JP4076638B2 - Manufacturing method of semiconductor device - Google Patents

Description

表１の成膜条件の欄において、第１段階の欄と第３段階の欄の上段は酸化温度を示しており、中段はウエット酸化又はドライ酸化の別を示しており、下段は酸化時間を示している。また、第２段階の欄の上段は窒化温度を示しており、中段はＮ₂ガスに対するＮＯガスの割合を示しており、下段は窒化時間を示している。
【００４２】
実施例１乃至３は、本実施形態による半導体装置の製造方法におけるシリコン窒化酸化膜の形成方法に該当するものである。即ち、第１段階としてウエット酸化を行い、第２段階として窒化を行い、第３段階としてドライ酸化を行った場合のものである。比較例１乃至４は、第１段階としてウエット酸化、第２段階として窒化、第３段階としてウエット酸化を行った場合のものである。また、比較例５は、第１段階としてドライ酸化、第２段階として窒化、第３段階としてウエット酸化を行った場合、比較例６は第１段階としてドライ酸化、第２段階として窒化、第３段階としてドライ酸化を行った場合のものである。
【００４３】
表１からわかるように、実施例１乃至３の界面準位密度は７．７７×１０¹⁰／ｅＶｃｍ²〜８．８４×１０¹⁰／ｅＶｃｍ²の範囲であり、界面準位密度が１．２２×１０¹¹／ｅＶｃｍ²〜２．７２×１０¹¹／ｅＶｃｍ²の範囲である比較例１乃至６に比べて極めて良好な結果が得られた。
また、実施例１乃至３では固定電荷は８．１６×１０¹⁰／ｅＶｃｍ²〜８．７５×１０¹⁰／ｅＶｃｍ²の範囲であり、固定電荷が１．２３×１０¹¹／ｅＶｃｍ²〜２．５９×１０¹¹／ｅＶｃｍ²の範囲である比較例１乃至６に比べて極めて良好な結果が得られた。
（界面ラフネス）
次に、上記のようにして形成されたシリコン窒化酸化膜の界面ラフネスを図５を用いて説明する。図５は、シリコン基板上にシリコン窒化酸化膜を形成した後に、ＨＦ溶液を用いてシリコン基板上からシリコン窒化酸化膜を剥離し、シリコン基板の表面をＡＦＭを用いて観察した結果を示す図である。
【００４４】
図５（ａ）は、本実施形態に該当する場合、即ち第１段階としてウエット酸化、第２段階として窒化、第３段階としてドライ酸化を行った場合の観察結果である。第１段階のウエット酸化では、５ｎｍのシリコン酸化膜を形成し、第２段階では、窒化温度９００℃、Ｎ₂ガス対するＮＯガスの割合を５％として窒化を行った。そして、第３段階では、酸化温度９００℃でドライ酸化を行った。
【００４５】
図５（ｂ）は、第１段階としてウエット酸化、第２段階として窒化、第３段階としてウエット酸化を行った場合の観察結果である。図５（ｂ）では、第１段階のウエット酸化では、５ｎｍのシリコン酸化膜を形成し、第２段階では、窒化温度９００℃、Ｎ₂ガス対するＮＯガスの割合を５％として窒化を行った。そして、第３段階では、酸化温度９００℃でウエット酸化を行った。
【００４６】
第１段階としてウエット酸化、第２段階として窒化、第３段階としてウエット酸化を行った場合は、界面ラフネスの二乗平均値（ＲＭＳ）は０．３６ｎｍであり、界面ラフネスの最大値と最小値の差（Ｒａｎｇｅ）は２．８７ｎｍであった（図５（ｂ）参照）。これに対し、本実施形態に該当する場合、即ち、第１段階としてウエット酸化、第２段階として窒化、第３段階としてドライ酸化を行った場合は、界面ラフネスの二乗平均値（ＲＭＳ）は０．２５ｎｍであり、界面ラフネスの最大値と最小値の差（Ｒａｎｇｅ）は２．０９ｎｍであった（図５（ａ）参照）。
【００４７】
このように、本実施形態によれば、第１段階としてウエット酸化、第２段階として窒化、第３段階としてドライ酸化を行うので、第１段階としてウエット酸化、第２段階として窒化、第３段階としてウエット酸化を行った場合に比べて、界面ラフネスの小さいシリコン窒化酸化膜を有する半導体装置を製造することができる。
【００４８】
［変形実施形態］
本発明は上記実施形態に限らず種々の変形が可能である。
例えば、上記実施形態では、トランジスタのゲート絶縁膜としてシリコン窒化酸化膜を用いる場合を例に説明したが、フローティングゲートを有するダブルゲート構造の不揮発性メモリのトンネル酸化膜としても、本発明により形成したシリコン窒化酸化膜を適用することができる。このような半導体装置は、シリコン基板１０上に、シリコン窒化酸化膜２２を形成し、この後、フローティングゲート３０、ＯＮＯ膜３２、コントロールゲート３４、及びソース／ドレイン拡散層２８等を形成することにより製造することができる（図６参照）。
【００４９】
また、上記実施形態では、第２段階として行われる窒化処理と同じ温度で、第３段階として行われるドライ酸化を行ったが、ドライ酸化の温度は、窒化の温度と必ずしも同様とする必要はなく、例えば、８５０〜９５０℃の範囲で適宜設定することができる。この場合、窒化処理後に電気炉内の雰囲気を不活性ガスより成る雰囲気に置換し、この後電気炉内の温度を適宜設定した後で、電気炉内の雰囲気を上記のようなドライ酸化の雰囲気に置換することが望ましい。
【００５０】
また、上記実施形態では、ドライ酸化を行う際に、Ｏ₂ガスより成る酸化雰囲気を用いたが、ＨＣｌやジクロルエチレン等のハロゲン化物が添加されたＯ₂ガスより成る酸化雰囲気を用いてもよい。シリコン窒化酸化膜中にハロゲンを導入することにより、絶縁破壊耐圧やＴＤＤＢ特性を向上することが可能となる。また、シリコン窒化酸化膜中にＦｅ（鉄）などの不要な重金属が含まれていた場合には、この不要な重金属をハロゲンにより除去することができる。
【００５１】
また、上記実施形態では、ドライ酸化を行う際にＯ₂ガスより成る酸化雰囲気を用いたが、Ｏ₃ガスより成る酸化雰囲気を用いてもよい。Ｏ₃ガスはＯ₂ガスに比べて酸化力が強く、酸化レートも早いので、酸化時間を短縮し、スムーズに酸化を行うことができる。また、Ｏ₂ガスを用いた場合に比べて、より緻密で膜質の良い成膜が可能となり、これにより絶縁破壊耐圧、ＴＤＤＢ特性、及びホットキャリア耐性を向上させることが可能となる。
