JP5339214B2 - Method for manufacturing silicon nitride substrate and silicon nitride substrate - Google Patents
Method for manufacturing silicon nitride substrate and silicon nitride substrate Download PDFInfo
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本発明は、パワー素子モジュール等の基板に用いられる窒化珪素基板の製造方法、及びこの製造方法によって製造される窒化珪素基板に関する。 The present invention relates to a method for manufacturing a silicon nitride substrate used for a substrate such as a power element module, and a silicon nitride substrate manufactured by this manufacturing method.
近年、各種のセラミックス（焼結体）基板が半導体モジュール用基板や構造用部材として広く用いられている。例えば、大電力で発熱量の大きな半導体素子を実装する半導体モジュール用基板としては、機械的強度の高さ、熱伝導率の高さ、電気的絶縁性の高さが要求される。窒化アルミニウムや窒化珪素等の窒化物焼結体はこれらの特性に優れており、例えば焼結体の窒化物基板が広く用いられている。 In recent years, various ceramic (sintered) substrates have been widely used as semiconductor module substrates and structural members. For example, a semiconductor module substrate on which a semiconductor element with a large electric power and a large calorific value is mounted is required to have high mechanical strength, high thermal conductivity, and high electrical insulation. A nitride sintered body such as aluminum nitride or silicon nitride is excellent in these characteristics. For example, a nitride substrate of a sintered body is widely used.
窒化物基板の元となる窒化物焼結体は、窒化物（ＡｌＮ、Ｓｉ３Ｎ４等）粉末を主成分としたグリーンシートを高温の窒素雰囲気中で焼結することによって作製される。この際、大面積の窒化物焼結体を製造し、この焼結体から所望の大きさをもつ上記の基板を複数枚切り出すという製造方法が一般的である。この焼結は電気炉等を用いて行われるが、製造コストを低減するために、複数のグリーンシートを積層して焼結することにより、複数の窒化物焼結体を同時に得るという手法が用いられる。 The nitride sintered body that is the basis of the nitride substrate is produced by sintering a green sheet mainly composed of nitride (AlN, Si 3 N 4, etc.) powder in a high-temperature nitrogen atmosphere. At this time, a general manufacturing method is to manufacture a nitride sintered body having a large area and cut out a plurality of the substrates having a desired size from the sintered body. This sintering is performed using an electric furnace or the like, but in order to reduce the manufacturing cost, a method of simultaneously obtaining a plurality of nitride sintered bodies by laminating and sintering a plurality of green sheets is used. It is done.
この焼結の際には、積層した窒化物焼結体間の接着を防止するため、窒化物焼結体とされるべきグリーンシートは、分離材を表面に塗布した上で積層される。焼結後、分離材によって複数の窒化物焼結体を分離することができる。 In this sintering, in order to prevent adhesion between the laminated nitride sintered bodies, the green sheets to be made into the nitride sintered bodies are laminated after applying a separating material on the surface. After sintering, a plurality of nitride sintered bodies can be separated by a separating material.
窒化アルミニウムや窒化珪素等の窒化物焼結体は１６００℃以上の高温で焼結する必要があるため、焼結温度以上の高温で安定な窒化ホウ素（ＢＮ）粉が窒化物焼結体間の剥離性を良好にするために分離材として広く用いられている。 Since nitride sintered bodies such as aluminum nitride and silicon nitride need to be sintered at a high temperature of 1600 ° C. or higher, boron nitride (BN) powder that is stable at a high temperature above the sintering temperature is formed between the nitride sintered bodies. Widely used as a separating material in order to improve releasability.
上記のように、ＢＮ粉は、窒化物焼結体間に介在させたたまま焼結が行われるするため、焼結時に窒化物焼結体を拘束したり、窒化物焼結体と反応したりすることにより、変形させることがないようにしなければならない。そのため、使用するＢＮ粉の性状やＢＮ粉の塗布方法等の製造条件を選択する必要がある。 As described above, since the BN powder is sintered while being interposed between the nitride sintered bodies, the BN powder restrains the nitride sintered body during the sintering or reacts with the nitride sintered body. To prevent deformation. Therefore, it is necessary to select manufacturing conditions such as the properties of the BN powder to be used and the application method of the BN powder.
特許文献１では、セラミックスグリーンシートにロールコーターによりＢＮ粉を塗布し平坦な窒化物焼結体を複数枚重ねて焼結するセラミックス焼結体の製造方法が開示されている。この発明ではＢＮ粉の酸素量を３重量％以下として、焼結助剤相との反応を抑制し、ＢＮ粉の平均粒径を２０μｍ以下とすることで塗布したＢＮ粉の密着性を良好にしている。また、ＢＮ粉の塗布量を０．３〜３ｍｇ／ｃｍ２とし、積層したグリーンシートの上下面をＢＮ製セッタで押さえながら焼結することで、剥離性を良好にし、かつ、焼結時の変形を抑制し反りを少なくしている。 Patent Document 1 discloses a method of manufacturing a ceramic sintered body in which BN powder is applied to a ceramic green sheet by a roll coater and a plurality of flat nitride sintered bodies are stacked and sintered. In this invention, the oxygen amount of the BN powder is set to 3% by weight or less, the reaction with the sintering aid phase is suppressed, and the average particle size of the BN powder is set to 20 μm or less to improve the adhesion of the applied BN powder. ing. In addition, the application amount of BN powder is 0.3 to 3 mg / cm 2, and sintering is performed while pressing the upper and lower surfaces of the stacked green sheets with a BN setter, and at the time of sintering, Deformation is suppressed and warpage is reduced.
しかしながら、窒化物焼結体の中で、窒化アルミニウム焼結体に比べて、特に窒化珪素焼結体の場合、以下のような課題があった。窒化珪素焼結体中の窒化珪素粒子は柱状の形状をしているため、窒化珪素焼結体の表面粗さは比較的大きくなる。そのため、焼結過程でＢＮ粉が表面の窒化珪素粒子間に容易に入り込み、窒化珪素焼結体の収縮を阻害する。特に窒化珪素焼結体間の剥離性を良くするために、ＢＮ粉の塗布量が多くした場合には、この収縮が阻害されやすくなるため、焼結体の相対密度が上がりにくく、必要な強度が得られないという課題があった。また、高熱伝導率を有する窒化珪素基板に用いられる窒化珪素焼結体では、比較的蒸気圧の高い酸化マグネシウム等が焼結助剤として添加されるため、この焼結助剤が酸素を含有したＢＮ粉と容易に反応することで変形を引き起こし、窒化珪素焼結体にうねりが発生しやすいという課題もあった。窒化珪素焼結体は窒化アルミニウムと比較すると強度が高いことから、窒化珪素基板では熱抵抗を低減するために比較的薄い基板例えば０．２〜０．６ｍｍの基板が使われることが多く、上記のうねりの発生が特に課題となる。上記説明したように、従来技術の方法では、窒化珪素焼結体の剥離性、密度、強度、熱伝導率などの基板性能、及びうねりは相反する関係にあるため、これら全てを満足することは困難であり、窒化珪素基板の製造歩留まりが低下するという課題があった。 However, among the nitride sintered bodies, there are the following problems, particularly in the case of a silicon nitride sintered body, as compared with the aluminum nitride sintered body. Since the silicon nitride particles in the silicon nitride sintered body have a columnar shape, the surface roughness of the silicon nitride sintered body becomes relatively large. Therefore, BN powder easily enters between the silicon nitride particles on the surface during the sintering process, and inhibits the shrinkage of the silicon nitride sintered body. In particular, when the application amount of BN powder is increased in order to improve the peelability between the silicon nitride sintered bodies, this shrinkage tends to be hindered, so that the relative density of the sintered body is difficult to increase, and the required strength. There was a problem that could not be obtained. In addition, in a silicon nitride sintered body used for a silicon nitride substrate having high thermal conductivity, magnesium oxide or the like having a relatively high vapor pressure is added as a sintering aid, so that this sintering aid contains oxygen. There also existed a subject that a deformation | transformation was caused by reacting easily with BN powder, and a wave | undulation was easy to generate | occur | produce in a silicon nitride sintered compact. Since the silicon nitride sintered body is higher in strength than aluminum nitride, a relatively thin substrate, for example, a 0.2 to 0.6 mm substrate is often used to reduce the thermal resistance of the silicon nitride substrate. The generation of undulation is particularly a problem. As described above, in the method of the prior art, the substrate performance such as the peelability, density, strength, thermal conductivity, and swell of the silicon nitride sintered body are in a contradictory relationship, and therefore satisfying all of them There is a problem that the production yield of the silicon nitride substrate is lowered.
