JPS6360532B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an insulating film, particularly a phosphosilicate glass film (hereinafter abbreviated as PSG film) suitable as an interlayer insulating film in a semiconductor device. As a method to form this type of RSG film, atmospheric pressure
CVD (chemical vapor deposition) methods and low pressure CVD methods are known. The atmospheric pressure CVD method is carried out using a batch-processing type rotation-revolution device, but the resulting PSG film has poor adhesion (step coverage), especially at step portions, is prone to cracks due to heat, and is prone to cracks between layers. It was discovered that the insulating film had a fatal defect. Furthermore, the PSG film produced by the low-pressure CVD method also has poor dielectric strength, low film strength, and problems such as Al hillocks, making it unsuitable as an interlayer insulating film. Insulating films other than PSG include silicon nitride films made by plasma deposition, but when used as interlayer insulating films, they have the disadvantage of having a high dielectric constant, causing polarization, and being easily damaged. There is. Therefore, an object of the present invention is to form an insulating film with excellent reliability, and in particular, it can be used not only as a protective film (final protection film) to protect the surface of a semiconductor element in a completed state, but also as a The object of the present invention is to eliminate the above-mentioned defects in interlayer insulating films that require more severe conditions. In other words, as an interlayer insulating film, the step coverage is good in both film quality and shape, and there are no cracks during heat treatment.
The dielectric strength is also sufficient, for example, 300 V/0.6 μm or more. To this end, according to the present invention, an insulating film, particularly a PSG film, is formed by plasma deposition, and the feature is that CO ₂ is used as an oxidizing gas together with silicon hydride such as monosilane. There is. In the process of arriving at the present invention, the present inventor discovered the method according to Japanese Patent Application No. 124100/1983, which the present applicant had already proposed,
That is, as a result of examining the plasma deposition method of PSG film using PH ₃ −SiH ₄ −N ₂ O−Ar system,
We have found that when CO ₂ is used in place of N ₂ O, the step coverage interlayer breakdown voltage including film quality is particularly improved, and a PSG film of high quality and sufficient strength can be formed. Furthermore, the present inventor has also found that an insulating film with properties as good as those described above can be obtained even if a glass film containing Si and O as the main component is grown without mixing phosphine (PH ₃ ) into the reaction gas system. I found it. Hereinafter, the present invention will be explained in more detail with reference to the drawings. First, referring to FIG. 1, a CVD apparatus for plasma deposition used to carry out the method of the present invention is illustrated. This device is of an induction coil type plasma excitation system configured to excite plasma using an induction coil 2 disposed around a quartz bell gear 1. Inside the bell gear 1, there are installed a shower-type lower electrode 3 made of Al and a flat plate-shaped upper electrode 4 made of stainless steel facing thereto. The reaction gas system consists of PH ₃ −SiH ₄ −CO ₂ (or N ₂ O as a comparative example) −Ar =.
PH ₃ and SiH ₄ are introduced from below the lower electrode 3 using Ar as a diluent gas, while CO ₂ (or N ₂ O) is introduced from the bottom of the bell gear 1 through the narrow through hole 5 of the shower electrode 3. It is supplied to the upper reaction chamber 7. The semiconductor wafer 6 is set on the upper electrode 4 as a susceptor with its front side facing downward. Note that 8 is an RF oscillator, and 9 is a semiconductor wafer transport drive section. Inside the reaction chamber 7, each of the supplied reaction gases is excited by plasma, and a PSG film is deposited on the wafer 6. With the plasma CVD apparatus described above, the semiconductor wafer 6 is coated with a PSG film or SiO2 film as illustrated in FIG.
A film 10 is deposited. Each semiconductor region constituting a bipolar transistor of a linear IC is formed in advance on this wafer 6, and 11 is a P-type silicon substrate, 12 is an N ^- type epitaxial layer, and 1 is a P-type silicon substrate.
3 is an N ⁺ type buried layer, 14 is a P ⁺ type isolation region for element isolation, 15 is an ohmic contact region for taking out the N ⁺ type collector electrode, 16 is a P type base region, and 17 is an N ⁺ type emitter region. , 18 is a surface SiO ₂ film. The PSG film or SixO _y film 10 is
After each emitter electrode 19, base electrode 20, and collector electrode 21 are formed by aluminum vapor deposition and patterning, they are grown over the entire surface by the plasma CVD described above. Reference numeral 22 denotes a second layer of aluminum wiring, forming a multilayer wiring structure using a PSG film or Si _x O _y film 10 as an interlayer insulating film. In addition, the first layer aluminum electrodes 19 to 21 and their wiring film thickness is 1 μm, width is 6 μm, and wiring spacing is 2 μm,
The thickness of the PSG film 10 may be 0.8 μm, and the second layer wiring 22 may have a thickness of 1 μm, a width of 10 μm, and a wiring interval of 2 μm. The above plasma CVD deposited films (PSG film,
Characteristics of Si _x O _y film) by other normal pressure and low pressure CVD methods
The data compared with PSG membrane is shown in the table below. According to this, it can be seen that the precipitated film grown by plasma deposition has low thermal stress, good step coverage and dielectric strength, and is particularly excellent as an interlayer insulating film in a multilayer wiring structure.

