Semiconductor structure and preparation method thereof
By forming a pretreatment layer and a growth buffer layer on the Si substrate, the difficulty of growing a high-quality AlN buffer layer on the Si substrate is solved, and the rapid growth of the high-quality buffer layer is achieved at a lower temperature, and the crystal quality and surface flatness of the epitaxial layer are improved.
Patent Information
- Application Number
- CN202311183251.3
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2023-09-13
- Publication Date
- 2025-03-14
AI Technical Summary
There is difficulty in growing high-quality AlN buffer layers on Si substrates. In the prior art, the MOCVD process requires high temperatures but the Si substrate cannot bear it, while the PVD process grows fast but the crystal orientation is difficult to control.
By forming a pretreatment layer on the surface of the Si substrate, including several nucleation points, the first buffer layer is grown using a physical vapor deposition process, and when necessary, a second buffer layer is formed by a MOCVD process to improve crystal quality and surface flatness.
The rapid growth of high-quality AlN buffer layer at relatively low temperatures is achieved, which solves the problems of crystal orientation control and high temperature stability, and improves the crystal quality and surface flatness of the epitaxial layer.
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Abstract
Description
Technical Field
[0001] The present invention relates to the field of semiconductor technology, and in particular to a semiconductor structure and a preparation method thereof. Background Art
[0002] At present, gallium nitride (GaN)-based epitaxial wafers are mostly manufactured on sapphire substrates, but the application of sapphire materials is limited due to their high hardness, poor electrical conductivity and thermal conductivity. Si (silicon) substrates are gaining more and more attention in the semiconductor industry due to their advantages such as low price, good thermal conductivity and compatibility with traditional silicon processes.
[0003] However, when using Si substrate as a base for epitaxial structure growth, due to the large lattice mismatch between Si substrate and GaN, and the reaction between Si substrate and Ga, an aluminum nitride (AlN) buffer layer needs to be introduced. The crystal quality of the AlN buffer layer plays a crucial role in the quality of the epitaxial growth later. At present, most of the existing epitaxial processes use MOCVD (metal organic chemical vapor deposition) and PVD (physical vapor deposition). When using MOCVD to grow AlN on Si substrate, not only is the growth rate slow, but also it is difficult to grow AlN with high crystal quality due to the restriction that the growth temperature cannot be too high, thus affecting the crystal quality of subsequent epitaxy. PVD plating of AlN has achieved great success on sapphire substrates, and high-quality epitaxy can be obtained on sapphire substrates. However, due to problems such as crystal orientation on Si substrates, the PVD plating of AlN method cannot obtain high-quality epitaxial structures.
[0004] Therefore, there is an urgent need in the art for a method for epitaxially growing high-quality AlN on a Si substrate. Summary of the invention
[0005] The object of the present invention is to provide a semiconductor structure and a method for preparing the same, so as to improve the crystal quality and surface flatness of an epitaxial layer grown on a silicon-containing substrate.
[0006] In order to achieve the above object, the present invention first provides a method for preparing a semiconductor structure, comprising:
[0007] providing a silicon-containing substrate;
[0008] Passing a pretreatment gas to induce formation of a pretreatment layer on the surface of the silicon-containing substrate, wherein the pretreatment layer includes a plurality of nucleation points;
[0009] A physical vapor deposition process is adopted to grow a first buffer layer on the surface of the silicon-containing substrate along the plurality of nucleation points.
[0010] Optionally, the silicon-containing substrate is a silicon substrate or a silicon carbide substrate.
[0011] Optionally, when the silicon-containing substrate is a silicon substrate, the surface of the silicon substrate is easily oxidized to form a silicon oxide layer; before forming the nucleation point, the silicon substrate is also cleaned; the cleaning method includes: placing the silicon substrate in a reaction chamber of an organic metal chemical vapor deposition device for cleaning to remove the silicon oxide layer.
[0012] Optionally, the cleaning process includes: the cleaning gas includes H2, the cleaning temperature is: 800°C to 1200°C; and the cleaning time is 1 minute to 30 minutes.
[0013] Optionally, the pretreatment layer is formed by metal organic chemical vapor deposition.
[0014] Optionally, the pretreatment layer is formed by an organic metal chemical vapor deposition process, comprising the following steps:
[0015] The pretreatment gas is ammonia gas, and the reaction chamber is heated at 700°C to 1200°C and 30 torr to 500 torr, with a flow rate of 0.1 L / min to 10 L / min of ammonia gas, and the treatment time is 1s to 60s.
[0016] Alternatively, the pretreatment gas is trimethylaluminum, and under the conditions of 700° C. to 1200° C. and 30 torr to 500 torr in the reaction chamber, trimethylaluminum is introduced at a flow rate of 2 μmol / min to 300 μmol / min, and the treatment time is 1 second to 60 seconds.
[0017] Optionally, the growth temperature of the first buffer layer is 700° C. to 1200° C.; and the first buffer layer is an aluminum nitride layer.
