JP3363782B2 - Highly selective oxide etching process for integrated circuit structures - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention uses a mixed gas of silicon tetrafluoride (SiF ₄ ) and one or more other fluorine-containing etchant gases in the presence of a silicon surface to plasma oxides of integrated circuit structures. Regarding the etching process. More specifically, the present invention provides a selectivity for preferentially etching silicon-related oxides in integrated circuit structures using a gas mixture of SiF ₄ and one or more other fluorine-containing etchant gases and a silicon surface. High plasma etching process, this plasma etching process is
It can be used with a capacitive discharge or an inductively coupled plasma generator.

[0002]

BACKGROUND OF THE INVENTION In integrated circuit structures, oxide layers are typically silicon or silicon containing surfaces as insulators, for example single crystal silicon such as silicon wafers, epitaxial silicon, polysilicon or silicides such as titanium silicide. Used as an overlying compound.
Such oxide layers are selectively etched to form vias, for example, for forming underlying silicon conductive contacts. Such oxide etching is conventionally performed with one or more fluorine-containing etching gases,
For example CF ₄ , CHF ₃ , CH ₂ F ₂ , CH ₃ F, C ₂ F ₆ , NF
₃ , plasma etching process using SF ₆ etc.

When using a conventional capacitive discharge plasma generator in such prior art oxide etching processes, the pressure in the etching chamber is typically about 1.
Maintained at 0 to 1000 millitorr (Torr) yields a selectivity for silicon of about 20: 1. That is,
Oxide instead of silicon is selectively etched in a ratio of about 20: 1.

However, when such high pressure is used for etching, the etching profile (profil
adversely affect the control of e). For example, less than 200 mtorr, preferably 3 to obtain a vertical wall of contacts and / or vias of 0.35 micrometer (μm) diameter.
Low pressures below 0 mTorr, especially about 10 mTorr should be used. However, using a conventional parallel plate capacitive discharge plasma generator under such a low pressure leads to a slow etching rate and a higher peak of the peak voltage, resulting in another form of plasma generation such as an electromagnetically coupled plasma generator. Need to use the machine.

While a pressure of about 10 mTorr and a plasma generated by an electromagnetically coupled plasma generator results in the etching of contact holes with vertical walls, the silicon of an etching system using the fluorine-containing etching gas chemistry described above. The selectivity for is reduced to about 6: 1. This is probably due to the difficulty of polymer formation in low pressure environments and the more aggressive nature of higher density plasmas due to the use of electromagnetically coupled plasma generators instead of capacitive discharge plasma generators. Is.

The low selectivity described above results in a high degree of planarization (pl
Sufficient for annealed structures and perfectly uniform etch / plasma chamber conditions. However, in many applications where it is desirable to etch as little silicon as possible when the overlying oxide etch exposes the silicon, the low selectivity described above is not acceptable. For example, in some cases, an oxide etch may etch the underlying silicon by about 50 angstroms (5x
It is preferably less than 10 ⁻³ μm).

The conventional plasma oxide etching process with one or more conventional fluorine-containing etching gases is due to the formation of polymers that normally interfere with the etching of silicon, where the liberation of oxygen during the etching of the oxide. Degrades the oxide surface polymer, but the absence of such generated oxygen prevents degradation of the polymer on the silicon surface. Therefore, in the case of electromagnetically coupled plasma, the above 6: 1
It is necessary to increase the production of such polymers in order to obtain a higher selectivity than the oxide etching ratio of silicon to silicon.

However, such increased polymer formation results in a lower oxide etch rate, process window (pr).
increase the selectivity of the process at the expense of reduced ocess window) and increased potential for particle generation. It also causes an unacceptable reduction in throughput and device yield.

Therefore, using an electromagnetically coupled plasma generator,
It is desirable to provide an oxide etch process that exhibits high selectivity to silicon without substantially reducing the etch rate of oxide materials even at low pressures, such as about 10 mTorr.

