KR101063591B1 - Recovery of hydrophobicity of low-k and ultra low-k organosilicate films used as inter metal dielectrics - Google Patents

Abstract

Often used to reduce the RC delay in integrated circuits, silica-like frameworks in which alkyl or aryl groups (to add hydrophobicity to materials and create free volume) are often attached directly to Si atoms in a network. There is a dielectric film of porous organosilicate having. Si-R bonds rarely survive exposure to plasma or chemical treatments commonly used in processing. This is especially true for materials with open cell pore structures. When the Si-R bond is broken, the material loses hydrophobicity due to the formation of hydrophilic silanol and the low dielectric constant is impaired. The present invention provides a method for restoring hydrophobicity of a material using a new class of silylating agents that may have the general formula (R ₂ N) _x SiR _y , wherein X and Y are each an integer of 1 to 3. And an integer from 3 to 1, and R and R 'are selected from the group consisting of hydrogen, alkyl, aryl, allyl and vinyl moieties. In addition, the mechanical strength of the porous organosilicate is likewise improved as a result of the silylation treatment.

Description

Methods of restoring the hydrophobicity of low and extremely low thickness organosilicate films used as intermetallic dielectrics and articles made therefrom }

BACKGROUND OF THE INVENTION The present invention relates to interconnect wiring networks on ultra high performance microelectronic chips used in computers, microprocessors, microcontrollers, sensors, communication devices, and the like. In particular, the inventive arrangements described herein relate to significantly reducing signal propagation delays associated with such wiring. The method of the present invention described in detail and claimed provides the chemistry and processing required to restore the dielectric properties of low dielectric constant dielectrics after the dielectric has been made hydrophilic by a given plasma exposure, and the porous organo Provided are the chemistry and methods required to maintain the low dielectric constant of the porous organosilicate dielectric and increase mechanical strength after deposition of the silicate dielectric and during the process of forming the interconnect structure comprising the film. The invention also relates to a method which enables the successful integration of these materials into such a chip.

High performance microprocessors, microcontrollers, and communication chips require ultrafast interconnects between active transistor devices used to perform various functions such as logical operations, storage and retrieval of data, provision of control signals, and the like. With advances in transistor device technology that currently lead to ultra large scale integration (ULSI), the overall operating speed of these advanced chips is limited by signal propagation delays in interconnect wiring between individual devices on the chip. Getting started. The signal propagation delay at the interconnect depends on the RC product, where R represents the resistance of the interconnect wiring and C represents the total capacitance of the interconnect scheme in which the wiring is embedded. The use of copper instead of aluminum as the interconnect wiring material allows for a reduction in the resistance contribution to the RC product. A current focus in the microelectronics industry is to reduce interconnect capacitance by using lower dielectric constant (k) insulators to form multilayer interconnect structures on a chip.

One prior art method of forming an interconnect interconnect network at such a small scale is the dual damascene (DD) process shown schematically in FIGS. 1A-1G. Referring to FIG. 1A, in a standard DD process, an inter metal dielectric (IMD), shown as two layers 1110 and 1120, is coated on the substrate 1100. Via level dielectric 1110 and line level dielectric 1120 are shown separately to clarify the process flow diagram description. In general, these two layers can be made of the same or different insulating films, in the former case being applied as a single monolithic layer. A hard mask layer or layered stack 1130 is optionally used to facilitate etch selectivity and to act as a polish stop. The interconnect wiring network consists of two types of features: a line feature that traverses a distance across the chip and a via feature that connects lines of different levels of interconnect in a multilayer stack. . Historically, the two layers are made from inorganic glass such as silicon dioxide (SiO ₂ ) or fluorinated silica glass (FSG) films deposited by plasma enhanced chemical vapor deposition (PECVD).

1B and 1C, in a dual damascene (DD) process, the locations of lines 1150 and vias 1170 are lithographically defined in photoresist layers 1500 and 1510, respectively, and reactive ion etching. It is transferred to a hard mask layer and an IMD layer using a reactive ion etching (RIE) process. The process sequence shown in FIGS. 1A-1D is referred to as a "line-first" approach. After the trench formation, lithography is used to define the via pattern 1170 in the photoresist layer 1510, which is transferred into the dielectric material and via openings, as shown in FIG. 1D. 1180 will be generated. The dual damascene trench and via structure 1190 after the photoresist is stripped is shown in FIG. 1E.

