JPH0666369B2 - Method for manufacturing semiconductor device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application] The present invention relates to an ohmic contact when forming a chip surface electrode of a semiconductor device. For example, the present invention relates to a method of nondestructively determining the quality of ohmic contact by a change in value of several nA.

(Prior Art) In manufacturing a semiconductor device, a conventional conventional evaluation method of ohmic contact between an active region silicon substrate surface and a surface electrode at the time of forming a chip surface electrode is described below. An example will be described below. FIG. 3 is a sectional view of a PN junction diode. In this case, the anode side electrode terminal 1 is taken out from one main surface of the chip, the cathode side electrode terminal 2 is taken out from the other main surface, and the ohmic contact of the cathode surface electrode is normal for convenience of explanation.

An outline of an example of the surface electrode forming method will be described with reference to FIG. In FIG. 3A, first, an electrode lead-out opening 4 is formed on the surface of the P ⁺ diffusion layer 3 which is an active region by PEP (Photo Engraving Process). Next, after depositing aluminum (Al), which is a general electrode material, on the main surface of the chip by vapor deposition, the surface electrode 5 is formed by PEP. In this case, in order to obtain a good ohmic contact between the active region surface 6 exposed in the electrode extraction opening and the Al surface of the surface electrode 5, a method of performing heat treatment (aluminum sintering treatment) at a temperature of about 500 ° C. for several minutes is used. . In this case, when a thin film (mainly a SiO ₂ film with a thickness of 300 Å or less) remains on the active region surface 6 of the electrode extraction opening due to incomplete etching, or when the conditions for aluminum deposition are inappropriate, this is the cause. normal ohmic contact after sintering process can not be obtained, the forward characteristics (V _F -I _F characteristics) of the diode becomes defect.

(A) In general, as a method for evaluating the forward characteristic of a diode, a forward bias voltage is applied between the anode terminal 1 and the cathode terminal 2 in FIG. 3, and as shown in FIG. 4 (b). While observing the V _F -I _F waveform curve tracer,
In order to determine whether the ohmic contact is normal or defective, a forward current I _F of several hundred mA or several A is passed and the difference in the forward voltage V _F at that time is used for the determination. That _V F -I _F waveform curve m is a normal product, curve n in (b) shows a defect characteristics. In this case, several hundred mA or several A
For requiring I _F, it causes a voltage drop at the contact portion between the pattern measurement needle 7 and the wafer rear surface and the stage 8 as shown in FIG. 4 (c), it is difficult to normal measurement. Particularly in high-speed automatic measurement, even if the measurement method such as the Kelvin method is improved, it is difficult to perform normal measurement due to the restrictions such as the size of the pattern.

The electrical evaluation of ohmic contact property is based on the above V _F
Besides -I _F waveform observation method is resistance method or the like, but have advantages and disadvantages rather than direct chip measurement.

(B) As another evaluation method of ohmic contact property,
After performing the aluminum sintering treatment, there is a method in which aluminum as a surface electrode is removed by an etching method and the surface is observed with a microscope. FIG. 4 (d) schematically shows a cross section of the surface state when the ohmic contact is normal.
Is an aluminum-silicon reaction layer called a sinter layer. When there is a problem, the sintering layer is low. Although this method can distinguish between normal and defective, it is a destructive test and total evaluation is impossible.

(Invention Problems to Solved) wherein (A) Electrical characterization of the term as an ohmic contact property evaluation method when the surface electrode forming a semiconductor device having a PN junction (V _F method) and (B) of claim The methods for observing changes in the surface state due to scientific reactions have been explained, but all have the following problems.

(A) an electrical characterization (V _F method) difficult to discriminate the normal state and defect ohmic contact when not conduct forward current I _F hundreds mA to several A to the PN junction, this pattern measurement The thickness of the needle is restricted by the front surface electrode, and a voltage drop occurs in the contact state between the other electrode (for example, the cathode side wafer back surface electrode () and the measuring device (stage), which makes accurate measurement difficult.

(B) A method of observing a change in surface state due to a chemical reaction.

After the sinter treatment, after chemically etching aluminum that is the surface electrode, it is possible to accurately distinguish between normal and defective ohmic contacts by observing the openings with a microscope, but this is a destructive test, and the total evaluation in production is Can not.

The object of the present invention is to solve the above-mentioned problems in the case of evaluating the ohmic contact property of the surface electrode of a semiconductor device having a PN junction, and to realize accurate and nondestructive 100% evaluation easily and at high speed in the element manufacturing process. Accordingly, it is an object of the present invention to provide a method for manufacturing a semiconductor device, which can reduce the processing loss in the subsequent process.

