Patent Publication Number: US-2021193470-A1

Title: Semiconductor manufacturing method and semiconductor manufacturing device

Description:
RELATED APPLICATIONS 
     The contents of Japanese Patent Application No. 2018-168229, and of International Patent Application No. PCT/JP2019/024914, on the basis of each of which priority benefits are claimed in an accompanying application data sheet, are in their entirety incorporated herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     Certain embodiments of the present invention relate to a semiconductor manufacturing method and a semiconductor manufacturing device. 
     Description of Related Art 
     A nitride semiconductor represented by AlN, AlGaN, GaN, InGaN, or InN has a wide band gap compared to silicon, and is advanced in application to a high frequency and high output transistor or the like that is operable even under a high temperature environment. With this, a significant reduction in size or high efficiency of equipment is expected. 
     For such a wide band gap semiconductor, in a manufacturing process, an entire substrate is annealed at a predetermined temperature by an annealing device (RTA) to form an ohmic electrode, thereby achieving improvement in ohmic characteristics (for example, see the related art). 
     SUMMARY 
     According to an embodiment of the invention, there is provided a semiconductor manufacturing method including a metal thin film deposition step of depositing a metal thin film on a donor or acceptor-doped nitride semiconductor; and a laser beam irradiation step of irradiating the deposited metal thin film with a laser beam. 
     According to another embodiment of the invention, there is provided a semiconductor manufacturing device including a metal thin film deposition unit that deposits a metal thin film on a donor or acceptor-doped nitride semiconductor; and a laser beam irradiation unit that irradiates the metal thin film deposited by the metal thin film deposition unit with a laser beam. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a cross-sectional view regarding a semiconductor using a donor or acceptor-doped nitride semiconductor that is an embodiment according to the invention. 
         FIG. 2  is a schematic configuration diagram of an electron beam deposition device of a semiconductor manufacturing device. 
         FIG. 3  is a schematic configuration diagram of a laser machining device of the semiconductor manufacturing device. 
         FIG. 4A  is an explanatory view showing a manufacturing method of a semiconductor. 
         FIG. 4B  is an explanatory view showing the manufacturing method of the semiconductor subsequent to  FIG. 4A . 
         FIG. 4C  is an explanatory view showing the manufacturing method of the semiconductor subsequent to  FIG. 4B . 
         FIG. 4D  is an explanatory view showing the manufacturing method of the semiconductor subsequent to  FIG. 4C . 
         FIG. 4E  is an explanatory view showing the manufacturing method of the semiconductor subsequent to  FIG. 4D . 
         FIG. 4F  is an explanatory view showing the manufacturing method of the semiconductor subsequent to  FIG. 4E . 
         FIG. 5  is a plan view of a mask member for laser. 
         FIG. 6  is an explanatory view showing a configuration for measuring an I-V characteristic of a sample where an electrode is subjected to laser annealing. 
         FIG. 7  is a diagram showing I-V characteristics of four samples where an electrode is subjected to laser annealing. 
     
    
    
     DETAILED DESCRIPTION 
     However, in the related art, the entire substrate is heated in a chamber of the annealing device. For this reason, heating also has an influence on portions other than the ohmic electrode, and there is a problem in that damage to characteristics as a semiconductor, such as high resistance due to the influence of heat, occurs, and electrical characteristics of the wide band gap semiconductor may not be utilized. 
     It is desirable to efficiently form an ohmic electrode by performing laser annealing locally. 
     According to the embodiments of the invention, it is possible to locally heat a metal thin film deposition portion (ohmic electrode) on a substrate, and to suppress an influence of heating on portions other than the ohmic electrode. 
     Hereinafter, the respective embodiments of the invention will be described in detail referring to the drawings. In the embodiment, a semiconductor manufacturing method and a semiconductor manufacturing device for a semiconductor using a donor or acceptor-doped nitride semiconductor will be described. 
     Semiconductor 
     Hereinafter, the invention will be specifically described.  FIG. 1  is a cross-sectional view regarding a semiconductor  10  using a p-type GaN substrate that is an embodiment according to the invention. 
     The semiconductor  10  includes a p-type GaN substrate  11 , and an electrode  16  made of a metal thin film formed on the p-type GaN substrate  11 . 