As shown in FIG. 1F, the recessed structure 1190 is then a conductive liner material or material that acts to protect the conductor metal interconnects and vias, and acts as an adhesion layer between the conductor and the IMD. Coated by a material stack 1200. The recess is then filled with a conducting fill material 1210 over the surface of the patterned substrate. This fill is most commonly accomplished by electroplating copper, but other methods such as chemical vapor deposition (CVD) and other materials such as aluminum or gold may also be used. The fill material and liner material are then treated with chemical-mechanical polish (CMP) to be coplanar with the surface of the hard mask and the structure at this stage is shown in FIG. 1F. As shown in FIG. 1G, a capping material 1220 is used to passivate the exposed metal surface and to act as a diffusion barrier between the metal and any additional IMD layer deposited thereon. It is deposited as a blanket film. Silicon nitride, silicon carbide, and silicon carbonitride films deposited by PECVD are generally used as capping material 1220. This process sequence is repeated for each level of interconnect on the device. This process is called a dual damascene process because two interconnect features are simultaneously defined to form a conductor embedded in an insulator by a single polishing step.

To lower capacitance, lower k, such as PECVD organosilicates or spin-on organosilicates with k values in the range of 2.5 to 3.1 instead of PECVD silicon dioxide based dielectrics (k = 3.6 to 4.1) It is necessary to use a dielectric of. Such organosilicates have a silica like backbone in which organic groups such as hydrogen and / or alkyl or aryl groups are attached directly to Si atoms in the network. Its elemental composition generally consists of Si, C, O, and H in various proportions. C and H are most often present in the form of a methyl group (-CH ₃ ). The main function of these methyl groups is to add hydrophobicity to the material. A secondary function is to form a free volume in the film and to reduce the polarizability of the film. The k value can be reduced to 2.2 (ultra low k), even less than 2.0 (extremely low k) by introducing porosity into the insulator of the film. For the sake of simplicity, such extremely low k materials and extremely low k materials are collectively referred to herein as very low k materials.

Although an adjustable range of k values is possible with this series of very low k materials, the integration of such materials into copper interconnects by the dual damascene process described above or by any other modification of the dual damascene process. There are some difficulties in this. The main difficulty is due to the relative ease of oxidation or cleavage of Si-organic group linkages (eg Si-methyl), i.e. as a result potential with water in the surrounding environment. The phosphorus reaction leads to the formation of silanol (Si-OH) groups in the film, which is why the organosilicate-based material is very sensitive to plasma exposure.

Silanol absorbs water and thus significantly increases the dielectric constant and dielectric loss factor of the film, thus negating the performance benefits expected from very low k films. Silanol also increases electrical leakage in the film, thus forming a potentially unreliable interconnect structure. As described above, since reactive ion etching and plasma etching are the key steps required in the formation of dual damascene trench and via structures and in the removal of the photoresist used to pattern very low k materials, dual While it is not impossible to avoid plasma damage of this class of films during damascene integration, it is quite difficult.

Several attempts have been made to minimize the loss of hydrophobicity in low k films using non-oxidizing resist strip plasmas consisting of some or all of He, H ₂ , N ₂ , CO, and the like. . Note, however, that none of these plasma chemistries is fully successful in preventing the loss of hydrophobicity of very low k materials. This is especially true for porous low k materials that have very large surface areas and are easily damaged during the resist stripping process.

Other methods to prevent low k materials from losing their hydrophobicity and their dielectric properties include fluorinated or non-fluorinated organic polymer based low k materials, such as SiLK ™ dielectrics from Dow Chemical, Honeywell. Flare ™ and other polyimides, benzocyclobutenes, polybenzoxazoles, polyphenylene ether based aromatic thermoset polymers; And the use of chemical vapor deposited polymers, such as poly paraxylylene, which is not easily damaged during traditional process plasma exposures associated with dual damascene processing. However, these materials do not have the other properties required for low k dielectric films such as low thermal expansion and small pore size.

Another problem faced with the successful integration of organosilicate-based porous materials is their low modulus of elasticity, fracture toughness, which often causes obstacles in CMP, dicing and packaging operations. toughness and hardness are mechanically very brittle. The mechanical strength of such resins depends on both the void volume and the chemical structure. Its mechanical strength decreases not only with increasing porosity but also with increasing cage-like structure of the siloxane backbone. Since it is essential to maintain a low dielectric constant, it is very difficult to reduce the void volume while maintaining the same mechanical strength.

Several methods for treating porous organosilicate materials with weak mechanical strength (Padhi et al., J. Electjcochem. Soc., 150 (1), G10-G14, (2003) and the same assignee as the assignee of the present invention) Although US Patent Application Publication US2004 / 0087135 A1) of Canaperi et al., Assigned to U.S., has been proposed, most of these methods are difficult to implement due to the fact that these methods require non-standard process flow diagrams or non-standard tools. Therefore, they are expensive to implement in production.

In the literature on porous silica based films, for example, in Prakash et al., Nature, 374, 439, (1995), surface modification for introducing hydrophobic end groups during film formation is a wet chemical. This is accomplished by treatment, in which a silylating agent (Trimethylchlorosilane (TMCS)) is introduced into the porous network by a low surface tension carrier solvent. This reaction, called silylation, is feasible in the case of a film under the formation process because of the large amount of free volume and the presence of a large amount of silanol to be condensed and crosslinked. To date, it is not clear whether similar reactions can be performed on fully formed films with less silanol than those under the forming process, even after exposure to process chemicals damaging the film. Attempts have been made to restore the hydrophobicity and carbon content of porous OSG films after damage using hexamethy disilazane (HMDS) as the silylating agent (Chang et al., J. Electrochem Soc, 149, 8, F81-F34, 2002). ] Has published a study. However, as can be clearly understood from the study results, HMDS in any medium cannot completely restore the properties of the porous OSG film.

Similarly, TMCS is also not completely effective in restoring dielectric properties. Both HMDS and TMCS are monofunctional silylating agents that attack only silanol groups per molecule on the surface of the low k material and on the pore walls. However, organosilicate low k materials have two different types of silanols classified as (Gun'ko et al., J. Colloid and Interface Sci 228, 157-170 (2000). Types of silanols are themselves (1) fully non-interactive single silanols (also called isolated silanols) that have no neighboring silanols nearby, (2) very weak interactive silas Nol, and (3) non-hydrogen bonded silanol consisting of weakly interactive or non-interactive geminal silanol (also called disilanol). The first type of silanol is hydrogen bonded silanol Most monofunctional silylating agents readily attack and replace isolated silanol, but generally do not readily attack the other two types of non-hydrogen bonded silanol . Such The reason for this is that steric hindrance prevents the easy capture of one or more silanols simultaneously with a monofunctional silylating agent, and also allows the use of low k materials without releasing erosive reaction byproducts. In order to easily silylate the surface and pore walls, it is important to use a silylating agent with the most reactive functionality.

Hu et al., J. of Electrochem. Soc., 150 (4) F61-F66 (2003) also discloses a study examining the efficacy of dimethyldichlorosilane (DMDCS) as a silylating agent to restore the properties of low k materials. However, in this study, it has been reported that dimethyldichlorosilane forms a monolayer on the top surface of the film and does not penetrate into the bulk of the porous low k material. Thus, it is difficult to restore the bulk dielectric properties of low k materials unless the conditions for silylation as well as the appropriate silylation medium are used. In addition, hydrogen chloride is present as a byproduct of any chlorine-based silylating agents such as dimethyldichlorosilane and TMCS, which is erosive and cannot be used in copper containing interconnect structures.

Therefore, an aspect of the present invention is to provide an inexpensive, non-destructive method of increasing mechanical strength by changing the cage to network ratio of porous organosilicate resin after deposition and curing.

It is therefore an object of the present invention to provide a process flow diagram using this silylating agent as well as a class of silylating agents that completely restore the hydrophobicity of the material after process exposure without yielding erosive byproducts.

It is a further object of the present invention to provide a method by which the silylating agents of the present invention can be introduced to penetrate the bulk of porous low k materials and restore their properties.

It is a further object of the present invention to alter the chemistry of the resin after deposition and pore formation in order to increase mechanical strength and to overcome some of the major obstacles encountered in the successful integration of porous organosilicates.

The method of changing the cage-to-network ratio in the present invention is also made by silylation, which introduces new network-forming siloxane bonds into the film, thereby improving mechanical properties without significantly increasing the dielectric constant. However, for the silylation reaction to occur, the organosilicate film must have a large amount of silanol. It is also an object of the present invention to provide such silanol prior to silylation, and to ensure that the silylation reaction takes place sufficient to strengthen the film.

An advantage of the present invention is that material selection for extremely low k intermetallic dielectrics does not have to be constrained by consideration of the effects of plasma and wet clean damage on the material, because the material This is because by using the silylation method disclosed in the above, it can be restored to its original property after being damaged. In addition, the availability of reliable methods to restore the properties of films damaged by plasma exposure allows for more process options in reactive ion etching (RIE) and resist stripping operations required for dual damascene production, As a result, more stable and cheaper processing can be obtained. Finally, the present invention provides a method of increasing the mechanical robustness of a porous organosilicate film to be used as an IMD.

Accordingly, the present invention provides a low or very low dielectric constant having a hydrogen atom or an alkyl or aryl group attached to a silicon atom, which is used in an insulating layer of a low or very low dielectric constant in a semiconductor chip or chip carrier or semiconductor wafer. A method for restoring the properties of an organosilicate film of wherein the organosilicate film performs processing that tends to degrade its properties. The method includes applying a silylating agent comprising aminosilane to the film such that the film is hydrophobic. The aminosilane may have the general formula (R ₂ N) _X SiR ' _Y , wherein X and Y are each an integer of 1 to 2 and an integer of 3 to 2, and R and R' are hydrogen, alkyl, aryl, Allyl, phenyl and vinyl moieties. The aminosilane is preferably bis (dimethylamino) dimethylsilane.

The aminosilane may have the general formula (R ₂ N) _X SiR ' _Y R " _Z , wherein X, Y and Z are each an integer of 1 to 3, an integer of 3 to 0, and an integer of 3 to 0, respectively. Provided that the sum of X, Y and Z is 4 and R, R 'and R "are hydrogen, alkyl, aryl, allyl, phenyl or vinyl moieties.

The present invention also provides a step of applying a silylating agent to a film such that the film is hydrophobic, wherein the silylating agent has a form of R _X H _Y Si-A, where X and Y are integers of 0 to 2 and 3 to 1, respectively. In which R is any hydrogen, alkyl, aryl, allyl, phenyl or vinyl moiety, and A is a silazane, chloro, amino or alkoxy moiety. The silylating agent may comprise amino, chloro and alkoxy terminated monofunctional silylating agents, wherein the methyl moiety on the silylating agent is at least partially replaced by hydrogen analogues. The silylating agent may also include polymeric siloxanes having amino, alkoxy or silazane terminated end groups. Terminal groups of polymeric siloxanes may include mono- or di-alkyl, aryl, vinyl or hydrogen moieties. The siloxanes may comprise amino terminated polydimethylsiloxanes.

The silylating agent also has the general formula R _X H _Y Si _Z A, where X and Y are each an integer from 0 to 5 and an integer from 6 to 1, Z is from 1 to 2, R is hydrogen, alkyl, aryl , Allyl, phenyl or vinyl moiety and A is a silazane, chloro, amino or alkoxy moiety.

According to the invention, the processing may include etching the film, and removing the photoresist material from the film, wherein the silylating agent is applied after the etching step and the removing step. The etching and removing may be performed by exposing the film to a plasma. Single damascene or dual damascene processing may be used, and the step of applying the silylating agent may be performed after defining at least one of the interconnect lines and vias, and prior to depositing the electrical conductor. The step of applying the silylating agent is performed prior to depositing the conducting liner.

The silylating agent may be obtained by spin coating a liquid, impregnating the substrate into a liquid, dissolving the substrate in a liquid, gaseous state or supercritical carbon dioxide, and preferably at least one of alkanes, alkenes, ketones, ethers and esters. It may be applied by spray coating with a cosolvent selected from the group comprising. It should be noted that the silylating agent should be applied in the absence of moisture. The film may be annealed, preferably at a temperature of at least 350 ° C. or at a temperature as high as 450 ° C. for more than one minute. This annealing can be performed before or after applying the silylating agent. The silylating agent is preferably applied at a temperature of at least 25 ° C. This annealing is performed to facilitate at least one of condensing the unsilylated silanol and forming additional siloxane bonds.

The silylating agent may be dissolved in a solvent, including a non-polar organic solvent having a low surface tension selected from the group consisting of alkanes, alkenes, ketones, ethers, esters, or any combination thereof. have. Preferably, this solvent has a surface tension low enough to penetrate the pores in the film. This silylating agent may preferably have a concentration of 2% to 10% by weight in the solvent, but may also have a concentration as low as 0.5% or more by weight in the solvent.

The silylating agent may be applied at room temperature or higher for a time of 1 minute to 1 hour. When the silylating agent is applied, agitation or ultrasonication may be used. This film can be cleaned to remove excess silylating agent. The film may preferably be calcined at temperatures up to 450 ° C.

