JPS5931981B2 - Failure analysis method for semiconductor devices - Google Patents

Description

【発明の詳細な説明】 この発明は半導体素子の不良解析方法に関し、特にＰＮ
接合領域の接合性の良否を解析する解析方法に関する。[Detailed Description of the Invention] The present invention relates to a failure analysis method for semiconductor devices, and in particular to a method for analyzing failures in semiconductor devices.
This invention relates to an analysis method for analyzing the quality of bonding in a bonding region.

半導体素子は周知のように、半導体基板主面に半導体基
板とは反対の導電型決定の不純物を拡散して形成するＰ
Ｎ接合領域が基本となつて構成されている。As is well known, semiconductor elements are formed by diffusing impurities with a conductivity type opposite to that of the semiconductor substrate onto the main surface of the semiconductor substrate.
It is basically constructed of an N-junction region.

そしてこのＰＮ接合領域に課せられた重要な電気的特性
のひとつとして逆方向特性があへ〜る。これはＰＮ接合
に逆方向電圧を与えたときの逆方向電圧と逆方向電流の
関係であるが、逆方向電流が規定の電流値を超過すると
ＰＮ接合リーク電流として半導体素子が動作しない不良
原因となる。しかしこのＰＮ接合リーク電流を半導体素
子に設けられた外部電極を利用して測定することは困難
である。One of the important electrical characteristics imposed on this PN junction region is the reverse direction characteristic. This is the relationship between the reverse voltage and reverse current when a reverse voltage is applied to the PN junction, but if the reverse current exceeds a specified current value, it will become a PN junction leak current and cause a failure in which the semiconductor device does not operate. Become. However, it is difficult to measure this PN junction leakage current using external electrodes provided on the semiconductor element.

それは外部電極から逆方向電圧を加えると絶縁膜のピン
ホールなどに起因するリーク電流も流れ、この電流とＰ
Ｎ接合リーク電流とを区別することができないからであ
る。したがつてＰＮ接合の不良を解析するには絶縁膜等
を除去してＰＮ接合領域だけを解析することが必要であ
る。このようにＰＮ接合領域だけを解析する方法として
従来行なわれている方法には、ＰＮ接合領域に金属電極
を形成させてこれと半導体基板との逆方向特性を調べる
とか、Ｐ戸接合領域に電子ビームを照射してＰＮ接合領
域又はその近傍に形成させた金属電極から電子ビーム誘
起電流を取出して調べるとかの方法がある。しかしこれ
ら従来の解析方法ではいずれもＰＮ接合領域又はその近
傍へ金属電極を形成しなければならず、しかもそこへの
探針接触を必要とする。半導体素子、特に集積回路など
高集積化高密度化された半導体素子では、その半導体素
子内には極めて多数の微細なパターン寸法のＰＮ接合領
域が作り込まれている。このような微細なパターン寸法
、たとえば数μｍ角のようなパターン領域のＰＮ接合領
域内に金属電極を形成することは、不良解析対象の試料
には通常はパツケージ等が設けられているため、半導体
素子製造プロセスによく用いられる写真製版の技術を用
いることができないので、極めて困難である。また数μ
ｍ角のような微小電極への電気接続を得るための探針接
触は、ウエ・・プローバでよく経験されるように極めて
難かしい。すなわち金属電極を形成し探針接触を必要と
する点が従来のＰＮ接合領域解析方法の欠点であつた〇
この発明は従来の方法における士述の欠点を除去するこ
とを目的とし、金属電極を形成することなくまた探針接
触を必要とすることなく、ＰＮ接合領域に光を照射して
光起電力を発生させ、ＰＮ接合領域の上に形成した電界
効果型液晶膜内に上記光起電力によつて生ずる複屈折を
偏光光線を用いて観測し、この観測によつて間接的にＰ
Ｎ接合部の解析を行なうものであつて、以下更に図面に
ついて詳細に説明する。This is because when a reverse voltage is applied from the external electrode, leakage current due to pinholes in the insulating film also flows, and this current and P
This is because it cannot be distinguished from the N junction leakage current. Therefore, in order to analyze defects in the PN junction, it is necessary to remove the insulating film and analyze only the PN junction region. Conventional methods for analyzing only the PN junction region include forming a metal electrode in the PN junction region and examining the reverse characteristics between this and the semiconductor substrate, or forming an electron electrode in the P junction region. There is a method of irradiating the electron beam and extracting the electron beam induced current from a metal electrode formed in or near the PN junction region and examining it. However, in all of these conventional analysis methods, a metal electrode must be formed in or near the PN junction region, and moreover, a probe needs to be brought into contact there. 2. Description of the Related Art In semiconductor devices, particularly in highly integrated and highly dense semiconductor devices such as integrated circuits, an extremely large number of PN junction regions with fine pattern dimensions are built into the semiconductor device. Forming a metal electrode in the PN junction region of a pattern area with such minute pattern dimensions, for example, several μm square, is difficult for semiconductors because the sample to be analyzed for failure usually has a package, etc. This is extremely difficult because photolithography, which is often used in device manufacturing processes, cannot be used. Also a few μ
Probe contact to obtain electrical connection to microelectrodes such as m-square is extremely difficult, as is often experienced with wafer probers. In other words, the disadvantage of the conventional PN junction region analysis method is that it requires forming a metal electrode and making contact with the probe. This invention aims to eliminate the above disadvantages of the conventional method. A photovoltaic force is generated by irradiating the PN junction region with light without forming a probe and without the need for probe contact, and the photovoltaic force is generated within a field effect liquid crystal film formed on the PN junction region. The birefringence caused by P is observed using polarized light, and this observation indirectly shows that P
The N-junction is analyzed, and the drawings will be explained in detail below.

第１図はこの発明の方法における試料作製の段階を示す
断面図である。FIG. 1 is a cross-sectional view showing the steps of sample preparation in the method of the present invention.

第１図に於いて１はＰＮ接合領域、２は半導体基板、３
は電界効果型液晶膜、４はガラス板、５は透明導電膜で
ある。また符号１ａはＰＮ接合線を示し、符号２ａは半
導体基板２の主面を示す。この発明の不良解析方法にお
ける第１の段階では第１図ａに示すように半導体基板２
の主面２ａ上にＰＮ接合領域１を露出虹せる。In FIG. 1, 1 is a PN junction region, 2 is a semiconductor substrate, and 3 is a PN junction region.
1 is a field effect liquid crystal film, 4 is a glass plate, and 5 is a transparent conductive film. Further, the reference numeral 1a indicates a PN junction line, and the reference numeral 2a indicates the main surface of the semiconductor substrate 2. In the first step in the failure analysis method of the present invention, as shown in FIG.
The PN junction region 1 is exposed and rainbowed on the main surface 2a.

このため必要な場合は絶縁膜、メタライゼーシヨン等を
除去する。次の段階では第１図ｂに示すように半導体基
板２の上に電界効果型液晶膜３を被覆する。For this reason, insulating films, metallization, etc. are removed if necessary. In the next step, as shown in FIG. 1b, a field effect liquid crystal film 3 is coated on the semiconductor substrate 2.

次には第１図ｃに示すように透明導電膜５を有するガラ
ス板４を液晶膜３と透明導電膜５が接触するように載置
する。液晶膜３の被覆範囲卦よび透明導電膜５を有する
ガラス板４の寸法大きさは、解析の対象としているＰＮ
接合領域１を充分にカバーできる範囲とする。第１図ｃ
に示す状態で不良解析の対象とする試料１００が完成す
る。次の段階は試料１００を光学系で観察する段階であ
る。Next, as shown in FIG. 1c, a glass plate 4 having a transparent conductive film 5 is placed so that the liquid crystal film 3 and the transparent conductive film 5 are in contact with each other. The coverage area of the liquid crystal film 3 and the dimensions of the glass plate 4 having the transparent conductive film 5 are determined based on the PN to be analyzed.
The area should be such that it can sufficiently cover the bonding area 1. Figure 1c
The sample 100 to be subjected to failure analysis is completed in the state shown in FIG. The next step is to observe the sample 100 using an optical system.

第２図はこの発明の方法に｝ける試料検査の段階を示す
系統図であつて符号１，２，２ａ，３，４，５，１００
は第１図の同一符号と同じく、全体を符号２００で示す
ものは光学系を表わし、６は光源、７は偏光子、８は偏
光された光、９はブリズム、１０は対物レンズ、１１は
検光子、１２は接眼レンズであり、１３は透明導電膜５
と半導体基板２との間に加れる直流電源である。試料１
００に直流電源１３を加えた状態で、光学系２００によ
り試料１００を照射して観測する。第２図に示す実施例
では、光源６からの光を偏光子７で偏光し、偏光された
光８は、プリズム９、対物レンズ１０、ガラス板４、透
明導電膜５、液晶膜３を通過してＰＮ接合領域１へ至り
そこで反射される。そして反射光は再び液晶膜３、透明
導電膜５、ガラス板４、対物レンズ１０を通過しプリズ
ム９に至る。プリズム９は半透明鏡であり、反射の偏向
された光は直進し、検光子１１．接眼レンズ１２を通過
して人間の眼またはテレビジヨン・カメラで観測される
。対物レンズ１０、接眼レンズ１２は微小な寸法のＰＮ
接合領域１を拡大して詳細観測できるように拡大鏡を構
成する。一般にＰＮ接合に光が照射されると光起電力を
生じる現象のあることはよく知られている。したがつて
偏向された光８がＰＮ接合領域１へ照射されてもＰＮ接
合領域１と半導体基板２の間に光起電力を発生する。光
起電力が誘起されればＰＮ接合領域１の半導体基板主面
２ａに現われているＰＮ接合線１ａ（第１図参照）にわ
たつても電界が形成される。この電界は、半導体基板２
と透明導電膜５の間に直流電圧を与えてできた直流電界
に重畳する。しかしもしＰＮ接合領域１のＰＮ接合特性
が不良であつて逆方向リーク電流が生じているならば上
記の光起電力はリーク電流によつて短絡され、直流電源
１３によつて生ずる直流電界に重畳する光起電力による
電界は著しく低下する。したがつて光起電力によつて生
ずる電界の強さを観測することによつてＰＮ接合性を検
査することができる。゛液晶膜３はさきに述べたように
電界効果型液晶膜であるため、電界が加えられるといわ
ゆる電気複屈折を起し偏光光線に対してはその偏光面を
回転する。FIG. 2 is a system diagram showing the steps of sample inspection in the method of the present invention, with reference numerals 1, 2, 2a, 3, 4, 5, and 100.
As with the same reference numerals in FIG. 1, the reference numeral 200 represents an optical system, 6 is a light source, 7 is a polarizer, 8 is polarized light, 9 is a prism, 10 is an objective lens, and 11 is an optical system. Analyzer, 12 is an eyepiece, 13 is a transparent conductive film 5
This is a DC power supply applied between the semiconductor substrate 2 and the semiconductor substrate 2. Sample 1
The sample 100 is irradiated and observed by the optical system 200 while the DC power supply 13 is applied to the sample 100. In the embodiment shown in FIG. 2, light from a light source 6 is polarized by a polarizer 7, and the polarized light 8 passes through a prism 9, an objective lens 10, a glass plate 4, a transparent conductive film 5, and a liquid crystal film 3. The light then reaches the PN junction region 1 and is reflected there. Then, the reflected light passes through the liquid crystal film 3, the transparent conductive film 5, the glass plate 4, and the objective lens 10 again, and reaches the prism 9. The prism 9 is a semi-transparent mirror, and the reflected and deflected light travels straight through the analyzer 11. It passes through the eyepiece 12 and is observed by the human eye or a television camera. The objective lens 10 and the eyepiece lens 12 are PN with minute dimensions.
A magnifying glass is configured so that the joining region 1 can be enlarged and observed in detail. It is generally well known that when a PN junction is irradiated with light, a photovoltaic force is generated. Therefore, even when the PN junction region 1 is irradiated with the deflected light 8, a photovoltaic force is generated between the PN junction region 1 and the semiconductor substrate 2. When a photovoltaic force is induced, an electric field is also formed across the PN junction line 1a (see FIG. 1) appearing on the main surface 2a of the semiconductor substrate in the PN junction region 1. This electric field is applied to the semiconductor substrate 2
It is superimposed on the DC electric field created by applying a DC voltage between the transparent conductive film 5 and the transparent conductive film 5. However, if the PN junction characteristics of the PN junction region 1 are poor and a reverse leakage current occurs, the photovoltaic force will be short-circuited by the leakage current and will be superimposed on the DC electric field generated by the DC power supply 13. The electric field caused by the photovoltaic force is significantly reduced. Therefore, the PN junction property can be tested by observing the strength of the electric field generated by the photovoltaic force. As mentioned above, the liquid crystal film 3 is a field effect liquid crystal film, so when an electric field is applied, so-called electric birefringence occurs and the plane of polarization of the polarized light is rotated.