[0018] Optionally, before growing the first buffer layer, the method further includes: using an organic metal chemical vapor deposition process to grow a second buffer layer on the surface of the silicon-containing substrate along the plurality of nucleation points.
[0019] Optionally, the second buffer layer includes at least one of a first buffer sublayer formed under a first temperature condition and a second buffer sublayer formed under a second temperature condition, and the second temperature is higher than the first temperature.
[0020] Optionally, the second buffer layer includes a first buffer sublayer formed under a first temperature condition and a second buffer sublayer formed under a second temperature condition, the first buffer sublayer and the second buffer sublayer are in a stacked structure, and the two are arranged alternately.
[0021] Furthermore, the first temperature is 700°C to 1000°C, and the second temperature is 1000°C to 1200°C; the thickness of the first buffer sublayer is not greater than 25nm, and the thickness of the second buffer sublayer is not greater than 175nm; and the second buffer layer is an aluminum nitride layer.
[0022] Optionally, reactants for forming the first buffer sublayer include ammonia and trimethylaluminum, the flow rate of the ammonia is 1 L / min to 10 L / min, and the flow rate of the trimethylaluminum is 2 μmol / min to 300 μmol / min.
[0023] Optionally, reactants for forming the second buffer sublayer include ammonia and trimethylaluminum, the flow rate of the ammonia is 0.2 L / min to 5 L / min, and the flow rate of the trimethylaluminum is 20 μmol / min to 300 μmol / min.
[0024] Optionally, after forming the first buffer layer, the method further comprises: growing Al on the surface of the first buffer layer. z Ga 1-z N layers, 0≤z≤1.
[0025] Another aspect of the present invention provides a semiconductor structure, comprising:
[0026] Silicon-containing substrate,
[0027] a pretreatment layer, the pretreatment layer being located on the surface of the silicon-containing substrate and comprising a plurality of nucleation points; and
[0028] A first buffer layer is located on the surface of the pretreatment layer.
[0029] Optionally, the material of the first buffer layer includes: aluminum nitride; and the thickness of the first buffer layer is 50 nm to 300 nm.
[0030] Optionally, the semiconductor structure further includes a second buffer layer located between the pretreatment layer and the first buffer layer; a material of the second buffer layer includes: aluminum nitride.
[0031] Optionally, the thickness of the second buffer layer is not greater than 200 nm.
[0032] Optionally, the semiconductor structure further comprises Al z Ga 1-z An N layer is located on the surface of the first buffer layer, wherein 0≤z≤1.
[0033] Furthermore, the Al z Ga 1-z The N layer is one or more of GaN, AlGaN and AlN.
[0034] Compared with the prior art, the beneficial effects of the technical solution of the present invention include at least:
[0035] (1) The present invention provides a preparation method and structure for forming a high-quality buffer layer on the surface of a silicon-containing substrate. Specifically, in the semiconductor structure of the present invention, a pretreatment layer and a first buffer layer formed by a PVD process are sequentially included on the surface of the silicon-containing substrate along the epitaxial direction. The pretreatment layer includes a number of nucleation points, which have a crystal orientation guiding effect on the first buffer layer formed by subsequent PVD deposition, solving the problem that the crystal orientation of the first buffer layer is difficult to control when the first buffer layer starts to grow due to the fast deposition rate of the PVD process. In addition, the PVD process used in the method of the present invention can quickly grow a high-quality first buffer layer at a relatively low temperature (750°C to 900°C), solving the contradictory problem that MOCVD needs to be grown at a high temperature (greater than 1350°C) to obtain a high-quality buffer layer, but the silicon-containing substrate cannot withstand high temperatures (melting will occur at 1400°C).
[0036] (2) In order to further solve the problem that the crystal orientation of the buffer layer is difficult to control when the PVD process is directly used to start growing, the present invention also forms a second buffer layer with better crystal quality by low-speed growth using the MOCVD process after forming the pretreatment layer and before forming the first buffer layer by PVD growth, thereby providing a two-dimensional plane with high crystal quality for the subsequent growth of the first buffer layer, thereby guiding the crystal orientation of the subsequent buffer layer. BRIEF DESCRIPTION OF THE DRAWINGS
[0037] Figure 1 The figure is a flow chart of a method for preparing a semiconductor structure according to an embodiment of the present invention.
[0038] Figure 2 FIG. 4 is a flow chart of a method for preparing a semiconductor structure according to another embodiment of the present invention.
[0039] Figures 3 to 8 Schematic diagrams of semiconductor structures according to different embodiments of the present invention.
[0040] Fig. 9 Graph showing in-situ monitoring results of semiconductor structures of Example 2 of the present invention and the comparative example.
[0041] Figure ID:
[0042] Silicon-containing substrate 1, nucleation point 2, first buffer layer 3, second buffer layer 4, first buffer sublayer 41, second buffer sublayer 42. DETAILED DESCRIPTION
[0043] In order to solve the above technical problems, an embodiment of the present invention provides a method for preparing a semiconductor structure, and an embodiment of a semiconductor structure obtained by the method.
[0044] The technical solution of the present invention will be described clearly and completely below in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.
[0045] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.
