Diode and method of forming the same

Abstract

A diode and a method for forming the same, the diode comprising: a drift adjustment band located in at least part of a drift region for adjusting the recombination velocity of minority carriers, the drift adjustment band having a first conductivity type, the drift adjustment band being doped with impurities of the first conductivity type and impurities of a second conductivity type, the total doping concentration of the drift adjustment band being higher than the doping concentration of the drift region. The present invention can reduce the reverse recovery time of the diode and improve the softness factor of the diode.

Description

Technical Field

[0001] The present invention relates to the technical field of semiconductor manufacturing, and in particular to a diode and a method for forming the diode. Background Art

[0002] Diodes are key components of circuit systems. With the development of electronic power technology, the performance requirements for diodes are getting higher and higher. High-speed soft recovery diodes are a type of high-speed switching diodes. The most important characteristics of the diodes are the fast turn-off capability and soft recovery characteristics.

[0003] When the PN junction of a diode switches from forward conduction to reverse cutoff, the minority carriers (i.e., minority charge carriers) stored during the forward conduction process need to be extracted and recombined, and the minority carrier concentration returns to the equilibrium state, so that the reverse-biased depletion layer can be established, and then switched to the reverse cutoff state. The extraction and recombination of minority carriers and the establishment of the reverse-biased depletion layer require corresponding time and processes, which causes a delay in the conversion from forward conduction to reverse cutoff. This delay time determines the switching speed of the diode. The soft recovery characteristic of a diode refers to the fact that when the diode switches from forward conduction to reverse cutoff, the rate of decrease of its reverse recovery current is small, which helps to reduce electromagnetic interference and switching losses.

[0004] Therefore, how to ensure that the diode has the ability to quickly turn off while reducing the loss of the switch so that it has a softer recovery characteristic is the direction that technicians in this field are committed to studying. Summary of the invention

[0005] The technical problem solved by the present invention is to provide a diode and a method for forming the same, which can reduce the reverse recovery time of the diode and improve the softness factor of the diode.

[0006] To solve the above technical problems, an embodiment of the present invention provides a diode, comprising: a first heavily doped region and a second heavily doped region with an interval, the first heavily doped region having a first conductivity type, the second heavily doped region having a second conductivity type, the first conductivity type and the second conductivity type being opposite, the interval between the first heavily doped region and the second heavily doped region constituting a drift region, the drift region being doped with impurities of the first conductivity type and having a doping concentration lower than that of the first heavily doped region and the second heavily doped region, the drift region having the first conductivity type; the diode further comprises: a drift adjustment band, located in at least a portion of the drift region, for adjusting the minority carrier recombination velocity, the drift adjustment band having the first conductivity type, the drift adjustment band being doped with impurities of the first conductivity type and impurities of the second conductivity type, the total doping concentration of the drift adjustment band being higher than the doping concentration of the drift region.

[0007] Optionally, the drift adjustment band includes a sub-drift adjustment band.

[0008] Optionally, the drift adjustment band includes a plurality of stacked sub-drift adjustment bands, and a total doping concentration of the sub-drift adjustment bands gradually increases along a direction from the drift adjustment band to the second heavily doped region.

[0009] Optionally, the drift adjustment band includes three stacked sub-drift adjustment bands, each of which has a thickness of 1 μm-50 μm and a net doping concentration of 1e13 cm -3 -1e18cm -3 .

[0010] Optionally, the drift region contains heavy metal impurities, and the concentration of the heavy metal impurities is related to the total doping concentration of the drift adjustment band.

[0011] Optionally, the total doping concentration of the drift adjustment band is related to the reverse recovery time of the diode.

[0012] Optionally, the material of the heavy metal impurities is Pt or Au.

[0013] Optionally, the first conductivity type and the second conductivity type are N-type or P-type.

[0014] To solve the above technical problems, an embodiment of the present invention provides a method for forming a diode, comprising: forming a first heavily doped region and a second heavily doped region with a gap in a substrate, the first heavily doped region having a first conductivity type, the second heavily doped region having a second conductivity type, the first conductivity type and the second conductivity type being opposite, the gap between the first heavily doped region and the second heavily doped region constituting a drift region, the drift region being doped with impurities of the first conductivity type and having a doping concentration lower than that of the first heavily doped region and the second heavily doped region, the drift region having the first conductivity type; the method further comprises: forming a drift adjustment band in at least a portion of the drift region, the drift adjustment band having the first conductivity type, the drift adjustment band being doped with impurities of the first conductivity type and impurities of the second conductivity type, the total doping concentration of the drift adjustment band being higher than the doping concentration of the drift region.

[0015] Optionally, the first heavily doped region and the second heavily doped region formed with a gap in the substrate include: providing a semiconductor substrate of the first conductivity type, a portion of the semiconductor substrate serving as the first heavily doped region; and performing epitaxial growth on the semiconductor substrate to form the drift region and the second heavily doped region.

[0016] Optionally, the drift region includes a first drift region, and forming the first drift region includes: performing epitaxial growth on the first heavily doped region, and introducing a first type of doping source gas during the epitaxial growth process.

[0017] Optionally, the drift adjustment band includes a sub-drift adjustment band, and forming the sub-drift adjustment band includes: performing epitaxial growth on the first drift region to form the sub-drift adjustment band, and simultaneously introducing the first type of doping source gas and the second type of doping source gas during the epitaxial growth process, and the sum of the flow rates of the first type of doping source gas and the second type of doping source gas is greater than the flow rate of the doping source gas forming the first drift region.