[0010]

SUMMARY OF THE INVENTION The oxide etching process of the present invention involves the plasma etching of an oxide on a silicon-containing surface using a mixed gas of SiF ₄ gas and one or more fluorine-containing etchant gases. Providing a process that is highly selective with respect to the containing surface. The etching chamber in which the process is performed also preferably includes an exposed silicon surface.

In a preferred embodiment, the etching process of the present invention is carried out with a plasma generated by an electromagnetically coupled plasma generator at a pressure of about 1 to 30 mTorr, typically about 10 mTorr. However,
The etching process is performed at a higher pressure of about 50 to 200 mTorr, typically about 100 mTorr using plasma generated by the electromagnetically coupled plasma generator or the capacitive discharge (parallel plate) type plasma generator. You can also

The oxide etching process of the present invention exhibits a high selectivity to silicon of about 30: 1, ie the oxide is either the type of plasma generator used or about 1-200.
Regardless of the pressure used over a range of millitorr, it etches at about 30 times the silicon etch rate.

The oxide etching process of the present invention uses Si
Includes highly selective plasma etching for plasma etching oxides on silicon-containing surfaces of integrated circuit structures in an etching chamber using a mixture of F ₄ gas and one or more fluorine-containing etchant gases. The etching chamber also preferably includes an exposed silicon surface.

The one or more fluorine-containing etchant gases used in the process of the invention in combination with SiF ₄ are:
Of course, it is understood to mean one (or more) fluorine-containing etchant gas other than SiF ₄ . Such a fluorine-containing etchant gas is 1 to 2
One or more fluorine-containing hydrocarbon gas having 1 carbon,
For example, CF ₄ , CHF ₃ , CH ₂ F ₂ , CH ₃ F, C ₂ F ₆ and mixed gas thereof are included. Other fluorine-containing etchant gases such as NF ₃ , SF ₆ and mixtures thereof as well as mixtures of such fluorine-containing etchant gases with fluorine-containing hydrocarbon gases having 1-2 carbons can also be used. .

The one or more fluorine-containing etchant gases used in combination with SiF _{4 in} the practice of the present invention also include one or more higher molecular weight fluorocarbons. Higher molecular weight fluorohydrocarbons have the general formula C _x
H _y F _z (where x is 3 to 6, y is 0 to 3, z in the case of 2x-y (cyclic compounds) or 2x-y +
2 (for acyclic compounds)) with 3 to 6 carbons. Such fluorocarbons having 3 to 6 carbons include carbon and fluorine or carbon, fluorine and hydrogen, and include organic molecules that are cyclic or acyclic but are not aromatic.

Specific examples of the cyclic fluorohydrocarbon compound having 3 to 6 carbons contained in the above formula include CH ₃ H ₃ F ₃ and
C ₃ H ₂ F ₄ , C ₃ HF ₅ , C ₃ F ₆ , C ₄ H ₂ F ₆ , C
₄ HF ₇ , C ₄ F ₈ , C ₅ H ₃ F ₇ , C ₅ H ₂ F ₈ , C ₅
HF ₉ , C ₅ F ₁₀ , C ₆ H ₃ F ₉ , C ₆ H ₂ F ₁₀ , C ₄ HF
₁₁ and C ₆ F ₁₂ . Specific examples of the acyclic fluorohydrocarbon compound having 3 to 6 carbons included in the above formula are C
₃ H ₃ F ₅ , C ₃ H ₂ F ₆ , C ₃ HF ₇ , C ₃ F ₈ , C ₄ H
₃ F ₇ , C ₄ H ₂ F ₈ , C ₄ HF ₉ , C ₄ F ₁₀ , C ₅ H
₃ F ₉ , C ₅ H ₂ F ₁₀ , C ₅ HF ₁₁ , C ₅ F _{12 2} , C ₆ H
₃ F ₁₁ , C ₆ H ₂ F ₁₂ , C ₄ HF ₁₃ and C ₆ F ₁₄ .
Cyclooctfluorobutane (C ₄ F ₈ ) in the above-mentioned fluorohydrocarbon compound having 3 to 6 carbons is preferable.

