JP4244074B2 - Manufacturing method of MONOS type semiconductor nonvolatile memory transistor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
  The present invention relates to a semiconductor nonvolatile memory transistorTo the manufacturing methodIn particular, the memory characteristics of a semiconductor nonvolatile memory transistor called a MONOS (Metal Oxide Nitride Oxide Semiconductor) type in which the memory insulating film is composed of a tunnel insulating film, a memory nitride film, and a top oxide film are improved and the reliability is improved. It is about technology.
[0002]
[Prior art]
  In general, the information in the MONOS type semiconductor nonvolatile memory transistor is rewritten by applying a bias voltage to the memory gate electrode, through the tunnel insulating film from the semiconductor substrate and in the memory nitride film and between the tunnel insulating film and the memory nitride film. In addition, electrons or holes are injected into the interface between the memory nitride film and the top oxide film.
[0003]
  Here, the structure of an N channel type transistor of a conventional MONOS type semiconductor nonvolatile memory transistor will be described with reference to a schematic cross-sectional view shown in FIG.
  As shown in FIG. 25, a field oxide film 2 is provided around a memory element region on the surface of a semiconductor substrate 1 having a P-type conductivity type (first conductivity type), and on the memory element region of the semiconductor substrate 1. The provided tunnel insulating film 31, memory nitride film 5 and top oxide film 6 constitute a memory insulating film 8, and a memory gate electrode 9 is provided on the memory insulating film 8 to constitute a MONOS structure.
[0004]
  Further, the memory element region of the semiconductor substrate 1 is provided with a source 10 and a drain 11 made of a high-concentration impurity layer exhibiting an N-type conductivity type (second conductivity type) self-aligned with the memory gate electrode 9. .
  Then, a multilayer wiring insulating film 12 mainly composed of a silicon dioxide film is provided on the entire surface of the semiconductor substrate 1, and the source 10, the drain 11, and the like are connected through the contact holes 13 formed in the multilayer wiring insulating film 12. Although not shown, wirings 14 connected to the memory gate electrodes 9 are provided.
[0005]
  Information rewriting in such a conventional MONOS type semiconductor nonvolatile memory transistor is performed by applying a bias voltage to the memory gate electrode 9.
  That is, in the case of an N-channel type memory transistor, a positive bias voltage is applied to the memory gate electrode 9 and the semiconductor substrate 1 and the source 10 and the drain 11 are grounded, so that the semiconductor substrate 1 passes through the tunnel insulating film 31. Electrons are injected into the memory insulating film 8 and captured in the memory nitride film 5, at the interface between the tunnel insulating film 31 and the memory nitride film 5, and at the interface between the memory nitride film 5 and the top oxide film 6.
[0006]
  The threshold voltage of the N-channel MONOS type semiconductor nonvolatile memory transistor that has captured the electrons becomes higher than usual. That is, an enhancement operation is performed. This case is called a write state.
[0007]
  On the contrary, when the memory gate electrode 9 is grounded and a positive bias voltage is applied to the semiconductor substrate 1 and the source 10 and drain 11, holes are injected from the semiconductor substrate 1 through the tunnel insulating film 31 into the memory insulating film 8. Then, holes are trapped in the memory nitride film 5, the interface between the tunnel insulating film 31 and the memory nitride film 5, and the interface between the memory nitride film 5 and the top oxide film 6.
[0008]
  The threshold voltage of the N-channel MONOS semiconductor nonvolatile memory transistor that captures the holes is lower than usual. That is, a depletion operation is performed. This case is called an erased state.
  As described above, the MONOS type semiconductor nonvolatile memory transistor writes information in a writing state or an erasing state by injecting electrons or holes from the semiconductor substrate 1 to the memory insulating film 8 through the tunnel insulating film 31. .
[0009]
  In the case of a P-channel memory transistor, the relationship between the polarity of the bias voltage and the writing state and the erasing state is opposite to that of the N-channel memory transistor described above, and holes are injected. When electrons are injected in the written state, the erased state is entered.
  In any case, the information rewriting operation in the MONOS type semiconductor nonvolatile memory transistor largely depends on the film thickness, material, and film quality of the tunnel insulating film 31.
[0010]
  For example, when the thickness of the tunnel insulating film 31 is increased, the efficiency of injection of electrons and holes from the semiconductor substrate is reduced, so that the writing speed is reduced and the trapping amount is reduced due to the reduced amount of electrons and holes injected. It becomes difficult to write information.
  Therefore, conventionally, the tunnel insulating film 31 is constituted by a silicon oxynitride film formed by nitriding a silicon oxide film.
  The operation of this silicon oxynitride film will be described with reference to the energy band diagram shown in FIG.
[0011]
  The energy band diagram shown in FIG. 26 shows the energy state in the vertical direction and the film configuration of the memory insulating film 8 of the MONOS type semiconductor nonvolatile memory transistor in the horizontal direction.
  This energy band diagram shows an erasing operation of an N-channel MONOS type semiconductor nonvolatile memory transistor when a positive bias voltage is applied to the semiconductor substrate 1, and the film configuration is inclined according to the bias. Show.
[0012]
  When the tunnel insulating film 31 in the memory insulating film 8 is constituted by the silicon oxide film 32 indicated by the broken line, the barrier (lower side in FIG. 26) of the silicon oxide film 32 to the holes of the semiconductor substrate 1 is about 3. 8 eV, which is higher than about 3.2 eV of the barrier (upper side in FIG. 26) of the silicon oxide film 32 against electrons.
  For this reason, when the silicon oxide film 32 is used as the tunnel insulating film 31, the writing speed on the erase side for injecting holes generally decreases.