[0046] It should also be noted that when an element is referred to as being "fixed on" or "disposed on" another element, it may be directly on the other element or there may be an intermediate element at the same time. When an element is referred to as being "connected to" another element, it may be directly connected to the other element or there may be an intermediate element at the same time.
[0047] As described in the background technology, it is difficult to obtain high-quality AlN using Si substrate as a base for epitaxial structure growth. Most existing epitaxial processes use MOCVD (metal organic chemical vapor deposition) and PVD (physical vapor deposition). Among them, the MOCVD process requires a higher growth temperature (above 1350°C) to obtain higher-quality AlN, but the Si substrate will melt at 1400°C. Therefore, the method of increasing the growth temperature to obtain high-quality AlN on the Si substrate is not feasible. In addition, although the PVD process can obtain higher-quality AlN at a relatively low temperature (750°C to 900°C), due to the fast growth rate of AlN by PVD, the crystal orientation is difficult to control at the beginning of growth, resulting in the failure to obtain higher-quality AlN; and because the surface of the Si substrate has an oxide layer, an additional step of pre-cleaning the substrate surface is required before growing AlN using the PVD process.
[0048] In summary, whether using the MOCVD process or the PVD process, the existing epitaxial structure growth methods are difficult to grow AlN with a smooth surface and high crystal quality on a Si substrate, which in turn affects the growth quality of other subsequent epitaxial structures, resulting in poor quality and uneven epitaxial wafers that cannot meet application requirements.
[0049] To solve the above technical problems, Figure 1 and Figure 3 As shown, an embodiment of the present invention provides a method for preparing a semiconductor structure, comprising:
[0050] Step 101 , providing a silicon-containing substrate 1 .
[0051] The silicon-containing substrate 1 is a silicon substrate or a silicon carbide substrate.
[0052] In some embodiments, when the silicon-containing substrate 1 is a silicon substrate, the surface of the silicon substrate is easily oxidized to form a silicon oxide layer. Therefore, before forming the pretreatment layer, the silicon substrate is also cleaned; the cleaning method includes: placing the silicon substrate in a reaction chamber of an organic metal chemical vapor deposition device, and using hydrogen at high temperature to remove oxides and other impurities on the surface of the substrate. As an example, the cleaning process includes the following steps:
[0053] The silicon substrate is treated at a high temperature of about 1 minute to 30 minutes in a hydrogen atmosphere at a temperature of 800° C. to 1200° C. with the pressure of the reaction chamber maintained at 30 torr to 500 torr.
[0054] Step 102 , introducing a pretreatment gas to induce formation of a pretreatment layer on the surface of the silicon-containing substrate 1 , wherein the pretreatment layer includes a plurality of nucleation points 2 .
[0055] The pretreatment layer may be formed by metal organic chemical vapor deposition (MOCVD), but is not limited thereto.
[0056] Optionally, in one embodiment of the present invention, placing the silicon-containing substrate 1 in a MOCVD reaction chamber to form the pretreatment layer specifically includes:
[0057] The reaction chamber is heated at 700°C to 1200°C and 30 torr to 500 torr, and a pretreatment gas of 0.1 L / min to 10 L / min of ammonia (NH3) is introduced, and the carrier gas is H2, and the treatment time is 1 s to 60 s, thereby forming a large number of uniformly distributed SiN on the surface of the silicon-containing substrate 1. x dot structure, as the subsequent first buffer layer 3 (see Figure 3 ) (such as AlN layer) growth island nucleation points.
[0058] In another embodiment, the silicon-containing substrate 1 is placed in a MOCVD reaction chamber to form the pretreatment layer, specifically including: under the conditions of 700°C to 1200°C and 30torr to 500torr in the reaction chamber, a pretreatment gas trimethylaluminum (TMAl) with a flow rate of 2μmol / min to 300μmol / min is introduced, the carrier gas is H2, and the treatment time is 1s to 60s, thereby forming a large number of uniformly distributed Si-Al bonds on the surface of the silicon-containing substrate 1, which serve as island nucleation points for the subsequent growth of the first buffer layer 3 (such as an AlN layer).
[0059] Among them, the pretreatment time determines the density of the nucleation points 2 formed on the surface of the silicon-containing substrate 1. If the time is too short, it will lead to insufficient number and low density of island nucleation points. When the first buffer layer 3 continues to grow, due to the insufficient number and long distance of the island structure, the growth and merging are difficult, which affects the growth quality of the first buffer layer 3 and then affects the growth of the subsequent epitaxial structure; if the time is too long, the density is high, which will produce a very high density of screw dislocations, affecting the crystal quality of the first buffer layer 3.
[0060] Step 103 , using a physical vapor deposition process, growing a first buffer layer 3 along the plurality of nucleation points 2 on the surface of the silicon-containing substrate 1 .
[0061] Among them, the physical vapor deposition process temperature is 700℃~1200℃, the deposition power is 2000w~5000w, the Ar flow rate is 10sccm~50sccm, and the N2 flow rate is 100sccm~400sccm.