The silylating agent may be applied in a gaseous state at a temperature between room temperature and 450 ° C. for a time of 30 seconds to 1 hour, or substantially at 250 ° C. for 5 minutes. The silylating agent may be applied in supercritical carbon dioxide, at a temperature of 25 ° C. to 450 ° C., at a pressure of 1000 to 10,000 psi, for a time of 30 seconds to 1 hour. The silylating agent may also be applied for over 30 seconds at a temperature above 75 ° C. in supercritical carbon dioxide or vapor medium.

The silylating agent is preferably difunctional. It may include (bis) dimethylaminodimethylsilane or (bis) dimethylaminomethylsilane.

The step of applying the silylating agent is carried out after treating the film with either ultraviolet radiation, exposure to ozone, exposure to mildly oxdizing plasma, or a combination thereof, which introduces the silanol into the film. This method can be performed in a chemical vapor deposition chamber or an atomic layer deposition chamber.

The properties restored by the method according to the invention include at least hydrophobicity, modulus of elasticity, low dielectric constant, fracture toughness and hardness, dielectric breakdown strength, low dielectric leakage and dielectric reliability. It includes one. The interconnect structures in which these restored films are integrated further comprise silicon dioxide, fluorinated tetraethyl orthosilicate, fluorinated silica glass, fluorinated or non-fluorinated organic polymers, thermoset polymers and chemical vapor deposition. And one or more intermetallic dielectrics selected from the group consisting of polymers. Thermosetting polymers consist mainly of polyphenylene ethers. The chemical vapor deposited polymer may be poly paraxylylene. The additional intermetallic dielectric may be an organic polymer selected from the group consisting of polyimides, benzocyclobutenes, polybenzoxazoles, aromatics.

The invention also relates to an insulating material having a plurality of electrical conductors formed therein; And an intermetallic dielectric comprising an organosilicate film having a hydrogen atom, an alkyl group or an aryl group attached to a silicon atom, the surface of the organosilicate film being one of the silylating agents mentioned in the above methods and the organo It relates to an article of manufacture comprising a reaction product between silicate films. The article may be configured as a semiconductor chip, semiconductor chip carrier or semiconductor wafer. The surface may be an outer surface of the film or a surface of pores inside the film.

These and other aspects, features and advantages of the present invention will be apparent from the following detailed description of the present invention when taken in conjunction with the drawings. A brief look at the drawing is as follows.
1A-1G are schematic diagrams illustrating a process flow diagram for a standard dual damascene integration scheme.
2 is a schematic diagram illustrating the effect of plasma exposure and silylation on the chemistry of very low k materials.
3A is a schematic diagram showing how a monofunctional silylating agent captures only one isolated silanol and blocks neighboring silanol.
FIG. 3B is a schematic diagram showing how the difunctional analog of the silencing agent used in FIG. 3A succeeds in simultaneously capturing two neighboring silanols.
4A shows a series of FTIR spectra illustrating the effects of mono-, di-, and tri-functional silylating agents.
4B is an enlarged view of a portion of FIG. 4A.
FIG. 5 shows a comparison of FTIR spectra and contact angle data of pristine IMD, plasma damaged IMD, BDMADMS treated IMD, and BDMADMS treated and annealed IMD.
FIG. 6 shows wave numbers for pristine porous organosilicate IMD, plasma damaged porous organosilicate IMD, BDMADMS treated porous organosilicate IMD, and BDMADMS treated and annealed porous organosilicate IMD. It is a graph showing infrared absorbance as a function.

Modifications described for the present invention can be realized in any combination desired for each specific application. Thus, the specific limitations and / or implementation improvements described herein that may have specific advantages for specific applications are not necessarily required for all applications. In addition, it should be understood that not all limitations need to be implemented in a method, system and / or apparatus that includes one or more concepts of the invention.

A primary embodiment of the present invention (hereinafter referred to as "first embodiment") relates to the use of a new class of silylating agents, which are silylating agents which are very effective in restoring dielectric properties. In addition, the first embodiment of the present invention also relates to a method of introducing such silylating agents into the process to ensure that the bulk (including all internal pore walls) as well as the outer surface of the porous low k material are hydrophobic. Finally, a second embodiment of the present invention discloses specific molecular modifications on moiety, such as silazane, used in the prior art, in order to be more effective as a silylating agent.