[0013]
  Therefore, as a means of improving the speed on the erase side, the memoryInsulation filmA silicon oxynitride film obtained by nitriding the silicon oxide film 32 is used as the tunnel insulating film 31 constituting the structure 8.
  That is, by using the silicon oxynitride film 3 as shown by the solid line in FIG. 26 in place of the silicon oxide film 32, the barrier against holes in the semiconductor substrate 1 (lower side in FIG. 26) becomes about 3.3 eV, The value is smaller than the barrier (about 3.8 eV) of the silicon oxide film 32. As a result, the hole injection efficiency is improved and the erase operation can be accelerated.
[0014]
  However, the barrier of tunnel insulating film 31 as viewed from the holes trapped in memory nitride film 5 and at the interface between tunnel insulating film 31 and memory nitride film 5 and at the interface between memory nitride film 5 and top oxide film 6 also decreases. Therefore, there is a problem that holes are likely to escape to the semiconductor substrate 1 side and data retention characteristics are deteriorated.
  In the case of a P-channel MONOS type semiconductor nonvolatile memory transistor, the hole injection efficiency can be improved to speed up the write operation, but the trapped holes can easily escape to the semiconductor substrate 1 side. Therefore, there is still a problem that the data retention characteristic is deteriorated.
[0015]
[Problems to be solved by the invention]
  As described above, even in the conventional MONOS type semiconductor nonvolatile memory transistor, by using the silicon nitride oxide film as the tunnel insulating film constituting the memory insulating film, the hole injection efficiency in the erasing operation or the writing operation is improved. The erase operation or the write operation can be speeded up.
[0016]
  However, by using a silicon oxynitride film as the tunnel insulating film, the memory nitride film in the memory insulating film and the interface between the tunnel insulating film and the memory nitride film, and the memory nitride film and the top oxide film can be erased or written. The barrier of the tunnel insulating film as viewed from the holes trapped at the interface with the substrate becomes lower, and the holes easily escape to the semiconductor substrate side, which causes a problem that data retention characteristics deteriorate.
[0017]
  The present invention has been made to solve such a problem, and it is possible to speed up an erasing operation or a writing operation without deteriorating data retention characteristics of a MONOS type semiconductor nonvolatile memory transistor. Objective.
  for that reason, Rewrite speedIs fastData retention characteristicsIs good,reliableMONOS typeSemiconductor non-volatile memory transistorEasy to manufactureA manufacturing method is provided.
[0018]
[Means for Solving the Problems]
  In order to achieve the above object, the present invention provides the followingMONOS typeSemiconductor non-volatileManufacturing method of memory transistorI will provide a.
[0019]
[0020]
[0021]
  That is,According to this inventionMONOS typeA method for manufacturing a semiconductor nonvolatile memory transistor includes providing a tunnel insulating film on a semiconductor substrate, providing a memory nitride film on the tunnel insulating film, and providing a top oxide film made of a silicon oxide film on the memory nitride film, Memory insulating filmMONOS typeA method for manufacturing a semiconductor nonvolatile memory transistor, comprising the following steps.
[0022]
[0023]
[0024]
[0025]
[0026]
[0027]
  That is, the surface of the semiconductor substrate is dinitrogen monoxide (N₂O) forming a silicon oxynitride film functioning as the tunnel insulating film by processing in an atmosphere;
  Subsequently, the vicinity of the surface of the silicon oxynitride film is heat-treated in an oxygen atmosphere,Memory nitride filmAnd a step of forming an oxygen-rich silicon oxynitride film having a large oxygen content in the vicinity of the side interface.
[0028]
  OrForming a silicon oxide film on the semiconductor substrate by an oxidation process;
  After nitrogen ions are implanted into the silicon oxide film, heat treatment is performed in a nitrogen atmosphere containing oxygen, so that the nitrogen content is greater than the oxygen content near the interface on the semiconductor substrate side, and near the interface on the memory nitride film side. You may make it implement the process of forming the said tunnel insulating film that oxygen content becomes larger than nitrogen content.
[0029]
  Or a step of forming a silicon oxide film on the semiconductor substrate by an oxidation treatment;
  Nitriding the silicon oxide film to form a silicon nitride oxide film, forming a thin film silicon oxide film on the surface of the silicon nitride oxide film on the memory nitride film side by a CVD method, and forming the tunnel insulating film; It can also be implemented.
[0030]
DETAILED DESCRIPTION OF THE INVENTION
  Hereinafter, this inventionManufactured by the manufacturing methodMONOS type semiconductor nonvolatile memory transistor structure and method of manufacturing the sameWith drawingsThis will be described in detail.
[0031]
[MONOS typeSemiconductor non-volatile memory transistor: FIGS. 1 and 17]
  This inventionManufactured by the manufacturing methodMONOS type semiconductor nonvolatile memory transistorStructure ofWill be described with reference to the schematic cross-sectional view of FIG. This MONOS type semiconductor nonvolatile memory transistor is shown as an N-channel type semiconductor device.
[0032]
  In the MONOS type semiconductor nonvolatile memory transistor shown in FIG. 1, a field oxide film 2 is provided around the memory element region on the surface of a semiconductor substrate 1 whose conductivity type is P type (first conductivity type).
[0033]
  A tunnel insulating film 31 comprising a silicon oxynitride film 3 and an oxygen-rich silicon oxynitride film 4 is provided on the semiconductor substrate 1, and the tunnel insulating film 31, the memory nitride film 5 and the top oxide film 6 provided thereon are provided. And the memory insulating film 8 is formed, and the memory gate electrode 9 is provided thereon.
[0034]
  The tunnel insulating film 31 is a silicon oxynitride film containing oxygen and nitrogen, and the underlying silicon oxynitride film 3 is made of silicon, oxygen, and nitrogen, and the content of nitrogen is higher than the content of oxygen. is there. The upper oxygen-rich silicon oxynitride film 4 is also an insulating film made of silicon, oxygen, and nitrogen and having an oxygen content higher than the nitrogen content.