[0062] In one embodiment of the present invention, the first buffer layer 3 is an aluminum nitride (AlN) layer, and the specific formation steps include: providing nitrogen as a nitrogen source and an aluminum target as an aluminum source under the conditions of 700°C to 1200°C in a reaction chamber and an argon (Ar) atmosphere, and quickly depositing a high-quality AlN layer on the surface of the pretreatment layer.
[0063] It should be noted that compared with the MOCVD process, the PVD process does not have a complex pre-reaction, so the AlN layer can be grown quickly and the growth rate can be increased. However, as mentioned above, it is difficult to control the crystal orientation of the AlN layer when it starts to grow, which ultimately affects the crystal quality and surface flatness of the AlN layer. To solve this problem, the researchers of the present invention have conducted a lot of research and innovative attempts. Before using PVD to grow the AlN layer in step 103, after the treatment of step 102, a number of island nucleation points are first formed on the surface of the silicon-containing substrate 1, and SiN x (x represents the number of N atoms or the atomic ratio of N to Si, a positive number is taken), Si-Al serves as the nucleation point for the subsequent growth of the AlN layer, making it easier for the AlN layer to grow on the nucleation point, ensuring that the AlN layer can first uniformly form a plurality of island structures on the surface of the silicon-containing substrate 1, which are easier to merge when continuing to grow, thereby improving the crystal orientation of the AlN layer growth and forming a dense and flat AlN layer, thereby obtaining a semiconductor structure that meets the process performance requirements and has high production efficiency and short production time.
[0064] The following is attached Figure 3 The semiconductor structure prepared by the method of this embodiment is described in detail, and the semiconductor structure includes: a silicon-containing substrate 1, and a pretreatment layer and a first buffer layer 3 formed by a PVD process and sequentially grown along the epitaxial direction on the surface of the silicon-containing substrate 1.
[0065] The silicon-containing substrate 1 is a silicon substrate or a silicon carbide substrate;
[0066] The pretreatment layer is located on the surface of the silicon-containing substrate 1 and includes a plurality of nucleation points 2 .
[0067] The first buffer layer 3 is located on the surface of the pretreatment layer.
[0068] In some embodiments, the material of the first buffer layer 3 includes but is not limited to aluminum nitride, and the thickness of the first buffer layer 3 is 50nm to 300nm. The nucleation point 2 in the pretreatment layer is a SiNx point structure formed by passing ammonia gas through the MOCVD process, or a Si-Al bonding structure formed by passing trimethylaluminum gas.
[0069] like Figure 2 and Figures 4 to 6 As shown, in order to further improve the quality of epitaxially growing the first buffer layer 3 on the silicon-containing substrate 1, an embodiment of the present invention provides another method for preparing a semiconductor structure.
[0070] As can be seen from the above, compared with the PVD process, the MOCVD process has a lower deposition rate due to the presence of complex pre-reactions. Based on this, in order to further solve the problem of difficulty in controlling the crystal orientation when the first buffer layer 3 starts to grow when the PVD process is directly used, this embodiment forms a second buffer layer 4 with good crystal quality by using MOCVD low-speed growth after forming the pretreatment layer and before PVD growth to form the first buffer layer 3, providing a two-dimensional plane with high crystal quality for the subsequent growth of the first buffer layer 3.
[0071] Specifically include:
[0072] Step 201 , providing a silicon-containing substrate 1 .
[0073] The silicon-containing substrate 1 is a silicon substrate or a silicon carbide substrate.
[0074] In some embodiments, when the silicon-containing substrate 1 is a silicon substrate, the step of cleaning and removing oxide on the surface of the silicon substrate is also included.
[0075] Step 202 , introducing a pretreatment gas to induce formation of a pretreatment layer on the surface of the silicon-containing substrate 1 , wherein the pretreatment layer includes a plurality of nucleation points 2 .
[0076] The pretreatment layer may be formed by metal organic chemical vapor deposition (MOCVD), but is not limited thereto. The nucleation sites 2 are beneficial to improving the crystal orientation of the subsequent second buffer layer 4 (such as an AlN layer) and improving the growth quality.
[0077] Step 203 , using an organic metal chemical vapor deposition process, growing a second buffer layer 4 on the surface of the silicon-containing substrate 1 along the plurality of nucleation points 2 .
[0078] The second buffer layer 4 includes at least one of a first buffer sublayer 41 formed under a first temperature condition and a second buffer sublayer 42 formed under a second temperature condition, and the second temperature is higher than the first temperature. Optionally, the first temperature is 700°C to 1000°C, and the second temperature is 1000°C to 1200°C. It can be understood that the first buffer sublayer 41 formed by low-temperature growth is conducive to releasing stress and reducing dislocations; the second buffer sublayer 42 formed by high-temperature growth can improve atomic mobility, increase the lateral epitaxial ability of the second buffer sublayer 42, and improve crystal quality.
[0079] In some embodiments, the second buffer layer 4 is composed of a first buffer sublayer 41 formed under a first temperature condition (see Figure 4 ); In some other embodiments, the second buffer layer 4 is composed of a first buffer sublayer 42 formed under a second temperature condition (see Figure 5 ); In some other embodiments, the second buffer layer 4 includes a first buffer sublayer 41 formed under a first temperature condition and a second buffer sublayer 42 formed under a second temperature condition, and the first buffer sublayer 41 and the second buffer sublayer 42 are a stacked structure (see Figures 6 to 8 ). In some embodiments, Figure 6 and Figure 7 As shown, the second buffer layer 4 is composed of a first buffer sublayer 41 and a second buffer sublayer 42; in other embodiments, such as Figure 8 As shown, the total number of the first buffer sublayer 41 and the second buffer sublayer 42 in the second buffer layer 4 is greater than or equal to 3 layers, and the two are arranged alternately, which is beneficial to improving the crystal quality of the second buffer layer 4 and reducing the degree of dislocation.
[0080] In some embodiments, the thickness of the second buffer layer 4 is not greater than 200 nm, wherein the total thickness of the first buffer sublayer 41 is not greater than 25 nm, and the total thickness of the second buffer sublayer 42 is not greater than 175 nm. It is understood that if it is too thin, it will not play a good crystal orientation guiding role for the subsequently grown first buffer layer 3; if it is too thick, it is difficult to produce a better crystal orientation guiding role, but it will also lead to reduced production efficiency and extended production time.
[0081] In one embodiment of the present invention, the second buffer layer 4 is an AlN layer, and the formation method includes: in a MOCVD reaction chamber at 700°C to 1000°C, introducing ammonia gas with a flow rate of 1L / min to 10L / min and trimethylaluminum with a flow rate of 2μmol / min to 300μmol / min, and using H2 as a carrier gas, to grow and form the first buffer sublayer 41; in a MOCVD reaction chamber at 1000°C to 1200°C, introducing ammonia gas with a flow rate of 0.2L / min to 5L / min and trimethylaluminum with a flow rate of 20μmol / min to 300μmol / min, and using H2 as a carrier gas, to grow and form the second buffer sublayer 42. In other embodiments, when the total number of layers of the first buffer sublayer 41 and the second buffer sublayer 42 in the second buffer layer 4 is greater than or equal to 3 layers, the aforementioned method of forming the first buffer sublayer 41 and the second buffer sublayer 42 is alternately used to prepare the semiconductor structure.
[0082] Step 204 , using a physical vapor deposition process to grow a first buffer layer 3 on the surface of the second buffer layer 4 .
[0083] Among them, the physical vapor deposition process temperature is 700℃~1200℃, the deposition power is 2000w~5000w, the Ar flow rate is 10sccm~50sccm, and the N2 flow rate is 100sccm~400sccm.
[0084] In some embodiments, the method for preparing the semiconductor structure further comprises: growing Al on the surface of the first buffer layer 3 z Ga 1-z N layer, where 0≤z≤1. For example, AlN, GaN, AlGaN, etc. z Ga 1-z The N layer is grown by MOCVD process.
[0085] It should be noted that the existing epitaxial structure needs to grow a certain thickness of GaN, and Ga will have a certain amount of residue in the reaction chamber, resulting in each newly placed substrate to produce a melt-back reaction with the Ga remaining in the process, affecting the quality of the epitaxial layer structure. To solve this problem, as an example, the MOCVD cleaning process before and after the PVD growth of the first buffer layer 3 and the MOCVD growth of the Ga-containing buffer layer in the present invention use two MOCVD devices, and no Ga-containing reactants are introduced into the MOCVD cleaning reaction chamber. Therefore, before the PVD growth of the first buffer layer 3, each newly placed substrate will not have the problem of a melt-back reaction with Ga; after the PVD growth of the first buffer layer 3, when the substrate is placed in another MOCVD reaction chamber to continue the epitaxial growth of the Ga-containing buffer layer, because the first buffer layer 3 has been formed on the surface of the substrate, the substrate surface will not react with the Ga remaining in the previous substrate epitaxial process. Therefore, this embodiment can ensure that the substrate will not contact with Ga during the entire epitaxial growth process without spending a lot of time and work to deal with Ga residues, avoiding the problem of melt-back reaction, and helping to form an epitaxial structure with high crystal quality and good surface flatness.
[0086] The following is attached Figure 4 To Attachment Figure 8 The different semiconductor structures prepared by the method of this embodiment are described in detail:
[0087] Figures 4 to 5 A schematic diagram of the structure of a semiconductor provided by an embodiment of the present invention, the semiconductor structure comprises: a silicon-containing substrate 1, and a pretreatment layer, a second buffer layer 4 and a first buffer layer 3 formed by a PVD process, which are sequentially grown on the surface of the silicon-containing substrate 1 along the epitaxial direction. Wherein:
[0088] The silicon-containing substrate 1 is a silicon substrate or a silicon carbide substrate;
[0089] The pretreatment layer is located on the surface of the silicon-containing substrate 1 and includes a plurality of nucleation points 2 .
[0090] The second buffer layer 4 is located on the surface of the pre-treated layer, wherein the second buffer layer 4 is composed of a first buffer sublayer 41 (see Figure 4 ) or a second buffer sublayer 42 (see Figure 5 ), the thickness of the second buffer layer 4 is not more than 200nm.
[0091] The first buffer layer 3 is located on the surface of the second buffer layer 4. The material of the first buffer layer 3 includes but is not limited to aluminum nitride, and the thickness is 50nm to 300nm.
[0092] Figure 6 to Figure 7A schematic diagram of the structure of a semiconductor provided by another embodiment of the present invention, the semiconductor structure comprises: a silicon-containing substrate 1, and a pretreatment layer, a second buffer layer 4 and a first buffer layer 3 formed by a PVD process, which are sequentially grown on the surface of the silicon-containing substrate 1 along the epitaxial direction. Wherein:
[0093] The silicon-containing substrate 1 is a silicon substrate or a silicon carbide substrate;
[0094] The pretreatment layer is located on the surface of the silicon-containing substrate 1 and includes a plurality of nucleation points 2 .
[0095] The second buffer layer 4 is located on the surface of the pretreatment layer, wherein the second buffer layer 4 is composed of a first buffer sublayer 41 and a second buffer sublayer 42. In some embodiments, the second buffer sublayer 42 is located above the first buffer sublayer 41. Figure 4 In some other embodiments, the first buffer sublayer 41 is located above the second buffer sublayer 42, such as Figure 5 shown.
[0096] The first buffer layer 3 is located on the surface of the second buffer layer 4. The material of the first buffer layer 3 includes but is not limited to aluminum nitride, and the thickness is 50nm to 300nm.
[0097] Figure 8 A schematic diagram of a semiconductor structure provided for another embodiment of the present invention, the semiconductor structure comprises: a silicon-containing substrate 1, and a pretreatment layer, a second buffer layer 4 and a first buffer layer 3 formed by a PVD process, which are sequentially grown on the surface of the silicon-containing substrate 1 along the epitaxial direction.
[0098] The silicon-containing substrate 1 is a silicon substrate or a silicon carbide substrate;
[0099] The pretreatment layer is located on the surface of the silicon-containing substrate 1 and includes a plurality of nucleation points 2 .
[0100] The second buffer layer 4 is located on the surface of the pretreatment layer, wherein the number of layers of the first buffer sublayer 41 and the second buffer sublayer 42 in the second buffer layer 4 is greater than 3 layers, the first buffer sublayer 41 and the second buffer sublayer 42 are a stacked structure, and the two are arranged alternately.
[0101] The first buffer layer 3 is located on the surface of the second buffer layer 4. The material of the first buffer layer 3 includes but is not limited to aluminum nitride, and the thickness is 50nm to 300nm.
[0102] In some embodiments, the semiconductor structure further comprises Al z Ga 1-z N layer, which is located on the surface of the first buffer layer 3, wherein 0≤z≤1. As an example, the Al z Ga1-z The N layer is one or more of GaN, AlGaN and AlN.
[0103] Example 1
[0104] This embodiment provides a method for preparing a semiconductor structure, comprising:
[0105] Step 101 , providing a silicon-containing substrate 1 .
[0106] The silicon-containing substrate 1 is a silicon substrate, which is placed in a MOCVD reaction chamber and treated at 1050° C., with the reaction chamber pressure maintained at 50 torr, in a hydrogen atmosphere for about 5 minutes to remove oxides and other impurities on the surface of the substrate.
[0107] Step 102 , introducing a pretreatment gas to induce formation of a pretreatment layer on the surface of the silicon-containing substrate 1 , wherein the pretreatment layer includes a plurality of nucleation points 2 .
[0108] Continuing to form the pretreatment layer in the MOCVD reaction chamber specifically includes:
[0109] The reaction chamber is heated at 800°C and 50 torr, and a pretreatment gas of 3 L / min of ammonia (NH3) is introduced, and the carrier gas is H2. The treatment time is 6 seconds, so that a large number of uniformly distributed SiN x The dot structure serves as an island nucleation point for the subsequent growth of the first buffer layer 3 (AlN layer).
[0110] Step 103, using a physical vapor deposition process, growing a first buffer layer 3 along the plurality of nucleation points 2 on the surface of the silicon-containing substrate 1, specifically comprising:
[0111] Under the conditions of 750° C. in the reaction chamber and argon (Ar) atmosphere, nitrogen gas is provided as a nitrogen source and an aluminum target is provided as an aluminum source, and an AlN layer is rapidly deposited on the surface of the pretreatment layer with a deposition power of 2000w, an Ar flow rate of 30sccm, and a N2 flow rate of 200sccm.
[0112] An AlGaN layer and a GaN layer are sequentially grown on the surface of the first buffer layer 3 (AlN layer).
[0113] Example 2
[0114] This embodiment provides a method for preparing a semiconductor structure, comprising:
[0115] Step 201 , providing a silicon-containing substrate 1 .
