Preparation method of TiN film and Schottky gate metal

Abstract

The invention discloses a preparation method of a TiN film and Schottky gate metal, relates to the technical field of semiconductor devices, and aims to solve the problem of poor stability when Ni is used as gate contact metal of a millimeter wave device in the prior art. The method comprises the steps of providing a substrate; forming a first photoresist layer on the substrate; preprocessing the first photoresist layer to obtain a target area on the substrate; the pretreatment comprises exposure and development treatment; multiple layers of TiN films with different metal components are prepared and formed in the target area; the content of TiN in the multi-layer TiN film is reduced layer by layer from the lower layer to the upper layer, and the contents of TiOxNy and TiO2 are increased layer by layer from the lower layer to the upper layer; when the TiN thin film is used as the grid contact metal, compared with Ni which is used as the grid contact metal, the adhesion and the stability of a TiN bottom layer are better, meanwhile, the TiN also avoids the problem of large electric leakage caused by low-potential-barrier silicide formed in the silicon nitride passivation process, and the stability of the millimeter wave device is improved.

Description

Technical Field

[0001] The invention relates to the technical field of semiconductor devices, in particular to a method for preparing a TiN film and a Schottky gate metal. Background Art

[0002] Compared with the first and second generation semiconductors represented by Si and GaAs, the third generation semiconductors represented by GaN materials have the characteristics of large bandgap width, strong polarization effect, high 2DEG concentration, high breakdown field strength, high thermal conductivity, stable chemical properties, and high electron saturation drift rate. They are ideal materials for manufacturing high-temperature, high-frequency, and high-power microwave and millimeter-wave devices.

[0003] HEMT devices with high-concentration 2DEG on the heterojunction surface using the polarization effect between different materials (such as AlGaN / GaN) are currently the most commonly used structures. Its working principle: Place a gate metal above the formed 2DEG channel, that is, between the source and drain, to form a Schottky contact, and control the electron concentration under the gate by applying different voltages to the gate. When the applied voltage is less than the turn-on voltage, the electrons in the channel are depleted and the device is turned off; when the applied gate voltage is greater than the turn-on voltage, the electrons in the channel are not depleted and the device is turned on. The introduction of the gate electrode, its own resistance and capacitance characteristics directly affect the frequency performance of the device.

[0004] At present, in the process flow of GaN HEMT millimeter wave devices, the commonly used Schottky gate metal is NiAu, which uses high work function metal Ni as the contact metal. In actual use, Ni is used as the gate contact metal. During the passivation process of the gate metal Ni and the passivation medium silicon nitride, Ni metal reacts with silicon nitride to form Ni-Si. The barrier of the Ni-Si reaction layer is low, resulting in a decrease in the Schottky forward turn-on voltage and an increase in leakage current. In addition, the adhesion of Ni metal to the substrate layer is poor, and the stability is poor, resulting in a decrease in the stability of the millimeter wave device.

[0005] Therefore, a design scheme that can optimize the performance of the gate electrode is urgently needed to solve the problem that in the prior art, Ni is used as the gate contact metal of the millimeter wave device, Ni-Si is formed at the edge of the gate foot during the passivation process of the gate metal Ni and the passivation medium silicon nitride, and the potential barrier of the Ni-Si reaction layer is low, resulting in a decrease in the Schottky forward turn-on voltage, an increase in leakage current, and a decrease in the stability of the millimeter wave device. Summary of the invention

[0006] The present invention aims to disclose a method for preparing a TiN film and a Schottky gate metal, so as to solve the problem of poor stability when Ni is used as the gate contact metal of a millimeter wave device in the prior art.

[0007] In order to achieve the above object, the present invention provides the following technical solutions:

[0008] In a first aspect, the present invention provides a method for preparing a TiN thin film, which may include:

[0009] providing a substrate;

[0010] forming a first photoresist layer on the substrate;

[0011] Pre-processing the first photoresist layer to obtain a target area on the substrate; the pre-processing includes exposure and development processing;

[0012] A multi-layer TiN film with different metal components is prepared in the target area; the TiN content in the multi-layer TiN film decreases layer by layer from the lower layer to the upper layer, and the TiOxNy and TiO2 contents increase layer by layer from the lower layer to the upper layer.

[0013] Preferably, the step of preparing a multilayer TiN film with different metal components in the target area may include:

[0014] According to preset preparation process parameters, a multilayer TiN film with different metal components is prepared in the target area; the preset preparation process parameters at least include a preset vacuum degree, a sputtering power of a Ti target material, a flow rate of a sputtering deposition mixed gas, and a preset thickness of the TiN film; wherein the mixed gas includes argon and nitrogen, and the input flow rate of the nitrogen is a dynamic flow rate.