In a first embodiment of the present invention, the silylating agent of the present invention is a single or dual damascene for forming interconnect structures after defining interconnect lines and vias and prior to depositing conductive liner and filler material comprising interconnect metal. Is introduced into the process. Specifically, the silylating agent is introduced after reactive ion etching (RIE) of the low k material followed by the resist stripping. When a dual damascene scheme such as that shown in Figure 1 is used, the silylating agent of the present invention is introduced between the process steps of Figures 1E and 1F. The silylating agents described in detail herein can be used in interconnect structures having a dense or porous organosilicate at the line level or via level, or both. In addition, the silylating agent may be combined with other organosilicates, or in combination with materials such as SiO ₂ , FSG, fluorinated tetraethyl orthosilicate (FTEOS), or fluorinated or non-fluorinated organic polymers. It can be used in structures when using silicates. While the other materials listed may be part of the structure, they are generally not subjected to the kind of damage described herein during processing and thus are not themselves altered for the silylation treatment.

The schematic diagram of FIG. 2 demonstrates how the silylating agent used in the present invention succeeds in restoring the methyl moiety after performing its removal during normal process plasma exposure in low k organosilicate films. The group of the silylating agent leaving the reaction site ("leaving group") is a group that reacts with silanol to form new siloxane bonds to deprotonate the silanol. Thus, the reactivity of the leaving group determines the efficacy of the silylation reaction.

In a first embodiment of the invention, one class of silylating agents commonly used in the formula (R ₂ N) _X SiR ' _Y where X and Y are integers of 1 to 2 and integers of 3 to 2, respectively, After defining the lines and vias that result in retaining the interconnect metal, they are introduced. In the above formula, R and R 'may be any hydrogen, alkyl, aryl, phenyl, allyl, or vinyl moiety that can make the film hydrophobic. Such silylating agents are generally referred to as aminosilanes and will be referred to as described later in this document. The silylating agent is used in terms of monofunctional or difunctional depending on whether the value of X is 1 or 2, respectively. The aminosilane is introduced by a spin-on process, in the liquid state, in the gaseous state (in the reactor or in the CVD chamber), or in the supercritical carbon dioxide medium, but in all cases It is very important to treat the silylating agent in the complete absence of ambient moisture because any moisture that may be present can reduce the efficacy of the silylation reaction. Furthermore, the combination of silylation and subsequent annealing thereof or a combination of annealing and subsequent silylation or high temperature silylation thereof (preferably higher than 350 ° C.) is better than silylation itself, for such a combination This results in the maximum reduction of silanol content in the film. The annealing step also allows the formation of additional siloxane bonds that condense and reinforce any remaining unsilylated silanol in the film.

When aminosilane is used in a liquid medium, it is preferred that the aminosilane is dissolved in any nonpolar organic solvent having a low surface tension so that the pores can effectively penetrate. Examples of such solvents include, but are not limited to, hexane, heptane, xylene, and the like. The solvent preferably, but not necessarily, has a low volatility, as measured by flash point and boiling point. The concentration of aminosilane required for effective silylation can be as low as 0.5 wt% solution, or aminosilane can be used as such in its diluted liquid form. The desired range for the most effective silylation is generally 2% to 10% of the solution. This solution can be spin coated onto a porous low k film or used in a wet chemical tank where the wafer with interconnect features defined in the porous low k film is impregnated for a time ranging from 1 minute to over 1 hour. have. The temperature of the silylation may be at or above room temperature. While stirring or sonication during impregnation is not necessary to promote the reaction, in some applications it may help to speed up the reaction. After performing the silylation, the wafer may be cleaned in pure solvent and then heated to a temperature of up to 450 ° C. on a hot plate or in a reactor. Liquid state silylation can also be carried out using the solution defined in the paragraph above and by spin coating or spray coating the solution.

When performing gaseous silylation with aminosilane, it is important that the carrier gas is inert and non-oxidative, and the chamber is free of moisture. If the chamber is free of moisture, bifunctional and trifunctional aminosilanes tend to oligomerize to form monolayers or films, respectively. The formation of such monolayers and films is undesirable, because the reactivity of the silylating agent with the film is generally slow, and furthermore the treatment is also localized on the top surface and the pores in the bulk of the film are not hydrophobic. Because it is not. Gas phase silylation may be performed at a temperature ranging from room temperature to 450 ° C. for a time ranging from 30 seconds to 1 hour or more. Preferred times and temperatures for gaseous silylation are 5 minutes at 250 ° C. After performing gaseous silylation, an optional hot plate firing treatment or reactor hardening treatment up to a temperature of 450 ° C. may be used. Gas phase treatment of the dielectric film is a flow-through chamber in a free standing furnace, used in the semiconductor industry for chemical vapor deposition (CVD) or atomic layer deposition (ALD). Or in a processing chamber. The last two options are particularly attractive because these chambers are designed to handle the formation of a base vacuum that substantially excludes moisture, introduction of gaseous species and substrate heating. And the dielectric may be silicified in situ just prior to the interconnect metal deposition step, which can be easily done using CVD or ALD using an appropriate vapor precursor.