本発明は、斯かる問題点に鑑みてなされたものであり、複数枚の薄いグリーンシートを積層して焼結した後に分離する窒化珪素基板の製造方法であって、剥離性が良好で、相対密度が高くかつ、高強度、高熱伝導であって、変形の少ない窒化珪素基板の製造方法を提供することを目的とする。また、相対密度が高くかつ、高強度、高熱伝導であって、変形の少ない窒化珪素基板を提供することを目的とする。 The present invention has been made in view of such problems, and is a method of manufacturing a silicon nitride substrate that is separated after laminating and sintering a plurality of thin green sheets, and has a good releasability and relative An object of the present invention is to provide a method for manufacturing a silicon nitride substrate having high density, high strength, high thermal conductivity, and little deformation. It is another object of the present invention to provide a silicon nitride substrate having a high relative density, high strength, high thermal conductivity, and little deformation.
本発明者らは上記課題を解消するため鋭意検討した結果、分離材として使用するＢＮ粉の、平均粒子径、比表面積、酸素量の所定の範囲とし、且つ塗布量などの製造条件を所定の範囲とすることにより、相反する関係にある、窒化珪素焼結体の剥離性、密度、強度、熱伝導率などの基板性能、及びうねりを両立させることができることを見出し本発明に想到した。 As a result of intensive studies to solve the above problems, the present inventors have determined that the BN powder used as the separation material has a predetermined range of average particle diameter, specific surface area, and oxygen amount, and manufacturing conditions such as coating amount are predetermined. By setting the range, the present inventors have found that it is possible to achieve both substrate performance such as peelability, density, strength, thermal conductivity, and swell of the silicon nitride sintered body, which are in a contradictory relationship, and swell.
すなわち、本願第1の発明は、分離材を介して、窒化珪素粉末および焼結助剤として少なくとも酸化マグネシウム（ＭｇＯ）を含む複数枚のグリーンシートを積層して焼結した後に分離することによって複数枚の窒化珪素焼結体を得て、該窒化珪素焼結体から窒化珪素基板を得る、窒化珪素基板の製造方法であって、前記分離材が酸素量０．０１〜０．５重量％、平均粒子径４〜２０μｍ、比表面積２０ｍ２／ｇ以下の窒化ホウ素（ＢＮ）粉であり、前記グリーンシートの厚さは０．２〜０．６ｍｍであり該グリーンシート表面に塗布された前記ＢＮ粉の塗布量は０．０５〜１．４ｍｇ／ｃｍ２であることを特徴とする窒化珪素基板の製造方法を提供するものである。
That is, the first invention of the present application includes a plurality of green sheets that are separated from each other by laminating and sintering a plurality of green sheets containing at least magnesium oxide (MgO) as a sintering aid through a separating material. A silicon nitride substrate manufacturing method for obtaining a single silicon nitride sintered body and obtaining a silicon nitride substrate from the silicon nitride sintered body, wherein the separating material has an oxygen content of 0.01 to 0.5% by weight, Boron nitride (BN) powder having an average particle diameter of 4 to 20 μm and a specific surface area of 20 m 2 / g or less, the thickness of the green sheet is 0.2 to 0.6 mm, and the BN applied to the surface of the green sheet The application amount of the powder is 0.05 to 1.4 mg / cm 2 , thereby providing a method for producing a silicon nitride substrate.
前記ＢＮ粉のグリーンシート表面への塗布は、前記ＢＮ粉と水とを樹脂製ボールを用いて混合して作製したスラリーを塗布して行うことを特徴とすることが好ましい。 The application of the BN powder to the surface of the green sheet is preferably performed by applying a slurry prepared by mixing the BN powder and water using a resin ball.
前記スラリーを作製後、２４時間以内にグリーンシート表面への塗布を行うことが好ましい。 It is preferable to apply to the surface of the green sheet within 24 hours after the slurry is prepared.
前記スラリーが塗布されたグリーンシートを大気中、６０℃以上の温度で乾燥した後、積層して焼結することが好ましい。 It is preferable that the green sheet coated with the slurry is dried in the atmosphere at a temperature of 60 ° C. or higher and then laminated and sintered.
前記ＢＮが六方晶窒化ホウ素であり、該六方晶窒化ホウ素が塗布されたグリーンシートの表面における六方晶窒化ホウ素の（００２）面と（１００）面のＸ線回折線ピーク強度の比が４以上であることが好ましい。 The BN is hexagonal boron nitride, and the ratio of the X-ray diffraction line peak intensity between the (002) plane and the (100) plane of the hexagonal boron nitride on the surface of the green sheet coated with the hexagonal boron nitride is 4 or more. It is preferable that
上記目的を達成するための本願第２の発明は、Ｓｉ３Ｎ４を主成分とし、少なくともＭｇを含む窒化珪素基板において、前記窒化珪素基板の表面に残留したＢＮに由来するＢ量の分布を示す変動係数Ｃｖが１．０以下であり、前記窒化珪素基板表面のうねりＷａが１．５μｍ以下であり（但し、うねりは、表面粗さ計を用いて、ろ波中心線うねりを測定して、その算術平均うねりＷａ、すなわち、表面高さの平均値からの偏差の絶対値の算術平均である量を用いるものとし、測定条件は評価長さ３０ｍｍ、測定速度０．３ｍｍ／ｓ、カットオフ値（λｃ）０．２５ｍｍ、カットオフ値（λｆ）８．０ｍｍとする）、相対密度が９８％以上である窒化珪素基板を提供するものである。 In order to achieve the above object, the second invention of the present application provides a distribution of B amount derived from BN remaining on the surface of the silicon nitride substrate in a silicon nitride substrate containing Si 3 N 4 as a main component and containing at least Mg. The coefficient of variation Cv shown is 1.0 or less, and the waviness Wa on the surface of the silicon nitride substrate is 1.5 μm or less (however, the waviness is measured by measuring the filtered center line waviness using a surface roughness meter). The arithmetic average waviness Wa, that is, the amount that is the arithmetic average of the absolute value of the deviation from the average value of the surface height is used, and the measurement conditions are an evaluation length of 30 mm, a measurement speed of 0.3 mm / s, and a cutoff. A silicon nitride substrate having a value (λ c ) of 0.25 mm, a cutoff value (λ f ) of 8.0 mm), and a relative density of 98% or more is provided.
第1の発明および第２の発明によれば、複数枚のグリーンシートをＢＮ粉を介して積層した後に窒化珪素焼結体を焼結した場合に、複数枚の窒化珪素焼結体を容易に剥離でき、高密度、高強度、高熱伝導の有し、かつうねりの小さな窒化珪素基板を得ることができる。特に、従来の技術ではうねりの生じやすい酸化マグネシウムを焼結助剤として用いる窒化珪素焼結体の場合や、板厚０．２〜０．６ｍｍ程度の薄い窒化珪素焼結体を焼結する場合に、特に本発明は有効である。 According to the first invention and the second invention, when the silicon nitride sintered body is sintered after laminating a plurality of green sheets via the BN powder, the plurality of silicon nitride sintered bodies can be easily formed. A silicon nitride substrate that can be peeled, has high density, high strength, high thermal conductivity, and small waviness can be obtained. In particular, in the case of a silicon nitride sintered body using magnesium oxide as a sintering aid, which is prone to waviness in the prior art, or in the case of sintering a thin silicon nitride sintered body having a thickness of about 0.2 to 0.6 mm In particular, the present invention is effective.
以下、本発明の実施形態を具体的に説明するが、本発明は以下の実施形態に限定されるものでなく、本発明の主旨を逸脱しない範囲で、当業者の通常の知識に基づいて、以下の実施形態に対して、適宜変更が加えられたものも本発明の範囲内にはいる。 Hereinafter, embodiments of the present invention will be specifically described, but the present invention is not limited to the following embodiments, and is based on the ordinary knowledge of those skilled in the art without departing from the gist of the present invention. The following embodiments are appropriately modified and are within the scope of the present invention.
