Method for forming titanium / titanium nitride film

Abstract

The invention provides a method for forming a titanium / titanium nitride film. The method comprises the following steps of: depositing a titanium metal layer on a semiconductor substrate; and performing thermal annealing treatment on the semiconductor substrate deposited with the titanium metal layer in a nitrogen-containing atmosphere, so that the titanium metal layer reacts with the semiconductor substrate to form a metal silicide, and meanwhile, the titanium metal layer reacts with the nitrogen-containing atmosphere to generate a titanium nitride layer. The silicide contact layer and the titanium nitride barrier layer are formed at the same time through the in-situ reaction, and the technological process is simplified. The titanium nitride layer formed by the method is thin, stress distribution of the wafer is effectively improved, the problem of wafer warping caused by the fact that the titanium nitride layer is too thick in a traditional process is solved, meanwhile, it is guaranteed that a silicon interface reacts sufficiently, contact resistance is reduced, and consistency of electrical parameters of a device is improved.

Description

Technical Field

[0001] This invention relates to the field of integrated circuit manufacturing, and in particular to a method for forming a titanium / titanium nitride thin film. Background Technology

[0002] In the manufacturing process of semiconductor integrated circuits, interlayer barrier layers (ILBs) or adhesion barrier layers (Glue Layers / Barrier Layers) play a crucial role. In the fabrication of power devices, a stacked structure composed of titanium (Ti) and titanium nitride (TiN) is typically used as the barrier layer. The titanium layer primarily reacts with the silicon (Si) substrate to form silicide, providing good ohmic contact and enhancing film adhesion; while the titanium nitride layer mainly serves to prevent the diffusion of subsequent filler metals and buffer stress.

[0003] Traditional titanium / titanium nitride thin film manufacturing processes typically employ a step-by-step deposition method: first, a titanium layer is deposited using physical vapor deposition (PVD), followed by a titanium nitride layer deposited using PVD, and then a high-temperature annealing process is performed to form a silicide structure.

[0004] However, the aforementioned traditional manufacturing process has the following technical problems: First, since the titanium layer and titanium nitride layer are deposited separately, the subsequent annealing process may not guarantee that the titanium layer reacts completely, easily forming a high-resistivity region at the interface, leading to increased contact resistance of the device. Second, the titanium nitride layer deposited in the traditional process is usually thicker, and a thicker titanium nitride layer can easily cause uneven stress within the wafer, leading to wafer warping and other problems, which in turn affect the implementation of subsequent processes and the final electrical parameters of the device (such as the convergence of the threshold voltage Vth). In addition, the process of depositing two metal layers separately and then annealing is also relatively complex.

[0005] Therefore, a new manufacturing method is needed that can simplify the process, improve thin film stress, and reduce contact resistance. Summary of the Invention

[0006] The technical problem to be solved by the present invention is to provide a method for forming titanium / titanium nitride thin films, so as to solve the problems of complex manufacturing process of titanium / titanium nitride thin films, uneven wafer stress caused by excessive thickness of titanium nitride layer and unstable contact resistance of device in the prior art.

[0007] To address the aforementioned technical problems, this invention provides a method for forming a titanium / titanium nitride thin film, comprising the following steps:

[0008] Step 1: Deposit a titanium metal layer on a semiconductor substrate;

[0009] Step 2: Perform thermal annealing on the semiconductor substrate with the deposited titanium metal layer under a nitrogen-containing atmosphere, so that the titanium metal layer reacts with the semiconductor substrate to form metal silicide, and at the same time the titanium metal layer reacts with the nitrogen-containing atmosphere to form titanium nitride layer.

[0010] Preferably, in step two, the nitrogen-containing atmosphere is selected from at least one of ammonia, nitrogen, or a mixture of nitrogen and hydrogen.

[0011] Preferably, in step two, the hot annealing process employs a rapid hot annealing process.

[0012] Preferably, in step two, by controlling the temperature and time of the thermal annealing process, the titanium metal layer located at the semiconductor substrate interface is transformed into titanium silicide, and the titanium metal layer located on the surface of the titanium metal layer reacts with the nitrogen-containing atmosphere to transform into titanium nitride.

[0013] Preferably, in step two, an excess of nitrogen-containing gas is introduced to ensure that the titanium metal layer reacts fully.

[0014] Preferably, the titanium / titanium nitride thin film is used in the contact hole process of semiconductor devices as an adhesion barrier layer before depositing the conductive metal layer.

[0015] Preferably, the material of the conductive metal layer includes tungsten.