All of these higher molecular weight fluorohydrocarbon etchant gases are used with SiF ₄ either alone or in combination with the other fluorine-containing etchant gases described above.

The amount of SiF ₄ gas used in the etching chamber can range from about 10 to 50% by volume of the total amount of the fluorine-containing etchant gas (s) used. Thus, for example, if one or more fluorine-containing etchants are run in a 9 liter etching chamber at a flow rate of about 20-60 standard cubic centimeters per minute (sccm), the SiF ₄ flow rate is about 2 (10 vol% of 20 sccm)- The range is 30 (50% by volume of 60 sccm) sccm. If larger or smaller etching chambers are used, the flow rates need to be adjusted above or below each, but the ratio of SiF _{4 to} the total amount of one or more fluorine-containing etchant gases used in the process is the same. There is.

A mixture of SiF ₄ and one or more fluorine-containing etching gases can be used alone in the etching chamber, but may also be mixed with one such as helium or argon.
It may be diluted with one or more inert gases. Such an inert gas may flow into the etching chamber at a rate of 0 to about 200 sccm. In some cases, nitrogen or other non-reactive gas (es) may also be used with a mixture of SiF ₄ and one or more fluorine-containing etching gas (with or without inert gas). .

The plasma etching process of the present invention using a combination of SiF ₄ and one or more fluorine-containing etching gases (with or without other gases) may be performed using conventional capacitive discharge (parallel plate) plasma generators or electromagnetic coupling. It can be used in combination with a plasma generator. Plasma associated with the etching chamber during the etching process of the present invention includes plasma generated within the etching chamber or outside the etching chamber but upstream of the chamber as a stream of etching gas.

Further, co-pending US patent application (application no. 07) filed June 27, 1991 by the present inventors assigned to the assignee of the present invention, cross-reference is described herein. An electrode having a silicon-containing surface may be placed in the etching chamber, as described in detail in US Pat. The silicon-containing electrode is optionally maintained with a high frequency bias. The presence of this silicon-containing electrode in the etching chamber during etching has been found to be advantageous with or without high frequency bias of the electrode. However, if no radio frequency bias is applied to the electrode, the silicon-containing surface of the electrode will be reduced to about 200 to prevent the polymer from adhering to the surface.
It is advantageous to maintain an elevated temperarue of ~ 300 ° C.

Without being bound by the theory of operation, the presence of the silicon-containing electrode during the etching process is
Free fluorine radicals in the chamber
It appears to prevent the presence of an excess of cals), ie act as a buffer.

The pressure used in the etching process of the present invention can vary from as little as 1 mTorr to as high as 200 mTorr. However, due to insufficient plasma generators to start or maintain the plasma at pressures less than about 50 Torr, it is possible to use pressures less than about 50 mtorr with a volumetric plate plasma generator. It is noted that this cannot be said.

Thus, when using a capacitive discharge plasma generator in the practice of the process of the present invention, the pressure will be about 50-.
It is preferably maintained in the range of 200 millitorr.

However, it is highly desirable to operate the process of the present invention at a pressure of less than about 50 mTorr to obtain vertical wall holes in the oxide layer, such as the vias described above, so the process of the present invention is preferred. Is in a wider pressure range of about 1 to 200 mtorr, most preferably about 1 to
Preference is given to using a plasma generator which can be operated in a pressure range of 30 mtorr. Therefore, it is advantageous to use an electromagnetically coupled plasma generator in the practice of the process of this invention.

"Electromagnetically coupled plasma generator" is meant to define any type of plasma generator that uses an electromagnetic field rather than a capacitively coupled generator to generate the plasma. Such an inductively coupled plasma generator is characterized herein as a "dense" plasma, about 10
A plasma having an ion density greater than ¹⁰ ions / cubic centimeter can be generated, which is the preferred plasma density useful in the process of the present invention.

