TW200423164A - Ferroelectric capacitors having BaPbO3 - Google Patents
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玖、發明說曝 (發明說0月應敘明:發明所屬之技術領域、先前技術、内容、實施方式及圖式簡單說明) 技術領域 本發明係關一種鐵電電容器(ferroelectric capacitor),尤指 一種含鉛酸鋇(BaPb03,以下簡稱BP0)氧化物導體之鐵電電 容器。 先前技術 一 一一一 隨著資訊產業的蓬勃發展與資訊媒體應用的日益普 及,各類的資訊儲存器,例如電子記憶體的需求與日遽 增。一般而言,電子記憶體依其功能性主要分為兩類,一 為揮發性記憶體,例如動態隨機存取記憶體(以下簡稱 DRAM)與靜態隨機存取記憶體(以下簡稱SRAM),強調高速 存取,但卻沒有永久記憶的功能;另一為非揮發性記憶 體,強調永久記憶的功能,但存在資料寫入速度較慢、寫 入次數有限與寫入時功耗較大等缺點,這類的記憶體包含 可抹除可程式化唯讀記憶體(EPROM)、可電抹除可程式化 唯讀記憶體(EEPR0M),及快閃記憶體等。近年來,一種新 型的鐵電記憶體(FeRAM)結合以上兩類的優點,是目前非 常受矚目的一種非揮發性隨機存取記憶體,因其具有讀寫 電壓低、讀寫速度快、耗電量低、製程簡單、重量輕與積 集度高等優點,在半導體業界已逐漸受到重視。 一般的電子記憶體,例如 SRAM及雙倍資料處理速度 (DDR) DRAM等,都是利用二氧化矽為材質所做的電容來 儲存π 0 ’’與” Γ’的邏輯狀態,而鐵電記憶體主要是利用鐵電 材料來當作記憶體的儲存介質,而利用鐵電材料所形成的 200423164发明 、 Invention of the invention (Inventory of the month of 0 shall be stated: the technical field to which the invention belongs, the prior art, the content, the embodiments, and a brief description of the drawings) TECHNICAL FIELD The present invention relates to a ferroelectric capacitor, especially a ferroelectric capacitor. A ferroelectric capacitor containing a barium lead oxide (BaPb03, hereinafter referred to as BP0) oxide conductor. Previous technologies One by one With the booming development of the information industry and the increasing popularity of information media applications, the demand and growth of various types of information storage, such as electronic memory, are increasing. Generally speaking, electronic memory is mainly divided into two types according to its functionality. One is volatile memory, such as dynamic random access memory (hereinafter referred to as DRAM) and static random access memory (hereinafter referred to as SRAM). High-speed access, but no permanent memory function; the other is non-volatile memory, which emphasizes the function of permanent memory, but has the disadvantages of slower data writing speed, limited number of writes, and large power consumption during write. This type of memory includes programmable erasable programmable read-only memory (EPROM), electrically erasable programmable programmable read-only memory (EEPR0M), and flash memory. In recent years, a new type of ferroelectric memory (FeRAM) combines the advantages of the above two types. It is currently a non-volatile random access memory that has attracted much attention because of its low read and write voltage, fast read and write speed, and high power consumption. The advantages of low power, simple process, light weight and high accumulation have gradually been paid attention in the semiconductor industry. General electronic memories, such as SRAM and double data processing speed (DDR) DRAM, use capacitors made of silicon dioxide to store the logic states of π 0 ″ and Γ ′, while ferroelectric memory The body is mainly made of ferroelectric materials as the storage medium of the memory, and 200423164 formed by the use of ferroelectric materials
(2) 電容稱之為鐵電電容器。鐵電材料具有優越的介電性、遲 滯性、壓電性及焦電性,其高介電係數的特性可以儲存更 多的電荷,亦即增加鐵電記憶體的儲存容量,而其遲滯特 性使得鐵電材料在達到極化飽和並將外加電場去除後,仍 具有極化量,此極化量稱為殘存極化量(remnant polarization),一般以Pr表示。殘存極化量對於記憶體材料 而言非常重要,因為殘存極化量的存在才使得記憶體可以_ 不需要持續地外加電場。另外,鐵電材料在外加電場為零 時,具有兩個穩定的殘存極化值(土 Pr),且施加電場可以 切換其極化狀態由正變負或由負變正,這兩種極化狀態可 用來儲存邏輯” 0 ’’與π 1 π,一般稱為 2Pr。此外,除了極化 量的大小之外,鐵電材料另一項重要特性稱為疲勞 (fatigue),因為記憶體在讀取時需要外加電壓,因此使用 久了之後會使得鐵電材料的2Pr變小,造成電路無法正確 判讀資料。 在鐵電記憶體的應用中,以具有#5鈇礦(perovskite)結構 的锆鈦酸鉛(PMZi^TVdOh以下簡稱PZT)為目前最受矚目 的鐵電材料之一,這是因為PZT具有高的殘存極化量與高 的居里溫度,且其成相溫度較低之故。此外,由於鉑(Pt) 具有高的導電度、熱及化學穩定性,因此適合用來當作電 極,一般都是將 PZT鍍覆在鉑電極上,以形成 Pt/PZT/Pt 的鐵電電容器結構。