[0015] Preferably, the step of preparing a multilayer TiN film with different metal components in the target area may include:

[0016] According to the preset vacuum degree, the sputtering power of the Ti target material and the flow rate of the sputtering deposition mixed gas, the mixed gas is sputtered and deposited to form a multi-layer TiN film with different metal components from the lower layer to the upper layer; wherein the input flow rate of the argon gas is a first constant flow rate, and the input flow rate of the nitrogen gas is a second variable flow rate; when the thickness of the multi-layer TiN film with different metal components meets the preset thickness of the TiN film, the sputtering is stopped; and the metal layer and the photoresist layer outside the target area are stripped and removed to obtain the multi-layer TiN film with different metal components.

[0017] Preferably, the second variable flow rate may include a variable flow rate that decreases step by step according to a preset time interval based on a preset initial flow rate; the mixed gas is sputtered and deposited according to the preset vacuum degree, the sputtering power of the Ti target material and the flow rate of the sputtering deposition mixed gas to form a multi-layer TiN film with different metal components from the lower layer to the upper layer, including: forming a power function of the TiN film in contact with the substrate that is greater than or equal to the power function of Ni metal, and the stability and reliability of the upper TiN film are greater than the stability and reliability of Ni metal.

[0018] Preferably, the substrate is a planar substrate, and the material of the substrate may include at least any one of gallium arsenide, silicon carbide, aluminum oxide or gallium nitride.

[0019] In a second aspect, the present invention provides a method for preparing a Schottky gate metal, which may at least include a TiN film prepared by the method for preparing a TiN film according to the first aspect; the method may include:

[0020] providing a substrate;

[0021] forming a second photoresist layer on the substrate;

[0022] Pre-processing the second photoresist layer to obtain a T-shaped target area on the substrate;

[0023] In the T-shaped target area, preparing a plurality of TiN films with different metal components on the substrate;

[0024] Forming a T-shaped gate metal layer on the surface of the multilayer TiN film away from the substrate;

[0025] The metal layer and the photoresist layer outside the T-shaped target area are stripped off to obtain the Schottky gate metal.

[0026] Preferably, the second photoresist layer may include multiple layers, and the forming of the second photoresist layer on the substrate includes: forming a first second photoresist layer on the substrate; forming a second second photoresist layer on the surface of the first second photoresist layer away from the substrate; and forming a third second photoresist layer on the surface of the second second photoresist layer away from the first second photoresist layer.

[0027] Preferably, the T-shaped target area includes a first width concave target area and a second width concave target area.

[0028] The pre-processing of the second photoresist layer to obtain a T-shaped target area on the substrate may include:

[0029] The second layer of the second photoresist layer and the third layer of the second photoresist layer are exposed and developed by electron beam lithography to obtain a concave target area of ​​the first width located on the first layer of the second photoresist layer; the first layer of the second photoresist layer is exposed and developed by electron beam lithography to obtain a concave target area of ​​the second width located on the substrate; the first width is greater than the second width.

[0030] Preferably, in the T-shaped target area, preparing a multilayer TiN film with different metal components on the substrate may include:

[0031] The multi-layer TiN film with different metal components is formed in the second width concave target area by magnetron sputtering titanium nitride; the thickness of the multi-layer TiN film is less than the thickness of the first photoresist layer.

[0032] Preferably, forming a T-shaped gate metal layer on the surface of the multilayer TiN film away from the substrate may include:

[0033] The T-shaped gate metal layer is formed on the surface of the multilayer TiN film away from the substrate based on the first width concave target area and the second width concave target area by evaporating metal.

[0034] Compared with the prior art, the present invention provides a method for preparing a TiN film, which provides a substrate, forms a first photoresist layer on the substrate; pre-treats the photoresist layer to obtain a target area on the substrate; the pre-treating includes exposure and development processing; prepares a multi-layer TiN film with different metal components in the target area; the TiN content in the multi-layer TiN film decreases layer by layer from the lower layer to the upper layer, and the TiOxNy and TiO2 contents increase layer by layer from the lower layer to the upper layer. Based on this, the TiN film can be used as the gate contact metal of the millimeter wave device. Compared with Ni as the gate contact metal of the millimeter wave device, since the titanium nitride content of the bottom layer of the TiN film is the highest, the adhesion and stability of the TiN film to the substrate are better than those of Ni metal; and the TiOxNy and TiO2 contents in the upper TiN film are the highest, so the problem of large leakage caused by the formation of low-barrier silicide by the passivation medium silicon nitride during the passivation process can also be avoided; thereby improving the stability of the millimeter wave device. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings described herein are used to provide a further understanding of the present invention and constitute a part of the present invention. The exemplary embodiments of the present invention and their descriptions are used to explain the present invention and do not constitute an improper limitation of the present invention. In the drawings:

[0036] Figure 1A schematic diagram of the main process of a method for preparing a TiN thin film provided by the present invention;

