A METHOD FOR PRODUCING A COPPER CONTACT

Field of the Invention [0001] The present invention is related to the production of integrated circuits, in particular to the production of a copper contact in the transition between Front End of Line and Back End of Line stages of the production process.

State of the Art

[0002] Contacts between FEOL and BEOL are typically obtained by producing holes in the Pre-metal dielectric (PMD) layer, e.g. Siθ2, and filling these holes with tungsten (W) metal. As contact dimensions shrink, replacing W by copper (Cu) is advantageous due to lower intrinsic resistivity of Cu metal. For both approaches (W and Cu) a metal barrier is required between the contact metal and suicided source/drain and gate areas, at the bottom of the hole. In the case of Cu this barrier is necessary to prevent the formation of harmful Cu-silicates . In order to control the resistance increase associated with the smaller contacting area, the barrier thickness has to be scaled down without compromising the reliability. Typically Cu barriers are deposited using Physical Vapour Deposition (PVD) -based techniques which inherently deliver aspect-ratio dependent bottom & sidewall coverage thicknesses, which is limiting the scalability of PVD barriers. Prior art techniques include the use of ALD TaN, delivering a conformal barrier, which is however

inefficient at preventing Cu-silicidation at very low thicknesses (2-3nm) , and tends to suffer from poor adhesion properties .

[0003] In conclusion, in order to use Cu in the contacts between FEOL and BEOL, a need exists in the prior art to provide a suitable barrier on the sidewalls and bottom of the contact hole, which on the one hand solves the problem of resistance increase due to the shrinkage in dimensions and on the other hand avoids the leakage of copper and hence the formation of copper suicides in and around the copper contact.

[0004] From Usui et al (IEEE Transactions on Electron Devices, vol. 53, n° 10, October 2006), it is known to produce copper dual-damascene interconnects in the Back End of Line, by filling a via with a CuMn alloy by sputtering a CuMn seed layer on the side walls of the via, performing Cu deposition by electrochemical plating, annealing and removal of excess Cu by Chemical Mechanical Polishing. During annealing, Mn reacts with Siθ2, resulting in the formation of MnSi _x Oy, on the sidewall of the hole, which acts as an effective barrier. This method cannot be used as a stand-alone option for Cu contacts since the technique would not provide a barrier on the metal suicide bottom of the contact hole. [0005] The self-aligned deposition of CoWP on a source or drain region is known from Pan et al (2006 Symposium on VLSI Technology - 1-4244-0005-8/06) . According to this technique, it is possible to deposit CoWP selectively on suicided areas using an electroless metal deposition process. The goal of the CoWP layer onto the suicided source and drain areas is to decrease the series resistance and hence improve the electrical contact.

Aims of the Invention

[0006] The present invention aims to provide a more effective and scalable way of producing a Cu contact between FEOL and BEOL. [0007] It is a first aim of the invention to provide a robust conductive barrier at the bottom of a Cu contact, said conductive barrier having at least a low contact resistance (preferably lower than in prior art) and said conductive barrier preventing Cu to react with suicide or Si.

[0008] It is a second aim of the invention to provide a thin barrier (preferably thinner than in prior art) at the contact sidewalls, said thin (ner) barrier serving as a barrier to avoid leakage of Cu into the surrounding Pre Metal Dielectric (PMD) .

Summary of the invention

[0009] The present invention is related to a method and device as disclosed in the appended claims. Preferred embodiments are described in combinations of the independent claims with claims dependent thereon. [0010] In particular, the invention is related to a method for providing a suitable barrier layer into copper contact vias situated in the Pre-Metal Dielectric (PMD) layer (e.g. Siθ2) of a semiconductor device.

[0011] The present invention is further related to a novel semiconductor device comprising copper contacts having a novel combination of barrier layer (s) on the bottom of the contact and on the sidewalls of the contact. [0012] The aim of the invention is achieved by depositing a first selective barrier at the bottom of the via whereby said first barrier layer is preferably selected from a CoWP layer or a CoWB layer and depositing a second thin barrier layer onto the sidewalls of the via whereby said second

barrier layer comprises an oxide comprising Mn. Hereafter the term ^λ Mn-oxide' is used to indicate an oxide comprising Mn and possibly other components, e.g MnSi _x Oy with x between 0 and 100% and y higher than 0%. [0013] The expression 'between FEOL and BEOL' is to be understood as follows : between source/drain and gate areas and a metal interconnect region (also called first metallisation region) of an integrated circuit. Furthermore, a 'barrier' in the context of the present invention is to be understood as a copper-barrier, i.e. a layer which inhibits the diffusion of Cu through said layer .

Brief Description of the Drawings [0014] The drawing is intended to illustrate some aspects and embodiments of the present invention. Not all alternatives and options are shown and therefore the invention is not limited to the content of the attached drawing . [0015] Fig. 1 shows a schematic view of a Cu contact produced according to the present invention.

Detailed description of the Invention

[0016] The above indicated aims are accomplished by methods and devices according to the present invention.

[0017] The methods according to embodiments of the invention are scalable and fully compatible with existing semiconductor processing.

[0018] With reference to fig. 1, the present invention is related to a method for producing a contact through the pre-metal dielectric layer (6) of an integrated circuit, between the Front End of Line and the Back End of Line, wherein said PMD layer comprises oxygen, said method comprising the steps of :

- producing a hole in the PMD,

- depositing a conductive barrier layer (3) at the bottom of the hole,

- depositing a CuMn alloy on the bottom and side walls of the hole,

- filling the remaining portion of the hole with Cu,

- performing an anneal step,

- performing a CMP step. [0019] The method is preferably performed on a substrate 1, e.g. a silicon substrate, having one or more suicided areas 2, typically nickel suicide areas (NiSi). These can be source/drain or gate areas of the integrated circuit. On top of the substrate is the pre-metal dielectric 6 which separates the gate and source/drain areas (FEOL) from the interconnect level (s) (BEOL) produced after the FEOL stage. The PMD can be a layer of Siθ2 or a CVD deposited low-k material, such as SiCO(H). An essential feature is that the PMD comprises oxygen. [0020] The production of the hole in the PMD can be performed by any known technique. The conductive barrier layer 3 can be a CoWP layer or a CoWB layer.