[0035]
  The specific composition ratio between the silicon oxynitride film 3 and the oxygen-rich silicon oxynitride film 4 constituting the tunnel insulating film 31 is obtained by X-ray photoelectron spectroscopy.
When estimated as the composition ratio of SiOx Ny,
  The silicon oxynitride film 3 has x = 0.5, y = 0.7,
  The oxygen-rich silicon oxynitride film 4 has x = 1.1 and y = 0.3.
An insulating film having a composition ratio of
[0036]
  Further, a source 10 and a drain 11 made of a high-concentration impurity layer whose conductivity type is N-type (second conductivity type) are provided on the surface of the semiconductor substrate 1 so as to be self-aligned with the memory gate electrode 9.
  Then, an insulating film 12 for multilayer wiring mainly comprising a silicon dioxide film is provided on the entire surface,
Wirings 14 connected to the source 10, the drain 11 and the memory gate electrode 9 (not shown) are provided through the contact holes 13 formed in the insulating film 12 for multilayer wiring.
[0037]
  In this MONOS type semiconductor nonvolatile memory transistor, the tunnel insulating film is composed of a silicon oxynitride film containing oxygen and nitrogen, and in the vicinity of the interface with the semiconductor substrate 1IsNitrogen content isConsists of silicon oxynitride film with more oxygen contentNear the interface with the memory nitride film 5Has oxygen contentMore than nitrogen contentOxygen-rich silicon nitride oxide filmThere is a feature in that.
[0038]
  As a result, the barrier of the tunnel insulating film 31 against holes in the semiconductor substrate is reduced by the silicon oxynitride film having a high nitrogen content, so that the efficiency of hole injection into the memory insulating film 8 is improved, and the N-channel MONOS semiconductor The erase operation of the nonvolatile memory transistor can be speeded up.
  However, the barrier of the tunnel insulating film 31 viewed from the holes trapped in the memory nitride film 5 or the like is kept large by the oxygen-rich silicon oxynitride film having a low nitrogen content, and the holes are difficult to escape to the semiconductor substrate side. Therefore, it is possible to prevent a decrease in data retention characteristics. Details of this operation and effect will be described later.
[0039]
  As shown in FIG.MONOS type semiconductor nonvolatile memory transistorThen, the vicinity of the interface between the tunnel insulating film 31 and the semiconductor substrate 1 is composed of the silicon oxynitride film 3 having a nitrogen content higher than the oxygen content, and the oxygen content near the interface with the memory nitride film 5 is higher than the nitrogen content. It consists of an oxygen-rich silicon oxynitride film 4.
  However, the tunnel insulating film of the MONOS type semiconductor nonvolatile memory transistor according to the present invention is not limited to this film configuration.
  For example, the MONOS type semiconductor nonvolatile memory transistor according to the present invention shown in FIG.likeThe tunnel insulating film 31 may be formed of the silicon nitride oxide film 3 in the vicinity of the interface with the semiconductor substrate 1 and the thin film silicon oxide film 41 in the vicinity of the interface with the memory nitride film 5.
[0040]
  Also, the aboveExampleIs N channel typeMONOS typeIn the case of a P-channel semiconductor device, the semiconductor substrate 1 is an N-type semiconductor substrate, and the source 10 and the drain 11 are P-type high-concentration impurities. The other structure is the same as that of the MONOS type semiconductor nonvolatile memory transistor shown in FIG.
  AndPIn the case of a channel type MONOS type semiconductor nonvolatile memory transistor, the write operation can be speeded up by improving the efficiency of hole injection into the memory insulating film 8. In addition, holes trapped in the memory nitride film 5 and the like are not easily released to the semiconductor substrate side, and deterioration of data retention characteristics can be prevented.
[0041]
[Manufacturing methodBasic example: FIGS. 1 to 16]
  Next, a method of manufacturing a MONOS type semiconductor nonvolatile memory transistor according to the present invention will be described.Basic exampleWill be explained.
  First, a manufacturing method of the MONOS type semiconductor nonvolatile memory transistor shown in FIG. 1 will be described with reference to FIGS. 2 to 16 are schematic cross-sectional views sequentially showing each stage of the process of manufacturing the MONOS type semiconductor nonvolatile memory transistor shown in FIG.
[0042]
  First, as shown in FIG. 2, a semiconductor substrate 1 having a P conductivity type is oxidized in a mixed gas of oxygen and nitrogen, and a pad oxide film 21 made of a silicon dioxide film having a thickness of 30 nm is formed on the semiconductor substrate 1. On the entire surface.
[0043]
  Next, dichlorosilane (SiH) is formed on the entire surface of the pad oxide film 21.₂Cl₂) And ammonia (NH₃), A silicon nitride film 22 made of a silicon nitride film is formed to a thickness of about 150 nm by a CVD method at a temperature of 740 ° C.
[0044]
  Then, as shown in FIG. 3, a photoresist 51, which is a photosensitive material, is formed on the entire surface of the silicon nitride film 22, and exposure and development are performed using a predetermined photomask. The photoresist 51 is patterned so as to open the field region.
[0045]
  Thereafter, using this photoresist 51 as an etching mask, as shown in FIG. 4, the field region portion of the silicon nitride film 22 is removed by etching. The etching of the silicon nitride film 22 is performed using SF.₆+ CHF₃A dry etching method is performed using a mixed gas of + He.
  Then, the photoresist 51 used as an etching mask is removed.