[0018] Optionally, the drift adjustment band includes multiple sub-drift adjustment bands, and forming the sub-drift adjustment bands includes: performing multiple epitaxial growths on the first drift region to form multiple stacked sub-drift adjustment bands, and simultaneously introducing the first type of doping source gas and the second type of doping source gas during each epitaxial growth process, so that the sum of the flow rates of the first type of doping source gas and the second type of doping source gas forming each sub-drift adjustment band is greater than the flow rate of the doping source gas forming the first drift region, and the sum of the flow rates of the first type of doping source gas and the second type of doping source gas gradually increases along the direction from the drift adjustment band to the second heavily doped region.

[0019] Optionally, the drift region further includes a second drift region, and forming the second drift region includes: performing epitaxial growth on the drift adjustment zone, and introducing the first type of doping source gas during the epitaxial growth process.

[0020] Optionally, forming the first heavily doped region and the second heavily doped region spaced apart in the substrate includes: performing ion implantation doping of the second conductive type impurities into the second drift region; and performing high temperature diffusion of the implanted second conductive type impurities to form the second heavily doped region.

[0021] Optionally, the method further includes: a step of doping heavy metal impurities into the diode.

[0022] Optionally, the step of doping with heavy metal impurities includes: forming a heavy metal layer on the surface of the second heavily doped region; and performing high-temperature diffusion on the formed heavy metal layer.

[0023] Optionally, the thickness of the heavy metal layer is greater than 50Å.

[0024] Compared with the prior art, the technical solution of the embodiment of the present invention has the following beneficial effects:

[0025] In an embodiment of the present invention, a drift adjustment band in which N-type impurities and P-type impurities compensate each other is set in the drift region of the diode, so that the net doping concentration of the drift adjustment band is lightly doped, and at the same time, the total doping concentration of the drift adjustment band is increased, which helps to accelerate the recombination of minority carriers when the diode recovers in reverse.

[0026] Furthermore, according to the minority carrier lifetime required by the diode and the characteristics of the concentration of heavy metal impurities related to the total doping concentration of the drift adjustment band, the total doping concentration of the drift adjustment band can be determined. For this purpose, heavy metal impurities are introduced into the drift adjustment band to form a recombination center, thereby reducing the reverse recovery time of the diode. In this way, by controlling the total doping concentration of the drift adjustment band, the concentration of the recombination center introduced by the heavy metal impurities is indirectly controlled, thereby achieving the control of the minority carrier lifetime in each region of the drift adjustment band, forming a controllable diode soft switching characteristic.

[0027] A plurality of sub-drift adjustment bands are formed, and the total doping concentration of each sub-drift adjustment band is distributed from low to high. This distribution provides different minority carrier recombination efficiencies for different stages of diode reverse recovery. In the initial stage of diode reverse recovery, the minority carriers stored in the sub-drift adjustment band closer to the PN junction interface are rapidly recombined due to the high concentration of recombination centers, and the time for the reverse recovery current to increase from zero to the peak value is reduced, that is, the reverse recovery process is faster. In the stage when the PN junction begins to reverse bias and the depletion layer is correspondingly widened, the concentration of the recombination center in the sub-drift adjustment band farther from the PN junction interface is relatively low, and the minority carrier lifetime in this area is relatively long, so that the rate of decrease of the reverse recovery current will not be very fast, thereby improving the soft recovery characteristics of the diode. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 It is a schematic diagram of the diode reverse recovery current waveform;

[0029] Figure 2 is a schematic flow chart of a method for forming a diode in an embodiment of the present invention;

[0030] Figures 3 to 11 is a cross-sectional schematic diagram of an intermediate structure corresponding to each step in a method for forming a diode in an embodiment of the present invention;

[0031] Fig.12 The figure is a schematic diagram comparing reverse recovery current waveforms of a diode in an embodiment of the present invention and a diode in the prior art. DETAILED DESCRIPTION

[0032] As mentioned above, it is hoped to design and manufacture a diode with the fastest possible turn-off speed while taking into account good soft recovery characteristics, so as to improve the working performance of the diode.

[0033] The prior art attempts to improve the reverse recovery time and soft recovery characteristics from the structure and manufacturing process of the diode, such as forming a P diode at the cathode and anode of the diode. + P、N + P +The use of high-energy hydrogen ion implantation technology can achieve regional minority carrier lifetime control, but it requires additional expensive high-energy ion implantation equipment and ultra-thin wafer process matching with thicknesses of tens to hundreds of microns, which increases costs and process difficulty.

[0034] Figure 1 This is a schematic diagram of the diode reverse recovery current waveform. Figure 1 , usually the diode current is changed from the forward conduction current I F From the moment the current turns to zero, until the current reverses and gradually increases to the peak value I RM The time is defined as t a , the reverse recovery current is transferred from I RM The time when it decreases to 20% is defined as t b , diode reverse recovery time t rr =t a +t b , shorter reverse recovery time t rr The diode can be quickly switched between on and off to achieve a higher switching speed. In addition, the diode reverse peak voltage V RM The reverse recovery current is determined by the rate at which the peak value decreases, di / dt. If the reverse recovery current decreases too quickly, a large reverse peak voltage V RM , too high reverse peak voltage V RM It is easy to cause parasitic inductance and capacitance in the circuit to resonate, reducing circuit performance. RM , the industry introduced the softness factor parameter S=t b / t a The larger the S value, the smaller the rate of reduction of the reverse recovery current di / dt, and the corresponding reverse peak voltage V RM The smaller the reverse recovery time t is, the better the soft recovery characteristics of the diode are. Therefore, it is hoped that the reverse recovery time t rr , while taking into account the larger softness factor S.

