CN113725006A - 一种高耐压低漏电的硅基AlN电容器及其制备方法 - Google Patents
一种高耐压低漏电的硅基AlN电容器及其制备方法 Download PDFInfo
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- 239000010703 silicon Substances 0.000 title claims abstract description 94
- XUIMIQQOPSSXEZ-UHFFFAOYSA-N Silicon Chemical compound [Si] XUIMIQQOPSSXEZ-UHFFFAOYSA-N 0.000 title claims abstract description 93
- 239000003990 capacitor Substances 0.000 title claims abstract description 75
- 238000002360 preparation method Methods 0.000 title claims abstract description 14
- 239000000758 substrate Substances 0.000 claims abstract description 54
- 239000010408 film Substances 0.000 claims description 61
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 claims description 36
- 238000000151 deposition Methods 0.000 claims description 31
- 238000000034 method Methods 0.000 claims description 27
- 229910052757 nitrogen Inorganic materials 0.000 claims description 18
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- 238000001755 magnetron sputter deposition Methods 0.000 claims description 8
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- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 38
- 239000002184 metal Substances 0.000 description 6
- 229910052751 metal Inorganic materials 0.000 description 6
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- 229910052782 aluminium Inorganic materials 0.000 description 2
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Abstract
本发明涉及一种高耐压低漏电的硅基AlN电容器，所述硅基AlN电容器包括由下至上设置的硅基板、AlN介质薄膜和顶部电极，还包括Pt缓冲层，所述Pt缓冲层沉积于所述硅基板上，所述AlN介质薄膜沉积于所述Pt缓冲层上。本发明还涉及一种高耐压低漏电的硅基AlN电容器的制备方法。本发明的技术方案可以解决现有AlN电容器中AlN介质层与硅基板之间的界面问题。
