JPH0224373B2 - - Google Patents

Description

[Detailed description of the invention]

TECHNICAL FIELD OF THE INVENTION The present invention relates to glass for semiconductor packaging, and particularly to improvements in lead-based glass compositions. [Technical background of the invention and its problems] Conventionally, passivation using glass has been widely used as a method for covering and holding the pn junction surface of a semiconductor. This passivation is effective in improving the performance and reliability of semiconductor elements, such as increasing withstand voltage. Glass materials for semiconductor packaging include:
Two types of glass are used: so-called zinc-based glass containing ZnO-B ₂ O ₃ -SiO ₂ as the main component, and so-called lead-based glass containing PbO-SiO ₂ as the main component. Among these, lead-based glass has the advantage of high chemical resistance, but has the disadvantage of poor reliability, especially high-temperature reliability against thermal stress. For example, in the so-called BT test, in which reliability is evaluated by leaving a semiconductor in a high temperature while applying a reverse bias, a semiconductor element passivated with lead-based glass has a temperature of 125%.
Test standards cannot be met unless the temperature is ~150 [℃] or less. Therefore, for products that require reliability at higher temperatures, it is necessary to perform passivation with zinc-based glass, which has low chemical resistance. In this case, an increase in cost was unavoidable due to an increase in the manufacturing process for glass protection and various restrictions. [Object of the Invention] The object of the present invention is to realize a lead-based passivation glass composition with excellent chemical resistance and high-temperature reliability;
It is an object of the present invention to provide a glass for semiconductor packaging that can contribute to improving the characteristics of a semiconductor device to be covered and protected. [Summary of the Invention] The gist of the present invention is to add F (fluorine) to lead-based glass. That is, according to the research conducted by the present inventors, it has been found that by adding F to lead-based glass, the high-temperature reliability of lead-based glass is significantly improved. For example, if F-doped lead-based glass is used in the passivation of mesa-type diodes, the diode will become smaller than conventional lead-based glass.
It was confirmed that the leakage current in the BT test was reduced and the initial leakage current was significantly reduced. The present invention focuses on such points, and the essential component composition of the glass for semiconductor passivation is 30 to 60 [wt%] of _SiO2 , 30 to 60 [wt%] of PbO,
Al ₂ O ₃ is 1 to 15 [wt%], B ₂ O ₃ is 0 to 20 [wt%],
The F content is 0.002 to 0.2 [wt%] or less, and the total of these components is 95 [wt%] or more. The reason why the composition of the glass for semiconductor packaging according to the present invention is limited as described above is as follows. (1) If SiO ₂ is less than 30 [wt%], the coefficient of thermal expansion becomes too large, causing cracks when covering silicon elements. Moreover, if it exceeds 60 [wt%], the viscosity of the glass becomes too high, making it difficult to obtain a homogeneous glass. (2) If PbO is less than 30 [wt%], good device characteristics cannot be obtained. Moreover, if it exceeds 60 [wt%], the coefficient of thermal expansion becomes too large. (3) If Al ₂ O ₃ is less than 1 [wt%], the breakdown voltage of the semiconductor device will be low. Moreover, when it exceeds 15 [wt%], the reverse leakage current of the element becomes large. (4) When B ₂ O ₃ exceeds 20 [wt%], metastable phase separation occurs, making it difficult to obtain a uniform glass. (5) Addition of F is effective even in a very small amount. 0.002[wt
%] had a clear effect. However, when F exceeds 0.2 [wt%], a so-called soft waveform occurs in the reverse voltage-current characteristics of the semiconductor element in which the reverse leakage current gradually increases near breakdown. (6) Furthermore, the effects of the present invention are maintained even for glasses to which metal oxides other than the main components are added, as long as the above components do not become less than 95 [wt%]. These additives include MgO, _{P2O5 ,
CaO} , TiO, _V2O5 , _CrO3 , _MnO2 , _{Fe2O3 ,}
CoO, NiO, CuO, ZnO, Ga ₂ O ₃ , GeO ₂ ,
As ₂ O ₃ , SrO, Y ₂ O ₃ , ZrO ₂ , Nb ₂ O ₅ , MoO ₃ ,
CdO, In ₂ O ₃ , SnO ₂ , Sb ₂ O ₃ , BaO, La ₂ O ₃ ,
These include CeO ₂ , Ta ₂ O ₅ , WO ₃ and Bi ₂ O ₃ and can be added in any combination. Another feature of the present invention is that the alkali ion concentration is defined to be 20 [ppm] or less. One of the causes of characteristic deterioration of silicon semiconductor devices is