【table】

[Table] Next, regarding the deposited film by plasma CVD described above, the
The etching rate of the PSG film (the etchant is, for example, buffer HF) is shown in FIG. From this result, the etching rate is much lower when the oxidizing gas is _CO2 than when it is _N2O , and the etching rate decreases as the phosphorus concentration in the film decreases (minimum at 0 mol% phosphorus). I understand. This means that plasma using CO ₂ as in the present invention
By CVD, the etching resistance of the obtained PSG film or SixOy film (for example, SiO film) is sufficient,
Second layer aluminum wiring 22 shown in Figure 2 above
It becomes difficult to be eroded during the patterning (etching) process. In addition, other
It can also be seen that the etching rate is lower than that of the PSG film produced by CVD. Figure 4 shows the concentration of oxidizing gas (oxide gas) in the reaction gas.
The etching rate of the PSG film is shown, but CO ₂
It can be seen that when phosphorus is used, the etching resistance increases as described above, and as the amount of oxidizing gas increases (the phosphorus concentration decreases), the etching rate decreases. In addition,
It seems that the etching rate is further reduced when O ₂ is used, but on the other hand, the reaction is too violent and foreign matter and defects increase, making it impossible to actually use it. Furthermore, from the above data, in the method of the present invention, the reaction gas composition is CO ₂ relative to the total flow rate of phosphine (PH ₃ ) and monosilane (SiH ₄ ).
It has been found that it is desirable to supply 20 to 40 parts of That is _, if CO ₂ is less than 20%, the oxygen content in the PSG film will decrease, the stoichiometric composition ratio as PSG will collapse, and the etching rate will also increase to a large extent. If it exceeds this, the oxygen content of PSG will become too large and its stoichiometric composition will be disrupted, as described above.
Therefore, it is suitable that the amount of CO ₂ is 20 to 40 relative to PH ₃ +SiH ₄ . FIG. 5 shows the number of defects (cracks) in the PSG film at each generation rate when heat treatment (annealing) is performed. This shows that when CO ₂ is used as the oxidizing gas, the number of cracks in the film is significantly reduced, although the generation rate is slow. Furthermore, when CO ₂ is used, the number of cracks does not change much before and after heat treatment and is very small, but when N ₂ O is used, the number of defects is significantly higher and changes greatly depending on the heat treatment conditions. . Figure 6 shows the plasma of the present invention using _CO2 .
The results show the dielectric breakdown voltage of the PSG film produced by CVD, expressed as the number of pellets (withstand voltage distribution) for each value. According to this, PSG by the above-mentioned atmospheric pressure CVD
Compared to the membrane's withstand voltage of about 400V, CO ₂
The withstand voltage of the PSG film has been significantly improved due to the plasma CVD system. Furthermore, FIG. 7 shows the infrared absorption spectrum of the PSG film according to the present invention, and according to this, a peak of P-O bond is seen in the part A, and P
It was found that the PSG film reacted sufficiently and bonded, and a very good PSG film was formed. As mentioned above, when the insulating film formed by the method of the present invention is applied to a semiconductor device,
It will be understood that the following remarkable effects are produced. (1) Good step coverage prevents breakage of the aluminum film for electrodes or wiring, improving yield. (2) Cracks are less likely to occur during heat treatment, increasing film strength. (3) The dielectric strength is sufficient as an interlayer insulating film, and breakdown voltage defects can be eliminated. (4) The reliability of semiconductor chips or wafers is improved. (5) Since CO ₂ is used as the oxidizing gas, costs can be reduced. The insulating film obtained by the present invention can be used not only as the above-mentioned interlayer insulating film, but also as a final insulation film and an insulating film formed at locations where electrical insulation is required. It has a wide range of uses.

[Brief explanation of drawings]

The drawings illustrate the present invention, and FIG. 1 is a schematic sectional view of a plasma CVD apparatus, and FIG. 2 is a schematic sectional view of a plasma CVD apparatus.
A cross-sectional view of a semiconductor wafer on which a PSG film is formed as an interlayer insulating film. Figure 3 is a graph showing the change in etching rate depending on the phosphorus concentration of the deposited film by plasma CVD. Figure 4 is a graph showing the change in etching rate of the PSG film as a function of the reaction gas composition during plasma CVD. A graph showing changes in film etching rate, Figure 5 shows PSG by plasma CVD.
A graph showing the relationship between the heat treatment temperature and the number of defects (cracks) for the film, Figure 6 is a PSG according to the present invention.
A graph showing the dielectric strength distribution of the film, and FIG. 7 is an infrared absorption spectrum diagram of the PSG film according to the present invention. In addition, in the symbols used in the drawings, 2
is an induction coil, 3 is a shower electrode, 4 is a susceptor, 6 is a semiconductor wafer, 7 is a reaction chamber, and 10 is a
In the PSG film, 19 is an emitter electrode, 20 is a base electrode, 21 is a collector electrode, and 22 is a second layer aluminum wiring.

Claims (1)

[Scope of Claims] 1. When forming an insulating film made of glass containing Si and O on a substrate by turning a reactive gas containing silicon hydride and an oxidizing gas into plasma, the oxidizing gas A method for forming an insulating film, characterized in that CO ₂ is used as an insulating film. 2 Mix a predetermined amount of phosphine into the reaction gas,
A method according to claim 1, whereby a phosphosilicate glass film is formed. 3. A method according to claim 2, in which _CO2 is supplied in a volume ratio of 20 to 40 relative to the total flow rate of phosphine and monosilane.