Preparation method of porous material

Abstract

The invention provides a preparation method of a porous material, which comprises a deposition step, a pre-protection step and an ultraviolet curing step, and is characterized in that introduction of a pore forming agent is stopped after deposition of a functional film layer is completed, and an oxidizing agent is added to participate in a reaction while a structural precursor is introduced; a more compact and smoother silicon oxide protective layer can be prepared on the functional film layer in the same machine without breaking vacuum, and the silicon oxide protective layer prevents ultraviolet light from excessively treating the upper part of the functional film layer in the ultraviolet curing step. The problem that holes in the porous material layer are not uniformly distributed up and down due to the fact that the upper portion of the functional film layer is excessively cured and the lower portion of the functional film layer is not sufficiently cured is solved, and the K value of the porous material layer can be further reduced. As the silicon oxide protective layer exists on the porous material layer obtained after curing, on one hand, the damage of the next process to the porous material layer can be reduced, and on the other hand, the adhesive force between the porous material layer and the structure above the porous material layer can be improved.

Description

Technical Field

[0001] The invention belongs to the technical field of semiconductors and relates to a method for preparing a porous material. Background Art

[0002] As the size of Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) devices continues to decrease, the equivalent capacitance and resistance of the back-end metal interconnect layer continue to increase. In order to solve the increased resistance-capacitance (RC) delay, the industry continues to develop low-k materials (k value less than 4) as dielectric layer media, among which Black Diamond II (BDII) is widely used as an ultra-low-k thin film material in 40nm, 28nm and other process nodes. The characteristics of BDII materials include low k value (about 2.5), porosity, and SiCOH material.

[0003] The deposition-curing (Dep-Cure) of BDII includes the following processes:

[0004] (1) Using diethoxymethylsilane (DEMS) as a structural precursor and α-terpinene (ATRP) / bicycloheptadiene (BCHD) as a pore-forming agent, the initial ultra-low K film is deposited on the wafer through plasma action. The reaction equation is: DEMS+BCHD / ATRP+O2→SiCOH.

[0005] (2) Treat with ultraviolet light (UV) to break unstable Si-H, CC, CH, Si-C and other chemical bonds, forming voids and pores in the film to reduce the k value of the film. The reaction equation is: SiCOH + ultraviolet light → Si-O + C x H y , where x and y are the atomic components of an element.

[0006] Different wavelengths of ultraviolet light have different energies and effectively target different chemical bonds. The key to preparing BDII lies in the uniformity of the initial ultra-low-k film and the time and intensity of ultraviolet light curing.

[0007] The following problems exist in the UV curing process: when light enters different substances (such as from air into glass), 5%-15% will be reflected. After the low-k material is UV-cured, multiple holes will be generated inside. When the UV light passes through the low-k medium, it is equivalent to returning in different media many times, resulting in huge light loss, causing uneven UV curing at the top and bottom of the low-k medium, or too long UV curing time, and low film hardening efficiency.

[0008] Therefore, how to enhance the UV curing uniformity of BDII materials, improve the uniformity of holes in low-k materials, and reduce the k value has become an important technical problem that needs to be solved urgently by those skilled in the art.

[0009] It should be noted that the above introduction to the technical background is only for the convenience of providing a clear and complete description of the technical solutions of the present application and for the convenience of understanding by those skilled in the art. It cannot be considered that the above technical solutions are well known to those skilled in the art simply because they are described in the background technology section of the present application. Summary of the invention

[0010] In view of the above-mentioned shortcomings of the prior art, an object of the present invention is to provide a method for preparing a porous material, so as to solve the problem of uneven pores in the porous material in the prior art.

[0011] To achieve the above object and other related objects, the present invention provides a method for preparing a porous material, comprising the following steps:

[0012] Deposition step: placing a substrate in a reaction chamber, introducing a structural precursor and a pore-forming agent into the reaction chamber, and depositing a functional film layer on the substrate;

[0013] Pre-protection step: stopping the introduction of the pore-forming agent, while maintaining the introduction of the structural precursor, introducing an oxidant into the reaction chamber, and depositing a silicon oxide protective layer on the functional film layer;

[0014] UV curing step: applying UV light from above the silicon oxide protective layer, allowing the UV light to penetrate the silicon oxide protective layer and enter the functional film layer to destroy unstable chemical bonds in the functional film layer, thereby converting the functional film layer into a porous material layer.