For example, Matsuo et al., US Pat. No. 4,401,054
U.S. Pat. No. 4,492,620 to Matsuo et al. And U.S. Pat.No. 4,778,561 to Ghanbari (cross-references to the three patents are set forth herein) and the Journal of Vac.
uum Science Technology B, Vol.4, No.4, Jul / Aug 19
86, pp818-821, "SiO ₂ by Machida et al.
Planarization Technology With Biasing and Electron
Cyclotron Resonance Plasma Deposition for Submicr
An electron cyclotron resonance (ECR) type plasma generator described in a paper entitled "On Interconnections" is included in the above "electromagnetically coupled plasma generator".

Also, for example, Steinberg et al., US Pat.
The electromagnetically coupled spiral or cylindrical resonators described in U.S. Pat. No. 4,918,031 to 8,092 or Flamm et al. Are also included in the above "inductively coupled plasma generator" and cross-references to both of these patents are described herein.

Further, for example, Boswell, US Pat. No. 4,810,
Helicon diffusion resonators, such as the plasma generator described in the '935 patent, are also included in the above "inductively coupled plasma generator" and the cross-reference to this patent is also described herein.

Still further, Ogle US Pat. No. 4,948,458 describes all types of electromagnetically coupled plasma generators, including transformer coupled plasma generators, and cross-references to this patent are also described herein. .

Plasma power level
Can vary from about 500 Watts to 5 kilowatts (kw) and depends on the particular type of plasma generator, chamber dimensions, desired etch rate, and the like. EC for example
Using an R-type electromagnetically coupled plasma generator with an etch chamber of about 6 liters and a desired etch rate of about 5000 angstroms per minute, the power is typically about 2
The range is up to 3 kw. For an inductively coupled plasma generator used with a 2 liter etch chamber and the desired etch rate of about 5000 angstroms per minute, the power is typically in the range of about 1-2 kW. When generating a high-density plasma, the power density (power de
power level in terms of plasma generation chamber capacity is about 1 in a 4 liter plasma generation chamber.
Equivalent to a power level of 000 watts is preferred.

A further advantage of the process of the present invention is the low polymer formation of SiF due to the high selectivity towards silicon exhibited by the use of silicon tetrafluoride (SiF ₄ ).
₄ gas with one or more “leaner”
) "A higher etch rate is possible because a fluorine-containing etching gas is used. A" less carbon "fluorine-containing etching gas that produces less polymer contains carbon such as NF ₃ or SF _6. No fluorine-containing etching gas or fluorine to carbon ratio of at least 3:
1 and eg CHF ₃ , preferably at least 4: 1 carbon and fluorine containing gas, eg CF ₄ .

The present invention will be described in more detail with reference to the following examples, but these examples do not limit the present invention in any way.

[0034]

EXAMPLE To further illustrate the practice of the present invention, a 6 inch diameter silicon wafer having an oxide layer thereon and a photoresist mask pattern formed on the oxide layer was deposited at about 10 millitorr. It was placed in a 9 liter plasma etching chamber maintained at a pressure of. SiF
₄ flowing 12sccm and CF ₄ 30 sccm mixed gas into the chamber, plasma is about using electromagnetic coupling plasma generator 25
It was ignited and maintained at a power level of 00 watts.

Oxide etching was carried out for about 60 seconds, after the plasma was extinguished, the gas flow was stopped and the etched wafer was removed from the etching chamber. Examination of the etched oxide layer using SEM showed that contact holes were formed in the oxide layer having vertical walls with an average diameter of about 0.35 microns with respect to the surface of the oxide layer.