[0035] As we all know, when some impurity atoms such as Pt and Au are doped into semiconductors, these impurity atoms can form recombination centers. These recombination centers can accelerate the recombination process of electrons and holes, thereby reducing the lifetime of minority carriers. Therefore, the reverse recovery time of the diode can be reduced by doping heavy metal impurities.

[0036] The inventors of the present invention have found through research that the saturated doping concentration of heavy metal impurities in silicon is related to the total doping concentration of N-type and P-type conductive impurities in silicon in addition to being related to temperature. Therefore, the concentration of the recombination centers introduced by heavy metal doping can be indirectly controlled by controlling the total doping concentration, and the minority carrier lifetimes in different regions of the diode can be effectively controlled, thereby changing t a and t b , improving the soft recovery characteristics of the diode.

[0037] In the embodiment of the present invention, the diode is doped with heavy metal impurities to form a recombination center to accelerate the recombination of electrons and holes, thereby reducing the reverse recovery time of the diode. On this basis, the total doping concentration of each sub-drift adjustment zone is designed to be distributed from low to high in the direction from the drift adjustment zone to the second heavily doped zone. This distribution can greatly reduce t a , and at the same time b The influence of is small, thereby improving the softness factor of the diode. Compared with the prior art, the embodiment of the present invention does not require additional structures and process equipment in design, and only needs to control the impurity doping amount in the original epitaxial growth process, which is simpler than the prior art.

[0038] In order to make the above-mentioned objects, features and beneficial effects of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0039] Figure 2 is a schematic diagram of a process for forming a diode in an embodiment of the present invention. Figure 2 , the method for forming the diode comprises steps S21 to S22:

[0040] Step S21: forming a first heavily doped region and a second heavily doped region with a gap in a substrate, wherein the first heavily doped region has a first conductivity type, and the second heavily doped region has a second conductivity type, the first conductivity type and the second conductivity type are opposite, the gap between the first heavily doped region and the second heavily doped region constitutes a drift region, the drift region is doped with impurities of the first conductivity type and the doping concentration is lower than that of the first heavily doped region and the second heavily doped region, and the drift region has the first conductivity type;

[0041] Step S22: forming a drift adjustment band in at least a portion of the drift region, wherein the drift adjustment band has the first conductivity type, is doped with impurities of the first conductivity type and impurities of the second conductivity type, and has a total doping concentration higher than a doping concentration of the drift region.

[0042] Figures 3 to 11is a cross-sectional schematic diagram of an intermediate structure corresponding to each step in a method for forming a diode in an embodiment of the present invention. Figure 1 Please explain in detail.

[0043] Reference Figure 3 , providing a heavily doped semiconductor substrate as a first heavily doped region 101, wherein the first heavily doped region 101 has the first conductivity type.

[0044] In some embodiments, the semiconductor substrate provided may be a silicon substrate. The resistivity of the first heavily doped region 101 is 0.0005Ω.cm-0.02Ω.cm.

[0045] The first conductivity type may be N-type, and its doping impurities may be N-type impurities, and the N-type impurities may be, for example, P, As, or Sb. The first conductivity type may also be P-type, and its doping impurities may be P-type impurities, and the P-type impurities may be, for example, B, Al. The following takes the first conductivity type being N-type and the second conductivity type being P-type as an example for explanation.

[0046] Afterwards, a drift region needs to be formed on the first heavily doped region 101 so that when the diode is reverse biased, minority carriers drift in a certain area, thereby enhancing the withstand voltage effect. In the embodiment of the present disclosure, the drift region includes multiple parts, which are described in detail below.

[0047] Reference Figure 4 , epitaxial growth is performed on the first heavily doped region 101 , and a first type of doping source gas is introduced during the epitaxial growth process to form an N-type first drift region 102 .

[0048] In a specific implementation, the first type of doping source gas may be phosphine (PH3), which may introduce N-type impurities into the growing first drift region 102 .

[0049] In some embodiments, the thickness of the first drift region 102 is 5 μm-200 μm, and the net doping concentration is 1e13 cm -3 -1e18cm -3 , the epitaxial growth temperature is 1000℃-1200℃.

[0050] In the process of epitaxial growth, determining the flow rate of the doping source gas is a key step. Due to the sensitivity of the doping concentration to the growth equipment and growth conditions, a doping gas flow deviation test is required. By changing the flow rate of the doping source gas, its effect on the impurity concentration of the formed epitaxial layer can be observed. The impurity concentration in the epitaxial layer after the growth is completed can be detected by spreading resistance profile (SRP), secondary ion mass spectrometry (SIMS) and other methods, which are correlated with the doping source gas flow rate during the epitaxial growth process, and the corresponding relationship between the two is summarized. The flow rate of the doping source gas is determined according to the final required doping concentration.

[0051] Reference Figure 5 , epitaxial growth is performed on the first drift region 102 , and the first type of doping source gas and the second type of doping source gas are introduced simultaneously during the epitaxial growth process to form an N-type drift adjustment zone 103 .

[0052] In a specific implementation, the first type of doping source gas may be phosphine (PH3), and the second type of doping source gas may be diborane (B2H6), and N-type impurities and P-type impurities may be introduced simultaneously into the growing drift adjustment band 103. The concentrations of N-type impurities and P-type impurities in the growing epitaxial layer may be detected by secondary ion mass spectrometry to determine the doping source gas flow rate required for the epitaxial growth process.