[0016] As described above, the method for forming titanium / titanium nitride thin films of the present invention has the following beneficial effects:

[0017] This invention achieves simultaneous silicide formation and titanium nitride barrier layer generation by directly introducing a nitrogen-containing atmosphere for thermal annealing after titanium layer deposition, simplifying the traditional process of separately depositing titanium and titanium nitride before annealing. This method utilizes in-situ reaction on the titanium layer surface to generate titanium nitride, resulting in a thinner titanium nitride layer compared to traditional deposition processes. This significantly improves wafer stress uniformity and warpage issues caused by excessively thick films. Simultaneously, thermal annealing in a nitrogen-containing atmosphere ensures sufficient titanium layer reaction, forming good ohmic contacts at the bottom and a dense barrier layer at the top, avoiding high-resistivity regions. This results in more convergent and stable electrical parameters such as the threshold voltage of the device, improving the yield and reliability of semiconductor devices. Attached Figure Description

[0018] Figure 1 The diagram shows a flow chart of a method for forming titanium / titanium nitride thin films according to an embodiment of the present invention.

[0019] Figure 2 The diagram shows a comparison of wafer warpage data between the formation method provided in this embodiment of the invention and the conventional process;

[0020] Figure 3The diagram shows a comparison of the threshold voltage distribution of devices manufactured by the formation method provided in this embodiment of the invention and those manufactured by conventional processes. Detailed Implementation

[0021] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0022] This application provides a method for forming a titanium / titanium nitride thin film, such as... Figure 1 As shown, it includes the following steps:

[0023] Step 1: Deposit a titanium metal layer on a semiconductor substrate.

[0024] In some embodiments, the semiconductor substrate may be an elemental semiconductor substrate, such as silicon or germanium with a crystalline structure; it may also be a compound semiconductor substrate, including silicon carbide (SiC), gallium arsenide (GaAs), gallium phosphide (GaP), indium phosphide (InP), indium arsenide (InAs), or indium antimonide (InSb); or it may be an alloy semiconductor substrate, including silicon germanium (SiGe), gallium arsenide phosphide (GaAsP), aluminum indium arsenide (AlInAs), aluminum gallium arsenide (AlGaAs), gallium indium arsenide (GaInAs), gallium indium phosphide (GaInP), or gallium arsenide phosphide indium (GaInAsP). Furthermore, the semiconductor substrate may also employ a semiconductor-on-insulator (SOI) structure, such as a silicon-on-insulator (SOI) substrate, a germanium-on-insulator (GOI) substrate, or a silicon-germanium-on-insulator (SGOI) substrate. To enhance device performance, the semiconductor substrate may include a strained layer or have an epitaxial layer. The semiconductor substrate may be undoped or doped according to design requirements (e.g., p-type, n-type, or a combination thereof). Various isolation structures, such as shallow trench isolation (STI) or localized silicon oxide (LOCOS), may be formed within or on the semiconductor substrate to define the active region. Various semiconductor device structures may have already been formed on the active region, including but not limited to planar metal-oxide-semiconductor field-effect transistors (MOSFETs), three-dimensional transistors, bipolar junction transistors (BJTs), resistors, capacitors, diodes, or fuses.

[0025] In typical application scenarios of this application, the target area for titanium metal layer deposition is usually the silicon-containing surface exposed in the source, drain, or gate regions of the aforementioned semiconductor devices. Before deposition, a pre-cleaning process is usually performed, such as using dilute hydrofluoric acid (DHF) solution, SiCoNi dry cleaning, or plasma cleaning processes, to remove natural oxides and contaminants from the semiconductor substrate surface, thereby ensuring good electrical contact and mechanical adhesion between the titanium metal layer and the underlying silicon material.

[0026] In some embodiments, the specific structure of the semiconductor substrate may include a lightly doped N-type region (N-), which typically serves as a drift region for power devices. N-type doped regions (N) and P-type doped regions (P), as well as P-type well regions located in specific areas, are also formed in the substrate to regulate the threshold voltage of the device or form a channel. High-concentration N-type doped regions (N+) are formed on the surface of the P-type well region or other active regions, serving as source or drain contact regions for transistors. To achieve electrical isolation between devices, a silicon dioxide (SiO2) isolation structure, such as a field oxide (FOX) or shallow trench isolation (STI), is provided on the substrate. A polysilicon layer is formed on top of the gate oxide or field oxide layer, forming the gate electrode or resistor structure. The deposition process in step one of this application typically occurs after the structure is covered by an interlayer dielectric (ILD). The interlayer dielectric (ILD) is formed with contact holes through photolithography and etching processes, exposing the underlying N+ region, P-type well region, or polysilicon surface. The method described in this application involves depositing a titanium metal layer on the inner walls and bottom of these exposed contact holes and then annealing it. The ILB (Inter-Layer Barrier) is a titanium / titanium nitride thin film formed using the method of this invention, which adheres closely to the contour of the contact hole. Subsequently, tungsten (W) is filled on the ILB layer to form contact plugs, and an aluminum-copper (Al / Cu) metal interconnect layer is formed on top. Finally, the device surface is covered with a passivation layer, which may be composed of materials such as silicon nitride and silicon-rich nitrides, to protect the device from environmental influences.

[0027] In some embodiments, in step one, a titanium metal layer is deposited using a physical vapor deposition (PVD) process. PVD processes can include techniques such as direct current (DC) magnetron sputtering, radio frequency (RF) sputtering, ion beam sputtering, or ionized metal plasma (IMP) sputtering. PVD processes can form dense titanium metal layers at relatively low temperatures. Besides PVD, depending on the aspect ratio requirements of the specific device, chemical vapor deposition (CVD), plasma-enhanced chemical vapor deposition (PECVD), or atomic layer deposition (ALD) processes can also be used to form the titanium metal layer. As a transition metal, the purity of the titanium metal layer affects the quality of subsequent reactions; therefore, high-purity titanium targets are typically selected for deposition. In this embodiment, the titanium metal layer provides a titanium source for subsequent reactions with silicon and also provides a titanium source for the formation of titanium nitride.

[0028] Step 2: The semiconductor substrate with the deposited titanium metal layer is thermally annealed under a nitrogen-containing atmosphere. This allows the titanium metal layer to react with the semiconductor substrate to form metal silicides, while simultaneously reacting with the nitrogen-containing atmosphere to form titanium nitride. This method combines the previously separate steps, achieving a dual purpose in a single heat treatment operation. The reaction process follows the chemical reaction mechanism of Ti + 4NH3 -> 3TiN + 6H2 (using ammonia as an example), achieving self-aligned silicide formation and surface nitriding. This in-situ formed structure avoids interface contamination and simplifies the process flow.

[0029] In some embodiments, in step two, the nitrogen-containing atmosphere is selected from at least one of ammonia, nitrogen, or a mixture of nitrogen and hydrogen. When ammonia (NH3) is used as the reactant, it readily decomposes at high temperatures to produce highly reactive nitrogen and hydrogen atoms, which can promote the nitriding reaction of the surface titanium layer, generating titanium nitride with a better stoichiometric ratio. Using nitrogen (N2) as the atmosphere offers advantages such as low cost and stable process control. Using a mixture of nitrogen and hydrogen can provide a nitrogen source while utilizing hydrogen to reduce trace oxides that may exist at the interface, further improving contact resistance. These gases are not limited to those listed above; any gas or combination of gases that can decompose to produce reactive nitrogen atoms at the annealing temperature can be used.

[0030] In some embodiments, step two involves a rapid thermal annealing process. Rapid thermal annealing (RTA) heats the wafer to the target temperature in a very short time, thereby precisely controlling the thermal budget and reducing the lateral diffusion of impurities. In addition to rapid thermal annealing, other short-time high-temperature processing processes such as laser annealing, flash annealing, or millisecond-level annealing can also be used, or conventional furnace tube annealing processes can be employed.

[0031] In some embodiments, in step two, by controlling the temperature and time of the thermal annealing process, the titanium metal layer at the semiconductor substrate interface is transformed into titanium silicide, and the titanium metal layer on the surface of the titanium metal layer reacts with a nitrogen-containing atmosphere to transform into titanium nitride. During this process, titanium atoms diffuse toward the semiconductor substrate (e.g., silicon) and react to form titanium silicide (TiSi or TiSi2), which provides low ohmic contact resistance and enhances film adhesion. Simultaneously, nitrogen atoms in the ambient atmosphere react with surface titanium atoms to form titanium nitride (TiN). Because the reaction is carried out using the upper surface of the titanium layer itself, the resulting titanium nitride layer is thinner than that of conventionally PVD-deposited titanium nitride. According to actual measurement data, the thicknesses (in angstroms) of the Ti / TiN thin films manufactured using the old process at the center, middle, and edge points are 709 / 219, 695 / 198, and 675 / 182, respectively; while the corresponding thicknesses of the Ti / TiN thin films manufactured using the new process described in this application are 603 / 160, 596 / 157, and 597 / 162, respectively. The data comparison shows that the TiN layer formed by the new process is significantly thinner (from approximately 200 angstroms to approximately 160 angstroms), and the overall thickness distribution is more uniform. This in-situ generated, thinner titanium nitride layer can significantly improve the problem of uneven wafer stress caused by thick film deposition in traditional processes.

[0032] like Figure 2 As shown, Figure 2 This is a comparison chart of wafer warpage-bow data, where the vertical axis represents the degree of warpage (usually in micrometers) and the horizontal axis represents different process stages. As can be seen from the chart, in the traditional "post-Ti / TiN Dep" stage (i.e., depositing thick titanium and thick titanium nitride, such as 400 Å titanium / 400 Å titanium nitride), the wafer exhibits extremely high negative stress (warpage values ​​are approximately -150° in the Y-axis direction and approximately -110° in the X-axis direction). However, in the "post-RTA (NH3) stage" corresponding to the embodiments of this application, the wafer warpage value is significantly reduced and approaches zero (approximately 35° in the Y-axis direction and approximately -10° in the X-axis direction). This indicates that the thin film formed by the new process effectively releases stress, solving the stress unevenness problem caused by excessively thick TiN layers in the traditional process, thereby reducing the risk of mechanical damage to the wafer in subsequent processing.

[0033] In some embodiments, in step two, an excess of nitrogen-containing gas is introduced to ensure that the titanium metal layer reacts fully. The excess reactant gas (e.g., NH3) ensures that the surface titanium is completely converted into titanium nitride, preventing the residual unreacted pure titanium layer from being oxidized or corroded in subsequent processes. Simultaneously, the sufficient reaction atmosphere combined with high-temperature annealing ensures that the bottom titanium reacts fully with the silicon, avoiding high-resistivity regions formed due to incomplete reaction, thereby improving the stability of the device.

[0034] In some embodiments, titanium / titanium nitride thin films are used in the contact hole process of semiconductor devices as an adhesion barrier layer before the deposition of a conductive metal layer. In contact holes or vias, this titanium / titanium nitride stack (Ti / TiN) acts as both a diffusion barrier and an adhesion layer, preventing subsequently filled metal atoms from diffusing into the silicon substrate and causing device failure, while also preventing metal layer peeling. The contact structure formed by this method also shows significant improvements in electrical performance. Figure 3 As shown, Figure 3 The distribution comparison of threshold voltage (Vth) is shown. The left area "T500" in the figure represents device data manufactured using the novel process of this application (depositing 500 Å thick titanium followed by ammonia annealing), while the right area "T400N400" represents device data manufactured using the conventional process (depositing 400 Å titanium and 400 Å titanium nitride, respectively). The box plot distribution shows that the Vth data of devices using the novel process (T500) is mainly concentrated between 3.3V and 3.5V, exhibiting a very convergent and consistent distribution; while the Vth data of devices using the conventional process (T400N400) is dispersed over a wider range, with more discrete points. This indicates that the method of this application, by ensuring sufficient reaction at the silicon interface and forming a uniform low-stress barrier layer, makes the key electrical parameter Vth of the device more convergent than that of the conventional process, improving product yield and performance consistency.

[0035] In some embodiments, the conductive metal layer is made of tungsten. Tungsten (W) is typically filled into contact holes to form tungsten plugs using a chemical vapor deposition (CVD) process. Besides tungsten, the conductive metal layer may also be made of cobalt (Co), copper (Cu), aluminum (Al), ruthenium (Ru), molybdenum (Mo), or alloys thereof. For example, during the CVD deposition of tungsten, the dense structure and good surface condition of the titanium nitride layer formed in this embodiment effectively prevent reactive precursors such as tungsten hexafluoride (WF6) from eroding the underlying silicide, thereby improving device reliability.

[0036] It should be noted that the illustrations provided in this embodiment are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0037] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for forming a titanium / titanium nitride thin film, characterized in that, At least including: Step 1: Deposit a titanium metal layer on a semiconductor substrate; Step 2: Perform thermal annealing on the semiconductor substrate with the deposited titanium metal layer under a nitrogen-containing atmosphere, so that the titanium metal layer reacts with the semiconductor substrate to form metal silicide, and at the same time the titanium metal layer reacts with the nitrogen-containing atmosphere to form titanium nitride layer.

2. The method for forming a titanium / titanium nitride thin film according to claim 1, characterized in that: In step two, the nitrogen-containing atmosphere is selected from at least one of ammonia, nitrogen, or a mixture of nitrogen and hydrogen.

3. The method for forming titanium / titanium nitride thin films according to claim 1, characterized in that: In step two, the thermal annealing process employs a rapid thermal annealing process.

4. The method for forming a titanium / titanium nitride thin film according to claim 1, characterized in that: In step two, by controlling the temperature and time of the thermal annealing process, the titanium metal layer at the semiconductor substrate interface is transformed into titanium silicide, and the titanium metal layer on the surface of the titanium metal layer reacts with the nitrogen-containing atmosphere to transform into titanium nitride.

5. The method for forming a titanium / titanium nitride thin film according to claim 4, characterized in that: In step two, an excess of nitrogen-containing gas is introduced to ensure that the titanium metal layer reacts fully.

6. The method for forming a titanium / titanium nitride thin film according to claim 1, characterized in that: The titanium / titanium nitride thin film is used in the contact hole process of semiconductor devices as an adhesion barrier layer before depositing the conductive metal layer.

7. The method for forming a titanium / titanium nitride thin film according to claim 6, characterized in that: The material of the conductive metal layer includes tungsten.

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