[Configuration of Invention] (Means and Actions for Solving Problems) The present invention is a method for evaluating ohmic contact property of a surface electrode in ohmic contact with an active region surface of a semiconductor substrate having a PN junction in a device manufacturing process. In the state where a low reverse bias voltage is applied to the PN junction in which the measurement input terminal of the measuring device is in contact with the surface electrode, a small photocurrent flowing through the measurement input terminal when light is irradiated on the substrate surface. For example, when a normal ohmic contact is obtained, a photocurrent of about several nA flows, and in the case of a defect, the photocurrent value decreases depending on the level. This is a method of manufacturing a semiconductor device in which whether the ohmic contact is good or bad is determined by utilizing the amount of change in that no current flows.

The present invention utilizes the phenomenon that when a substrate is irradiated with light, carriers are photoexcited in the PN junction and a region in the vicinity of the PN junction, and the resulting minute current changes depending on the ohmic contact property of the surface electrode.

(Example) An example of the PN junction diode which is the basis of the semiconductor device will be described as an example of the present invention. FIG. 1A is a sectional view of a PN junction diode. The N-type semiconductor substrate 10 is
PN junction 1 by this and P ⁺ diffusion layer 13 (active region)
4 and a protective oxide film (SiO ₂
An electrode extraction opening is provided in the film 11 by the PEP technique. An aluminum surface electrode 15 is provided which makes ohmic contact with the active area surface 16 exposed in the opening. Thereafter, the surface electrode 15 is subjected to aluminum sintering treatment.

Next, with reference to FIG. 1 (b), a method for evaluating the ohmic contact property of the surface electrode will be described. The wafer subjected to the sintering treatment is placed on the stage 18 of the measuring instrument, the pattern measuring needle (measurement input terminal) 17 is brought into contact with the surface electrode 15, and the measuring instrument is turned on to reverse bias voltage (low voltage close to 0 to the PN junction). ) Is applied. That is, if the potential of the stage 18 is set to the reference (0 V), the potential on the anode side becomes a non-potential.
The current I _R flowing through the measuring needle 17 in this state is almost 0 (0.1 nA or less) without illumination. Then the wafer surface (anode side) to 10nA or more current I _R flows photocurrent as shown by Q ₁ point of FIG. 1 is irradiated with a spotlight 19 (c). In this case, the ohmic contact of the surface electrode 15 is normal. However, the ohmic contact between the stage 18 and the wafer is normal. When the ohmic contact of the surface electrode 15 is completely defective, almost no current flows as indicated by the point Q ₂ in the figure, and no current change due to light irradiation occurs. That is, if the irradiation light energy is constant, I _R decreases depending on the degree of failure of ohmic contact, and the ohmic contact property can be evaluated.

Although the above description has been focused mainly on the surface electrode 15, the diode having the cathode surface electrode 12 formed on the lower surface (on the drawing) of the substrate 10 can also be evaluated in the same manner. That photocurrent _{I R} if both electrodes 12 and 15 are both normal
Indicates Q ₁ point, and Q ₂ point when either of them is completely defective. In the case of an intermediate value, trials are performed in advance for a plurality of wafers or pellets of the same type of element, and it is possible to determine which electrode is defective and to what extent by referring to the result.

FIG. 2 shows another embodiment in which the manufacturing method of the present invention is applied to an epitaxial double diffusion type transistor. An emitter diffusion layer 23 and a base diffusion layer 27 are formed on the epitaxial wafer 20, an oxide film 21, an emitter electrode 25 and a base electrode 26 are provided on the main surface of the substrate, and a collector electrode 22 is provided on the other main surface of the substrate. FIG. 9A shows a method for determining the quality of ohmic contact of the emitter electrode 25. The wafer 20 is placed on the stage 18 which is one measurement input terminal of the measuring instrument, the pattern measuring needle 17 which is the other measurement input terminal is brought into contact with the emitter electrode 25, the measuring instrument is turned on and the emitter junction 24E is reverse biased. The current flowing through the measuring needle 17 when the voltage is applied and the substrate surface is not irradiated with light, that is, the leak current is obtained, and then the current when the spotlight 19 is irradiated on the substrate surface is obtained, and the difference is calibrated current. Based on the value, the quality of the ohmic contact of the emitter electrode 25 is determined as in the first embodiment. If the leakage current is small and can be ignored, it is not necessary to calibrate. Also base electrode 2
In order to determine the quality of the ohmic contact of No. 6, the pattern measuring needle 17 is brought into contact with the base electrode 26 in FIG.
The polarity of the measurement input terminal of the measuring instrument is changed, that is, the collector junction 24C is reverse-biased, and then the measurement may be performed by the same method as described above.