【００５２】
また、上記実施形態では、第３段階として行うドライ酸化においてＯ₂ガスより成る酸化雰囲気を用いたが、ＮＯガス、ＮＯ₂ガス、又はＮ₂Ｏガス等、即ち酸化性と窒化性とを有する雰囲気を用いてドライ酸化を行ってもよい。これにより、第２段階として行う窒化処理においてシリコン窒化酸化膜に所望の濃度の窒素が導入できていない場合には、第３段階として行うドライ酸化において酸化性と窒化性とを有する雰囲気を用いることにより、シリコン窒化酸化膜中の窒素濃度を所望の濃度にすることが可能となる。また、第３段階として行うドライ酸化において窒化性を有さない雰囲気を用いた場合には、シリコン基板とシリコン窒化酸化膜との界面には窒素はほとんど存在しないこととなるが、第３段階として行うドライ酸化において酸化性と窒化性とを有する雰囲気を用いた場合には、シリコン基板とシリコン窒化酸化膜との界面に窒素を導入することが可能となる。これにより、シリコン窒化酸化膜における深さ方向の窒素分布を制御することができるので、所望の膜質のシリコン窒化酸化膜を得ることができ、また、リーク電流、絶縁破壊特性、ＴＤＤＢ特性、及びホットキャリア特性等の電気的特性を向上することができる。
【００５３】
また、第３段階としてドライ酸化を行う際に、ＮＯガス、ＮＯ₂ガス、又はＮ₂Ｏガス等に更にＯ₂ガスを添加した雰囲気を用いてもよい。これにより、窒化性と酸化性とを有する雰囲気を用いるため、シリコン窒化酸化膜における深さ方向の窒素分布を上記と同様に制御することができ、しかもＯ₂ガスの添加量を多くすることにより酸化レートを早くすることができる。これにより、低温でドライ酸化を行う場合であっても、所望の酸化レートで酸化することが可能となる。
【００５４】
また、上記実施形態では、ドライ酸化を行う際にＯ₂ガスより成る酸化雰囲気を用いたが、更に不活性ガスで希釈した酸化雰囲気を用いてもよい。これにより、酸化レートを遅くすることができる。即ち、成膜装置の性能等に起因して酸化レートが早くなりすぎてしまう場合や、薄いシリコン窒化酸化膜を形成したい場合には、不活性ガスの流量を大きくすることにより酸化レートを遅くすることができ、これにより所望の膜厚のシリコン窒化酸化膜を形成することが可能となる。
【００５５】
【発明の効果】
以上の通り、本発明によれば、水蒸気を含む酸化雰囲気中でシリコン酸化膜を形成し、シリコン酸化膜に窒素を導入し、この後、水蒸気を含まない酸化雰囲気中で更に追加酸化するので、界面ラフネスが小さく、界面準位密度も低いシリコン窒化酸化膜を形成することができる。しかも、シリコン基板の表面に下地酸化膜を形成しておくので、大気中にシリコン基板を露出した場合であっても、膜質の悪い自然酸化膜がシリコン基板の表面に形成されることを防止することができる。
【００５６】
また、本発明によれば、Ｏ₂ガスと不活性ガスとを含む雰囲気中にシリコン基板を導入するので、シリコン基板の表面が荒れてしまうのを抑制することができる。
また、本発明によれば、Ｏ₂ガスと不活性ガスとを含む雰囲気中でシリコン基板の温度を昇温した後に、ウエット雰囲気に置換するため、シリコン基板の温度を上昇する過程においてシリコン基板の表面に膜質の悪いシリコン酸化膜が形成されてしまうのを防止することができる。また、Ｏ₂ガスと不活性ガスとを含む雰囲気中のＯ₂ガスの割合を約１％〜約１０％と低くすることにより、シリコン基板表面に形成される酸化膜を無視できる程度にまで抑えることができる。また、水蒸気を含む酸化雰囲気中における水蒸気の割合を２／３以下とすることにより、シリコン酸化膜の信頼性を向上することができ、ホットキャリア耐性を向上することができ、また、良好なＴＤＤＢ特性を得ることができる。
【００５７】
また、本発明によれば、不活性ガスより成る雰囲気中でシリコン基板の温度を所定の温度に設定するので、膜質の悪い不要な酸化膜が形成されてしまうのを防止することができる。
また、本発明によれば、不活性ガスにより希釈されたウエット雰囲気中やドライ雰囲気中で酸化を行うので、酸化レートを低減することができる。
【図面の簡単な説明】
【図１】本発明の一実施形態による半導体装置の製造方法を示す工程断面図（その１）である。
【図２】本発明の一実施形態による半導体装置の製造方法を示す工程断面図（その２）である。
【図３】本発明の一実施形態による半導体装置の製造方法を示す工程断面図（その３）である。
【図４】シリコン窒化酸化膜を形成する際の成膜シークエンスを示す図である。
【図５】シリコン基板の表面をＡＦＭを用いて観察した結果を示す図である。
【図６】本発明の変形実施形態による半導体装置を示す断面図である。
【符号の説明】
１０…シリコン基板
１２…素子領域
１３…パッド酸化膜
１４…素子分離膜
１６…下地酸化膜
１８…シリコン酸化膜
１９…シリコン窒化酸化膜
２０…シリコン酸化膜
２２…シリコン窒化酸化膜
２４…ゲート電極
２６…サイドウォール絶縁膜
２７ａ…低濃度領域
２７ｂ…高濃度領域
２８…ソース／ドレイン拡散層
３０…フローティングゲート
３２…ＯＮＯ膜
３４…コントロールゲート[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a method for manufacturing a semiconductor device, and more particularly to a method for manufacturing a semiconductor device having a silicon oxynitride film having a low interface roughness and a low interface state density.