Description
技术领域
本发明涉及薄膜电容器领域，特别是涉及一种高耐压低漏电的硅基AlN电容器及其制备方法。
背景技术
在射频集成电路中，无源器件和有源器件一样是必不可少的存在。因此对无源器件性能的改善工作，也是提升电路系统性能的一项重要工作。薄膜无源器件制造技术由于承接了成熟的半导体制造工艺，可获得具有严格的电气和物理特性的无源器件。其线宽尺寸和绝缘层厚度分别可达到1μm和10nm以下，严格的线宽和薄膜尺寸带来了严格的参数容差(电容值和损耗值)；由于采用了高真空电极沉积工艺，不同批次产品之间以及同一批次不同产品之间的ESR值极其稳定；通过半导体薄膜技术得到的超纯净、高K值的绝缘层使得器件具有高且稳定的Q值。这些特性使得薄膜无源器件制造技术成为了提升电路系统性能的一种优秀解决方案。
金属-绝缘体-金属(Metal-Insulator-Metal，MIM)电容器是射频集成电路和模拟/混合信号集成电路中的基本无源器件。通过采用金属作为两个电极，MIM结构有效降低了寄生电容和介质与电极的接触电阻，具有导电性好，低损耗的特点。在MIM电容中，为了获得更高的单位面积电容和更低的漏电流，需要选用有高K值，较大禁带宽度的介质来取代传统SiO2和Si3N4介质。
AlN电子薄膜是一种超宽禁带的Ⅲ-Ⅴ族材料，由于AlN薄膜具有优异的介电特性、压电特性、高频特性和温度稳定特性，使其在射频电容器、表面/体声波器件、MEMS传感器和功率半导体器件等领域有着广阔的应用前景。AlN薄膜的本征击穿场强可达10MV/cm以上，介电常数约为9-11，这就意味着AlN电容可获得接近相同规格SiO2电容的耐压能力，和三倍于SiO2电容的容量。随着近年来移动通讯技术的迅猛发展，高性能AlN电子器件的巨大需求有望被引爆。
现有对于AlN电容器的研究主要存在AlN与硅基板的匹配问题、界面问题和电容器耐压低漏电流大的问题：
1、AlN与Si之间的晶格失配度接近20％，较大的失配会导致介质薄膜产生大量缺陷且薄膜在制备和应用过程中容易开裂，进而严重影响器件的制备良率和使用寿命。
2、AlN介质薄膜的制备往往需要在高温和氮气环境下进行，硅基板在高温环境下极易与氮气发生剧烈的界面反应生成硅氮化合物，这些化合物会在后续器件的制备中影响AlN介质薄膜的生长。另外，在硅基板上直接沉积AlN会导致大量的Si、O原子扩散进入AlN层，从而在AlN/Si界面处引入载流子陷阱态，增加了电容器的漏电流和损耗，严重影响器件性能。
3、AlN介质薄膜的制备是AlN电子器件性能优劣的核心问题。在现有技术条件下制备的AlN介质薄膜常常出现N元素缺失的情况，富Al缺N的元素比例会增加AlN介质薄膜的电导，降低其绝缘特性，从而直接增加AlN电容的漏电流并降低耐压值。
4、现有的AlN介质薄膜制备方法中磁控溅射难以生长结晶性好，缺陷少的AlN介质薄膜；原子层沉积所使用的前驱体会在高温生长条件下发生严重而不可逆的预反应；分子束外延主要运用于前沿科学探索，难以实现商业化生产。
对于面向集成化射频电路应用的MIM电容必须做到硅基制备高质量AlN介质层，并解决AlN与硅基板之间的界面问题。
发明内容
基于此，本发明提供一种高耐压低漏电的硅基AlN电容器，以解决现有AlN电容器中AlN介质层与硅基板之间的界面问题和AlN介质层N元素缺失的问题。
本发明采取的技术方案如下：
一种高耐压低漏电的硅基AlN电容器，包括由下至上设置的硅基板、AlN介质薄膜和顶部电极，还包括Pt缓冲层，所述Pt缓冲层沉积于所述硅基板上，所述AlN介质薄膜沉积于所述Pt缓冲层上。
本发明在硅基AlN电容器中引入Pt缓冲层，具有以下作用：
①引入的Pt缓冲层能够解决AlN与硅基板之间存在接近20％的晶格失配的问题。
②在高温氮气氛围沉积条件下，AlN会与硅基板发生剧烈的界面反应，而引入的Pt缓冲层可以保护硅基板；