[0015] Optionally, the oxidant includes O3.

[0016] Optionally, in the pre-protection step, the flow rate range of O3 is 3000sccm-5000sccm, and the flow rate range of the structural precursor is 500mg / min-1500mg / min.

[0017] Optionally, the oxidant comprises O2 plasma.

[0018] Optionally, the radio frequency power used to form the O2 plasma is not higher than 1600W, and the flow rate range of the introduced O2 is 450sccm-1000sccm.

[0019] Optionally, in the silicon oxide, the atomic ratio of oxygen to silicon is less than 2.

[0020] Optionally, the thickness of the porous material layer is greater than 2500 angstroms, and the thickness of the silicon oxide protective layer is no more than 300 angstroms; or the thickness of the silicon oxide protective layer is no more than 12% of the thickness of the porous material layer.

[0021] Optionally, the structural precursor includes diethoxymethylsilane, the pore-forming agent includes α-terpinene or bicycloheptadiene, and the porous material layer includes BDII.

[0022] Optionally, in the deposition step, the structural precursor and the pore-forming agent are introduced into the reaction chamber, and O2 is introduced, wherein the flow rate range of the introduced O2 is 150sccm-300sccm, and the RF power range is 800W-900W.

[0023] Optionally, the light transmittance of the silicon oxide protective layer is greater than that of the functional film layer, and the uniformity of the silicon oxide protective layer is higher than that of the porous material layer.

[0024] As described above, in the method for preparing the porous material of the present invention, after the functional film layer is deposited, the introduction of the pore-forming agent is stopped, and an oxidant is added to participate in the reaction while the structural precursor is introduced, so that a denser and smoother silicon oxide protective layer can be formed on the functional film layer without breaking the vacuum in the same machine. The silicon oxide protective layer prevents the ultraviolet light from excessively treating the upper part of the functional film layer in the ultraviolet curing step, improves the problem of uneven distribution of holes in the porous material layer due to excessive curing of the upper part of the functional film layer and insufficient curing of the lower part, and helps to further reduce the K value of the porous material layer. The porous material layer obtained after curing can reduce the damage to the porous material layer by the next process on the one hand, and can improve the adhesion between the porous material layer and the structure above it on the other hand. In addition, since the introduction of the oxidant in the method for preparing the porous material of the present invention does not require breaking the vacuum, it is beneficial to improve production efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Flow chart showing the method for preparing the porous material of the present invention

[0026] Figure 2 It is a schematic diagram showing the structure obtained after a functional film layer is deposited on a substrate in the deposition step of the method for preparing a porous material of the present invention.

[0027] Figure 3 It is a schematic diagram showing the structure obtained after a silicon oxide protective layer is deposited on a functional film layer in the pre-protection step of the method for preparing a porous material of the present invention.

[0028] Figure 4The schematic diagram shows that the ultraviolet curing step of the method for preparing the porous material of the present invention uses an ultraviolet light source to treat the functional film layer with a silicon oxide protective layer on the top to transform the functional film layer into a porous material layer.

[0029] Figure 5 It is a schematic diagram showing the use of an ultraviolet light source to treat a functional film layer without a silicon oxide protective layer on the top so as to transform the functional film layer into a porous material layer.

[0030] Figure 6 Shown is a contour map of the functional film layer obtained using the preparation parameters in Table 1.

[0031] Figure 7 Shown is a contour map of the porous material layer obtained after UV curing of the functional film layer obtained using the preparation parameters in Table 1.

[0032] Figure 8 Shown is a contour map of the functional film layer obtained using the preparation parameters in Table 2.

[0033] Fig. 9 Shown is a contour map of the porous material layer obtained after UV curing of the functional film layer obtained using the preparation parameters in Table 2.

[0034] Component number description

[0035] 101 Base

[0036] 102 Functional film layer

[0037] 103 Silicon oxide protective layer

[0038] 104 UV light source

[0039] 105 porous material layer

[0040] 201 UV light source

[0041] 202 porous material layer

[0042] 203 Base DETAILED DESCRIPTION

[0043] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0044] See also Figures 1 to 9It should be noted that the illustrations provided in this embodiment are only used to illustrate the basic concept of the present invention in a schematic manner, and the drawings only show components related to the present invention rather than being drawn according to the number, shape and size of components in actual implementation. In actual implementation, the type, quantity and proportion of each component may be changed arbitrarily, and the component layout may also be more complicated.