然而許多文獻,例如美國專利第 6,194,228號指出習知的Pt/PZT/Pt鐵電電容器在經過多次的 電壓反轉極化後,PZT的反轉極化量會隨著電壓施加的次 200423164(2) The capacitor is called a ferroelectric capacitor. Ferroelectric materials have superior dielectric properties, hysteresis, piezoelectricity, and pyroelectricity. Their high dielectric constant characteristics can store more charges, that is, increase the storage capacity of ferroelectric memories, and their hysteresis characteristics. After the ferroelectric material reaches polarization saturation and the applied electric field is removed, it still has a polarization amount. This polarization amount is called residual polarization and is generally expressed in Pr. The amount of residual polarization is very important for the memory material, because the existence of the amount of residual polarization allows the memory to _ do not need to continuously apply an electric field. In addition, ferroelectric materials have two stable residual polarization values (soil Pr) when the applied electric field is zero, and the applied electric field can switch their polarization state from positive to negative or from negative to positive. State can be used to store logic "0" and π 1 π, generally called 2Pr. In addition, in addition to the amount of polarization, another important feature of ferroelectric materials is called fatigue, because the memory is reading An external voltage is required when taking it, so after a long time of use, the 2Pr of the ferroelectric material will become smaller, which will cause the circuit to fail to correctly read the data. In the application of ferroelectric memory, a zirconium titanium with a # 5 鈇 矿 (perovskite) structure is used. Lead acid (PMZi ^ TVdOh hereinafter referred to as PZT) is one of the most noticeable ferroelectric materials at present. This is because PZT has a high residual polarization and a high Curie temperature, and its phase forming temperature is low. In addition, because platinum (Pt) has high electrical conductivity, thermal and chemical stability, it is suitable for use as an electrode. Generally, PZT is plated on a platinum electrode to form a Pt / PZT / Pt ferroelectric capacitor. Structure, however, many documents such as the United States Patent No. 6,194,228 indicates that the conventional Pt / PZT / Pt ferroelectric capacitors have undergone multiple voltage inversion polarizations, and the amount of PZT reverse polarization will follow the voltage application times.
⑶ 數大幅劣化,大約只能極化ίο6次,這種抗疲勞性不佳的 缺點是鐵電記憶體應用上的一大阻礙。 為了解诀上述問題,有許多研究指出以氧化物電極,例 如氧化銥(Ir02)、氧化铷(Ru02),及氧化銦錫(ΙΤΟ)等來取代 始電極,由於氧化物電極可以吸收氧空缺(oxygen vacancy) 以避免氧空缺在鐵電薄膜與電極之間累積,因此可改善鐵 電薄膜的李勞特性,然而有些氧化物電極與鐵電薄膜之間_ 的交互擴散,反而使得漏電流更為嚴重與電性劣化的情況 產生。 為改善上述問題,有許多文獻例如美國專利第5,155,658 號、第 5,519,235 號、第 5,248,564 號、第 5,838,035 號,及 第6,194,228號等提出,利用與PZT同為鈣鈦礦結構的氧化 物電極,例如鎳酸鑭(LaNi03,以下簡稱 LNO)、姑酸鳃鑭 ((La,Sr)Co03,以下簡稱 LSCO)、釕酸鳃(SrRu03,以下簡稱 SRO),及釔鋇銅氧化物(YBa2Cu307_x,以下簡稱YBCO)等金屬 氧化物導體來作為鐵電電容器的上下電極,由於這些氧化 物電極的結構及化性與PZT相近,除可改善PZT的疲勞性 質之外,也有助於PZT薄膜的成長。 然而由於上述金屬氧化物導體的鍍製溫度過高(約為 600至810°C之間),因此使得習知鐵電電容器的製程並不 適合與半導體製程整合,這是因為過高的製程溫度將使得 鐵電電容器下方的電子元件,例如互補式金氧半導體 (CMOS)電路在高溫鍍膜過程中產生劣化,而影響產品的電 性表現。雖然使用 LNO作為氧化物電極的製程溫度較低 200423164⑶ The number is greatly degraded, and can only be polarized about 6 times. The disadvantage of this poor fatigue resistance is a major obstacle to the application of ferroelectric memory. In order to understand the above problems, many studies have pointed out that oxide electrodes, such as iridium oxide (Ir02), hafnium oxide (Ru02), and indium tin oxide (ITO), are used to replace the starting electrode. Since oxide electrodes can absorb oxygen vacancies ( oxygen vacancy) to avoid the accumulation of oxygen vacancies between the ferroelectric film and the electrode, so the Lloyd characteristic of the ferroelectric film can be improved. Serious and electrical deterioration occurs. In order to improve the above problems, many documents such as U.S. Patent Nos. 5,155,658, 5,519,235, 5,248,564, 5,838,035, and 6,194,228 have proposed the use of