本発明の一実施形態では、パワー半導体モジュール等に使用される絶縁性セラミックス基板としての窒化珪素基板の製造方法であって、まず、原料調整・混合工程として、窒化珪素粉末に焼結助剤となるセラミックス粉末を分散媒となる有機溶剤を使用し、ボールミル等で混合し、さらに、バインダー及び可塑剤と混合してスラリーを作製する。高熱伝導率の窒化珪素基板を得るため焼結助剤としては、酸化マグネシウム（ＭｇＯ）および希土類元素の酸化物（ＲＥxＯy）が好ましい。酸化マグネシウムは比較的低温で液相を形成するため、窒化珪素焼結体の焼結を促進することができ、且つ、窒化珪素粒子に固溶し難いため、窒化珪素基板の熱伝導率を高くすることができる。また希土類元素としてはＹ、Ｌａ、Ｃｅ、Ｎｄ、Ｐｍ、Ｓｍ、Ｅｕ、Ｇｄ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ等があげられるが、中でもＹの酸化物Ｙ２Ｏ３は窒化珪素基板の高密度化に有効であり、より好ましい。酸化マグネシウムの添加量は０．５〜４．０重量％、希土類元素の酸化物の添加量は１．５〜１５重量％であることが好ましい。 In one embodiment of the present invention, a method of manufacturing a silicon nitride substrate as an insulating ceramic substrate used for a power semiconductor module or the like, first, as a raw material adjustment / mixing step, a silicon nitride powder and a sintering aid The resulting ceramic powder is mixed with a ball mill or the like using an organic solvent as a dispersion medium, and further mixed with a binder and a plasticizer to prepare a slurry. As a sintering aid for obtaining a silicon nitride substrate having high thermal conductivity, magnesium oxide (MgO) and rare earth element oxide (RExOy) are preferable. Since magnesium oxide forms a liquid phase at a relatively low temperature, it can promote the sintering of the silicon nitride sintered body and is difficult to dissolve in silicon nitride particles, so that the thermal conductivity of the silicon nitride substrate is increased. can do. Examples of rare earth elements include Y, La, Ce, Nd, Pm, Sm, Eu, Gd, Dy, Ho, Er, Tm, Yb, and Lu. Among them, Y oxide Y 2 O 3 is silicon nitride. This is effective for increasing the density of the substrate and is more preferable. The amount of magnesium oxide added is preferably 0.5 to 4.0% by weight, and the amount of rare earth element oxide added is preferably 1.5 to 15% by weight.
次に、成形工程として、上記混合して作製したスラリーを必要に応じて粘度調整し、これをドクターブレード法、押し出し成形法、もしくはそれに準じた方法により所定厚さのシート状に成形する。このときのシート成形体の板厚は、半導体パワーモジュールに応じて適宜決定できるが、０．２〜０．６ｍｍ程度とすることが好ましい。 Next, as a forming step, the viscosity of the slurry prepared by mixing is adjusted as necessary, and formed into a sheet having a predetermined thickness by a doctor blade method, an extrusion forming method, or a method according thereto. Although the plate | board thickness of the sheet molded object at this time can be suitably determined according to a semiconductor power module, it is preferable to set it as about 0.2-0.6 mm.
次に、グリーンシートを所望の形状に切断した後、切断されたグリーンシートの片面もしくは両面に酸素量０．０１〜０．５重量％、平均粒子径４〜２０μｍ、比表面積２０ｍ２／ｇ以下、酸素量０．０１〜０．５重量％のＢＮ粉を０．０５〜１．４ｍｇ／ｃｍ２の塗布量で塗布した後、ＢＮ粉が塗布されたグリーンシートを復数枚、積層して焼結する。 Next, after the green sheet is cut into a desired shape, an oxygen amount of 0.01 to 0.5 wt%, an average particle diameter of 4 to 20 μm, and a specific surface area of 20 m 2 / g or less are applied to one or both sides of the cut green sheet. After applying BN powder having an oxygen amount of 0.01 to 0.5% by weight in an application amount of 0.05 to 1.4 mg / cm 2, a plurality of green sheets coated with BN powder were laminated. Sinter.
ＢＮ粉の酸素量を０．０１〜０．５重量％としたのは、焼結時にＢＮ粉が窒化珪素焼結体の焼結助剤成分と、適度に反応して、窒化珪素焼結体の表面に存在して、隣接する窒化珪素焼結体同士の接着を防ぎ、剥離性を良くするとともに、窒化珪素焼結体の変形を防止できるためである。酸素量が０．５重量％より多い場合、焼結時にグリーンシート中の焼結助剤と著しく反応して、局所的な変形を引き起こし、窒化珪素基板にうねりが生じるためである。特に、この現象は、焼結助剤として酸化マグネシウムを用いた場合、焼結助剤との反応が起こり易く、窒化珪素基板の厚さが０．２〜０．６ｍｍの場合に顕著になる。一方、酸素量が０．０１％未満の場合は、焼結時にＢＮ粉と窒化珪素焼結体の反応がほとんど起こらないため、焼結収縮に伴いＢＮ粉が基板表面を移動することもあり、グリーンシート表面に塗布されたＢＮ粉の均一性が損なわれ、ＢＮ粉の存在割合の少ない場所が発生して隣接する窒化珪素焼結体が接着し剥離性が損なわれる。ＢＮ粉の酸素量は上記観点から０．０２〜０．４重量％が好ましく、０．０５〜０．３重量％がより好ましい。本発明の窒化珪素基板の製造方法において、酸素量が０．０１〜０．５重量％のＢＮ粉を使用するが、焼結前の製造工程でＢＮ粉の酸素量が増えないような操作をすることが好ましい。 The oxygen content of the BN powder is set to 0.01 to 0.5% by weight because the BN powder reacts appropriately with the sintering aid component of the silicon nitride sintered body during sintering, and the silicon nitride sintered body This is because it is possible to prevent adhesion between adjacent silicon nitride sintered bodies, improve peelability, and prevent deformation of the silicon nitride sintered body. This is because when the amount of oxygen is more than 0.5% by weight, it significantly reacts with the sintering aid in the green sheet during sintering, causing local deformation and causing undulation in the silicon nitride substrate. In particular, when magnesium oxide is used as a sintering aid, this phenomenon is likely to react with the sintering aid, and becomes prominent when the silicon nitride substrate has a thickness of 0.2 to 0.6 mm. On the other hand, when the amount of oxygen is less than 0.01%, the reaction between the BN powder and the silicon nitride sintered body hardly occurs at the time of sintering, so the BN powder may move on the substrate surface along with the sintering shrinkage. Uniformity of the BN powder applied to the surface of the green sheet is impaired, a place where the BN powder is present in a small proportion is generated, and the adjacent silicon nitride sintered bodies are bonded to each other and the peelability is impaired. From the above viewpoint, the oxygen content of the BN powder is preferably 0.02 to 0.4% by weight, and more preferably 0.05 to 0.3% by weight. In the method for manufacturing a silicon nitride substrate according to the present invention, BN powder having an oxygen amount of 0.01 to 0.5% by weight is used, but the operation is performed so that the oxygen amount of the BN powder does not increase in the manufacturing process before sintering. It is preferable to do.
ＢＮ粉の平均粒子径を４〜２０μｍとしたのは、平均粒子径が４μm未満であると、窒化珪素焼結体表面の柱状窒化珪素粒子により形成される凹凸の凹部にＢＮ粉が容易に入り込み、窒化珪素焼結体の収縮を阻害し、高密度の窒化珪素基板が得られないからであり、平均粒子径が２０μｍを超えると、ＢＮ粉のグリーンシート表面への密着性が悪くなって取り扱い時に剥離しやすくなるからである。上記観点からＢＮ粉の好ましい平均粒子径は６〜１５μｍである。 The average particle diameter of the BN powder is set to 4 to 20 μm. When the average particle diameter is less than 4 μm, the BN powder easily enters the concave and convex recesses formed by the columnar silicon nitride particles on the surface of the silicon nitride sintered body. This is because the shrinkage of the silicon nitride sintered body is inhibited, and a high-density silicon nitride substrate cannot be obtained. When the average particle diameter exceeds 20 μm, the adhesion of the BN powder to the green sheet surface is deteriorated and handled. This is because sometimes it becomes easy to peel off. From the above viewpoint, the preferable average particle diameter of the BN powder is 6 to 15 μm.