[0002]
[Prior art]
Conventionally, a silicon oxide film has been widely used as a gate insulating film of a transistor.
However, recently, since the film quality can be improved compared to the silicon oxide film and the trap density can be reduced, the silicon nitride oxide film to which a small amount of nitrogen is added is used as the gate insulating film of the transistor. It has been proposed to be used as
[0003]
As a method of forming such a silicon oxynitride film on a silicon substrate, for example, N, which is a nitriding gas, is used.₂A method for forming a silicon oxynitride film directly on a silicon substrate by using O gas or NO gas is known.
Also, there is a method of forming a silicon oxynitride film by forming a thermal oxide film on a silicon substrate in a wet atmosphere or a dry atmosphere and then heat-treating in a nitriding atmosphere to introduce nitrogen into the film. Are known.
[0004]
However, when the silicon nitride film is formed as described above, since a large amount of nitrogen is distributed in the vicinity of the interface between the silicon substrate and the silicon oxynitride film, it is difficult to reduce the trap density. In addition, it has been difficult to improve electrical characteristics such as dielectric strength characteristics.
As a technique that can reduce the trap density and improve the electrical characteristics such as the withstand voltage characteristics, the first stage is oxidized, the second stage is nitrided, and the third stage is oxidized. A method of forming a silicon oxynitride film with a small amount of nitrogen distribution at the interface with the silicon oxynitride film has been proposed. As a method of forming a silicon nitride film in three stages as described above, wet oxidation is performed as the first stage, nitridation is performed as the second stage, and wet oxidation is performed as the third stage. There has been proposed a method of performing dry oxidation, performing nitriding as the second stage, and performing dry oxidation as the third stage.
[0005]
[Problems to be solved by the invention]
However, in the conventional manufacturing method of a semiconductor device in which wet oxidation is performed as the first stage, nitridation is performed as the second stage, and wet oxidation is performed as the third stage to form a silicon oxynitride film, The interface roughness with the oxide film is large, and further improvement has been desired.
[0006]
Further, in the conventional method of manufacturing a semiconductor nitriding film in which dry oxidation is performed as the first stage, nitridation is performed as the second stage, and dry oxidation is performed as the third stage, the interface state density is low. It was expensive and further improvement was desired.
An object of the present invention is to provide a method of manufacturing a semiconductor device having a silicon oxynitride film having a low interface roughness and a low interface state density.
[0007]
[Means for Solving the Problems]
  The object is to form a base oxide film on a silicon substrate and to thermally oxidize the silicon substrate on which the base oxide film is formed in a first oxidizing atmosphere containing water vapor, thereby A step of forming a silicon oxide film in which the film is additionally oxidized, and the silicon substrate on which the silicon oxide film is formed are formed by nitriding gasAnd N ₂ Gas andA step of forming a first silicon oxynitride film in which nitrogen is introduced into the silicon oxide film, and a step of forming the silicon substrate on which the first silicon oxynitride film is formed, Oxidizing without water vapor, NO gas, NO ₂ Gas or N ₂ Contains O gasAnd forming a second silicon oxynitride film in which the first silicon oxynitride film is additionally oxidized and thermally oxidized in a third atmosphere. Is done. As a result, a silicon oxide film is formed in an oxidizing atmosphere containing water vapor, nitrogen is introduced into the silicon oxide film, and then additional oxidation is performed in an oxidizing atmosphere that does not contain water vapor. A silicon oxynitride film having a low unit density can be formed. Moreover, since the base oxide film is formed on the surface of the silicon substrate, it is possible to prevent a natural oxide film having poor film quality from being formed on the surface of the silicon substrate even when the silicon substrate is exposed to the atmosphere. be able to.
[0008]
In the method of manufacturing a semiconductor device, in the step of forming the silicon oxide film, O₂After raising the temperature to a first temperature, which is the formation temperature of the silicon oxide film, in a fourth atmosphere containing a gas and an inert gas, the fourth atmosphere is replaced with the first atmosphere, and the silicon It is desirable to form an oxide film. As a result, O₂Since the silicon substrate is introduced into the fourth atmosphere containing the gas and the inert gas, the surface of the silicon substrate can be prevented from being roughened. O₂Since the temperature of the silicon substrate is raised in the fourth atmosphere containing the gas and the inert gas and then replaced with the first atmosphere, the film quality is poor on the surface of the silicon substrate in the process of raising the temperature of the silicon substrate. The formation of the silicon oxide film can be prevented.
[0009]
In the method for manufacturing a semiconductor device, the first silicon oxynitride film forming step may be a first silicon oxynitride film formation temperature in a fifth atmosphere made of an inert gas. After the temperature is stabilized at 2, the fifth atmosphere is preferably replaced with the second atmosphere to form the first silicon oxynitride film. Thereby, since the temperature of the silicon substrate is set to the second temperature in the fifth atmosphere made of an inert gas, it is possible to prevent an unnecessary oxide film from being formed.
[0010]
Further, in the method of manufacturing a semiconductor device, in the step of forming the second silicon oxynitride film, a temperature at which the second silicon oxynitride film is formed in a sixth atmosphere made of an inert gas. After the temperature is stabilized at 3, the sixth atmosphere is preferably replaced with the third atmosphere to form the second silicon oxynitride film. Thereby, since the temperature of the silicon substrate is set to the third temperature in the sixth atmosphere made of an inert gas, it is possible to prevent an unnecessary oxide film from being formed.
[0011]
In the method for manufacturing a semiconductor device, it is preferable that the first atmosphere and / or the third atmosphere is diluted with an inert gas. Thereby, the oxidation rate can be slowed. That is, when the oxidation rate becomes too fast due to the performance of the film forming apparatus or when it is desired to form a thin silicon oxynitride film, the oxidation rate is slowed by increasing the flow rate of the inert gas. Thus, a silicon oxynitride film having a desired film thickness can be formed.