oxide electrodes with the same perovskite structure as PZT, such as nickel Lanthanum acid (LaNi03, hereinafter referred to as LNO), lanthanum gill ((La, Sr) Co03, hereinafter referred to as LSCO), ruthenium ruthenate (SrRu03, hereinafter referred to as SRO), and yttrium barium copper oxide (YBa2Cu307_x, hereinafter referred to as YBCO Metal oxide conductors such as) are used as the upper and lower electrodes of ferroelectric capacitors. Since the structure and chemical properties of these oxide electrodes are similar to those of PZT, in addition to improving the fatigue properties of PZT, it also contributes to the growth of PZT films. However, because the above-mentioned metal oxide conductor has a high plating temperature (between about 600 and 810 ° C), the conventional ferroelectric capacitor manufacturing process is not suitable for integration with the semiconductor process, because the excessively high process temperature will The electronic components under the ferroelectric capacitor, such as complementary metal-oxide-semiconductor (CMOS) circuits, are degraded during the high-temperature coating process, which affects the electrical performance of the product. Although the process temperature of using LNO as an oxide electrode is lower 200423164
(4) (約為350°C ),然而鑭的擴散卻會造成PZT的殘存極化量 大幅下降。因此,尋找出一種能低溫鍍製、抗疲勞性佳、 不會引起產品劣化,並適用於以ΡΖΤ為鐵電薄膜之鐵電電 容器的金屬氧化物電極,在目前鐵電記憶體的應用上是一 大重要的課題。 發明内容 本發明之主要目的在於提供一種鐵電電容器,其利用具 一 — 有鈣鈦礦結構之ΒΡΟ氧化物導體當作鐵電電容器之上下 電極,以改善鐵電電容器的疲勞性質與漏電性質、增進鐵 電性質,並可降低整個電容結構的製程溫度,適合與半導 體製程整合。 本發明之鐵電電容器主要包含有一下方導電性金屬氧 化物電極、一上方導電性金屬氧化物電極,及一作為該上 方與該下方導電性金屬氧化物電極之介電層的鐵電薄 膜,其中該鐵電薄膜為ΡΖΤ薄膜,該上方與該下方導電性 金屬氧化物電極均包含 ΒΡΟ氧化物導體,以形成一 ΒΡΟ/ΡΖΤ/ΒΡΟ的電容結構,除可改善ΡΖΤ的疲勞性質與漏 電流性質、增進鐵電性質,及降低整個結構的製程溫度 外,更具有降低ΡΖΤ結晶溫度之功效。 實施方式 本發明利用含ΒΡΟ氧化物導體之材料當作鐵電電容器 的上與下電極,可有效降低鐵電薄膜的結晶溫度、改善疲 勞特性與鐵電性,及降低漏電流。 圖1為本發明之鐵電電容器10的結構示意圖。如圖1 200423164(4) (approximately 350 ° C), but the diffusion of lanthanum will cause the residual polarization of PZT to decrease significantly. Therefore, a metal oxide electrode that can be plated at low temperature, has good fatigue resistance, does not cause product degradation, and is suitable for ferroelectric capacitors using PTZ as a ferroelectric film is currently used in ferroelectric memory applications. A major issue. SUMMARY OF THE INVENTION The main object of the present invention is to provide a ferroelectric capacitor, which uses a BPO oxide conductor with a perovskite structure as the upper and lower electrodes of the ferroelectric capacitor to improve the fatigue and leakage properties of the ferroelectric capacitor. Improve the ferroelectric properties and reduce the process temperature of the entire capacitor structure, which is suitable for integration with semiconductor processes. The ferroelectric capacitor of the present invention mainly includes a lower conductive metal oxide electrode, an upper conductive metal oxide electrode, and a ferroelectric thin film serving as a dielectric layer of the upper and lower conductive metal oxide electrodes. The ferroelectric thin film is a PTZ thin film, and the upper and lower conductive metal oxide electrodes include a BPO oxide conductor to form a BPO / PZVT / BPO capacitor structure. In addition to improving the fatigue properties and leakage current properties of the PZO In addition to improving ferroelectric properties, and reducing the process temperature of the entire structure, it also has the effect of reducing the crystallization temperature of PTZ. Embodiments The present invention uses a material containing a BPO oxide conductor as the upper and lower electrodes of a ferroelectric capacitor, which can effectively reduce the crystallization temperature of the ferroelectric thin film, improve fatigue characteristics and ferroelectricity, and reduce leakage current. FIG. 1 is a schematic structural diagram of a ferroelectric capacitor 10 according to the present invention. Figure 1 200423164
