Pretreatment method for improving selectivity in a selective deposition process

Abstract

A method for improving the selectivity of a metal in a selective deposition process. The pretreatment process for the metal modifies the metal surface and includes first reducing the metal by removing organic contaminants from the metal, and then oxidizing the metal to grow a monolayer of metal oxide on the surface. The metal modification enables inhibitor molecules to adsorb to the monolayer of metal oxide, thereby improving selectivity.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Patent Application No. 16 / 056,260, filed on August 6, 2018, which is incorporated herein by reference for all purposes. Technical Field

[0003] The present invention relates to methods for semiconductor processing. More particularly, the present invention relates to methods for improving selectivity in selective deposition processes. Background Art

[0004] The manufacture of semiconductor devices generally requires interconnect structures that include metal wires for connecting devices in a semiconductor chip. The wires include metal lines formed in a dielectric layer extending across the chip and vias that connect the lines to different layers of the chip. In many applications, selective deposition is performed on a substrate to form vias. The metal lines and vias are generally formed of aluminum or copper and insulated by dielectric materials.

[0005] In semiconductor manufacturing, it is expected that vias can be perfectly aligned with the two layers they connect. When drilling down to form a via to the metal line below, if there is any misalignment, the via may miss the desired metal line and contact another metal line, thus causing a short circuit.

[0006] In the process of forming fully aligned vias, aluminum oxide (Al2O3) is selectively deposited on the dielectric surface as an etch stop layer, typically after depositing the metal line (i.e., copper). It is known that Al2O3 will only deposit on dielectric surfaces (such as silicon oxide) and not on native copper surfaces that have been exposed to inhibitor molecules. However, forming vias using this selective deposition process requires a native copper surface, such as a surface deposited using physical vapor deposition (PVD), which requires high operating temperatures and is also difficult to deposit on complex geometries. Prior art techniques for modifying copper surfaces to improve selectivity use a two-step process: (1) exposing the native copper surface to an inhibitor; and (2) depositing Al2O3 using thermal atomic layer deposition (ALD). This process is only applicable to copper deposited by PVD and not to copper deposited by electrofill (EF) or copper deposited by chemical mechanical polishing (CMP) after EF.

[0007] However, in the process of forming perfectly aligned vias, copper is usually deposited using an EF process and then chemical mechanical polishing is performed to form the vias. Such copper deposited by the EF / CMP process cannot adsorb inhibitor molecules, and therefore, the subsequent ALD Al2O3 process used to deposit the etch stop layer is not selective. Therefore, it is desirable to improve the selectivity of the deposition process performed on copper deposited by EF / CMP in the process of forming perfectly aligned vias. Summary of the invention

[0008] According to one embodiment, a method for improving the selectivity of a metal is provided. A substrate is provided in a semiconductor processing chamber. The substrate has a metal line formed in a dielectric layer. The metal is reduced from a metal oxide to a metal by removing organic contaminants from the metal. After reducing the metal, the metal is then oxidized and a monolayer of metal oxide is grown on the surface of the metal.

[0009] According to another embodiment, a method for improving the selectivity of copper deposited by an electrofill process is provided. A substrate is provided in a semiconductor processing chamber. The substrate has copper lines formed in a dielectric layer. The copper is reduced from copper oxide to copper by removing organic contaminants from the copper. After reducing the copper, the copper is oxidized and a monolayer of copper oxide is grown on the surface of the copper. After the monolayer is grown, an inhibitor molecule that is selective only for the copper is deposited and adsorbed onto the monolayer of copper oxide.

[0010] According to another embodiment, a method for improving the selective deposition of an etch stop layer is provided. A substrate is provided in a semiconductor processing chamber. The substrate has a dielectric layer on its surface. Copper is deposited onto the surface of the substrate by an electric filling process. The copper is chemically mechanically polished. A plasma mixture of ammonia and nitrogen is then flowed into the processing chamber to reduce the copper from copper oxide to copper by removing organic contaminants from the copper. After reducing the copper, an oxygen plasma or oxygen is flowed into the chamber to oxidize the copper and grow a monolayer of copper oxide on the surface of the copper. After the monolayer is grown, a thiol molecule that is selective only for the copper is deposited and adsorbed onto the monolayer of copper oxide. An etch stop layer is selectively deposited over the dielectric layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The present disclosure is illustrated by way of example and not by way of limitation in the figures of the accompanying drawings in which like reference numerals refer to similar elements and in which:

[0012] Figure 1 is a flow chart of a method for improving the selectivity of metals according to one embodiment.

[0013] Figure 2 is a flow chart of a method for improving the selectivity of copper deposited by an electrofill process according to one embodiment.

[0014] Figure 3 is a flow chart of a method for selectively depositing an etch stop layer according to one embodiment. DETAILED DESCRIPTION

[0015] The present invention will now be described in detail with reference to several preferred embodiments shown in the accompanying drawings. In the following description, a number of specific details are set forth to provide a comprehensive understanding of the present invention. However, it should be understood that it is possible for those skilled in the art to implement the present invention without some or all of these specific details. In other cases, known process steps and / or structures are not described in detail to avoid unnecessarily obscuring the present invention.

[0016] Embodiments herein generally relate to selective deposition processes. In particular, embodiments herein relate to pretreatment methods for improving selectivity in selective deposition processes. Metals (e.g., copper, cobalt, and tungsten) can be pretreated to modify the metal surface to accept inhibitor molecules. By using a two-step pretreatment, for example, an EF / CMP copper surface can be modified to accept inhibitor molecules and enable subsequent net selective deposition of etch stop layers (e.g., Al2O3, silicon oxide (SiO2), and other low-k films).

[0017] refer to Figure 1-3 Embodiments of pretreatment processes for improving selectivity of copper surfaces are described. Pretreatment processes for improving selectivity are particularly useful in processes for forming fully aligned vias. According to embodiments disclosed herein, a pretreatment process modifies the surface of a metal (not necessarily a native metal) to improve selectivity. For example, copper deposited by EF or EF / CMP can be modified using a pretreatment process to improve selectivity. As will be discussed in more detail below, a two-step pretreatment process is used to improve the selectivity of metals (e.g., copper, cobalt, tungsten) deposited by EF or EF / CMP to enable adsorption of inhibitors, thereby enabling subsequent selective deposition only on dielectric materials.

[0018] Improved selectivity is particularly useful in processes for forming perfectly aligned vias. Via alignment is critical to reliability in semiconductor devices because maximum contact is generally desired and a misaligned via as described above may result in a short circuit. Generally, an electrofill process is used in processes for forming perfectly aligned vias, which is used to deposit copper lines followed by CMP of the copper lines. In order to recess the copper lines, an Al2O3 dielectric layer is selectively deposited over the dielectric layer (but not over the copper) as an etch stop layer. As described above, the copper deposited by electrofill and then subjected to chemical mechanical polishing cannot adsorb the inhibitor, so the subsequent ALD process for depositing Al2O3 is not selective.

[0019] According to the embodiments disclosed herein, the metal surface is modified to improve selectivity by: (1) removing organic contaminants to reduce the metal, and (2) performing controlled oxidation after reduction. Plasmas can be used to remove organic contaminants from metals, such as plasma mixtures of ammonia (NH3) and nitrogen (N2), hydrogen (H2) plasma, ammonia (NH3) plasma, and non-thermal diborane (B2H6) plasma. In other embodiments, citric acid or acetic acid can be used to remove organic contaminants. Controlled oxidation can be performed by exposing the metal to oxygen (O2) plasma, oxygen (O2), ozone (O3), or hydrogen peroxide (H2O2). Oxidation of the metal surface results in thermal regeneration of a monolayer of metal oxide. The monolayer is preferably thicker than 100%. It will be appreciated that ideally the monolayer should be as thin as possible, as metal oxides do not conduct electricity as well as pure metals, so reduced conductivity may degrade the semiconductor device. Reduction and subsequent oxidation of the metal surface results in the adsorption of inhibitor molecules on the surface.

[0020] After oxidation, the metal is then exposed to inhibitor molecules, which adsorb on the metal surface. Suitable inhibitors include mercaptans (such as butane mercaptan and dodecanethiol) and phosphonic acids (such as octadecylphosphonic acid). It should be understood that mercaptans are preferably adsorbed on modified copper surfaces, while phosphonic acids are preferably adsorbed on modified cobalt surfaces. However, if phosphonic acids are used as inhibitors, wet chemicals must be used because phosphonic acids are not volatile and are not suitable for use in gas phase chemical processes. On the other hand, mercaptans are volatile, so wet chemicals do not necessarily have to be used when mercaptans are used as inhibitors.

[0021] According to a specific embodiment, the copper surface is modified to achieve selectivity by: (1) removing organic contaminants to convert CuO x The copper surface is then oxidized by exposing it to an O2 plasma or O2 to thermally regenerate a CuOx monolayer. The monolayer is preferably thicker than Although typical preparation of copper surfaces is accomplished by a single reduction step using NH3 / N2 plasma, it may seem counterintuitive to follow this reduction process with an oxidation step (as it would appear to defeat the purpose of the initial reduction step), but this oxidation step is critical to achieving selectivity as it enables copper to adsorb inhibitor molecules such as thiols or phosphonic acids.

[0022] refer to Figure 1, describes an embodiment of a method for improving the selectivity of a metal. Method 100 begins by providing a substrate in a semiconductor processing chamber in step 110, the substrate having a metal line formed in a dielectric layer (e.g., silicon oxide (SiO2)). The metal is deposited by an electrofill process and then subjected to chemical mechanical polishing. In step 120, the metal is reduced from a metal oxide to a metal by removing organic contaminants from the metal. In step 130, the metal is oxidized to produce a thermally regenerated metal oxide monolayer. After the metal oxide monolayer is regenerated, inhibitor molecules that are selective only for the metal are deposited in step 140. The thermally regenerated metal oxide monolayer enables the inhibitor molecules to be adsorbed, so that the resulting metal oxide layer has improved selectivity compared to the metal surface before the pretreatment steps 120-140.

[0023] refer to Figure 2 , describes an embodiment of a method for improving the selectivity of copper deposited by an electric filling process. Method 200 begins with providing a substrate in a semiconductor processing chamber in step 210, the substrate having copper lines formed in a dielectric layer. Copper is deposited by an electric filling process. In some embodiments, chemical mechanical polishing is performed on the copper after the electric filling process. In step 220, NH3 / N2 plasma is flowed into the chamber to remove organic contaminants from copper and reduce copper from CuOx to Cu. In step 230, O2 plasma or O2 is flowed into the processing chamber to oxidize copper. If the oxidation uses O2 plasma, the O2 plasma is flowed into the processing chamber for about 1-5 seconds. If the oxidation uses O2, the duration of the O2 flow to the processing chamber can range from several minutes to several hours. It should be understood that higher temperatures can be used to increase the oxidation rate. Oxidation produces a thermally regenerated CuOx monolayer. After the CuOx monolayer is regenerated, inhibitor molecules that are selective only to copper are deposited in step 240. According to one embodiment, thiol molecules are deposited as inhibitors. The thermally regenerated CuOx monolayer enables the adsorption of inhibitor molecules, so the resulting copper layer has improved selectivity compared to the copper surface prior to the pretreatment steps 220-240.

[0024] According to other embodiments, some other suitable pretreatment options capable of removing organic contaminants while reducing the metal include hydrogen plasma, ammonia plasma, non-thermal diborane plasma, citric acid and acetic acid. In addition to oxygen plasma and oxygen (O2), other suitable pretreatment options capable of oxidizing the reduced metal include exposing the substrate to a 20% oxygen and nitrogen mixture (such as ambient air) at room temperature for about 5 minutes, ozone (O3) and hydrogen peroxide (H2O2). It should be understood that the pretreatment process includes a reduction step followed by an oxidation step, and different combinations of reduction and oxidation methods can be used.

[0025] The pretreatment process described herein can be carried out in a reactor such as that manufactured by Lam Research Corporation (Fremont, California). and Deposition reactor.

[0026] Figure 3 Flow chart of another embodiment of a method 300 for selectively depositing an etch stop layer. The method 300 begins by providing a substrate in a semiconductor processing chamber in step 310, the substrate having a dielectric layer on its surface. In step 320, copper is deposited by an electric filling process. Then in step 330, the electric filled copper is chemically mechanically polished. In step 340, NH3 / N2 plasma is flowed into the processing chamber to remove organic contaminants from copper and reduce copper from CuOx to Cu. In step 350, O2 plasma or O2 is flowed into the processing chamber to oxidize the copper. Oxidation produces a thermally regenerated CuOx monolayer. After the CuOx monolayer is regenerated, mercaptan inhibitor molecules are deposited and adsorbed onto the CuOx layer in step 360. The thermally regenerated CuOx monolayer enables the inhibitor molecules to be adsorbed, so the resulting copper layer has improved selectivity compared to the copper surface before the pretreatment steps 340-360. In step 370, the etch stop layer is selectively deposited above the dielectric layer. According to one embodiment, the etch stop layer is an Al2O3 layer. In certain embodiments, the Al2O3 layer is deposited using a thermal atomic layer deposition (ALD) process. However, it should be understood that other deposition methods can be used to deposit the Al2O3 layer. Generally speaking, the etch stop layer is deposited using a thermal process because the thermal process does not damage the inhibitor molecules. It should be understood that a plasma deposition process may damage the inhibitor molecules, thereby compromising selectivity.

[0027] Although only a few embodiments of the present invention are described in detail, it should be understood that the present invention can be implemented in many other forms without departing from the spirit and scope of the present invention. In view of the above, it should be understood that the embodiments of the present invention are exemplary and non-restrictive, and the present invention is not limited to the details listed in the text, and the present invention can be modified within the scope and equivalent scheme of the appended claims.

Claims

1. A method for improving the selectivity of a metal, comprising: providing a substrate in a semiconductor processing chamber, the substrate having metal lines formed in a dielectric layer; reducing the metal from a metal oxide to a metal by removing organic contaminants from the metal; After reducing the metal, oxidizing the metal and growing a monolayer of metal oxide on a surface of the metal; and After growing the monolayer, inhibitor molecules selective only for the metal are deposited and adsorbed onto the monolayer of the metal oxide. The method of claim 1 , wherein the metal is deposited by an electrofill process. The method of claim 2 , wherein the metal is chemically mechanically polished after depositing the metal.

4. The method of claim 1, wherein the metal is selected from the group consisting of copper, cobalt, and tungsten. The method of claim 1 , wherein the dielectric layer comprises silicon oxide.

6. The method of claim 1, wherein reducing comprises flowing hydrogen plasma, a plasma mixture of ammonia and nitrogen, ammonia plasma, non-thermal diborane plasma, citric acid, or acetic acid into the chamber.

7. The method of claim 1, wherein oxidizing comprises flowing oxygen plasma, oxygen, ozone, or hydrogen peroxide into the chamber.

8. The method of claim 1, wherein the inhibitor molecule comprises a thiol or a phosphonic acid.

9. A method for improving the selectivity of copper deposited by an electrofill process, comprising: providing a substrate in a semiconductor processing chamber, the substrate having copper lines formed in a dielectric layer; reducing the copper from copper oxide to copper by removing organic contaminants from the copper; After reducing the copper, oxidizing the copper and growing a monolayer of copper oxide on a surface of the copper; and After growing the monolayer, suppressor molecules selective only for the copper are deposited and adsorbed onto the monolayer of copper oxide.

10. The method of claim 9, wherein the copper is chemically mechanically polished after the electrofill process and before the copper is reduced. The method of claim 9 , wherein the dielectric layer comprises silicon oxide.

12. The method of claim 9, wherein reducing comprises flowing hydrogen plasma, a plasma mixture of ammonia and nitrogen, ammonia plasma, non-thermal diborane plasma, citric acid, or acetic acid into the processing chamber.

13. The method of claim 9, wherein oxidizing comprises flowing oxygen plasma, oxygen, ozone, or hydrogen peroxide into the chamber.

14. The method of claim 9, wherein the inhibitor molecule comprises a thiol.

15. A method for improving the selectivity of depositing an etch stop layer, the method comprising: providing a substrate in a semiconductor processing chamber, the substrate having a dielectric layer on a surface thereof; depositing copper onto the surface of the substrate by an electrofill process; chemically mechanically polishing the copper deposited by the electrofill process; flowing a plasma mixture of ammonia and nitrogen into the processing chamber after chemically mechanically polishing the copper to reduce the copper from copper oxide to copper by removing organic contaminants from the copper; After reducing the copper, flowing oxygen plasma or oxygen into the chamber to oxidize the copper and grow a monolayer of copper oxide on a surface of the copper; After growing the monolayer, depositing thiol molecules selective only for the copper and allowing the thiol molecules to adsorb onto the monolayer of copper oxide; as well as An etch stop layer is selectively deposited over the dielectric layer. The method of claim 15 , wherein the dielectric layer comprises silicon oxide. The method of claim 15 , wherein the etch stop layer comprises aluminum oxide.

18. The method of claim 15, wherein the etch stop layer is deposited by a thermal atomic layer deposition process.

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