[0045] The present invention provides a method for preparing a porous material. Figure 1 , shown as a flow chart of the preparation method, comprising the following steps:

[0046] Deposition step: placing a substrate in a reaction chamber, introducing a structural precursor and a pore-forming agent into the reaction chamber, and depositing a functional film layer on the substrate;

[0047] Pre-protection step: stopping the introduction of the pore-forming agent, while maintaining the introduction of the structural precursor, introducing an oxidant into the reaction chamber, and depositing a silicon oxide protective layer on the functional film layer;

[0048] UV curing step: applying UV light from above the silicon oxide protective layer, allowing the UV light to penetrate the silicon oxide protective layer and enter the functional film layer to destroy unstable chemical bonds in the functional film layer, thereby converting the functional film layer into a porous material layer.

[0049] Specifically, the substrate includes a doped silicon carbide (NDC) layer or other suitable material layer, and transistors or other required components may be pre-formed in the substrate. The substrate may be in the form of a wafer.

[0050] As an example, see Figure 2 , which is a schematic diagram showing a structure obtained after a functional film layer 102 is deposited on a substrate 101 in the deposition step.

[0051] In some embodiments, the porous material to be formed includes a BDII layer, i.e., a type II black diamond (Black DiamondII) layer, which is a SiCOH material with the characteristics of porosity and ultra-low k value, and can be used as a dielectric material for the back-end metal interconnect layer of semiconductor devices such as MOSFET.

[0052] As an example, for the BDII layer, in the deposition step, the structural precursor introduced into the reaction chamber includes diethoxymethylsilane (DEMS), and its chemical formula is:

[0053]

[0054] The pore-forming agent introduced into the reaction cavity includes α-terpinene (ATRP) or bicycloheptadiene (BCHD).

[0055] Through the action of O2 plasma, the functional film layer 102 is deposited on the substrate 101, and the reaction equation is: DEMS + BCHD / ATRP + O2 → SiCOH. The functional film layer 102 will be transformed into the final porous material layer in the subsequent process.

[0056] As an example, in the deposition step, the flow rate range of O2 introduced is 150 sccm - 300 sccm, and the radio frequency power range is 800 W - 900 W. In one embodiment, the O2 flow rate is selected as 220 sccm, the radio frequency power used to form O2 plasma is set to 850 W, and the fluctuation range of the radio frequency power is controlled not to exceed 5%.

[0057] As an example, please refer to Figure 3 which shows a schematic diagram of the structure obtained after depositing the silicon oxide protective layer 103 on the functional film layer 102 in the pre-protection step.

[0058] Specifically, the silicon oxide protective layer 103 is obtained by the reaction of the continuously introduced structure precursor with the newly introduced oxidant. The introduction of the oxidant is achieved without breaking the vacuum in the same machine, which is beneficial to improving production efficiency.

[0059] As an example, the flow rate of the structure precursor introduced in the pre-protection step is less than the flow rate of the structure precursor introduced in the deposition step.

[0060] In some embodiments, the oxidant includes O3, and its reaction equation with the structure precursor diethoxymethylsilane (DEMS) is: DEMS + O3 → SiO 2-x +C x H y , where 0 < x < 2, both x and y are greater than 0, x is the atomic component of C, and y is the atomic component of H. That is to say, in the silicon oxide, the atomic ratio of oxygen to silicon is less than 2.

[0061] As an example, in the pre-protection step, the flow rate range of O3 introduced is 3000 sccm - 5000 sccm, and the flow rate range of the structure precursor introduced is 500 milligrams per minute - 1500 milligrams per minute.

[0062] It should be noted that when the oxidant is selected as O3, in the pre-protection step, while stopping the introduction of the pore-forming agent, the introduction of O2 is also stopped, that is, the generation of O2 plasma is stopped.

[0063] In other embodiments, the oxidant may also include O2 plasma, which can play a similar role as O3.

[0064] Specifically, in the pre-protection step, if O2 plasma is used as an oxidant, then relative to the O2 introduced in the deposition step, the O2 introduced in the pre-protection step as the main reactant needs to increase the corresponding flow rate.