(5) 所示,本發明之鐵電電容器10主要包含一半導體基底 1 2、一含BPO氧化物導體之下方電極14、一鐵電薄膜16, 及至少一含BPO氧化物導體之上方電極18。此外,本發 明之半導體基底12與下方電極14之間可另包含至少一緩 衝層,在本發明中係以一二氧化矽層 20、一鈦層 22,及 一鉑層24為例,以避免鐵電電容器10與半導體基底12表 面的直接接觸,且在每一上方電極18上方皆設有一鉑層 26,用來當作電子接點(electrical contact),以利本發明之鐵 鲁 電電容器10與後續形成的其他電子元件(未顯示於圖1中) 電連接。 一般而言,用於形成半導體基底12的材料係選自由單 晶矽、氧化鎂、鈦酸鳃(SrTi03)及鑭鋁氧化物(LaA103)及其 混合物所構成群組;形成上方電極14與下方電極18之材 料包含有BP0或含BP0之化合物,例如添加銀、鋅及/或 鉍之BP0化合物;形成鐵電薄膜16的材料包含有PZT、含(5) As shown, the ferroelectric capacitor 10 of the present invention mainly includes a semiconductor substrate 1 2, a lower electrode 14 containing a BPO oxide conductor, a ferroelectric thin film 16, and at least an upper electrode 18 containing a BPO oxide conductor . In addition, the semiconductor substrate 12 and the lower electrode 14 of the present invention may further include at least one buffer layer. In the present invention, a silicon dioxide layer 20, a titanium layer 22, and a platinum layer 24 are used as examples to avoid The ferroelectric capacitor 10 is in direct contact with the surface of the semiconductor substrate 12, and a platinum layer 26 is provided above each of the upper electrodes 18, and is used as an electrical contact to facilitate the iron electric capacitor 10 of the present invention. It is electrically connected to other electronic components (not shown in FIG. 1) formed subsequently. In general, the material used to form the semiconductor substrate 12 is selected from the group consisting of single crystal silicon, magnesium oxide, gill titanate (SrTi03), lanthanum aluminum oxide (LaA103), and mixtures thereof; forming the upper electrode 14 and the lower electrode The material of the electrode 18 includes BP0 or a compound containing BP0, for example, a BP0 compound added with silver, zinc, and / or bismuth; and the material forming the ferroelectric thin film 16 includes PZT,
PZT之化合物,例如锆鈦酸鉛鑭(PLZT)、鈕酸鳃鉍 (SrBi2Ta209,SBT)或鈦酸鉍鑭((Bi,La)4Ti3012,BLT)等; 形成緩衝層20,22,24的材料係選自由氧化矽、氮化矽、鉑、 鈦、鋰、LNO、SRO、YBCO、LSC0、經釔穩定之氧化锆(Yttdum Stabilized Zirconia,YSZ)及鈦酸鉍(Bi4Ti3012,BIT)及其混合 物所構成群組。 由於 BP0是一種具有假立方晶(pseudocubic)#5鈥礦結構 的金屬氧化物導體,其晶格常數約為0.427奈米(nm),室 溫下的電阻係數為0 · 3至0 · 8毫歐姆-公分(m Ω - cm)之間, -10 - 200423164PZT compounds, such as lead lanthanum zirconate titanate (PLZT), bismuth niobate (SrBi2Ta209, SBT) or lanthanum lanthanum titanate ((Bi, La) 4Ti3012, BLT), etc .; materials forming the buffer layers 20, 22, 24 It is selected from the group consisting of silicon oxide, silicon nitride, platinum, titanium, lithium, LNO, SRO, YBCO, LSC0, Yttdum Stabilized Zirconia (YSZ), and bismuth titanate (Bi4Ti3012, BIT) and mixtures thereof. Form a group. Since BP0 is a metal oxide conductor with a pseudocubic # 5 'ore structure, its lattice constant is about 0.427 nanometers (nm), and the resistivity at room temperature is 0. 3 to 0. 8 millimeters. Ohm-centimeter (m Ω-cm), -10-200423164
⑹ 在低溫下有超導性,臨界溫度約為0.38K,而添加適量的 鉍可使臨界溫度升高至13K左右。值得注意的是,BPO氧 化物的薄膜製程溫度約在350°C時便可成相,且具有較佳 的導電性,因此適合與PZT搭配作為電極使用。再者,由 於鋇與鉛同價數,因此即使BPO氧化物導體内的鋇擴散進 入PZT中,對鐵電薄膜16的電性並無影響。 以下實#例將對本發明做進一步說明,為非用以限制本_ 發明之範圍,任何熟習此項技藝之人士可輕易達成之修飾 擊 及改變,均涵蓋於本發明之範圍内。 實施例⑹ It is superconducting at low temperature, the critical temperature is about 0.38K, and adding an appropriate amount of bismuth can increase the critical temperature to about 13K. It is worth noting that the thin film of BPO oxide can form phases at about 350 ° C and has good conductivity, so it is suitable for use with PZT as an electrode. Furthermore, since barium has the same valence as lead, even if barium in the BPO oxide conductor diffuses into PZT, it does not affect the electrical properties of the ferroelectric thin film 16. The following examples will further illustrate the present invention. In order not to limit the scope of the present invention, modifications and changes that can be easily achieved by anyone skilled in the art are included in the scope of the present invention. Examples