[0053] It should be noted that the drift adjustment band 103 is doped with both N-type impurities and P-type impurities. After the N-type impurities and the P-type impurities compensate each other, the final net doping concentration of the drift adjustment band 103 is N-type.

[0054] In some embodiments, the drift adjustment band 103 may include a sub-drift adjustment band, and the sum of the flow rates of the first type of dopant source gas and the second type of dopant source gas is greater than the flow rate of the dopant source gas forming the first drift region 102, so that the total doping concentration of the sub-drift adjustment band is higher than the total doping concentration of the first drift region 102. The drift adjustment band 103 and the PN structure of the diode form a stacked structure.

[0055] In some other embodiments, the drift adjustment band 103 may also include a plurality of stacked sub-drift adjustment bands ( Figure 5In the embodiment, three sub-drift adjustment bands 1031, 1032, and 1033 are taken as examples), the sum of the flow rates of the first type of doping source gas and the second type of doping source gas forming each of the sub-drift adjustment bands 1031, 1032, and 1033 is greater than the flow rate of the doping source gas forming the first drift region 102, so that the total doping concentration of the sub-drift adjustment bands 1031, 1032, and 1033 is higher than the total doping concentration of the first drift region 102, and the sum of the flow rates of the first type of doping source gas and the second type of doping source gas gradually increases from bottom to top, so that the total doping concentration of each sub-drift adjustment band 1031, 1032, and 1033 increases layer by layer from bottom to top. The multiple stacked sub-drift adjustment bands 1031, 1032, and 1033 form a stacked structure with the PN structure of the diode.

[0056] Since the multiple stacked sub-drift adjustment bands 1031 , 1032 , 1033 are formed in the same manner, they can be formed in the same epitaxial growth process, and different distributions of the total doping concentration in the longitudinal direction can be achieved only by controlling the flow rate of the doping source gas.

[0057] In some embodiments, Figure 5 Taking the three sub-drift adjustment bands 1031, 1032, and 1033 in the embodiment as an example, the thickness of the sub-drift adjustment bands 1031, 1032, and 1033 is 1 μm-50 μm, the epitaxial growth temperature is 1000°C-1200°C, and the net doping concentration is 1e13 cm -3 -1e18cm -3 , where the concentration of N-type impurities is 1e13cm -3 -1e18cm -3 , the concentration of P-type impurities is 1e13cm -3 -1e18cm -3 .

[0058] Reference Figure 6 , epitaxial growth is performed on the drift adjustment zone 103 , and the first type of doping source gas is introduced during the epitaxial growth process to form an N-type second drift region 104 .

[0059] In a specific implementation, the doping concentration in the growing epitaxial layer can be detected by using methods such as extended resistance testing and secondary ion mass spectrometry to determine the doping source gas flow rate required for the epitaxial growth process.

[0060] In some embodiments, the thickness of the second drift region 104 is 1 μm-50 μm, and the net doping concentration is 1e13 cm -3 -1e18cm -3 , the epitaxial growth temperature is 1000℃-1200℃.

[0061] After the above process, a drift region is formed, including the first drift region 102 , the drift adjustment zone 103 and the second drift region 104 , wherein the drift adjustment zone 103 includes one or more sub-drift adjustment zones.

[0062] Reference Figure 7 , a dielectric layer 105 is grown on the second drift region 104, and then a patterned first mask layer is formed on the dielectric layer 105. Using the first mask layer as a mask, the dielectric layer 105 is etched to form a process window exposing a portion of the upper surface of the second drift region 104, and the first mask layer is removed.

[0063] Specifically, the dielectric layer 105 may be formed by a thermal oxidation process, the patterned first mask layer may be a patterned photoresist layer, and the process window may be formed by a wet etching process or a dry etching process.

[0064] In some embodiments, the dielectric layer 105 is made of SiO 2 and has a thickness of 0.5 μm-2 μm.

[0065] Reference Figure 8 , using the retained dielectric layer 105 as a mask, an ion implantation process is used to perform ion implantation doping of P-type impurities on the second drift region 104 through the exposed process window, and then a high-temperature furnace tube is used to diffuse the injected P-type impurities to form a P-type second heavily doped region 106.

[0066] The doping depth of the ion implantation process may be less than the thickness of the second drift region 104, so that the second heavily doped region 106 formed is located in the second drift region 104. The doping depth of the ion implantation process may also be greater than the thickness of the second drift region 104, so that the second heavily doped region 106 formed will penetrate into the drift adjustment zone 103. The specific thickness of the second heavily doped region 106 is designed according to actual needs. The second heavily doped region 106 is doped with both N-type impurities and P-type impurities, and the final net doping concentration of the second heavily doped region 106 is P-type.

[0067] In some embodiments, the thickness of the second heavily doped region 106 is 1 μm-50 μm, and the net doping concentration is 1e17 cm -3 -1e19cm -3 The ion implantation energy is 40keV-200keV, and the ion implantation dose is 1e14cm -2 -2e16cm -2 The constant temperature range of the high temperature furnace tube is 800°C-1300°C, and the constant temperature time is 30min-24h.

[0068] After the above process, the first heavily doped region 101 and the second heavily doped region 106 are formed in the substrate with intervals, and the substrate includes the first heavily doped region 101, the drift region and the second heavily doped region 106. The first heavily doped region 101 and the second heavily doped region 106 constitute the N region and the P region of the diode. The interval between the first heavily doped region 101 and the second heavily doped region 106 constitutes the drift region, for example, the first drift region 102, the drift adjustment zone 103 and the second drift region 104 in this embodiment. The drift region is originally lightly doped, which can improve the voltage resistance of the diode and enable the diode to work stably in a high voltage environment. The drift adjustment zone 103 is located in the drift region and is used to accelerate the recombination speed of minority carriers during the reverse recovery process of the diode.