ＢＮ粉の比表面積を２０ｍ２／ｇ以下としたのは、比表面積が２０ｍ２／ｇを超えると、上記したＢＮ粉の酸素量が多くなって、０．５重量％を超えやすくなり、窒化珪素基板にうねりが生じるためである。上記観点からＢＮ粉の好ましい比表面積は１０ｍ２／ｇ以下である。 The specific surface area of the BN powder is set to 20 m 2 / g or less because when the specific surface area exceeds 20 m 2 / g, the amount of oxygen in the BN powder increases, and the BN powder tends to exceed 0.5 wt%. This is because undulation occurs in the silicon substrate. From the above viewpoint, the preferred specific surface area of the BN powder is 10 m 2 / g or less.
ＢＮ粉のグリーンシート表面への塗布量を０．０５〜１．４ｍｇ／ｃｍ２としたのは、ＢＮ粉の塗布量が１．４ｍｇ／ｃｍ２を超える場合、多量のＢＮ粉が焼結過程で窒化珪素焼結体表面の窒化珪素粒子間に容易に入り込み、収縮を阻害するため、窒化珪素焼結体の密度が低下し、強度も低下するためである。一方、ＢＮ粉の塗布量が０．０５ｍｇ／ｃｍ２未満の場合、ＢＮ粉が不十分となる箇所が出現し、隣接する窒化珪素焼結体間の反応により、窒化珪素焼結体同士が付着してしまい、剥離性が低下する。上記観点からＢＮ粉の好ましい塗布量は０．１０〜１．０ｍｇ／ｃｍ２である。 The coating amount of the green sheet surface of the BN powder was 0.05~1.4mg / cm 2, when the coating amount of the BN powder exceeds 1.4 mg / cm 2, a large amount of BN powder sintering process This is because the silicon nitride sintered body easily enters between the silicon nitride particles and inhibits the shrinkage, so that the density of the silicon nitride sintered body is lowered and the strength is also lowered. On the other hand, when the application amount of BN powder is less than 0.05 mg / cm 2, a portion where the BN powder becomes insufficient appears, and silicon nitride sintered bodies adhere to each other due to a reaction between adjacent silicon nitride sintered bodies. As a result, the peelability decreases. From the above viewpoint, the preferred coating amount of BN powder is 0.10 to 1.0 mg / cm 2 .
また、ＢＮ粉の純度は９９％以上とすることが好ましい。１％を超える不純物を含有する場合、不純物とグリーンシートを構成する成分との反応が起こり、窒化珪素焼結体の変形を引き起こす可能性がある。特に、ＢＮ粉中の含有Ｃ量は０．１％以下とすることが好ましい。含有Ｃ量が０．１％より多い場合、焼結時にグリーンシート中の窒化珪素や焼結助剤成分の還元反応が起こりやすくなり、窒化珪素焼結体の変形を引き起こす場合がある。 Moreover, it is preferable that the purity of BN powder shall be 99% or more. When it contains an impurity exceeding 1%, a reaction between the impurity and a component constituting the green sheet occurs, which may cause deformation of the silicon nitride sintered body. In particular, the C content in the BN powder is preferably 0.1% or less. When the content of C is more than 0.1%, the reduction reaction of silicon nitride and the sintering aid component in the green sheet is likely to occur during sintering, which may cause deformation of the silicon nitride sintered body.
なおＢＮ粉の塗布は、グリーンシート表面へ均一に塗布するため、前記ＢＮ粉を水に分散させたスラリーを作製した後に、スプレー式の塗布機により霧状にして塗布してもよいし、ＢＮ粉を刷毛で直接塗布して行うことが好ましい。ここで、スラリーを作製する際には、前記ＢＮ粉と水とを樹脂製ボールを用いて混合することが好ましい。水を用いてスラリーとする理由は、有機溶剤を用いてスラリーを作製した場合、スラリーをグリーンシートに塗布した際にグリーンシートに含まれる有機溶剤に可溶なバインダーを溶解させてグリーンシートを変形させるためであるが、水を使用した場合にはこの問題を解消できる。ＢＮ粉と水の割合は重量比でＢＮ粉／水＝１／１０〜１／２程度が適当である。また、樹脂ボールを用いて混合するのは、ＢＮ粉の粉砕を抑制するためであり、通常用いられるセラミックスボールに比較して硬度が低いため、ＢＮ粉の粉砕が抑制され、結果的にＢＮ粉の酸素量の増加を低減できるためである。尚、樹脂製ボールは混合を均一に行わせるため、内部に鋼などの金属製のボールを内包しても良い。 In order to apply the BN powder uniformly to the surface of the green sheet, after preparing a slurry in which the BN powder is dispersed in water, it may be applied in the form of a mist with a spray-type applicator. It is preferable to apply the powder directly with a brush. Here, when producing a slurry, it is preferable to mix the BN powder and water using a resin ball. The reason for making the slurry using water is that when the slurry is made using an organic solvent, the green sheet is deformed by dissolving the binder soluble in the organic solvent contained in the green sheet when the slurry is applied to the green sheet. This is to solve this problem when water is used. The ratio of BN powder to water is suitably about BN powder / water = 1/10 to 1/2 by weight. Further, the mixing using the resin balls is to suppress the pulverization of the BN powder, and since the hardness is lower than that of the ceramic balls that are normally used, the BN powder is suppressed from being pulverized. This is because an increase in the amount of oxygen can be reduced. In addition, in order to mix the resin balls uniformly, metal balls such as steel may be included inside.
なお、本発明者らが鋭意検討した結果、水の存在下でＢＮ粉の酸素量が増加することが判明したため、酸素量の増加による、窒化珪素基板のうねりの発生を抑制するため混合時間は短い方が好ましい。具体的には２４時間以内、より好ましくは１時間以内、更に好ましくは０．５時間以内である。 In addition, as a result of intensive studies by the present inventors, it was found that the amount of oxygen in the BN powder increases in the presence of water, so the mixing time is set to suppress the occurrence of undulation of the silicon nitride substrate due to the increase in the amount of oxygen. The shorter one is preferable. Specifically, it is within 24 hours, more preferably within 1 hour, still more preferably within 0.5 hour.
本発明の窒化珪素基板の製造方法において、前記スラリーを作製後、２４時間以内にグリーンシート表面への塗布を行うことが好ましい。本発明のような窒化珪素基板を効率よく生産する製造方法では、あらかじめ大量に製造したスラリーを準備しておき、塗布するのが通常のやり方であるが、上記したように、ＢＮ粉を水に分散させたスラリーを作製後、塗布までの時間が２４時間を越えると、ＢＮ粉末の酸素量が増加して、窒化珪素基板のうねりが大きくなることもあるためである。前記スラリーを作製後、グリーンシート表面への塗布までの時間は、より好ましくは１時間以内、更に好ましくは０．５時間以内である。 In the method for producing a silicon nitride substrate of the present invention, it is preferable that the slurry is applied to the surface of the green sheet within 24 hours. In a manufacturing method for efficiently producing a silicon nitride substrate as in the present invention, it is a common practice to prepare and apply a slurry manufactured in large quantities in advance, but as described above, BN powder is made into water. This is because if the time until coating after the dispersed slurry is produced exceeds 24 hours, the amount of oxygen in the BN powder increases and the swell of the silicon nitride substrate may increase. The time from the preparation of the slurry to the application to the green sheet surface is more preferably within 1 hour, and even more preferably within 0.5 hour.