本發明之鐵電電容器10的製作方法是先提供一半導體 基底12,接著進行一濕式熱氧化法,以於半導體基底12 表面形成一厚度約為150 nm的二氧化矽層20,用來當作阻 絕層,接著利用雙電子槍蒸鍍法於二氧化矽層20上鍍覆 一厚度約為50 nm之鈦層22,用來加強後續形成的鉑層24 與二氧化矽層20之間的附著性,然後再於鈦層22上鍍覆 一厚度約為150 nm之鉑層24,用來增加導電性,接著進行 一射頻磁控濺鍍製程(RF magnetron sputtering),以於舶層24 上形成一厚度約為200 nm的含BPO氧化物導體之薄膜,用 來當作下方電極 14,再進行一溶凝膠( sol-gel)法,以於下 方電極14上形成一厚度介於100至500 nm之間,最佳約為 300 nm的PZT薄膜,用來當作鐵電薄膜層16,之後利用RF 磁控濺鍍法於鐵電薄膜層16上形成另一厚度約為200 nm 之含BPO氧化物導體之薄膜,然後進行一微影暨蝕刻製程 -11 - 200423164 ⑺ (photo-etching process, PEP) » 以形成至少一個上方電極 18, 每一個上方電極18具有約為100微米(# m)之寬度。最後 於每一個上方電極18上形成一鉑層26,用來當作電子接 點,完成本發明之鐵電電容器10的製作方法。 ’ 值得注意的是,本發明之含BP0氧化物導體之薄膜的製 備方法是先混和碳酸鋇(BaC03)與二氧化鉛(Pb02)粉末,然 後利用乙將混合的粉末壓製成球狀,接著在純氧的環境_ 下以溫度約為800°C鍛燒及乾燥此混合物,再將經過鍛燒 φ 後的混合物置於一直徑為2英吋(inch)之圓形模具中,然 後將此壓製後的混合物置於純氧的環境下以溫度約為800 °C燒結,以得到適當強度,同時需控制氧氣的流量以確保 得到均相(homogeneous)及品質佳的標乾(target)以供後續的 濺鍍製程使用。而RF磁控濺鍍製程為於濺鍍艙内通入90% 氬氣與10%氧氣的混合氣體,以功率50瓦特,壓力40毫The manufacturing method of the ferroelectric capacitor 10 of the present invention is to first provide a semiconductor substrate 12 and then perform a wet thermal oxidation method to form a silicon dioxide layer 20 with a thickness of about 150 nm on the surface of the semiconductor substrate 12 to be used as As a barrier layer, a dual electron gun evaporation method is then used to deposit a titanium layer 22 with a thickness of about 50 nm on the silicon dioxide layer 20 to strengthen the adhesion between the platinum layer 24 and the silicon dioxide layer 20 formed later. And then a platinum layer 24 with a thickness of about 150 nm is plated on the titanium layer 22 to increase the conductivity, and then an RF magnetron sputtering process is performed to form a layer on the ship layer 24 A thin film containing a BPO oxide conductor having a thickness of about 200 nm is used as the lower electrode 14, and then a sol-gel method is performed to form a thickness between 100 and 500 on the lower electrode 14. The PZT film with a thickness of about 300 nm is preferably used as the ferroelectric thin film layer 16, and then another RF-containing BPO with a thickness of about 200 nm is formed on the ferroelectric thin film layer 16 by RF magnetron sputtering. Thin film of oxide conductor, and then a lithography and etching process-11-20 0423164 ⑺ (photo-etching process, PEP) »to form at least one upper electrode 18, each upper electrode 18 has a width of about 100 microns (#m). Finally, a platinum layer 26 is formed on each of the upper electrodes 18, which is used as an electronic contact to complete the manufacturing method of the ferroelectric capacitor 10 of the present invention. '' It is worth noting that the method for preparing the BP0 oxide-containing conductor film of the present invention is to first mix barium carbonate (BaC03) and lead dioxide (Pb02) powders, and then press the mixed powder into a spherical shape with B, and then Pure oxygen environment _ calcined and dried the mixture at a temperature of about 800 ° C. The calcined mixture was placed in a circular mold with a diameter of 2 inches and then pressed. The resulting mixture is sintered in a pure oxygen environment at a temperature of about 800 ° C to obtain appropriate strength. At the same time, the oxygen flow rate needs to be controlled to ensure that homogeneous and high-quality targets are obtained for subsequent use. Used in the sputtering process. The RF magnetron sputtering process is to pass a mixture of 90% argon and 10% oxygen in the sputtering chamber, with a power of 50 watts and a pressure of 40 milliwatts.