[0014]
In the method of manufacturing a semiconductor device, the third atmosphere is O₂It is desirable to further include a gas. As a result, O₂By increasing the amount of gas added, the oxidation rate can be increased, and even when dry oxidation is performed at a low temperature, it is possible to oxidize at a desired oxidation rate.
In the method of manufacturing a semiconductor device, in the step of forming the base oxide film,_ThreeO exposure to gas or UV irradiation_ThreeGas or O₂It is desirable that the base oxide film be formed by a gas exposure process. As a result, a dense base oxide film with stable film quality can be formed.
[0015]
  Further, the object is to form a base oxide film on a silicon substrate, thermally oxidize the silicon substrate on which the base oxide film is formed in an oxidizing first atmosphere containing water vapor, and A step of forming a silicon oxide film in which a base oxide film is additionally oxidized; and the silicon substrate on which the silicon oxide film is formed is formed into a nitride gasAnd N ₂ Gas andA step of forming a first silicon oxynitride film in which nitrogen is introduced into the silicon oxide film, and a step of forming the silicon substrate on which the first silicon oxynitride film is formed, Oxidizing without water vapor, NO gas, NO ₂ Gas or N ₂ Contains O gasForming a second silicon oxynitride film by thermally oxidizing in a third atmosphere and additionally oxidizing the first silicon oxynitride film; and forming a gate electrode on the second silicon oxynitride film This is achieved by a method for manufacturing a semiconductor device, comprising: forming a source / drain diffusion layer on the silicon substrate on both sides of the gate electrode. As a result, a silicon oxide film is formed in an oxidizing atmosphere containing water vapor, nitrogen is introduced into the silicon oxide film, and then additional oxidation is performed in an oxidizing atmosphere that does not contain water vapor. A silicon oxynitride film having a low unit density can be formed. By using such a silicon nitride oxide film as a gate oxide film of a transistor or a tunnel oxide film of a nonvolatile memory having a double gate structure having a floating gate, a semiconductor device having good characteristics can be provided.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
A method of manufacturing a semiconductor device according to an embodiment of the present invention will be described with reference to FIGS. 1 to 3 are process cross-sectional views illustrating the method for fabricating the semiconductor device according to the present embodiment. FIG. 4 is a diagram showing a film forming sequence when forming a silicon oxynitride film. FIG. 5 is a diagram showing a result of observing the surface of the silicon substrate using an AFM (Atomic Force Microscope).
[0017]
The present invention is widely applied to a method of manufacturing a semiconductor device in which a silicon oxynitride film is formed on a silicon substrate. In this embodiment, a silicon oxynitride film is formed as a gate insulating film of a transistor. Will be described as an example.
First, as shown in FIG. 1A, an element isolation film 14 for defining an element region 12 is formed on the surface of a silicon substrate 10 by, for example, a LOCOS (LOCal Oxidation of Silicon) method. FIG. 1A shows a state where the pad oxide film 13 remains on the surface of the element region 12.
[0018]
Next, the pad oxide film 13 is removed, and immediately thereafter, a base oxide film 16 is formed on the entire surface (see FIG. 1B). Since the base oxide film 16 is formed immediately after the pad oxide film 13 is removed, the base oxide film 16 is formed on the surface of the silicon substrate 10 without forming a natural oxide film.
Here, the base oxide film referred to in this specification is a dense oxide film having a stable film quality, unlike a natural oxide film that is naturally formed on the surface of the silicon substrate when the silicon substrate is exposed to the atmosphere. means.
[0019]
In general, since the surface of a silicon substrate is chemically unstable, when the silicon substrate is exposed to the atmosphere, a natural oxide film with an unstable film quality is formed on the surface of the silicon substrate by oxygen in the atmosphere. Is done. If such a natural oxide film having a non-uniform film thickness and film quality is formed, the oxidation reaction may become non-uniform in the subsequent oxidation process.
[0020]
On the other hand, in the present embodiment, since the dense base oxide film 16 having a stable film quality is formed on the surface of the silicon substrate 10, even if the silicon substrate 10 is exposed to the atmosphere, such a natural oxide film is formed. Can be prevented from being formed on the surface of the silicon substrate 10. Further, the base oxide film 16 has a uniform film thickness and film quality, and has a function of making the subsequent oxidation reaction uniform.
[0021]
The underlying oxide film 16 is, for example, SC-1 solution, SC-2 solution, or HNO._ThreeIt can form by the chemical | medical solution process using this. When the base oxide film 16 is formed by the chemical treatment using the SC-1 solution, the film formation condition can be set to 60 to 80 ° C., for example, and the film is formed when the film is formed at such a temperature. The film thickness of the silicon oxide film 16 is 1 nm or less, for example, about 0.7 nm. SC-2 liquid or HNO_ThreeIn the case where the base oxide film 16 is formed by chemical treatment using a film, the film formation condition can be set to 60 to 80 ° C., for example. When the film is formed at such a temperature, the film thickness of the base oxide film 16 is It is about 0.8 to 1.2 nm, for example, about 1 nm.
[0022]
In addition, the base oxide film 16 is formed of O_ThreeIt can also be formed by chemical treatment using water containing water. When mere water is used, a dense oxide film having a stable film quality cannot be formed on the surface of the silicon substrate._ThreeContaining water, ie O_ThreeIf water in which is dissolved is used, a dense oxide film with stable film quality can be formed. O_ThreeIn the case where the base oxide film 16 is formed by a chemical treatment using water containing water, the film forming conditions can be set to 60 to 80 ° C., for example._ThreeThe concentration of can be, for example, 1 to 10 ppm. When the film is formed under such conditions, the thickness of the silicon oxide film 16 is about 1 nm or less, for example, about 0.7 nm.
[0023]
In addition, the base oxide film 16 forms the silicon substrate 10 with O_ThreeIt can also be formed by exposure to gas or the like. In this case, the film formation temperature can be, for example, about room temperature to about 200 ° C. When the film formation temperature is 200 ° C. or higher, O_ThreeBecause it will be decomposed. Further, when the film forming temperature is 200 ° C. or higher, a thermal oxide film having different properties from a dense base oxide film having stable film quality is formed on the surface of the silicon substrate. When the film formation temperature is about room temperature to about 200 ° C., a base oxide film 16 having a film thickness of about 1 nm is formed.