[0037] Figure 2 A schematic diagram of the first decomposition step of a method for preparing a TiN thin film provided by the present invention;

[0038] Figure 3 A schematic diagram of the second decomposition step of a method for preparing a TiN thin film provided by the present invention;

[0039] Figure 4 A schematic diagram of the third decomposition step of a method for preparing a TiN thin film provided by the present invention;

[0040] Figure 5 A schematic diagram of the fourth decomposition step of a method for preparing a TiN thin film provided by the present invention;

[0041] Figure 6 A schematic diagram of component structures corresponding to different etching times of a multi-layer TiN film with different metal components prepared by a TiN film preparation method provided by the present invention;

[0042] Figure 7 A schematic diagram of the main process of a method for preparing a Schottky gate metal provided by the present invention;

[0043] Figure 8 A schematic diagram of the first decomposition step of a method for preparing a Schottky gate metal provided by the present invention;

[0044] Fig. 9 A schematic diagram of the second decomposition step of a method for preparing a Schottky gate metal provided by the present invention;

[0045] Fig.10 A schematic diagram of the third decomposition step of a method for preparing a Schottky gate metal provided by the present invention;

[0046] Fig.11 A schematic diagram of the fourth decomposition step of a method for preparing a Schottky gate metal provided by the present invention;

[0047] Fig.12 A schematic diagram of the fifth decomposition step of a method for preparing a Schottky gate metal provided by the present invention.

[0048] Figure numerals: 61 - first TiN film layer, 62 - second TiN film layer, 63 - third TiN film layer, 20 - substrate, 30 - second photoresist layer, 31 - first layer of second photoresist layer, 32 - second layer of second photoresist layer, 33 - third layer of second photoresist layer, 41 - TiN film, 42 - T-type gate metal layer, 40 - Schottky gate metal. DETAILED DESCRIPTION

[0049] In order to facilitate the clear description of the technical solutions of the embodiments of the present invention, in the embodiments of the present invention, the words "first", "second" and the like are used to distinguish the same items or similar items with substantially the same functions and effects. For example, the first threshold and the second threshold are only used to distinguish different thresholds, and do not limit their order of precedence. Those skilled in the art can understand that the words "first", "second" and the like do not limit the quantity and execution order, and the words "first", "second" and the like do not necessarily limit them to be different.

[0050] It should be noted that, in the present invention, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the present invention should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

[0051] In the present invention, "at least one" means one or more, and "plurality" means two or more. "And / or" describes the association relationship of associated objects, indicating that three relationships may exist. For example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone, where A and B can be singular or plural. The character " / " generally indicates that the associated objects in the previous time are in an "or" relationship. "At least one of the following items" or similar expressions refers to any combination of these items, including any combination of single items or plural items. For example, at least one of a, b or c can mean: a, b, c, the combination of a and b, the combination of a and c, the combination of b and c, or the combination of a, b and c, where a, b, c can be single or multiple.

[0052] In the prior art, metal Ni is usually used as the gate contact metal. Although it can meet the use requirements, in actual use, when Ni is used as the gate contact metal, Ni-Si is formed during the passivation process of the gate metal Ni and the passivation medium silicon nitride. The barrier of the Ni-Si reaction layer is low, resulting in a decrease in the Schottky forward turn-on voltage and an increase in leakage current. In addition, the adhesion between the Ni metal and the substrate layer is poor, and the stability is poor, which will lead to a decrease in the performance of the millimeter wave device.

[0053] In addition, TiN's excellent conductivity can be used as semiconductor device electrodes, buffer layers, and barrier layers. Although some research has been conducted to adjust the work function of TiN by annealing it in a N2 atmosphere, the redundant heat treatment process will cause new damage to the performance of GaN RF devices. It is very meaningful to control the Ti:N ratio by continuously adjusting the flow rate of N2 gas during the growth process, thereby achieving regulation of the work function.

[0054] In view of this, the present invention provides a method for preparing a TiN film and a Schottky gate metal, wherein the TiN film is used as the gate contact metal of a millimeter wave device, and Ni metal is used instead of Ni metal as the cover layer of the ohmic metal and the electrode layer of the Schottky contact, so that the problem that in the prior art, Ni is used as the gate contact metal, and during the passivation process of the gate metal Ni and the passivation medium silicon nitride, the Ni metal reacts with silicon nitride to form Ni silicide, and the Ni-Si reaction layer barrier is low, resulting in a decrease in the Schottky forward turn-on voltage, an increase in leakage current, and a decrease in the stability performance of the millimeter wave device; the stability of the millimeter wave device is improved.

[0055] Next, the technical solution of the present invention is described in detail with reference to the accompanying drawings:

[0056] See also Figure 1 , Figure 1 A schematic diagram of the main process of a method for preparing a TiN film provided by the present invention; its execution subject is a server or lithography equipment equipped with the technical solution disclosed in the embodiment of the present invention, such as a lithography service platform or a lithography terminal device, etc.

[0057] exist Figure 1 In, the method may include:

[0058] Step 110: providing a substrate; and forming a first photoresist layer on the substrate.

[0059] Step 120: pre-processing the first photoresist layer to obtain a target area on the substrate; the pre-processing includes exposure and development processing.

[0060] Step 130: forming a plurality of TiN films with different metal components in the target area; wherein the TiN content in the plurality of TiN films decreases layer by layer from the lower layer to the upper layer, and the TiOxNy and TiO2 contents increase layer by layer from the lower layer to the upper layer.

[0061] In step 110 to step 130, a first photoresist layer is uniformly formed on the substrate, and the photoresist is deposited on the substrate surface by atomization under a spraying process, and the droplet size is usually in the micrometer range; these droplets are formed by, for example, a nitrogen nozzle or by ultrasonic atomization and are carried by air or nitrogen and deposited on the substrate surface, and a continuous photoresist is formed on the substrate surface. Further exposure and development are performed on the first photolithography, and a target shape and a window are formed after development; and then a TiN metal with adjustable components is prepared on the developed substrate; thereby, a multi-layer TiN film with different metal components is obtained, in which the TiN content decreases layer by layer from the lower layer to the upper layer, and the TiOxNy and TiO2 contents increase layer by layer from the lower layer to the upper layer; based on this, the TiN film can be used as a gate contact metal. Compared with Ni as a gate contact metal, the bottom layer adhesion and stability of TiN are better, and TiN also avoids the problem of large leakage caused by the formation of low barrier silicides during the passivation of silicon nitride, thereby improving the stability of millimeter wave devices.

[0062] As a specific example of how to prepare multiple layers of TiN films with different metal compositions, see Figures 2 to 4 , Figure 2 A schematic diagram of the first decomposition step of a method for preparing a TiN thin film provided by the present invention; Figure 3 A schematic diagram of the second decomposition step of a method for preparing a TiN thin film provided by the present invention; Figure 4 A schematic diagram of the third decomposition step of a method for preparing a TiN thin film provided by the present invention; Figure 5 This is a schematic diagram of the fourth decomposition step of the method for preparing a TiN film provided by the present invention.

[0063] exist Figures 2 to 3 In the method, a first photoresist layer is uniformly formed on a substrate, and then exposure and development are performed on a photolithography process to form a target shape and a window on the substrate and between the first photoresist layers; for example Figure 3 The rectangular target shape shown.

[0064] exist Figure 4 In the step 120, a multi-layer TiN film with different metal components is prepared based on the target shape obtained in step 120. The Ti metal can be directly sputtered by magnetron sputtering, and argon and nitrogen are introduced and mixed in a certain proportion to form a multi-layer TiN film layer with different components.

[0065] Preferably, in step 130, the preparing a plurality of TiN films with different metal components in the target area may include: preparing a plurality of TiN films with different metal components in the target area according to preset preparation process parameters; the preset preparation process parameters include at least a preset vacuum degree, a sputtering power of a Ti target material, a flow rate of a sputtering deposition mixed gas, and a preset thickness of the TiN film; wherein the mixed gas includes argon and nitrogen, and the input flow rate of the nitrogen is a dynamic flow rate.

[0066] Preferably, the preparation of forming a multi-layer TiN film with different metal components in the target area may include: sputtering and depositing the mixed gas according to the preset vacuum degree, the sputtering power of the Ti target material and the flow rate of the sputtering deposition mixed gas to form a multi-layer TiN film with different metal components from the lower layer to the upper layer; wherein the input flow rate of the argon gas is a first constant flow rate, and the input flow rate of the nitrogen gas is a second variable flow rate.

[0067] When the thickness of the multi-layer TiN film with different metal components meets the preset thickness of the TiN film, the sputtering is stopped; the metal layer and the photoresist layer outside the target area are stripped off to obtain the multi-layer TiN film with different metal components.

[0068] Preferably, the second variable flow rate may include a variable flow rate that is gradually decreased according to a preset time interval based on a preset initial flow rate.

[0069] The sputtering and depositing of the mixed gas according to the preset vacuum degree, the sputtering power of the Ti target material and the flow rate of the sputtering deposition mixed gas to form a multi-layer TiN film with different metal components from the lower layer to the upper layer may include: forming a power function of the TiN film in contact with the substrate greater than or equal to the power function of the Ni metal, and the stability and reliability of the upper TiN film being greater than the stability and reliability of the Ni metal.