托耳(mTorr)之操作條件來進行濺鍍,再將半導體基底 12 利用一鹵素燈加熱其背面至350°C,在此條件下所製備而 成的含BPO氧化物導體之薄膜的電阻值約為1.4 X 10_3毫歐 姆-公分(πιΩ - cm)。 此外,本發明之鐵電薄膜16的製備方法主要是利用溶 凝膠法,以得到厚度約為300 nm之PZT,在本發明之較佳 實施例中,PZT的化學式為 Pb(Zi*〇.53,Ti〇.47)03。然本發明並 不侷限於此,本發明之PZT薄膜也可利用其他方法製備, 例如RF磁控濺鍍法。此外,可另外添加1至10%的鑭及 /或鈮(Nb)於鐵電薄膜中以改善其鐵電性質。值得注意的 -12- 200423164The operating conditions of mTorr are used for sputtering, and then the semiconductor substrate 12 is heated by a halogen lamp to the rear surface to 350 ° C. The resistance value of the film containing the BPO oxide conductor prepared under this condition is about It is 1.4 X 10_3 milliohm-cm (πmΩ-cm). In addition, the preparation method of the ferroelectric thin film 16 of the present invention mainly uses a sol-gel method to obtain a PZT with a thickness of about 300 nm. In a preferred embodiment of the present invention, the chemical formula of PZT is Pb (Zi *. 53, Ti 0.47) 03. However, the present invention is not limited to this, and the PZT film of the present invention can also be prepared by other methods, such as RF magnetron sputtering. In addition, 1 to 10% of lanthanum and / or niobium (Nb) may be added to the ferroelectric thin film to improve its ferroelectric properties. Notable -12- 200423164
⑻ 是’若是同樣以溶凝膠法來製備PZT,則習知以鉑當電極 之ΡΖΤ的成相溫度約為650°C,而在本發明中以ΒΡ0為電 極之· ΡΖΤ的成相溫度約為550°c,可知使用Βρ〇氧化物導 體當作下方電極可以有效降低ρζτ沈積於Βρ〇上方之溫 , 度。再者’利用原子力顯微鏡(AFM)觀察ρΖΤ表面可知, 鐘覆於銷電極上之ΡΖΤ表面具有玫瑰花型琢型結構 (rosette) ’而—鍍覆於βρο電極上之ρΖΤ則具有均勻的微結構 與平坦的表面。舉例言之,當以相同的方法分別於鉑電極 鲁 與ΒΡ0電極上製備ρζτ,所得到的ΡΖΤ於銘電極表面上的 粗糙程度約為8 · 4 nm ’於ΒΡ0電極表面上的粗糙程度則僅 約為1 ·7 nm,因此利用BP0當作電極可以有效地避免粗糙 表面的形成,同時也可降低Ρζτ薄膜的厚度,並降低其操 作電壓。 為了更清楚瞭解本發明鐵電電容器1〇確實較習知的鐵 電電容器為佳’因此發明人進行多種試驗,以針對本發明 之ΒΡ0/ΡΖΤ/ΒΡ0電容器與習知Pt/PZT/Pt電容器之鐵電薄膜 的鐵電性質、疲勞性質,及漏電性質。 圖 2為本發明 BP0/PZT/BP0(a)鐵電電容器與習知 Pt/PZT/Pt(b)鐵電電容器之鐵電薄膜的電滯曲線圖 (ferroelectric hysteresis loop),亦即電場強度(E)與極化量(P) 的關係圖。本發明是利用 RT-66A儀器來測量本發明 BPO/PZT/BPO(a)電容器與習知pt/PZT/Pt(b)電容器之鐵電薄 膜在不同的外加電場強度下,其極化量的改變。如圖2 所示,當外加電場為零時,(a)與(b)兩者之殘存極化量(pr) -13- 200423164⑻ Yes' If PZT is also prepared by the sol-gel method, it is known that the phase formation temperature of PZT with platinum as the electrode is about 650 ° C, and in the present invention, the phase formation temperature of PZT with PPO as the electrode is about It is 550 ° C. It can be seen that the use of a Bpo oxide conductor as the lower electrode can effectively reduce the temperature and degree of ρζτ deposited above the Bpo. Furthermore, 'using the atomic force microscope (AFM) to observe the ρZΤ surface, it can be seen that the PZVT surface covered with the pin electrode has a rosette-shaped structure (rosette)', and the ρTZ which is plated on the βρο electrode has a uniform microstructure With a flat surface. For example, when ρζτ is prepared on a platinum electrode and a BPO electrode by the same method, the roughness of the obtained PZT on the surface of the Ming electrode is about 8.4 nm. The roughness on the surface of the BPO electrode is only It is about 1 · 7 nm, so using BP0 as an electrode can effectively avoid the formation of rough surfaces, and also reduce the thickness of the Pζτ film and reduce its operating voltage. In order to understand more clearly that the ferroelectric capacitor 10 of the present invention is indeed better than the conventional ferroelectric capacitors', the inventors conducted various tests to target the BPO / PZT / BPO capacitors of the present invention and the conventional Pt / PZT / Pt capacitors. Ferroelectric thin film ferroelectric properties, fatigue properties, and leakage properties. Fig. 2 is a ferroelectric hysteresis loop diagram of the ferroelectric thin film of the BP0 / PZT / BP0 (a) ferroelectric capacitor and the conventional Pt / PZT / Pt (b) ferroelectric capacitor, that is, the electric field strength ( E) Relation diagram with polarization (P). The invention uses an RT-66A instrument to measure the polarization of the ferroelectric thin film of the BPO / PZT / BPO (a) capacitor of the invention and the conventional pt / PZT / Pt (b) capacitor under different external electric field strengths. change. As shown in Figure 2, when the applied electric field is zero, the residual polarization of (a) and (b) (pr) -13- 200423164
