or 2, wherein the nitrogen-containing compound is at least one selected from polyalkyleneimines, alkylamines, allylamine polymers, and diallylamine/sulfur dioxide copolymers. The method for storing an etching solution composition according to any one of claims 1 to 3, wherein the etching solution composition does not contain hydrogen peroxide. The method for storing an etching solution composition according to any one of claims 1 to 4, wherein the metal contained in the layer to be etched is at least one metal selected from tungsten, tantalum, zirconium, hafnium, molybdenum, niobium, ruthenium, osmium, rhenium, rhodium, copper, nickel, cobalt, titanium, titanium nitride, alumina, aluminum, and iridium. An etching solution package having a configuration in which an etching solution composition is filled in a container,
The etching solution composition comprises a nitrogen-containing compound, an acid including at least nitric acid and phosphoric acid , and water;
The container is made of polyethylene resin or polypropylene resin,
The etching solution package, wherein the etching solution composition is an etching solution composition for etching a layer to be etched that contains at least one metal. The etching solution package according to claim 6, wherein the metal contained in the layer to be etched is at least one metal selected from tungsten, tantalum, zirconium, hafnium, molybdenum, niobium, ruthenium, osmium, rhenium, rhodium, copper, nickel, cobalt, titanium, titanium nitride, alumina, aluminum, and iridium.