本発明の窒化珪素基板の製造方法において、前記ＢＮ粉が六方晶窒化ホウ素であり、該六方晶窒化ホウ素が塗布されたグリーンシートの表面における六方晶窒化ホウ素の（００２）面と（１００）面のＸ線回折線ピーク強度の比が４以上であることが好ましい。上記したＢＮ粉と及びＢＮ粉スラリーの条件、及び塗布条件を調整することにより、グリーンシートの表面における六方晶窒化ホウ素の（００２）面と（１００）面のＸ線回折線ピーク強度の比は４以上となる。このような構成とすることにより、六方晶窒化ホウ素粒子のｃ軸がグリーンシート表面に対して、凡そ垂直になるようにＢＮ粉を配向存在させることができるため、ＢＮ粉を塗布したグリーンシートは焼結時にグリーンシート間での摩擦抵抗が低減され、結果的に窒化珪素基板のうねりの発生を抑制することができる。 In the method for manufacturing a silicon nitride substrate of the present invention, the BN powder is hexagonal boron nitride, and the (002) plane and (100) plane of hexagonal boron nitride on the surface of the green sheet coated with the hexagonal boron nitride. The X-ray diffraction line peak intensity ratio is preferably 4 or more. By adjusting the conditions of the BN powder and the BN powder slurry and the application conditions, the ratio of the X-ray diffraction line peak intensity of the (002) plane and the (100) plane of hexagonal boron nitride on the surface of the green sheet is 4 or more. By adopting such a configuration, the BN powder can be oriented so that the c-axis of the hexagonal boron nitride particles is substantially perpendicular to the surface of the green sheet. Friction resistance between the green sheets is reduced during sintering, and as a result, generation of waviness of the silicon nitride substrate can be suppressed.
本発明の窒化珪素基板の製造方法において、前記ＢＮ粉を水に分散させたスラリーが塗布されたグリーンシートを大気中、６０℃以上の温度で乾燥した後、積層して焼結することが好ましい。６０℃未満の温度で乾燥させた場合は、乾燥に時間を要するため、ＢＮ粉の酸素量が増加して、窒化珪素基板のうねりが大きくなることもあるためである。乾燥温度は、時間を短くする観点から、７０〜１２０℃が好ましく、更に８０〜１２０℃がより好ましい。 In the method for producing a silicon nitride substrate of the present invention, it is preferable that the green sheet coated with the slurry in which the BN powder is dispersed in water is dried in the atmosphere at a temperature of 60 ° C. or higher and then laminated and sintered. . This is because when drying is performed at a temperature of less than 60 ° C., it takes time to dry, and thus the amount of oxygen in the BN powder increases and the undulation of the silicon nitride substrate may increase. From the viewpoint of shortening the time, the drying temperature is preferably 70 to 120 ° C, and more preferably 80 to 120 ° C.
ＢＮ粉を水に分散させたスラリーが塗布、乾燥されたグリーンシートは数枚〜数十枚重ねて、積層された後、グリーンシート中のバインダー等の有機成分を除去するために脱脂を行う。脱脂は９００℃以下の大気中、もしくは窒素、アルゴン等の不活性雰囲気中で行うことが好ましい。積層するグリーンシートの枚数は５〜５０枚が好ましい。 After applying and drying several to several tens of green sheets coated and dried with BN powder dispersed in water, the green sheets are degreased to remove organic components such as binders in the green sheets. Degreasing is preferably performed in the air at 900 ° C. or lower or in an inert atmosphere such as nitrogen or argon. The number of green sheets to be laminated is preferably 5 to 50.
脱脂後のグリーンシートは３０Ｐａ以下の真空にした後、窒素で置換した雰囲気中で焼結することが好ましい。窒素雰囲気中１６００〜２０００℃の温度で焼結し、窒化珪素焼結体とする。このとき、積層したグリーンシートはＢＮ製のセッタの上に配置される。また、その上部にも焼結時の焼結助剤成分や窒化珪素成分の揮発を抑制するためにＢＮ製セッタを配置することが好ましい。 The degreased green sheet is preferably sintered in an atmosphere substituted with nitrogen after being evacuated to 30 Pa or less. Sintering is performed at a temperature of 1600 to 2000 ° C. in a nitrogen atmosphere to obtain a silicon nitride sintered body. At this time, the stacked green sheets are placed on a BN setter. Further, it is preferable to dispose a setter made of BN at the upper part in order to suppress volatilization of the sintering aid component and the silicon nitride component during sintering.
窒化珪素焼結体はそのまま窒化珪素基板として用いてもよいが、熱処理やブラスト加工等による表面処理を施すことが好ましい。熱処理は例えば、焼結温度以下の窒素雰囲気中で加熱することにより、基板表面の粒界相量を調整し、金属板との接合性を良好にしたり、荷重をかけて加圧しながら加熱することで表面のそりを矯正したり、もしくは、８００〜１５００℃の大気中もしくは酸素雰囲気中で表面を酸化処理し、金属板との接合性を良好にするために実施する。ブラスト加工は例えば、１０〜１００μｍのアルミナ砥粒を窒化珪素基板表面に噴射することによって、表面に突出した窒化珪素粒子を削り、表面粗さを低減して、金属板との接合性を良好にするために実施する。 Although the silicon nitride sintered body may be used as it is as a silicon nitride substrate, it is preferable to perform a surface treatment such as heat treatment or blasting. For example, heat treatment is performed in a nitrogen atmosphere at a temperature lower than the sintering temperature to adjust the amount of grain boundary phase on the substrate surface, to improve the bondability with the metal plate, or to heat while applying pressure while applying a load. This is carried out in order to correct the warpage of the surface or to oxidize the surface in the air at 800 to 1500 ° C. or in an oxygen atmosphere to improve the bondability with the metal plate. Blasting, for example, by spraying 10 to 100 μm alumina abrasive grains onto the surface of the silicon nitride substrate, scrapes the silicon nitride particles protruding on the surface, reduces the surface roughness, and improves the bondability with the metal plate To implement.
上記した窒化珪素基板の製造方法を採用することにより、複数枚の窒化珪素焼結体を容易に剥離でき、高密度、高強度、高熱伝導率を有し、かつうねりの小さな窒化珪素基板を得ることができ、製造歩留まりの低下を阻止することが可能となる。具体的には、Ｓｉ３Ｎ４を主成分とする窒化珪素基板において、前記窒化珪素基板の表面に残留したＢＮに由来するＢ量の分布を示す変動係数Ｃｖが１．０以下であり、前記窒化珪素基板表面のうねりＷａが１．５μｍ以下であり（但し、うねりは、表面粗さ計を用いて、ろ波中心線うねりを測定して、その算術平均うねりＷａ、すなわち、表面高さの平均値からの偏差の絶対値の算術平均である量を用いるものとし、測定条件は評価長さ３０ｍｍ、測定速度０．３ｍｍ／ｓ、カットオフ値（λｃ）０．２５ｍｍ、カットオフ値（λｆ）８．０ｍｍとする）、相対密度が９８％以上である窒化珪素基板を得ることができる。ＢＮ粉はグリーンシートの一方の面に塗布するが、グリーンシートを重ねることで、塗布していない面もＢＮ粉に接して、焼結後にはＢＮ粉が付着しているためＢの変動係数は窒化珪素基板の両面でほぼ同じ値となる。 By adopting the above-described method for manufacturing a silicon nitride substrate, a plurality of silicon nitride sintered bodies can be easily peeled, and a silicon nitride substrate having high density, high strength, high thermal conductivity, and small waviness is obtained. Therefore, it is possible to prevent a decrease in manufacturing yield. Specifically, in a silicon nitride substrate containing Si 3 N 4 as a main component, a variation coefficient Cv indicating a distribution of B amount derived from BN remaining on the surface of the silicon nitride substrate is 1.0 or less, The waviness Wa on the surface of the silicon nitride substrate is 1.5 μm or less (however, the waviness is measured by measuring the waviness centerline waviness using a surface roughness meter, and the arithmetic average waviness Wa, ie, the surface height An amount that is an arithmetic average of absolute values of deviation from the average value is used, and measurement conditions are an evaluation length of 30 mm, a measurement speed of 0.3 mm / s, a cutoff value (λ c ) of 0.25 mm, and a cutoff value ( λ f ) of 8.0 mm), and a silicon nitride substrate having a relative density of 98% or more can be obtained. The BN powder is applied to one side of the green sheet, but by overlapping the green sheet, the non-coated surface is also in contact with the BN powder, and the BN powder adheres after sintering, so the coefficient of variation of B is The values are almost the same on both sides of the silicon nitride substrate.
ここで、基板表面のＢ量の分布を示す変動係数（Ｃｖ：Coefficient of variation）は、熱処理やブラスト加工等による表面処理を施した後の上記基板表面の任意の位置においてＥＰＭＡによりビーム径１μｍで１ｍｍの範囲を走査し、２μｍ間隔で測定したＢのＸ線強度の値から、その標準偏差をその平均値で割ることによって求めた値である。 Here, the coefficient of variation (Cv) indicating the distribution of the B amount on the substrate surface is 1 μm in beam diameter by EPMA at any position on the substrate surface after the surface treatment such as heat treatment or blasting. This is a value obtained by scanning the range of 1 mm and dividing the standard deviation by the average value from the X-ray intensity values of B measured at intervals of 2 μm.