[0070] Specifically, in order to obtain a TiN thin film layer with better device performance, the vacuum of the preparation environment for preparing a multilayer TiN thin film with different metal components can be set to 2×10 -6 mbar, the sputtering power of the Ti target is set to 100w, 700w or 1200w; the sputtering deposition gas can be a mixed gas of argon and nitrogen, wherein the argon flow rate is always kept at a constant value input, preferably 50sccm, 30sccm or 10sccm; the nitrogen flow rate is an adjustable parameter, and the initial nitrogen flow rate is preferably 50sccm, 30sccm or 10sccm, and the nitrogen flow rate value can be gradually reduced at intervals of 10s, each time by 15%; the thickness of the deposited multi-layer TiN film with different metal components is preferably 80nm / 40nm / 5nm.

[0071] Preferably, the substrate is a planar substrate, and the material of the substrate may include at least any one of gallium arsenide, silicon carbide, aluminum oxide or gallium nitride.

[0072] In order to further verify the performance of the multi-layer TiN film with different metal components, the present invention provides a component testing experiment of the multi-layer TiN film with different metal components and the TiN film prepared by conventional process.

[0073] For details, please refer to Figure 6 A schematic diagram of component structures corresponding to different etching times of a multi-layer TiN film with different metal components prepared by a TiN film preparation method provided by the present invention.

[0074] exist Figure 6 In the figure, the first TiN film layer 61 represents a film layer obtained after etching the multiple layers of TiN films with different metal components for 60 seconds, the second TiN film layer 62 represents a film layer obtained after etching the multiple layers of TiN films with different metal components for 30 seconds, and the third TiN film layer 63 represents a film layer obtained after etching the multiple layers of TiN films with different metal components for 10 seconds.

[0075] The composition of the TiN film prepared according to the process in the prior art is shown in Table 1.

[0076] Table 1. Statistical table of component distribution of TiN films prepared by processes in the prior art.

[0077]

[0078] The composition of the TiN film prepared according to the process provided by the present invention is shown in Table 2.

[0079] Table 2. Statistical table of component distribution of TiN films prepared by the process provided by the present invention.

[0080]

[0081] The data shown in Tables 1 and 2 are based on Figure 6The composition data of TiN film at different positions shown in the figure are the results obtained by using XPS technology (X-ray photoelectron spectroscopy). According to the data shown in Table 1 and Table 2, it can be obtained that compared with TiN reactive sputtering with conventional constant nitrogen flow and TiN reactive sputtering with variable nitrogen flow, the TiN content of the bottom layer of the film produced by conventional constant nitrogen flow is low at 75.27%, while the TiN content of the bottom layer of the film produced by the variable nitrogen flow provided by the present invention is higher at 81.14%. Therefore, the TiN metal content of the bottom metal and semiconductor contact area of ​​the TiN film produced by variable flow reactive sputtering is high, with less impurities, which is an ideal contact for metal and semiconductor contact, with good Schottky characteristics and high viscosity.

[0082] Furthermore, the second factor of using variable flow TiN reactive sputtering is that after using variable flow nitrogen for reactive sputtering, the TiN metal content of the upper TiN film will gradually decrease (the TiN content gradually decreases from 81.14% in the bottom layer to 67.41%), and the TiOxNy and TiO2 contents will gradually increase (the TiOxNy content gradually increases from 5.7% in the bottom layer to 15.47%; the TiO2 content increases from 13.16% in the bottom layer to 17.13%). After the TiOxNy and TiO2 contents increase, the upper TiN film will be stable and the reliability will be enhanced. Based on this, the problem of high leakage current caused by the reaction between Ni metal and silicon nitride during the passivation process of the upper metal and the passivation medium silicon nitride is avoided, thereby improving the performance of millimeter wave devices.

[0083] Based on this, the present invention provides a method for preparing a TiN film, which forms a TiN film by reacting Ti with nitrogen, and based on a method of changing the nitrogen input flow rate in real time, a variable Ti:N ratio is formed in the TiN preparation process to form TiN films with different components; the work function of the TiN metal in contact with the substrate is similar to that of Ni, or even higher; the TiN component in the deposited TiN film is gradually reduced from the lower layer to the upper layer, and the components of TiOxNy and TiO2 are gradually increased from the lower layer to the upper layer, thereby enhancing the stability and reliability of the TiN metal film in the upper layer; therefore, the TiN film prepared by the method provided by the present invention can replace Ni as a Schottky contact gate metal, and can avoid reacting with the passivation medium silicon nitride passivation process in the subsequent process to form a low-barrier silicide, thereby solving the problem of large leakage after passivation; and because the TiN film adopts a sputtering process, compared with conventional Ni metal, the adhesion is improved, and the yield of millimeter wave devices is also improved.

[0084] It should be noted that the formation of the TiN film in the preparation method of the TiN film provided by the present invention includes but is not limited to a reactive ion sputtering method; the application scenarios of the TiN film include but are not limited to GaN HEMT millimeter wave device "T-type gate structure" Schottky gate metal, microwave millimeter wave devices, diode gate structure, triode gate structure and MOS tube gate structure, etc.