When aminosilanes are introduced by inclusion in a supercritical (SC) carbon dioxide (CO ₂ ) medium, they can be introduced on their own or with any suitable cosolvent. The temperature, pressure and time range for the SC CO ₂ based silylation may be as follows: temperature: 25 ° C. to 450 ° C., pressure: 1,000 to 10,000 psi, time: 30 seconds to 1 hour or more.

Use bifunctional aminosilane, such as (bis) dimethylaminodimethylsilane (BDMADMS) or (bis) dimethylaminomethylsilane, in SC CO ₂ or vapor medium for a time greater than 30 seconds at a temperature above 75 ° C. and then for 1 minute. It is preferred to anneal at 40 ° C. for more than a time. Bifunctional silylating agents are generally more effective than their monofunctional counterparts, as shown in FIG. 3B, where the bifunctional silylating agent has two neighboring non-hydrogen bonded silanols, in particular Geminal silanol. This is because it has the capacity to simultaneously capture geminal silanol (FIG. 3B shows two neighboring isolated silanols). The monofunctional silylating agent generally contains two neighboring silanols due to three methyl moieties that steric hindrance prevents other monofunctional silylating agents from easily reacting with the neighboring silanol, as shown in FIG. 3A. It cannot be captured. Trifunctional silylating agents have a tendency to crosslink to form films that do not penetrate the pores of low k films. Moreover, due to the fact that the trifunctional silylating agent is not capable of capturing three silanols simultaneously, there is the possibility of additional silanol formation on the unreacted ends of the silylating agents.

4 shows a comparison between mono-, bi- and trifunctional chlorine terminated silylating agents, where the silylation is carried out in the liquid state in a moisture free environment. From the FTIR spectrum of FIG. 4, it can be seen that the difunctional agent shows the optimal combination of increasing methyl content and decreasing silanol content of the film. Similar effects can be achieved using amino terminated silylating agents with the additional advantage that the byproducts of the reaction are not erosive.

As shown in FIG. 5, liquid state silylation by BDMADMS and subsequent annealing at 400 ° C. restore the hydrophobicity and methyl content of the porous low k film.

Tables 1 and 2 show a comparison between the contact angle achieved by the preferred formulation BDMADMS of the present invention and the contact achieved by the silylating agent HMDS used in the prior art. As can be seen in Table 1, BDMADMS is more effective at restoring contact angle. Table 2 shows that the effect of BDMADMS does not decrease after 4 weeks of exposure to ambient, while the contact angle of HMDS silylated low k material decreases, indicating a gradual degradation of dielectric properties. Table 3 shows that BDMADMS restores k of the porous low k film after k has been increased after exposure to a typical process plasma. Similarly, dielectric loss as well as dielectric breakdown strength are restored to their original values for films treated with BDMADMS.

Immediately after silylation process Contact angle (degrees) Original film
After plasma exposure
Annealing at + 400 ° C after HMDS silylation
Annealing at + 400 ° C after BDMADMS silylation 104
0.5
85
107.8

4 weeks after silylation process Contact angle (degrees) Original film
After plasma exposure
Annealing at + 400 ° C after HMDS silylation
Annealing at + 400 ° C after BDMADMS silylation 104
0
81.3
107.7

Film / processing Dielectric constant Original film
+ 400 ° C annealing after plasma exposure
Annealing at + 400 ° C after BDMADMS silylation 2.1
2.42
1.95

From FIG. 6, the silylation alters the structural morphology of the organosilicate and makes the skeleton more network like than the cage like, from which the mechanical properties are improved. Can be. This is due to the fact that the silylation reaction forms a new network that forms siloxane bonds that enhance the mechanical strength of the film. An infrared peak at a wavenumber of about 1067 (1 / cm) indicating the range of the network structure in the film shows a significant height increase due to the silylation treatment, as can be seen in the FTIR spectrum of FIG. 6. See Table 4.