また、熱処理やブラスト加工等による表面処理を施した後の窒化珪素基板のうねりは、例えば触針式の表面粗さ計を用いて測定される。具体的には、表面粗さ計を用いて、ろ波中心線うねりを測定し、その算術平均うねりＷａ、すなわち、表面高さの平均値からの偏差の絶対値の算術平均である量を用いた。測定条件は評価長さ３０ｍｍ、測定速度０．３ｍｍ／ｓ、カットオフ値（λｃ）０．２５ｍｍ、カットオフ値（λｆ）８．０ｍｍとした。 Further, the undulation of the silicon nitride substrate after the surface treatment such as heat treatment or blasting is measured using, for example, a stylus type surface roughness meter. Specifically, the centerline waviness of the filtered wave is measured using a surface roughness meter, and the arithmetic average waviness Wa, that is, the arithmetic average of the deviation from the average value of the surface height is used. It was. The measurement conditions were an evaluation length of 30 mm, a measurement speed of 0.3 mm / s, a cutoff value (λc) of 0.25 mm, and a cutoff value (λf) of 8.0 mm.
焼結前の工程でグリーンシート表面に塗布されたＢＮ粉の一部は、窒化珪素基板表面に一部残留している。基板表面のＢ量の分布を示す変動係数が１．０より大きい場合は、ＢＮ粉が不均一に残留していることを示すが、この場合、局所的なＢＮ粉の偏析により、半導体モジュールとして使用するために、金属板を接合する際に両者間で接合不良が発生し、実装信頼性が低下する。基板表面のＢ量の分布を示す変動係数は、０．９以下が好ましく、０．８以下がより好ましい。 A part of the BN powder applied to the surface of the green sheet in the process before sintering partially remains on the surface of the silicon nitride substrate. When the coefficient of variation indicating the distribution of B amount on the substrate surface is larger than 1.0, it indicates that BN powder remains unevenly. In this case, as a semiconductor module due to local segregation of BN powder. In order to use, when joining a metal plate, a joining defect generate | occur | produces between both, and mounting reliability falls. The variation coefficient indicating the distribution of B amount on the substrate surface is preferably 0.9 or less, and more preferably 0.8 or less.
上記のＷａが１．５μｍを超える窒化珪素基板では、半導体モジュールとして使用するために、金属板との接合等の他の部材と接触させる実装時において、他の部材との密着度が悪くなり、実装信頼性が低下する。 In the silicon nitride substrate in which the above Wa exceeds 1.5 μm, in order to use it as a semiconductor module, the degree of adhesion with other members becomes worse at the time of mounting in contact with other members such as bonding with a metal plate, Mounting reliability decreases.
以下、本発明の実施例と比較例を説明する。ただし、本発明は、以下に述べる実施例に限定されるものではない。 Examples of the present invention and comparative examples will be described below. However, the present invention is not limited to the examples described below.
（実施例１〜９）
平均粒径０．８μｍ、酸素量１％、α化率９７％の窒化珪素粉末９４重量％、平均粒径０．５μｍの酸化マグネシウム粉末３重量％、及び平均粒径０．５μｍの酸化イットリウム粉末３重量％の合計１００重量部に対して、バインダーとしてポリビニルブチラール２０重量部、可塑剤としてジ−２−エチルヘキシルフタレートを５重量部、有機溶剤としてエチルアルコールと１−ブチルアルコールの混合物を１５０重量部を樹脂で内張りされた容器に入れ、窒化珪素ボールを用いて２０時間混合してスラリーを作製した。得られたスラリーの粘度を調整した後、ドクターブレード装置により、厚さが０．４ｍｍのシート状に成形した。その後、これをプレス装置により１５０ｍｍ×１５０ｍｍの寸法に打ち抜いてグリーンシートとした。
(Examples 1-9)
94% by weight of silicon nitride powder with an average particle size of 0.8 μm, oxygen content of 1%, 97% alpha, 3% by weight of magnesium oxide powder with an average particle size of 0.5 μm, and yttrium oxide powder with an average particle size of 0.5 μm For a total of 100 parts by weight of 3% by weight, 20 parts by weight of polyvinyl butyral as a binder, 5 parts by weight of di-2-ethylhexyl phthalate as a plasticizer, and 150 parts by weight of a mixture of ethyl alcohol and 1-butyl alcohol as an organic solvent Was put into a container lined with resin and mixed for 20 hours using silicon nitride balls to prepare a slurry. After adjusting the viscosity of the obtained slurry, it was formed into a sheet having a thickness of 0.4 mm by a doctor blade device. Thereafter, this was punched out into a size of 150 mm × 150 mm by a press device to obtain a green sheet.
表１に示す各種六方晶ＢＮ粉と水とを、六方晶ＢＮ粉／水＝１／５の割合で直径１０ｍｍの樹脂製ボールを用いて１時間混合して、ＢＮ粉スラリーを作製した後、３０分後にＢＮ粉スラリーをグリーンシートの片側の表面に、表１に示す塗布量で塗布した。塗布はスプレー式の塗布機を使用してＢＮスラリー塗布する方法、及び、ＢＮスラリーを刷毛で塗布する方法を採用した。また、塗布量はスプレー式の塗布機を使用する方法では塗布時間を変えることにより調整し、刷毛で塗布する方法では塗布回数を変えることにより調整した。また、塗布量は塗布・乾燥工程前後のシートの重量を測定し、その重量の差をシートの塗布面の面積で割ることにより算出した。 Various hexagonal BN powders and water shown in Table 1 were mixed for 1 hour using a resin ball having a diameter of 10 mm at a ratio of hexagonal BN powder / water = 1/5 to prepare a BN powder slurry. After 30 minutes, the BN powder slurry was applied to the surface of one side of the green sheet in the application amount shown in Table 1. For the application, a method of applying BN slurry using a spray type application machine and a method of applying BN slurry with a brush were adopted. Further, the coating amount was adjusted by changing the coating time in the method using a spray-type coating machine, and was adjusted by changing the number of coatings in the method using a brush. The coating amount was calculated by measuring the weight of the sheet before and after the coating / drying process and dividing the difference in weight by the area of the coated surface of the sheet.
ＢＮ粉のスラリーを塗布したグリーンシートの乾燥は８０℃大気中で２分間行った。 The green sheet coated with the BN powder slurry was dried in the air at 80 ° C. for 2 minutes.
ＢＮ粉スラリー塗布、乾燥後のグリーンシート表面をＸ線回折法により測定し、六方晶窒化ホウ素の（００２）と（１００）の回折線ピーク強度の比を計算した。この値は、上記の使用するＢＮ粉と塗布条件により表１に示すように変動している。 The green sheet surface after BN powder slurry application and drying was measured by X-ray diffraction method, and the ratio of the diffraction line peak intensities of (002) and (100) of hexagonal boron nitride was calculated. This value fluctuates as shown in Table 1 depending on the BN powder used and the application conditions.
ＢＮ粉１が塗布されたグリーンシート２は塗布された面を上面とし１０枚積層して、ＢＮ製のセッタ３上に配置し、ＢＮ製セッタ３上の積層されたグリーンシート２の脇にＢＮ製スペーサ４を配置して、その上にＢＮ製セッタ３を載せた（図１）。次に、６００℃で５時間、大気中で脱脂した。 10 sheets of green sheet 2 coated with BN powder 1 are laminated with the coated surface as the upper surface, placed on a setter 3 made of BN, and placed on the side of the stacked green sheet 2 on the setter 3 made of BN. A spacer 4 made of BN was placed, and a setter 3 made of BN was placed thereon (FIG. 1). Next, degreasing was performed in the air at 600 ° C. for 5 hours.
焼結は２０Ｐａまで真空にした後、窒素で置換した雰囲気中で行った。１４００〜１６００℃の昇温速度は１００℃／ｈ以下とし、１８００℃で５時間焼結し、１０枚の窒化珪素焼結体が積層された窒化珪素焼結体を得た。その後、各窒化珪素焼結体を分離し、窒化珪素焼結体間が剥離できるか否かを確認した。剥離性の評価は窒化珪素基板に割れやクラックが発生することなく容易に剥離できた場合を（○）、木ハンマーで衝撃を加えることで窒化珪素基板に割れやクラックが発生することなく剥離できた場合を（△）、木ハンマーで衝撃を加えて剥離する際に窒化珪素基板に割れやクラックが発生する基板が一枚でもあった場合を（×）と判定した。 Sintering was performed in an atmosphere replaced with nitrogen after evacuating to 20 Pa. The temperature increase rate of 1400-1600 degreeC was 100 degrees C / h or less, and it sintered at 1800 degreeC for 5 hours, and obtained the silicon nitride sintered compact by which ten silicon nitride sintered bodies were laminated | stacked. Thereafter, each silicon nitride sintered body was separated, and it was confirmed whether or not the silicon nitride sintered bodies could be separated. Evaluation of peelability is when the silicon nitride substrate can be easily peeled without cracks or cracks (○), and by applying an impact with a wooden hammer, the silicon nitride substrate can be peeled without cracks or cracks. In the case of (.DELTA.), The case where even one substrate on which the silicon nitride substrate was cracked or cracked when it was peeled off by applying an impact with a wooden hammer was determined as (.times.).
分離した窒化珪素焼結体に平均粒子径５０μｍのアルミナ砥粒と水を混合したスラリーを０．２ＭＰａの圧力で噴射することによってホーニング処理を行い、厚さ０．３２ｍｍの窒化珪素基板を得た。 The separated silicon nitride sintered body was subjected to a honing process by injecting a slurry in which alumina abrasive grains having an average particle diameter of 50 μm and water were mixed at a pressure of 0.2 MPa to obtain a silicon nitride substrate having a thickness of 0.32 mm. .
得られた窒化珪素基板のうねり、曲げ強度、密度、熱伝導率、表面におけるＢの変動係数、及び金属板を接合した際の接合ボイド率を以下の方法で測定した。 The obtained silicon nitride substrate was measured for the swell, bending strength, density, thermal conductivity, coefficient of variation of B on the surface, and the bonding void ratio when the metal plates were bonded.
窒化珪素基板のうねりは、表面粗さ計を用いて、ろ波中心線うねりを測定して、その算術平均うねりＷａ、すなわち、表面高さの平均値からの偏差の絶対値の算術平均である量を用いた。測定条件は評価長さ３０ｍｍ、測定速度０．３ｍｍ／ｓ、カットオフ値（λｃ）０．２５ｍｍ、カットオフ値（λｆ）８．０ｍｍとした。 The waviness of the silicon nitride substrate is the arithmetic mean waviness Wa, that is, the arithmetic average of the absolute value of the deviation from the average value of the surface height, by measuring the waviness centerline waviness using a surface roughness meter. Amount was used. The measurement conditions were an evaluation length of 30 mm, a measurement speed of 0.3 mm / s, a cutoff value (λc) of 0.25 mm, and a cutoff value (λf) of 8.0 mm.
曲げ強度は、上記の窒化珪素基板を幅４ｍｍに加工し、支持ロール間距離７ｍｍである３点曲げ治具にセットし、ＪＩＳＲ１６０１に準拠した方法で求めた。ここでは、クロスヘッド速度０．５ｍｍ／分で加重を印加して、破断時に印加された加重から算出した。 The bending strength was determined by a method in accordance with JIS R1601, by processing the silicon nitride substrate to a width of 4 mm, setting it on a three-point bending jig having a distance between support rolls of 7 mm. Here, a load was applied at a crosshead speed of 0.5 mm / min, and calculation was performed from the load applied at the time of breakage.
密度は水中置換法により測定し、真密度を３．２７Ｍｇ／ｍ３として、相対密度に換算した。 The density was measured by an underwater substitution method, and converted to a relative density with a true density of 3.27 Mg / m 3 .
熱伝導率は、上記の窒化珪素基板を５ｍｍ角に加工し、カーボンスプレーで表裏面を黒化処理後、ＪＩＳＲ１６１１に準拠したレーザーフラッシュ法により求めた。 The thermal conductivity was determined by a laser flash method in accordance with JIS R1611 after processing the silicon nitride substrate to 5 mm square and blackening the front and back surfaces with carbon spray.
基板表面のＢ（ホウ素）の変動係数はＥＰＭＡにより加速電圧１０ｋＶ、ビーム径１μｍで１ｍｍの範囲を走査し、２μｍ間隔でＢのＫαのＸ線強度を測定し、その標準偏差を平均値で割ることにより求めた。 The variation coefficient of B (boron) on the substrate surface is scanned by EPMA with an acceleration voltage of 10 kV, a beam diameter of 1 μm and a 1 mm range, the X-ray intensity of Bα is measured at 2 μm intervals, and the standard deviation is divided by the average value. Was determined by
金属板を接合した際の接合ボイド率は、以下のようにして求めた。上記の窒化珪素基板に０．５ｍｍ厚の銅板を８００℃のろう付け温度で真空中で接合して回路基板とした。その接合部における接合ボイド率を測定した。接合ボイド率は、超音波探傷法により、窒化珪素基板と銅板の接合界面を調べ、接合がなされていない箇所の面積比率を調べた。 The joint void ratio when the metal plates were joined was determined as follows. A circuit board was obtained by bonding a 0.5 mm thick copper plate to the above silicon nitride substrate in a vacuum at a brazing temperature of 800 ° C. The joint void ratio at the joint was measured. The bonding void ratio was determined by examining the bonding interface between the silicon nitride substrate and the copper plate by an ultrasonic flaw detection method, and examining the area ratio of the unbonded portions.
（実施例１０）
ＢＮ粉スラリーを作製する際に窒化珪素ボールを用いたこと以外は実施例１と同じ方法で窒化珪素基板を製造し、同様の評価を行った。
(Example 10)
A silicon nitride substrate was produced in the same manner as in Example 1 except that silicon nitride balls were used when producing the BN powder slurry, and the same evaluation was performed.
（実施例１１）
ＢＮ粉スラリーを作製する際のＢＮ粉と水の混合時間を５時間とした以外は実施例１と同じ方法で窒化珪素基板を製造し、同様の評価を行った。
(Example 11)
A silicon nitride substrate was produced in the same manner as in Example 1 except that the mixing time of BN powder and water when producing the BN powder slurry was 5 hours, and the same evaluation was performed.
（実施例１２）
ＢＮ粉スラリーを作製した後、ＢＮスラリーを塗布するまでの時間を２４時間とした以外は実施例１と同じ方法で窒化珪素基板を製造し、同様の評価を行った。
(Example 12)
A silicon nitride substrate was manufactured by the same method as in Example 1 except that the time until the BN powder slurry was applied and then the time until the BN slurry was applied was 24 hours, and the same evaluation was performed.
（実施例１３）
ＢＮ粉スラリーをグリーンシートに塗布した後、３０℃で２４時間乾燥した以外は実施例１と同様の方法で窒化珪素基板を製造し、同様の評価を行った。
(Example 13)
A silicon nitride substrate was produced in the same manner as in Example 1 except that the BN powder slurry was applied to a green sheet and then dried at 30 ° C. for 24 hours, and the same evaluation was performed.
（比較例１〜６）
表２に示した六方晶ＢＮ粉末及びＢＮ塗布量を用いた以外は、実施例１〜９と同様の方法で窒化珪素基板を製造し、同様の評価を行った。
(Comparative Examples 1-6)
A silicon nitride substrate was produced in the same manner as in Examples 1 to 9 except that the hexagonal BN powder and the BN coating amount shown in Table 2 were used, and the same evaluation was performed.
実施例１〜１３及び比較例１〜６の窒化珪素基板の剥離性、うねり、曲げ強度、相対密度、熱伝導率、Ｂの変動係数、及び接合ボイド率の結果について表１，表２に示す。 Tables 1 and 2 show the results of the peelability, waviness, bending strength, relative density, thermal conductivity, coefficient of variation of B, and bonding void ratio of the silicon nitride substrates of Examples 1 to 13 and Comparative Examples 1 to 6. .