[0065] As an example, in the pre-protection step, the RF power used to form the O2 plasma is not higher than 1600W, and the flow rate of the introduced O2 is in the range of 450sccm-1000sccm. In a preferred embodiment, the RF power used to form the O2 plasma is in the range of 800W-1200W.

[0066] Specifically, compared with the functional film layer 102 , the silicon oxide protection layer 103 is denser, has a smoother film layer, and has higher light transmittance.

[0067] As an example, see Figure 4 , which is a schematic diagram showing that in the UV curing step, the functional film layer 102 having the silicon oxide protective layer 103 on the top is treated with an ultraviolet light source 104 to transform the functional film layer 102 into a porous material layer 105.

[0068] Specifically, the ultraviolet light source 104 is placed above the silicon oxide protection layer 103 , that is, the ultraviolet light is applied from above the silicon oxide protection layer 103 .

[0069] Specifically, the ultraviolet light penetrates the silicon oxide protective layer 103 and enters the functional film layer 102 , and generates a plurality of voids inside the functional film layer 102 by destroying unstable chemical bonds in the functional film layer 102 , so that the functional film layer 102 is transformed into a porous material layer 105 .

[0070] As an example, Figure 4 Arrows are used as an example to show the direction of light transmission.

[0071] For comparison, see Figure 5 , which is a schematic diagram showing a process of using an ultraviolet light source 201 to treat a functional film layer without a silicon oxide protective layer on the top so as to transform the functional film layer into a porous material layer 202, wherein the porous material layer 202 is located on a substrate 203. Figure 5In the scheme shown, since there is no silicon oxide protective layer on the top of the functional film layer, when the light is transmitted downward, there is a problem that the upper and lower parts of the functional film layer are not uniformly cured due to excessive light loss, that is, the upper part of the functional film layer is over-cured and the lower part is under-cured, and the porous material layer 202 finally obtained has more holes in the upper part and fewer holes in the lower part. At the same time, since it is difficult for ultraviolet light to reach the bottom of the functional film layer, there is a problem that the ultraviolet curing time is too long and the film hardening efficiency is low.

[0072] See also Figure 4 In the technical solution of the present invention, since the functional film layer 102 has the silicon oxide protective layer 103 in the UV curing step, the light transmittance of the silicon oxide protective layer 103 is higher than that of the functional film layer 102, and the uniformity is higher than that of the porous material layer 105 after UV curing, which is more conducive to the transmission of ultraviolet light and increases the uniform transmission of ultraviolet light. It can improve the problem that the upper part of the functional film layer 102 is over-cured and the lower part is under-cured, so that the upper and lower distribution of holes in the obtained porous material layer 105 is more uniform, which helps to further reduce the K value of the obtained porous material layer. In addition, the porous material layer 105 obtained after curing can reduce the damage to the porous material layer 105 by the next process because of the presence of the silicon oxide protective layer 103 on it, and can improve the adhesion between the porous material layer 103 and the structure above it.

[0073] As an example, the dielectric constant of the porous material layer 105 is less than 4. When the porous material layer 105 is a BDII layer, the dielectric constant thereof is about 2.5.

[0074] As an example, the thickness of the porous material layer 105 is greater than 2500 angstroms, and the thickness of the silicon oxide protection layer 103 is no more than 300 angstroms; or the thickness of the silicon oxide protection layer 103 is no more than 12% of the thickness of the porous material layer 105 .

[0075] As an example, see Table 1 and Table 2, where Table 1 is Figure 5 Table 2 shows an example of preparation parameters of the BDII porous material layer in the corresponding scheme. Figure 4 An exemplary preparation parameter of the BDII porous material layer in the corresponding scheme.

[0076] Table 1: Figure 5 Preparation parameters of BDII porous material layer in the corresponding scheme

[0077]

[0078]

[0079] Table 2: Figure 4 Preparation parameters of BDII porous material layer in the corresponding scheme

[0080]

[0081] As an example, see Figures 6 to 9 ,in, Figure 6 The contour map of the functional film layer obtained by using the preparation parameters in Table 1 is shown (the average value is 1540, and the sigma% is 2.15%). Figure 7 The contour map of the porous material layer obtained after UV curing of the functional film layer prepared using the parameters in Table 1 is shown (the average value is 1236, and the sigma% is 3.18%). Figure 8 The contour map of the functional film layer obtained by using the preparation parameters in Table 2 is shown (the average value is 1510, and the sigma% is 2.22%). Fig. 9 The contour map of the porous material layer obtained after UV curing of the functional film layer prepared by the parameters in Table 2 is shown (average value is 1219, sigma% is 2.69%). It can be seen that the presence of the silicon oxide protective layer 103 can improve the pore uniformity of the porous material layer. In addition, the electrical test data (not shown) also shows that when the dielectric layer of the back-end metal interconnection layer adopts the porous material layer prepared by the present invention (lower k value), the RC delay problem can be improved.

[0082] In summary, the preparation method of the porous material of the present invention stops the introduction of the pore-forming agent after the functional film layer is deposited, and at the same time, an oxidant is added to participate in the reaction while the structural precursor is introduced, so that a denser and smoother silicon oxide protective layer can be formed on the functional film layer without breaking the vacuum in the same machine. The silicon oxide protective layer avoids excessive treatment of the upper part of the functional film layer by ultraviolet light in the ultraviolet curing step, improves the problem of uneven distribution of holes in the porous material layer due to excessive curing of the upper part of the functional film layer and insufficient curing of the lower part, and helps to further reduce the K value of the porous material layer. The porous material layer obtained after curing can reduce the damage to the porous material layer by the next process on the one hand, and can improve the adhesion between the porous material layer and the structure above it on the other hand. In addition, since the introduction of the oxidant in the preparation method of the porous material of the present invention does not require breaking the vacuum, it is beneficial to improve production efficiency. Therefore, the present invention effectively overcomes various shortcomings in the prior art and has a high industrial utilization value.

[0083] The above embodiments are merely illustrative of the principles and effects of the present invention, and are not intended to limit the present invention. Anyone familiar with the art may 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 a person of ordinary skill in the art without departing from the spirit and technical concept disclosed by the present invention shall still be covered by the claims of the present invention.

Claims

1. A method for preparing a porous material, characterized in that: The following steps are involved: Deposition step: placing a substrate in a reaction chamber, introducing a structural precursor and a pore-forming agent into the reaction chamber, and depositing a functional film layer on the substrate; Pre-protection step: stopping the introduction of the pore-forming agent, while maintaining the introduction of the structural precursor, introducing an oxidant into the reaction chamber, and depositing a silicon oxide protective layer on the functional film layer; UV curing step: applying UV light from above the silicon oxide protective layer, so that the UV light penetrates the silicon oxide protective layer and enters the functional film layer to destroy unstable chemical bonds in the functional film layer, thereby converting the functional film layer into a porous material layer.

2. The method for preparing a porous material according to claim 1, characterized in that: The oxidant includes O3.

3. The method for preparing a porous material according to claim 2, characterized in that: In the pre-protection step, the flow rate of O3 is in the range of 3000sccm-5000sccm, and the flow rate of the structural precursor is in the range of 500mg / min-1500mg / min.

4. The method for preparing a porous material according to claim 1, characterized in that: The oxidant includes O2 plasma.

5. The method for preparing a porous material according to claim 4, characterized in that: The radio frequency power used when forming the O2 plasma is no higher than 1600W, and the flow rate range of the introduced O2 is 450sccm-1000sccm.

6. The method for preparing a porous material according to claim 1, characterized in that: In the silicon oxide, an atomic ratio of oxygen to silicon is less than 2.

7. The method for preparing a porous material according to claim 1, characterized in that: The thickness of the porous material layer is greater than 2500 angstroms, and the thickness of the silicon oxide protective layer is no more than 300 angstroms; or the thickness of the silicon oxide protective layer is no more than 12% of the thickness of the porous material layer.

8. The method for preparing a porous material according to claim 1, characterized in that: The structural precursor includes diethoxymethylsilane, the pore-forming agent includes α-terpinene or bicycloheptadiene, and the porous material layer includes BDII.

9. The method for preparing a porous material according to claim 8, characterized in that: In the deposition step, the structural precursor and the pore-forming agent are introduced into the reaction chamber, and O2 is introduced, wherein the flow rate range of the introduced O2 is 150sccm-300sccm, and the RF power range is 800W-900W.

10. The method for preparing a porous material according to claim 1, characterized in that: The light transmittance of the silicon oxide protective layer is greater than that of the functional film layer, and the uniformity of the silicon oxide protective layer is higher than that of the porous material layer.

Images