[0069] The drift region is doped with N-type impurities and the doping concentration is lower than that of the first heavily doped region 101 and the second heavily doped region 106, and the conductivity type of the drift region is N-type. The resistivity of the drift adjustment band 103 may be consistent with or inconsistent with the resistivity of the drift region. In some embodiments, the resistivity of the drift adjustment band 103 is consistent with the resistivity of the drift region. The drift adjustment band 103 may occupy part of the drift region or the entire drift region. This embodiment is described by taking the drift adjustment band 103 occupying part of the drift region as an example.

[0070] After the N-type impurities and P-type impurities of the sub-drift adjustment zones 1031 , 1032 , and 1033 compensate each other, their total doping concentration is higher than that of the drift region, and the final net doping concentration is lightly doped and exhibits N-type.

[0071] Reference Fig. 9 , a heavy metal layer 107 is formed on the second heavily doped region 106, and then the formed heavy metal layer 107 is diffused into the diode through high temperature heat treatment to form a recombination center.

[0072] Specifically, the heavy metal layer 107 may be formed by a physical vapor deposition (PVD) process, and the heavy metal layer 107 may be diffused into the diode by a high-temperature furnace tube diffusion process.

[0073] In some embodiments, the material of the heavy metal layer 107 is Pt or Au, and in order to achieve the saturated diffusion concentration of heavy metal impurities, the thickness of the heavy metal layer 107 is greater than 50 Å. The temperature of the high-temperature furnace tube diffusion process is 800°C-1000°C, and the diffusion time is 10min-120min, which can reduce the correlation between the heavy metal diffusion concentration and time.

[0074] After the heavy metal layer 107 diffuses into the interior of the diode, these heavy metal impurity atoms can occupy positions in the silicon lattice, thereby introducing energy level defects, which are recombination centers. The presence of the recombination centers makes it easier for minority carriers to be recombined during the reverse recovery process, reducing the lifetime of minority carriers, thereby reducing the reverse recovery time of the diode.

[0075] When the heavy metal impurities are saturated diffused, the doping concentration of the heavy metal impurities is related to the solid solubility at the corresponding diffusion temperature. The higher the diffusion temperature, the higher the doping concentration of the heavy metal impurities, the more recombination centers introduced, the shorter the minority carrier lifetime, and the shorter the reverse recovery time of the diode. The relationship between the reverse recovery time of the diode and the diffusion temperature is close to a linear relationship, so the reverse recovery time of the diode can be controlled by adjusting the diffusion temperature.

[0076] When the heavy metal impurities are saturated diffused, the doping concentration of the heavy metal impurities is also related to the total doping concentration of N-type impurities and P-type impurities in the diode. The concentration of the recombination centers introduced by heavy metal doping can be indirectly controlled by controlling the total doping concentration, thereby achieving control of the minority carrier lifetimes in different regions of the diode.

[0077] The total doping concentration of the drift adjustment band 103 is related to the reverse recovery time of the diode. In a specific implementation, the total doping concentration of the drift adjustment band 103 is determined according to the minority carrier lifetime required by the diode and the characteristics of the concentration of the heavy metal impurities related to the total doping concentration of the drift adjustment band 103.

[0078] In the embodiment of the present invention, the drift adjustment band 103 in which N-type impurities and P-type impurities deeply compensate each other is introduced into the drift region. The drift adjustment band 103 realizes a light net doping concentration through the mutual compensation of N-type impurities and P-type impurities, maintains a high blocking reverse voltage, and increases the total doping concentration of the drift adjustment band 103. In addition, by designing the direction from the drift adjustment band 103 to the second heavily doped region 106, the total doping concentration of each of the sub-drift adjustment bands 1031, 1032, and 1033 is distributed from low to high. This distribution realizes that in the initial stage of the reverse recovery of the diode, the minority carriers stored in the sub-drift adjustment bands closer to the PN junction interface are rapidly recombined due to the high concentration of the recombination center, so that the reverse recovery current increases from zero to the peak value I RM Time t a The reverse peak current I RMWhen the PN junction begins to reverse bias and the depletion layer widens accordingly, the concentration of the recombination center in the minority drift adjustment band far from the PN junction interface is relatively low, and the minority carrier lifetime in this area is relatively long, so that the reverse recovery current will not decrease very quickly, which will affect the reverse recovery current from the peak current I RM The time t b The effect is small, thus improving t b / t a , increasing the softness factor S of the diode.

[0079] Reference Fig.10 , forming a first electrode metal layer 108 on the dielectric layer 105 and the second heavily doped region 106, and then forming a patterned second mask layer on the first electrode metal layer 108, using the second mask layer as a mask, etching the first electrode metal layer 108 to form a desired pattern, and removing the second mask layer.

[0080] Specifically, the forming of the first electrode metal layer 108 may be implemented by a PVD process, the patterned second mask layer may be a patterned photoresist layer, and the etching of the first electrode metal layer 108 may be implemented by a wet etching process.

[0081] In some embodiments, the first electrode metal layer 108 is made of Al.

