JPH0437143A - Semiconductor device - Google Patents

Abstract

PURPOSE:To lower base resistance in a bipolar transistor and lessen base transit time to the utmost by distributing uniformly, in the direction of base width, impurity concentration in a base layer that is formed to a thickness which allows a tunnel current to flow at a face junctioned with an emitter layer if impurity concentration is distributed in the form of Gaussian distribution. CONSTITUTION:If impurity concentration is distributed in the form of Gaussian distribution, this device is equipped with a bipolar transistor where impurity concentration in a base layer that is formed to a thickness which allows a tunnel current to flow at a face junctioned with an emitter layer E is distributed uniformly in the direction of base width WB. For example, in a state that an opening 6 is formed at an Si02 film 4 on a collector layer 3, a silicon film 7 is deposited by MBE so that p-type impurity concentration distribution becomes uniform. Then the single crystal of the silicon film 7 in a base of the opening 6 is obtained selectively and crystallization in polycrystalline form is allowed to take place at the periphery of the film 7 as well. Then, out of the silicon film 7, a part of single crystal that is laminated on a collector layer 3 is used for a base layer B and further, the silicon film 7 around the base layer B and a polycrystal silicon film 5 below the film 7 are used for a base extraction electrode 8.

Description

[Detailed Description of the Invention] [Summary] Regarding a method for manufacturing a semiconductor device equipped with a bipolar transistor, the impurity concentration distribution is Gaussian in order to lower the base resistance of the bipolar transistor and further shorten the base transit time. The structure includes a bipolar transistor in which the impurity concentration of the base layer, which is formed to a thickness such that a tunnel current flows at the junction surface with the emitter layer, is uniformly distributed in the width direction of the base.

[Industrial application field]

The present invention relates to a method of manufacturing a semiconductor device, and more particularly, to a method of manufacturing a semiconductor device 1 including a bipolar transistor.

[Conventional technology]

In the bipolar transistor, as shown in FIG. 6, the base layer 61 is formed by ion-implanting impurities into the semiconductor layer 62 which becomes the collector.
The impurity concentration distribution in the base layer 61 is made into a Gaussian distribution as shown in FIG. Efforts are being made to shorten the transit time, thereby increasing the speed of transistors.

By the way, if the base width W is narrowed, the base resistance will increase and this will impede high speed. To solve this problem, the impurity concentration of the base layer 61 is increased to reduce the resistivity. ing.

In the figure, reference numeral 63 indicates an emitter layer formed on the base layer 61, 64 indicates a base extraction electrode, 65 indicates an interlayer insulating film, 66 indicates an emitter extraction electrode, 67 indicates a buried layer, and 68 indicates a semiconductor substrate. ing.

[81 Problems to be Solved by the Invention] However, when the impurity concentration of the base layer 61 becomes higher than a predetermined value, a current due to the tunnel effect flows through the junction with the emitter layer 63 having a high impurity concentration, and the transistor stops working properly.

For example, if we change the base width while adjusting the impurity concentration of the base layer 61 so that the base resistance is constant at 5Ω, the base width W becomes 45Ω, as shown by the dashed line in FIG.
When the impurity concentration becomes around 10 nm, the base impurity concentration near the junction with the emitter layer 63 becomes about 10''/cd, and tunnel current is likely to occur. There is a problem of not being able to find time.

The present invention has been made in view of such problems, and an object of the present invention is to provide a method for manufacturing a semiconductor device that can lower the base resistance of a bipolar transistor and further shorten the base transit time.

[Means for solving the problem] The problem described above is that if the impurity concentration distribution is made into a Gaussian distribution, the impurity concentration of the base layer, which is formed to a thickness that allows a tunnel current to flow at the junction surface with the emitter layer, can be adjusted to the base width. A semiconductor device characterized by having a bipolar transistor uniformly distributed in the direction of the base width, or a bipolar transistor characterized by having the impurity concentration of the base layer uniformly distributed in the direction of the base width such that the base width is 30 nm or less This is achieved by a semiconductor device that

[For production]

According to the present invention, if the impurity concentration distribution in the base layer of a bipolar transistor is made into a Gaussian distribution, a tunnel current will be generated at the junction with the emitter layer. The impurity concentration near the surface is kept low.

By the way, if we make the impurity concentration a Gaussian distribution, we get the result shown in Figure 5 (
As shown in a), the concentration decreases and the resistance component increases as it approaches the collector layer, but according to the BOX distribution, as shown in Figure 1.2, the concentration increases from the junction surface with the emitter layer to the collector layer. The impurity concentration is constant up to the junction surface of
The resistance component becomes uniform. Therefore, even if the impurity concentration of the base layer is the same in the vicinity of the junction surface with the emitter layer having a high impurity concentration, the base layer subjected to the BOX distribution method has a higher overall concentration and a lower base resistance.

Therefore, if the Heas resistance of the base layer with a BOX distribution and the base layer with a Gaussian distribution are made the same and the film thickness is lowered to the limit where the tunnel effect does not occur, the BOX distribution becomes clearer and the tunnel current The base width can be made smaller so that water does not flow.

On the other hand, according to the BOX distribution, since there is no difference in impurity concentration in the depth direction within the base layer and no potential difference occurs, it is not possible to shorten the carrier transit time due to the electric field.

However, since the base transit time τ is expressed as τ-WRz/ηD, it is proportional to the square of the base width W (η: distribution constant, D: diffusion coefficient), and the electric field within the base layer B This means that making the base width narrower contributes to shortening the base travel time τ more than making the base width more narrow.

As a result, if the base width W is made small (and its impurity concentration distribution is BOX), the base transit time τ can be made small.An example of this is as shown by the solid line in Figure 3.4. Become.

Further, when the base width is set to 30n* or less, if the impurity concentration distribution is BOX, it is possible to prevent the generation of tunnel current and shorten the base transit time.

〔Example〕

Therefore, the details of the present invention will be explained below based on the drawings.

FIG. 1 is a cross-sectional view showing the formation process of a device according to an embodiment of the present invention, in which reference numeral 1 indicates a highly doped n-type buried layer formed on an n-type semiconductor substrate 2. A collector layer 3 having an n-type impurity concentration of 5×10''/d is formed thereon by epitaxial growth.

Further, on the collector layer 3, silicon oxide (SiO□
) film 4 and an n-type polycrystalline silicon film 5 are formed, and an opening 6 is formed in the base formation region of these films 4.5 by photolithography.

In this state, a silicon film 7 is deposited by the MBE method so that the concentration distribution of n-type impurities such as boron is uniform. As a result, the silicon film 7 on the bottom surface of the opening 6 is selectively made into a single crystal, and the surrounding portion is made into a polycrystal (FIG. 1(b)).

After this, a silicon film 7 and a polycrystalline silicon film 5 are formed.
is patterned by a photolithography method, the films 5 and 7 are left only in the opening 6 and its surroundings, and the single crystal part of the silicon film 7 stacked on the collector layer 3 is used as the base layer B, Further, the silicon film 7 around the base layer B and the polycrystalline silicon film 5 thereunder are used as the base lead electrode 8 (FIG. 1(c)).

Next, after laminating the SiO□ film 9 over the entire base layer B, a window 10 is provided in the center of the base layer B, and an n-type silicon film 11 having an impurity concentration of 10"/cii is formed by the MBE method. 11 becomes a single crystal on the base layer B and becomes a polycrystal in other regions (Fig. 1(d))
.

Then, by patterning the silicon film 11, parts other than the inside of the window 10 and its surroundings are removed, and the film on the base layer B is used as the emitter layer, and the other part is used as the emitter extraction electrode 12 ( Figure 1(e)).

After this, a glabellar insulating film 13 is formed on the whole, contact holes 14 = 16 are provided in this, and aluminum electrodes 18 to 20 connected to the emitter extraction electrode 12, the base extraction electrode 8, and the collector extraction layer 17 are connected to the contact holes. Formed through 14-16.

By the way, the silicon film 7 that becomes the base layer B mentioned above is
The impurity concentration is formed so as to be uniformly distributed in the depth direction by the MBE method, and the relationship between them is rectangular as shown in FIG. 2, so this distribution is generally referred to as a BOX distribution.

In the base layer B with such an impurity distribution, if the film thickness of the base layer B and its impurity concentration are changed while keeping the base resistance at a constant value, the film thickness of the base layer B, that is, the base width W, and The relationship with the base transit time τ of the carrier is the third one.
An example is shown in Figure 4.

For example, if the impurity concentration and base width WI are adjusted so that the base resistance is 5Ω/gate, as shown by the solid line in FIG. 3, when the base width W is 2On-, the base transit time is o, sps, and if the base width is made smaller than that, a tunnel current will flow.

On the other hand, if the impurity concentration of the base layer is made to have a Gaussian distribution as shown in FIG.
m, the base transit time is 1.5 ps, and if the base width W is less than that, the impurity concentration will become too high in the upper part of the base layer B and a tunnel current will flow. It becomes impossible to increase the speed.

Therefore, we set the base resistance to 5 Ω/mouth and 1.5p
When trying to obtain a base transit time of s or less, the base width W is set to 3 Onm or less and the impurity concentration distribution is
It turns out that it is best to use a distribution.

This is considered to be due to the following reasons.

That is, in order to keep the base resistance constant, the base width W,
The narrower the impurity concentration, the higher the impurity concentration needs to be.In this case, the limit at the junction with the emitter layer E is 10"/d, and if the concentration is higher than that, a tunnel current will be generated at the junction with the emitter layer E. will occur.

By the way, if we make the impurity concentration a Gaussian distribution, we get the result shown in Figure 5 (
As shown in a), as it approaches the collector layer 3, its concentration decreases and the resistance component increases, but according to the BOX distribution, as shown in FIG. The impurity concentration is constant up to the junction surface with the material, and the resistance component thereof is uniform. Therefore, even if the impurity concentration of the base layer B is the same near the junction surface with the emitter layer E, which has a high impurity concentration, the overall concentration of the base layer B due to the BOX distribution becomes high, and the base resistance becomes low. .

Therefore, if we examine the limit film thickness at which no tunneling effect occurs by setting the base resistances of the base layer B with the BOX distribution and the base layer B with the Gaussian distribution the same, we find that the film thickness with the BOX distribution is thinner and the tunnel current The base width W1 at which no flow occurs can be made smaller.

On the other hand, according to the BOX distribution, since there is no difference in impurity concentration in the depth direction within the base layer B and no potential difference occurs, it is not possible to shorten the carrier transit time due to the electric field.

However, the base running time τ is τ==W,! Since it is expressed by the formula /ηD, it is proportional to the square of the base width W (η: distribution constant, D: diffusion coefficient), and the base width is made thinner than creating an electric field in the base layer B. This will contribute to shortening the base travel time τ.

As is clear from Fig. 3, the base running time τ
If you want to make it 1.5ps or less, set the base width W to 3O
It is sufficient if the impurity concentration distribution is set to be n- or less and the impurity concentration distribution is defined as a BOX distribution.

Furthermore, as shown in Figure 4, when the base resistance is set to 10 Ω/mouth, the running time is 0.5 ps according to the Gaussian distribution.
is the limit, below which tunnel effect flow will occur.On the other hand, according to the BOX distribution, the base width W
It is possible to reduce l to approximately Ion-, and its base travel time τ to 0.2 ps.

Note that when the impurity concentration distribution is made into an exponential distribution as shown in Figure 5(b), the concentration decreases rapidly as it approaches the collector layer, so the characteristics shown at the two points [1s in Figure 3.4] When the base resistance is 5Ω/mouth, the base width W* 75 n-, the base running time 2.0p
s or less, a tunnel current will occur, and if the base resistance is set to IOkΩ/mouth, the base width Wm35r
v, when the base travel time is less than 0.5 ps, a tunnel current flows, so it is not effective in reducing the base width.

〔Effect of the invention〕

As described above, according to the present invention, if the impurity concentration distribution in the base layer of a bipolar transistor is made into a Gaussian distribution, a tunnel current will be generated at the junction with the emitter layer. Since the impurity concentration near the surface is lowered, the impurity concentration is constant from the junction surface with the emitter layer to the junction surface with the collector layer, and the base resistance is lower than in the case of Gaussian distribution. It becomes possible to lower the impurity concentration at the junction surface with the base, and the base width can be reduced by that amount, thereby shortening the base travel time of carriers.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the formation process of a device according to an embodiment of the present invention, FIG. 2 is an impurity concentration distribution diagram of a base layer in a device according to an embodiment of the present invention, and FIG. FIG. 4 is a characteristic diagram showing a first example of the relationship between the base width and the base running time in the embodiment device in comparison with a conventional one. FIG. A characteristic diagram showing a second example of the relationship in comparison with the conventional device; FIG. 5 is a right diagram showing the impurity concentration of the base layer of the conventional device; FIG. 6 is a cross-sectional view showing an example of the conventional device. (Explanation of symbols) 1...Buried layer, 3...Collector layer, 7...Silicon film, B...Base layer, E...Emitter layer. Fujitsu Limited

Claims (2)

[Claims] (1) Having a bipolar transistor in which the impurity concentration of the base layer, which is formed to such a thickness that a tunnel current flows at the junction surface with the emitter layer, is uniformly distributed in the direction of the base width if the impurity concentration distribution is Gaussian. A semiconductor device characterized by: (2) A semiconductor device comprising a bipolar transistor in which the impurity concentration of the base layer is uniformly distributed in the direction of the base width so that the base width is 30 nm or less.