この偏光面の回転角度はほマ電界の強さに比例するので
この偏光面の回転角度を観測することによつて電界の強
さを観測することができる。ところで偏光子７と検光子
１１の偏光面に関する相対関係が、反射の偏光された光
を遮断するような相対関係であれば、人間の眼４たはテ
レピジヨン・カメラで見られる視野は暗黒状態であり、
また逆に反射の偏光された光を通過させるような相対関
係であれば、人間の眼またはテレビジヨン・カメラで見
られる視野は明視野である。したがつて液晶膜３の部分
を通過する際に偏光された光に対して偏光面の回転が起
れば暗黒状態の中に明るい視野、あるいは明視野の中に
暗い部分が現われる。偏光子７と検光子１１の偏光面に
対する相対関係を適当に設定して｝けば液晶膜３の中の
各部で起る偏光面の回転価の大きさを接眼レンズ１２を
通過する光の強さとして観測し、したがつて液晶膜３内
の電界分布を知り、これからＰＮ接合領域１の良、不良
を解析することができる。第１図では示してないが、集
積回路のような半導体素子では、数多くのＰＮ接合領域
が形成されているので、良否判定を要するＰＮ接合領域
の周辺には必ずいくつかの他のＰＮ接合領域も存在して
いるから、この良否判定対象外のＰＮ接合領域群と良否
判定対象のＰＮ接合領域とを比較することができる。Since the rotation angle of this plane of polarization is proportional to the strength of the electric field, the strength of the electric field can be observed by observing the rotation angle of this plane of polarization. By the way, if the relative relationship between the polarizer 7 and the analyzer 11 in terms of the polarization plane is such that the reflected polarized light is blocked, the visual field seen by the human eye 4 or the television camera will be in a dark state. can be,
Conversely, if the relative relationship is such that reflected polarized light passes through, the visual field seen by the human eye or a television camera is bright field. Therefore, if the plane of polarization of the polarized light is rotated when it passes through the liquid crystal film 3, a bright field appears in a dark state, or a dark part appears in a bright field. By appropriately setting the relative relationship between the polarizer 7 and the analyzer 11 with respect to the plane of polarization, the magnitude of the rotation of the plane of polarization occurring at each part of the liquid crystal film 3 can be controlled by the intensity of the light passing through the eyepiece 12. Therefore, the electric field distribution within the liquid crystal film 3 is known, and from this it is possible to analyze whether the PN junction region 1 is good or bad. Although not shown in Figure 1, many PN junction regions are formed in a semiconductor device such as an integrated circuit, so there are always several other PN junction regions around the PN junction region that requires a pass/fail determination. Since there is also a group of PN junction regions that are not subject to quality determination, it is possible to compare this group of PN junction regions that are not subject to quality determination with the PN junction regions that are subject to quality determination.