[0082] Reference Fig.11 , the lower surface of the first heavily doped region 101 is thinned to a required thickness. The first heavily doped region 101 after thinning is a part of the semiconductor substrate. Then, the mechanical damage layer and the stress layer on the lower surface of the first heavily doped region 101 are removed, and a second electrode metal layer 109 is formed on the lower surface of the first heavily doped region 101.

[0083] Specifically, the first heavily doped region 101 can be thinned by mechanical grinding, the removal of the mechanical damage layer and the stress layer on the lower surface of the first heavily doped region 101 can be achieved by a wet etching process, and the second electrode metal layer 109 can be formed by a PVD process.

[0084] In the embodiment of the present invention, the first electrode metal layer 108 and the second electrode metal layer 109 serve as the anode and cathode of the diode respectively.

[0085] The above description is made by taking the first conductivity type being N type and the second conductivity type being P type as an example. If the first conductivity type is P type and the second conductivity type is N type, the method of forming the diode is similar and will not be repeated here.

[0086] Fig.121 is a schematic diagram comparing the reverse recovery current waveforms of a diode in an embodiment of the present invention and a diode in the prior art. Fig.12 , where I F1 ,I RM1 ,t rr1 ,t a1 ,t b1 They are respectively the forward conduction current, reverse peak current, reverse recovery time, and the reverse recovery current from zero to peak value I of a diode in the prior art. RM1 time, the reverse recovery current from the peak value I RM1 Reduced to 20% of its time, I F2 ,I RM2 ,t rr2 ,t a2 ,t b2 They are respectively the forward conduction current, reverse peak current, reverse recovery time, and the reverse recovery current from zero to peak value I of a diode in an embodiment of the present invention. RM2 time, the reverse recovery current from the peak value I RM2 It can be found that the forward conduction current of the two diodes is the same, and the reverse recovery time t of the diode in the embodiment of the present invention is rr2 Compared to rr1 Shorter, reverse peak current I RM2 Less than I RM1 , t a2 Less than t a1 And t b2 With t b1 Therefore, the softness factor t of a diode in the embodiment of the present invention is b2 / t a2 Greater than the softness factor t of a diode in the prior art b1 / t a1 , a diode in the embodiment of the present invention has better soft recovery characteristics. The reverse recovery characteristic indicators of a diode in the embodiment of the present invention and a diode in the prior art are summarized in the following Table 1:

[0087] Table 1. Comparison of reverse recovery characteristics of a diode in an embodiment of the present invention and a diode in the prior art

[0088]

[0089] In an embodiment of the present invention, a diode is also provided. Fig.11The diode comprises: a first heavily doped region 101 and a second heavily doped region 106 with an interval, the first heavily doped region 101 having a first conductivity type, the second heavily doped region 106 having a second conductivity type, the first conductivity type and the second conductivity type being opposite, the interval between the first heavily doped region 101 and the second heavily doped region 106 constituting a drift region, the drift region being doped with impurities of the first conductivity type and having a doping concentration lower than that of the first heavily doped region 101 and the second heavily doped region 106, the drift region having the first conductivity type; the diode further comprises: a drift adjustment band 103, located in at least a portion of the drift region, for adjusting the recombination velocity of minority carriers, the drift adjustment band 103 having the first conductivity type, the drift adjustment band 103 being doped with impurities of the first conductivity type and impurities of the second conductivity type, the total doping concentration of the drift adjustment band 103 being higher than the doping concentration of the drift region.

[0090] Furthermore, the drift adjustment band 103 includes a sub-drift adjustment band.

[0091] Further, the drift adjustment zone 103 includes a plurality of stacked sub-drift adjustment zones, and the total doping concentration of the sub-drift adjustment zones gradually increases along a direction from the drift adjustment zone 103 to the second heavily doped region 106 .

[0092] Furthermore, the drift adjustment band 103 includes three stacked sub-drift adjustment bands 1031, 1032, 1033, each of which has a thickness of 1 μm-50 μm and a net doping concentration of 1e13 cm -3 -1e18cm -3 .

[0093] Furthermore, the drift region contains heavy metal impurities, and the concentration of the heavy metal impurities is related to the total doping concentration of the drift adjustment zone 103 .

[0094] Furthermore, the total doping concentration of the drift adjustment band 103 is related to the reverse recovery time of the diode.

[0095] Furthermore, the material of the heavy metal impurities is Pt or Au.

[0096] Furthermore, the first conductivity type and the second conductivity type are N type or P type.

[0097] For more information about the principle, specific implementation and beneficial effects of the diode, please refer to the previous description of a method for forming a diode, which will not be repeated here.

[0098] In an embodiment of the present invention, by setting the drift adjustment band 103 in which N-type impurities and P-type impurities compensate each other in the drift region of the diode, the net doping concentration of the drift adjustment band 103 is lightly doped, and the total doping concentration of the drift adjustment band 103 is increased, which helps to accelerate the recombination of minority carriers when the diode recovers in reverse.

[0099] Further, according to the minority carrier lifetime required by the diode and the characteristics of the concentration of heavy metal impurities related to the total doping concentration of the drift adjustment band 103, the total doping concentration of the drift adjustment band 103 can be determined. For this purpose, heavy metal impurities are introduced into the drift adjustment band 103 to form a recombination center, thereby reducing the reverse recovery time of the diode. In this way, by controlling the total doping concentration of the drift adjustment band 103, the concentration of the recombination center introduced by the heavy metal impurities is indirectly controlled, thereby achieving minority carrier lifetime control in each region of the drift adjustment band 103, forming a controllable diode soft switching characteristic.