     The semiconductor  10  shown herein is merely an example of a semiconductor using a p-type GaN substrate, and the invention can be applied to a variety of semiconductors using a donor or acceptor-doped nitride semiconductor. 
     In the p-type GaN substrate  11 , as shown in the drawing, a low-temperature (LT)-GaN layer  13  is formed on an upper surface of a substrate  12 , and a high-temperature (HT)-GaN layer  14  is formed on an upper surface of the LT-GaN layer  13 . In addition, the p-type GaN substrate  11  has a configuration in which a GaN layer  15  as a nitride semiconductor layer is formed on an upper surface of the HT-GaN layer  14 . 
     The substrate  12  is not particularly limited and may be made of any crystal as long as a nitride semiconductor layer can be formed on a surface of the substrate  12 , and for example, a silicon (Si) substrate, a sapphire substrate, a SiC substrate, and a GaN substrate, and the like can be used. Here, a sapphire substrate is exemplified. A thickness of the substrate  12  may be a normal thickness (about 100 to 1000 [μm]) in a field of semiconductor technology, and is not particularly limited. 
     The LT-GaN layer  13  is a buffer layer that is laminated at a lower temperature than the HT-GaN layer  14  and the GaN layer  15  to relax lattice mismatch. The buffer layer may be a layer that is generally used in a field of semiconductor technology. 
     The HT-GaN layer  14  is laminated and formed at a higher temperature than the LT-GaN layer  13 . As the HT-GaN layer  14 , a next generation semiconductor material is laminated. 
     The GaN layer  15  is made of additive-doped GaN in which any of AlGaN, indium gallium nitride (InGaN), and aluminum indium gallium nitride (AlInGaN), which is mixed crystal obtained by mixing GaN or GaN and AlN at a predetermined ratio, is doped with an impurity. The impurity-doped GaN may be any of p-type GaN where GaN is doped with a p-type impurity and n-type GaN where GaN is doped with an n-type impurity. Here, a GaN layer made of p-type GaN is exemplified. 
     The GaN layer  15  made of p-type GaN is doped with Mg as an impurity. It is desirable that a doping amount of Mg is within a range equal to or greater than 1.0E+17 and equal to or smaller than 6.0E+19 [cm −3 ]. 
     Furthermore, a thickness of the GaN layer  15  is equal to or greater than two times, more desirably, five times, a thickness of a lower electrode  161  of the electrode  16  formed on the GaN layer  15 . 
     Note that, in a case where the GaN layer  15  consists of n-type GaN, Si is doped as an impurity. 
     On an upper surface of the GaN layer  15 , a plurality of electrodes  16  (in  FIG. 1 , only two electrodes are shown) are formed at predetermined intervals. 
     The electrodes  16  are formed to cover only a portion of one surface of the GaN layer  15 , which is a semiconductor layer, without covering the whole of one surface. Then, all electrodes  16  are formed on one surface side of the GaN layer  15  that is a semiconductor layer. 
     Such electrodes  16  are formed as ohmic electrodes showing ohmic characteristics. Examples of a metal material used for such electrodes include gold (Au), titanium (Ti), nickel (Ni), aluminum (Al), vanadium (V), and molybdenum (Mo). Alternatively, such metal materials may be laminated in a plurality of combinations to form electrodes. 
     Here, a case where the electrode  16  consists of a laminated electrode where the lower electrode  161  on the GaN layer  15  side is formed of Ni and an upper electrode  162  laminated on the lower electrode  161  is formed of Au is exemplified. For example, as the upper electrode  162  is formed of Au, it is possible to protect the lower electrode  161  made of Ni from oxidation or the like. 
     Furthermore, it is desirable that the lower electrode  161  has a film thickness equal to or greater than 5 nm and less than 30 nm. In regard to the lower electrode  161 , while ohmic junction is achieved by laser annealing described below, the thickness is set within the range, whereby heating by laser is effectively performed and satisfactory ohmic contact is realized. 
     Semiconductor Manufacturing Device 
     A semiconductor manufacturing device is a semiconductor manufacturing device suitable for manufacturing the semiconductor  10  described above, and primarily includes an electron beam deposition device  20  (see  FIG. 2 ) and a laser machining device  30  (see  FIG. 3 ). 
     The electron beam deposition device  20  functions as a metal thin film deposition unit that deposits the electrode  16  as a metal thin film on the p-type GaN substrate  11 . 