[0021] A pre-treatment of the suicide is preferably performed. This can be a cleaning step. The pre-treatment may involve an HF-based activation of the NiSi by e.g. Pd atoms to initiate CoWP electroless deposition. [0022] The deposition of the conductive barrier 3 at the bottom can be a selective electroless metal deposition step of any one of the following metals: CoWP, CoWB, CoWP(N), CoWB(N), wherein N is Nitrogen, being present in the grain boundaries of the CoWP or CoWB. According to the invention, this particular structure of CoWP (N) or CoWB (N) can be obtained by performing a plasma treatment in an

atmosphere comprising NH ₃ or N ₂ , i.e. with a plasma being generated from a gaseous mixture comprising at least nitrogen and/or NH ₃ , after depositing the barrier layer. The presence of N in the grain boundaries diminishes the diffusion of Cu through these boundaries (i.e. the presence of N avoids the fact that the grain bounderies act as diffusion paths for Cu) .

[0023] A standard electroless CoWP (or CoWB) plating bath may be used with the typical process conditions inherent to a CoWP (or CoWB) deposition process in micro-electronics. In order to improve the selective electroless metal deposition step, the bottom of the contact hole (suicide) may be pre-treated, or in other words the bottom of the contact via is activated to improve the electroless process (e.g. performing a seeding step).

[0024] The thickness of the barrier layer 3 (e.g. CoWP or CoWB) is preferably in the range of IOnm up to lOOnm, most preferably around 30nm. [0025] After depositing the barrier layer 3 at the bottom of the via, a pre-treatment step of said barrier layer is preferably performed, to clean the surface of the barrier layer, and specifically in order to substantially remove oxides from the surface of the barrier layer. [0026] The deposition of the CuMn alloy can be performed by depositing a thin layer of CuMn alloy by PVD, for example an alloy comprising Cu and 2-8% Mn. The alloy may be deposited using the same PVD-based process and process conditions as for the subsequent deposition of a pure Cu seed layer which may be needed to perform electrochemical plating of copper to fill the copper contacts with copper. [0027] The filling of the remaining gap with Cu 4 can take place by ECP (Electro-Chemical Plating) . A standard acidic Cu plating bath may be used, as used in the microelectronics industry for interconnect fabrication.

[0028] The anneal step forms a Mn-Oxide layer 5 at the contact side wall, having a thickness of preferably around 3nm (which is thinner than the known TaN barrier) . The annealing step may be performed by a Furnace Thermal Anneal. The temperature and time period of this step depends on the particular alloy used and the nature of the dielectric onto which the barrier has to be formed. Typical temperatures are around 400 ⁰ C for 20-40min. When the PMD layer comprises Silicon (e.g. PMD is SiO2), the oxide formed may be MnSi _x Oy with x between 0 and 100% and y higher than 0%. The self-formed Mn-Oxide diffusion barrier can only be formed at the contact sidewall. No Mn-Oxide will be formed at the contact bottom because there is no oxygen supply at the bottom of the contact hole (the PMD is giving the required oxygen through Siθ2) .

[0029] The Mn-oxide (e.g. MnSi _x Oy) barrier at the sidewalls of the copper contact has a further advantage that it adheres very well to both the copper and the PMD (e.g. Siθ2) , in contrast to state of the art barrier materials such as an ALD deposited TaN barrier layer.

[0030] The removal of excess Cu takes place by Chemical Mechanical polishing (CMP) .

[0031] The present invention introduces the novel use of CoWP or CoWB as a barrier material in cooperation with Cu, for the production of Cu contacts between FEOL and BEOL, the layer of CoWP or CoWB being applied at the bottom of a hole filled thereafter with the Cu contact.

[0032] The present invention further introduces the novel combination of a CoWP or CoWB as a barrier material at the bottom of a copper contact with a self-forming Mn-oxide barrier layer at the sidewalls of the copper contact. Using this combination it is possible to avoid copper leakage out of the copper contact as well as a low contact resistance within the copper via.

[0033] The present invention is further related to a device comprising Cu contact vias through a pre-metal dielectric layer (PMD) comprising oxygen, said contact vias being between source/drain/gate areas 2 and a metal interconnect region, wherein a conductive barrier layer 3 is present at the bottom of the vias and a barrier layer 5 comprising an oxide comprising Mn is present at the sidewalls of the vias. According to the preferred embodiment, the conductive barrier layer comprises or consists of CoWP or CoWB, possibly with N being present in the grain boundaries of the CoWP or CoWB. Preferably, the PMD layer comprises Si (e.g. Siθ2) and said barrier layer on the side walls comprises MnSi _x Oy with x between 0 and 100% and y higher than 0%. The conductive barrier layer 3 preferably has a thickness of between IOnm and lOOnm, most preferably around 30nm.

[0034] The present invention also discloses the use of the novel combination of a CoWP or CoWB as a barrier material at the bottom of a copper contact with a self-forming Mn- oxide barrier layer at the sidewalls of the copper contact in the manufacturing process of a semiconductor device. [0035] It is to be understood that although preferred embodiments, specific constructions and configurations, as well as materials, have been discussed herein for devices according to the present invention, various changes or modifications in form and detail may be made without departing from the scope of this invention as defined by the appended claims.