Contamination by alkali ions and transition metal ions is well known. Therefore, it can be easily estimated that the lower the alkali ion concentration in the glass, the less chance of contamination. Therefore, it is known to limit the concentration of alkali, as disclosed in Japanese Patent Publication No. 53-17607, for example. However, the present inventors have found that there are differences in the allowable limit depending on the type of glass. In other words, in a glass mainly composed of zinc borate as shown in the known examples, the element characteristics are maintained even when the alkali concentration is about 50 [ppm], but when SiO ₂ as treated in the present invention is 30 [ppm]
In glass whose main component is lead silicate, a trace amount of alkali significantly deteriorates the properties. As an example, SiO ₂ 41 [wt%], Al ₂ O ₃ 2.5
[wt%], B ₂ O ₃ 8.5 [wt%], and PbO48 [wt%] glass. High-purity silicon oxide, high-purity boric acid, lead oxide, and high-purity alumina are used as raw materials. After mixing, they are melted in an electric furnace in a platinum crucible for 6 hours, then rapidly cooled and crushed to produce glass with the above composition. Obtained. Impurities in glass after crushing
Na0.8 [ppm] and K0.2 [ppm]. By adding alkali to this glass and remelting it, glasses with various alkali concentrations were created. In addition, as reference examples, SiO ₂ 10 [wt%], ZnO60 [wt%],
B ₂ O ₃ 24 [wt%], Al ₂ O ₃ 1.0 [wt%], PbO5 [wt%]
Zinc borate glasses with the composition of 1 and 2 were prepared in a similar manner by adding trace amounts of alkali at various concentrations. These glass powders were coated on a mesa diode wafer using a doctor blade method and baked at 700[° C.], after which a mesa diode as shown in FIG. 1 was assembled using a conventional method. In the figure, 1 is an n ⁺ Si substrate, 2 is an n ^- layer, 3 is a p layer, 4 and 5 are metal electrodes,
6 indicates a passivation glass. The breakdown voltage design value of this element is 700 [V], and the leakage current at room temperature at 600 [V] is less than 1 [μA]. While applying a reverse voltage of 600 [V] to this element,
Changes in characteristics after the temperature was raised to 175 [°C] and held for 100 hours were determined from changes in leakage current. The results are shown in Figure 2. In Fig. 2, the ● marks are for lead silicate glass, and the ○ marks are for zinc borate glass. Zinc borate glass does not deteriorate in properties even when the alkali concentration increases to around 50 [ppm], but lead silicate glass starts to deteriorate at around 20 [ppm]. Similar behavior was observed for lead-silicate glasses with different compositions. Such characteristic behavior suggests that the deterioration is not simply due to alkali contamination on the element surface, but is due to a new deterioration mechanism related to the glass composition. Therefore,
The alkali ion concentration is preferably 20 [ppm] or less. [Effects of the Invention] The passivation glass according to the present invention has superior high-temperature reliability compared to conventional lead-based passivation glasses. That is, in a BT test using a mesa diode, the leakage current is significantly smaller than that of a conventional lead-based glass passivation, and the initial leakage current is also significantly smaller. Therefore, it is extremely effective for passivation of semiconductor devices. Moreover, the passivation glass according to the present invention can be produced by a conventional method. That is, glass raw materials prepared to a desired composition are melted in a platinum crucible in an electric furnace, crushed into small pieces using a water-cooled roller or water grinder, and then crushed using a ball mill or the like to obtain a patency glass powder. . As the raw material for glass, it is convenient to use lead fluoride for fluorine, and other components may be high purity oxides or boric acid. Furthermore, passivation of the semiconductor can also be performed using conventional methods. That is, glass powder may be applied to the part to be passivated by, for example, a precipitation method, electrodeposition, or a doctor blade method, and then baked at a temperature at which the glass flows for 10 minutes or more to form a glass coating. [Embodiments of the invention] First, high-purity silica, trilead tetroxide, alumina,
Boric acid, lead fluoride, and zinc white were mixed to have the composition shown in Table 1 below. Next, each of these was melted into glass using a platinum crucible in an electric furnace at 1,400 to 1,500 [°C]. All of the produced glasses were homogeneous, with no phase separation or devitrification. Furthermore, when the alkali impurities in the glass were analyzed, they were found to be 1.5 to 2.1 [ppm] as shown in Table 1.

