氫氧化鉀(KOH)是一種用于各向異性濕法蝕刻技術(shù)的堿金屬氫氧化物，是用于硅晶片微加工常用的硅蝕刻化學(xué)物質(zhì)之一。各向異性蝕刻優(yōu)先侵蝕襯底。也就是說，它們在某些方向上的蝕刻速度比在其他方向上的蝕刻速度快，而各向同性蝕刻(如HF)會(huì)向所有方向侵蝕。

Potassium hydroxide (KOH) is an alkali hydroxide used in anisotropic wet etching technology, and is one of the silicon etching chemicals commonly used in silicon wafer micromachining. Anisotropic etching prioritizes substrate erosion. That is to say, their etching speed in certain directions is faster than that in other directions, while isotropic etching (such as HF) erodes in all directions.

使用KOH工藝是因?yàn)槠湓谥圃熘械目芍貜?fù)性和均勻性，同時(shí)保持了較低的生產(chǎn)成本。異丙醇(IPA)經(jīng)常添加到溶液中，以改變從{110}壁到{100}壁的選擇性，并提高表面光滑度。

The use of KOH process is due to its repeatability and uniformity in manufacturing, while maintaining lower production costs. Isopropanol (IPA) is often added to the solution to change the selectivity from {110} wall to {100} wall and improve surface smoothness.

氧化物和氮化物在KOH中都蝕刻緩慢。氧化物可以在KOH蝕刻浴中用作短時(shí)間的蝕刻掩模。對于更長的時(shí)間，氮化物是更好的掩模，因?yàn)樗贙OH中蝕刻得更慢。另一種選擇(對許多其他功能有用)是用硼摻雜晶片。這也將降低蝕刻速率，實(shí)際上停止富硼硅的蝕刻。

Both oxides and nitrides etch slowly in KOH. Oxides can be used as short-term etching masks in KOH etching baths. For longer periods of time, nitrides are better masks because they etch more slowly in KOH. Another option (useful for many other functions) is to use boron doped wafers. This will also reduce the etching rate, effectively stopping the etching of boron rich silicon.

當(dāng)KOH濃度在80℃時(shí)達(dá)到18wt%時(shí)，蝕刻速率隨著KOH濃度的增加而增加。當(dāng)KOH濃度增加超過18wt%時(shí)，蝕刻速率降低。蝕刻過程中發(fā)生的化學(xué)反應(yīng)就是這種變化的結(jié)果。這將在后面更深入地討論。然而，通常不使用大蝕刻速率的濃度，因?yàn)楸砻婀饣入S著濃度的增加而提高(明顯高于30%)。Si{100}在KOH中的蝕刻速率可以使用下面的等式來計(jì)算:

When the KOH concentration reaches 18wt% at 80 ℃, the etching rate increases with the increase of KOH concentration. When the KOH concentration increases by more than 18wt%, the etching rate decreases. The chemical reaction that occurs during the etching process is the result of this change. This will be discussed in more depth later. However, concentrations with high etching rates are usually not used, as surface smoothness increases with increasing concentration (significantly higher than 30%). The etching rate of Si {100} in KOH can be calculated using the following equation:

r =[H2O]4[氫氧化鉀]1/4實(shí)驗(yàn)值(-個(gè)/kT)

R=[H2O] 4 [potassium hydroxide] 1/4 experimental value (- pieces/kT)

等式1: {100}蝕刻速率

Equation 1: {100} Etching rate

其中濃度以摩爾/升為單位，k0 = 413米/分鐘*(摩爾/升)-4.25，EA = 0.595電子伏。KOH的密度和分子量分別為2.055克/立方厘米和56.11克/摩爾，水的密度和分子量分別為1.00克/立方厘米和18.02克/摩爾。

The concentration is measured in moles per liter, with k0=413 meters per minute * (moles per liter) -4.25 and EA=0.595 electron volts. The density and molecular weight of KOH are 2.055 grams per cubic centimeter and 56.11 grams per mole, respectively, while the density and molecular weight of water are 1.00 grams per cubic centimeter and 18.02 grams per mole, respectively.

使用KOH蝕刻有幾個(gè)缺點(diǎn)。大的問題是蝕刻過程中H2氣泡的產(chǎn)生。這些H2氣泡充當(dāng)了一個(gè)偽面具。這增加了粗糙度，并可能損壞微結(jié)構(gòu)。與KOH蝕刻相關(guān)的另一個(gè)問題是KOH含有堿離子。KOH是MOS器件的終生殺手。使用KOH的人必須小心不要污染任何其他過程。KOH還會(huì)腐蝕鋁，這可能是片上電路的一個(gè)問題。

There are several drawbacks to using KOH etching. The big problem is the generation of H2 bubbles during the etching process. These H2 bubbles act as a fake mask. This increases the roughness and may damage the microstructure. Another issue related to KOH etching is the presence of alkali ions in KOH. KOH is the lifelong killer of MOS devices. People using KOH must be careful not to contaminate any other processes. KOH can also corrode aluminum, which may be a problem with on-chip circuits.

KOH蝕刻速率與成分和溫度的關(guān)系

The Relationship between KOH Etching Rate and Composition and Temperature

蝕刻速率隨著溫度的增加而增加；然而，隨著蝕刻速率的增加，會(huì)導(dǎo)致不太理想的蝕刻行為。當(dāng)KOH濃度增加超過18wt%時(shí)，蝕刻速率降低。這是因?yàn)榘l(fā)生了蝕刻反應(yīng)。當(dāng)強(qiáng)堿，如KOH(含有大量的OH-離子)存在時(shí)，硅-硅鍵斷裂。該蝕刻導(dǎo)致Si(OH)4的形成、四個(gè)水分子的消耗和兩個(gè)氫氣分子的釋放。

The etching rate increases with the increase of temperature; However, as the etching rate increases, it can lead to less ideal etching behavior. When the KOH concentration increases by more than 18wt%, the etching rate decreases. This is because an etching reaction occurred. When strong bases such as KOH (containing a large amount of OH ions) exist, the silicon silicon bond breaks. This etching leads to the formation of Si (OH) 4, the consumption of four water molecules, and the release of two hydrogen molecules.

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