上記表１に示されるように、分離材として酸素量０．０１〜０．５重量％、平均粒子径４〜２０μｍ、比表面積２０ｍ２／ｇ以下、の窒化ホウ素（ＢＮ）粉を用いＢＮ粉のグリーンシート表面への塗布量を０．０５〜１．４ｍｇ／ｃｍ２としているため、実施例１〜１３のすべてにおいて焼結後の剥離性が良好であり、曲げ強度は７５０ＭＰａ以上、相対密度は９９％以上、熱伝導率は８５Ｗ／ｍ・Ｋ以上の高い値を示し、うねりは１．５μｍ以下と小さく、変形の少ない窒化珪素基板の得られることを確認した。また、表面に残留したＢＮに由来するＢ量の分布を示す変動係数が１．０以下であるため銅板との接合において接合ボイド率は５％以下が得られることを示し、実装信頼性の高い窒化珪素基板が得られることが確認された。 As shown in Table 1 above, boron nitride (BN) powder having an oxygen content of 0.01 to 0.5% by weight, an average particle diameter of 4 to 20 μm, and a specific surface area of 20 m 2 / g or less is used as the separating material. Since the coating amount on the green sheet surface is 0.05 to 1.4 mg / cm 2 , the peelability after sintering is good in all of Examples 1 to 13, the bending strength is 750 MPa or more, the relative density Was 99% or more, and the thermal conductivity was as high as 85 W / m · K or more, and the swell was as small as 1.5 μm or less, and it was confirmed that a silicon nitride substrate with little deformation was obtained. In addition, since the coefficient of variation indicating the distribution of B amount derived from BN remaining on the surface is 1.0 or less, it indicates that a bonding void ratio of 5% or less can be obtained in bonding with a copper plate, and the mounting reliability is high. It was confirmed that a silicon nitride substrate was obtained.
一方、比較例１では、ＢＮ粉の酸素量を０．８重量％としたため、得られた窒化珪素基板のうねりは１．８μｍと実施例に比べて高い値を示し、接合ボイド率は８％と高くなった。 On the other hand, in Comparative Example 1, since the oxygen content of the BN powder was 0.8% by weight, the obtained silicon nitride substrate had a swell of 1.8 μm, which was higher than that of the Example, and the bonding void ratio was 8%. It became high.
比較例２では、ＢＮ粉の塗布量を０．０１ｍｇ／ｃｍ２としたため得られた窒化珪素基板のうねりは２．０μｍと実施例に比べて高い値を示し、また、Ｂの変動係数も１．２と高い値を示したため、接合ボイド率は７％と高くなった。また、焼結後の剥離性も悪く、曲げ強度は６２０ＭＰａと低い値を示した。 In Comparative Example 2, the undulation of the silicon nitride substrate obtained by setting the coating amount of BN powder to 0.01 mg / cm 2 is 2.0 μm, which is higher than that of the example, and the coefficient of variation of B is 1 Since the value was as high as .2, the bonding void ratio was as high as 7%. Moreover, the peelability after sintering was also poor, and the bending strength was as low as 620 MPa.
比較例３では、ＢＮ粉の塗布量を２．０ｍｇ／ｃｍ２としたため得られた窒化珪素基板の相対密度は９４％と低い値を示した。また、相対密度が低く、窒化珪素基板として不適当なため、接合ボイド率の確認は実施しなかった。 In Comparative Example 3, the relative density of the obtained silicon nitride substrate was as low as 94% because the amount of BN powder applied was 2.0 mg / cm 2 . Moreover, since the relative density was low and it was unsuitable as a silicon nitride substrate, the bonding void ratio was not confirmed.
比較例４では、平均粒子径２μｍとしたため比表面積３０ｍ２／ｇと大きいＢＮ粉を使用し、グリーンシート表面における六方晶窒化ホウ素の（００２）／（１００）のＸ線回折線強度比が２と低い値になったこともあり、得られた窒化珪素基板のうねりは１．８μｍと実施例に比べて高い値を示し、また、相対密度は９６％と低く、曲げ強度も６７３ＭＰａと低い値を示した。また、相対密度が低く、窒化珪素基板として不適当なため、接合ボイド率の確認は実施しなかった。 In Comparative Example 4, since the average particle diameter was 2 μm, BN powder having a specific surface area of 30 m 2 / g was used, and the (002) / (100) X-ray diffraction line intensity ratio of hexagonal boron nitride on the green sheet surface was 2. The swell of the obtained silicon nitride substrate is 1.8 μm, which is a high value compared to the example, the relative density is as low as 96%, and the bending strength is as low as 673 MPa. showed that. Moreover, since the relative density was low and it was unsuitable as a silicon nitride substrate, the bonding void ratio was not confirmed.
比較例５では、酸素量が０．０１重量％未満と少ないＢＮ粉を使用して窒化珪素基板を製造した。焼結後の剥離性が悪く、また、Ｂの変動係数が１．３と高い値を示したため、接合ボイド率は９％と高くなった。 In Comparative Example 5, a silicon nitride substrate was manufactured using BN powder having an oxygen content of less than 0.01% by weight. The peelability after sintering was poor, and the coefficient of variation of B was as high as 1.3, so the bonding void ratio was as high as 9%.
比較例６では、比表面積３０ｍ２／ｇと大きいＢＮ粉を使用して窒化珪素基板を製造した。ＢＮ粉の酸素量が０．７重量％と高くなったため、得られた窒化珪素基板のうねりは１．８μｍと実施例に比べて高い値を示し、接合ボイド率は８％と高くなった。 In Comparative Example 6, a silicon nitride substrate was manufactured using BN powder having a large specific surface area of 30 m 2 / g. Since the amount of oxygen in the BN powder was as high as 0.7% by weight, the resulting silicon nitride substrate had a swell of 1.8 μm, which was higher than that of the example, and the bonding void ratio was as high as 8%.
本発明の窒化珪素基板の製造方法により、複数枚のグリーンシートを積層して焼結した後に分離することによって得られる窒化珪素基板であって、剥離性がよく高い相対密度、高い曲げ強度及び高い熱伝導率を有し変形の少ない窒化珪素基板を得ることができる。この窒化珪素基板はパワー素子モジュール等の基板として用いることができる。 A silicon nitride substrate obtained by laminating and sintering a plurality of green sheets by the method for producing a silicon nitride substrate of the present invention, and having good peelability and high relative density, high bending strength and high A silicon nitride substrate having thermal conductivity and less deformation can be obtained. This silicon nitride substrate can be used as a substrate for a power element module or the like.
１ ＢＮ粉
２ グリーンシート
３ ＢＮ製セッタ
４ ＢＮ製スペーサ
1 BN powder 2 Green sheet 3 BN setter 4 BN spacer
Claims (6)
前記分離材が酸素量０．０１〜０．５重量％、平均粒子径４〜２０μｍ、比表面積２０ｍ２／ｇ以下の窒化ホウ素（ＢＮ）粉であり、前記ＢＮ粉を０．０５〜１．４ｍｇ／ｃｍ２の塗布量でグリーンシート表面に塗布することを特徴とする窒化珪素基板の製造方法。
A plurality of silicon nitride sintered bodies are obtained by stacking and sintering a plurality of green sheets containing silicon nitride powder and at least magnesium oxide (MgO) as a sintering aid through a separating material and then separating them. A silicon nitride substrate manufacturing method for obtaining a silicon nitride substrate from the silicon nitride sintered body,
The separating material is boron nitride (BN) powder having an oxygen amount of 0.01 to 0.5% by weight, an average particle diameter of 4 to 20 μm, and a specific surface area of 20 m 2 / g or less, and the BN powder is 0.05 to 1. A method for producing a silicon nitride substrate, which is applied to the surface of a green sheet at a coating amount of 4 mg / cm 2 .
In a silicon nitride substrate containing Si 3 N 4 as a main component and containing at least Mg, the coefficient of variation Cv indicating the distribution of B amount derived from BN remaining on the surface of the silicon nitride substrate is 1.0 or less, and the nitride The waviness Wa of the silicon substrate surface is 1.5 μm or less (however, the waviness is measured by using a surface roughness meter to measure the waviness centerline waviness, and the arithmetic average waviness Wa, that is, the average of the surface height) An amount that is an arithmetic average of absolute values of deviations from values is used, and measurement conditions are an evaluation length of 30 mm, a measurement speed of 0.3 mm / s, a cutoff value (λ c ) of 0.25 mm, and a cutoff value (λ f ) 8.0 mm), and a silicon nitride substrate having a relative density of 98% or more.
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