     Furthermore, the laser machining device  30  functions as a laser beam irradiation unit that irradiates the electrode  16  made of the metal thin film deposited by the electron beam deposition device  20  with a laser beam. 
     Semiconductor Manufacturing Device: Electron Beam Deposition Device 
       FIG. 2  is a schematic configuration diagram of the electron beam deposition device  20 . 
     As shown in the drawing, the electron beam deposition device  20  includes a stage  21  on which the p-type GaN substrate  11  of the semiconductor  10  is installed, a chamber  22  that stores the stage  21 , a cryopump  23  that is connected to an exhaust port  221  of the chamber  22  through a valve  222 , a target  24  that is made of a material for forming a metal thin film provided to face the stage  21  at a given interval, a cathode electrode  25  that applies a voltage to a surface opposite to a surface of the target  24  facing the stage  21 , and a cathode shield  26  that supports the cathode electrode  25 . 
     The chamber  22  can cut off outside air to bring an inside into an airtight state. Then, the chamber  22  is provided with a gas introduction port  223  and a valve  224  configured to introduce gas, which generates plasma, in addition to the above-described exhaust port  221  that exhausts inside gas. 
     Inert gas (for example, Ar gas) is supplied from the gas introduction port  223  into the chamber  22 . 
     In the chamber  22 , the stage  21  is grounded. Then, a predetermined voltage can be applied to the target  24  facing the stage  21  by the cathode electrode  25 . With this, in a case where discharge is generated between the target  24  and the p-type GaN substrate  11  in a state in which inert gas is supplied into the chamber  22 , particles made of a target material can be attached to the p-type GaN substrate  11  to be deposited. 
     Note that a permanent magnet or an electromagnet may be disposed on a rear surface side (cathode electrode  25 ) of the target  24  to perform deposition. 
     Semiconductor Manufacturing Device: Laser Machining Device 
       FIG. 3  is a schematic configuration diagram of the laser machining device  30 . 
     The laser machining device  30  is a laser annealing device that has the electrode  16  of the semiconductor  10  as a machining subject and irradiates the electrode  16  with a laser beam to perform annealing processing. 
     The laser machining device  30  includes a laser beam source  31 , an attenuator  32 , a beam homogenizer  34 , a beam scanner  35 , a lens  36 , a chamber  37 , a stage  38 , and a photodetector  39 . 
     The laser beam source  31  outputs a pulsed laser beam in an ultraviolet range. For example, the laser beam source  31  can output the pulsed laser beam with a pulse width within a range equal to or greater than 1 [ns] and less than 1000 [ns]. That is, the laser beam source  31  that outputs pulsed laser beam having a desired pulse width within the above-described range is used. 
     For the laser beam source  31 , for example, a Nd:YVO4 laser oscillator that outputs third harmonics having a wavelength of 355 [nm] is used. In addition, a Nd:YLF laser oscillator or a Nd:YAG laser oscillator may be used. 
     The p-type GaN substrate  11  on which the lower electrode  161  is formed can be placed on the stage  38 . 
     The chamber  37  stores the stage  38  inside and can cut off outside air to bring the inside into an airtight state. 
     The chamber  37  is provided with a laser transmission window  371 , and can introduce the laser beam from the laser beam source  31  onto the stage  38  inside. 
     The lens  36  and the laser transmission window  371  are optical parts that are disposed on a path of the pulsed laser beam scanned by the beam scanner  35 . The laser transmission window  371  has a structure in which an antireflection film is coated on a surface of a synthetic quartz plate, for example. 
     Furthermore, the chamber  37  is provided with an introduction port and an exhaust port (not shown) of oxygen or inert gas (argon, nitrogen, or the like), and can be made into an oxygen atmosphere, air atmosphere, inert atmosphere, or vacuum during laser annealing. Note that a supply source and an exhaust pump of oxygen or inert gas are omitted in the drawing. 
     The attenuator  32  changes an attenuation factor of the pulsed laser beam based on a command from a controller (not shown) of the semiconductor manufacturing device. 
     The beam homogenizer  34  homogenizes a beam profile on the surface of the p-type GaN substrate  11 . 
     The beam scanner  35  scans the pulsed laser beam in a two-dimensional direction based on a scanning command from the controller (not shown) of the semiconductor manufacturing device. For the beam scanner  35 , for example, a galvanoscanner having a pair of movable mirrors can be used. 
     The lens  36  consists of, for example, an fθ lens, and realizes a substantially image side telecentric optical system. A movement speed of an incidence position of the pulsed laser beam scanned by the beam scanner  35  on the surface of the electrode  16  of the semiconductor  10  is, for example, 200 [mm/s]. 
     In the chamber  37 , the photodetector  39  is disposed. The pulsed laser beam can be made to be incident on the photodetector  39  by controlling the beam scanner  35 . In this state, the photodetector  39  can measure light intensity of the pulsed laser beam, for example, average power or pulse energy. The photodetector  39  inputs a measurement result to the controller (not shown), and the controller can confirm the normality of the laser beam source  31 , the attenuator  32 , and the beam homogenizer  34  based on the measurement result. In addition, the presence or absence of dirt or deterioration of the lens  36  and the laser transmission window  371  at a place where the pulsed laser beam is transmitted can be confirmed. 
     Manufacturing Method of Semiconductor 
       FIGS. 4A to 4F  are explanatory views showing a manufacturing method of the semiconductor  10  in order. 
     As shown in  FIG. 4A , first, the substrate  12  made of a sapphire substrate having a thickness of 0.43 [μm] is prepared. 
     Next, as shown in  FIG. 4B , the LT-GaN layer  13 , the HT-GaN layer  14 , and the GaN layer  15  are formed on the substrate  12  in order (semiconductor layer forming step). In forming the respective layers, vapor phase epitaxy, such as metal organic vapor phase epitaxy (MOCVD), hydride vapor phase epitaxy (HVPE), molecular beam epitaxy (MBE), or pulsed laser deposition (PLD), can be used. 
     Next, as shown in  FIG. 4C , the lower electrode  161  of the electrode  16  made of a metal thin film is formed using the electron beam deposition device  20  (metal thin film deposition step). Note that, prior to forming the lower electrode  161 , the GaN layer  15  of the p-type GaN substrate  11  is sufficiently cleaned by organic cleaning, SPM cleaning, acid cleaning, or pure water cleaning, and is sufficiently dried. 
     An electrode, such as the lower electrode  161 , can be formed by deposition with Ni as the target  24  using the electron beam deposition device  20  after application of a photoresist to the upper surface of the GaN layer  15 , exposure and development of the photoresist with a photomask in which a desired electrode pattern is formed, removal of the photoresist in a region where an electrode is formed, and cleaning. 
     Alternatively, the lower electrode  161  may be formed using a mask member M for laser that is used in laser annealing, instead of a photoresist. 
     The mask member M for laser is a flat plate made of a material (stainless steel, nickel alloy, or the like) having a predetermined thickness that bears irradiation of the laser beam. As shown in  FIG. 5 , the mask member M for laser has openings M 1  corresponding to a forming pattern of an electrode. 
     Then, as shown in  FIG. 4C , the mask member M for laser is closely attached to an electrode forming surface side of the GaN layer  15  of the p-type GaN substrate  11 , and is installed on the stage  21  in the chamber  22  of the electron beam deposition device  20 . Then, the target  24  made of Ni is mounted to face the stage  21 , and the chamber  22  is deaerated and filled with inert gas. In addition, a voltage is applied to the target  24 , and Ni is deposited on the surface of the GaN layer  15  viewed from the mask member M for laser and the openings M 1  by electron beam deposition. 
     With this, the lower electrode  161  is formed on the electrode forming surface of the GaN layer  15  according to the forming pattern of the electrode. 
     Next, as shown in  FIG. 4D , laser annealing of the lower electrode  161  by the laser machining device  30  is performed (laser beam irradiation step). 
     The p-type GaN substrate  11  on which the lower electrode  161  is formed is installed on the stage  38  in the chamber  37  of the laser machining device  30  along with the mask member M for laser. 
     The inside of the chamber  37  is maintained in an air atmosphere state. 
     The pulsed laser beam having a pulse width within a range equal to or greater than 1 ns and less than 1000 ns is output from the laser beam source  31 . 
     The irradiation energy of the laser beam is controlled by the attenuator  32  such that the lower electrode  161  is not melted, and an interface temperature of the lower electrode  161  and the p-type GaN substrate  11  is equal to or lower than 800° C. Furthermore, the interface temperature is set to be at least equal to or higher than 300° C. 