⑼ 相差不多,然而當鐵電薄膜的極化量為零時,(a)之鐵電 薄膜的橋頑電場(coercive field)強度較(b)為低,可知(a)較(b) 易驅動其極化轉向,亦即(a)較(b)具有較佳的鐵電性質。 圖3為本發明BPO/PZT/BPO(a)電容器與習知Pt/PZT/Pt(b) 、 電容器之鐵電薄膜之極化反轉週期與淨極化量(2Pr)的關 係圖。本發明是使用HP8116A脈衝產生器並連結至RT-66A 以產生 1MHz的矩形波來測量(a)與(b)之鐵電薄膜的疲勞_ 特性。如圖3所示,(b)之鐵電薄膜在經過109循環的極化 φ 反轉後,其淨極化量衰減約 90%,而(a)之鐵電薄膜在經 過1011循環的極化反轉後,其淨極化量幾乎沒有衰減。由 此可知,本發明之利用BPO氧化物導體當作電極的電容結 構可以大幅地增加鐵電薄膜的抗疲勞性。此外,BPO與其 他的氧化物電極一樣,也可以避免氧空缺累積在 BPO與 PZT的界面,因此利用BPO當作鐵電電容器的電極可更有 效地避免反轉極化量的降低,改善鐵電薄膜的疲勞性質。The ⑼ phase is similar, but when the polarization of the ferroelectric thin film is zero, the coercive field strength of the ferroelectric thin film of (a) is lower than that of (b). It can be seen that (a) is easier to drive than (b) Its polarization turning, that is, (a) has better ferroelectric properties than (b). Fig. 3 is a relationship diagram between the polarization inversion period and the net polarization amount (2Pr) of the BPO / PZT / BPO (a) capacitor of the present invention and the conventional Pt / PZT / Pt (b) and capacitor ferroelectric thin film. The invention uses the HP8116A pulse generator and is connected to the RT-66A to generate a 1MHz rectangular wave to measure the fatigue characteristics of the ferroelectric thin films of (a) and (b). As shown in Fig. 3, after the polarization of φ of the ferroelectric thin film of (b) is reversed after 109 cycles, its net polarization is attenuated by about 90%, and the ferroelectric thin film of (a) is polarized after 1011 cycles After the reversal, its net polarization is hardly attenuated. From this, it can be seen that the capacitance structure using the BPO oxide conductor as an electrode of the present invention can greatly increase the fatigue resistance of the ferroelectric thin film. In addition, BPO, like other oxide electrodes, can also prevent the accumulation of oxygen vacancies at the interface between BPO and PZT. Therefore, using BPO as the electrode of a ferroelectric capacitor can more effectively avoid the reduction of the amount of reverse polarization and improve the ferroelectricity. Fatigue properties of films.
圖4為本發明BPO/PZT/BPO(a)電容器與習知Pt/PZT/Pt(b) 電容器之鐵電薄膜之外加電場強度與漏電流量的關係 圖。本發明之測量方式是利用HP4140B pa meter/dc電壓源來 測量(a)與(b)之鐵電薄膜的漏電流,當施加相同的電場強 度於(a)與(b)之鐵電薄膜時,由圖4可知,(a)之鐵電薄膜 的漏電流遠較(b)之鐵電薄膜的漏電流為低,例如當外加 電場為200千伏/公分(kV/cm)時,(a)之鐵電薄膜的漏電流 約為0.1微安培/平方公分(/z A/cm2),而(b)之鐵電薄膜的 漏電流約為4.5微安培/平方公分,因此本發明之利用含 -14- 200423164 (10) BPO氧化物導體之薄膜當作電極之電容結構可有效減少 鐵電薄膜之漏電流的產生。 综上所述,由於具有鈣鈦礦結構之BPO氧化物導體具有 約為1.4χ1(Γ3 Ω cm之低電阻值,且利用RF磁控濺鍍法的製Fig. 4 is a graph showing the relationship between the electric field strength and the amount of leakage current between the ferroelectric thin film of the BPO / PZT / BPO (a) capacitor and the conventional Pt / PZT / Pt (b) capacitor of the present invention. The measurement method of the present invention uses the HP4140B pa meter / dc voltage source to measure the leakage current of the ferroelectric thin films of (a) and (b). When the same electric field strength is applied to the ferroelectric thin films of (a) and (b) As can be seen from Fig. 4, the leakage current of the ferroelectric thin film of (a) is much lower than that of the ferroelectric thin film of (b). For example, when the applied electric field is 200 kV / cm (kV / cm), (a The leakage current of the ferroelectric thin film is about 0.1 microamperes per square centimeter (/ z A / cm2), and the leakage current of the ferroelectric thin film of (b) is about 4.5 microamperes per square centimeter. Therefore, the use of the present invention includes -14- 200423164 (10) The capacitor structure of the BPO oxide conductor film as an electrode can effectively reduce the leakage current of the ferroelectric film. In summary, since the BPO oxide conductor with perovskite structure has a low resistance value of about 1.4 × 1 (Γ3 Ω cm), and is manufactured by RF magnetron sputtering method
備溫度約介於350至 400°C之間,因此適合用來當作PZT 鐵電薄膜之電極,並可降低PZT的成相溫度。此外,本發 明之PZT亦可利用射頻磁控濺鍍法來形成,其成相溫度 約為400至45 0°C,使得整個電容結構的製程溫度最高不 超過450°C,因此可與半導體製程整合,不會造成下方的 CMOS電路因其上方電極與鐵電薄膜的鍍膜過程中產生劣 化。The preparation temperature is about 350 to 400 ° C, so it is suitable to be used as the electrode of PZT ferroelectric thin film, and can reduce the phase forming temperature of PZT. In addition, the PZT of the present invention can also be formed by radio frequency magnetron sputtering. Its phase formation temperature is about 400 to 45 ° C, so that the maximum process temperature of the entire capacitor structure does not exceed 450 ° C, so it can be used with semiconductor processes. The integration will not cause the lower CMOS circuit to be degraded during the coating process of the upper electrode and the ferroelectric thin film.