[0046]
  Next, the field region around the memory element region of the semiconductor substrate 1 and the pad oxide film 21 is oxidized using the silicon nitride film 22 as an oxidation resistant mask. By this so-called selective oxidation treatment, a field oxide film 2 is formed with a thickness of 700 nm in the field region as shown in FIG.
  This selective oxidation treatment is performed at a temperature of 1000 ° C. in a steam oxidation atmosphere.
[0047]
  Then, hot phosphoric acid (H₃PO₄), And the pad oxide film 21 is removed by etching with a hydrofluoric acid buffer solution. FIG. 6 shows a state in which the silicon nitride film 22 and the pad oxide film 21 are removed by these steps.
[0048]
  Next, an oxidation process is performed in a mixed gas of oxygen and nitrogen to form a sacrificial oxide film 23 made of a silicon dioxide film having a thickness of about 20 nm as shown in FIG. The sacrificial oxide film 23 is removed by etching with a hydrofluoric acid buffer.
  The formation and removal of the sacrificial oxide film 23 is performed in order to improve the reliability of the memory insulating film formed in the subsequent processing steps.
[0049]
  That is, when the field isolation film 2 for element isolation is formed by the selective oxidation process as described above, the nitrogen constituting the silicon nitride film 22 reacts with the hydrogen in the water vapor atmosphere during the selective oxidation process, and ammonia is converted. Form.
  Therefore, a silicon nitride film is formed in the vicinity of the interface between the pad oxide film 21 and the semiconductor substrate 1 by the reaction of ammonia, and this silicon nitride film acts as an oxidation mask in a subsequent process, and the film thickness of the memory insulating film is not uniform. As a result, the reliability is lowered. In order to eliminate this phenomenon, the sacrificial oxide film 23 is formed and removed.
[0050]
  Next, oxidation treatment is performed in a mixed gas of oxygen and nitrogen, and a silicon oxide film 24 made of a silicon dioxide film having a thickness of about 2.2 nm is formed on the entire surface of the memory element region of the semiconductor substrate 1 as shown in FIG. Form.
  Then, this silicon oxide film 24 is formed by using ammonia (NH₃) Nitriding is performed in an atmosphere to form a silicon oxynitride film 3 on the entire surface of the memory element region of the semiconductor substrate 1 as shown in FIG.
[0051]
  Thereafter, an oxidation treatment is performed in a nitrogen atmosphere containing about 0.2% oxygen at a temperature of 900 ° C. to form an oxygen-rich silicon nitride oxide film 4 on the surface of the silicon nitride oxide film 3 as shown in FIG. Then, a tunnel insulating film 31 composed of the silicon oxynitride film 3 and the oxygen-rich silicon oxynitride film 4 is formed.
[0052]
  By this treatment in a nitrogen atmosphere containing a small amount of oxygen, the tunnel insulating film 31 is changed to the silicon oxynitride film 3 having a nitrogen content higher than the oxygen content on the semiconductor substrate 1 side. The upper layer can be an oxygen-rich silicon oxynitride film 4 having a low nitrogen content.
[0053]
  Next, as shown in FIG. 11, a memory nitride film 5 made of a silicon nitride film is formed on the entire surface including the tunnel insulating film 31 by a CVD method to a thickness of about 9 nm. The memory nitride film 5 is formed by dichlorosilane (SiH₂Cl₂) And ammonia (NH 3) gas at a temperature of 700 ° C. by a CVD method.
[0054]
  Further, oxidation is performed in a steam oxidation atmosphere at a temperature of 950 ° C. to oxidize the memory nitride film 5 and form a top oxide film 6 made of a silicon dioxide film on the memory nitride film 5.
  By this oxidation treatment, the thickness of the memory nitride film 5 becomes about 7 nm, and the thickness of the top oxide film 6 becomes about 3 nm.
[0055]
  In addition, monosilane (SiH₄), A memory gate electrode material 9b made of a polycrystalline silicon film is formed on the entire surface to a thickness of about 450 nm by a CVD method at a temperature of 600 ° C.
[0056]
  Next, after a photoresist is formed on the entire surface, exposure and development are performed using a predetermined photomask to form a photoresist 52 in a region where a memory gate electrode is to be formed as shown in FIG.
[0057]
  Thereafter, using this photoresist 52 as an etching mask, the polycrystalline silicon film as the memory gate electrode material 9b is formed into SF.₆+ O₂Etching is performed by a dry etching method using a mixed gas of
[0058]
  Next, similarly, using the photoresist 52 as an etching mask, the top oxide film 6, the memory nitride film 5, the oxygen-rich silicon nitride oxide film 4, and the silicon nitride oxide film 3 are CF₄+ He + CBrF₃+ O₂ Etching is performed by a dry etching method using a mixed gas of Thereafter, the photoresist 52 is removed.
[0059]
  As a result, as shown in FIG. 13, the tunnel insulating film 31 formed of the silicon nitride oxide film 3 and the oxygen-rich silicon nitride oxide film 4 provided on the semiconductor substrate 1, the memory nitride film 5, and the top oxide film 6 are formed. A MONOS structure including the memory insulating film 8 and the memory gate electrode 9 is formed.
[0060]
  Next, using the memory gate electrode 9 as a mask for ion implantation, phosphorus, which is an N-type impurity having a conductivity opposite to that of the semiconductor substrate 1, is accelerated by an energy of 50 keV and an ion implantation amount is 3.5 × 10.¹⁵atoms / cm² Ion implantation at a degree.
  As a result, an N-type high concentration impurity layer is formed on the semiconductor substrate 1 as the second conductivity type source 10 and drain 11 as shown in FIG.
[0061]
  Thereafter, as shown in FIG. 14, a multilayer wiring insulating film 12 mainly comprising a silicon dioxide film is formed on the entire surface.
