Semiconductor device and method for manufacturing the same

Abstract

A semiconductor device comprises a first substrate (11), a second substrate (12), an oxide film (13), and a protective film (14). The first substrate comprises a first surface (11c). The second substrate comprises a second surface (12b) a portion of which is bonded to a portion of the first surface by atmospheric pressure plasma activation. The oxide film is formed on the first surface. The protective film is laminated on the surface of the oxide film on the side opposite to the first substrate. The method for manufacturing a semiconductor device comprises the following steps: after forming the protective film, subjecting the first surface to plasma activation treatment in the atmosphere.

Description

[0001] Cross-reference of related applications

[0002] This application is based on Japanese Application No. 2017-116207 filed on June 13, 2017, the contents of which are incorporated herein by reference. Technical Field

[0003] The present invention relates to a semiconductor device formed by plasma bonding and a method for manufacturing the same. Background Art

[0004] As disclosed in Patent Document 1, a method for bonding two silicon wafers to form a semiconductor device is known. During the bonding process, the wafers are brought into contact with each other and then subjected to a heat treatment to complete the bonding. However, the heating temperature required is approximately 1200°C, which can cause unnecessary thermal diffusion of impurity ions that form additional impurity regions. In particular, if outdiffusion occurs, where ions diffuse into spaces outside the wafers, impurities can accumulate again on the wafer surface, potentially leading to undesirable electrical characteristics.

[0005] Therefore, a method based on the activity of atmospheric pressure plasma can be considered. If atmospheric pressure plasma is irradiated on the surface of the silicon wafer to be bonded, the OH groups on the surface will be activated, which can increase the bonding strength. However, this case also requires heat treatment during bonding, which can cause outward diffusion. Therefore, a method is adopted to physically suppress the diffusion of impurities to the outside by forming an oxide film on the surface of the wafer where the wiring and impurity regions are formed.

[0006] Prior art literature

[0007] Patent Literature

[0008] Patent Document 1: Japanese Patent Application Laid-Open No. 2010-263160

[0009] In addition, regarding the oxide film used to suppress the outward diffusion phenomenon, based on reasons such as reducing the number of manufacturing steps, for example, by not removing the oxide film formed as a mask during ion implantation, leaving it remaining, or by utilizing a new film formed after ion implantation to achieve insulation relative to the wiring, the film thickness is mostly 10nm to 1000nm.

[0010] The inventors have discovered that when atmospheric pressure plasma treatment is performed with an oxide film of such a thickness remaining, the oxide film becomes charged, and the oxide film and the underlying silicon wafer are scratched by the shock of the discharge. Summary of the Invention

[0011] An object of the present invention is to provide a semiconductor device and a method for manufacturing the same, in which the occurrence of scratches on an oxide film and a base can be suppressed in a semiconductor device utilizing plasma bonding.

[0012] According to a first aspect of the present invention, a semiconductor device includes a first substrate, a second substrate, an oxide film, and a protective film. The first substrate has a first surface. The second substrate has a second surface, a portion of which is bonded to a portion of the first surface by atmospheric pressure plasma activation. The oxide film is formed on the first surface. The protective film is laminated on the surface of the oxide film opposite the first substrate.

[0013] According to a second aspect of the present invention, a method for manufacturing a semiconductor device comprising a first substrate having a first surface and a second substrate having a second surface, a portion of which is bonded to a portion of the first surface by atmospheric pressure plasma activation, comprises the following steps: preparing the first substrate; forming an oxide film on the first surface; forming an impurity region on the first substrate; after forming the oxide film and the impurity region, forming a protective film on the surface of the oxide film opposite to the first substrate; after forming the protective film, subjecting the first surface to plasma activation treatment in the atmosphere; after the plasma activation treatment, laminating the first surface of the first substrate to the second surface of the second substrate; and after laminating the first and second surfaces, heat treating the first and second substrates to bond the first and second surfaces.

[0014] By stacking the protective film in addition to the oxide film, the overall thickness of the film stacked on the first surface can be increased. A thicker film improves dielectric strength, making it less likely to generate discharge that could cause dielectric breakdown during atmospheric pressure plasma surface treatment. This also reduces the formation of scratches in the oxide film and the substrate. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] The above objects and other objects, features and advantages of the present invention are Figure 1 This will become clearer through the detailed description below.

[0016] Figure 1 It is a cross-sectional view showing the structure of the semiconductor device according to the first embodiment.