③在硅基AlN电容器的制备和应用过程中，Si、O原子会扩散进入AlN中，而引入的Pt缓冲层可以解决界面扩散问题。在微电子领域的常见金属材料中：Al、Cu的熔点较低，与后续薄膜沉积工艺不兼容；Ti、Ni在高温氮气环境下会生成氮化物薄膜，影响后续薄膜的沉积。本发明创新性地采用引入Pt缓冲层的方法，金属Pt具有高达5.6eV的功函数和1770℃的熔点，且在高温氮气环境下极为稳定，是综合考虑最优的金属缓冲层。本发明利用Pt具有导电性好、熔点高、热稳定好和具备化学惰性等突出优点，在AlN薄膜沉积的高温氮气环境条件限制下解决了现存问题。
进一步地，所述Pt缓冲层的厚度为5-10nm。
进一步地，所述硅基板为低阻型硅衬底。
进一步地，所述顶部电极为Au电极，Au电极功函数高、化学稳定性好，有利于减小电容器的漏电流，增大使用寿命。
本发明还提供一种高耐压低漏电的硅基AlN电容器的制备方法，包括如下步骤：
(1)清洗硅基板；
(2)在硅基板上沉积Pt缓冲层；
(3)在沉积有Pt缓冲层的硅基板上沉积AlN介质薄膜；
(4)对AlN介质薄膜退火处理；
(5)在AlN介质薄膜上沉积顶部电极。
进一步地，步骤(1)采用RCA标准清洗工艺清洗硅基板。基板的清洁程度会影响电容器的漏电流大小，采用RCA标准清洗工艺可以达到足够的清洁程度。
进一步地，步骤(2)中，采用磁控溅射法沉积Pt缓冲层，沉积厚度为5-10nm。更优地，磁控溅射的条件为：磁控溅射功率设定为20-30W，使用氩气作为保护气，气氛压为0.1-0.5Pa。
进一步地，步骤(3)中，采用脉冲激光沉积法沉积AlN介质薄膜，其工艺条件为：脉冲激光能流密度为2-2.5J/cm2，激光重复频率为5Hz，沉积温度为700-850℃，生长气氛为高纯氮气，氮气分压为5-20Pa。
高纯氮气作为生长气氛有利于AlN介质薄膜的结晶，高的气氛压可以在AlN介质薄膜生长过程中补充缺失的N元素，提高薄膜的N/Al比，从而增强介质薄膜的绝缘性能，降低漏电并增大耐压。
进一步地，步骤(3)中沉积AlN介质薄膜的厚度150nm。
进一步地，步骤(4)中，AlN介质薄膜沉积完毕后进行原位退火30min，退火条件为保持AlN介质薄膜沉积时的温度与氮气分压。该步骤及其退火条件能改善薄膜的结晶状态，释放AlN介质薄膜中的残余应力，并进一步补充介质薄膜缺失的氮元素。
相对于现有技术，本发明实现了以下有益效果：
1)本发明采用脉冲激光沉积法制备硅基AlN电容器中的介质层，制得的介质薄膜质量好，有商业生产的潜力。
2)本发明创新性地采用Pt层作为AlN与硅基板之间缓冲层，解决了AlN与硅基板的失配问题和界面问题，极大的降低了硅基AlN电容器漏电流，提高了耐压值。
3)本发明创新性地采用高氮气分压作为介质薄膜的沉积气压，补充了AlN介质薄膜缺失的N元素，增加了介质薄膜的绝缘性能。
4)本发明所述的硅基AlN电容器还具有较低的介电损耗，和较好的偏压稳定性。
5)本发明所述的硅基AlN薄膜电容器适合应用于射频电路。
为了更好地理解和实施，下面结合附图详细说明本发明。
附图说明
图1为本发明的硅基AlN电容器的结构示意图。
图2示出利用台阶仪测量的实施例1制得的硅基AlN电容器中AlN介质层的厚度。
图3为硅基AlN电容器的电压-漏电流图和电场强度-电流密度图；其中，图3a为实施例1制得的含Pt缓冲层的电容器与无缓冲层的电容器的电压-漏电流对比图，图3b为实施例1制得的含Pt缓冲层的电容器与无缓冲层的电容器的电场强度-电流密度对比图。
图4为实施例1制得的硅基AlN电容器的频率-电容-损耗图。
图5为实施例1制得的硅基AlN电容器的电压-电容图。
具体实施方式
如图1所示，本发明所述的高耐压低漏电的硅基AlN电容器，包括由下至上设置的硅基板、Pt缓冲层(金属铂层)、AlN介质薄膜(氮化铝薄膜)和顶部电极。所述AlN介质薄膜沉积于所述Pt缓冲层上。
更优地，所述Pt缓冲层的厚度为5-10nm。
所述硅基板优选为低阻型硅衬底，可以使用p型硅，也可以使用n型硅。
另外，所述硅基板不局限于为低阻型硅衬底，但高阻型硅衬底的导电性差，不能直接充当电容器的底电极，使用高阻型硅衬底时需要对底电极进行引线处理。低阻硅导电性好，高阻硅导电性差。硅基板使用低阻硅时，可与导电性同样良好的Pt缓冲层共同充当电容器的底电极；若硅基板使用高阻硅时，则只能由Pt缓冲层作为电容器的底电极，实际使用过程中需要对Pt缓冲层做引线处理以达到使用要求。
所述顶部电极优选为Au电极(金电极)，也可以选择其他具有高功函数、化学稳定性好、粘附性好的类似金属电极。
所述硅基AlN电容器的制备方法包括如下步骤：
(1)清洗硅基板。优选采用RCA标准清洗工艺清洗硅基板。
(2)在硅基板上沉积Pt缓冲层。具体采用磁控溅射法沉积Pt缓冲层，沉积厚度可以在5-10nm之间。
(3)在沉积有Pt缓冲层的硅基板上沉积AlN介质薄膜。优选采用脉冲激光沉积法沉积AlN介质薄膜，并使用高纯氮气作为生长气氛。
(4)对AlN介质薄膜退火处理。更优地，AlN介质薄膜沉积完毕后进行原位退火30min，退火条件为保持AlN介质薄膜沉积时的温度与氮气分压。
(5)在AlN介质薄膜上沉积顶部电极。具体采用热蒸发镀膜法沉积顶部电极，可以采用硬掩膜直接生长图形化电极或采用光刻工艺定义电极。
(6)测试制得的硅基AlN电容器的电学性能。
另外，为了解决AlN与硅基板匹配问题和界面问题，所引入的缓冲层不局限于Pt，导电性好、化学稳定性和热稳定性高的类似金属材料也可以作为缓冲层。
实施例1
具体按如下步骤制备硅基AlN电容器：
(1)硅基板的选择与处理：选用低阻p型硅衬底作为硅基板，并采用RCA标准清洗工艺清洗硅基板。
(2)在硅基板上沉积Pt缓冲层：采用射频磁控溅射法在硅基板上沉积一层厚度为5-10nm的Pt缓冲层，磁控溅射功率设定为20-30W，使用氩气作为保护气，气氛压为0.1-0.5Pa。
(3)在沉积有Pt缓冲层的硅基板上沉积AlN介质薄膜：采用脉冲激光沉积法在沉积有Pt缓冲层的硅基板上沉积厚度为150nm的AlN介质薄膜，脉冲激光能流密度为2-2.5J/cm2，激光重复频率为5Hz，沉积温度为700-850℃，生长气氛为高纯氮气，气氛压为5-20Pa。
(4)对AlN介质薄膜退火处理：AlN介质薄膜沉积完毕后在脉冲激光沉积腔内对其进行原位退火30min，退火条件为保持AlN介质薄膜沉积时的温度与氮气分压。
(5)在AlN介质薄膜上沉积顶部电极：采用热蒸发镀膜法在AlN介质薄膜上沉积厚度为40-80nm、直径为100μm的圆点形Au电极，采用硬掩膜直接生长图形化电极或采用光刻工艺定义电极。制得的硅基AlN电容器为图1所示的MIM结构。
(6)测试制得的硅基AlN电容器的电学性能：使用台阶仪测量电容器介质层厚度，使用阻抗分析仪E4990A测试电容器的容量与损耗，使用电流源B2911测量电容器的漏电流值与耐压值。
测试结果
请参阅图2，其示出利用台阶仪测量的实施例1制得硅基AlN电容器中AlN介质层的厚度，平坦处约为150nm。目前，随着射频电路系统集成度的不断提高，单个器件所占面积的降低是一个必然趋势。在所需总电容不变的前提下，减小面积就意味着要提高电容密度。电容器的电容值与介质层厚度成反比，而与介质的介电常数成正比，但过薄的介质层会引起很大的漏电流，影响器件的可靠性，甚至造成器件失效。由于AlN是一种绝缘性能极好的high-k介质(介电常数约为9-11)，在相同规格下，AlN电容的容量可达传统SiO2电容的三倍。本发明所述电容器可以通过对介质层厚度的调控得到实际使用所需的容量和耐压值。
请参阅图3，图3a示出了实施例1的AlN/Pt/Si电容器与AlN/Si电容器的电压-漏电流图，图3b示出了实施例1的AlN/Pt/Si电容器与AlN/Si电容器的电场强度-电流密度图。
图3a反映了电容器在工作时的泄漏电流大小，漏电流过大则电容器容易发热损坏。在相同工艺条件但未引入Pt缓冲层时，电容器的漏电流在50V后由nA级迅速升高到μA级并发生击穿；而引入Pt缓冲层后解决了AlN/Si的匹配问题和界面问题，电容器的漏电流始终维持在nA级水平。图3b反映了电容器的击穿场强即耐压能力，引入Pt缓冲层后，电容器击穿场强可由未引入前的7.1MV/cm提升至9.5MV/cm。由于常见应用场景对电容器工作电压的要求为10-50V，所以本发明所述电容器还可以进一步降低介质层厚度以获得更大的电容量，并同时保持优异的漏电和耐压水平。
请参阅图4，其为实施例1制得的硅基AlN电容器的频率-电容-损耗图。较大的电容量有利于减小器件面积，提高集成度，较低的损耗可以减少发热和能耗，提升器件性能。由该图4可看出，实施例1的含150nm介质层的硅基AlN电容器，在1k-1M Hz频率下有着较为稳定的电容和损耗值，在1k Hz时电容值约为5.1pF，损耗角正切约为0.006，在1M Hz时电容值约为4.8pF，损耗角正切约为0.01。
请参阅图5，其为实施例1制得的硅基AlN电容器的电压-电容图。理想情况下，电容不应该随着外加偏压的改变而变化，而实际使用中则相反。电容随外加偏压的变化而变化称为电容电压系数，这是射频电路系统中非常关键的参数，电容变化越小，则电容电压系数越小，器件工作越稳定。由该图5可看出，实施例1制得的硅基AlN电容器的电容值随外加偏压(-40V至40V范围)变化极小，在1kHz频率下保持在4.9-5.1pF，在1M Hz频率下保持在4.8-4.9pF，电容器的电容电压系数小。
以上所述实施例仅表达了本发明的几种实施方式，其描述较为具体和详细，但并不能因此而理解为对发明专利范围的限制。应当指出的是，对于本领域的普通技术人员来说，在不脱离本发明构思的前提下，还可以做出若干变形和改进，这些都属于本发明的保护范围。
Claims (10)
1.一种高耐压低漏电的硅基AlN电容器，包括由下至上设置的硅基板、AlN介质薄膜和顶部电极，其特征在于：还包括Pt缓冲层，所述Pt缓冲层沉积于所述硅基板上，所述AlN介质薄膜沉积于所述Pt缓冲层上。
2.根据权利要求1所述的硅基AlN电容器，其特征在于：所述Pt缓冲层的厚度为5-10nm。
3.根据权利要求1或2所述的硅基AlN电容器，其特征在于：所述硅基板为低阻型硅衬底。
4.根据权利要求1或2所述的硅基AlN电容器，其特征在于：所述顶部电极为Au电极。
5.一种高耐压低漏电的硅基AlN电容器的制备方法，其特征在于：包括如下步骤：
(1)清洗硅基板；
(2)在硅基板上沉积Pt缓冲层；
(3)在沉积有Pt缓冲层的硅基板上沉积AlN介质薄膜；
(4)对AlN介质薄膜退火处理；
(5)在AlN介质薄膜上沉积顶部电极。
6.根据权利要求5所述的制备方法，其特征在于：步骤(1)采用RCA标准清洗工艺清洗硅基板。
7.根据权利要求5所述的制备方法，其特征在于：步骤(2)中，采用磁控溅射法沉积Pt缓冲层，沉积厚度为5-10nm。
8.根据权利要求5所述的制备方法，其特征在于：步骤(3)中，采用脉冲激光沉积法沉积AlN介质薄膜，其工艺条件为：脉冲激光能流密度为2-2.5J/cm2，激光重复频率为5Hz，沉积温度为700-850℃，生长气氛为高纯氮气，氮气分压为5-20Pa。
9.根据权利要求8所述的制备方法，其特征在于：步骤(3)中沉积AlN介质薄膜的厚度150nm。
10.根据权利要求8或9所述的制备方法，其特征在于：步骤(4)中，AlN介质薄膜沉积完毕后进行原位退火30min，退火条件为保持AlN介质薄膜沉积时的温度与氮气分压。
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