     In addition, under the control of the beam scanner  35 , the irradiation of the pulsed laser beam is performed in a two-dimensional manner of a main scanning direction and a sub-scanning direction, and the irradiation of the pulsed laser beam is performed such that the whole of the electrode forming surface of the GaN layer  15  of the p-type GaN substrate  11  is within an irradiation range. With this, the irradiation of the pulsed laser beam is performed from each opening M 1  to each lower electrode  161 , and the irradiation of the remaining pulsed laser beam is performed to the mask member M for laser. 
     With the laser annealing, satisfactory ohmic contact of the lower electrode  161  with the p-type GaN substrate  11  is realized. 
     Next, as shown in  FIG. 4E , the upper electrode  162  of the electrode  16  made of a metal thin film is formed using the electron beam deposition device  20  again (Au deposition step). 
     The upper electrode  162  can also be formed by application of a photoresist to the upper surface of the GaN layer  15 , exposure and development of the photoresist with a photomask in which a desired electrode pattern is formed, removal of the photoresist in a region where an electrode is formed, cleaning, and film formation with Au as the target  24  using the electron beam deposition device  20  while removing the mask member M for laser. 
     Furthermore, instead of the photoresist, the upper electrode can be formed by film formation with Au as the target  24  using the electron beam deposition device  20  in a state in which the mask member M for laser is mounted. 
     Then, as shown in  FIG. 4F , after the upper electrode  162  is formed, the mask member M for laser is detached, and the formation of the electrode  16  on the p-type GaN substrate  11  is completed. 
     Technical Effects According to Embodiment of the Invention 
     In the above-described semiconductor manufacturing method, the lower electrode  161  of the electrode  16  deposited by the laser beam irradiation step is irradiated with the laser beam to perform laser annealing, and thus, it becomes easy to selectively heat only the lower electrode  161  of the p-type GaN substrate  11 , and it is possible to achieve satisfactory ohmic junction of the lower electrode  161 . 
     In addition, it is possible to suppress heating portions other than the lower electrode  161 , and to minimize an influence of heating on the portions other than the lower electrode  161  in the p-type GaN substrate  11 . In particular, in a case where configurations other than the lower electrode  161  are already formed on the p-type GaN substrate  11 , it is possible to particularly effectively suppress an influence of heating on other configurations. 
     The semiconductor manufacturing device includes the electron beam deposition device  20  that deposits the metal thin film, and the laser machining device  30  that irradiates the lower electrode  161  made of the metal thin film with the laser beam. For this reason, it is possible to provide a semiconductor manufacturing device that effectively suppresses the influence of heating on the configurations other than the lower electrode  161  while achieving satisfactory ohmic junction of the lower electrode  161 . 
     In the semiconductor manufacturing method, the upper electrode  162  made of Au is deposited on the lower electrode  161  after the laser beam irradiation step, and thus, it is possible to effectively perform laser annealing to the lower electrode while preventing the laser beam from being reflected by the upper electrode  162 . 
     The laser beam by the laser machining device  30  is pulsed laser, and irradiation of the laser beam is performed with a pulse width equal to or greater than 1 ns and less than 1000 ns. With this, it is possible to suppress and control a heat influence in a substrate depth direction. 
     The irradiation energy of the laser beam by the laser machining device  30  is set within a range in which the lower electrode  161  is not melted, and the interface temperature of the lower electrode  161  and the GaN layer  15  is equal to or lower than 800° C. With this, it is possible to avoid melting of the lower electrode  161 , to suppress a shortage of nitrogen of the p-type GaN substrate  11 , and to achieve satisfactory ohmic junction of the lower electrode  161 . 
     The lower electrode  161  is formed to have a thickness smaller than 30 nm and equal to or greater than 5 nm. As the thickness is set within the range, the lower electrode  161  is effectively heated by laser, and satisfactory ohmic contact is realized. 
     Example 
     An example of the invention will be described. 
     The GaN layer  15  of the semiconductor  10  shown in the example is made of Mg-doped p-type GaN, and a doping amount of Mg is 1.6×10 18  [cm −3 ]. A sapphire substrate was used for the substrate  12 , and the GaN layer  15  was formed by a MOCVD device. 
     The substrate  12  of the p-type GaN substrate  11  was formed to have a thickness of 430 [μm], the LT-GaN layer  13  was formed to have a thickness of 0.02 [μm], the HT-GaN layer  14  was formed to have a thickness of 0.96 [μm], and the GaN layer  15  was formed to have a thickness of 1.0 [μm]. 
     A plurality of lower electrodes  161  were made of Ni, and were formed to have a thickness of 20 [nm] by the electron beam deposition device  20 . The respective lower electrodes  161  were formed with a width in an arrangement direction of 1 [mm], and the respective lower electrodes  161  were formed at an interval in the arrangement direction of 5 to 500 [μm], and specifically, 500 [μm]. 
     Laser annealing was performed on the p-type GaN substrate  11 , on which the lower electrodes  161  were formed, by the laser machining device  30 . 
     The laser beam source  31  output pulsed laser of third harmonics having a wavelength of 355 [nm], and scanned the pulsed laser with a pulse width of 40 [ns], a frequency of 20 [kHz], and a speed of 200 [mm/s]. An overlap ratio was 80%/80%. The overlap ratio indicates a proportion of overlap of beam spots of laser output in a pulsed manner in the main scanning direction and the sub-scanning direction. 
     The above-described laser annealing was performed at a normal temperature in a state in which the chamber  37  was made into an oxygen atmosphere of a concentration of 20%. 
     Under the above-described machining conditions, four samples where laser annealing was performed with laser energy density of 0.5, 1.0, 1.5, and 2.0 [J/cm 2 ], respectively, were prepared. 
     In the respective samples, after the laser annealing, the upper electrode  162  made of Au was formed to have a thickness of 40 [μm] on the lower electrode  161 . 
     In regards to the four samples, as shown in  FIG. 6 , a direct current power supply E was connected to two electrodes  16 , and a current flowing in the two electrodes  16  was measured by an ammeter T to measure I-V characteristics of the respective samples. 
       FIG. 7  is a diagram showing the I-V characteristics of the four samples where laser annealing is performed with 0.5, 1.0, 1.5, and 2.0 [J/cm 2 ]. The vertical axis indicates a voltage, and the horizontal axis indicates a current. 
     As a result, a characteristic of Schottky contact was indicated in three samples where laser annealing was performed with 1.0, 1.5, and 2.0 [J/cm 2 ], and a characteristic of satisfactory ohmic contact was obtained in a sample where laser annealing is performed with 0.5 [J/cm 2 ]. In this sample, it was confirmed by an optical microscope that a surface state after laser irradiation was not melted. 
     Others 
     The embodiment of the invention has been described above. However, the invention is not limited to the above-described embodiment, and suitable changes can be made in the details described in the embodiment without departing from the concept of the invention. 
     For example, the semiconductor  10  may have a configuration in which an electrode is provided on one surface of a GaN layer, and suitable change can be made in other configurations. 
     Alternatively, in the laser machining device  30 , although a configuration for irradiation of pulsed laser has been made, the invention is not limited thereto, and for example, a configuration for irradiation of CW laser may be made. 
     Furthermore, in a case where laser annealing is performed on the lower electrode  161 , the mask member M for laser may not be used, two-dimensional data of an electrode pattern for forming the lower electrode  161  may be prepared in the controller of the semiconductor manufacturing device, and control may be performed such that the beam scanner  35  irradiates only a forming position of the lower electrode  161  with the laser beam. 
     For the metal thin film deposition unit of the semiconductor manufacturing device, a diode sputtering type or magnetron sputtering type sputtering device or an ion beam type sputtering device may be employed. 
     In addition, for the metal thin film deposition unit, a vacuum deposition type, molecular beam deposition type, ion plating type, or ion beam deposition type deposition device may be employed. 
     The term “deposition” in the embodiment and the claims is a concept including both sputtering by various sputtering devices described above and deposition for attaching a target metal evaporated and vaporized by heating to a substrate. 
     The semiconductor manufacturing method and the semiconductor manufacturing device according to the invention have industrial applicability in heating a nitride semiconductor. 
     It should be understood that the invention is not limited to the above-described embodiment, but may be modified into various forms on the basis of the spirit of the invention. Additionally, the modifications are included in the scope of the invention.