[0116] The silicon-containing substrate 1 is a silicon substrate, which is placed in a MOCVD reaction chamber and treated at 1050° C., with the reaction chamber pressure maintained at 50 torr, in a hydrogen atmosphere for about 5 minutes to remove oxides and other impurities on the surface of the substrate.
[0117] Step 202 , introducing a pretreatment gas to induce formation of a pretreatment layer on the surface of the silicon-containing substrate 1 , wherein the pretreatment layer includes a plurality of nucleation points 2 .
[0118] Continuing to form the pretreatment layer in the MOCVD reaction chamber specifically includes:
[0119] The reaction chamber is heated at 800°C and 50 torr, and a pretreatment gas of 3 L / min of ammonia (NH3) is introduced, and the carrier gas is H2. The treatment time is 6 seconds, so that a large number of uniformly distributed SiN x The dot structure serves as an island nucleation point for the subsequent growth of the first buffer layer 3 (AlN layer).
[0120] Step 203, using an organic metal chemical vapor deposition process, growing a second buffer layer 4 along the plurality of nucleation points 2 on the surface of the silicon-containing substrate 1, comprising:
[0121] Under the condition of 850℃ in the MOCVD reaction chamber, ammonia gas with a flow rate of 3L / min and trimethylaluminum with a flow rate of 100μmol / min, H2 as the carrier gas, and the treatment time is 3 minutes, a first buffer sublayer 41 is grown and formed; under the condition of 1100℃ in the MOCVD reaction chamber, ammonia gas with a flow rate of 1L / min and trimethylaluminum with a flow rate of 200μmol / min, H2 as the carrier gas, and the treatment time is 5 minutes, a second buffer sublayer 42 is formed on the surface of the first buffer sublayer 41.
[0122] Step 204, using a physical vapor deposition process, growing a first buffer layer 3 along the plurality of nucleation points 2 on the surface of the silicon-containing substrate 1, specifically comprising:
[0123] Under the conditions of 750°C in the reaction chamber and argon (Ar) atmosphere, nitrogen is provided as a nitrogen source and an aluminum target is provided as an aluminum source, and an AlN layer is rapidly deposited on the surface of the second buffer sublayer 42, with a deposition power of 2000w, an Ar flow rate of 30sccm, and a N2 flow rate of 200sccm.
[0124] An AlGaN layer and a GaN layer are sequentially grown on the surface of the first buffer layer 3 (AlN layer).
[0125] Comparative Example
[0126] A silicon substrate is provided, and after the surface of the silicon substrate is wet cleaned, a first buffer layer 3 (AlN layer) is directly grown on the surface of the silicon substrate by PVD, and the PVD process conditions are the same as those in Examples 1 and 2. An AlGaN layer and a GaN layer are continuously grown in sequence on the surface of the first buffer layer 3 (AlN layer), and the process conditions are the same as those in Examples 1 and 2.
[0127] The surface flatness of the semiconductor structure obtained in Example 2 and the comparative example is monitored in situ by the in-situ monitoring system of the MOCVD equipment. According to the working principle of in-situ monitoring, when the surface flatness of the epitaxial layer is high, the intensity of the reflected light alternately increases and decreases with the increase of the thickness of the epitaxial layer during growth, forming a waveform; on the contrary, when the surface flatness of the epitaxial layer is not high, the reflected light cannot form a waveform due to the diffuse reflection of the reflected light. The in-situ monitoring results are shown in FIG. Fig. 9 As shown, in the entire epitaxial growth process of Example 2 of the present invention, as the growth time goes by, the reflected light keeps forming a waveform, which means that the epitaxial layer structure formed in Example 2 can maintain good crystal quality and high surface flatness throughout the growth process; while the epitaxial layer structure formed in the comparative example only forms a waveform in the early stage, and no waveform is formed at all in the later stage, which means that in the comparative example, as the epitaxial growth time goes by, the surface flatness of the epitaxial layer gradually decreases, until the subsequent epitaxial layer structure cannot grow flat and cannot meet the process application.
[0128] In summary, the present invention improves the crystal orientation of the first buffer layer grown by subsequent PVD deposition through a number of nucleation points in the pretreatment layer, and solves the problem that the crystal orientation is difficult to control at the beginning of growth due to the fast deposition rate of the PVD process. The preparation method of the present invention can achieve rapid growth of a high-quality buffer layer at a relatively low temperature, and the buffer layer has good crystal quality and high surface flatness. Furthermore, the present invention also uses MOCVD low-speed growth to form a second buffer layer with better crystal quality before the formation of the first buffer layer, so as to improve the growth quality of the epitaxial layer.
[0129] Although the content of the present invention has been described in detail through the above preferred embodiments, it should be appreciated that the above description should not be considered as a limitation of the present invention. After reading the above content, it will be apparent to those skilled in the art that various modifications and substitutions of the present invention will occur. Therefore, the protection scope of the present invention should be limited by the appended claims.
Claims
1. A method for preparing a semiconductor structure, characterized in that: include: providing a silicon-containing substrate; Passing a pretreatment gas to induce formation of a pretreatment layer on the surface of the silicon-containing substrate, wherein the pretreatment layer includes a plurality of nucleation points; A physical vapor deposition process is adopted to grow a first buffer layer on the surface of the silicon-containing substrate along the plurality of nucleation points.