[0036]

The process of the present invention thus provides an improved plasma etching process for oxides, wherein the use of a combination of silicon tetrafluoride and one or more fluorine-containing etching gas is To provide an etching system with high selectivity to. Due to this high selectivity, a low carbon fluorine-containing etching gas, such as a low carbon to fluorine ratio gas, can optionally be used, which gives faster etching rates due to less polymer formation. A capacitive discharge or inductively coupled plasma generator can also be used in the process to use this etching gas mixture. This process can be carried out at pressures in the range of about 1 to 200 mtorr. This process can be carried out using an inductively coupled plasma generator, preferably at a low pressure in the range of about 1-30 mTorr, typically about 10 mtorr, or with a capacitive discharge plasma generator. High pressures, preferably about 50 to 200 mTorr, typically about 100 mTorr. Due to the use of an inductively coupled plasma generator, the process can be used at low pressures of about 1-30 mTorr and can form vertical sidewall holes in the oxide layer to be etched.

[Brief description of drawings]

FIG. 1 is a flow sheet showing one aspect of the process of the present invention.

─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Jerry Yuen Quy Wong Cougar Circle, Fremont, California, USA 44994 (72) Inventor David W. Gloechel Via Ventana, Los Altos Hills, California, USA 27985 (72) Inventor Peter Earl. Keswick United States, California, Newark, Joe Quinn Murrieta Avenue 6371-A (72) Inventor Chan Rong Young United States, California, Los Gatos, Leroy Avenue 16788 (56) Reference JP-A-3-295231 (JP, A) JP-A-2-16730 (JP, A) JP-A-3-12922 (JP, A) JP-A-62-142326 (JP, A) JP-A-55-154582 (JP, A) JP-A-61 -184823 (JP, A) JP-A-64-57600 (JP, A) JP-A-55-154581 (JP, A) US Patent 4806199 (US, A) US Patent 4844775 (US, A) European Patent 210605 (EP , B1) (58) Fields investigated (Int.Cl. ⁷ , DB name) H01L 21/3065 C23F 4/00

Claims (10)

(57) [Claims] 1. A plasma etch process for oxide etching on the silicon-containing surface of an integrated circuit structure on a semiconductor wafer, an etching chamber containing the wafer, one or more fluorine If Yes etching gas And hydrogen gas
Or the fluorine-containing etching gas containing no oxygen or oxygen gas
A scan, the steps of flowing, the step of maintaining a plasma of the edge <br/> Chingugasu the etch chamber at a pressure of 1-30 mTorr, the silicon-containing surface of the etch chamber, wherein
During the inflow of process and the step of maintaining the temperature above 200 ° C.
A plasma etching process having . Wherein said silicon-containing surface, the process according to claim 1, wherein is maintained at a temperature of 300 ° C. or less. Wherein the one or more fluorine-containing etching gas, the process according to claim 1, further comprising one or more fluorine-containing hydrocarbon gas. Wherein said one or more fluorine-containing hydrocarbon gas, the process of claim 3 having one or more fluorine-containing hydrocarbon gas having 1 to 2 carbons. 5. The one or more fluorine-containing hydrocarbon gas has a general formula CxHyFz (x is 3 to 6 , y is 0 to 3 , z
Is (2x-y) or (2x-y + 2)) having 3 to 6 carbon atoms.
4. The process according to claim 3, which comprises one or more kinds of the fluorinated hydrocarbon compound. Wherein said silicon-containing surface, is used to maintain the plasma process of claim 1, further comprising a silicon-containing electrode of the etch chamber. 7. Furthermore, the process according to claim 6, further comprising the step of applying RF power to said silicon-containing electrode. 8. The process of claim 1, wherein maintaining the plasma inductively couples energy into the chamber. 9. The process of claim 8 , wherein the plasma is maintained at an ion density of 10 ¹⁰ ions or more per cubic centimeter. Wherein said silicon-containing surface, a single crystalline silicon, and epitaxial silicon, polysilicon
When process of claim 1 wherein is selected from the group consisting of a silicide.