  Then, heat treatment at a temperature of 900 ° C. is performed in a nitrogen atmosphere in order to activate the N-type high-concentration impurity layer and to reflow the multilayer wiring insulating film 12.
  Further, as shown in FIG. 15, a photoresist 53 for opening a contact hole as a connection hole is formed in the multilayer wiring insulating film 12.
[0062]
  Then, the contact hole 13 is provided as shown in FIG. 15 using the photoresist 53 as an etching mask.
  Etching to form the contact hole 13 is performed using C₂F₆+ He + CHF₃ Is performed by a dry etching method using a mixed gas of Thereafter, the photoresist 53 is removed.
[0063]
  Next, as shown in FIG. 16, aluminum is provided as the wiring material 14b on the entire surface including the inside of each contact hole 13, and a photoresist 54 for forming a wiring is formed thereon by pattern formation.
[0064]
  Thereafter, the wiring material 14b is etched using a photoetching technique.
  This etching is performed using BCl₃+ CHCl₃+ Cl₂+ N₂1 is formed by the dry etching method using the mixed gas as an etching gas. Thereby, the MONOS type semiconductor nonvolatile memory transistor shown in FIG. 1 is completed.
[0065]
  Then thisOther methods for manufacturing a MONOS type semiconductor nonvolatile memory transistorExampleexplain.
  Other described belowProduction method2 to 16 described above with reference to FIG.Production methodThe only difference is the step of forming the tunnel insulating film 31 of the MONOS type semiconductor nonvolatile memory transistor shown in FIG.Production methodSince this is the same, the description thereof is omitted.
[0066]
  According to another manufacturing method that forms the basis of the present inventionA tunnel insulating film forming process will be described with reference to FIGS.
  As shown in FIG. 7, the periphery of the memory element region on the semiconductor substrate 1Field areaAfter forming the field oxide film 2 and forming the sacrificial oxide film 23 in the memory element region, the field oxide film 2 is removed.
[0067]
  Then, oxidation treatment is performed in a mixed gas of oxygen and nitrogen, and as shown in FIG. 8, a silicon oxide film 24 made of a silicon dioxide film having a thickness of about 2.2 nm is formed in the memory element region of the semiconductor substrate 1. Form on the entire surface. Further, the silicon oxide film 24 is nitrided in an ammonia (NH 3) atmosphere at a temperature of 950 ° C. until the silicon nitride oxide film 3 is formed as shown in FIG. Perform the following process.
[0068]
  Thereafter, in place of the oxidation treatment in the nitrogen atmosphere containing oxygen in the above-described manufacturing method, a lamp annealing apparatus is used, and a dinitrogen monoxide (N₂O) Processing for 20 seconds is performed in a gas atmosphere to form an oxygen-rich silicon oxynitride film 4 on the surface of the silicon oxynitride film 3 as shown in FIG.
  Thereby, the tunnel insulating film 31 composed of the silicon oxynitride film 3 and the oxygen-rich silicon oxynitride film 4 can be formed on the memory element region of the semiconductor substrate 1.
[0069]
  N₂By the treatment in the O 2 gas atmosphere, the tunnel insulating film 31 is the silicon oxynitride film 3 having a nitrogen content higher than the oxygen content on the semiconductor substrate 1 side, and the upper layer of the tunnel insulating film 31 not in contact with the semiconductor substrate 1 is The oxygen-rich silicon oxynitride film 4 having a low nitrogen content can be obtained.
  Thereafter, as shown in FIG. 11, the steps after the step of sequentially forming the memory nitride film 5, the top oxide film 6, and the memory gate electrode material 9b on the tunnel oxide film 31 are the same as the respective steps of the manufacturing method described above. is there.
[0070]
[Embodiment of Manufacturing Method According to the Present Invention]
  Next,First Embodiment of Manufacturing Method of MONOS Type Semiconductor Nonvolatile Memory Transistor according to the InventionWill be described with reference to FIGS. 7, 9 and 10. FIG.
  As shown in FIG. 7, the field oxide film 2 is formed in the field region around the memory element region on the semiconductor substrate 1, and the sacrificial oxide film 23 is formed in the memory element region, and then removed. Up to this point, the same processes as in the manufacturing method described above are performed.
[0071]
  Then, after the sacrificial oxide film 23 is removed, the lamp annealing apparatus is used immediately without forming the silicon oxide film 24 shown in FIG. Dinitrogen (N₂O) Processing for 20 seconds is performed in a gas atmosphere to form a silicon oxynitride film 3 in the memory element region of the semiconductor substrate 1 as shown in FIG.
[0072]
  Thereafter, using the same lamp annealing apparatus, a treatment for 10 seconds is performed in an oxygen atmosphere at a temperature of 1000 ° C., and oxygen rich silicon oxynitride is formed on the surface of the silicon oxynitride film 3 as shown in FIG. A film 4 is formed.
  Thus, a tunnel insulating film 31 composed of the silicon oxynitride film 3 and the oxygen-rich silicon oxynitride film 4 is formed on the memory element region of the semiconductor substrate 1.
[0073]
  In this manufacturing methodThereforeThe tunnel insulating film 31 is a silicon oxynitride film 3 having a nitrogen content higher than the oxygen content on the semiconductor substrate 1 side, and the upper layer of the tunnel insulating film 31 not in contact with the semiconductor substrate 1 is an oxygen-rich silicon with a low nitrogen content. The nitrided oxide film 4 can be formed.
  Each process after this is the same as each process of the above-mentioned manufacturing method.
[0074]
  Next,Second Embodiment of Manufacturing Method of MONOS Type Semiconductor Nonvolatile Memory Transistor according to the InventionA tunnel insulating film forming step according to FIG. 8 will be described with reference to FIGS.
  As shown in FIG. 8, until the field oxide film 2 is formed in the field region around the memory element region on the semiconductor substrate 1 and then the silicon oxide film 24 is formed in the memory element region, the manufacturing method described first is performed. Processes similar to those in the above are performed.
[0075]
  Then, after forming the silicon oxide film 24 as shown in FIG. 8, by using the ion implantation apparatus, nitrogen ions are implanted into the silicon oxide film 24 and then heat treatment is performed in a nitrogen atmosphere containing oxygen. As shown in FIG. 10, the upper layer of the silicon oxynitride film 3 is an oxygen-rich silicon oxynitride film 4.Tunnel insulation film31 can be formed.
[0076]
  Next,Third Embodiment of Manufacturing Method of MONOS Type Semiconductor Nonvolatile Memory Transistor according to the InventionThe tunnel insulating film formation process byFIG.To FIG.
  As shown in FIG. 7, after the field oxide film 2 is formed in the field region around the memory element region on the semiconductor substrate 1 and the sacrificial oxide film 23 is formed in the memory element region, the first step is to remove it. The same steps as in the manufacturing method described above are performed.
[0077]
  Then, oxidation treatment is performed in a mixed gas of oxygen and nitrogen, and as shown in FIG. 18, a silicon oxide film 24 made of a silicon dioxide film is formed on the entire surface of the memory element region of the semiconductor substrate 1 to a thickness of about 1.1 nm. To form. This process is also the same as the process described with reference to FIG.IsHowever, the film thickness of the silicon oxide film 24 to be formed is about 2.2 nm in the case of the manufacturing method described above, but in this example, the film thickness is about half that.
[0078]
  Thereafter, the silicon oxide film 24 is formed into ammonia (NH₃) Nitriding is performed in an atmosphere to form a silicon oxynitride film 3 as shown in FIG. The thickness of the silicon oxynitride film 3 is also about 1.1 nm.
  Next, monosilane (SiH₄) And oxygen (O₂20) as a reactive gas, a thin silicon oxide film 41 made of a silicon dioxide film is formed on the entire surface of the silicon oxynitride film 3 to a thickness of about 1.2 nm as shown in FIG. A tunnel insulating film 31 composed of the nitrided oxide film 3 and the thin silicon oxide film 41 is formed.
[0079]
  Then the first manufacturing methodInThe MONOS type semiconductor nonvolatile memory transistor shown in FIG. 17 can be completed by performing the same processes as those described with reference to FIGS.
[0080]
  Also in the MONOS type semiconductor nonvolatile memory transistor of FIG. 17 produced by this manufacturing method, the tunnel insulating film 31 is the silicon oxynitride film 3 having a nitrogen content higher than the oxygen content on the semiconductor substrate 1 side. Since the upper layer of the tunnel insulating film 31 that is not in contact with the substrate 1 is a thin silicon oxide film 41 that does not contain nitrogen, the same effects as those of the MONOS type semiconductor nonvolatile memory transistor of FIG. It is done.
[0081]
  The above embodiments of the manufacturing method have been mainly described with respect to an example of manufacturing an N-channel type MONOS type semiconductor nonvolatile memory transistor, but in the case of manufacturing a P-channel type MONOS type semiconductor nonvolatile memory transistor. The semiconductor substrate may be an N-type semiconductor substrate, and the source and drain may be formed of a high-concentration impurity layer having a P-type conductivity. The other steps are the same as the above-described manufacturing methods.
[0082]
[Explanation related to the effects of the present invention]
  Here, in this inventionSo manufacturedThe effect of the MONOS type semiconductor nonvolatile memory transistor will be described with reference to the energy band diagram shown in FIG.
  This energy band diagram shows a case where the conventional tunnel insulating film 31 is a silicon oxide film 32 (indicated by a broken line in the figure), and the tunnel insulating film 31 according to the present invention is formed of a silicon oxynitride film 3 and an oxygen-rich silicon oxynitride film. The case of the film 4 (shown by a solid line in the figure) is shown in comparison.
[0083]
  Figure 1N channel type shownIn the MONOS type semiconductor nonvolatile memory transistor, the tunnel insulating film 31 is provided with a silicon oxynitride film 3 obtained by nitriding a silicon oxide film on the semiconductor substrate 1 side as a technique for improving the speed on the erase side.
[0084]
  That is, as shown in FIG. 21, the vicinity of the interface between the tunnel insulating film 31 and the semiconductor substrate 1 is the silicon oxynitride film 3, so that the barrier against the holes of the semiconductor substrate 1 is the silicon oxide film 32 indicated by the broken line. The value (about 3.3 eV) is smaller than the barrier (about 3.8 eV).
  As a result, the hole injection efficiency is improved, and the erase operation can be improved.
[0085]
  Further, the tunnel as viewed from the holes trapped in the memory nitride film 5, the interface between the tunnel insulating film 31 and the memory nitride film 5, and the interface between the memory nitride film 5 and the top oxide film 6, which has been a problem in the past. The reduction in the data retention characteristics due to the reduction in the barrier of the insulating film 31 is solved by using the oxygen-rich silicon oxynitride film 4 in the vicinity of the interface between the tunnel insulating film 31 and the memory nitride film 5.
  That is, since the barrier of the tunnel insulating film 31 viewed from the captured holes shows the same value as the barrier of the silicon oxide film 32 shown by the broken line, it is difficult for holes to escape to the semiconductor substrate 1 side, and data retention characteristics Can be prevented.
[0086]
    Also,When the present invention is applied to a P-channel type MONOS type semiconductor nonvolatile memory transistor, it is possible to improve the writing efficiency and prevent the data retention characteristic from deteriorating.