[0024]
In addition, the base oxide film 16 is formed of O_ThreeIt can also be formed by a UV ozone method in which an oxide film is formed by irradiating an oxidizing atmosphere containing gas with ultraviolet rays. In this case, the film formation temperature is set so that the silicon substrate 10 is O._ThreeFor the same reason as in the case of forming the base oxide film 16 by exposure to a gas or the like, the temperature can be, for example, about room temperature to 200 ° C. In this case, a base oxide film 16 having a thickness of about 1 nm is formed.
[0025]
In addition, the base oxide film 16 is formed of O₂It can also be formed by a UV oxygen method in which an oxide film is formed by irradiating an oxidizing atmosphere containing gas with ultraviolet rays. In this case, the film formation temperature can be, for example, about room temperature to about 200 ° C. This is because when the film forming temperature is 200 ° C. or higher, a thermal oxide film having different properties from a dense base oxide film having a stable film quality is formed on the surface of the silicon substrate. When the film formation temperature is about room temperature to about 200 ° C., a base oxide film 16 having a film thickness of about 1 nm is formed.
[0026]
Next, O₂The silicon substrate 10 on which the base oxide film 16 is formed is introduced into an electric furnace filled with an atmosphere containing a gas and an inert gas. As the inert gas, for example, Ar gas, He gas, N₂Gas or the like can be used. O₂O in an atmosphere in an electric furnace containing a gas and an inert gas₂The gas ratio is, for example, about 1% to about 10%. The temperature in the electric furnace is, for example, 750 ° C. as shown in FIG. Moreover, as an electric furnace, a horizontal electric furnace etc. can be used, for example.
[0027]
In this embodiment, O₂The silicon substrate is introduced into the atmosphere containing the gas and the inert gas for the following reason. That is, in general, O₂If a silicon substrate is introduced into an atmosphere containing no gas, that is, an atmosphere composed of only an inert gas, the surface of the silicon substrate may be roughened. On the other hand, in this embodiment, O₂Since the silicon substrate is introduced into the atmosphere containing the gas, the surface of the silicon substrate can be prevented from being roughened.
[0028]
Next, the inside of the electric furnace is O₂While maintaining the atmosphere containing the gas and the inert gas, the temperature in the electric furnace is raised to 800 ° C., which is a temperature for performing wet oxidation described later. Then, for example, the substrate temperature is stabilized by being left for 10 minutes (stabilization). In addition, the temperature in an electric furnace is not limited to 800 degreeC, For example, it can set suitably in the range of 750 to 900 degreeC.
[0029]
When the temperature of the silicon substrate is raised in an oxygen-rich atmosphere, a silicon oxide film is formed on the surface of the silicon substrate in the process of raising the temperature of the silicon substrate. Becomes worse. In addition, since the temperature of each part in the electric furnace varies, the film thickness becomes non-uniform. On the other hand, in this embodiment, O₂Since the atmosphere is replaced after the temperature of the silicon substrate is raised in an atmosphere containing a gas and an inert gas, a silicon oxide film having poor film quality is formed on the surface of the silicon substrate in the process of raising the temperature of the silicon substrate. There is nothing. O₂O in an atmosphere containing a gas and an inert gas₂By reducing the gas ratio to about 1% to about 10%, the oxide film on the surface of the silicon substrate can be suppressed to a negligible level.
[0030]
Next, the atmosphere in the electric furnace is replaced with an oxidizing atmosphere containing water vapor, and wet oxidation is performed (first stage). Thereby, a silicon oxide film 18 is formed on the surface of the silicon substrate 10 (see FIG. 1C). In general, it is known that the silicon oxide film 18 formed by wet oxidation has a lower interface state density than the silicon oxide film formed by dry oxidation. The interface state density in the silicon oxynitride film formed in the embodiment can also be reduced.
[0031]
The flow rate of the gas introduced into the electric furnace when performing the wet oxidation is, for example, H₂2133cc of gas, O₂The gas is 6400 cc.
As the wet oxidation conditions, the ratio of water vapor in an oxidizing atmosphere containing water vapor is desirably 2/3 or less, for example. This is because, when the proportion of water vapor in the oxidizing atmosphere containing water vapor is large, OH groups and the like due to water are large, so that the reliability of the silicon oxide film is deteriorated and hot carrier resistance is deteriorated. Further, when the ratio of water vapor in the oxidizing atmosphere containing water vapor is 2/3 or more, TDDB (Time Dependent Dielectric Breakdown) characteristics deteriorate.
[0032]
Further, when wet oxidation is performed, N is further added.₂An inert gas such as a gas may be introduced into the electric furnace. Thereby, the oxidation rate during wet oxidation can be reduced.
Next, after the silicon oxide film 18 having a predetermined thickness is formed, the wet atmosphere in the electric furnace is replaced with an atmosphere made of an inert gas (purge), and the first-stage oxidation is completed. As the inert gas, for example, Ar gas, He gas, N₂Gas or the like can be used. Here, O in the electric furnace₂The gas is not introduced because the silicon oxide film 18 has already been formed on the surface of the silicon substrate 10, so that there is no possibility that the surface of the silicon substrate 10 will be rough even in an inert gas atmosphere.
[0033]
Next, while maintaining the atmosphere in the electric furnace in an atmosphere made of an inert gas, the temperature in the electric furnace is increased until the temperature reaches 900 ° C., which is a temperature for nitriding described later (temperature increase). The temperature inside the electric furnace is raised at, for example, 10 ° C./min. In addition, the temperature in an electric furnace is not limited to 900 degreeC, For example, it can set suitably in the range of 800 to 1000 degreeC. In this embodiment, since the temperature of the silicon substrate 10 is raised in an atmosphere made of an inert gas, it is possible to prevent an unnecessary oxide film from being formed.
[0034]
Next, after the temperature in the electric furnace reaches 900 ° C., the substrate temperature is stabilized (stabilization), for example, by leaving it for 5 minutes.
Next, the atmosphere in the electric furnace is replaced with a nitriding atmosphere, and nitriding is performed (second stage). As a result, nitrogen is introduced in the vicinity of the interface between the silicon oxide film 18 and the silicon substrate 10 to form a silicon oxynitride film 19 (see FIG. 2A). N introduced into the electric furnace₂The gas flow rate is, for example, 14850 cc, and the NO gas flow rate is, for example, 150 cc. N₂The flow rate of gas and the flow rate of NO gas are not limited to these values, and it is desirable to set appropriately according to the concentration of nitrogen to be introduced.
[0035]
Next, the atmosphere in the electric furnace is replaced with an atmosphere made of an inert gas (purge), and the second-stage oxidation is completed. As the inert gas, for example, Ar gas, He gas, N₂Gas or the like can be used. For example, by leaving it for 20 minutes after the introduction of the inert gas, the atmosphere in the electric furnace becomes almost completely an atmosphere composed of the inert gas. Here, O in the electric furnace₂The gas is not introduced because the silicon oxynitride film 19 has already been formed on the surface of the silicon substrate 10, so that the surface of the silicon substrate 10 is not likely to be rough even in an atmosphere of an inert gas alone.
[0036]
Next, the atmosphere in the electric furnace is replaced with an oxidizing atmosphere that does not contain water vapor, and dry oxidation is performed (third stage). As a result, the silicon oxynitride film 19 is additionally oxidized to form a silicon oxide film 20 on the surface of the silicon substrate 10, thereby forming a silicon oxynitride film 22 (see FIG. 2B). This oxidation treatment is performed by dry oxidation for the following reason. That is, when the present inventor diligently studied, it became clear that the atmosphere during the oxidation treatment has a great influence on the interface roughness. This is because roughness can be suppressed.
[0037]
In addition, O introduced into the electric furnace₂The gas flow rate is, for example, 15000 cc. O₂The gas flow rate is preferably set as appropriate so that a desired silicon oxide film 20 is formed.
Next, the temperature of the silicon substrate 10 is lowered to room temperature at a rate of 3 ° C./min (temperature drop).
[0038]
Thus, a silicon oxynitride film 22 is formed on the silicon substrate 10.
Next, for example, a polysilicon layer is formed on the entire surface, and then the gate electrode 24 is formed by patterning the polysilicon layer using a photolithography technique (see FIG. 2C).
Next, a low concentration region 27a is formed by introducing impurities into the gate electrode 24 in a self-aligned manner at a low concentration.
[0039]
Next, for example, a silicon oxide film is formed on the entire surface, and then anisotropic etching is performed to form a sidewall insulating film 26 made of a silicon oxide film on the side surface of the gate electrode 24.
Next, a high concentration region 27b is formed by introducing impurities in a high concentration by self-alignment with the sidewall insulating film 26 and the gate electrode 24.
[0040]
Next, by performing heat treatment, a source / drain diffusion layer 28 having an LDD (Lightly Doped Drain) structure composed of a low concentration region 27a and a high concentration region 27b is formed (see FIG. 3).
Thus, the semiconductor device according to the present embodiment is manufactured.
(Interface state density, fixed charge)
Next, the characteristics of the silicon oxynitride film formed as described above will be described with reference to Table 1. Table 1 shows the interface state density and the fixed charge of the silicon oxynitride film when the film formation conditions in each stage are changed.
[0041]
[Table 1]

In the column of the film formation conditions in Table 1, the upper stage shows the oxidation temperature, the middle stage shows the wet oxidation or the dry oxidation, and the lower stage shows the oxidation time. Show. The upper part of the second stage column shows the nitriding temperature, and the middle part shows N₂The ratio of NO gas to gas is shown, and the lower part shows nitriding time.
[0042]
Examples 1 to 3 correspond to the silicon oxynitride film forming method in the semiconductor device manufacturing method according to the present embodiment. That is, the wet oxidation is performed as the first stage, the nitridation is performed as the second stage, and the dry oxidation is performed as the third stage. In Comparative Examples 1 to 4, wet oxidation is performed as the first stage, nitridation is performed as the second stage, and wet oxidation is performed as the third stage. In Comparative Example 5, when dry oxidation was performed as the first stage, nitridation was performed as the second stage, and wet oxidation was performed as the third stage, Comparative Example 6 was dry oxidation as the first stage, nitrided as the second stage, and third. This is a case where dry oxidation is performed as a step.
[0043]
As can be seen from Table 1, the interface state density of Examples 1 to 3 is 7.77 × 10.^Ten/ EVcm²~ 8.84 × 10^Ten/ EVcm²The interface state density is 1.22 × 10¹¹/ EVcm²~ 2.72 × 10¹¹/ EVcm²As a result, extremely good results were obtained as compared with Comparative Examples 1 to 6.
In Examples 1 to 3, the fixed charge is 8.16 × 10 6.^Ten/ EVcm²~ 8.75x10^Ten/ EVcm²The fixed charge is 1.23 × 10¹¹/ EVcm²~ 2.59 × 10¹¹/ EVcm²As a result, extremely good results were obtained as compared with Comparative Examples 1 to 6.
(Interface roughness)
Next, the interface roughness of the silicon oxynitride film formed as described above will be described with reference to FIG. FIG. 5 is a diagram showing a result of observing the surface of a silicon substrate using an AFM after forming the silicon oxynitride film on the silicon substrate and then peeling the silicon oxynitride film from the silicon substrate using an HF solution. is there.
[0044]
FIG. 5A shows observation results when the present embodiment is applicable, that is, when wet oxidation is performed as the first stage, nitridation is performed as the second stage, and dry oxidation is performed as the third stage. In the first stage wet oxidation, a 5 nm silicon oxide film is formed. In the second stage, the nitriding temperature is 900 ° C., N₂Nitriding was performed at a ratio of NO gas to gas of 5%. In the third stage, dry oxidation was performed at an oxidation temperature of 900 ° C.
[0045]
FIG. 5B shows observation results when wet oxidation is performed as the first stage, nitridation is performed as the second stage, and wet oxidation is performed as the third stage. In FIG. 5B, in the first stage wet oxidation, a 5 nm silicon oxide film is formed, and in the second stage, the nitriding temperature is 900 ° C., N₂Nitriding was performed at a ratio of NO gas to gas of 5%. In the third stage, wet oxidation was performed at an oxidation temperature of 900 ° C.
[0046]
When wet oxidation is performed as the first stage, nitridation is performed as the second stage, and wet oxidation is performed as the third stage, the root mean square value (RMS) of the interface roughness is 0.36 nm, and the maximum and minimum values of the interface roughness are The difference (Range) was 2.87 nm (see FIG. 5B). On the other hand, when this embodiment is applicable, that is, when wet oxidation is performed as the first stage, nitridation is performed as the second stage, and dry oxidation is performed as the third stage, the root mean square value (RMS) of the interface roughness is 0. The difference between the maximum value and the minimum value of the interface roughness (Range) was 2.09 nm (see FIG. 5A).
[0047]
Thus, according to the present embodiment, wet oxidation is performed as the first stage, nitridation is performed as the second stage, and dry oxidation is performed as the third stage. Therefore, wet oxidation is performed as the first stage, nitridation is performed as the second stage, and third stage. As compared with the case where wet oxidation is performed, a semiconductor device having a silicon oxynitride film having a small interface roughness can be manufactured.
[0048]
[Modified Embodiment]
The present invention is not limited to the above embodiment, and various modifications can be made.
For example, in the above embodiment, the case where a silicon oxynitride film is used as a gate insulating film of a transistor has been described as an example. However, a tunnel oxide film of a non-volatile memory having a double gate structure having a floating gate is also formed according to the present invention. A silicon oxynitride film can be applied. In such a semiconductor device, a silicon oxynitride film 22 is formed on a silicon substrate 10, and then a floating gate 30, an ONO film 32, a control gate 34, a source / drain diffusion layer 28, and the like are formed. Can be manufactured (see FIG. 6).
[0049]
In the above embodiment, the dry oxidation performed as the third stage is performed at the same temperature as the nitriding process performed as the second stage. However, the dry oxidation temperature is not necessarily the same as the nitriding temperature. For example, it can set suitably in the range of 850-950 degreeC. In this case, after the nitriding treatment, the atmosphere in the electric furnace is replaced with an atmosphere made of an inert gas, and then the temperature in the electric furnace is appropriately set, and then the atmosphere in the electric furnace is changed to the dry oxidation atmosphere as described above. It is desirable to replace
[0050]
In the above embodiment, when dry oxidation is performed, O₂Oxidized atmosphere consisting of gas was used, but O, to which halides such as HCl and dichloroethylene were added₂An oxidizing atmosphere made of gas may be used. By introducing halogen into the silicon oxynitride film, it is possible to improve breakdown voltage and TDDB characteristics. Further, when an unnecessary heavy metal such as Fe (iron) is contained in the silicon oxynitride film, the unnecessary heavy metal can be removed by halogen.
[0051]
In the above embodiment, when dry oxidation is performed, O₂An oxidizing atmosphere consisting of gas was used._ThreeAn oxidizing atmosphere made of gas may be used. O_ThreeGas is O₂Compared with gas, the oxidizing power is strong and the oxidation rate is fast, so the oxidation time can be shortened and the oxidation can be performed smoothly. O₂Compared with the case of using a gas, it is possible to form a denser film with better film quality, thereby improving dielectric breakdown voltage, TDDB characteristics, and hot carrier resistance.
[0052]
Moreover, in the said embodiment, in dry oxidation performed as a 3rd step, O₂An oxidizing atmosphere consisting of gas was used, but NO gas, NO₂Gas or N₂You may perform dry oxidation using O gas etc., ie, the atmosphere which has oxidizing property and nitriding property. As a result, when a desired concentration of nitrogen cannot be introduced into the silicon oxynitride film in the nitriding process performed as the second stage, an atmosphere having oxidizing and nitriding characteristics is used in the dry oxidation performed as the third stage. Thus, the nitrogen concentration in the silicon oxynitride film can be set to a desired concentration. In addition, when an atmosphere having no nitriding property is used in the dry oxidation performed as the third stage, there is almost no nitrogen at the interface between the silicon substrate and the silicon oxynitride film. When an atmosphere having oxidizing properties and nitriding properties is used in dry oxidation, nitrogen can be introduced into the interface between the silicon substrate and the silicon nitride oxide film. Thereby, since the nitrogen distribution in the depth direction in the silicon oxynitride film can be controlled, a silicon oxynitride film having a desired film quality can be obtained, and leakage current, dielectric breakdown characteristics, TDDB characteristics, and hot Electrical characteristics such as carrier characteristics can be improved.
[0053]
Further, when dry oxidation is performed as the third stage, NO gas, NO₂Gas or N₂In addition to O gas₂An atmosphere to which a gas is added may be used. Accordingly, since an atmosphere having nitriding properties and oxidizing properties is used, the nitrogen distribution in the depth direction in the silicon oxynitride film can be controlled in the same manner as described above.₂The oxidation rate can be increased by increasing the amount of gas added. As a result, even when dry oxidation is performed at a low temperature, it is possible to oxidize at a desired oxidation rate.
[0054]
In the above embodiment, when dry oxidation is performed, O₂Although an oxidizing atmosphere made of gas is used, an oxidizing atmosphere diluted with an inert gas may be used. Thereby, the oxidation rate can be slowed. That is, when the oxidation rate becomes too fast due to the performance of the film forming apparatus or when it is desired to form a thin silicon oxynitride film, the oxidation rate is slowed by increasing the flow rate of the inert gas. Thus, a silicon oxynitride film having a desired film thickness can be formed.
[0055]
【The invention's effect】
As described above, according to the present invention, a silicon oxide film is formed in an oxidizing atmosphere containing water vapor, nitrogen is introduced into the silicon oxide film, and then additional oxidation is performed in an oxidizing atmosphere that does not contain water vapor. A silicon oxynitride film having low interface roughness and low interface state density can be formed. Moreover, since the base oxide film is formed on the surface of the silicon substrate, it is possible to prevent a natural oxide film having poor film quality from being formed on the surface of the silicon substrate even when the silicon substrate is exposed to the atmosphere. be able to.
[0056]
Moreover, according to the present invention, O₂Since the silicon substrate is introduced into an atmosphere containing a gas and an inert gas, the surface of the silicon substrate can be prevented from being roughened.