[0017] Figure 2 It is a cross-sectional view showing the preparation step of the first substrate and the formation step of the impurity region.

[0018] Figure 3 It is a cross-sectional view showing the step of forming an oxide film.

[0019] Figure 4 It is a cross-sectional view showing the process of forming a protective film.

[0020] Figure 5It is a cross-sectional view showing the activation process using atmospheric pressure plasma.

[0021] Figure 6 It is a cross-sectional view showing the step of bonding the first substrate and the second substrate.

[0022] Figure 7 This is a cross-sectional view showing part of the membrane forming process.

[0023] Figure 8 It is a cross-sectional view showing the structure of a semiconductor device according to a second embodiment. DETAILED DESCRIPTION

[0024] Hereinafter, various embodiments for implementing the present invention will be described with reference to the accompanying drawings. In each embodiment, portions corresponding to matters described in a previous embodiment may be assigned the same reference numerals, and repeated descriptions may be omitted. In each embodiment, when only a portion of a structure is described, other previously described embodiments may be applied to the remaining portions of the structure. In each embodiment, not only are specific combinations of parts that can be combined explicitly indicated, but also, as long as there is no particular obstacle to the combination, the various embodiments may be partially combined even without explicit indication.

[0025] (First embodiment)

[0026] First, refer to Figure 1 , describing the schematic structure of the semiconductor device of this embodiment.

[0027] This semiconductor device is, for example, a diaphragm-type pressure sensor. A diaphragm-type pressure sensor has multiple resistor elements formed as a bridge circuit on a diaphragm formed on a semiconductor substrate. As the diaphragm deforms in response to pressure changes, the resistance of the resistor elements changes, which in turn causes changes in the output of the bridge circuit. This allows pressure detection.

[0028] This type of pressure sensor has a chamber for maintaining a reference pressure. The chamber is formed by bonding two semiconductor substrates together. The semiconductor substrates are bonded together using plasma bonding, particularly plasma bonding using atmospheric pressure plasma.

[0029] like Figure 1 As shown, the semiconductor device 100 includes a first substrate 11 , a second substrate 12 , an oxide film 13 , and a protective film 14 .

[0030] The first substrate 11 is a semiconductor substrate mainly composed of silicon. The first substrate 11 is formed as a flat plate having a main surface 11c and a back surface 11d. The first substrate 11 has a recess 11a excavated from the back surface 11d by etching or other methods, and the thickness from the bottom surface to the main surface 11c is thinner than the area outside the area where the recess 11a is formed. This thinner portion is the diaphragm 11b. An impurity region not shown is formed on the diaphragm 11b by ion implantation, and wiring is formed. In addition, the impurity region constitutes a resistor element, a diode, etc., and the wiring contributes to the electrical connection with the bridge circuit and other external elements. In other words, the first substrate 11 has an impurity region formed on the main surface 11c side, and a sensor element constituting a part of the pressure sensor is formed. The main surface 11c is equivalent to the first surface.

[0031] The second substrate 12 is a semiconductor substrate primarily composed of silicon. The second substrate 12 is formed as a flat plate having a main surface 12b. A recess 12a, excavated by etching or other methods, is formed on the main surface 12b of the second substrate 12. The recess 12a is sized to completely cover the diaphragm 11b formed on the first substrate 11. Furthermore, the depth of the recess 12a is sufficient to accommodate the oxide film 13 and protective film 14, described later. The main surface 12b of the second substrate 12 corresponds to the second surface.

[0032] The first and second substrates 11 and 12 are bonded so that their respective principal surfaces 11c and 12b face each other. When the principal surfaces 11c and 12b are viewed from the front, the second substrate 12 is positioned so that the recess 12a formed on the principal surface 12b entirely covers the diaphragm 11b. In other words, when the first and second substrates 12 are bonded, a space is formed on the opposite side of the recess 11a, across the diaphragm 11b. This space is isolated from the outside and functions as a chamber for maintaining a reference pressure.

[0033] The principal surface 11c (first surface) of the first substrate 11 and the principal surface 12b (second surface) of the second substrate 12 are plasma-bonded. In particular, in this embodiment, the principal surface 11c is activated using atmospheric pressure plasma before bonding. Consequently, the OH groups on the principal surface 11c before bonding are activated, resulting in a stronger bond strength after bonding than, for example, vacuum plasma treatment.

[0034] Oxide film 13 is a silicon oxide film formed on diaphragm 11b on primary surface 11c. Oxide film 13 is laminated to cover the impurity region formed in diaphragm 11b. Oxide film 13 prevents impurity ions forming the impurity region from escaping from first substrate 11 when first substrate 11 is heated.

[0035] The oxide film 13 is the portion remaining after the oxide film formed for masking or insulation in the steps related to ion implantation and wiring formation is not removed. Typically, the thickness of such an oxide film is 10 nm to 1000 nm, and in this embodiment, it is, for example, 100 nm.

[0036] The protective film 14 is a film stacked on the oxide film 13 and is formed as an insulating film in this embodiment. Specifically, the protective film 14 is mainly composed of silicon nitride. The protective film 14 is formed to cover the entire surface of the oxide film 13 opposite to the surface in contact with the diaphragm 11b. The film thickness is, for example, 50 nm.

[0037] The entire membrane 11b is covered by the chamber, so that the oxide film 13 and the protective film 14 are necessarily contained within the chamber. The recess 12a formed in the second substrate 12 has a depth sufficient to accommodate the oxide film 13 and the protective film 14, with a gap between its bottom and the protective film 14.

[0038] Next, refer to Figures 2 to 7 , a method for manufacturing the semiconductor device 100 of this embodiment is described.

[0039] First, if Figure 2 As shown, the first substrate 11 is prepared, and an oxide film 200 is formed on the main surface 11c of the first substrate 11. The oxide film 200 is formed by a common method such as thermal oxidation or CVD. After the oxide film 200 is formed on the entire main surface 11c, a mask resist is formed and etched. By removing the mask resist, the Figure 2 The patterned oxide film 200 as shown is formed.

[0040] Next, ion implantation is performed from the main surface 11c side of the first substrate. This creates an impurity region on the surface of the main surface 11c, forming resistors and diodes. Wiring and pads are also formed. The unnecessary oxide film 200 is then removed.

[0041] Then, if Figure 3 As shown, an oxide film 13 is formed. The oxide film 13 is formed in the same process as the process for forming an insulating film for the purpose of insulating wiring, etc. Alternatively, the oxide film 13 may be formed in a separate process from the process for forming the insulating film for the purpose of insulating wiring, etc.

[0042] The oxide film 13 is formed to cover the element formation region of the resistor element or diode formed by forming the impurity region. This oxide film 13 functions as a film against outdiffusion, preventing ions from escaping from the impurity region during subsequent heating steps.

[0043] Since the oxide film 13 in this embodiment is formed simultaneously with the insulating film for insulating wiring, etc., its thickness is also set to sufficiently achieve insulation for the wiring, etc. For example, it is set to approximately 100 nm. The film thickness varies depending on the formation conditions of other semiconductor elements formed on the surface of the main surface 11c, ranging from approximately 10 nm to approximately 1000 nm.

[0044] Then, if Figure 4 As shown, a protective film 14 is formed. As described above, the protective film 14 in this embodiment is mainly composed of silicon nitride and is laminated on the oxide film 13 by CVD. As CVD, plasma induced CVD (PECVD), low-pressure chemical vapor deposition (LPCVD), etc. can be used. Alternatively, lamination can be performed by sputtering. The thickness of the protective film 14 in this embodiment is, for example, approximately 50 nm.

[0045] Next, plasma activation treatment is performed. The first substrate 11 on which the oxide film 13 and the protective film 14 are laminated is placed in the atmosphere. Figure 5 As shown, atmospheric pressure plasma is irradiated onto the main surface 11c ( Figure 5 The atmospheric pressure plasma is irradiated in such a manner as to activate at least the bonding surface with the second substrate 12. By irradiating the atmospheric pressure plasma, the hydroxyl groups (OH groups) are activated on the main surface 11c.

[0046] Then, if Figure 6 As shown in FIG. 1 , the second substrate 12 is prepared and bonded to the first substrate. The second substrate 12 has a recess 12a dug in advance on the main surface 12b side. The recess 12a can be formed by etching, for example.

[0047] To bond the second substrate 12 to the first substrate 11, the main surface 12b of the second substrate 12 is positioned opposite the main surface 11c of the first substrate 11, bringing them into contact. The first and second substrates 11 and 12 are then heated to approximately 200°C to 800°C. This secures the two main surfaces 11c and 12b to each other. The main surface 11c of the first substrate 11 is treated with atmospheric pressure plasma to activate OH groups, resulting in a stronger bond than plasma bonding under vacuum.

[0048] Then, if Figure 7 As shown in FIG. 1 , a patterned oxide film 300 is formed on the back surface 11d of the first substrate 11 except for the region where the recess 11a is dug. Then, the recess 11a is formed by etching, and further, as shown in FIG. Figure 1 The membrane 11b is formed as shown.

[0049] Through the above-described steps, the semiconductor device 100 serving as a pressure sensor can be manufactured.

[0050] Next, the effects of the semiconductor device 100 and the method for manufacturing the same according to this embodiment will be described.

[0051] Semiconductor device 100 includes an oxide film 13 on main surface 11c, which forms a circuit including an impurity region. Therefore, for example, during the heating process associated with bonding first substrate 11 and second substrate 12, ions and other components that form the impurity region can be prevented from escaping from main surface 11c. In other words, outdiffusion can be suppressed.

[0052] Since semiconductor device 100 includes protective film 14 in addition to oxide film 13, the overall thickness of the film stacked on the first surface (main surface 11c) can be increased. This increased film thickness improves dielectric strength, making it less likely to generate discharge that could cause dielectric breakdown during atmospheric pressure plasma surface treatment. This also reduces the formation of flaws in oxide film 13 and the substrate.

[0053] Regarding the thickness of the protective film 14, the combined thickness of the protective film 14 and the oxide film 13 is preferably set to a level that provides a dielectric breakdown voltage exceeding the charge of the first substrate 11, and is stacked to a thickness of approximately 10 nm to 100 nm. In contrast, the protective film 14 in this embodiment is a film primarily composed of silicon nitride, which produces an electric field relaxation effect due to the ONO structure between the protective film 14 and the oxide film 13, which is a silicon oxide film. This allows for further thinning of the protective film 14. Experiments by the inventors have confirmed that, for example, even with a film thickness of 4 nm to 10 nm, the formation of scratches caused by atmospheric pressure plasma can be suppressed.

[0054] Specifically, by using a silicon nitride film as protective film 14, the thickness of protective film 14 can be reduced, thereby suppressing deformation of diaphragm 11b caused by, for example, a difference in linear expansion coefficient between oxide film 13 and protective film 14. This can also suppress a decrease in pressure detection sensitivity caused by the formation of protective film 14.

[0055] (Variation)

[0056] In the above embodiment, an example of using silicon nitride as the insulating film for the protective film 14 is shown. However, the total film thickness of the protective film 14 and the oxide film 13 is not limited to silicon nitride as long as the total film thickness can be formed to a degree that provides a dielectric breakdown voltage exceeding the charge of the first substrate 11. In other words, the protective film 14 can also be formed using thermally oxidized SiO2, BPSG film, TEOS film, SiO2 by CVD, and the like.

[0057] Furthermore, the protective film 14 is not limited to an insulating film and may also be a conductive film. For example, polysilicon or a metal may be used as the protective film 14. Examples of metal films include aluminum, titanium, titanium nitride, copper, and tungsten. Polysilicon is particularly preferred because it can be easily laminated onto the oxide film 13 by CVD or the like.

[0058] If a conductive film is used as protective film 14, charge exchange between oxide film 13 and protective film 14 and the plasma flow can proceed smoothly during atmospheric pressure plasma activation, thereby suppressing the charge levels of oxide film 13 and protective film 14. Charge exchange with the plasma flow is governed by the effect of protective film 14 as a conductive film, so the aforementioned effect can be achieved if at least a conductive film is present on oxide film 13. In this case, protective film 14 can have a thickness of approximately 1 to 10 nm.

[0059] (Second embodiment)

[0060] In the first embodiment and its modified examples, the protective film 14 is described as a single-layer film composed mainly of one component. In contrast, the semiconductor device 110 of this embodiment is as follows. Figure 8 As shown in FIG. 1 , the protective film 14 has a structure including a first layer 14 a and a second layer 14 b . Except for the structure of the protective film 14 , the other structures are the same as those of the semiconductor device 100 described in the first embodiment.

[0061] The first layer 14a of the protective film 14 is a silicon nitride film, similar to the protective film 14 in the first embodiment. Furthermore, the second layer 14b is a silicon oxide film. Thus, when the protective film 14 has a multilayer structure, the silicon nitride film of the first layer 14a improves insulation resistance due to the electric field relaxation effect, and the second layer 14b can also suppress the influence of deformation on the diaphragm 11b.

[0062] Specifically, since the first layer 14a is primarily composed of silicon nitride, it generally acts as a tensile stress on the silicon substrate in response to heat application. Therefore, compared to conventional structures without the protective film 14, this acts to suppress deformation of the diaphragm 11b. In contrast, the silicon oxide film of the second layer 14b acts as a compressive stress on the silicon substrate. In other words, the second layer 14b acts to offset the tensile stress of the first layer 14a, thereby suppressing the effects of deformation on the diaphragm 11b.

[0063] In addition, in this embodiment, as the multi-layer protective film 14, an example is described in which a silicon nitride film is used for the first layer 14a and a silicon oxide film is used for the second layer 14b. However, the combination of the first layer 14a and the second layer 14b is arbitrary without distinction between an insulating film and a conductive film. For example, a TEOS film may be used for the first layer 14a and an aluminum film may be used for the second layer 14b.

[0064] However, in order to achieve an electric field relaxation effect with the oxide film 13, it is preferable to use a silicon nitride film for the first layer 14a, and in order to smoothly exchange charges with the plasma flow, it is preferable to use a conductive film for the second layer 14b directly exposed to the plasma flow.

[0065] Furthermore, the protective film 14 is not limited to a two-layer structure and may also be a multilayer structure of three or more layers. Furthermore, each layer may be formed using a film forming method appropriate to the constituent components of each layer. For example, the silicon nitride film serving as the first layer 14a may be formed by CVD, while the silicon oxide film serving as the second layer 14b may be formed by sputtering.

[0066] (Other embodiments)

[0067] In the above-mentioned embodiments, the semiconductor devices 100 and 110 are described by taking the pressure sensor as an example. However, as long as the first substrate 11 having the oxide film 13 as a film for outward diffusion and the second substrate 12 that is separate from the first substrate 11 are joined by atmospheric pressure plasma, the effect of the protective film 14 can be achieved, and the scope of application is not limited to pressure sensors.

[0068] The present invention is described based on embodiments, but it should be understood that the present invention is not limited to these embodiments and configurations. The present invention also includes various modifications and variations within the scope of the invention. In addition, the present invention shows various combinations and configurations, but other combinations and configurations including only one element, more than one element, or less than one element also fall within the scope and spirit of the present invention.

Claims

1. A semiconductor device, characterized in that: have: A first substrate (11) having a first surface (11c); A second substrate (12) having a second surface (12b) a portion of which is bonded to a portion of the first surface by atmospheric pressure plasma activity; an oxide film (13) formed on the first surface; and a protective film (14) laminated on the surface of the oxide film opposite to the first substrate; The total film thickness of the oxide film and the protective film is such that the dielectric strength voltage exceeds the charge amount of the first substrate.

2. The semiconductor device according to claim 1, wherein The protective film is an insulating film.

3. The semiconductor device according to claim 2, wherein The protective film includes a silicon nitride film.

4. The semiconductor device according to claim 3, wherein The protective film is a multilayer film in which a silicon oxide film and a silicon nitride film are stacked.

5. The semiconductor device according to claim 1, wherein The protective film is a conductive film.

6. The semiconductor device according to claim 5, wherein The protective film is a polysilicon film.

7. A method for manufacturing a semiconductor device comprising a first substrate (11) having a first surface (11c), and a second substrate (12) having a second surface (12b) a portion of which is bonded to a portion of the first surface by atmospheric pressure plasma activity, The method for manufacturing a semiconductor device is characterized by comprising the following steps: preparing the first substrate; forming an oxide film (13) on the first surface; forming an impurity region on the first substrate; After forming the oxide film and the impurity region, forming a protective film (14) on the surface of the oxide film opposite to the first substrate; After forming the protective film, performing plasma activation treatment on the first surface in the atmosphere; After the plasma activation treatment, laminating the first surface of the first substrate to the second surface of the second substrate; After laminating the first surface and the second surface, heat treating the first substrate and the second substrate to bond the first surface and the second surface; The total film thickness of the oxide film and the protective film is such that the dielectric strength voltage exceeds the charge amount of the first substrate.

8. The method for manufacturing a semiconductor device according to claim 7, wherein: The protective film is an insulating film.

9. The method for manufacturing a semiconductor device according to claim 8, wherein: The protective film includes a silicon nitride film.

10. The method for manufacturing a semiconductor device according to claim 9, wherein: The protective film is a multilayer film in which a silicon oxide film and a silicon nitride film are stacked.

11. The method for manufacturing a semiconductor device according to claim 7, wherein: The protective film is a conductive film.

12. The method for manufacturing a semiconductor device according to claim 11, wherein: The protective film is a polysilicon film.

Images