[0100] The following provides a specific embodiment of a diode formed by the diode forming method of the present invention. Fig.11 The reverse working voltage of the diode is 1200V, and the maximum forward conduction current is 20A (refer to Table 1 for the reverse recovery characteristic index of the diode). The diode includes:

[0101] The first heavily doped region 101 is an N-type silicon substrate with a thickness greater than 100 μm and doped with As impurities at a doping concentration of 2.3e19 cm -3 ;

[0102] The first drift region 102 is N-type lightly doped, with a thickness of 50 μm, and is doped with P impurities at a doping concentration of 1e14 cm -3 The epitaxial growth temperature of the first drift region 102 is 1100° C., the epitaxial growth rate is 2 μm / min, the doping source gas is phosphine (PH3 and H2 mixed gas, PH3 ratio is 30 PPM), and the doping source gas flow rate is 70 ml / min;

[0103] The drift adjustment zone 103 includes sub-drift adjustment zones 1031, 1032, and 1033. The sub-drift adjustment zones 1031, 1032, and 1033 are N-type and P-type impurities deeply compensate each other, have the same net doping concentration, and are N-type. The total doping concentration of the sub-drift adjustment zones 1031, 1032, and 1033 gradually increases along the direction from the drift adjustment zone 103 to the second heavily doped region 106. The epitaxial growth temperature of the drift adjustment zone 103 is 1100°C, the epitaxial growth rate is 2μm / min, and the doping source gas is phosphine (PH3 and H2 mixed gas, PH3 ratio is 30PPM) and diborane (B2H6 and H2 mixed gas, B2H6 ratio is 30PPM). The thickness of the sub-drift adjustment zone 1031 is 30μm, and the doping impurities are P and B, wherein the doping concentration of P is 1.1e15cm -3 , the doping concentration of B is 1e15cm -3 , corresponding to a net doping concentration of 1e14cm -3 The thickness of the sub-drift adjustment band 1032 is 20 μm, and the doping impurities are P and B, wherein the doping concentration of P is 5.1e15 cm -3 , the doping concentration of B is 5e15cm -3 , corresponding to a net doping concentration of 1e14cm -3 The thickness of the sub-drift adjustment band 1033 is 10 μm, and the doping impurities are P and B, wherein the doping concentration of P is 1.01e16 cm -3 , the doping concentration of B is 1e16cm -3 , corresponding to a net doping concentration of 1e14cm -3 ;

[0104] The second drift region 104 is N-type lightly doped, with a thickness of 15 μm, and is doped with P impurities at a doping concentration of 1e14 cm -3 , the epitaxial growth temperature is 1100°C, the epitaxial growth rate is controlled to be 2μm / min, and the doping source gas is phosphine;

[0105] The second heavily doped region 106 is formed in the second drift region 104. The second drift region 104 is doped with B ions by an ion implantation process, wherein the ion implantation energy is 60 keV and the ion implantation dose is 2e15 cm -2 Then, a furnace tube is used for high temperature diffusion, the diffusion temperature is 1200° C., and the diffusion time is 300 minutes, and finally the second heavily doped region 106 of heavily doped P type is formed in the second drift region 104;

[0106] Heavy metal impurities Pt, the heavy metal impurities Pt are located in the diode. The step of forming the heavy metal impurities Pt includes: forming a Pt heavy metal layer with a thickness of 100Å on the surface of the second heavily doped region 106, and then diffusing it in a high-temperature furnace tube so that Pt atoms diffuse into the diode, wherein the furnace tube diffusion temperature is 900°C and the diffusion time is 30 minutes.

[0107] The first heavily doped region 101 serves as a cathode of the diode, and the second heavily doped region 106 serves as an anode of the diode.

[0108] It should be understood that the term "and / or" herein is merely an association relationship describing associated objects, indicating that three relationships may exist, for example, A and / or B may represent: A exists alone, A and B exist at the same time, and B exists alone. In addition, the character " / " herein indicates that the associated objects before and after are in an "or" relationship. As used herein, unless otherwise expressly stated, the term "or" covers all possible combinations unless not feasible. For example, if a component is stated to include A or B, then unless otherwise expressly stated or not feasible, the component may include A, or B, or A and B. As a second example, if a component is stated to include A, B, or C, then unless otherwise expressly stated or not feasible, the component may include A, or B, or C, or A and B, or A and C, or B and C, or A and B and C.

[0109] The "plurality" appearing in the embodiments of the present application refers to two or more.

[0110] Relational terms appearing in the embodiments of the present application, such as first, second, etc., are only used to distinguish an entity or operation from another entity or operation, and do not require or imply any actual relationship or order between these entities or operations. In addition, the words "include", "have", "include" and other similar forms are intended to be equivalent in meaning and are open-ended, and one or more items following any of these words are not meant to be an exhaustive list of such one or more items, or to be limited to the listed one or more items.

[0111] It should be pointed out that the serial numbers of the steps in this embodiment do not limit the execution order of the steps.

[0112] In the foregoing description, embodiments have been described with reference to many specific details, which may vary depending on the implementation. Certain changes and modifications may be made to the described embodiments. In view of the description and practice of the present application disclosed herein, other embodiments will be clear to those skilled in the art. The description and examples are intended to be considered as merely exemplary, and the true scope and spirit of the present application are indicated by the following claims. The order of steps shown in the accompanying drawings is also intended to be used for illustrative purposes only and is not intended to be limited to any particular order of steps. Therefore, it will be appreciated by those skilled in the art that these steps may be performed in different orders while implementing the same method.

[0113] In the drawings and the specification, exemplary embodiments have been disclosed. However, many variations and modifications may be made to these embodiments. Therefore, although specific terms are employed, they are used only in a general and descriptive sense and not for the purpose of limitation.

[0114] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A diode, comprising: A first heavily doped region and a second heavily doped region having an interval, the first heavily doped region having a first conductivity type, the second heavily doped region having a second conductivity type, the first conductivity type and the second conductivity type being opposite, the interval between the first heavily doped region and the second heavily doped region constituting a drift region, the drift region being doped with impurities of the first conductivity type and having a lower doping concentration than the first heavily doped region and the second heavily doped region, the drift region having the first conductivity type; Characterized in that the diode further comprises: a drift adjustment band, located in at least a portion of the drift region, for adjusting the minority carrier recombination velocity, the drift adjustment band having the first conductivity type, doped with impurities of the first conductivity type and impurities of the second conductivity type, and having a total doping concentration higher than that of the drift region; The drift region contains heavy metal impurities, and the concentration of the heavy metal impurities is related to the total doping concentration of the drift adjustment zone.

2. The diode according to claim 1, characterized in that The drift adjustment band includes a sub-drift adjustment band.

3. The diode according to claim 1, characterized in that The drift adjustment zone includes a plurality of stacked sub-drift adjustment zones, and a total doping concentration of the sub-drift adjustment zones gradually increases along a direction from the drift adjustment zone to the second heavily doped region.

4. The diode according to claim 3, characterized in that The drift adjustment band includes three stacked sub-drift adjustment bands, each of which has a thickness of 1 μm-50 μm and a net doping concentration of 1e13 cm -3 -1e18cm -3 .

5. The diode according to claim 1, characterized in that The total doping concentration of the drift adjustment band is related to the reverse recovery time of the diode.

6. The diode according to claim 1, characterized in that The material of the heavy metal impurities is Pt or Au.

7. The diode according to claim 1, characterized in that The first conductivity type and the second conductivity type are N type or P type.

8. A method for forming a diode, comprising: A first heavily doped region and a second heavily doped region are formed with a gap in the substrate, the first heavily doped region has a first conductivity type, the second heavily doped region has a second conductivity type, the first conductivity type is opposite to the second conductivity type, the gap between the first heavily doped region and the second heavily doped region constitutes a drift region, the drift region is doped with impurities of the first conductivity type and the doping concentration is lower than that of the first heavily doped region and the second heavily doped region, and the drift region has the first conductivity type; Characterized in that the method further comprises: forming a drift adjustment band in at least a portion of the drift region, the drift adjustment band having the first conductivity type, the drift adjustment band being doped with impurities of the first conductivity type and impurities of the second conductivity type, and the total doping concentration of the drift adjustment band being higher than the doping concentration of the drift region; The method further comprises: The step of doping heavy metal impurities in the diode, wherein the concentration of the heavy metal impurities is related to the total doping concentration of the drift adjustment band.

9. The method for forming a diode according to claim 8, characterized in that: The first heavily doped region and the second heavily doped region formed with a gap in the substrate include: Providing a semiconductor substrate of the first conductivity type, wherein a portion of the semiconductor substrate serves as the first heavily doped region; Epitaxial growth is performed on the semiconductor substrate to form the drift region and the second heavily doped region.

10. The method for forming a diode according to claim 9, characterized in that: The drift region includes a first drift region, and forming the first drift region includes: Epitaxial growth is performed on the first heavily doped region, and a first type of doping source gas is introduced during the epitaxial growth process.

11. The method for forming a diode according to claim 10, characterized in that: The drift adjustment band includes a sub-drift adjustment band, and forming the sub-drift adjustment band includes: Epitaxial growth is performed on the first drift region to form the sub-drift adjustment band. During the epitaxial growth process, the first type of doping source gas and the second type of doping source gas are simultaneously introduced, and the sum of the flow rates of the first type of doping source gas and the second type of doping source gas is greater than the flow rate of the doping source gas forming the first drift region.

12. The method for forming a diode according to claim 10, characterized in that: The drift adjustment band includes a plurality of sub-drift adjustment bands, and forming the sub-drift adjustment bands includes: Multiple epitaxial growths are performed on the first drift region to form multiple stacked sub-drift adjustment bands, and the first type of doping source gas and the second type of doping source gas are introduced simultaneously during each epitaxial growth process, so that the sum of the flow rates of the first type of doping source gas and the second type of doping source gas forming each sub-drift adjustment band is greater than the flow rate of the doping source gas forming the first drift region, and the sum of the flow rates of the first type of doping source gas and the second type of doping source gas gradually increases in the direction from the drift adjustment band to the second heavily doped region.

13. The method for forming a diode according to claim 11 or 12, characterized in that: The drift region further includes a second drift region, and forming the second drift region includes: Epitaxial growth is performed on the drift adjustment band, and the first type of doping source gas is introduced during the epitaxial growth process.

14. The method for forming a diode according to claim 13, characterized in that: The first heavily doped region and the second heavily doped region formed with a gap in the substrate include: Performing ion implantation doping of the second conductivity type impurities on the second drift region; The implanted impurities of the second conductivity type are diffused at high temperature to form the second heavily doped region.

15. The method for forming a diode according to claim 14, characterized in that: The step of doping with heavy metal impurities comprises: forming a heavy metal layer on the surface of the second heavily doped region; The formed heavy metal layer is subjected to high temperature diffusion.

16. The method for forming a diode according to claim 15, characterized in that: The thickness of the heavy metal layer is greater than 50Å.

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