Moreover, according to the present invention, O₂Since the temperature of the silicon substrate is raised in an atmosphere containing a gas and an inert gas and then replaced with a wet atmosphere, a silicon oxide film with poor film quality is formed on the surface of the silicon substrate in the process of raising the temperature of the silicon substrate. Can be prevented. O₂O in an atmosphere containing a gas and an inert gas₂By reducing the gas ratio to about 1% to about 10%, the oxide film formed on the silicon substrate surface can be suppressed to a negligible level. Further, by setting the ratio of water vapor in the oxidizing atmosphere containing water vapor to 2/3 or less, the reliability of the silicon oxide film can be improved, the hot carrier resistance can be improved, and a good TDDB can be obtained. Characteristics can be obtained.
[0057]
Further, according to the present invention, since the temperature of the silicon substrate is set to a predetermined temperature in an atmosphere made of an inert gas, it is possible to prevent an unnecessary oxide film having poor film quality from being formed.
Furthermore, according to the present invention, oxidation is performed in a wet atmosphere or a dry atmosphere diluted with an inert gas, so that the oxidation rate can be reduced.
[Brief description of the drawings]
FIG. 1 is a process cross-sectional view (part 1) illustrating a method for manufacturing a semiconductor device according to an embodiment of the present invention;
FIG. 2 is a process cross-sectional view (part 2) illustrating the method for manufacturing the semiconductor device according to the embodiment of the present invention;
FIG. 3 is a process cross-sectional view (part 3) illustrating the method for manufacturing the semiconductor device according to the embodiment of the present invention;
FIG. 4 is a diagram showing a film forming sequence when a silicon oxynitride film is formed.
FIG. 5 is a diagram showing a result of observing the surface of a silicon substrate using an AFM.
FIG. 6 is a cross-sectional view showing a semiconductor device according to a modified embodiment of the present invention.
[Explanation of symbols]
10 ... Silicon substrate
12 ... Element region
13 ... Pad oxide film
14: Element isolation film
16 ... Base oxide film
18 ... Silicon oxide film
19 ... Silicon oxynitride film
20 ... Silicon oxide film
22 ... Silicon oxynitride film
24 ... Gate electrode
26. Sidewall insulating film
27a ... low concentration region
27b ... high concentration region
28 ... Source / drain diffusion layer
30 ... Floating gate
32 ... ONO film
34 ... Control gate

Claims (9)

Forming a base oxide film on a silicon substrate;
Thermally oxidizing the silicon substrate on which the base oxide film is formed in an oxidizing first atmosphere containing water vapor to form a silicon oxide film in which the base oxide film is additionally oxidized;
The silicon substrate on which the silicon oxide film is formed is heat-treated in a second atmosphere containing a nitriding gas and N ₂ gas to form a first silicon nitride oxide film in which nitrogen is introduced into the silicon oxide film. And a process of
The silicon substrate on which the first silicon oxynitride film is formed is thermally oxidized in a third atmosphere containing NO gas, NO ₂ gas, or N ₂ O gas that does not contain water vapor and has an oxidizing property, And a step of forming a second silicon oxynitride film formed by additionally oxidizing the first silicon oxynitride film. In the manufacturing method of the semiconductor device according to claim 1,
In the step of forming the silicon oxide film, the temperature is raised to a first temperature, which is a temperature for forming the silicon oxide film, in a fourth atmosphere containing O ₂ gas and an inert gas, and then the fourth atmosphere. Is replaced with the first atmosphere to form the silicon oxide film. A method of manufacturing a semiconductor device, comprising: In the manufacturing method of the semiconductor device of Claim 1 or 2,
In the step of forming the first silicon oxynitride film, the first silicon oxynitride film is stabilized at a second temperature, which is a formation temperature of the first silicon oxynitride film, in a fifth atmosphere made of an inert gas, and then the fifth The first atmosphere is replaced with the second atmosphere to form the first silicon oxynitride film. A method for manufacturing a semiconductor device, comprising: In the manufacturing method of the semiconductor device according to any one of claims 1 to 3,
In the step of forming the second silicon oxynitride film, the sixth silicon oxynitride film is stabilized at a third temperature, which is the formation temperature of the second silicon oxynitride film, in a sixth atmosphere of an inert gas, and then the sixth The second atmosphere is replaced with the third atmosphere, and the second silicon oxynitride film is formed. In the manufacturing method of the semiconductor device of any one of Claims 1 thru / or 4,
The method for manufacturing a semiconductor device, wherein the first atmosphere and / or the third atmosphere is diluted with an inert gas. In the manufacturing method of the semiconductor device according to any one of claims 1 to 5,
The method for manufacturing a semiconductor device, wherein the third atmosphere includes NO gas, NO ₂ gas, or N ₂ O gas. The method of manufacturing a semiconductor device according to claim 6 .
The method for manufacturing a semiconductor device, wherein the third atmosphere further contains O ₂ gas. In the manufacturing method of the semiconductor device according to any one of claims 1 to 7 ,
Wherein in the step of forming the underlying oxide film, a method of manufacturing a semiconductor device characterized by O ₃ exposure to the gas, or by ultraviolet radiation while the radiation exposure to the O ₃ gas or O ₂ gas treatment for forming the underlying oxide film . Forming a base oxide film on a silicon substrate;
Thermally oxidizing the silicon substrate on which the base oxide film is formed in an oxidizing first atmosphere containing water vapor to form a silicon oxide film in which the base oxide film is additionally oxidized;
The silicon substrate on which the silicon oxide film is formed is heat-treated in a second atmosphere containing a nitriding gas and N ₂ gas to form a first silicon nitride oxide film in which nitrogen is introduced into the silicon oxide film. And a process of
The silicon substrate on which the first silicon oxynitride film is formed is thermally oxidized in a third atmosphere containing NO gas, NO ₂ gas, or N ₂ O gas that does not contain water vapor and has an oxidizing property, Forming a second silicon oxynitride film obtained by additionally oxidizing the first silicon oxynitride film;
A method of manufacturing a semiconductor device, comprising: forming a gate electrode on the second silicon oxynitride film; and forming a source / drain diffusion layer on the silicon substrate on both sides of the gate electrode. .

Images