Chlorosilanes Aminosilane Alkoxysilane Leaving machine
Harry energy
Me ₃ Si-X (kcal / mol) HCL
117 NHR ₂
98 ROH
123

As noted above, the silylation reaction, followed by the reactor annealing treatment, condenses any remaining silanol and forms new siloxane bonds that further enhance mechanical strength.

Second embodiment

The first embodiment generally shows the efficacy of the bifunctional silylating agent, specifically the efficacy of BDMADMS. The first embodiment also shows that due to the steric hindrance provided by the three methyl sites for the silylating agent, monofunctional silylating agents such as HMDS and TMCS are not as effective as their bifunctional counterparts. However, it is possible to overcome this problem by appropriately replacing the methyl moiety on the silylating agent with a smaller hydrogen moiety. For example, using tetramethyldisilazane (TMDS) instead of BEMDS results in reducing steric hindrance and producing more effective silylation reactions. Similarly, greater success in silylation can be demonstrated with amino, chloro, and alkoxy terminated monofunctional silylating agents, wherein the methyl moiety is at least partially substituted by hydrogen analogs. Thus, silylating agents having the general formula R _X H _Y Si-A, wherein X and Y are integers from 0 to 2 and integers from 3 to 1, respectively, can be used as effective silylating agents. As described in the above embodiments, the silylation reaction and subsequent annealing treatment condenses any remaining silanol and forms new siloxane bonds that further enhance mechanical strength.

Third embodiment

For applications that do not need to penetrate the pores of a porous low k film, the polymer siloxane with amino, alkoxy, chloro or silazane terminated end groups with mono- or di-alkyl, aryl, vinyl or hydrogen moieties is a low k film. It can be used to form a monolayer on the upper surface of the and to restore surface hydrophobicity. One example of such a siloxane is an amino terminated polydimethylsiloxane. It is important to ensure that the siloxane is sufficiently low in molecular weight to allow the silylating agent to flow into the gap created by the etching process to form trenches and vias in the organosilicate for the formation of the interconnect structure. As described in the above embodiments, the silylation reaction and subsequent annealing treatment condenses any remaining silanol and forms new siloxane bonds that further enhance mechanical strength.

Fourth embodiment

The silylating agent may also be introduced immediately after the film is deposited. The efficacy in this case depends on how much is present in the silanol film after deposition. In this embodiment, the silylating agent may also be introduced after treatment such as UV / ozone or mild oxidative plasma exposure to introduce silanol into the film. In previous embodiments, a thermal annealing treatment is performed after silylation. The silylating agents described in any of the three embodiments described above may be used in this manner. In the case of a CVD deposited film, the silylating agent may be co-deposited or introduced into the chamber with a precursor for the CVD dielectric.

It should be noted that what has been described above has been described with respect to some of the more suitable objects and embodiments of the invention. The concept of the present invention can be used for many applications. Thus, although descriptions of specific configurations and methods have been described, the objects and concepts of the present invention are suitable and applicable to other configurations and applications. It will be apparent to those skilled in the art that other modifications to the disclosed embodiments can be made without departing from the spirit and scope of the invention. The described embodiments are to be construed as merely illustrative of some of the more salient features and applications of the present invention. Other beneficial results can be realized by applying the disclosed invention in other ways, or by modifying the invention in a manner known to those skilled in the art. Thus, it will be appreciated that the present embodiments are provided by way of example and not as limitation. It is intended that the scope of the invention be defined by the claims appended hereto.

Claims (2)

A method for restoring the properties of an organosilicate film having a hydrogen atom or an alkyl or aryl group attached to a silicon atom in an insulating layer of dielectric constant of 3.1 or less in a semiconductor chip or chip carrier or semiconductor wafer, wherein the organosilicate film To the film, wherein the silylating agent is applied to the film such that the film is hydrophobic, wherein the silylating agent is a bifunctional amino or difunctional chlorine terminated terminal group. And a polymeric siloxane having a siloxane. An article of manufacture comprising an intermetallic dielectric comprising an insulating material having a plurality of electrical conductors formed therein, and an organosilicate film having a hydrogen atom or an alkyl group or an aryl group attached to a silicon atom, wherein the organosilicate film Wherein the surface comprises a product of a silylating agent and an organosilicate of the film, wherein the silylating agent comprises a polymeric siloxane having a bifunctional amino or difunctional chlorine terminated end group.

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