[0087]
  That is, the present invention can speed up the erasing operation or the writing operation while preventing the deterioration of the data retention characteristics, and can achieve the improvement of the rewriting speed and the improvement of the data retention characteristics of the MONOS type semiconductor nonvolatile memory transistor. .
  Therefore, a highly reliable semiconductor nonvolatile element can be provided.
[0088]
  Next, the effect of the present invention will be described with reference to the characteristic diagrams of FIGS.
  FIG. 22 shows information rewriting characteristics in the case of an N-channel transistor of a MONOS type semiconductor nonvolatile memory transistor created by the manufacturing method of the present invention and a MONOS type semiconductor nonvolatile memory transistor created by a conventional manufacturing method. Yes.
[0089]
  In the information rewrite characteristic chart of FIG. 22, the program voltage is 7 V, the horizontal axis indicates the program time in logarithm, and the vertical axis indicates the amount of change in threshold voltage at each program time by ΔVth. The operation of increasing the threshold voltage due to the injection of hydrogen is represented by plus, and the operation of lowering the threshold voltage due to hole injection is represented by minus.
  Here, the operation of increasing the threshold voltage due to electron injection is called writing, and the operation of decreasing the threshold voltage due to hole injection is called erasing.
[0090]
  As shown in FIG. 22, the information rewriting characteristics according to the conventional example when the tunnel insulating film is a silicon oxide film (indicated by a circle) and a silicon oxynitride film (indicated by a Δ in the figure) A characteristic in the case where the film is made of a silicon oxide film is characterized in that the change in threshold voltage on the erase side is particularly slow.
  That is, a long time is required as an erasing time when rewriting information, and erasing is impossible in the example shown in FIG.
[0091]
  As described above with reference to FIG. 26, the problem that the erasing time becomes long is that the erasing operation is a method by hole injection from the semiconductor substrate. This is because the barrier of the tunnel insulating film seen is high and the probability that holes will cross this barrier is low.
[0092]
  For this reason, in another conventional technique, in order to shorten the erasing time, the tunnel insulating film is made of a silicon oxynitride film to reduce the barrier against holes. That is, as shown by a plot of triangular points in FIG. 22, the characteristics on the erasing side are improved by changing the tunnel insulating film from the silicon oxide film to the silicon oxynitride film, and the information of the MONOS type semiconductor nonvolatile memory transistor is improved. Write operation can be speeded up.
[0093]
  According to the present invention in which the tunnel insulating film is composed of a silicon oxynitride film and an oxygen-rich silicon oxynitride film, the tunnel insulating film is formed of a conventional silicon oxynitride film as shown by a black dot plot in FIG. The same write characteristics as those obtained are shown.
[0094]
  As described above, when the erasing side write characteristics are improved, the data retention characteristics become a problem in the conventional tunnel insulating film made of only the silicon oxynitride film. The effect of improving the data retention characteristic will be described with reference to FIGS.
[0095]
  23 and 24, the horizontal axis shows the conditions of the tunnel insulating film, the conventional tunnel insulating film is a silicon oxide film and a silicon oxynitride film, and the case according to the present invention, and the vertical axis is The slope of the data retention characteristic (Decay rate), which is the slope of the threshold voltage with respect to time investigated from the data retention characteristic, is shown.
  The closer the slope of the data retention characteristic is to zero, the better the data retention characteristic.
[0096]
  FIG. 23 shows characteristics on the writing side where electrons are injected. Therefore, since the threshold voltage shifts with time as it decreases after writing, the slope of the data retention characteristic on the vertical axis is indicated by a negative value.
[0097]
  In the present invention, as shown in the energy band diagram of FIG. 21, since the film thickness is increased by the nitriding process and the barrier viewed from the captured electrons is equivalent to the silicon oxide film, Shows a value near zero, and the data retention characteristics are improved compared to the conventional one.
[0098]
  FIG. 24 shows the characteristics on the erase side where holes are injected. Therefore, since the threshold voltage shifts with time as the time elapses after erasure, the slope of the data retention characteristic on the vertical axis is indicated by a positive value.
[0099]
  Even on the erase side, as shown in the energy band diagram of FIG. 21, the barrier viewed from the trapped holes is larger than that of the silicon oxynitride film, so that the data retention characteristics are improved.
  Further, when the conventional tunnel insulating film is a silicon oxide film, holes can hardly be injected as shown in FIG. 22, and therefore, data in the case of a silicon oxide film is not shown in FIG.
[0100]
  Thus, the structure in which the conventional tunnel insulating film used to improve the characteristics on the erasure side is a silicon oxynitride film reduces the barrier of the tunnel insulating film as seen from the injected holes, and the holes are transferred to the semiconductor substrate. However, according to the present invention, the barrier on the semiconductor substrate side is lowered to increase the probability of hole injection to improve the erasing characteristics, and the memory nitriding The data retention characteristics are improved by increasing the barrier on the film side to reduce the escape of holes to the semiconductor substrate side.
  In the case of a P-channel type MONOS type semiconductor nonvolatile memory transistor, the write operation can be speeded up without deteriorating data retention characteristics.
[0101]
【The invention's effect】
  As described above, according to the manufacturing method of the present invention, the data retention characteristics are good, the reliability is high, and the data rewriting speed is fast.MONOS typeA semiconductor nonvolatile memory transistor can be easily manufactured.
[Brief description of the drawings]
FIG. 1 of the present inventionMONOS type manufactured by manufacturing methodSemiconductor non-volatile memory transistorCompleted stateIt is typical sectional drawing which shows this structure.
FIG. 2 is shown in FIG.MONOS typeIt is typical sectional drawing for demonstrating the first several process of one Embodiment of the manufacturing method of a semiconductor non-volatile memory transistor.
FIG. 3 is a schematic cross-sectional view for explaining the next step in the same manner.