またＰＮ接合リーク電流によつて生じた不良解析対象の
ＰＮ接合領域１に向けて偏光された光８の光路以外から
通常光を照射することにより、この通常光による光起電
力でＰＮ接合リーク電流を補償し、あたかもＰＮリーク
電流が発生していないような状態となるようにしてＰＮ
接合の良否を判定することもできる〇半導体基板２と透
明導電膜５の間に直流電源１３によつて与える直流電圧
の極性は、光の照射を受けた場合のＰＮ接合領域１の電
位と透明導電膜５の電位の差が、半導体基板２の電位と
透明導電膜５の電位の差よりも大きくなるような極性を
選んだ方が観測に便利である。In addition, by irradiating normal light from a path other than the optical path of the polarized light 8 toward the PN junction region 1 to be analyzed for failure caused by the PN junction leakage current, the PN junction leakage current is generated by the photovoltaic force generated by this normal light. By compensating for the PN leakage current, the PN leakage current is
It is also possible to judge the quality of the bond. The polarity of the DC voltage applied between the semiconductor substrate 2 and the transparent conductive film 5 by the DC power supply 13 is the same as the potential of the PN junction region 1 when irradiated with light. It is more convenient for observation to select polarity such that the difference in potential of the conductive film 5 is larger than the difference in potential between the semiconductor substrate 2 and the transparent conductive film 5.

更に電界効果型液晶の種類によつては、比較的長時間の
光照射によつて電気複屈折の度合が緩和されて、電界効
果型液晶膜３の光学的性質が電界依存性を示さなくなる
場合がある０この場合には偏光された光８または通常光
のような偏光されない光を、両者またはいずれかを断続
光とすることによつて明確なＰＮ接合良否判定を行なう
ことができる〇液晶膜３にはたとえばＭＢＢＡ（Ｐ ｍｅｔｈＯｘｙｂｅｎｚｙｌｌｄｅｎｅ−Ｐ−Ｂｕｔｔ
ｙｌａｎｉｌｉｎｅ）などのネマチツク液晶を用いる。Furthermore, depending on the type of field-effect liquid crystal, the degree of electrical birefringence is alleviated by light irradiation for a relatively long period of time, and the optical properties of the field-effect liquid crystal film 3 no longer exhibit electric field dependence. In this case, by using polarized light 8 or non-polarized light such as normal light, or by using either or both as intermittent light, it is possible to clearly determine the quality of the PN junction.〇Liquid crystal film For example, MBBA (P methOxybenzylldene-P-Butt
A nematic liquid crystal such as ylaniline is used.

ＭＢＢＡのごとき液晶の絶縁抵抗は１０１０Ω？以上で
あつてＰＮ接合領域上へ直接塗布しても液晶によるリー
ク電流は非常に小さいｏな｝液晶膜３の液晶分子を半導
体基板２と透明導電膜５のそれぞれの面により整然と配
列させるため、界面活性剤の薄膜を半導体基板２と透明
導電膜５の面に液晶膜３を設けるまえに形成しておくこ
ともできる。Is the insulation resistance of a liquid crystal like MBBA 1010Ω? Even if the liquid crystal is applied directly onto the PN junction region, the leakage current due to the liquid crystal is very small.} In order to arrange the liquid crystal molecules of the liquid crystal film 3 more orderly on each surface of the semiconductor substrate 2 and the transparent conductive film 5, A thin film of a surfactant can also be formed on the surfaces of the semiconductor substrate 2 and the transparent conductive film 5 before providing the liquid crystal film 3.

以上の説明によつて明らかなように、この発明によれば
、ＰＮ接合領域に何ら金属電極を形成することなく、簡
単な操作で作製した試料を用い簡単な観測装置によつて
微細なパターンのＰＮ接合領域を不良解析することがで
きる。As is clear from the above description, according to the present invention, fine patterns can be observed using a simple observation device using a sample prepared by simple operations without forming any metal electrodes in the PN junction region. Failure analysis can be performed on the PN junction region.