2. The method for preparing a semiconductor structure according to claim 1, characterized in that: The silicon-containing substrate is a silicon substrate or a silicon carbide substrate.
3. The method for preparing a semiconductor structure according to claim 2, characterized in that: When the silicon-containing substrate is a silicon substrate, the surface of the silicon substrate is easily oxidized to form a silicon oxide layer; before forming the nucleation point, the silicon substrate is also cleaned; the cleaning method includes: placing the silicon substrate in a reaction chamber of an organic metal chemical vapor deposition device for cleaning to remove the silicon oxide layer.
4. The method for preparing a semiconductor structure according to claim 3, characterized in that: The cleaning process includes: the cleaning gas includes H2, the cleaning temperature is: 800°C to 1200°C; and the cleaning time is 1 minute to 30 minutes.
5. The method for preparing a semiconductor structure according to claim 1, wherein: The pretreatment layer is formed by metal organic chemical vapor deposition.
6. The method for preparing a semiconductor structure according to claim 5, characterized in that: The pretreatment layer is formed by an organic metal chemical vapor deposition process, comprising the following steps: The pretreatment gas is ammonia gas, and the reaction chamber is heated at 700°C to 1200°C and 30 torr to 500 torr, with a flow rate of 0.1 L / min to 10 L / min of ammonia gas, and the treatment time is 1s to 60s. Alternatively, the pretreatment gas is trimethylaluminum, and under the conditions of 700° C. to 1200° C. and 30 torr to 500 torr in the reaction chamber, trimethylaluminum is introduced at a flow rate of 2 μmol / min to 300 μmol / min, and the treatment time is 1 second to 60 seconds.
7. The method for preparing a semiconductor structure according to claim 1, wherein: The growth temperature of the first buffer layer is 700° C. to 1200° C.; the first buffer layer is an aluminum nitride layer.
8. The method for preparing a semiconductor structure according to any one of claims 1 to 7, characterized in that: Before growing the first buffer layer, the method further includes: using an organic metal chemical vapor deposition process to grow a second buffer layer along the plurality of nucleation points on the surface of the silicon-containing substrate.
9. The method for preparing a semiconductor structure according to claim 8, characterized in that: The second buffer layer includes at least one of a first buffer sublayer formed under a first temperature condition and a second buffer sublayer formed under a second temperature condition, the second temperature being higher than the first temperature.
10. The method for preparing a semiconductor structure according to claim 8, characterized in that: The second buffer layer includes a first buffer sublayer formed under a first temperature condition and a second buffer sublayer formed under a second temperature condition. The first buffer sublayer and the second buffer sublayer are in a stacked structure and are arranged alternately.
11. The method for preparing a semiconductor structure according to claim 9 or 10, characterized in that: The first temperature is 700° C. to 1000° C., and the second temperature is 1000° C. to 1200° C.; the thickness of the first buffer sublayer is not greater than 25 nm, and the thickness of the second buffer sublayer is not greater than 175 nm; The second buffer layer is an aluminum nitride layer.
12. The method for preparing a semiconductor structure according to claim 11, characterized in that: The reactants for forming the first buffer sublayer include ammonia and trimethylaluminum. The flow rate of the ammonia is 1 L / min to 10 L / min, and the flow rate of the trimethylaluminum is 2 μmol / min to 300 μmol / min.
13. The method for preparing a semiconductor structure according to claim 11, characterized in that: The reactants for forming the second buffer sublayer include ammonia and trimethylaluminum. The flow rate of the ammonia is 0.2 L / min to 5 L / min, and the flow rate of the trimethylaluminum is 20 μmol / min to 300 μmol / min.
14. The method for preparing a semiconductor structure according to claim 1, wherein: After forming the first buffer layer, the method further includes: growing Al on the surface of the first buffer layer. z Ga 1-z N layers, 0≤z≤1.
15. A semiconductor structure, characterized in that: include: Silicon-containing substrate, A pretreatment layer, located on the surface of the silicon-containing substrate, comprising a plurality of nucleation sites; The first buffer layer is located on the surface of the pretreatment layer.
16. The semiconductor structure according to claim 15, wherein: The material of the first buffer layer includes aluminum nitride; the thickness of the first buffer layer is 50 nm to 300 nm.
17. The semiconductor structure according to claim 15, wherein: The semiconductor structure further includes a second buffer layer located between the pre-processing layer and the first buffer layer; the material of the second buffer layer includes: aluminum nitride.
18. The semiconductor structure according to claim 17, wherein: The thickness of the second buffer layer is no more than 200 nm.
19. The semiconductor structure according to claim 15, wherein: The semiconductor structure also includes Al z Ga 1-z An N layer is located on the surface of the first buffer layer, wherein 0≤z≤1.
20. The semiconductor structure according to claim 19, wherein: The Al z Ga 1-z The N layer is one or more of GaN, AlGaN and AlN.