FIG. 4 is a schematic sectional view for explaining the next step.
FIG. 5 is a schematic cross-sectional view for explaining the next step in the same manner.
FIG. 6 is a schematic sectional view for explaining the next step.
FIG. 7 is a schematic cross-sectional view for explaining the next step in the same manner.
FIG. 8 is a schematic cross-sectional view for explaining the next step in the same manner.
FIG. 9 is a schematic cross-sectional view for explaining the next step in the same manner.
FIG. 10 is a schematic cross-sectional view for explaining the next step in the same manner.
FIG. 11 is a schematic cross-sectional view for explaining the next step in the same manner.
FIG. 12 is a schematic cross-sectional view for explaining the next step in the same manner.
FIG. 13 is a schematic cross-sectional view for explaining the next step in the same manner.
FIG. 14 is a schematic cross-sectional view for explaining the next step in the same manner.
FIG. 15 is a schematic sectional view for explaining the next step in the same manner.
FIG. 16 is a schematic cross-sectional view for explaining the next step in the same manner.
FIG. 17 is according to the present invention.MONOS type manufactured by other manufacturing methodsSemiconductor non-volatile memory transistorCompleted stateIt is typical sectional drawing which shows this structure.
FIG. 18 shows in FIG.MONOS typeIt is typical sectional drawing for demonstrating the first process of forming a tunnel insulating film with the manufacturing method of a semiconductor non-volatile memory transistor.
FIG. 19 is a schematic cross-sectional view for explaining the next step in the same manner.
FIG. 20 is a schematic sectional view for explaining the next step in the same manner.
FIG. 21 shows the present invention.MONOS type manufactured by this manufacturing methodIt is an energy band figure for demonstrating the effect of a semiconductor non-volatile memory transistor.
FIG. 22 shows the present invention.Manufactured by the manufacturing methodFIG. 5 is a diagram showing a correlation characteristic between a program time and a threshold voltage change amount (ΔVth) of a MONOS type semiconductor nonvolatile memory transistor and a conventional MONOS type semiconductor nonvolatile memory transistor.
FIG. 23 shows the present invention.Manufactured by the manufacturing methodIt is a figure which shows the inclination characteristic of the data retention characteristic of the writing side of a MONOS type | mold semiconductor non-volatile memory transistor and the conventional MONOS type | mold semiconductor non-volatile memory transistor.
FIG. 24 shows the present invention.Manufactured by the manufacturing methodIt is a figure which shows the inclination characteristic of the data retention characteristic of the erasing side of a MONOS type | mold semiconductor non-volatile memory transistor and the conventional MONOS type | mold semiconductor non-volatile memory transistor.
FIG. 25 is a schematic cross-sectional view showing the structure of a conventional MONOS type semiconductor nonvolatile memory transistor.
FIG. 26 is an energy band diagram of a conventional MONOS type semiconductor nonvolatile memory transistor.
[Explanation of symbols]
1: Semiconductor substrate 2: Field oxide film
3: Silicon oxynitride film
4: Oxygen-rich silicon oxynitride film
5: Memory nitride film 6: Top oxide film
8: Memory insulating film 9: Memory gate electrode
9b: Memory gate electrode material
10: Source 11: Drain
12: Insulating film for multilayer wiring
13: Contact hole 14: Wiring
21: Pad oxide film 22: Silicon nitride film
23: Sacrificial oxide film 24, 32: Silicon oxide film
31: Tunnel insulating film
51, 52, 53, 54: Photoresist

Claims (3)

A MONOS type semiconductor nonvolatile memory in which a tunnel insulating film is provided on a semiconductor substrate, a memory nitride film is provided on the tunnel insulating film, a top oxide film made of a silicon oxide film is provided on the memory nitride film, and a memory insulating film is used. A method for manufacturing a transistor, comprising:
Treating the surface of the semiconductor substrate in a dinitrogen monoxide gas atmosphere to form a silicon oxynitride film functioning as the tunnel insulating film;
Heat treating the vicinity of the surface of the silicon nitride oxide film in an oxygen atmosphere so that the vicinity of the interface on the memory nitride film side becomes an oxygen-rich silicon nitride oxide film having a high oxygen content;
A method for manufacturing a MONOS type semiconductor nonvolatile memory transistor, comprising: A MONOS type semiconductor nonvolatile semiconductor memory device is provided with a tunnel insulating film on a semiconductor substrate, a memory nitride film on the tunnel insulating film, and a top oxide film made of a silicon oxide film on the memory nitride film. A method for manufacturing a memory transistor, comprising:
Forming a silicon oxide film on the semiconductor substrate by oxidation treatment;
After nitrogen ions are implanted into the silicon oxide film, heat treatment is performed in a nitrogen atmosphere containing oxygen, and the nitrogen content is greater than the oxygen content near the interface on the semiconductor substrate side, and near the interface on the memory nitride film side. Forming the tunnel insulating film such that the oxygen content is greater than the nitrogen content;
A method for manufacturing a MONOS type semiconductor nonvolatile memory transistor, comprising: A MONOS type semiconductor nonvolatile semiconductor memory device is provided with a tunnel insulating film on a semiconductor substrate, a memory nitride film on the tunnel insulating film, and a top oxide film made of a silicon oxide film on the memory nitride film. A method for manufacturing a memory transistor, comprising:
Forming a silicon oxide film on the semiconductor substrate by oxidation treatment;
Nitriding the silicon oxide film to form a silicon nitride oxide film, forming a thin film silicon oxide film by a CVD method on the surface of the silicon nitride oxide film on the memory nitride film side, and forming the tunnel insulating film;
A method for manufacturing a MONOS type semiconductor nonvolatile memory transistor, comprising:

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