In the same figure (b), the measurement input terminals are the pattern measuring needles 37, 3
8 shows a method of determining whether the ohmic contact between the emitter electrode 25 and the base electrode 26 is good or bad by using the measuring instrument composed of 8; applying a reverse bias voltage to the emitter junction 24E,
The value of the current flowing through the pattern measuring needle 37 or 38 is obtained.

It is desirable that the low voltage reverse bias value does not exceed 10 V as described in claim 2, but this bias value is limited by the reverse breakdown voltage value of the PN junction of the device and the leakage current on the substrate surface. In order to reduce the risk of partial conduction such as, it is preferable to set the low voltage as close to 0 as possible, and this low voltage value is determined by trial.

The light energy can be determined in consideration of the low current detection sensitivity of the measurement system, the frequency characteristics of the photoexcitation efficiency of the substrate, or the degree of light incident on the substrate, but when no special irradiation is performed, that is, general illumination (or spot) Illuminance in case of (light)
100 lx to 1000 lx is desirable, and the sensitivity of the measuring instrument at that time needs to be several nA. In addition, P to apply reverse bias
The N-junction is preferably shallow from the substrate surface and at least one of the semiconductor regions forming the PN junction is in the substrate surface layer.

In the above embodiment, the description has been made after the sintering process,
Of course, the ohmic contact property can be evaluated immediately after the electrode is formed, and the state of the active region surface (for example, 16 in FIG. 1A) exposed after forming the electrode extraction opening can also be evaluated by the method of the present invention. I confirmed that.

[Advantages of the Invention] As described above, in the conventional evaluation method of the ohmic contact property between the active region surface of the substrate and the surface electrode at the time of forming the chip surface electrode, the determination at the time of failure in the wafer element state is not complete, There was a high rate that defects were discovered after assembly processing, resulting in processing loss.

Since the method for evaluating the ohmic contact property of the surface electrode of the present invention uses a small photocurrent, the inaccuracy caused by a large current in the related art is eliminated, and accurate and nondestructive total evaluation in a wafer element state is easily and quickly performed. It is possible to detect defective products before assembly processing, reduce processing loss in the post process, and improve yield and reliability.

[Brief description of drawings]

1A is a sectional view of a PN junction diode used for explaining the present invention, FIG. 1B is an explanatory view of a manufacturing method of the present invention,
FIG. 2C is a current distribution diagram showing the quality of ohmic contact, the second
FIG. 4 is an explanatory view of another embodiment of the manufacturing method of the present invention, FIG. 3 is an electrode lead-out drawing of a PN junction diode used for explaining the conventional manufacturing method, and FIG. 4 (a) is an explanation of the conventional manufacturing method. sectional view of a PN junction diode is used, FIG. (b) is _V F -I _F (forward) characteristic diagram of a diode of FIG (a), FIG. (c) and (d) a description of a conventional manufacturing method It is a figure. 3, 13 ... P ⁺ diffusion layer, 4 ... Electrode extraction opening,
5, 15 ... Anode surface electrode, 6, 16 ... Active region surface, 7, 17, 37, 38 ... Measurement input terminal (pattern measuring needle), 8, 18 ... Measurement input terminal (stage), 1
0 ... Semiconductor substrate, 14, 24E, 24C ... PN junction, 19 ... Spotlight, 20 ... Semiconductor substrate (epitaxial wafer), 21 ... Oxide film (Si
O ₂ ), 23 ... Emitter diffusion layer, 25 ... Emitter electrode, 26 ... Base electrode, 27 ... Base diffusion layer.

Claims (4)

[Claims] 1. A step of forming a surface electrode in ohmic contact with an active region surface of a semiconductor substrate having a PN junction,
When the measurement input terminal of the measuring instrument is brought into contact with the surface electrode, the P
Applying a low-voltage reverse bias to the N-junction, determining a current value flowing through the measurement input terminal when the substrate surface is irradiated with light, and measuring the quality of the ohmic contact. Of manufacturing a semiconductor device. 2. The method for manufacturing a semiconductor device according to claim 1, wherein the low voltage reverse bias value does not exceed 10V. 3. The method for manufacturing a semiconductor device according to claim 1 or 2, wherein the illuminance of the irradiation light is 100 lx to 1000 lx. 4. The method according to claim 1, wherein the current value when the substrate surface is irradiated with light is a difference from the current value which flows through the measurement input terminal when the substrate surface is not irradiated with light. 4. The method for manufacturing a semiconductor device according to any one of 3 above.