[0085] In the second aspect, based on the same technical concept as the first aspect, the present invention provides a method for preparing a Schottky gate metal. Figure 7 , Figure 7 A schematic diagram of the main process of a method for preparing a Schottky gate metal provided by the present invention. Figure 7 This is a specific example of applying the method for preparing a TiN film provided in the first aspect of the present invention to preparing a Schottky gate metal. This application scenario should not constitute a specific limitation on how to prepare the TiN film.

[0086] exist Figure 7 In the present invention, a method for preparing a Schottky gate metal at least comprises a TiN film prepared by the method for preparing a TiN film described in the first aspect. The method for preparing a Schottky gate metal may include:

[0087] Step 710: Provide a substrate; and form a second photoresist layer on the substrate.

[0088] Step 720: pre-treating the second photoresist layer to obtain a T-shaped target region on the substrate.

[0089] In step 710 to step 720, first, a second photoresist layer is formed on a substrate, and then the second photoresist layer is pretreated to obtain a T-shaped target area on the substrate; wherein the substrate may be a substrate of the same material as the substrate described in the first aspect, or a substrate of a different material, which may be determined according to the actual application scenario. The second photoresist layer may be a multi-layer photoresist layer, and the specific number of layers may be determined according to the actual application scenario of the Schottky gate metal. In addition, the second photoresist layer may also be pretreated by exposing and developing the photoresist to form a T-shaped target area; this is not specifically limited in the present invention.

[0090] Step 730: In the T-shaped target area, prepare a plurality of TiN films with different metal components on the substrate.

[0091] Step 740: Form a T-shaped gate metal layer on the surface of the multi-layer TiN film away from the substrate.

[0092] Step 750: stripping and removing the metal layer and the photoresist layer outside the T-shaped target area to obtain the Schottky gate metal.

[0093] In step 730 to step 750, firstly, according to the method described in the first aspect, a plurality of TiN films with different metal components are prepared on the substrate in the T-shaped target region, wherein the TiN content in the plurality of TiN films decreases layer by layer from the lower layer to the upper layer, and the TiOxNy and TiO2 contents increase layer by layer from the lower layer to the upper layer. A T-shaped gate metal layer is further formed, and finally the metal layer and the photoresist layer outside the T-shaped target region are removed to obtain a Schottky gate metal on the substrate.

[0094] Based on this, the present invention provides a method for preparing a Schottky gate metal, which forms a plurality of TiN films on a substrate, wherein the TiN content in the TiN films decreases layer by layer from the lower layer to the upper layer, and the TiOxNy and TiO2 contents increase layer by layer from the lower layer to the upper layer, and forms a T-shaped gate metal layer on the TiN film; in essence, the Ni metal in the prior art is replaced by the TiN film as the gate contact metal, thereby avoiding the reaction between the gate metal Ni and the passivation medium silicon nitride passivation process in the back-end process after the gate metal is manufactured in the millimeter wave device process, and the Ni-Si reaction layer barrier is low, which reduces the Schottky forward turn-on voltage and increases the leakage current; at the same time, it can also avoid the problem of poor adhesion and poor stability between the Ni metal and the substrate layer; the stability of the millimeter wave device is improved.

[0095] It should be noted that compound semiconductor materials (such as GaAs, GaN) have many excellent properties, such as high critical breakdown electric field, high electron mobility, high two-dimensional electron gas concentration and good high-temperature working ability. Devices such as high electron mobility transistors (HEMT) and heterostructure field effect transistors (HFET) based on compound semiconductors have been widely used, especially in the fields of radio frequency and microwave that require high power and high frequency. In the manufacturing process of compound semiconductor radio frequency power devices, the production of gate electrodes is a key process step. At present, in the production of deep submicron compound semiconductor devices, electron beam lithography and multi-layer glue are generally used to make T-gates. T-gate refers to a T-shaped gate electrode with a mushroom-shaped cross-section, so that the gate root at the bottom that contacts the semiconductor surface is very narrow, thereby increasing the cutoff frequency of the device, and the gate cap at the top is very wide, which can reduce the resistance of the gate. A three-layer glue solution is adopted, which is also a common photoresist matching solution in the T-gate production process. It mainly uses three electron beam photoresists with different sensitivities to develop different widths after exposure to realize the T-gate shape. The common three-layer glue solution can have the following photoresist options: PMMA (top layer) + Copolymer (middle layer) + PMMA (bottom layer).

[0096] Preferably, see Figure 8, Figure 8 A schematic diagram of the first decomposition step of a method for preparing a Schottky gate metal provided by the present invention.

[0097] exist Figure 8 In the embodiment, the second photoresist layer 30 may include multiple layers, and the forming of the second photoresist layer 30 on the substrate 20 may include:

[0098] A first second photoresist layer 31 is formed on the substrate 20; a second second photoresist layer 32 is formed on the surface of the first second photoresist layer 31 away from the substrate 20; and a third second photoresist layer 33 is formed on the surface of the second second photoresist layer 32 away from the first second photoresist layer 31. Three photoresist layers with different thicknesses can be formed on the substrate by uniform coating. Preferably, the thickness of the first second photoresist layer 31 is greater than that of the second second photoresist layer 32, and the thickness of the first second photoresist layer 31 is less than that of the third second photoresist layer 33.

[0099] For further information, see Fig. 9 , Fig. 9 The second decomposition step of the method for preparing a Schottky gate metal provided by the present invention is a schematic diagram showing how to form a T-shaped target region.

[0100] exist Fig. 9 In the method, the T-shaped target region includes a concave target region of a first width and a concave target region of a second width. The pre-processing of the second photoresist layer to obtain the T-shaped target region on the substrate may include:

[0101] First, the second photoresist layer 32 and the third photoresist layer 33 may be exposed and developed by electron beam lithography to obtain a concave target region of a first width on the first photoresist layer 31 .

[0102] Secondly, the first second photoresist layer 31 can also be exposed and developed by electron beam lithography to obtain the second width concave target area on the substrate 20; the first width is greater than the second width. A T-shaped target area is formed based on the first width concave target area and the second width concave target area.

[0103] For further information, see Fig.10 , Fig.10 The third decomposition step of the method for preparing Schottky gate metal provided by the present invention is a schematic diagram showing how to form a multi-layer TiN film with different metal components, that is, how to form a TiN layer of gate contact metal.

[0104] exist Fig.10 In the T-shaped target area, preparing a plurality of TiN films with different metal components located on the substrate can include: using a magnetron sputtering titanium nitride method to form the plurality of TiN films 41 with different metal components in the second width concave target area; the thickness of the plurality of TiN films is less than the thickness of the first photoresist layer.

[0105] It should be noted that the method for preparing multiple TiN films with different metal components on a substrate in a T-shaped target area is the same as the method for preparing multiple TiN films with different metal components on a substrate described in the first aspect, and will not be repeated here.

[0106] For further information, see Fig.11 , Fig.11 A schematic diagram of the fourth decomposition step of a method for preparing a Schottky gate metal provided by the present invention; the fourth decomposition step represents the step of how to form a T-shaped gate metal layer, that is, the step of how to form an Au layer of a gate contact metal.

[0107] exist Fig.11 In the method, the T-shaped gate metal layer is formed on the surface of the multilayer TiN film away from the substrate, which may include: using a method of evaporating metal, based on the first width concave target area and the second width concave target area, forming the T-shaped gate metal layer 42 (Au layer) on the surface of the multilayer TiN film away from the substrate; the thickness of the T-shaped gate metal layer 42 of the gate contact metal is greater than the thickness of the TiN film 41 of the gate contact metal.

[0108] Finally, see Fig.12 , Fig.12 The fifth decomposition step of the method for preparing a Schottky gate metal provided by the present invention is a schematic diagram showing how to obtain the Schottky gate metal.

[0109] exist Fig.12 In the process, the metal layer and the photoresist layer outside the T-shaped target area can be removed by stripping and degumming to obtain a method for preparing a Schottky gate metal according to the present invention, and the prepared Schottky gate metal 40 is obtained.

[0110] It should be noted that, in the prior art, when Ni metal is used as the contact metal between the substrate, the deposition processes of the Ni metal and the Au layer are both electron beam evaporation deposition processes; in the preparation method of a Schottky gate metal provided by the present invention, the TiN film layer is a multi-layer TiN film layer with different metal components formed by a magnetron sputtering process. Because after the use of variable flow TiN reactive sputtering, the TiN metal content of the upper TiN film will gradually decrease, and the contents of TiOxNy and TiO2 will gradually increase; after the contents of TiOxNy and TiO2 increase, the upper TiN film will be stable and the reliability will be enhanced; in this way, the problem of reaction between the upper metal and the passivation medium silicon nitride during the passivation process is solved, and a reaction occurs between Ni-Si to form a low-barrier silicide, thereby solving the problem of large leakage after passivation; the Schottky forward turn-on voltage is improved, the leakage is reduced, and the performance of the millimeter wave device is improved.

[0111] Although the present invention is described herein in conjunction with various embodiments, in the process of implementing the claimed invention, those skilled in the art may understand and implement other variations of the disclosed embodiments by viewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "one" or "an" does not exclude multiple situations. A single processor or other unit may implement several functions listed in the claims. Certain measures are recorded in different dependent claims, but this does not mean that these measures cannot be combined to produce good results.