相較於習知的鐵電電容器,本發明之BPO/PZT/BPO鐵電 電容器,並無習知因氧化物電極與鐵電薄膜間的交互擴散 導致高的漏電流或其他電性上劣化的情形發生。此外,由 於形成於BPO上的PZT具有較低的矯頑電場,且其殘存極 化量與形成於鉑電極上的 PZT差不多,因此可有效改善 PZT的鐵電性質。再者,本發明之BPO/PZT/BPO鐵電電容 器尚具有良好的抗疲勞性。又利用BPO當作下方電極可以 避免習知因 PZT形成於鉑電極上所產生的粗糙界面。因 此,本發明之鐵電電容器不但具有一平坦的電極/鐵電薄 膜界面,且其鐵電、疲勞與漏電流性質皆獲得大幅的改善。 圖式簡單說明 圖1為本發明之鐵電電容器的結構示意圖。 圖2為本發明BPO/PZT/BPO鐵電電容器與習知Pt/PZT/Pt -15- 200423164Compared with the conventional ferroelectric capacitors, the BPO / PZT / BPO ferroelectric capacitors of the present invention are not known to have high leakage current or other electrical deterioration due to the interdiffusion between the oxide electrode and the ferroelectric thin film. The situation happened. In addition, since the PZT formed on the BPO has a lower coercive electric field and its residual polarization is similar to that of the PZT formed on the platinum electrode, the ferroelectric properties of the PZT can be effectively improved. Furthermore, the BPO / PZT / BPO ferroelectric capacitors of the present invention have good fatigue resistance. By using BPO as the lower electrode, it is possible to avoid the rough interface caused by PZT formed on the platinum electrode. Therefore, the ferroelectric capacitor of the present invention not only has a flat electrode / ferroelectric thin film interface, but also greatly improves its ferroelectric, fatigue and leakage current properties. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic structural diagram of a ferroelectric capacitor of the present invention. Figure 2 shows the BPO / PZT / BPO ferroelectric capacitor of the present invention and the conventional Pt / PZT / Pt -15- 200423164
(11) 鐵電電容器之鐵電薄膜的電滯曲線圖。 圖3為本發明BPO/PZT/BPO電容器與習知Pt/PZT/Pt電容 器之鐵電薄膜之極化反轉週期與淨極化量的關係圖。 圖4為本發明BPO/PZT/BPO電容器與習知Pt/PZT/Pt電容 器之鐵電薄膜之外加電場強度與漏電流量的關係圖。 圖式元件符號之簡單說明 10 鐵電電容器 12 半導體基底 14 含BPO氧化物導體之上方電極 16 鐵電薄膜 18 含BPO氧化物導體之下方電極 20 二氧化矽層 22 鈦層 24 鉑層 26 鉑層 -16-(11) Hysteresis curve of a ferroelectric thin film of a ferroelectric capacitor. Fig. 3 is a graph showing the relationship between the polarization reversal period and the net polarization of a BPO / PZT / BPO capacitor and a conventional Pt / PZT / Pt capacitor ferroelectric thin film according to the present invention. Fig. 4 is a graph showing the relationship between the applied electric field strength and the amount of leakage current between the ferroelectric thin film of the BPO / PZT / BPO capacitor of the present invention and the conventional Pt / PZT / Pt capacitor. Brief Description of Symbols of Schematic Elements 10 Ferroelectric Capacitors 12 Semiconductor Substrate 14 Upper Electrode with BPO Oxide Conductor 16 Ferroelectric Film 18 Lower Electrode with BPO Oxide Conductor 20 Silicon Dioxide Layer 22 Titanium Layer 24 Platinum Layer 26 Platinum Layer -16-
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