【table】

[Table] Next, diodes were passivated using these glasses, and their initial device characteristics and thermal reliability were investigated. First, the glass melt was passed through a water-cooled roller to form thin flakes, which were then ground in a ball mill to form a powder with a size of 325 mesh. This powder was filled into the mesa groove of a mesa-type diode wafer using a doctor blade method, and baked at a temperature of 750 to 800 [°C] for 10 minutes in an electric furnace in an oxygen atmosphere to perform glass pruning. The obtained device has a structure as shown in FIG. 1 above. The reverse leakage current of the device at 600 [V] was measured. Furthermore, the leakage current was measured when a reverse voltage 50 [V] lower than the voltage at which breakdown occurred was applied, and a leakage current exceeding 5 [μA] was defined as a soft waveform. In addition, we conducted a BT test in which the product was left in a high temperature of 150 [°C] or 175 [°C] for up to 168 hours while applying a reverse voltage of 600 [V], and high-temperature reliability was investigated from the change in leakage current value. . These results are shown in Table 2 below.

【table】

[Table] From Table 2 above, for the compositions limited by the present invention, the initial leakage current value is the standard 1 [μA].
It can be seen that the initial leakage current decreases by adding fluorine. In particular, the composition of Experimental Example (9) has extremely low leakage current, and the experimental Examples (10) to (13) in which fluorine is added to the composition of Experimental Example (9) have even less leakage current. No increase in leakage current was observed in any of the BT tests at 150 [°C]. 168 at 175 [℃]
There was a considerable increase after hours, but the increase was smaller with the fluorine-containing glass. From this, it is clear that the high temperature reliability is improved by the addition of fluorine. Regarding Table 2, experimental examples (1) and (2) are
B ₂ O ₃ =0 [ωt%], and the probability of soft generation is increasing. In experimental examples (3) and (4), in which B ₂ O ₃ was added to the composition of experimental examples (1) and (2) (B ₂ O ₃ = 1.0ωt%), the soft occurrence rate was 0. . From this,
It can be seen that the addition of B ₂ O ₃ as part of the composition reduces the soft occurrence rate. moreover,
Experimental examples (17) and (18) were soft with B ₂ O ₃ = 25 [ωt%], and it was found that tip-opening occurred during firing. This is because the composition ratio of B ₂ O ₃ exceeds 20 [ωt%]. In addition, in experimental example (14), F=0.3 [ωt
%], and the initial leakage current is extremely large and soft. From this, the composition ratio of F is 0.2
It can be seen that when it exceeds [ωt%], it becomes soft. In this way, the composition ratio of B ₂ O ₃ needs to be within a range that does not exceed 20 [ωt%], and even more than 0 [ωt%].
It is preferable that it is 20 [ωt%] or less. In addition, if the composition ratio of F is less than 0.002 [wt%], the desired effect will not be exhibited, and if it exceeds 0.2 [wt%], various disadvantages will occur, so it should be in the range of 0.002 to 0.2 [wt%]. There is a need. As Comparative Examples (1) and (2), glasses having the same composition as in Experimental Examples (9) and (12) were made using raw materials with low purity, and had an alkali ion concentration of 25 [ppm]. A diode was packaged with this glass in the same manner as before, and the same test was performed. As a result, the initial leakage current was not significantly different from experimental examples (9) and (12), but
Leakage current increased by 50% during the 24-hour BT test at [℃], and could not withstand the test at 175[℃]. Note that the present invention is not limited to the embodiments described above, and can be implemented with various modifications without departing from the gist thereof. For example, the alkali ion concentration is preferably 20 [ppm] or less, but even if the alkali ion concentration is 20 [ppm] or more, the high temperature reliability can be improved by adding fluorine. Furthermore, it goes without saying that the present invention can be applied not only to diodes but also to various semiconductor devices.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing the schematic structure of a mesa diode for evaluation, and FIG. 2 is a characteristic diagram showing the relationship between the alkali ion concentration in the passivation glass and the diode wetting current increase rate. 1... n+Si substrate, 2... n ^- layer, 3... p layer,
4, 5...electrode, 6...passivation glass.

Claims (1)

[Claims] 1. A glass for semiconductor packaging that covers the surface of a semiconductor to protect the semiconductor, the essential components of which are SiO ₂ 30-60 [wt%], PbO 30-60 [wt%],
Al ₂ O ₃ 1 to 15 [wt%], F0.002 to 0.2 [wt%],
A glass for semiconductor packaging, characterized in that the total of these is 95 [wt%] or more. 2. The glass for semiconductor packaging according to claim 1, wherein the alkali ion concentration is 20 [ppm] or less. 3 In the glass for semiconductor passivation that covers the surface of a semiconductor and protects the semiconductor, its essential components are SiO ₂ 30-60 [wt%], PbO 30-60 [wt%],
Al ₂ O ₃ 1 to 15 [wt%], F0.002 to 0.2 [wt%],
A glass for semiconductor packaging, further comprising B ₂ O ₃ in a range of 20 [wt%] or less, and the total of these is 95 [wt%] or more. 4. The glass for semiconductor packaging according to claim 3, wherein the alkali ion concentration is 20 [ppm] or less.