[0112] Although the present invention has been described in conjunction with specific features and embodiments thereof, it is apparent that various modifications and combinations may be made thereto without departing from the spirit and scope of the present invention. Accordingly, this specification and the accompanying drawings are merely exemplary illustrations of the present invention as defined by the appended claims and are deemed to cover any and all modifications, variations, combinations or equivalents within the scope of the present invention. Obviously, those skilled in the art may make various modifications and variations to the present invention without departing from the spirit and scope of the present invention. Thus, the present invention is intended to include such modifications and variations if they fall within the scope of the claims of the present invention and their equivalents.

Claims

1. A method for preparing a TiN thin film, characterized in that: include: providing a substrate; forming a first photoresist layer on the substrate; Preprocessing the first photoresist layer to obtain a target area on the substrate; The pre-treatment includes exposure and development treatment; A multi-layer TiN film with different metal components is prepared in the target area; the TiN content in the multi-layer TiN film decreases layer by layer from the lower layer to the upper layer, and the TiOxNy and TiO2 contents increase layer by layer from the lower layer to the upper layer.

2. The method according to claim 1, characterized in that The step of preparing a multi-layer TiN film with different metal components in the target area comprises: According to preset preparation process parameters, a multilayer TiN film with different metal components is prepared in the target area; the preset preparation process parameters at least include a preset vacuum degree, a sputtering power of a Ti target material, a flow rate of a sputtering deposition mixed gas, and a preset thickness of the TiN film; wherein the mixed gas includes argon and nitrogen, and the input flow rate of the nitrogen is a dynamic flow rate.

3. The method according to claim 2, characterized in that The step of preparing a multi-layer TiN film with different metal components in the target area comprises: According to the preset vacuum degree, the sputtering power of the Ti target material and the flow rate of the sputtering deposition mixed gas, the mixed gas is sputtered and deposited to form a multi-layer TiN film with different metal components from the lower layer to the upper layer; wherein the input flow rate of the argon gas is a first constant flow rate, and the input flow rate of the nitrogen gas is a second variable flow rate; When the thickness of the multi-layer TiN film with different metal components meets the preset thickness of the TiN film, the sputtering is stopped; The metal layer and the photoresist layer outside the target area are stripped off to obtain the multi-layer TiN film with different metal components.

4. The method according to claim 3, characterized in that The second variable flow rate includes a variable flow rate that is gradually reduced according to a preset time interval based on a preset initial flow rate; The method comprises: forming a multi-layer TiN film having different metal components from a lower layer to an upper layer by sputtering and depositing the mixed gas according to the preset vacuum degree, the sputtering power of the Ti target material and the flow rate of the sputtering deposition mixed gas, including: forming the multi-layer TiN film having a power function greater than or equal to the power function of the Ni metal in contact with the substrate, and having the stability and reliability of the upper TiN film greater than the stability and reliability of the Ni metal.

5. The method according to claim 1, characterized in that The substrate is a planar substrate, and the material of the substrate includes at least any one of gallium arsenide, silicon carbide, aluminum oxide or gallium nitride.

6. A method for preparing a Schottky gate metal, characterized in that: At least a TiN film prepared by a TiN film preparation method according to any one of claims 1 to 5; the method comprising: providing a substrate; forming a second photoresist layer on the substrate; Pre-processing the second photoresist layer to obtain a T-shaped target area on the substrate; In the T-shaped target area, preparing a plurality of TiN films with different metal components on the substrate; Forming a T-shaped gate metal layer on the surface of the multilayer TiN film away from the substrate; The metal layer and the photoresist layer outside the T-shaped target area are stripped off to obtain the Schottky gate metal.

7. The method according to claim 6, characterized in that The second photoresist layer includes multiple layers, and the forming of the second photoresist layer on the substrate includes: forming a first second photoresist layer on the substrate; forming a second second photoresist layer on a surface of the first second photoresist layer away from the substrate; A third second photoresist layer is formed on a surface of the second second photoresist layer which is away from the first second photoresist layer.

8. The method according to claim 7, characterized in that The T-shaped target area includes a first width concave target area and a second width concave target area; The pre-processing of the second photoresist layer to obtain a T-shaped target area on the substrate includes: Using electron beam lithography, the second second photoresist layer and the third second photoresist layer are exposed and developed to obtain a concave target area of ​​the first width located on the first second photoresist layer; The first second photoresist layer is exposed and developed by electron beam lithography to obtain a concave target area of ​​the second width on the substrate; the first width is greater than the second width.

9. The method according to claim 8, characterized in that The step of preparing a multilayer TiN film with different metal components on the substrate in the T-shaped target area comprises: The multi-layer TiN film with different metal components is formed in the second width concave target area by magnetron sputtering titanium nitride; the thickness of the multi-layer TiN film is less than the thickness of the first photoresist layer.

10. The method according to claim 9, characterized in that The forming of a T-shaped gate metal layer on the surface of the multilayer TiN film away from the substrate comprises: The T-shaped gate metal layer is formed on the surface of the multilayer TiN film away from the substrate based on the first width concave target area and the second width concave target area by evaporating metal.

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