またこの方法によれば単に良否の判定だけでなく、不良
個所、不良の度合等も観測できることは上述の説明から
明らかであろう。ますます高集積化され微細パターン化
する集積回路等に対しこの発明は極めて好適な不良解析
方法を提供し、ひいては接合形成の手掛り、改善をもた
らすものであつて半導体素子製造技術の進歩を促すもの
である。Furthermore, it will be clear from the above description that this method not only allows determination of pass/fail but also allows observation of defective locations, degree of defect, etc. This invention provides an extremely suitable failure analysis method for integrated circuits, etc., which are becoming increasingly highly integrated and have fine patterns, and in turn provides clues and improvements to bond formation, and promotes progress in semiconductor device manufacturing technology. It is.

【図面の簡単な説明】[Brief explanation of the drawing]

第１図はこの発明の方法に訃ける試料作製の段階を示す
断面図、第２図はこの発明の方法に卦ける試料検査の段
階を示す系統図である。 図にお一いて１はＰＮ接合領域、２は半導体基板、３は
電界効果型液晶膜、４はガラス板、５は透明導電膜、６
は光源、７は偏光子、８は偏光された光、９はプリズム
、１０は対物レンズ、１１は検光子、１２は接眼レンズ
、１３は直流電極、１００は試料、２００は光学系であ
る。FIG. 1 is a sectional view showing the steps of sample preparation according to the method of the present invention, and FIG. 2 is a system diagram showing the steps of sample inspection according to the method of the present invention. In the figure, 1 is a PN junction region, 2 is a semiconductor substrate, 3 is a field effect liquid crystal film, 4 is a glass plate, 5 is a transparent conductive film, and 6
1 is a light source, 7 is a polarizer, 8 is polarized light, 9 is a prism, 10 is an objective lens, 11 is an analyzer, 12 is an eyepiece, 13 is a DC electrode, 100 is a sample, and 200 is an optical system.

Claims (1)

【特許請求の範囲】[Claims] １ 半導体基板主面の限定された領域範囲に形成される
ＰＮ接合領域のＰＮ接合性を検査する半導体素子の不良
解析方法において、上記ＰＮ接合領域が露出した上記半
導体基板主面上に電界効果型液晶膜を形成する段階、上
記液晶膜上に透明導電膜を有するガラス板を載せ上記液
晶膜に上記透明導電膜を接触させる段階、上記透明電導
膜と上記半導体基板の間に直流電圧を加え、当該直流電
圧の極性は、上記光起電力との合成により上記ＰＮ接合
領域と上記透明導電膜間に生ずる電位差が上記半導体基
板と上記透明導電膜間に生ずる電位差より大きくなるよ
うな極性とする段階、上記ＰＮ接合領域に光を照射して
光起電力を発生させる段階、上記直流電圧と上記光起電
力とによる電界のため上記液晶膜が与える偏光面の回転
を偏光光線を用いて観測する段階を有することを特徴と
する半導体素子の不良解析方法。1. In a semiconductor element failure analysis method for inspecting the PN junction property of a PN junction region formed in a limited range of a main surface of a semiconductor substrate, a field effect type forming a liquid crystal film, placing a glass plate having a transparent conductive film on the liquid crystal film, bringing the transparent conductive film into contact with the liquid crystal film, applying a DC voltage between the transparent conductive film and the semiconductor substrate; The polarity of the DC voltage is such that the potential difference generated between the PN junction region and the transparent conductive film upon combination with the photovoltaic force is larger than the potential difference generated between the semiconductor substrate and the transparent conductive film. , irradiating the PN junction region with light to generate a photovoltaic force, and observing the rotation of the plane of polarization given by the liquid crystal film due to the electric field caused by the DC voltage and the photovoltaic force using polarized light. 1. A method for analyzing failure of a semiconductor device, comprising: