JPS6352783B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention particularly relates to a diffused resistor in a semiconductor integrated circuit.

Resistors in semiconductor integrated circuits are often required to have relative accuracy rather than absolute accuracy. The object of the present invention is to obtain good resistance ratio accuracy. Hereinafter, the ratio accuracy will be referred to as a relative ratio, and the ratio of resistances will be referred to as a resistance ratio.

Before explaining the present invention, we will briefly touch on diffused resistance. The resistance value R of the diffused resistance is expressed by equation (1).

R=R _C +ρ _S・α・L/W+ρ _S /2・n ...(1) The first term on the right side of equation (1), that is, R _C is the resistance value at the contact part between the external wiring and the resistor. show. In addition, ρ _S is the layer resistance of the diffused resistor, α is the correction coefficient for the resistance width, L is the resistance length on the mask of the diffused resistor, W is the resistance width on the mask of the diffused resistor, and n is the number of corners of the resistor (number of bends). ). That is, the resistance value of the semiconductor resistor is determined by the contact resistance with the electrode, the resistance of the resistance region, and the number of corners of the resistance region.

In integrated circuits mainly using bipolar transistors, diffused resistors are usually formed by introducing P-type impurities into the base of an NPN transistor and performing a thermal process. The problem here is when this diffused resistor has a corner and takes a relative ratio with another diffused resistor that also has a corner.

In general, the main causes of errors in resistors that take relative ratios are changes in the resistance length due to lateral diffusion during the diffusion process at the corners of the resistance, and changes in the resistance length due to underetching, overetching, etc. in the PR process. It's a change. Note that the influence at the contact portion of the resistor with the electrode can be ignored since the plurality of resistors are affected in the same way.

The above will be briefly explained with reference to FIG. From equation (1), the resistance length L (L ₁ + L ₂ ) obtained by substituting parameters such as resistance value and number of corners is the dimension 1 on the mask.
corresponds to The resistance length after diffusion after introduction of P-type impurity and thermal process is L'(L' ₁ + L' _{2 )} as shown by broken line 2 due to the lateral spread of diffusion at the corner and etching conditions, and is designed as follows. It's out of sync with the value. Note that the value W of the resistance width before diffusion and the value W' after diffusion are included in the α resistance correction coefficient in equation (1). Thus, having a bent portion in the resistance region increases the deviation of the resistance from the designed value. Therefore, it has been difficult to obtain the relative ratio of two resistors having different numbers of corners.

Two resistance patterns requiring a relative ratio have conventionally been formed as shown in FIG. 2, for example. Since there are no corners in these two resistor patterns 3 and 4, the resistance length does not change due to lateral spread of diffusion due to etching conditions at the corner portions. Therefore, to obtain resistors R ₁ and R ₂ with a resistance ratio (1:2), the resistance length of resistor R ₂ is equal to 2 of that of resistor R ₁ .
Just double it.

However, the above method is often not practical due to limitations on the chip size of the integrated circuit. That is, when a relative ratio of resistors having a large resistance ratio is taken, or when a large number of resistors have a relative ratio, it is almost impossible to form all the resistance regions in a straight line. Therefore, the resistive region usually has at least one corner. Therefore, the conventional method for realizing a resistance ratio other than 1 simply sets the resistance length according to the resistance ratio, and completely ignores the number of corners of the resistance. The number of corners of the resistor is
In the prior art, the resistors are provided appropriately according to the space for arranging the resistors, and the relative ratio is determined by the resistor length, assuming that only the resistor width is the same.

Therefore, due to the lateral spread of diffusion at the corners and the etching conditions, the relative ratio could not be accurately determined. For example, two resistors R ₃ and R ₄ for which a resistance ratio of 1:10 is desired have a pattern as shown in FIG. Resistors R ₃ and R ₄ are shown as solid lines 9 on the mask,
The pattern shape is shown in FIG. 11, and the resistance lengths of these resistors are designed to be 1:10. When impurities are substantially introduced to form a region, changes occur as shown by broken lines 10 and 12. Further, the number of corners is 1 for both resistors R ₃ and R ₄ .

In such a configuration, the resistance value of resistor R ₅ is
From equation (1), equation (2) is obtained, and R ₅ =R _C +ρ _S /2+ρ _S ·αL/W ...(2). Resistance R ₆ is also shown in the same way from equation (1), but
Since the contact part resistance R _C has 1 corner,
It is shown by equation (3).

R ₆ = 10・R ₅ = R _C +ρ _S /2+ρ _S・α・10L+9・
R・W/ρ _S・α・9/2・W/α/W……(3) The numerator of the third term on the right side of equation (3) (10・L+9・R _C・
W/ρ _S・α+9/2・W/α) is R5:R6=1:10
5 means the resistance length obtained from the calculation of R6 for the resistance length L.

Here, actually substitute the following appropriate values. L=85μ, ρ _S =200Ω, R _C =200Ω, α=1,
W=10μ, ΔL=5μ, ΔL/2 is the lateral spread of diffusion occurring at the corner and the change in resistance length due to etching conditions. The resistance ratio on the mask dimensions is R′ ₄ /
R′ ₃ and the resistance ratio after diffusion is R ₄ /R ₃ , then the relative ratio K
is expressed as K=R ₄ /R ₃ /R' ₄ /R' ₃ .

K=R ₄ /R ₃ /R' ₄ /R' ₃ ×100=105 (%) ...(4) R ₄ =R _C +ρ _S /2+ρ _S・α・(10L+9W・R _C /ρ _S
・α+9/2 W/α−△L)/W R′ ₄ = R _C +ρ _S /2+ρ _S・α・(10L+9W・R _C /
ρ _S・α+9/2 W/α)/W R ₃ =R _C +ρ _S /2+ρ _S・α・(L−△L)/W R′ ₃ =R _C +ρ _S /2+ρ _S・α・L/W Equation (4) shows that the relative ratio of resistance deviates by 5% from the resistance design value due to the lateral spread of diffusion at the corner after diffusion and the etching conditions.

As described above, an accurate relative ratio has not been achieved with the prior art.

It is an object of the present invention to provide an integrated circuit having semiconductor resistors formed with precise relative ratios.

The present invention is characterized in that the ratio of the number of corners of the resistor is also set according to the relative ratio. That is, in the present invention, by setting the ratio of the number of corners in accordance with the resistance ratio of the resistor that takes the relative ratio, it is possible to prevent the diffusion lateral spread that occurs at the corner part and the deterioration of the relative ratio under etching conditions. If you are careful, you can obtain a good relative ratio of resistors regardless of the space in which the resistors are arranged.

FIG. 4 shows one embodiment of the present invention.
As shown in the figure, a resistance ratio of 1:10 was achieved.
However, while resistor R ₅ has one corner, resistor R ₆ has 10 corners, so that the resistor region is bent 10 times between both ends. Also, the resistance length of resistor R ₆ is 10% longer than that of resistor R ₅ .
It's double. Solid lines 13 and 15 are pattern diagrams of the resistors R ₅ and R ₆ on the mask, and broken lines 14 and 16 are pattern diagrams formed when impurities are actually introduced to form a resistance region.

In such a resistance pattern, the same values as shown in FIG. 3 (L = 85μ, ρ _S = 200Ω, R _C = 200
Ω, α=1, W=10μ, ΔL=5μ), the relative ratio K becomes equation (5).

K=R ₆ /R ₅ /R' ₆ /R' ₅ ×100=100 (%) ...(5) R ₆ = R _C +5ρ _S +10L+9W・R _C /ρ _S・α−△L・10/W R′ ₆ = R _C +5ρ _S +10L+9・W・R _C /W R ₅ =R _C +ρ _S /2+ρ _S・α・(L−△L)/W R′ ₅ =R _C +ρ _S /2+ρ _S・α・L/W Equation (5) shows a good relative ratio depending on the diffusion lateral spread and etching conditions.

FIG. 5 shows another embodiment of the invention, in which a resistor
We are aiming for R ₇ :R ₈ =1:2. Therefore, the resistance length of resistor _R8 is set to 2 for the resistance region 5 of resistor _R7 .
The number of corners has also been doubled. However, resistance R ₈ is formed by two resistance regions 6 and 8,
A wiring conductor 7 connects them. This example also provides accurate relative ratios for the reasons mentioned above.

Deriving the general formula from the above explanation, R ₁ = R _C + n ₁・ρ _S /2+ρ _S・α・L/W …(6) R ₂ /R ₁ = n ₂ /n ₁ …(7) n ₁ , n ₂ : Number of corners of resistance From (6) and (7), the relative ratio is expressed as formula (8).

K=
R _C +n ₂ ρ _S /2+ρ _S・α・{(n ₂ /n ₁ L)+W(n ₂ /n ₁
−1) R _C /ρ _S・α−n ₂・△L}/WR _C +n ₁ ρ _S /2+ρ
_S・αL−n ₁・△L/WR _C +n ₂ ρ _S /2+ρ _S・α・{(n
₂ /n ₁ L) + W (n ₂ /n ₁ -1) R _C /ρ _S・α/WR _C +n ₁ ρ
_S /2+ρ _S・α・L/W (8) In this way, the present invention essentially cancels out the error occurring at the corner by providing the number of corners in accordance with the resistance ratio.

Figure 6 shows the layout function R ₉ :R ₁₀ 1:6
This is an example of a case where six corners of resistance R ₁₀ cannot be realized in one area with a resistance ratio of 1 corner of resistance R _9. In this case, R ₁₀ is This is possible by forming a series connection body in which two resistors 18 and 20 are connected by a wiring conductor 19, and the total number of corners is six.

Next, the setting of the number of corners when the resistance ratio is not an integral multiple will be described below.

The first method is to take the least common multiple so that the number of resistance corners becomes an integer. To give a specific example, in the case of R ₁ : R ₁₂ = 1kΩ : 3.5kΩ, the number of corners is set according to the resistance ratio, but in this case, one pair
There will be 3.5 locations and this will cause problems. In this case, the number of corners in the areas 21 and 22 may be 2 versus 7 by multiplying by 2 to 2:7, as shown in FIG. For reference, the following values W = 10μ, R _C =
200Ω, α=1, L=85μ, △L=5μ, ρ _S =200Ω,
Substituting n ₁ = 2 and n ₂ = 7, the relative ratio after forming the resistance region is obtained from equation (8): K = R ₁₂ /R ₁₁ /R' ₁₂ /R' ₁₁ = 100 (%)...
9), and a good relative ratio is obtained even after diffusion.

The second method is to roughly match the number of corners to the resistance ratio. That is, for example, R ₁₃ :R ₁₄ = 2.2k
When taking the relative ratio of resistances such as Ω: 8.2kΩ, if you use the first method described above to make the number of corners an integer, R ₁₃ means 11 corners, and R ₁₄ means 11 corners.
There will be 41 locations, and there will be some layout difficulties. Therefore, in such a case, it is sufficient to approximately match the number of corners to the resistance ratio. That is, as shown in FIG. 8, by providing one corner in the resistance region 23 of R ₁₃ and four corners in the resistance region 24 of R ₁₄ , the relative ratio can be realized almost accurately.

As mentioned above, if the ratio of the number of corners of the resistor is taken to match the resistance ratio, the relative ratio of the resistor will be reduced by the deterioration of the relative ratio due to the deviation of the resistor length due to diffusion, etching, etc., and the variation in ρ _S at the corner part. This can be prevented and a highly accurate relative ratio can be obtained.

The above has been explained using P-type impurity diffused resistance,
This application deals with resistors such as ion implantation resistors, pinch resistors, etc.
It can also be applied to resistance due to type impurities.

As an example, FIG. 9 shows a case where the relative ratio of pinch resistance is 1:3. Pinch resistance is resistance area 2
A region 26 is provided that overlaps a part of the resistor region 5, and the portion of the resistor region ₂₅ below the region ₂₆ is used as a high resistance. It is provided so that it overlaps with the

As described above, the present invention is suitable for cases where there are many resistances having relative ratios, or cases where a good relative ratio is required, such as a resistance for setting idling in a power IC, etc., and where the resistance ratio is large. That is, since a good relative ratio can be obtained with a free space for arranging the resistors, it is very useful for increasing the degree of integration in semiconductor integrated circuits.

[Brief explanation of drawings]

1 to 3 are pattern plan views showing a conventional semiconductor resistor, FIGS. 4 to 8 are resistor pattern diagrams showing an embodiment in which the present invention is applied to a diffused resistor, and FIG. 9 is a pattern diagram showing the present invention. An example in which the invention is applied to a pinch resistance will be shown. 1, 3, 4, 5, 6, 8, 9, 11, 13, 1
5, 17, 18, 20, 21, 22, 23, 2
4, 25, 27...Dimensional area on P-type impurity mask, 7, 19... Al wiring for connection, 2, 10, 1
2, 14, 16: P-type impurity resistance regions after diffusion, 26, 27: N-type impurity layers, respectively.

Claims (1)

[Claims] 1 At least a first and second semiconductor resistance element is provided, and the ratio of the number of bends of each of the first and second resistance elements is approximately equal to the resistance ratio between the first and second resistance elements. A semiconductor device characterized by: